Image Forming Apparatus

The present invention relates to an image forming apparatus, such as an electrophotographic copying apparatus and a laser beam printer wherein an image bearing member thereof is heated for stabilized image formation. In the image forming apparatus such as electrophotographic copying machine or the like, the image bearing member thereof such as a photosensitive member exhibits a dependency on the temperature thereof with the result that the image quality changes depending on the ambient temperature. Also, when the surface of the image bearing member is moist, the image formed on the image bearing member is not stable, and a clear image can not be obtained.

In order to solve these problems, it is known that a drum heater is provided within the image bearing member to heat the image bearing member to a proper temperature and maintain it, which is also effective to remove the moisture on the surface of the image bearing member.

However, when the power source for the image bearing member is rendered "off", the drum heater is also deenergized, and the ambient moisture condenses on the drum surface. If this occurs, the subsequent image formation is not stable. Particularly when the image bearing member surface is uniformly charged by an ion generating means such as a corona charger, the uniform charging operation is not assured, resulting in non-uniformly charged surface of the image bearing member to such an extent that portions of the image may become absent. In order to remove the candensation deposited on the surface of the image bearing member, a long period of time is required by the heater. Further, even if the temperature of the image bearing member is controlled by a drum heater, there is a case where it is not satisfactory under a highly humid conditions. In this case, an increase of the temperature of the image bearing member can give rise to non-uniform images.

Accordingly, it is a principal object of the present invention to provide an image forming apparatus by which clear images can be provided under stabilized operation.

It is another object of the present invention to provide an image forming apparatus wherein the moisture can be satisfactorily removed.

It is a further object of the present invention to provide an image forming apparatus wherein an ion generating portion of an ion generating means such as a corona wire is prevented from contamination.

It is a further object of the present invention to provide an image forming apparatus wherein noxious products of an electric charging action, such as ozone are effectively removed, and wherein the moisture can be removed from the image bearing member.

It is a further object of the present invention to provide an image forming apparatus wherein a good image forming operation can be effected by accomplishing those objects.

It is a further object of the present invention wherein the time required for the image bearing member to be sufficiently deprived of the moisture is reduced, so that a good image forming operation becomes possible quickly.

It is a further object of the present invention to provide an image forming apparatus wherein the image bearing member is always satisfactorily dried without influence to the image bearing member property depending on the temperature.

These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

FIG. 1 is a sectional view of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of the image forming apparatus according to the embodiment of the present invention.

FIG. 3 is an enlarged sectional view of a part of an image forming apparatus according to another embodiment of the present invention.

FIG. 4 is a sectional view of an image forming apparatus according to a further embodiment of the present invention.

FIG. 5 is a sectional view of an image forming apparatus around a charger to illustrate the action of air flow.

FIG. 6 is a block diagram of a control according to an embodiment of the present invention.

FIG. 7 is a timing chart according to an embodiment of the present invention.

FIG. 8 is a block diagram according to an embodiment of the present invenion.

FIG. 9 is a timing chart according to an embodiment of the present invention.

FIG. 10 is a block diagram of a control used with a modified embodiment of the present invention.

FIG. 11 is a timing chart of operation in an apparatus according to an embodiment of the present invention.

FIG. 12 is a timing chart of operation of an apparatus according to an embodiment of the present invention.

Referring to FIG. 1, there is shown an electrostatic photographic copying apparatus as an example of an image forming apparatus according to an embodiment of the present invention.

The electrophotographic copying apparatus comprises an image bearing member in the form of a photosensitive member 1 which is rotatable in a direction indicated by an arrow A. With its rotation, the photosensitive member 1 is uniformly charged by an ion generating means in the form of a corona charger 2 in this embodiment at the start of an image forming process. In this embodiment, the photosensitive member 1 has a photosensitive layer of amorphous silicon. Then, the photosensitive member 1 is exposed to image light which is provided by the light produced by an illumination light source 3 illuminate to an original O to be copied and then reflected thereby. The image light is projected and is imaged on the surface of the photosensitive member 1 by way of mirrors 4, 5 and 6, a lens 7 and mirrors 8, 9 and 10, so that an electrostatic latent image is formed thereon in accordance with the image light. Then, a blank exposure lamp 11 is turned on, and it illuminates the following surface of the photosensitive member 1 in its entirety so as to eliminate the electric charge which has been applied by the primary charger.

The thus formed electrostatic latent image is visualized by a developing device 12 into a toner image, which is then transferred by a corona charger 16 onto a transfer material which is fed from the feeding cassette 13, 14 or 15. After receiving the toner image, the transfer material is separated from the photosensitive member 1 by a separation charger 17. The transfer material is conveyed to an image fixing device 18, where the toner image is fixed on the transfer material. The transfer material having the fixed image is discharged onto a discharge tray 21 by discharging rollers 19 and 20. On the other hand, the toner remaining on the photosensitive drum 1 is removed by a cleaning device 22 and is collected into an toner container (not shown) disposed at a front position. The electric charge remained on the photosensitive member 1 is removed by an illumination device 23 illuminating the surface of the photosensitive member 1. Then, the photosensitive drum 1 is again charged by the charger 2, and the above described operations are repeated.

FIG. 2 is an enlarged sectional view of a part of the apparatus according to this embodiment, wherein a drum heater la is shown. The drum heater 1a is effective to heat the amorphous silicon photosensitive member 1 up to 30.degree.-60.degree. C., preferably, 40.degree.-45.degree. C. The amorphous silicon photosensitive member exhibits a relatively high temperature depending property. And, a preferred temperature therefor is higher than an ordinary room temperature, so that the drum heater is particularly effective. Additionally, a stable property can be used without being influenced by the change in the ambient temperature, when the drum heater is used. The drum heater is also effective when a selenium or OPC photosensitive member or the like is used, although it is particularly effective when the amorphous silicon photosensitive member is used. In this Figure and the following Figures, the same reference numerals are assigned to the means and elements having the same functions.

The apparatus comprises a fan 25 to produce flow of air. The suction opening of a suction side duct (or guide) 30a is provided with a filter 24 so as to remove dust from the air introduced to the fan, so that the air from the fan 25 does not adversely affect the image forming operation. The air from the fan 25 is guided by ducts 30b and 30c along the inside surfaces thereof, and it flows to the surface of the photosensitive member 1. The ducts or guides 30a, 30b and 30c constitute an entire duct or guide 30. The outlet opening of the duct 30c is disposed between the cleaning device 22 and the charger 2. The flow of the air is indicated by an arrows B. The filter 24 is disposed between the space occupied by optical means and the fan 25 with respect to flow of the air. An air heater 26 is located downstream of the fan and upstream of the photosensitive member 1 with respect to the flow of the air. As described, the air introduced to the surface of the photosensitive member 1 has been substantially dust free because of the provision of the filter 24, and therefore, the air does not damage the photosensitive member 1, or disturb an image formation. Since the air heater 26 is located at such a position, the decrease of the temperature in the duct is not large.

It is possible that the fan 25 may be located upstream of the filter 24, as shown by broken lines indicated by the reference 25. This arrangement requires less total space so that it is effective when the space around the photosensitive member 1 is not abundant.

In order to not restrict the air delivering power of the fan 25 by the filter 24, it is preferable that the filter 24 is an electrostatic type filter which can electrostatically remove the dust and foreign matter.

The air is heated by the air heater 26 to 30.degree.-60.degree. C. and is discharged to the surface of the photosensitive member 1 in a position upstream of the corona charger 2 with respect to movement of the periphery of the photosensitive member 1 to remove moisture from the surface thereof. The moisture removing effect is very high since the flow of warm air is used. The photosensitive member 1 is thus substantially dried before being subjected to the corona charger 2. The corona charger 2 can electrically charge the dried photosensitive member 1, thus avoiding non-uniform charging and providing stabilized image formation.

FIG. 5 illustrates the air flow around the corona charger 2. The corona charger which produces ions to be applied to the photosensitive member is not able to charge the photosensitive member uniformly when the ion generating portion is contaminated. As shown in FIG. 5, the air flow M which naturally occurs in the neighborhood of the surface of the photosensitive member 1 when it rotates in the direction of the arrow A, which air flow will be hereinafter called "drum wind", reaches a corona wire 2a of the corona charger 2, which is the ion generating portion thereof. Since the drum wind M contains scattered particles of the developer or fine foreign matter, it contaminates the corona wire 2a, which can cause disturbance of the image.

Since, the products in the form of gases as a result of the charging operation, such as ozone, ammonium nitrate and other ions, are hydrophilic, they absorb the moisture and cover the surface of the photosensitive member 1. If this occurs, the electric charge applied by the corona charger is not stable, and as a result, a portion of the image may not be formed or that the image, which should be uniform is not. This problem is not solved in the arrangements shown in FIG. 2, because the air is directed to the surface of the photosensitive member 1 in the direction opposite to the drum wind M.

FIG. 3 is a sectional view of a part of an apparatus according to another embodiment of the present invention, whereby this problem is solved without increasing the size of the apparatus and without the necessity of the space for the opening. In this embodiment, the corona charger 2 is provided with a shield having a longitudinal openings in the entirety of the corona charging portion. The air flow B is blown through the opening to the photosensitive member 1. More particularly, the air is deprived of the dust or foreign matter by the filter 24 as in the embodiment of FIG. 2 and guided by the guide 30. The air is heated by the heater 24 up to a proper temperature and is directed into the corona charger 2 at a speed of 0.5-3 m/sec. The air passes around the corona wire 2a, and then is discharged to the surface of the photosensitive member 1, along which the air then flows out. The fan 25 disposed immediately before the heater 26 is substantially effective to produce this flow of air B. To do this, the position of the fan 25 also be immediately after the heater 26 or immediately before the filter 24.

Thus, without decreasing the moisture removing effect of FIG. 2, this embodiment is able to more effectively prevent contamination of the ion generating portion, and is able to blow out the noxious products of the charging action produced during ion generation (ozone, NOx and the like). Thus, a better image formation is possible.

The air conveyed to the photosensitive member 1 is taken from the side where the optical means are arranged. This is preferable because the illumination optical source is disposed in that side, and it necessarily heats the surrounding air several degrees (.degree. C.) higher than the room temperature. The utilization of this heated air assists the heater 26. On the other hand, it is preferable that the ambient temperature around the optical system is preferably not increased, and therefore, it is cooled by a fan 32. Therefore, it is preferable that heat insulating material 31 is disposed between the duct 30c and the space for optical system. The insulating material 31 is effective to prevent the possibility that the ambient air around the optical system is heated by the heater 26. Simultaneously, the decrease of the temperature of the air flow B can be prevented, which may be caused by the ambient air around the optical system, which is cooled by the fan 25. The air conveyed from the heater 26 to the photosensitive member 1 is maintained at the desired temperature and is not cooled significantly before reaching the photosensitive member 1, thus, the provisions of the duct or guide 30 and the heat insulating material 31 are preferable.

In FIGS. 2 and 3, the heater 26 is provided particularly for this purpose, but a heater for an image fixing device may be used also for this purpose. Usually to heat-fix the image, the image fixing device is provided with a heater. Therefore, it is possible that the guide 30 is extended from the fixing device to the image bearing member so as to utilize the air existing around the image fixing device and heated thereby. In this case, the necessity of using the heater 26 may be eliminated.

FIG. 4 illustrates an image forming apparatus according to a further embodiment of the present invention, wherein the heat provided by the image fixing device is utilized. In this embodiment, a part of the duct 30 is disposed right above or adjacent to the fixing device 18 so that the part of the duct 30 is sufficiently heated by heat radiation and conduction from the fixing device 18. Then, the air flowing in the duct 30 is heated by heat conduction to warm air, which is introduced into the corona charger 2. It is preferable to provide or form heat exchanger fins 26a on the surface of the duct wall facing to the heat fixing device, since this arrangement increases the amount of heat transfer is increased. In this embodiment, the particular heater for the air flow is not used, but it is possible to use a heater such as the heater 26 in the foregoing embodiment, and the heat from the fixing device is utilized as an asisting heat.

In an image forming apparatus comprising a lamp heater for heating the illumination source 3, it is possible to utilize the heat provided by the lamp heater. In this case, a duct or guide is extended to the neighborhood of the lamp heater without interference with the optical path of the optical system. By doing so, it is possible to utilize the air heated by the lamp heater.

In the embodiments shown in FIGS. 2 and 3, the air in the optical system side is fed to the image bearing member, that is, the photosensitive member 1 in this embodiment, the optical system serving to form an image of the original thereon. This is preferable because the temperature of that air is more or less higher than the outside ambient air due to the light producing energy.

An example of control for the heating means in FIGS. 2 and 3 embodiments will be described.

Condensation tends to occur when the photosensitive member is moist or when the image forming apparatus has been kept rest for a relatively long period of time. This tendency is increased when the drum heater has been deenergized during the rest period. Therefore, it is preferable to use control means for the heater, by which the heater is energized during the initial stage of operation, which is the stage from the start of supplying electric power to the apparatus to the image bearing member being sufficiently dried (moisture removal).

FIGS. 6 and 7 illustrate the sequential control and the timing chart, from which it will be understood that the heater is energized during the initial stage. After the completion of the moisture removing operation, the drum heater may be deenergized, however, it may be kept energized when a further moisture removing operation is desired. Many of the image forming machines of the type shown in FIG. 1 are such that the machine is kept in a waiting condition until the image formation is enabled. It is possible that the drum heater is operated during this waiting time to remove the moisture from the image bearing member by the warm air provided in the manner described above. After the moisture has been removed from the image bearing member, that is, during the stabilized operation of the apparatus, the heater may be deenergized, or it may be supplied with lower energy as shown in FIG. 7. During the initial stage, the heater is supplied with the relatively higher energy so as to discharge to the image bearing member the higher temperature air than the stabilized operation period. In this case, the time required for the moisture removal can be reduced to make it possible to obtain the desirable images without delay. In this case, it is possible to employ plural heaters, wherein a greater number of heaters are energized during the intial stage.

As an alternative, when the fan 25 is used, the speed of the air flow may be changed between the initial stage and the stabilized period. More particularly, the speed is higher in the initial stage to enhance the moisture removing power. To do this, the rotational speed of the fan 25 is made higher during the initial stage. As an alternative, plural fans may be used which are selectively actuated to obtain the similar effects, or a control damper may be employed at the suction side or delivery side thereof. When the speed or rate of the air flow is increased, the temperature rise of the air is decreased, so that it is preferable to increase the heating power, too. As an alternative of the method of control, the time period sufficient to remove the moisture from the image bearing member is predetermined, and the heater is energized during the predetermined period in the initial stage. FIG. 8 relates to a further embodiment according to the present invention, and shows a block diagram for the control of the heater. In this embodiment, there is provided a temperature sensor 1b (FIGS. 2 and 3) for detecting the temperature of the image bearing member. In accordance with the output of the temperature sensor, both of the drum heater and the air heater is controlled.

By controlling the drum heater and the air heater in accordance with the output of the temperature sensor, it is possible to keep a substantially constant temperature of the photosensitive member, whereby further stabilized image formation is possible. In this embodiment it is also preferable that the air heater is energized during the initial stage.

FIG. 9 is a timing chart of an example of the control. Upon plugging in the apparatus, the drum heater 1a is directly energized to increase the surface temperature of the photosensitive member 1. When a main switch is actuated thereafter, the fan 25 and the air heater 26 are energized so that a warm air is applied to the surface of the photosensitive member 1 through the corona charger 2, thus removing moisture from the surface. Inside the photosensitive member 1, there is provided a temperature detecting thermister 1b. When the temperature of the surface of the photosensitive member 1 reaches a temperature with which the moisture can be removed by the drum heater 1a (40.degree.-45.degree. C., for example), and is controlled at that temperature, the air heater 26 is deenergized. This temperature is preferably 30.degree.-60.degree. C. for an amorphous silicon photosensitive member, and particularly preferably 40.degree.-45.degree. C.

As mentioned before the propert of the image bearing member is dependent upon the temperature thereof, and therefore, it is preferable to keep it in a preferable range of temperature by the drum heater. The temperature can change depending on the temperature of the air applied thereto. For this reason, it is preferable that the warm air discharged to the image bearing member is generally equal to the temperature of the image bearing surface at which the drum heater is to keep. By this, the temperature dependence properties of the photosensitive member can be kept within a preferable state so that desired image quality can be assured.

FIGS. 10 and 11 are a block diagram and a timing chart illustrating another example of control, wherein the power for the heater for the image fixing device is utilized. As shown in FIG. 1, the fixing device 18 comprises within a frame 27 a fixing (heating) roller 28 and a pressing roller 29, and the fixing roller 28 is provided therewithin two heaters 28a and 28b, which are independently actuated and deactivated.

When the main switch is turned on after a long period of inactivity, the main heater 28a is energized to heat the fixing roller 28, and simultaneously, the fan 25 and the air heater 26 are energized to discharge warm air to the surface of the photosensitive member 1 through the charger 2, and in addition, the drum heater 1a is energized, whereby the surface temperature of the photosensitive member 1 increases. However, the subheater 28b is kept "off". The power to be distributed to the sub-heater 28b is used during this period for the air heater 26. When the surface temperature of the photosensitive member 1 reaches the moisture removable temperature, which is detected by the thermister 1b, the air heater 26 is deenergized, instead, the subheater 28b is energized to assist the heating of the fixing roller 28. By this, the waiting time determined by the entire electrophotographic system is reduced. When the apparatus is kept being plugged in, the drum heater 1a has already been energized as shown in FIG. 12, so that the surface of the photosensitive member 1 has been dried, and therefore, it is not necessary to apply the air flow to the surface. In this case, therefore, the two heaters 28a and 28b are simultaneously energized upon the actuation of the main switch Thus, the waiting time is further reduced.

The data obtained with this embodiment will be described. The capacities of the elements were as follows:

Drum heater 1a: 160 W,

Air heater 26: 400 W,

Main heater 28a of the fixing roller: 800 W, and

Sub-heater 28b of the fixing roller: 400 W.

The data for the air when the fan 25 and the air heater 26 are energized, were, adjacent the surface of the photosensitive member, as follows:

Temperature: approx. 52.degree. C.,

Speed of the air flow: 1.5 m/sec, and

Rate of the air flow: 0.54 m.sup.3 /min.

(1) The initial stage under the condition that the apparatus being kept plugged in:

Since the drum heater 1a has been kept "on", there is no possibility of image deterioration, such as flow of the image. Upon actuation of the main switch, the main heater 28a and the sub-heater 28b are energized whereby the fixing roller 28 is heated. It required approximately 3 min. for the fixing device 18 to reach the temperature at which the toner image can be sufficiently fixed on the transfer material (approx. 180.degree. C.). This was the waiting time from the actuation of the main switch.

(2) The apparatus has been kept unplugged, and the warm air is not applied after actuation of the main switch:

When the apparatus is plugged in, and the main switch is actuated, the drum heater 1a, the main heater 28a and the sub-heater 28b are energized. It required approximately 3 min. for the fixing device 18 to reach the fixable temperature. However, it required approximately 12 min. for the surface temperature of the photosensitive member 1 to reach the temperature at which the flow or washing of the image was sufficiently prevented. In this case, only the drum heater 1a was used for heating the drum. This period was the waiting time of the entire system of the apparatus.

(3) The warm air impinges on the drum surface, and the main heater 28a is used:

When the apparatus is plugged in, and the main switch was actuated, the drum heater 1a, the fan 25, the air heater 26 and the main heater 28a are energized. The moisture was removed from the surface of the photosensitive member 1 by both of the drum heater 1a and the warm air. It required approximately 3 min. for the surface temperature of the drum 1 to reach the temperature at which the flow of the image was sufficiently prevented.

When the surface temperature of the photosensitive member was controlled at the proper level, the air heater 26 was deenergized, and the sub-heater 28b was energized. The image fixing device 18 had been heated only by the main heater 28a, but after the surface temperature of the photosensitive member was controlled at the proper level, the sub-heater 28b was energized. The waiting time required by the fixing device was approximately 4 min. Therefore, the waiting time of the entire system of the apparatus was approximately 4 min. This means that the waiting time was reduced by one fourth of the conventional apparatus.

In the foregoing description, an apparatus is taken wherein the drum heater is actuated when the apparatus is plugged in. It is possible to use the present invention in an apparatus of the type wherein the drum heater is actuated after the main switch is actuated. This apparatus requires a longer period of time for the drum heater to reach the moisture removable temperature, and therefore, the present invention is further effective.

It is possible to combine any of the above described embodiments without losing the respective advantages.

While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.