Self-Tensioning Coronode Structure

The present invention relates generally to charging devices for use in electrostatographic devices and more particularly to corona charging devices for use in such machines, which provide repairable and replaceable structures.

In electrostatographic applications such as xerography, a charge retentive surface is electrostatically charged, and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface forms an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. The process is well known, and is useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be discharged in a variety of ways.

It is common practice in electrophotography to use corona charging devices to provide electrostatic fields driving various machine operations. Thus, corona charging devices are used to deposit charge on the charge retentive surface prior to exposure to light, to implement toner transfer from the charge retentive surface to the substrate, to neutralize charge on the substrate for removal from the charge retentive surface, and to clean the charge retentive surface after toner has been transferred to the substrate. These corona charging devices normally incorporate at least one coronode held at a high voltage to generate ions or charging current to charge a surface closely adjacent to the device to a uniform voltage potential, and may contain screens and other auxiliary coronodes to regulate the charging current or control the uniformity of charge deposited. A common configuration for corotron corona charging devices is to provide a thin wire coronode tightly suspended between two insulating end blocks which support the coronode in charging position with respect to the photoreceptor and also serve to support connections to the high voltage source required to drive the coronode to corona producing conditions. The coronode is partially enclosed by a conductive shield held at ground potential which serves to increase corona current produced. It is often desirable to have two coronodes within the same structure, which effectively increases the width of the charging zone for the improvement of charging uniformity, and which may be provided by a single wire of double the required length, having free ends of the wire anchored at one end block and a looped end anchored at the opposite end block. It is common in wire coronode structures to provide a spring connector to anchor an end of the coronode to an insulating end block. Scorotron corona charging devices have a similar structure, but are characterized by a conductive screen or grid interposed between the coronode and the photoreceptor surface, and held at a voltage corresponding to the desired charge on the photoreceptor surface. The screen tends to share the corona current with the photoreceptor surface. As the voltage on the photoreceptor surface increases towards the voltage level of the screen, corona current flow to the screen is increased, until all the corona current flows to the screen and no further charging of the photoreceptor takes place. It is to be noted that it is desirable that the screen be supported in a rigid, flat manner, so that it is uniformly spaced from the photoreceptor.

In use, wire coronode corotrons and scorotrons are noted for the ability to produce a reasonably uniform charge on a charge retentive surface. However, over time, the environment to which the coronode is exposed begins to cause irregularities and degradation in charging uniformity. These irregularities may be traced to surface irregularities on the coronode surface which over time becomes pitted, or coated with toner or fuser release agent or other process by-products which must be removed. While cleaning the coronode serves to improve the charging characteristics, coronodes eventually require replacement due to further degradation in performance, or breakage which often occurs while cleaning.

Heretofore, stringing the coronode into position between the insulating end blocks has required a degree of expertise outside the ability of most users. The primary difficulty in the procedure is to obtain the appropriate tension on the wire. If the tension is too low, undesirable sagging of the wire occurs, with resultant charging non-uniformity. If the tension is too high, breakage of the coronode may result. It would be highly desirable to have a corona charging device with a coronode allowing stringing in a simple manner so that a moderately trained user, rather than a service representative, could change or replace the coronode. Such an arrangement would allow significant savings in service time, machine dcown time and allow operator participation in maintaining copy quality. Of course, an added advantage would be the ease of coronode replacement by the service representative, decreasing his time in performing this job on a regular service call.

In the past a wide variety of arrangements have been used to support coronodes in position with respect to the charging device, and maintain a satisfactory degree of tension on the coronode. Thus, for example, U.S. Pat. No. 3,499,143 to Martin discloses a corona charging device including a spool of wire supported within the device so that it is readily available for use. The spool is supported so that it is selectably rotatable to remove wire from the spool for stringing the device, or to hold the end of the coronode in a fixed position. At an opposite end of the corona charging device, a pulley is provided around which the wire is supported and returned to the spool end of the device, where the free end of the wire is anchorable with a screw. A spring biased lever rotates the spool unitl the wire is in a taut condition, prior to fixing the free end at the screw anchor. This arrangement requires significant judgment in the installation of the wire, observing the wire and spring tension. U.S. Pat. No. 4,110,811 to Hubble, III et al discloses a useful arrangement which removes most judgment from the installation, providing a compression spring fixed to a coronode wire at a first end and a fixed ball terminator at a second end, and relies on the compression spring to maintain tension. Such a termination arrangement is relatively expensive, however, and the dielectric materials commonly used for the terminations cannot withstand long exposures to high voltages normally found in corona devices. U.S. Pat. No. 4,258,258 to Laing et al shows a generally similar arrangement in which one end of a coronode is provided with a bead termination and supported within a channel, while the other end extends through an insert to a tensioning means, where cooperating collars serve to retain the coronode end in the insert against any force pulling it out of the insert. Inserts supporting the coronode in position can be made chemically non-reactive. U.S. Pat. No. 3,566,223 to Salger teaches an adjustable wedge-type clamping mechanism. One end of the corona charging device includes a double clamping arrangement to fix both ends of the wire in position, while the opposite end provides a spring loaded abutment, wherein tension on the wire is achieved by removal of the spring.

In accordance with the invention there is provided a corotron or scorotron corona charging device having a wire coronode member which allows easy insertion into operational charging position in the device.

In accordance with one aspect of the invention, a charging device such as a corotron or scorotron generally includes a pair of insulating end blocks supporting a coronode in operational relationship to a surface to be charged. A first end block is provided with a coronode support for receiving the looped portion of a double length coronode. The second end block provides a cover hingedly mounted adjacent an enclosure formed in the end block. Coronode receiving anchors are provided on the pivotably movable cover which receive connectors attached to the ends of the coronode. Pivoting movement of the cover on the end block supports the anchors in a first, open position allowing connection of the coronode connectors to the anchors while the coronode is untensioned, and tensions the coronode when moved to a second, closed position which encloses the connectors and anchors within the end block enclosure.

In accordance with another aspect of the invention, the coronode support on the first end block provides a spring member normally extending to a position above the end block for receiving the untensioned coronode, and biasable by a cover to an enclosure in the first end block on completion of mounting the coronode.

The described arrangement finds particular utility in use with prefabricated coronodes, supplied to the installer at predetermined lengths, and having wire connectors already in place on the coronode ends.

These and other aspects of the invention will become apparent from the following description used to illustrate a preferred embodiment of the invention read in conjunction with the accompanying drawings in which:

FIG. 1 is a partially exploded perspective view of a corona charging device in a scorotron configuration;

FIG. 2 is a cutaway view of a first end of the inventive corona charging device; and

FIG. 3 is a cutaway view of second end of the inventive corona charging device.

Referring now to the drawings where the showings are for the purpose of describing a preferred embodiment of the invention and not for limiting same, FIG. 1 shows a corona charging device 10, in this case configured as a scorotron. Corona charging device 10 is generally provided with first and second end blocks 12 and 14, a shield comprising shield members 16 and 18 which in the preferred embodiment provide a rigid support for the device, a double length coronode 20 supported between first and second end blocks 12 and 14, and screen member 22. The description hereinafter is applicable to a corotron, without modification other than removal of the screen 22.

With reference now to FIGS. 1 and 2, and in accordance with the invention, first end block 12 is molded from an insulative resin material and generally includes a main body 24 and a cover 26 hingedly mounted with a hinge 28 to main body 24. Main body 24 supports an electrical connector 30 suitable for connection to a high voltage power source (not shown) for driving coronode 20 to a corona producing condition, and a coronode wire guide 32 around which the double length coronode 20 will be looped and supported at the first end block. Main body 24 forms a partial enclosure around coronode wire guide 32, having walls 34, 36 and 38 extending upwardly from a base portion 40 on which coronode wire guide 32 is supported. An opening in the enclosure is provided along the side of end block 12 opposing second end block 14, through which coronode 20 extends to coronode wire guide 32. In the described embodiment, coronode wire guide 32 is generally a closed loop having a generally rectangular shape, with a fastener receiving portion 42 extending from rectangular portion 44 to receive a fastener 46 such as a screw therethrough and extending into base 40 to secure coronode wire guide 32 into position. The rectangular portion of coronode wire guide 32 extends from fastener receiving portion 42 along base 40 towards the opposite end block 14, and is then bent back upon itself to form a V-shaped receiving portion 48 which will support the looped end of coronode 20 in position at the coronode support member 32 on end block 12. Coronode wire guide 32 is formed from a conductive metal material having a spring constant associated with it. The portion of the coronode wire guide 32 which is bent back on itself is formed at an angle which normally allows a portion of the guide to extend somewhat above walls 34, 36 and 38, to allow the coronode to be easily looped around the coronode wire guide 32, and is compressible into the enclosure with the closure of cover 26 after receiving coronode 20 thereabout. Electrical connector 30 generally includes a contact support 50 integrally formed with end block 12 supporting contact 52 which extends through contact support 50 and the main body of end block 12 into electrical connection with fastener 46 to provide an electrical connection with coronode wire guide 32 and accordingly, coronode 20. Cover 26 and walls 36 and 38 may be provided with complementary locking tabs and receiving openings (not shown) molded thereon to lock cover 26 into a closed position thereby enclosing coronode wire guide 32. Cover 26 is provided with an extension wall 54 which extends downwardly from the cover to substantially complete the patial enclosure of the main body 24 around the coronode wire guide 32 as the cover is closed.

With reference now to FIGS. 1 and 3, and in accordance with another aspect of the invention, second end block 14 is provided with a coronode tensioning arrangement for easily anchoring the coronode 20 and exerting the proper tension thereon. Second end block 14 may be molded from a non-conductive resin material and generally includes a main body 60 and a cover 62 hingedly mounted with hinge 66 to main body 60 for pivotal movement between open and closed positions, illustrated respectively in FIGS. 1 and 3. Cover 62 supports a pair of coronode connector anchors 68 in the form of generally C-shaped hooks. Anchors 68 are supported on an extension member 70 which extends perpendicularly from cover 62 at a position close to hinge 66. Anchors may be integrally molded with the cover and extension member, or formed from a metal member and fixed with fasteners to extension member 70. Main body 60 is provided with walls 72, 74 and 76 extending upwardly from a base 78 to form a partial enclosure around the coronode connection. A partial front wall 80 is provided with detents 82 to position the coronode wire as it extends therepast. A complementary cover front wall 84 is also provided at the front of cover 62 to complete the enclosure when the cover is closed.

With reference to FIG. 3, coronode 20 is generally a thin wire member, commonly a tungsten alloy. In the present embodiment, coronode 20 is supplied for installation with connectors 90 attached to either end of the coronode at a length selected in accordance with the particular device into which the coronode will be installed. In the particular embodiment shown, (as shown by the rotated inset to FIG. 3) connectors 90 may advantageously be small coil spring members, provided with a closed loop 92 at one end for securing the connectors 90 to the coronode, and an open hook 94 for securing the connector to anchors 68. It will no doubt be appreciated that the coronode wire could be also supplied in bulk, with separate connectors for assembly by the installer. Additionally, while providing spring members at either end of the coronode as connectors serves to assist in tensioning the coronode, by taking up slack in the wire, it may also be possible to preform the ends of the coronode with integral looped portions suitable for direct connection to the hooks or other support arrangements. In such a case the looped portions would integrally comprise the connectors 90.

With reference again to FIGS. 1 and 3, when cover 62 of second mounting block 14 is in a first, open position (as shown in FIG. 1) for stringing the coronode, anchors 68 are positioned at a first distance from the first end block 12, to allow connection of connectors 90 on coronode 20 in an untensioned condition to anchors 68. In pivoting cover 68 to a second, closed position (shown in FIG. 2), the arcuate movement of the anchors carries the attached coronode ends to a position more distant from the first end block, thereby applying tension to the coronode. Additionally, the second position carries the ends of the coronode to a position slightly below the partial front wall 80, positioning coronode 20 in detents 82. The bend applied to the coronode by its impingement on partial front wall 80, serves to further tension the coronode, prevents undesirable lateral movement and aids in the prevention of coronode vibration, a charging non-uniformity factor. Complementary interlocking tabs 100 and slots 102 in cover 68 and walls 74 and 76, respectively, serve to lock the cover into a closed position thereby maintaining the tensioned position. Assuming a constant predetermined length of corona wire mounted in the described arrangement, an identical amount of tension will be applied in stringing coronode 20 each time the task is performed.

Screen 22 may be comprised of a relatively thin sheet metal member having a generally U-shaped cross section with a mesh portion 110 formed in a central portion of the member, and supported adjacent the surface to be charged. The scorotron screen which can be inserted over end blocks 12 and 14 into slots 112 (shown only on first end block 12 for clarity) provided for such a purpose on the upper outside edges of each block. complementary mounting tabs 116 may integrally be provided on the screen for insertion into slots 112 to position the screen on the mounting blocks. Connection of the screen to a power supply is not shown, but could be accomplished in a variety of ways, including by way of example, connection to electrical contacts positioned within a machine frame.

It will no doubt be appreciated that single length coronodes may be used in a similar arrangements with minor modifications to end block 12. For example, a fixed anchor structure could be provided at the second end block, which would receive a connector similar to connector 90. The tensioning arrangement of the second end block 14 could also be modified to support only a single anchor on the pivoting cover assembly. Any number of coronodes could similarly be accommodated. Of course, it is also contemplated that the tensioning arrangement could be used on both end blocks, to simultaneously tension the coronode from both ends of the charging device. It will also be recognized that similar arrangements which integrally provide coronode tensioning for the stringing operation of the coronode with a mechanical advantage device movable from a position allowing untensioned mounting of the coronode, to a position applying a preselected tension to the coronode, may also come within the scope of the invention.

The invention has been described with reference to a preferred embodiment. Obviously modifications will occur to others upon reading and understanding the specification taken together with the drawings. This embodiment is but one example, and various alternatives, modifications, variations or improvements may be made by those skilled in the art from this teaching which are intended to be encompassed by the following claims .