Cleaning Apparatus for Electrophotography Comprising Lubricant Film Applicator Means

The present invention generally relates to electrophotographic copying machines and, more particularly, to a cleaning apparatus included in such a machine which applies a film-forming material of a small coefficient of friction onto a photosensitive element while removing a toner residual thereon by means of a cleaning blade.

An electrophotographic copying machine to which the present invention is applicable is of the type which forms a latent image electrostatically on a surface of a photosensitive element, processes the latent image with a toner powder into a visible toner image, transfers the toner image onto a sheet material to form a copy, and cleans the photosensitive element to remove residual particles of the toner therefrom so that the photosensitive element becomes prepared for another copying cycle.

In this type of copying machine, transfer of a powdery toner image from the photosensitive element to a sheet is under the influence of a relative humidity. Particularly, it is adversely affected by high relative humidities. When the relative humidity is high, an electrostatic force, Van der Waals force and other various influential forces cause a major part of the powder to constitute deposits adhered to the photosensitive element. This not only lowers the density of an image reproduced on a sheet but allows the toner image to remain on the photosensitive element. Therefore, complete image transfer and complete removal of the residual toner image in a copying cycle are key factors to the prevention of a ghost image during image transfer in the next copying cycle as well.

It is well known to clear residual toner particles from the surface of the photosensitive element using a cleaning blade. A cleaning effect attainable with a cleaning blade is excellent because the cleaning blade has its leading end or edge usually held in positive pressing contact with the photosensitive element to remove toner particles by intense friction. However, where use is made of a photosensitive element formed of a relatively soft material, the cleaning blade tends to damage the surface of the photosensitive element and/or cause wear of the same surface resulting in a short service life of the photosensitive element. An expedient to settle this problem may be the use of a cleaning blade formed of polyurethane rubber or like highly wear resistant material and a photosensitive element formed of a material which stands relatively intense friction. This expedient still fails to preclude incomplete cleaning due to wear of an edge portion at the leading end of the cleaning blade. Experiments showed that an expected cleaning effect becomes unattainable when the edge portion of such a cleaning blade wears by 20-50 microns.

Japanese Patent Publication No. 51-22380/1976 for instance discloses a method designed to eliminate such drawbacks inherent in the cleaning system of the type using a blade while promoting efficient transfer of a toner image from the photosensitive element to a sheet and efficient removal of a residual toner image by the blade. According to this method, a certain film-forming material having a small coefficient of friction is applied to a surface of the photosensitive element at the cleaning station so as to serve as a kind of lubricant. Zinc stearate is generally accepted as a film-forming material which gives a favorable result. Another example of such a material may be a metal salt which is dense, hydrophobic and with a stable fatty acid. Various kinds of dense and hydrophobic metal salts with stable fatty acids are stated in Japanese Patent Publication No. 51-22380/1967. A problem encountered here is that, the larger the amount of application of such a material onto the photosensitive drum, the greater the cleaning efficiency grows but, at the same time, the lower the image density becomes because the total amount of toner allowed to adhere to the photosensitive element during development is limited; the smaller the amount of the material, the poorer the cleaning efficiency though the higher the image density due to an increase in the total amount of toner adhesion during development.

It has been a common practice to apply a film-forming material of the type described either periodically or continuously, all in a fixed amount. With this mode of application, however, whether a current amount of the material supplied to the photosensitive element is proper cannot be known at all. If the amount of supply is short, the image density becomes excessive and, if the amount of supply is excessive, the image density becomes short.

A principle concept of the present invention resides in that, though the image density and cleaning efficiency show opposite tendencies with respect to the amount of supply of a film-forming material, both of them can be improved to satisfactory levels by controlling the amount of material supply to a certain appropriate one.

A cleaning apparatus according to the present invention is operable in an application mode in which a brush is in a first position engaged with a photosensitive element or in a non-application mode in which the brush is disengaged from the photosensitive element. In the first position, the brush applies a film-forming material to a surface of the photosensitive element undergone a major cleaning operation so as to increase the cleaning efficiency of the cleaning apparatus. The brush comprises a rotary brush held in pressing contact with a moulded mass of film-forming material. The amount of application of the material is controlled to a proper one by adjusting a time period of contact of the brush with the photosensitive element, an amount of contact of the brush with the photosensitive element, an amount of contact of the brush with the agent or like factor in matching relation with a number of rotations of the photosensitive element, a number of copy sheets produced and/or a coefficient of friction on the surface of the photosensitive element.

A cleaning apparatus for an electrophotographic copying machine embodying the present invention comprises a photosensitive member, scraper blade means engaging with the photosensitive member to scrapingly remove residual toner particles therefrom, applicator means for applying a film-forming material onto the circumference of the photosensitive member, and drive means for moving the applicator means into and out of contact with the photosensitive member in dependence on a parameter indicating a varying operating condition of the photosensitive member, whereby a proper amount of the film-forming material is applied onto the circumference of the photosensitive member under a varying operating condition of the photosensitive member.

It is an object of the present invention to provide a cleaning apparatus for electrophotography which attains an improved cleaning efficiency by applying an appropriate volume of film-forming material having a small coefficient of friction uniformly onto a photosensitive element.

It is another object of the present invention to provide a generally improved cleaning apparatus for electrophotography.

Other objects, together with the foregoing, are attained in the embodiments described in the following description and illustrated in the accompanying drawings.

FIG. 1 is a partly broken away perspective view of an example of an electrophotographic copying machine to which the present invention is applicable;

FIG. 2 is a sectional front elevation of the machine;

FIG. 3 is a plan view of a control panel;

FIG. 4 is section of a developing unit;

FIG. 5 is a fragmentary sectional front elevation of a toner supply mechanism;

FIG. 6 is a sectional front elevation of a toner density sensor;

FIG. 7 is a front view showing positions of cooling fans;

FIG. 8 is a perspective view of a container for collecting a developer therein;

FIG. 9 demonstrates an operation for collecting the developer into the container;

FIG. 10 is a sectional front elevation of a quenching lamp for lowering a potential on a photosensitive drum before image transfer;

FIG. 11 is a front view of an optical exposure system;

FIG. 12 is a plan view of a mechanism adapted to compensate for an irregular light intensity distribution;

FIG. 13 is a perspective view of a mechanism for driving the optical system;

FIG. 14 is an exploded perspective view of a reversible clutch mechanism associated with the drive system;

FIG. 15 is a fragmentary sectional side elevation of the reversible clutch mechanism;

FIG. 16 is a front view of a gear train of the reversible clutch mechanism;

FIG. 17 is a partly sectional fragmentary plan view of a mechanism for positioning the filament of an exposing lamp;

FIG. 18 is a section of the positioning mechanism shown in FIG. 17;

FIG. 19 is a fragmentary side elevation of the same positioning mechanism;

FIG. 20 is a perspective view of a sheet cassette;

FIG. 21 is a schematic front elevation of a sheet feed section;

FIG. 22 is a front elevation of a pressure release mechanism;

FIG. 23 is a fragmentary perspective view of a knob which joins in the detection of a sheet size;

FIG. 24 is a perspective view of a mechanism for pressing a bottom plate of the sheet cassette;

FIG. 25 is a perspective view of a sheet size detecting mechanism which is coactive with the knob of FIG. 23;

FIG. 26 is a front view of a paper end detecting mechanism adapted to check whether a sheet cassette is loaded with sheets;

FIG. 27 is a view similar to FIG. 26 but showing another position of the paper end detecting mechanism;

FIG. 28 is a front view of a transfer, separation and conveyance section;

FIG. 29 is an inverted perspective view of a transfer and separation charger assembly;

FIG. 30 is a sectional front elevation of a fixing unit;

FIG. 31 is a rear view of a pressure release mechanism associated with the fixing unit;

FIG. 32 is a fragmentary side elevation of the fixing unit;

FIG. 33 is a perspective view of a half rotation clutch mechanism also associated with the fixing unit;

FIG. 34 is a front view of an oil applying mechanism also included in the fixing unit;

FIG. 35 is a sectional front view of a quenching lamp which removes a charge from the drum after cleaning;

FIG. 36 is a fragmentary perspective view of a quenching lamp;

FIG. 37 shows a construction of a 1-chip central processing unit;

FIG. 38 indicates a relationship between mechanical actions and inputs and outputs at a control section and central processing units;

FIG. 39 is a flowchart showing subroutines;

FIG. 40 is a timing chart showing a subroutine;

FIGS. 41-44 are flowcharts showing main routines;

FIGS. 45-49 are timing charts showing the main routines;

FIG. 50 is a flowchart indicating an operation in the event of a failure;

FIG. 51 is a timing chart indicating the operation of FIG. 50;

FIG. 52 is a timing chart showing a timing pulse check for a service call;

FIG. 53 is a timing chart indicating a failure in the movement of the optical system;

FIG. 54 is a circuit diagram showing an unusual fixing temperature detector;

FIG. 55 is a timing chart showing an operation of the unusual fixing temperature detector;

FIG. 56 is a circuit diagram showing a lower fixing temperature limit detector;

FIG. 57 is a timing chart showing an operation of the lower fixing temperature limit detector;

FIG. 58 is a circuit diagram showing an upper fixing temperature detector;

FIG. 59 is a circuit diagram showing a toner sensor stop-up detector;

FIGS. 60 and 61 are circuit diagrams showing two different detectors responsive to failures in control power sources;

FIG. 62 is a circuit diagram showing a detector responsive to an unusual energization of an illuminating lamp;

FIG. 63 is a circuit diagram of control power sources;

FIG. 64 is a circuit diagram of a key switch input circuit;

FIG. 65 shows a matrix of the circuit shown in FIG. 64;

FIG. 66 is a timing chart relevant with the matrix;

FIG. 67 is a circuit diagram of a segment energization circuit;

FIGS. 68-70 are block diagrams demonstrating a principle of toner density detection;

FIGS. 71-73 are circuit diagrams showing a toner density detection circuit;

FIG. 74 is a circuit diagram showing a toner sensor stop-up detector;

FIGS. 75 and 76 are timing charts explanatory of an operation of the toner sensor stop-up detector;

FIG. 77 is a circuit diagram of a toner end detector;

FIG. 78 is a timing chart showing an operation of the toner end detector;

FIG. 79 is a circuit diagram of a toner end reset circuit;

FIG. 80 is a timing chart showing an operation of the toner end reset circuit;

FIG. 81 is a circuit diagram of an initial main motor control;

FIG. 82 is a timing chart showing an operation of the initial main motor control;

FIG. 83 is a circuit diagram of a toner density control;

FIG. 84 is a circuit diagram of a fixing temperature control;

FIG. 85 is a circuit diagram of a lower heater temperature control;

FIG. 86 is a timing chart for the control of a fixing temperature;

FIG. 87 is a circuit diagram of an AC drive and lamp turn-on detector;

FIG. 88 is a circuit diagram showing a part of the AC drive and lamp turn-on detector;

FIG. 89 is a circuit diagram of a lamp turn-on circuit;

FIG. 90 is a timing chart showing an operation the lamp turn-on detector;

FIG. 91 is a timing chart showing an operation of the copying machine;

FIG. 92 is a sectional side elevation of a cleaning apparatus embodying the present invention;

FIG. 93 is an exploded perspective view of an essential part of the cleaning apparatus;

FIG. 94 is a perspective view of means for supporting a block of film-forming material which has a small coefficient of friction;

FIG. 95 is an enlarged section of a cleaning apparatus according to another embodiment of the present invention; and

FIG. 96 is a diagram representing an electric circuit associated with the apparatus of FIG. 95 to apply a controlled amount of film-forming material onto a photosensitive drum.

While the cleaning apparatus for electrophotography of the present invention is susceptible of numerous physical embodiments, depending upon the environment and requirements of use, substantial numbers of the herein shown and described embodiments have been made, tested and used, and all have performed in an eminently satisfactory manner.

Before entering detailed description of the invention a reference will be made to an exemplary electrophotographic copying machine which is optimum for practicing the method of the present invention. Referring to FIGS. 1 and 2, a copying machine generally designated by the reference numeral 10 is provided with a document presser plate 14 on its top which is hinged thereto to uncover a glass platen 12 when desired. A control panel 16 is mounted on a rightward part of the top of the machine 10. A cover 18 is openably disposed at the front of the machine 10. Mounted in the machine 10 are a light emitting diode or LED display plate 20 and a developer agitating switch 22 which will become accessible when an operator opens the front cover 18. When out of use, the switch 22 is sheltered by a cover 24.

As viewed in FIG. 2, a photosensitive drum 26 is disposed below the glass platen 12 and rotatable in a direction indicated by an arrow. Located around the photosensitive drum 26 are a charger 28 for depositing an electrostatic charge on the drum 26, a developing unit 30, a quenching lamp 32, a transfer charger 34, a separation charger 36, a separation pawl 38, a cleaning unit 40 and a second quenching lamp 42.

A optical system 44 for exposure is interposed between the glass platen 12 and drum 26. In a lower leftward area of the machine 10, there are mounted a fan 46 for cooling mainly the optical system 44, a power pack 48 for generating a high voltage, a main motor 50 for driving the machine and a second fan 52 directly connected an output shaft of the motor 50 to cool the developing section.

The machine 10 also has a sheet feed section 54 in its lower rightward portion. A sheet fed out from the sheet feed section 54 is moved through a sheet passage 56 over to a tray 58 adapted to receive copy sheets. Arranged along the sheet passage 56 are a pair of registration rollers 58, an endless conveyor belt 60, a fixing unit 62 and a pair of sheet discharge rollers 64. A third fan 66 is positioned above the fixing unit 62 to avoid an increase in the temperature inside the machine.

As shown in FIG. 3, the control panel 16 comprises a flat panel provided with a print button 68, a lever 70 for the adjustment of an amount of exposure and a failure display section 72 which provides visual indication of a paper jam, a short supply of toner, a service call, a non-set condition of a key counter or that of doors, a stand-by condition (e.g. "WAIT") etc. The control panel 16 also comprises an interruption button 74 for setting and resetting an interruption copy mode and an interruption display section 76 for indicating an interruption copy mode of the machine. The control panel 16 further comprises ten keys 78 for setting a desired number of copies, a sheet number display section 80 for indicating a preset number of copies by segments, sheet size display sections 82 for indicating sizes of transfer sheets with which the sheet feed section 54 is loaded, and sheet selection buttons 84 for selecting sheets in the sheet feed section.

Details of the developing unit 30 are illustrated in FIG. 4. The developing unit 30 includes a casing 88 which stores a developer 1 made up of a toner and a carrier (iron powder). A developing roller 90 is rotatably supported by the casing 88 to supply the drum 26 with the toner. A drawing roller 92 draws the developer up from the bottom of the casing 88 and supplies it to the developing roller 90. A doctor blade 94 is adapted to regulate the height of the nib of a magnetic brush by removing an excessive part of the developer on the developing roller 90. The developer removed by the doctor blade 94 is guided by a scraper 96 back into the bottom of the casing 88. Mounted to a part of the scraper 96 is a toner density sensor 98 which consists of a bobbin allowing a part of the developer guided by the scraper 96 to flow down therethrough and a coil. A shaft 100 agitates the developer flown down into the casing 88. A toner supply mechanism 102 is adapted to supply a supplementary amount of toner into the casing 88. As shown, the toner supply mechanism 102 comprises a container 104 storing a toner 86 therein, a roller 106 located adjacent to an opening of the container 104 and driven for rotation by a toner supply command signal as will be described, and an agitator 108 functioning to prevent toner particles in the container 104 from being solidified. The mechanism 102 is rigidly mounted to the casing 88 with its opening aligned with a toner supply opening of the casing 88 which is located above the agitator shaft 100. The edges of the casing 88 which define an opening facing the drum 26 are provided with a seal member 110 made of sponge rubber or the like and thin flexible seal plates 112 and 114 made of Miler (trade name) or the like. A scraper 116 spans the developing and drawing rollers 90 and 92 with its intermediate portion inclined relative to a side wall of the casing 88. A rightward side wall of the casing 88 is formed with a developer discharge opening 118 which is usually closed by a plate 120. As viewed in FIG. 5, the toner supply roller 106 is located in a position where it blocks an opening 122 of the container 104. Axial channels or recesses 124 extend on the periphery of the rollers 106 such that they deliver toner particles 86 from the opening 122 of the container 104 in accordance with the rotation of the roller 106. Each recess 124 is so shaped as to be rubbed by a rubber blade 126 and thereby supply a constant amount of toner particles into the casing 88 of the developing unit.

As shown in FIG. 6, the toner density sensor 98 comprises a bobbin 128 secured to a part of the scraper 96 and a coil 130 wound on a lower portion of the bobbin 128.

As shown in FIG. 4, a pair of guides 132 and 134 are fixed to the machine body so that the developing unit 30 can be pulled out from the machine body therealong. As indicated in FIG. 7, the cooling fan 52 cools the developing unit 30 from a side while an additional cooling fan 136 cools it from below. The fans 52 and 136 are provided with detachable filters 138 and 140 at their suction openings, respectively.

The guide 134 serves also as a guide for the quenching lamp 32 (see FIG. 2). The lamp 32 is fixed to a common frame together with a turn guide plate 142 (see FIG. 2) and it can be moved out of the machine body along the guide 134 and a second guide 144.

The developer 86 in the developing unit 30 is collectable without demounting the unit 30 from the machine body. As shown in FIG. 8, a collecting box 146 is usually accommodated within the frame formed by the lamp 32 and turn guide 142. The box 146 comprises a body 148, a lid 150 openably hinged to the body 148 and a lever 152 for opening and closing the lid 150. The box 146 is detachable from the machine body along the guides 134 and 144. To collect the developer 86, the quenching lamp 32 is pulled out from the machine body and the cover plate 120 (see FIG. 4) is removed from the developing unit 30 whereupon the collecting box 146 is drawn out from the frame consisting of the lamp 32 and turn guide 142 and then inserted into the machine body along the guides 134 and 144 as viewed in FIG. 9. Subsequently, the lever 154 is manipulated until the lid 150 enters the casing 88 via the opening 118 into abutting engagement with the scraper 116. Under this condition, the switch 22 (see FIG. 1) is turned on so that the rollers 90 and 92 and the shaft 100 are driven individually in the directions of arrows to draw up the developer in the casing 88 and discharge it into the box 148 via the scraper 116 and lid 150.

The quenching lamp 32 is adapted to illuminate a toner image on the drum 26 before the toner image advances to a transfer station and thereby lower a potential on the drum, facilitating removal of a transfer sheet from the drum 26. As seen in FIG. 10, the quenching lamp 32 comprises an assembly made up of a casing 156, a support plate 158 detachably mounted to the casing 156, a tungsten lamp 160 securely mounted on the support plate 158 and a filter 162 disposed in an opening or window of the casing 156. The casing 156 is formed with a second opening 164.

The optical exposure system 44 functions to transmit an image on a document layed on the glass platen 12 to the photosensitive drum 26. The system 44 comprises, as shown in FIG. 11, a halogen lamp 168 having a reflector 166 therewith, a first mirror 170 movable with the lamp 168 at a velocity V to the left in the drawing, a second mirror 172 movable at a velocity 1/2 V in the same direction as the first mirror 170, an in-mirror lens 174 fixed in place, a fourth mirror 176 also fixed in place and a drive line which will be described. Power is supplied to the halogen lamp 168 by leads 178 which are surrounded by a coil spring as illustrated. A light image of the document formed by the halogen lamp 168 is transmitted to the photosensitive drum 26 via the first mirror 170, second mirror 172, in-mirror lens 174 and fourth mirror 176 successively. The halogen lamp 168 illuminates the document through an elongate slit. A problem encountered here is that, since a slit-shaped light image of the document passes through the lens before reaching the drum 26, opposite end portions of the slit shape become darker than the other portion when projected onto the drum 26; an uneven distribution of illumination intensity is brought about though the halogen lamp 168 is controlled to compensate for such an uneven distribution. With this in view, the illuminating section of the optical system 44 is designed to adjust the intensity of illumination at opposite ends of a slit. As seen in FIGS. 11 and 12, the first mirror 170 is supported on a carriage 178 which is provided with a pair of light intersepting plates 180 and 182 each of which is movable toward and away from a slit 184 independently of the other. Screws are engaged in elongate slots of the respective plates 180 and 182 such that, when lossened, they permit the plates 180 and 182 to be moved either linearly or angularly until a proper illumination intensity distribution is established. After the adjustment, the screws will be tightened to fix the plates 180 and 182 in selected positions.

The first and second mirror 170 and 172 are movable along a guide rod 186 (see FIG. 11) in parallel with the glass platen 12 on the principle of a running pulley. The carriage 178 (see FIG. 11) for the first mirror 170 is fixed to a wire 188 whereas a carriage 190 for the second mirror 172 supports a running pulley 192. The wire 188 is fixed at one end 194 to a stationary member, passed over the running pulley 192 to be turned thereby, fixed to the first mirror 170, turned by a standing pulley 196, passed over an idle pulley 198, wound several turns on a main pulley 200, again passed over the idle pulley 198, passed over a second standing pulley 202 to be turned thereby, passed over the running pulley 192, and fixed at the other end 206 to a second stationary member through a guide 204. A tightener 208 imparts a suitable magnitude of tension to the wire 188. The reference numeral 210 denotes a home position switch which functions to detect arrival of the optical system at a home position (rightmost position in FIG. 2).

FIG. 14 illustrates a reversible clutch mechanism for driving the wire 188 selectively in forward and reverse directions. The clutch mechanism includes a shaft 212 on which a disc 214 is fixedly mounted. The main pulley 200 is connected with the disc 214 through a damper 216. As viewed in FIG. 15, a sleeve 218 is free to rotate on the shaft 212. Fastened to an end portion of the sleeve 218 is a sprocket 220 which is connected with a drive source (not shown) to be driven therefrom as indicated by an arrow. Also fastened to the sleeve 218 is a disc 222 which faces a coil for forward rotations. An output shaft 226 is rigid on the shaft 212 while first and second armature plates 228 and 230 sandwitch the output shaft 226 and are freely rotatable about the shaft 212. The armature plate 228 is engagable with a projection on the output shaft 226. The armature disc 230 has lugs 232 on its periphery which are coupled in respective notches 234 formed in the disc 222. A disc 238 is free to rotate on the shaft 212 together with a coil 236 for reverse rotations. A gear element 242 is rigidly connected to the disc 238. A gear element 242 is securely mounted on an end of the shaft 212. Interposed between the gear elements 240 and 242 is a gear train comprising a gear element 244 meshing with the gear element 240, a gear element 246 coaxial and integral with the gear element 244 and a gear element 248 meshing with the gear elements 242 and 246.

Rotations of the sprocket 220 are usually transmitted to the disc 222 and armature plate 230. For a scan stroke for exposure, the coil 224 is energized so that the disc 222 in rotation attracts the armature plate 228 thereonto to drive the output shaft 226 engaged with the armature plate 228 in a forward direction. The rotations of the output shaft 226 are transferred by the shaft 212 to the main pulley 200 which then moves the first and second mirrors 170 and 172 via the wire 188. At the end of a scan stroke, the coil 224 is deenergized and, instead, the coil 236 is energized to attract the other armature plate 230 onto the disc 238. Then the armature plate 230 has its lugs 232 held in engagement with the notches 234 of the disc 222. Under this condition, rotations of the sprocket 220 are transmitted to the shaft 212 via the disc 222, armature plate 230, disc 238, gear 240, gears 244 and 246, gear 248 and gear 242 whereby the main pulley 200 is driven for reverse rotations. During this reverse drive, it will be seen from the gear train shown in FIG. 16 that the rotation speed of the sprocket 220 is transmitted to the main pulley 200 after being increased and, accordingly, the first mirror 170 and other components of the optical system are returned to the home position at a speed higher than that of a scan stroke. In the exploded perspective of FIG. 15, the reference numeral 250 indicates the reverse side of the clutch which will be referred to as a return clutch hereinafter while the reference numeral 252 indicates the forward side which will be referred to as a forward clutch. If shocks are imparted to the drum 26 at forward starts and returns of the optical system, projection of a light image onto the drum 26 and/or transfer of a toner image onto a sheet will be disturbed. To avoid this, the rubber damper 216 and disc 214 intervene between the main pulley 200 and shaft 212 to serve as shock absorbers.

The filament of the halogen lamp 168 for illuminating a document must be positioned strictly in parallel with the slit 184 along the length of the latter. Since the relative position of the tube and filament may differ from one halogen lamp to another, it is undesirable to attain the parallelism by simply adjusting the tube of the halogen lamp. In order to facilitate such positioning of the filament, the reflector 166 is formed with holes and provided with means for adjusting the position of the filament. As shown in FIGS. 17 and 18, the reflector 166 is secured to a support 256 by fixtures 254. A lamp holder 262 is provided to one end of the support 256 through an insulator 258. Likewise, a lamp holder 264 is provided to the other end of the support 256 through an insulator 260. The halogen lamp 166 is retained by the lamp holder pair 262, 264. The insulator 258 has a short stub 266 about which the lamp holder 262 is angularly movable. More specifically, the lamp holder 262 moves angulary about the stub 266 when a thumb piece 268 is rotated because, as shown in FIG. 19, a part of the thumb piece 268 engaged with the lamp holder 262 constitutes an eccentric cam. Stated another way, one end of the halogen lamp 168 is movable in the vertical direction. A screw 270 for adjustment is threaded into the lamp holder 262 such that, when driven, it moves one end of the lamp 168 in the horizontal direction. The insulator 258 partly extends throughout the support 256 and, in this part, it is formed with a peep hole 272. The reflector 166 is formed with a peep hole 274 concentric with the peep hole 272 of the insulator 258. The support 256 is formed with a peep hole 276 as seen in FIG. 18 while the reflector 166 is formed with a peep hole 278 concentric with the peep hole 276. These peep holes are adapted to properly position the halogen lamp 168, more particularly its filament 280, and constitute coactive aims and foresights a target of which is the filament 280. When an operator cannot find the filament 280 looking through the peep hole 276, he or she will move the lamp 168 in the horizontal direction by manipulating the adjusting screw 270; when the filament 272 is absent within the visual range through the peep hole 272, the thumb piece 268 will be manipulated to move the lamp 168 up or down. A position of the lamp where its filament 280 is visible in the two directions indicates the proper filament position.

Likewise, the other lamp holder 264 is swingable about a short stub 282 of the insulator 260. Turning a thumb piece 284 causes the corresponding end of the lamp 168 to move up or down whereas driving an adjusting screw 286 causes it to move in the horizontal direction. The insulator 260 is formed with a peep hole 288 and the reflector 166 with a peep hole 290 concentric with the peep hole 288; these peep holes 288 and 290 will be used to position the filament 280 in the vertical direction. The support 256 and reflector 166 are formed at their other end with concentric peep holes 290 and 292 similar to the peep holes 276 and 278 (see FIG. 18) in order to facilitate positioning of the filament 280 at the other end. The lamp holders 262 and 264 are commonly formed of an electroconductive resilient material. The lamp holder 264 comprises two independent members which are pivoted to each other for replacement of the lamp. In the event of lamp replacement, one of the two members will be swinged to a position indicated by a dot-and-dash line in FIG. 17.

The filament 280 of the halogen lamp 168 will be in a position parallel to the slit both horizontally and vertically when aligned visually through the individual peep holes at the opposite ends thereof. With this position of the filament 280, the halogen lamp 168 will illuminate a document uniformly.

As shown in FIG. 2, the sheet feed section 54 can accommodate two different sheet cassettes 294 and 296 at the same time. Sheets can be fed selectively from the two sheet cassettes 294 and 296. Though the sheet cassettes 294 and 296 are common to each other concerning the overall size or the widthwise dimension only, partition plates within the sheet cassettes can be located to store various formats of sheets from A3 to B5 for example. As seen in FIG. 20, each of the sheet cassettes 294 and 296 comprises a body 298 and a cover 300 pivoted to the body 298. One side wall 302 of the body 298 defines a reference side edge position for sheets and has a corner pawl 304 pivoted thereto. A side fence 306 regulates the other side edge of sheets and can have its position varied in the widthwise direction of the sheet cassette. A corner pawl 308 is pivoted to the side fence 306. An end fence 310 regulates the rear edge of sheets. Sheets are directly layed on a bottom plate 312 (see FIG. 21) which is swingable relative to the body 306. A release lever 316 (see FIG. 22) is pivoted to the other side wall 302 of the body 306 to move the bottom plate 314 to a predetermined release position. A size detector knob 318 (see FIG. 23) is fixed to the outer surface of the side wall 314.

The sheet feed section 54 and the sheet cassettes 294 and 296 are so designed that the latter can be mounted in the former without any manipulation of levers, that is, the sheet cassettes 294 and 296 can assume predetermined sheet feed positions if inserted simply into the machine through openings or mouths 320 and 322 (see FIG. 2). Sheet feed rollers 324 and 326 are arranged in the individual openings 320 and 322 as shown in FIG. 2 such that sheets stored in the sheet cassette 294 and 296 are automatically engaged by the rollers 324 and 326 when the sheet cassettes are placed in the machine. This type of sheet pressing mechanism is commonly employed by upper and lower arrangements of the sheet feed section 54 and, therefore, only one of the sheet pressing mechanisms will be described with components of the other denoted by the same reference numerals. As indicated in FIG. 24, a presser shoe 328 is rigidly mounted on a support shaft 330 and serves to press a sheet atop a stack in the sheet cassette 294 or 296 into contact with the sheet feed rollers 324 or 326 while abutting against the bottom plate 312 (see FIG. 21) from below. A lever 332 is rigid on one end of the shaft 330 and retains one end of a spring 334 so that the presser shoe 328 on the shaft 330 is biased in a direction to push up the bottom plate 312. The shaft 330 is rotatably journalled to a side plate (not shown) to which a retainer 336 is pivoted. The retainer 336 formed as a double arm angled lever has a pin 338 studded on its one arm, the pin 338 abutting against the free end of the lever 332. A spring 340 biases the retainer 336 such that the latter tends to move angularly pushing the lever 332 against the tendency of the lever 332. When the upper or lower subsection of the sheet feed section 54 is empty, the retainer 336 holds the lever 332 and, therefore, the presser shoe 328 in a position which does not interfere with insertion of a sheet cassette. Studded on the other arm of the lever 336 is a relatively long pin 342 adapted to be engaged by a lug 344 on the front end of a sheet cassette when the sheet cassette is placed in the machine. Also secured to the shaft 330 is a pressure release arm 346 on which a pin 350 is studded. One end of the release lever 348 on the body 298 of a sheet cassette is exposed to the outside through the side wall 314 so as to be engagable with the pin 350 on the pressure release arm 346.

In FIG. 24, when a sheet cassette is inserted in an opening of the machine body, its lug 344 engages the pin 342 on the retainer 336 to push the retainer 336 against the action of the spring 340 until the lever 332 is released. Then the lever 332 swings under the action of the spring 334 whereby the bottom plate 312 of the sheet cassette is pushed upward by the presser shoe 328 causing a sheet atop the stack thereon into abutment against the sheet feed rollers 324 or 326. Simultaneously the presser release arm 346 is caused to swing into engagement with one end 348 of the release lever 316 as viewed in FIG. 22 to thereby swing it. When the print button 68 is depressed thereafter, a main drive mechanism drives the sheet feed rollers 324 or 326 via a sheet feed clutch (not shown) to feed sheets in the sheet cassette one by one from the stack to the registration roller pair 58.

Where it is desired to manually feed sheets into the machine while a copying operation is under way, the pressing action on the bottom plate 312 must be released. When in FIG. 22 the cover 300 is moved as indicated by an arrow, a lever 352 integral therewith engages an upper edge of the release lever 316 through a lever 354 pivoted to the side wall 314 and thereby urges the release lever 316 counterclockwise. This angular movement of the release lever 316 pushes the pressure release arm 346 clockwise about the shaft 330 until the presser shoe 328 becomes unable to exert any pressure on the bottom plate 312. Then a sheet on top of the sheet stack becomes spaced from the sheet feed rollers 324 or 326 to permit desired sheets to be inserted manually onto the top sheet from below the opened cover 300. Closing the cover 300 to its original position frees the pressure release arm 346 from restraint and, thus, the presser shoe 328 again presses the bottom plate 312 until a manually inserted sheet on top of the stack abuts against the sheet feed rollers 324 or 326.

When the sheet cassette 294 or 296 has its body 298 pulled out a bit from the machine, the lug 344 is disengaged from the pin 342 on the retainer 336 so that the retainer 336 swings under the action of the spring 340. Upon another bit of outward pull of the body 298, the bottom of the sheet cassette moves the presser shoe 328 to a non-pressing position while the other pin 338 on the retainer 336 is brought into engagement with the lever 332 to maintain the non-pressing condition.

The sheet feed section 54 is provided with a mechanism for detecting a size or format of transfer sheets. This mechanism includes a plurality of adjacent near-by switches fixed on the machine body, switches SW.sub.0, SW.sub.1 and SW.sub.2 in this example as shown in FIG. 25. Actuators 356, 358 and 360 are associated with the switches SW.sub.0, SW.sub.1 and SW.sub.2, respectively, to be capable of angular movements. These actuators 356, 358 and 360 are located at positions which will neighbor the outer surface of the side wall 302 of the cassette body 298. As shown in FIG. 23, the outer surface of the side wall 302 carries a knob 318 securely therewith. Up to three knobs 318 can be fitted to the side wall 302 though only one is shown fixed to the lowermost position in FIG. 23. A plurality of knobs can be combined together in various ways in accordance with formats of sheets. For example, only one knob fixed to the lowermost position as in FIG. 23 may indicate that the sheet cassette is loaded with sheets of format A3. When a sheet cassette with the single knob 318 is inserted into the opening 320 of the machine body, the switch SW.sub.2 will be actuated by the knob 318 to indicate the format A3 on the sheet size display 82 on the control panel 16 (see FIG. 3). If under this condition a sheet cassette loaded with a stack of A4 sheets is mounted in the other opening 322 (see FIG. 2), a knob arrangement predetermined for said sheet format will selectively actuate the switches SW.sub.0 -SW.sub.2 to provide a visual indication of the A4 format on the same sheet size display 82. The sheet size display 82 therefore indicates that sheet cassettes loaded with A3 sheets and A4 sheets individually are mounted in the machine body. If an operator desires the A3 sheets, he or she will depress the "UPPER" selection button 84. This causes a lamp 362 displaying the selected sheet cassette side to glow and, upon depression of the print button 68, sheets are fed one by one from the sheet cassette loaded with the A3 sheets.

FIGS. 26 and 27 illustrate a paper end detection mechanism which is located adjacent to each set of sheet feed rollers 324 and 326 and adapted to check whether a corresponding sheet cassette is full or empty. A paper end feeler 364 is pivoted to a stationary member such that, when a sheet cassette is absent or a sheet cassetted mounted runs out of sheets, the feeler 364 swings about a pivot shaft 366 to a position shown in FIG. 26 where its lower end is located below the sheet feed rollers 324 or 326. An actuator 368 is integral with the feeler 364 to turn on and off a paper end detection switch SW.sub.3 which is a near-by switch. As seen in FIG. 25, this switch SW.sub.3 neighbors the aforesaid switches SW.sub.0 -SW.sub.2.

When a sheet cassette storing a desired format of sheets is mounted in the sheet feed section 54, a sheet atop the stack abuts against the sheet feed rollers 324 or 326 while urging the feeler 364 about the pivot shaft 366 to a position shown in FIG. 27. Then the actuator 368 operates the switch SW.sub.3 to produce a paper present signal. Under the paper end condition shown in FIG. 26, the switch SW.sub.3 produces a paper end signal which causes the sheet size display section 82 on the control panel 16 (see FIG. 3) to display that sheets have run out. At this instant, the format display and selection display will disappear.

The sheet feed section 54 further includes an upper guide plate 370, an intermediate guide plate 372 and a lower guide plate 374 as shown in FIG. 21. These guide plates 370-374 are adapted to guide sheets selectively fed by the upper and lower sheet feed rollers 324 and 326 over to the registration roller pair 58.

When the print button 68 is depressed, the sheet feed rollers 324 or 326 associated with a selected sheet cassette are driven to advance a sheet to the registration roller pair 58 and stop it temporarily thereat. The main drive mechanism drives the registration roller pair 58 through a registration clutch (not shown) at a timing which will allow the leading end of the sheet to register with a toner image on the drum 26 at a transfer station, thereby feeding the sheet further to the transfer station. It is preferable to maintain the stand-by position of a sheet at the registration roller pair 58, that is, the amount of sheet feed by the rollers 324 or 326 at predetermined one with a view to promoting stable registry of a toner image and a sheet. To meet this, a photosensor 376 is positioned adjacent to the registration roller pair 58. The photosensor 376 serves to detect an entry position of each sheet and control the rotation of the rollers 324 or 326 in accordance the detected entry position to suppress irregularity in the amount of sheet feed, thereby setting up a constant stand-by position of sheets at the registration roller pair 58 which suppresses irregular registration. Another function of the photosensor 376 consists in sensing jams of sheets in its neighborhood. As the photosensor 376 detects a paper jam, the failure display 72 on the control panel 16 provides an indication representing a paper jam.

FIG. 28 illustrates a section of the machine for image transfer, sheet separation and sheet conveyance. A sheet fed out from the registration roller pair 58 is routed by the turn guide 142 and a turn guide 378 fixed together with the turn guide 142 until it is brought into intimate contact with the surface of the drum 26. The transfer charger 34 deposits on the back of the sheet an electrostatic charge opposite in polarity to that on the toner to thereby attract the toner on the drum onto the sheet. The separation charger 36 applies an AC corona charge to the sheet to expel the charge on the sheet, removing the sheet clear of the drum surface. A farther guide plate 380 is disposed to an inlet side of the transfer charger 31 to extend along the length of the drum 26 at a constant parallel spacing of 1-2 mm. A sheet is guided by this guide plate 380 into even and intimate contact with the drum surface throughout its area. The guide plate 380 thus serves to prevent the rear end of a sheet from being left white. The separation pawl 38 assists the separation charger 36 in separating a sheet from the drum surface and, when out of operation, it remains spaced from the drum surface as indicated by a phantom line in the drawing. The pawl 38 is mounted on a shaft 384 through a holder 382 to be swingable through a predetermined angle. The shaft 384 is connected operatively with a plunger of a solenoid by way of a lever 386, a link 388, a lever 390 and a link 392. When the link 388 is moved, the shaft 384 rotates a predetermined angle in the clockwise direction through the linkage mentioned. This rotation of the shaft 384 causes the holder 382 to rotate by gravity to bring the pawl 38 into light contact with the surface of the drum 26. When the link 392 is returned, the shaft 384 is rotated counterclockwise to rotate the holder 382 in the same direction until the pawl 38 becomes spaced from the drum surface.

The endless conveyor belt 60 conveys a sheet separated from the drum over to the fixing unit 62 while sucking it by vacuum 394. The transfer charger 34 and separation charger 36 are mounted in a common casing 396 which is in turn detachably mounted on the machine body. A back cover 398 forming the bottom of the casing 396 is detachably fitted to the casing 396. With this construction, the chargers 34 and 36 can have their wires cleaned by removing the back cover 398 from the casing 396. A guide member 400 extends on that side of the casing 396 which faces the drum 26 to prevent ingress of a sheet into the chargers 34 and 36, which makes cleaning of their wires quite troublesome. Such a problem can also be settled by the provision of a detachable back cover 398.

A sheet carrying a toner image is moved from the transfer station to the subsequent fixing station where the toner image is fused on the sheet under heat and pressure.

As shown in FIG. 30, the fixing unit 62 includes a fixing roller 404 with a heater 402 built therein, a pressurizing roller 408 which has a heater 406 therein and moves into and out of contact with the fixing roller 404, and a thermistor 410 adapted to measure a temperature at the fixing roller 404. Also included in the fixing unit 62 are a pawl 412 for preventing a sheet from being wound on the fixing roller 404 or from being jammed in the fixing unit, a piece of cleaning felt 414 for removing toner and/or sheet particles adhered to the surface of the fixing roller 404, an offset prevention mechanism 416 for supplying an anti-offset liquid onto the surface of the fixing roller 404 and a mechanism 418 (see FIG. 31) for pressurizing and depressurizing the roller 408.

The fixing roller 404 comprises an aluminum roller whose peripheral surface is applied with an anti-offset layer. The heater 402 inside the roller 404 is controlled to a predetermined temperature by the thermistor 410 which senses the surface temperature of the roller 404. The pressurizing roller 408 comprises a roller made of a heat-resistive resilient material. The heater 406 inside the roller 408 remains deenergized while the halogen lamp 168 is being turned on, but it is energized during a return stroke of the optical system for exposure. During the other periods, the heater 406 is energized and deenergized in synchronizm with energization and deenergization of the heater 402, thus saving electric power consumed by the fixing unit. Concerning the separator pawl 412, a plurality of such pawls 412, six for example, are arranged at spaced locations along the length of the fixing roller 404. Of these pawls 412, four at a reference side for the passage of sheets are engaged with the fixing roller 404 but not the other two at the other side. Should sheets of a relatively small size be passed continuously through the fixing unit 62, a comparatively large amount of anti-offset liquid would be left on the surface of that side of the roller 404 opposite to the reference side. The two pawls 412 on the side opposite to the reference side serve to remove the residual part of the liquid for thereby avoiding deposition of the liquid on a relatively large size sheet which may be passed through the fixing unit after the continuous passage of relatively small sheets.

As indicated in FIG. 32, the fixing roller 404 is rotatably journalled to opposite side panels 420 and 422 of the fixing unit by bearings 424 and 426 having a diameter which is larger than that of the roller 404. A hollow shaft 428 on which the roller 404 is mounted carries rigidly therewith a gear 430 operatively connected with a drive source (not shown) and a sprocket 432 connected to the discharge rollers 64.

The pressurizing roller 408 is mounted on a hollow shaft 434 which has its opposite ends supported by flanged bearings 436 and 438. As viewed in FIG. 31, the bearings 436 and 438 are movably engaged in elongate slots 440 formed in the individual side panels 420 and 422 of the unit and extending therefrom toward the axis of the fixing roller 404. One end of the hollow shaft 434 carries a gear 444 which selectively meshes with the gear 430 on the shaft 428 through a clutch 442. Presser levers 446 and 448 abut against the individual bearings 436 and 438 from below as shown in FIG. 32. As seen in FIGS. 30 and 31, the presser levers 446 and 448 are individually pivoted to shafts 450 and 452 on the side panels 420 and 422 while springs 454 and 456 are retained at their one end by the free ends of the shafts 450 and 452. The other end of each spring 454 and 456 is anchored to an adjusting screw 458 or 460 threaded into the corresponding side panel 420 or 422. The roller 408 therefore is held in pressing engagement with the roller 404 by the springs 454 and 456. It will be seen that the nipping width of the rollers 404 and 408 is adjustable to a desired optimum width by manipulating the adjusting screws 458 and 460.

A pressure release mechanism 418 is engaged with each of the pressurizing levers 446 and 448 to cancel the pressing contact between the rollers 404 and 408. The pressurizing lever 448 is shown in FIG. 31 engaged by one end 464 of an arm 462 of the pressure release mechanism 418. The other end 466 of the arm 462 is pivoted to one arm of a bell crank lever 468 which is pivotally supported by the side wall 420. A cam follower 472 is carried on the other arm of the bell crank lever 468. Though not shown, a similar arrangement of an arm, a bell crank lever and a cam follower is associated with the other pressurizing lever 446. Disposed to an upper rightward area of the fixing roller 404 is a shaft 474 which is rotatably journalled to the side panels 420 and 422 of the fixing unit (see FIG. 32). The shaft 474 carries a cam 476 coactive with the cam follower 472 included in the mechanism 418. As viewed in FIG. 33, a gear 480 is mounted on the shaft 474 through a spring clutch 478 and meshed with the gear 430 on the hollow shaft 428.

Forming a part of a half rotation clutch mechanism, the spring clutch 478 includes a ratchet wheel 482 which has a boss member 484 secured to an end thereof. The boss member 484 is partly cut away at its circumferential edge as shown in FIG. 33. An upper lever 486 and a lower lever 488 are pivoted to the side panel 422 by shafts 490 and 492, respectively. These levers 486 and 488 are connected together by a cross bar 494. The levers 486 and 488 have angled pawl portions 490 and 492 which are located above and below the ratchet wheel 482, respectively. A spring 496 is anchored at one end thereof to the lower lever 488 to pull the lower lever 488 downward whereby the upper lever 486 is provided with a tendency to pivot downward about the shaft 490 through the cross bar 494 until its pawl portion 490 becomes engaged with the ratchet wheel 482. Connected with the other end of the upper lever 486 is a plunger 500 which extends out from a solenoid 498.

The pressure release mechanism shown in FIG. 31 functions to avoid deformation of the pressurizing roller 408 and facilitate removal of jammed sheets out of the fixing unit. Another function of the mechanism consists in keeping the roller 408 spaced from the fixing roller 404 under stand-by conditions of the fixing unit so that heat transfer from the roller 404 to the roller 408 may be substantially prevented. When the solenoid 498 is deenergized, the upper lever 486 is pulled by the spring 496 through the lower lever 468 and cross bar 494 until its pawl 490 is engaged with the ratchet wheel 482 to hold the shaft 474 stationary. In this situation, the cam 215 on the shaft 474 assumes an angular position indicated by a phantom line in FIG. 31 in which the bell crank lever 468 is moved clockwise about the shaft 470 to a position also indicated by a phantom line. At this position of the bell crank lever 468, the pressurizing lever 448 remains in a position swinged about the shaft 452 through the arm 462 to maintain the roller 408 spaced from the roller 404. Upon energization of the solenoid 498, the upper lever 486 is operated by the plunger 500 to pivot to a position where its pawl 490 releases the ratchet wheel 482 accompanying a pivotal movement of the pawl 492 of the lower lever 488 into locking engagement with the ratchet wheel 482. Thus, the ratchet wheel 482 is rotated one half of a full rotation and then locked again. The shaft 474 is therefore stopped after one half of its full rotation; at this instant, the cam 476 stops in a position indicated by a solid line in FIG. 31. With the cam 476 held in the solid line position, the pressurizing lever 448 is urged by the spring 456 counterclockwise about the shaft 452 whereby the roller 408 is caused into pressing contact with the roller 408. A sheet discharge sensor is located adjacent to the sheet discharge rollers 64 as viewed in FIG. 30 in order to check a sheet jam thereat.

The anti-offset mechanism 416 is employed to preclude offsetting attributable to toner particles by supplying the surface of the fixing roller 404 with such an anti-offset liquid as silicone oil. Turning back to FIG. 30, an oil applying roller 502 is engaged with the periphery of the fixing roller 404 to be selectively driven thereby. An upper surface of the roller 502 is engaged by a piece of oil applying felt 504. The roller 502 and felt 504 are provided to an upper plate 506 of the mechanism 416. A screw 508 is threaded into the upper plate 506 to adjust the contact pressure of the roller 502 on the roller 404 and, therefore, the amount of oil applied to the roller 404. The felt 504 extends from the roller 502 to an area above a container 512 which stores silicone oil 510 therein. Another piece of felt 514 spans the felt 504 and oil container 512 to form an oil supply path from the container 512 to the felt 504. The silicone oil 510 is drawn by a solenoid operated pump (not shown) from a reservoir to the container 512 while a part of the oil 521 overflown the container 512 is recirculated back to the reservoir. When the amount of oil on the fixing roller 404 becomes short resulting in an increase in the friction between the rollers 404 and 502, the roller 502 is driven by the roller 404 due to the friction so as to apply the silicone oil onto the surface of the roller 404. After the supply of a given amount of oil, the roller 502 has its rotation interrupted by the friction with the felt 504 while slipping on the surface of the roller 404. In this way, the supply of anti-offset liquid onto the roller 404 can be controlled automatically without resort to any control mechanism. The mechanism 416 additionally includes a member 514 (see FIG. 34) disposed to the downstream side relative to the roller 502 with respect to the direction of rotation of the fixing roller 404. This member 514 is adapted to be engated with the surface of the roller 404 so that a layer of oil on the roller surface formed by the roller 502 is leveled out all over the roller surface.

The cleaning unit 40 (see FIG. 2) serves to remove toner particles which may remain on the drum 26 after the transfer of a toner image, getting the drum 26 prepared for the next copying cycle.

The subject matter of the present invention resides in the novel and unique cleaning unit 40. The construction and operation thereof will be described in detail hereinafter.

Though the drum 26 is free from residual toner particles after a cleaning step, a negative image may remain due to the action of the separation charger 36. To remove the residual potential on the drum 26, the drum 26 is illuminated after each cleaning step. The quenching lamp 42 shown in FIG. 35 has exactly the same construction as that of the quenching lamp 32 shown in FIG. 10 except for the optical transmissibility of its filter 516. For this reason, description of the lamp 42 will be omitted herein with the same reference numerals employed for the lamp 42. In any of the quenching lamps 32 and 42, the tungsten lamp 160 can be pulled out of the casing 56 together with the support plate 158 as depicted in FIG. 36.

Now, the electrophotographic copying machine described hereinabove and illustrated in the drawings is controlled by two different 1-chip central processing units or CPU. An electric arrangement of the machine will be discussed hereafter.

Referring to FIG. 37, there is shown a 1-chip CPU which is made up of a 4-bit CPU, a read-only memory or ROM, a random access memory or RAM, a programable timer and a clock pulse oscillator integrated into a single chip. One of the two 1-chip CPU's is used for controlling mechanical actions of the machine and the other for controlling inputs and outputs of the control section. Thus, the two CPU's control the mechanical actions and the inputs and outputs of the control section at the same time. Such a manner of control is illustrated in FIG. 38.

FIG. 39 is a flowchart representing subroutines of the control while FIG. 40 is a timing chart indicating a subroutine for checking a sheet jam at the sheet discharge section.

At a stage 1 in FIG. 39, selected keys on the control panel 23 are depressed to enter and store necessary data together with other data while such data are displayed on the control panel 16. At a stage 2 , whether to suspend a repeat copy mode is checked. A repeat copy mode will be suspended when sheets have run out as indicated by "paper end", when a sheet feed operation different from one currently in use is selected through a button 84, when a key counter is not set, or when a clear stop key 518 is depressed. A copying cycle will be repeated (in the case of a 1 to 1 copy mode) if the print switch 68 is turned on during an interval from a coupling of the return clutch 250 to a making of the home position switch 210 (see FIG. 11). Then at a stage 3 , one timing pulse is added and "1" is added to each timer counter. At a stage 4 , the need for a service call is checked. Input of timing pulses and failure in the drive of the optical system are checked by software and the others by hardware. At a stage 5 , if a copying operation is under way, a sheet jam at the sheet discharge section is checked.

FIGS. 41 to 44 show main routines and FIGS. 46 to 49 are timing charts relevant therewith. When a main switch is made at a stage 1 , the random access memory RAM and others of a 1-chip CPU are cleared back to their initial statuses. The "initial statuses" mentioned here refers to indication of a "WAIT" sign on the failure display 72, energization of a red lamp built in the print switch 68, energization of the "UPPER" cassette selection display 362 and indication of "1" on the preset sheet number display 518 (see FIG. 3). Here, the blade solenoid and main motor 50 are energized by a signal which activates a motor of a toner density control device (see FIG. 4). If the carriage 178 is out of the home position, the above-mentioned motor on signal is also used to couple the return clutch 250. At stage 2 , whether the sheet feed sensor 376 or the sheet discharge sensor is turned on is checked to determine whether the sheet path is jammed with a sheet. This will not be the case, however, if a free run switch or a jam off switch has been turned off. The free run switch and jam switch will be used for the inspection of operations of the machine. When the free run switch is closed, the machine can be operated with the supply of sheets inhibited and the respective chargers 28, 34 and 36 disabled. When the jam off switch is closed, the machine can be operated with the supply of sheets inhibited. At a stage 3 , if the fixing temperature fails to reach a predetermined level even after 6 minutes, a service call will be produced. If it safely builds up to the predetermined level within 6 minutes, the operation proceeds to the next step. A flow at a stage 4 represents a case wherein the fixing unit 62 is pulled out of the machine to remove a jamming sheet for example and the carriage 178 is moved. If the carriage 178 is not at the home position at the stage 4 , the return clutch 250 is coupled and the blade solenoid is energized. After 0.3 second, the main motor 50 is activated to return the carriage 178. If the carriage 178 is brought to the home position, the return clutch 250 is uncoupled and the blade solenoid is deennergized. After 1 second, the main motor 50 is deactivated while the "WAIT" lamp on the failure display 72 goes out. If the developer agitating switch 26 has been turned on, the main motor 39 is kept activated until the switch 22 is turned off.

At a stage 5 , if the machine is not under a "paper end" condition or a "toner end" condition, the preset sheet number counter is loaded with "1" after 60 seconds. If the machine has run out of sheets or toner, if the key counter has not been set yet, if the fixing temperature is lower than a predetermined lower limit, if the carriage 95 is out the home position, if a service call has been produced, if a sheet jam has been detected, or if a printing operation is under way, a red lamp in the print button 68 glows; otherwise, a green lamp glows inside the print button 68. When 60 seconds lapses before the machine is manipulated, the preset sheet number display 518 is reset to "1". However, this will not occur under a "paper end" condition or a "toner end" condition. A stage 6 indicates a routine for ending a copying operation. At stage 6 , after the main charger 28 has been turned off, the fixing end solenoid 498 is deenergized upon appearance of the 100th pulse. In response to the 125th pulse, the blade solenoid and the chargers 34 and 36 are deenergized. Upon the lapse of 1 second, the main motor 50 is deactivated.

At a stage 7 , when the print switch 68 is closed, the blade solenoid is energized and the red button in the print button 68 is turned on while a copy counter built in the CPU is reset to "0". After 0.3 second, the main motor 50 is energized and the fixing end solenoid 498 is energized while main timing pulses are reset. Also, the chargers 34 and 36 are turned on. The halogen lamp 168 is turned on by the 65th pulse after the activation of the main motor; the main charger 28 is energized by the 68th pulse and main timing pulses are reset. At a stage 8 , a 60-second timer is set. If the fixing temperature remains below the lower limit for 60 seconds, the machine does not advance to the next step but produces a service call. If the fixing temperature is above a reference level, there are activated the key counter, solenoid for operating the silicone oil drawing pump, and the sheet feed clutch for trasmitting a drive to the sheet feed rollers 324 (326). At the same time, "1" is added to a copy number display 520. If the toner has run out, "1" is added to a toner end counter in the CPU. This is to permit up to 50 copies to be produced sequentially after a turn-on of the toner end display lamp but to inhibit further copying cycles when the toner end counter reaches "50", thereby preventing deposition of the carrier on a transfer sheet attributable to a drop of the developer density. If the machine is in a repeat copy mode, main timing pulses are reset and the halogen lamp 168 is turned on at the instant the carriage 178 regains the home position. (The step will jump directly to B when a copying cycle is to be repeated.) It will thus be seen that an on timing of the halogen lamp 168 and charger 28 for the first sheet (discussed at the stage 8 ) after a depression of the print button 68 is distinguished from an on timing for the second copy and onward (discussed at stages 9 and 10 ). With this specific design, a time period from a turn-on of the halogen lamp 168 and charger 28 for processing the first sheet after a depression of the print button 68 to a start of a forward stroke of the carriage 178 is made longer than a time period consumed on the second sheet and onward, so that there is prevented misregistry of the carriage 178 with the home position after a turn-on of the main switch or after removal of a failure which would otherwise affect a reproduced image.

At stage 10 , upon a lapse of 40 miliseconds after the sheet feed sensor 376 has been turned on, the sheet feed clutch is uncoupled. The 7th pulse after the sheet feed clutch has been coupled couples the forward clutch 252. If in a repeat copy mode, the 4th pulse after the coupling of the sheet feed clutch energizes the charger 28. At a stage 11 , if a registry switch 522 (see FIG. 11) is not turned on even after 0.5 second since a coupling of the sheet feed clutch, a service call is produced. When the registry switch 522 is turned on, a bias for development is turned on, main timing pulses are reset to check a sheet feed jam, and the key counter and registry clutch are turned on. A sheet feed jam is determined to have occurred when no sheets are found in the sheet feed sensor area at the instant the registry switch 522 is turned on. At a stage 12 , when the main charger 28 is deenergized, main timing pulses are reset; the main charger 28 remains turned on for a time which depends on the sheet size. At a stage 13 , after the main charger 28 has been turned off and main timing pulses have been reset, the forward clutch 252 is uncoupled by the 7th pulse whereupon the return clutch 250 is coupled by the 8th pulse. If sheets have run out at this moment, the sheet feed clutch is coupled so that the sheet feed rollers 324 and 326 are rubbed against friction pads which are adhered to those portions of the bottom plates 312 of the sheet cassettes which will confront the rollers 324 and 326 when the sheet cassettes are mounted in the machine body. The rollers 324 and 148 are in this way protected from deposition of containments. When the return clutch 250 is coupled, the green lamp inside the print button 68 will glow under conditions: sheets present, toner present, key counter set, desired number of copies fully produced, and 1 to 1 copy mode. Thereafter, the halogen lamp 168 is turned off by the 9th pulse and the developing bias, sheet feed clutch (in the case of "paper end") and registry clutch are all turned off by the 23th pulse. At a stage 14 , when the carriage 178 fails to regain home position even after 1.5 seconds since a turn-on of the return clutch 250, a service call is produced. If the carriage 178 succeeds in regaining the home position and a repeat copy mode is under way, a printing cycle is repeated with the key counter, oil supply solenoid and sheet feed clutch turned on. If a repeat copy mode has been completed, the fixing end solenoid 498 is turned off by the 100th pulse after a turn-off of the charger 28, the blade solenoid and chargers 34 and 36 are deenergized by the 125th pulse, and the main motor 50 is deactivated after 1 second. The respective units are thus caused into a stand-by condition.

FIG. 50 is a flowchart for coping with various failures in the machine. FIG. 51 is a timing chart according to which various components are controlled in the event of a sheet jam.

First, a procedure for settling a sheet jam in the sheet feed section will be discussed. Suppose that the sheet feed sensor 376 is turned on under a stand-by condition or that the sheet feed sensor 376 is off when the registry switch 522 is turned on; in each case the fan 66 at the fixing station remains turned on. Under any of these conditions, all the component elements except the fixing end solenoid 498, main motor 50 and fan 66 are deactivated. The turn-off of the fixing end solenoid 498 occurs after 1 second in order to ensure normal discharge of a sheet fed before the sheet is fed out of the machine. The turn-off of the main motor 50 occurs after 0.3 second for releasing the pressure on the fixing roller 404. If it is the first sheet after a depression of the print button 68 that jammed the path, all the component units except the main motor 50 are turned off as soon as the jam is detected and, after 0.3 second, the main motor 50 is turned off.

When a sheet jam occurs in the sheet discharge section, all the drive lines except the main motor 50 are deactivated while the main motor is turned off after 0.3 second. The fan 66 at the fixing station is turned off in this case. When a sheet jam occurs in a stand-by state of the machine, it is reflected by a turn-on of the sheet discharge sensor. When a sheet jam occurs during a copying operation of the machine, all the drive lines are turned off except the main motor 39 and this main motor 50 is deactivated after 0.3 second. Conditions which cause this are: when a sheet is absent at the sheet discharge sensor when 79 jam timing pulses 2 are counted since a start of the count which occurs when 40 jam timing pulses 1 are counted up from the instant the forward clutch 111A is coupled, or when a sheet fails to move past the sheet sensor when 26 jam timing pulses 4 are counted up since a start of the count which occurs 81 jam timing pulses 3 are counted up from the instant the return clutch 250 is uncoupled. It will be noted that the above-mentioned specific counts of the jam timing pulses 1 and 2 are reached after a period of time which is somewhat longer than a period of time which a sheet fed properly takes to arrive at the sheet discharge sensor. Also, the counts of the jam timing pulses 3 and 4 are reached after a period of time which is somewhat longer than a time period which a sheet fed properly moves past the discharge sensor.

Now, various conditions which result in a service call will be described. Procedures based on software are employed for a failure in timing pulses, a failure in the optical system drive, a case wherein the fixing temperature remains below a predetermined level for 6 minutes or more under a stand-by condition, and a case wherein the fixing temperature remains lower than a lower limit for 6 minutes or more. For other conditions, procedures are based on hardware. The kind of each service call is displayed by light emitting diodes on the LED display 20.

When a timing pulse does not arrive within 0.2 second after the arrival of an immediately preceding timing pulse, the drive is determined failed and the procedure shown in FIG. 52 occurs. When the registry switch 522 does not turn on within 0.5 second after coupling of the sheet feed clutch, or when the home position switch 210 does not turn on within 1.5 seconds after coupling of the return clutch 250, the drive of the optical system is determined as failed and the procedure shown in FIG. 53 takes place. When the fixing temperature remains below a predetermined level for 6 minutes or more under a stand-by condition, the fixing temperature is judged abnormal and the procedure shown in FIG. 55 is performed through a circuitry of FIG. 54. When the fixing temperature remains below a lower limit for 1 minute or more, the fixing temperature is determined abnormal and the procedure shown in FIG. 57 is performed through a circuitry of FIG. 56.

The following actions for producing a service call relay on hardware. When the fixing temperature rises beyond 240.degree. C., a transistor Q 401 in a circuitry of FIG. 58 is turned on to make the base voltage of a transistor Q 28 "L" so that the transistor Q 28 is turned off. Then a capacitor C 10 is charged. Upon an increase in the voltage in the capacitor C 10 above 12.6 V, a transistor Q 29 is rendered conductive energizing a light emitting diode LED 1 on the LED display 20. Since the transistor Q 29 is turned on, a 1-pin of a transistor array IC 26 is at a "L" level and a 14-pin is at a "H" level whereby a power relay RA is turned off. Seeing that the transistor Q 29 is turned off, the CPU turns on a service call lamp.

When the toner density sensor in the developing system remains clogged with the toner for more than 4.9 seconds, a comparator IC 306 in a circuitry of FIG. 59 produces a "H" output which is coupled to a CP terminal 11 of a flip-flop IC 309. Accordingly, the flip-flop IC 309 produces a "H" output at its output terminal 13 whereby a transistor array IC 307 is caused to produce a "L" output at an output terminal 10 thereof. As a result, a light emitting diode LED 2 on the LED display 20 is energized. The 1-pin of the transistor array IC 26 becomes "L" and the 14-pin "H" deenergizing the power relay RA. The CPU receiving the output of the transistor array IC 307 turns on the service call lamp.

Referring to FIG. 60,. when a 10 V power source for control is lowered beyond 7 V, a transistor Q 32 is turned off because its base voltage drops below 0.7 V. This turns on a transistor Q 33 and thereby energizes a light emitting diode LED 3 on the LED display 20. The 14-pin of the transistor array IC 26 becomes "H" to deenergize the power relay RA. The CPU turns on the service call lamp in response to the output of the transistor Q 33.

Referring to FIG. 61, when a 24 V power source for DC load drive is lowered beyond a predetermined level, the base voltage of a transistor Q 30 becomes lower than 0.7 V rendering the transistor Q 30 nonconductive. This turns on a transistor Q 31 which in turn energizes a light emitting diode LED 4 on the LED display 20. The 14-pin of the transistor array IC 26 becomes "H" deenergizing the power relay RA. The CPU turns on the service call lamp supplied with the output of the transistor Q 31.

Referring to FIG. 62, when the halogen lamp 168 is kept energized for more than 4.3 seconds or a wire breakdown continues for more than the same period, a transistor Q 4 is made conductive to turn on a light emitting diode LED 5 on the LED display 20. The 1-pin of the transistor array IC 26 becomes "L" and the 14-pin "H" turning off the power relay RA. The CPU turns on the service call lamp supplied with the output of the transistor Q 4.

FIG. 63 illustrates a control power source circuit which includes a power source of AC 20 V for the power pack. A 3-terminal regulator IC 202 prepares a voltage DC 8 V from a voltage AC 10 V. A 3-terminal regulator IC 204 prepares a voltage DC 10 V from a voltage AC 15.5 V. A constant voltage power source IC 205 prepares a voltage DC 24 V from a voltage AC 27 V.

The control section is furnished with a key switch input circuit shown in FIGS. 64, 65 and 66 and a segment energization circuit shown in FIG. 67. Inputs through a key switch are entered and identified by the CPU through a KT-KIN matrix. The segment energization circuit turns on the various segments dynamically. For example, to energize "A" segments of the leftmost "8" in FIG. 67, a SEG 38 V is set up and the data are "L" at SEG A and "H" at the others SEG B to SEG G.

A toner density control will be described hereinafter.

Concerning a power source, use is made of 3-terminal regulators to prepare constant voltage sources of DC +10 V and DC +6 V from a voltage of DC 24 V.

Principles of toner density detection will be outlined first with reference to FIGS. 68 to 70. FIGS. 71 to 73 are circuit diagrams representing details of the toner density detection.

A block diagram shown in FIG. 68 will be described first.

While a constant volume of developer will flow down through the bobbin 530 of the toner density sensor, the inductance of the coil 532 wound on the bobbin 530 is varied depending on the toner density, that is, the ratio of the carrier and the toner to each other which dictates the permeability of the coil 532. A change of the inductance of the coil 532 is reflected by a change of the output frequency f.sub.r of an oscillator 534 which is coactive with the coil 532 on the bobbin 530. A second oscillator 536 produces a reference oscillation frequency f.sub.s. Outputs f.sub.r and f.sub.s of these oscillators 534 and 536 are coupled to an adder 538 an output of which is in turn coupled to an integral amplifier 540. An integrated and amplified output of the amplifier 540 is applied through a detector 542 to a DC amplifier 544. A comparator 554 compares an output voltage V.sub.r of the DC amplifier 544 with a reference voltage V.sub.s1. If an actual toner density is lower than a reference density, the comparator 554 actuates the toner supply mechanism 63 through a driver 546 to cause a supply of toner particles into the casing of the developing unit. The output voltage V.sub.r of the Dc amplifier 544 is also applied to a bobbin stop-up detector 550 so that, if the bobbin 530 is clogged, the detector 550 activates the display while interrupting the drive of the machine body.

More specifically, in FIG. 71, when an actual toner density is lower than a reference level an output terminal 6-pin of a DC amplifier IC 305 produces a voltage which is lower than the reference voltage V.sub.s1. If an actual toner density is higher than the reference level, a voltage higher than the reference voltage V.sub.s1 appears at the output terminal 6-pin of the DC amplifier IC 305. A voltage appearing at the output terminal 6-pin of the DC amplifier IC 305 indicated by b in FIG. 72 is coupled to an inverting input terminal of a comparator IC 306. A voltage at a point a in FIG. 72 which is the reference voltage V.sub.s1 is coupled to a non-inverting input terminal of the comparator IC 306. When an actual toner density is lower than the reference level, the voltage coupled to the comparator IC 306 from the point b is lower than the reference voltage V.sub.s1 coupled from the point a . Then the comparator IC 306 produces a "H" output at its output terminal 1-pin whereby a light emitting diode LED 301 is turned on for monitoring a toner supply operation and, at the same time, a transistor array IC 307 is turned on to in turn energize an electromagnet clutch MC. This clutch MC drives the toner supply roller 106 for supplying a supplementary amount of toner into the 56. In case where an actual toner density is higher than the reference level, a voltage appearing at the output terminal 6-pin of the DC amplifier IC 305 is higher than the reference voltage V.sub.s1. Comparing the voltages at the points a and b , the comparator IC 306 produces a "L" output at the output terminal 1-pin which turns off the light emitting diode LED 301 and deenergizes the clutch MC adapted to drive the clutch MC. Where the developer agitating switch 22 has been turned on, the input level of the 3-pin of the transistor array IC 307 is "L" turning the transistor array off and maintaining the clutch MC deenergized.

A switch SW 301 is employed to compensate for a change of the image density attributable to a change in a surrounding condition by altering the reference voltage at the point a . That is, when air surrounding the machine is relatively humid, the switch SW 301 operates to lower the reference voltage beyond a predetermined level and thereby promote a control of the toner density at a relatively low level because a high humidity would increase the image density. When the air is relatively dry, the reference voltage at the point a will be raised beyond the predetermined level so as to control the toner density at a relatively high level because a low humidity would lower the image density.

Referring to FIG. 73, when the main motor 50 is activated, the signal level at an input terminal 1-pin of an IC 317 turns from "H" to "L" and, therefore, the signal at an output terminal 2-pin from "L" to "H". At the buildup of the output at the 2-pin of the IC 317, a timer in an IC 311 is activated to hold a "L" output at an output terminal 7-pin of the IC 311 for a time period which is determined by a resistor R 342 and a capacitor C 322. Where the signal level at the output terminal 7-pin of the IC 311 is "L", the input level at the 3-pin of the transistor array IC 307 is kept at "L" regardless of the toner density so as to disable the toner supply mechanism. More specifically, since the amount of flow of the developer through the bobbin is unstable in an initial stage of operation of the developing unit 30, actions of the toner supply mechanism 106 are inhibited to avoid a supply of a needless volume of toner for a given time period from an instant the unit 30 is activated to an instant the flow of the developer grows stable.

Reference will be made to FIG. 74 showing a sensor stop-up detection circuit and FIGS. 75 and 76 which are timing charts concerned with the circuit of FIG. 74, for explaining a procedure for detecting a stop-up of the toner density sensor.

When the power source is turned on, a capacitor C 327 is charged through a resistor R 338. Before the voltage charged in the capacitor C 327 exceeds a threshold level of an inverter IC 316, an output terminal 12-pin of the inverter IC 316 remains at a "H" level which is coupled to a CL input 309 10-pin of a flip-flop IC 309 to reset it. The flip-flop IC 309 serves as a circuit for memorizing a stop-up of the toner density sensor and memorizes a stop-up condition even after a developing operation has been interrupted and drawing of the developer stopped.

As the flow of the developer is fully stopped or almost stopped, an output voltage of the DC amplifier IC 305 coupled to an input 5-pin of a comparator IC 306a rises beyond a voltage at an input 6-pin of the comparator IC 306a which is a voltage divided by resistors R 312 and R 320. This makes the signal level at an output 7-pin of the comparator IC 306a "H". If in this instance the main motor is turned on, that is, the input level at the inverter IC 317 is "L" and the output level is "H" and if the developer agitating switch 26 is turned off, an output 3-pin of a NAND gate IC 314 is at a "L" level which renders a transistor Q 303 nonconductive so that a capacitor C 335 is charged through resistors R 370 and R 374. As the voltage charged in the capacitor C 335 increases beyond a voltage divided by resistors R 371 and R 362, the signal level at an output 8-pin of a comparator IC 306b changes from "L" to "H". This output of the comparator IC 306b is supplied to a CP input of the flip-flop IC 309 to set it (Q output becomes "H"), informing the display and machine control with the failure.

When an actual toner density is proper, the voltage at the 5-pin of the comparator IC 306a remains lower than the voltage at the 6-pin maintaining the output level at the 7-pin "L". Therefore, the output 8-pin of the comparator IC 306b is kept at the "L" level and the flip-flop IC 309 is not set. However, if the developing agitating switch 22 is turned on or the main motor 39 is turned off, either a 1-pin or a 2-pin of the NAND gate IC 314 is "L" and thus the 3-pin is "H" whereby the transistor Q 303 is turned on to release the charge from the capacitor C 335. As a result, a stop-up check on the toner density sensor is not carried out even though the signal level at the 7-pin output of the comparator IC 306a may be "H". The flip-flop IC 309 will be reset when the main switch changes its state from off to on.

A toner density control has been described in connection with a case wherein the flow of the developer through the bobbin 8 is fully or almost stopped. It will be seen that clogging of the bobbin can be detected in the same way when the developer is caused to stay within the bobbin. In such a case, the output voltage of the DC amplifier IC 305 will be lowered sufficiently beyond an output voltage under normal conditions. Thus, it suffices to compare an output voltage of the DC amplifier IC 305 with a predetermined reference voltage by a comparator. Details will be described later.

FIG. 77 shows a toner end detection circuit and FIG. 78 is a timing chart demonstrating its operation.

When the toner density in the casing drops beyond a predetermined reference density, the voltage coupled from the DC amplifier IC 305 to the input 2-pin of the comparator IC 306 is lowered beyond the voltage at the input 3-pin (point a ). This renders the output level of the comparator IC 306 "H" and this output is applied to an input 5-pin of a NAND gate IC 314a. Since the developer agitating switch 26 is turned off, an output 4-pin of the NAND gate IC 314a is "L" and a transistor Q 302 is nonconductive. Then a timer IC 308 is activated and, when the "H" output level of the comparator IC 306 lasts a given period of time determined by a capacitor C 321 and resistors R 348 and R 373, said "H" output changes into "H" output. At this instant, the signal level at an input 12-pin of a NOR gate IC 312 is "L" so that an output 12-pin of the NOR gate IC 312 turns from "L" to "H". A flip-flop IC 309a therefore has its Q terminal set to "H" level whereby a toner end signal is delivered through a transistor array IC 307a to the display and machine body control.

An input 12-pin of a NAND gate IC 314b is connected with an output 6-pin of the inverter IC 316 and, therefore, at a "H" level. If the front cover 24 of the machine is closed, an input 13-pin of the NAND gate IC 314b is at a "H" level. Therefore, an output level of the NAND gate IC 314b is "L" under these conditions.

FIG. 79 indicates a toner end reset circuit and its operation is represented by a timing chart in FIG. 80. As shown, when the main switch is turned on or the front cover 18 of the machine is closed, a toner end reset signal is supplied to the toner end reset circuit for thereby resetting a toner end condition.

FIG. 81 is a circuit diagram showing an initial main motor control circuit while FIG. 82 is a timing chart corresponding to this circuit. This circuit functions to control the operation of the main motor 50 so that a toner density is detected for a toner density control when the main switch is turned on and that, when the front cover 18 is closed after a supply of a supplementary volume of toner which naturally requires opening of the front cover 18, the toner is safely supplied to increase an actual toner density to a normal level.

A monostable multivibrator IC 311a in FIG. 81 serves to determine an operating time of the main motor 50.

When the power source is turned on, an integrator made up of the resistor R 338 and capacitor C 327 produces a pulse signal based on which the monostable multivibrator IC 311a is triggered. When the front cover 18 is closed, the monostable multivibrator IC 311a is triggered by a signal prepared by a differentiator which consists of the resistor 340 and capacitor C 326. While the monostable multivibrator IC 311a produces a pulse whose duration is determined by a maximum time period determined by a resistor R 349 and a capacitor C 328, it is reset by a reset circuit made up of the NAND gate IC 315, NOR gate IC 314 and inverter IC 316 when an actual toner density is determined high. Then the command to the main motor drive is stopped to thereby deactivate the motor 39.

Furthermore, the toner density control method in the present invention will be described in detail hereinafter.

Referring to FIGS. 68 and 83, the sensor oscillator 534 comprises the funnel-shaped bobbin 530 and an oscillation circuit. A change of the inductance L.sub.r of the coil is reflected by a change of the output oscillation frequency f.sub.r. A toner density attained through this change of the output oscillation frequency f.sub.r will be used as a first level of toner density. The oscillation frequency f.sub.r may be expressed as: ##EQU1##

The reference oscillator 536 is essentially similar to the sensor oscillator 534 except that it does not involve a flow of the developer through a coil. An output frequency of the sensor oscillator f.sub.r is compared with an output frequency f.sub.s of the reference oscillator. An output frequency f.sub.s of the reference oscillator is also utilized to compensate for an initial drift and a drift attributable to temperature of an output frequency f.sub.r of the sensor oscillation circuit.

A multivibrator 552 is connected with the sensor oscillator 534 and reference oscillator 536 to change over their oscillation intervals. Another function of the multivibrator 552 is to clamp a portion of an input of the DC amplifier 544 based on the reference oscillation to a predetermined voltage. The adder 538 combines oscillation frequencies f.sub.r and f.sub.s and produces an AC component only through a coupling capacitor C.sub.9. The integral amplifier 540 modulates its input frequency with respect to a voltage (amplitude) by reducing an amplitude amplification ratio as the input frequency differs more from a resonance frequency which is expressed as: ##EQU2##

The detector 542 is adapted to process an output of the integral amplifier 540 on amplitude modulation basis. An amplified output of the detector 542 is passed through a coupling capacitor C.sub.14 of the DC amplifier 544 so that a DC component of the input is picked up. At the same time, controlled by the multivibrator 552, the DC amplifier 544 forcibly clamps a signal component produced by the reference oscillator 536 to a predetermined voltage. Thus, the DC amplifier 552 produces a DC signal which is an inverted, integrated and amplified version of a difference between the two oscillators 534 and 536. The comparator 554 compares an output voltage V.sub.r of the DC amplifier 544 with the reference voltage V.sub.s1 to control a supply of toner particles. A "H" level output of the comparator 287 indicates a drop of the toner density and urges the toner supply mechanism 548 to supplement the toner. The drive 546 amplifies an output of the comparator 554 for thereby driving the toner supply mechanism 548. The mechanism 548 includes an electromagnetic clutch, a motor and the like as well as a supply mechanism. The stop-up detector 550 includes a comparator 552 supplied with a reference voltage V.sub.s2, a second comparator 554 supplied with a reference voltage V.sub.s3, a timer 556, flip-flop 558 etc. The comparator 552 compares an output voltage V.sub.r of the DC amplifier 544 with the reference voltage V.sub.s2 for checking a stop-up at the bobbin 530. As the bobbin 530 becomes clogged, the input voltage V.sub.r increases beyond a level V.sub.r1 which will be supplied during normal operations of the toner density sensor. The voltage V.sub.r higher than the voltage V.sub.r1 will be referred to as a voltage V.sub.r2. The reference voltage V.sub.s2 coupled to the comparator 552 is predetermined to be higher than the voltage V.sub.r1 but lower than the voltage V.sub. r2. In the event of a stop-up, the voltage V.sub.r2 becomes higher than the reference voltage V.sub.s2 making the output level of the comparator 552 "H". The other comparator 554 serves to compare an output voltage V.sub.r of the DC amplifier 544 with the reference voltage V.sub.s3 for checking a stop-up at the bobbin 530. When the bobbin 530 is choked up, the voltage V.sub.r grows lower than the voltage V.sub.r1 under normal conditions of the toner density sensor. The voltage V.sub.r higher than the voltage V.sub.r1 will be referred to as a voltage V.sub.r3. The reference voltage V.sub.s3 coupled to the comparator 554 is predetermined to be higher than the voltage V.sub.r3 but lower than the voltage V.sub.r1. As the bobbin 530 becomes choked up, the voltage V.sub.r3 is lowered beyond the reference level V.sub.s3 turning the output level of the comparator 554 from "L" to "H". The toner densities thus measured by the comparators 552 and 554 will be used as second and third levels of toner density, respectively. An output of each comparator 552 or 554 is applied to the timer 556. The timer 556 normally produces a "H" output, but this output level turns into "L" when the input signal holds the "H" level over a given period of time dependent on the time constant of its C-R network. A "L" level output of the timer 556 sets the flip-flop 558 which then supplies an output to the display and machine body control. The timer 556 is effective to prevent a malfunction of the machine which will result from a relation V.sub.s2 <V.sub.r2 or V.sub.r3<V.sub.s3 which may temporarily hold due to fluctuation of the flow of the developer. When the developing unit is in a stand-by state, the developer will not flow through the bobbin 530. An arrangement is made such that the timer 566 remains inoperative during a stand-by of the developing unit.

In summary, a toner density control method in this case eliminates a short or excessive supply of a toner which would adversely affect an image quality by measuring, apart from a usual first level of toner density, a second level of toner density and a third level of toner density each for checking a stop-up of a bobbin.

FIG. 84 shows a fixing temperature control circuit and FIG. 85 shows a lower heater control circuit. FIG. 86 is a timing chart indicating an operation of the fixing temperature control circuit.

The circuit depicted in FIG. 84 generally comprises a lower temperature sensing section, a temperature control section (upper heater 402), an upper temperature limit sensing section and a circuit for forcibly energizing the lower heater 406.

When an actual fixing temperature is lower than a predetermined lower limit 180.degree. C. allowable for fixing operations, the thermistor 410 connected in parallel with a resistor R 401 for sensing a temperature at the fixing roller increases its resistance. Then a voltage at a terminal 2 of a volume VR 401 is lowered beyond a lower limit reference voltage determined by resistors R 406 and R 409. More specifically, a comparator IC 401 determines a voltage at an input 4-pin lower than a voltage at an input 5-pin, producing a "H" output at its input 2-pin. This turns on a transistor Q 404 an output of which is coupled to the central processing unit CPU. Thus, if an actual fixing temperature is lower than the lower limit, a signal is applied from the transistor Q 404 to the central processing unit CPU to disenable printing actions. As the fixing temperature is elevated beyond 180.degree. C., the voltage relation between the 5-pin and 4-pin of the comparator IC 401 is inverted so that a "L" output appears from the output 2-pin. This turns off the transistor Q 404 informing the central processing unit CPU of an increase in the actual fixing temperature above the lower limit.

The temperature control section will operate as follows. When an actual fixing temperature is below 195.degree. C. which suffices for fixing operations, a resistance of the thermistor 186 is higher than a resistance at the fixing temperature of 195.degree. C. Under this condition, a voltage at a 2 terminal of the volume VR 401 is lower than a reference voltage determined by resistors R 405 and R 408. The comparator IC 401 judges a voltage at an input 6-pin lower than the voltage at an input 7-pin producing a "H" output at its output 1-pin. Then a transistor Q 403 is made conductive to turn on a light emitting diode LED 401 adapted to monitor operations of the heaters 402 and 406. The transistor Q 403 also turns on a transistor Q 405 and turns off a transistor Q 402. Then the transistor Q 403 energizes the upper heater 402 and the transistor Q 405 the lower heater 406. The transistor Q 402 turned off shows the central processing unit CPU that an actual fixing temperature is short of the reference level 195.degree. C. Upon an increase in the temperature beyond 195.degree. C., a voltage at the input 6-pin of the comparator IC 401 grows higher than the reference voltage at the input 7-pin, an output "L" appearing from the output 1-pin. Then the transistors Q 403 and Q 405 are turned off while the transistor Q 402 is turned on. The transistor Q 403 turned off deenergizes the upper heater 402, the transistor Q 405 turned off deenergizes the lower heater 406, and the transistor Q 402 turned on informs the central processing unit CPU of the rise of the temperature above 195.degree. C. (a reload condition). Once a reload condition is set up, it is maintained until the actual temperature drops down to a level lower than the lower limit 180.degree. C. It should be noted, however, the lower heater 406 is controlled in a different manner as will be described.

The upper temperature limit detecting section will operate as follows. When an actual temperature rises above a predetermined level 230.degree. C. which is the thermal breakdown level of the rollers 404 and 408, the resistance of the thermistor 410 is reduced to increase a voltage at the 2 terminal of the volume VR 401 beyond an upper limit reference voltage which is determined by resistors R 404 and R 407. The comparator IC 401 produces a "H" output at its output 14-pin because a voltage at an input 9-pin is higher than that at an input 8-pin. This turns on a transistor Q 401 an output of which is passed to the central processing unit CPU so as to produce a service call. Simultaneously, a power relay is turned off to kill the power source. If an actual fixing temperature is lower than 230.degree. C., a voltage at the input 9-pin of the comparator IC 401 becomes lower than that at the input 8-pin. Then a "L" output appears from the output 14-pin which turns off the transistor Q 401.

The lower heater control section will operate as follows in the course of copying cycles. To save power consumption, the lower heater 406 is controlled independently of the upper heater 402. In FIG. 85, a point A is connected to a turn-on timing signal for the halogen lamp 168 such that a voltage at the circled point A is "L" when the lamp 168 is turned on. Therefore, while the lamp 168 is turning on, the transistor Q 405 is turned off to deenergize a lower heater drive relay AD.sub.1 and thereby the lower heater 406. A point B is connected to an operation timing signal for the return clutch 250 and, thus, becomes "L" in voltage level during an operation of the return clutch 250. Accordingly, when the halogen lamp 168 is turned off and the return clutch 250 is coupled to return the carriage 178 to the home position, the transistor Q 405 is rendered conductive to energize the lower heater drive relay AD.sub.1 and thereby the lower heater 406.

In this way, the lower heater 406 is controlled regardless of a temperature detected by the thermistor 410 throughout copying cycles by timing signals supplied to the halogen lamp 168 and return clutch 250.

The circuitry of FIG. 85 additionally includes a relay AD.sub.5 for driving the upper heater 402.

FIG. 87 shows a circuit for AC drive and lamp turn-on detection and FIG. 88 indicates an essential part of the circuit in detail. FIG. 89 shows a lamp turn-on circuit. A timing chart indicated in FIG. 90 demonstrates an operation of the lamp turn-on detection circuit.

In FIG. 87, input terminals ADI.sub.1 -ADI.sub.6 are connected with the central processing unit CPU so as to be supplied with signals therefrom at predetermined timings. These input terminals ADI.sub.1 -ADI.sub.6 are individually connected to relays RA.sub.1 -RA.sub.6 which function to trigger load driving Triacs TR.sub.1 -TR.sub.6, respectively. The lamp turn-on detection circuit is designed to turn off the power relay while producing a service call when detected an endless turn-on of the halogen lamp 168 or a cut-off of its associated wiring. As shown in FIG. 87, this circuit consists of a lamp turn-on and wire cut-off detector section A, a timer section B, a holding section C and an output section D.

A timing chart indicated in FIG. 91 represents a general operation of the copying machine described hereinabove.

The above description will suffice to clarify the construction and arrangement of an electrophotographic copying machine to which the present invention is applicable.

The following pages will indicate Table 1 which is a program list of the 1-chip IC.sub.1 shown in FIG. 38 and Table 2 which is a program list for the other 1-chip IC.sub.2. ##SPC1## ##SPC2## ##SPC3## ##SPC4## ##SPC5## ##SPC6## ##SPC7## ##SPC8## ##SPC9## ##SPC10##

Preferred embodiments of a cleaning apparatus which constitutes the gist of the present invention will be described hereinafter.

A first embodiment of the cleaning apparatus is illustrated in FIG. 92. The cleaning apparatus includes a casing 600 to which a cleaning blade 602, an agitator 604 and others are rigidly mounted. A block or mass of film-forming material 606 having a small coefficient of friction is supported by means which is mounted to the casing 600 as will be described. A cylindrical rotatable brush 608 is driven by drive means, which will be discussed with reference to FIG. 93, into and out of pressing contact with a photosensitive drum 26 and the block 606 of film-forming material. The block 606, block support means, brush 608 and brush drive means form an essential part of the cleaning apparatus. The casing 600 is detachable from the machine body along elongate guides 610 integral with the machine body in a direction perpendicular to the surface of the drawing.

Before describing the essential part of the present invention, a general arrangement and operation of the cleaning apparatus will be outlined.

The cleaning blade 602 is supported by a holder 612 within the casing 600 to clear a worked part of a toner powder which remains on the surface of the drum 26. The holder 612 is rigidly mounted on a shaft 614 which is rotatable at an appropriate timing. A rotation of the shaft 614 will move the cleaning blade 602 into or out of pressing contact with the drum 26 through the holder 612. Toner particles scraped by the blade 602 off the drum 26 flows down along an upper surface of a first inlet seal member 616 which comprises a thin resilient plate which is rigidly connected to the unit casing 600 at one end and held in contact with the drum 26 at the other end. Then the toner particles reach a collector coil 618 which serves as a screw conveyor. The collector coil 618 in rotation moves the toner particles in a predetermined direction parallel to its axis whereafter the toner particles are advanced through a predetermined path until they are collected in a toner tank within a developing unit 30 to be used again. As shown, the first inlet seal 616 is provided with bristles on a lower end thereof (facing the drum 26) for the purpose of attaining a sealing effect. The agitator 604 is interposed between the coil 618 and blade 602 and located above the first inlet seal 616 in order to prevent toner particles from stopping up the space between the coil 618 and blade 602. More specifically, the agitator 604 is suitably driven for oscillation at a high frequency to break up gathered toner particles and thereby surely feed them to the coil 618. A seal guide 620 is disposed below the casing 600 in such a manner as to surround a lower portion of the latter. The seal guide 620 carries at an end thereof a second inlet seal member 622 which is constructed and arranged in exactly the same way as the first inlet seal 616. The second inlet seal 622 has a function of receiving toner particles which may fall while the cleaning apparatus is being mounted to or demounted from the machine body.

As viewed in FIG. 94, the block 606 of film-forming material is adhered or otherwise secured to a holder 628 which comprises guides 624 and a knob 626. The casing 600 on the other hand is formed with guide channels 630. Thus, the block 606 can be placed in a predetermined position on the casing 600 by holding the knob 620 with a hand and inserting the guides 624 on the holder 628 into the guide channels 630 on the casing 600. In this respect, the holder 628 and guide channels 630 constitute support means for the block 606 in combination. With this arrangement, the block 606 on the holder 628 can be easily replaced with another as desired.

The brush 608 is located in a position within the casing 600 and downstream of the cleaning blade 602 with respect to the direction of rotation of the drum 26; it is rotatable in a direction which opposes the rotation of the drum 26 (see FIG. 92). The brush 608 is employed to apply the film-forming material evenly onto a surface of the drum 26 which is cleared of residual toner particles by the cleaning blade 602. In an application mode of operation, the brush 608 is positioned as indicated by a solid line in FIG. 92 to pressingly contact the peripheries of the drum 26 and block 606. The brush 608 in this position will apply the film-forming material 606 onto the drum 26 therethrough. In a non-application mode, the brush 608 is shifted to a position 632 indicated by a phantom line in FIG. 92 where it becomes spaced at least from the drum 26. These application and non-application modes are controllably switched from one to the other to match a condition of the layer of the film-forming material on the drum 26. For example, a time period for an application mode may be prolonged if an amount of the material on the drum 26 is short and a time period for a non-application mode may be prolonged if an amount of the material is excessive. The condition of the film on the drum 26 continuously varies rubbed by the cleaning blade 602 for instance. Additionally, the film has its thickness increased little by little over a long time of operation of the copying machine. For these reasons, it is very important to control the film on the drum 26 by switching the application and non-application modes from one to the other.

Selection of an application mode or a non-application mode is made by moving the rotatable brush 608. Reference will be made to FIG. 93 for describing the means for shifting the brush 608 into and out of contact with the drum 26. As shown in FIG. 93, the casing 600 is provided with a front side panel 634 and a rear side panel 636 which individually closes openings formed at front and rear ends of the casing 600 with respect to the axial direction of the drum 26. The brush 608 is mounted on a shaft 642 by pins 638 and brushes 640. The front and rear side panels 634 and 636 are formed with elongate slots 644 and 646, respectively; each of these elongate slots is sufficiently larger than the diameter of the shaft 642. The shaft 642 extends throughout the elongate slots 644 and 646 to protrude outward therefrom at its opposite ends. Passed through the front side panel 634, the shaft 642 is further passed rotatably through a bearing 650 which is fitted in one or free end of a swingable lever 648. This end of the shaft 642 carries a gear element G.sub.1 rigidly therewith. A snap ring 652 is attached to the shaft 642 to prevent the gear element G.sub.1 from slipping out of the shaft 642. Likewise, the other end of the shaft 642 passed through the rear side panel 636 is further passed rotatably through a bearing 656 fitted in one or free end of a second swingable lever 654. Separation of the shaft 642 at said other end from the panel 636 is prevented by a snap ring 658.

The other or base end of the first swingable lever 648 is coupled on a connecting shaft 664 which rotatably extends through the front side panel 634. A set screw 666 keeps the lever 648 from rotation relative to the shaft 664. The other or base end of the second swingable lever 654 is coupled on an end of a connecting shaft 660 which extends rotatably through the rear side panel 636. The lever 654 is prevented by a set screw 662 from rotating relative to or separating from the shaft 660. A gear element G.sub.2 is mounted on the other end of the shaft 660 and prevented by a snap ring 668 from separating therefrom. This gear element G.sub.2 is in driven connection with a drive line adapted to drive the copying machine and, in this respect, it functions as a drive gear. A stub shaft 670 is studded on the swingable lever 648 intermediate between the gear elements G.sub.1 and G.sub.2. An intermediate gear element G.sub.3 is mounted on the stub shaft 670 and meshed with 60th of the gear elements G.sub.1 and G.sub.2. A snap ring 672 keeps the gear element G.sub.3 from separating from the stub shaft 670.

Other two gear elements G.sub.4 and G.sub.5 are rotatably mounted to the front side panel 634 and meshed with each other. The gear element G.sub.4 is adapted to impart power to the agitator 604 for causing it to oscillate while the gear element G.sub.5 is adapted to transmit power to the collector coil 618 to rotate it. A rotational movement generated by a drive line (not shown) is delivered first to the gear G.sub.2 and therefrom to the gear G.sub.1 via the intermediate gear G.sub.3. The rotation is also transmitted to the intermeshed gears G.sub.4 and G.sub.5 whereby the agitator 604 is oscillated and the coil 618 rotated. As already mentioned, the base ends of the swingable levers 648 and 664 are integral with the shafts 664 and 660, respectively. The levers 648 and 654 therefore are caused to swing individually about the shaft 660, accompanying a swinging action of the brush 608. It is noteworthy here that despite such actions of the swingable members the gears G.sub.1 -G.sub.5 are kept in the same meshing relations.

A pin 674 extends out from the free end of the swingable lever 648 into engagement with one arm 678 of an L-shaped lever 676 which is provided to a stationary side plate 680 integral with the machine body. A first tension spring 684 is anchored at one end to the free end of the other arm 682 of the lever 676 and at the other end to a plunger 688 of a solenoid 686 which is rigid on a stationary member such as the side plate 680. A second tension spring 690 is retained at one end by said one end of the arm 682 and at the other end by a pin studded on the side plate 680 though not shown in the drawing. As will become apparent from the following description, the spring 684 serves as a pressure applying spring and the spring 690 as a pressure releasing spring.

The swingable lever 648 has an upright lug 692 disposed generally above that portion of the lever through which the shaft 660 extends. The top of the lug 692 retains one end of a tension spring 694 the other end of which is anchored to a pin 696 studded on the front side panel 634. Serving as a release spring as will be described, the spring 694 constantly biases the swingable lever 648 clockwise about the shaft 660. This clockwise motion of the lever 648 is limited when the pin 644 is engaged with the arm 678 of the L-shaped lever 676 or when the shaft 642 abuts against the upper end of the slot 644. When the shaft 642 abuts against the upper end of the slot 644, the brush 608 is disengaged from both the drum 26 and block 606 setting up a non-application mode.

When the solenoid 686 is deenergized, the spring 690 pulls the plunger 688 out of the solenoid 686 to its stroke end against the action of the spring 684 while, at the same time, moving the L-shaped lever 676 clockwise. This movement of the L-shaped lever 676 is stopped when the plunger 688 reaches a stroke end position thereof. In this situation, the arm 678 of the lever 676 is positioned above and spaced a little from the pin 674 which is then stationary in an uppermost position defined by the slot 644. Stated another way, the pin 674 and arm 678 do not interfere with each other under the condition mentioned above and such positions of the pin 674 and arm 678 will facilitate easy removal of the casing 600 bodily from the machine body.

When the solenoid 686 is energized, the plunger 688 is drawn into the solenoid 686 to swing the L-shaped lever 676 counterclockwise against the action of the spring 690 and the arm 678 of the lever 676 soon comes to abut against the pin 674. Thereafter, the swingable lever 648 is rotated counterclockwise about the shaft 660 not only against the force of the spring 690 but against the force of the spring 694 this time, conditioning the cleaning apparatus for a non-application mode. The counterclockwise movement of the lever 648 is limited by a stop 694 against which the lever 648 abuts. It will be noted that the brush 608 is engaged with both the drum 26 and block 606 when the pin 674 abuts against the stop 694. The stop 694 is connected to the side plate 680 at an intermediate part thereof by an adjusting screw 696. A set screw 700 is threaded into the side plate 680 through an elongate slot 698 formed in the stop 694. A position the stop 694 limits the action of the lever 648 as mentioned is adjustable by loosening the set screw 700, moving the stop 694 about the screw 696 to a desired position and tightening the set screw 700 at the desired position. By so adjustably positioning the stop 694, the brush 608 can be held in pressing contact with the drum 26 and block 606 for a controlled period of time, by a controlled amount, etc.

The cleaning blade 602 is so controlled as to remain engaged with the drum 26 only when the drum 26 is in rotation. The brush 608 is controlled such that it contacts the drum 26 only when the cleaning blade 602 is kept in contact with the drum 26. This manner of control will prevent the brush 608 from being contaminated by toner particles and thereby preserve the expected function of the brush 608 over a long time of use.

It will be understood from the foregoing that the cleaning apparatus constantly maintains an appropriate amount of application of the film-forming material by on-off controlling the solenoid 686 to shift the brush 608 between two different positions.

In the embodiment described, an automatic control of the thickness of the film is possible as by controlling the solenoid 686 such that it is deenergized to move the brush 608 out of contact with the drum 26 when a given number of copies or that of rotations of the drum is reached and is energized again to bring the brush 608 into contact with the drum 26 and block 606 when a given number of copies or that of rotations of the drum 26 is reached after the deenergization of the solenoid 686. For this purpose, the cleaning apparatus will be operatively connected with a counter for counting copies produced or rotations of the drum 26.

Another embodiment of the present invention is shown in FIGS. 95 and 96. A major difference of this embodiment from the embodiment described with reference to FIGS. 92-94 is that a member 800 serving as a friction coefficient sensor is located in a position downstream of the film-forming material applying device with respect to the direction of rotation of the drum 26. As shown, the member 800 comprises a blade 802, a blade holder 806 carrying the blade 802 integrally therewith and rotatable about a shaft 804, a lever 808 integral with the blade holder 806 and extending upward and rightward away therefrom, and a switch 810 engagable with a free end 818 of the lever 808.

FIG. 96 illustrates an electric circuit for operating the film-forming material applying device. The switch 810 is connected in series with a timer circuit 812 which comprises a monostable multivibrator circuit or the like. A coil 816 is connected to the collector of a transistor or equivalent switching element 814. The coil 816 constitutes an electromagnetic switch which intervenes between the brush 608 and a drive source for the brush 608.

The blade 802 is engaged with the drum 26 either constantly or only during copying cycles under a predetermined pressure to function as a feeler of the friction coefficient sensor. The blade 802 therefore varies its position depending on the varying coefficient of friction on the surface of the drum 26. The switch 810 has a specific position which is determined such that the switch turns on when the coefficient of friction on the drum surface is large and turns off when it is small. This is attainable by determining a position of the blade 802 on the drum 26 before application of the film-forming material and then a relation between a position of the lever 808 of that instant and an amount of stroke of the lever 808 caused by a decrease in the coefficient of friction on the drum. The switch 810 comprises a normally open switch which preferably has as small a tolerance as possible. FIG. 95 represents a situation in which the coefficient of friction on the drum is large and the material applying device is operative. A large coefficient of friction causes the sensor blade 802 to rotate clockwise about the shaft 804 as viewed in FIG. 95 so that the lever 808 integral with the blade 802 is rotated also clockwise about the shaft 804 with its free end 818 moved downward. Then the switch 810 shown in FIG. 96 is opened to activate the timer 812 which in turn renders the switching element 814 conductive. This activates the electromagnetic clutch adapted to drive the brush 608 of the material applying device for rotation. The conduction period of time of the switching element 814 after each opening of the switch 810 is determined by the timer 812. As the brush 608 is driven for rotation, it scrapes a necessary amount of film-forming material 606 from a source 816 and supplies the material onto the surface of the drum 26 carrying the material on its filaments. As will be recalled, the film-forming material 606 has a small coefficient of friction. Concerning the necessary amount of application of the material, an optimum amount can be determined through experiments.

The switch 810 is mounted to a board 818 which is movable up and down through an adjusting screw 820 as seen in FIG. 95. The board 818 thus joins in the adjustment of a position of the switch 810 where the switch 810 will be actuated.

When the sensor blade 802 and lever 808 is rotated clockwise about the shaft 804 by a large coefficient of friction on the drum 26, the contact pressure between the blade 802 and drum 26 tends to be decreased. With this in view, a stop 822 is provided to the casing 600 to be abutted by the free end of the lever 808. When engaged by the lever 808, the stop 822 gives the blade 802 a force large enough to bring it back to the original position when the material 606 is applied to the drum 26 to reduce the coefficient of friction on the drum 26. Upon a decrease in the coefficient of friction, the blade 802 rotates slightly counterclockwise from the position illustrated in FIG. 95 whereby the free end 818 of the lever 808 is moved upward turning on the switch 810.

As has been discussed, the film-forming material is supplied onto a surface of the drum 26 when the coefficient of friction on the drum surface increases. The blade 802 positioned just past of the brush 608 immediately senses the application of the material and, therefore, the resulting decrease in the coefficient of friction. However, a major part of the periphery of the drum 26 is still left bare and, particularly, the coefficient of friction is still large in an area of the drum 26 at and adjacent to the cleaning blade 602 which is positioned ahead of the brush 608. The timer 812 is thus designed to activate the material applying device for a given period of time which is long enough to supply the material over the entire surface of the drum 26. More specifically, the timer 812 operates for each predetermined period of time necessary for the drum 26 to complete one full rotation.

In any of the foregoing embodiments, the operation of the device for supplying the film-forming material may be controlled on the basis of an on-off control of the brush 608, shift of the brush into or out of contact with the film-forming material, rotation of the brush at a controlled speed, variation of the time periods of contact and non-contact of the brush with the drum 26, or the like, all in accordance with the varying coefficient of friction on the drum 26.

While the switch 810 is shown in FIG. 96 connected with the timer 812, the timer 812 may be omitted so that the material applying device is operated directly in response to an action of the switch 810.

The sensor blade 802 may be located ahead of the brush 608 or the cleaning blade 602 with respect to the direction of rotation of the drum 26. This will surely make up for the omission of the timer 812. Also, the material applying device may be positioned past the sensor blade 802.

The rotary brush serving as the material applying device in the drawings may be replaced by a magnetic brush or a suitable arrangement which lets a material concerned fall onto the drum 26 by gravity.

In summary, it will be seen that the present invention provides a cleaning apparatus for electrophotography which maintains a substantially constant coefficient of friction between a photosensitive element and a cleaning blade and thereby minimizes wear of the photosensitive element while reducing wear of the cleaning blade down to 1/10 or less compared with wear thereof which would result from non-application of a material concerned. Additionally, the material is supplied in a controlled volume to avoid an excessive supply which would otherwise bring about various problems including a fall of the image density, degradation of a reproduced image and a fall of the developing ability.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.