JPH09197933A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the decrease of the resticking efficiency of toner and the shortening of the life of a cleaning roller by constituting an image forming device so that when the toner recovered onto a cleaning member is restuck on an image carrier, the cleaning member comes into press-contact with the image carrier with strong pressing force required for resticking. SOLUTION: The image forming device is provided with a pressing force switching cam 22 for making the pressing force of the cleaning roller 12 against a photoreceptor 1 strong, when the toner T2 remaining after a transfer and recovered onto a cleaning roller 12 is restuck to the photoreceptor 1 and the pressing force weak, when the toner T1 remaining on the photoreceptor 1, after the transfer is performed is recovered onto the cleaning roller 12. The pressing force of the pressing force switching cam 22 against a cleaning case 17 is made stronger than that when a cam surface part 22a is in press-contact with the cleaning case 17, because a cam surface part 22b is set in a position further away from the shaft center of a cam shaft 21 than the cam surface part, 22a. In other words, the pressing force is made stronger than that when the toner remaining after the transfer is recovered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms an electrostatic latent image on a rotationally driven image carrier by means of latent image forming means,
The electrostatic latent image is visualized as a toner image by a developing device, the toner image on the image carrier is transferred to a recording medium by a transfer device, and transfer residual toner on the image carrier after the toner image transfer is removed. The present invention relates to an image forming apparatus that collects by a cleaning member and cleans the surface of the image carrier.

[0002]

2. Description of the Related Art In an image forming apparatus of the above type configured as a copying machine, a printer, a facsimile, or a complex machine thereof, an image carrier is repeatedly used, and therefore, the surface of the image carrier after the toner image is transferred. It is necessary to clean the surface of the image bearing member by removing and collecting the residual toner remaining on the image carrier by a cleaning member. Therefore, conventionally, various cleaning devices for cleaning the image carrier have been proposed and put into practical use, but the conventional cleaning device generally stores the toner collected from the image carrier in a waste toner tank or the like, It is configured to discard this.

By the way, in recent years, in an image forming apparatus of this type which employs an electrophotographic process, it is possible to further reduce the cost and further reduce the amount of toner to be discarded as part of measures against environmental problems. Is requested.

In view of such a point, if the transfer rate of the toner image from the image carrier to the recording medium is set to 100% to eliminate the residual toner after the toner image is transferred, a so-called cleanerless system is adopted. be able to. As a result, not only can the toner to be discarded be eliminated, but also the cleaning device can be omitted, and the image forming system can be simplified and the cost of the image forming device can be reduced. However, at present, it is difficult to make the transfer rate of the toner image 100%, and there is a problem from the viewpoint of reliability.

Therefore, as a next best measure, the transfer residual toner remaining on the surface of the image carrier after the toner image is transferred is adhered to the cleaning member to be recovered, and then the recovered toner is re-adhered to the image carrier. , A method of collecting with a developing device and reusing it has been proposed (for example, Japanese Patent Publication No.
-30274 publication). After the toner image is transferred, the transfer residual toner remaining and attached on the image carrier is temporarily collected by the cleaning member, and the collected toner is affected by the formation of the next electrostatic latent image on the image carrier. The toner re-adhered to the non-existing surface portion and further re-adhered to the surface of the image carrier is collected by the developing device. This eliminates the need for a dedicated means for transferring the collected toner to a waste toner tank or a developing device, thus reducing the cost of the image forming apparatus and reusing the toner. It can be lost.

In the conventional image forming apparatus of this type,
The cleaning member is configured to press-contact the surface of the image carrier to collect the transfer residual toner and to reattach the collected toner to the surface of the image carrier. At that time, regarding the pressure contact force of the cleaning member with respect to the image bearing member, if the pressure contact force is too weak, the re-adhesion efficiency of the toner from the cleaning member to the image bearing member decreases, and a large amount of toner remains on the cleaning member, which Accumulate on the cleaning member. Then, finally, the toner on the cleaning member adheres to the image forming area of the image bearing member, whereby the toner image formed on the image bearing member is stained, and the image quality is deteriorated. To do.

Therefore, in the past, in order to prevent a reduction in the re-adhesion efficiency of toner from the cleaning member to the image carrier, the cleaning member is always pressed against the image carrier with a strong force. . However, in this case, since a large external force is always applied to the cleaning member from the image carrier, the surface of the cleaning member is permanently deformed or deteriorated relatively early, and its life is shortened. I cannot escape.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to collect transfer residual toner on a cleaning member, reattach the recovered toner to an image carrier, and then collect the reattached toner on a developing device. SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus which can solve the above-mentioned problems in the image forming apparatus of the above type and can prevent the reduction of the re-adhesion efficiency of toner and the reduction of the life of the cleaning member.

[0009]

In order to achieve the above object, the present invention is directed to an image carrier which is driven to rotate, a latent image forming means for forming an electrostatic latent image on the carrier, and an electrostatic latent image forming means. A developing device that visualizes the latent image as a toner image, a transfer device that transfers the toner image on the image carrier to a recording medium, and a transfer residual toner on the image carrier after the toner image transfer is temporarily collected. And a cleaning member for reattaching the collected toner to the surface portion of the image bearing member that does not affect the formation of the next electrostatic latent image, and the toner reattached to the surface of the image bearing member. In the image forming apparatus that collects the transfer residual toner and reattaches the collected toner to the surface of the image carrier by bringing the cleaning member into pressure contact with the surface of the image carrier, Transfer than when reattaching to the image carrier When the toner recovery, as the pressing force of the cleaning member becomes weak against an image bearing member, proposes an image forming apparatus characterized in that a pressing force switching means for switching pressing force of the cleaning member against the image bearing member.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus according to the present invention. In the figure, a drum-shaped photoconductor 1 which is an example of the structure of an image carrier is rotationally driven in the clockwise direction in the figure by a drive device (not shown), and at this time, a static elimination lamp 13 which is an example of the static eliminator removes static electricity. The surface of the photoconductor 1 is uniformly charged to a predetermined polarity by the action of the charging roller 2 which is an example of a charging device. In this example, the charging roller 2 is connected to the voltage power source E ₁₀ , and uniformly charges the surface of the photoconductor 1 to a negative (negative) polarity while rotating in contact with the photoconductor 1. Due to the action of the charging roller 2, the surface of the photoconductor 1
For example, it is charged to -850V. As a charging device for uniformly charging the photoreceptor 1, a charging device disposed apart from the photoreceptor, such as a corona discharger, can be used.

Next, in the exposure unit 3, an exposure scanning device (not shown) performs optical writing scanning with, for example, the light-modulated laser beam 11, so that a predetermined electrostatic latent image is formed on the surface of the photoconductor 1. Is formed. Photoconductor 1
The surface potential of the upper part A irradiated with the laser beam 11, that is, the surface potential of the electrostatic latent image is, for example, about −150 V, and the surface potential of the part B not irradiated with the laser beam 11, that is, the background potential of the background portion of the electrostatic latent image is almost It is maintained at -850V. As described above, in this example, the charging roller 2 and the exposure scanning device form a latent image forming unit that forms an electrostatic latent image on the image carrier made of the photoconductor 1.

The developing device 4 is provided with a developing roller 5 which is an example of a developer carrying and conveying member disposed opposite to the photoconductor 1 and a pair of stirring paddles 10A and 10B, which form the main body of the developing device. Each of the developing casings 9 is provided and rotatably supported by the casing 9. A voltage of about -600 V, for example, is applied to the developing roller 5 by the voltage power source E ₁ . A voltage having the same polarity as the charging polarity of the photoconductor 1 is applied to the developing roller 5.

In the developing device 4 illustrated here, a two-component developer D having a toner and a carrier is used, and the developer D is contained in the developing casing 9. Then, as the stirring paddles 10A and 10B rotate, the toner is charged to a predetermined polarity by friction with the carrier, that is, the same polarity as the charging polarity of the photoconductor 1 in this example, that is, a negative polarity. As described above, in the image forming apparatus of this example, the charging polarity of the toner during development is negative. A developing device using a one-component developer having no carrier may be employed.

The developing roller 5 is driven to rotate counterclockwise in the drawing, and the developer carried on the peripheral surface of the developing roller 5 is conveyed in the rotating direction of the developing roller 5, and the roller 5 is rotated.
The developer regulating member 15 oppositely arranged with a predetermined gap therebetween is scraped. The developer whose conveyance amount is regulated by the developer regulating member 15 is conveyed toward the developing section 6 where the developing roller 5 and the photoconductor 1 face each other, and the toner in the developer is conveyed to the photoconductor by the developing section 6. 1 is electrostatically attracted to the electrostatic latent image on 1 and adheres to that portion. That is, the toner charged to the negative polarity, which is the same as the charging polarity of the photoconductor, adheres to the surface portion A of the photoconductor irradiated with the laser beam, and the electrostatic latent image is visualized as a toner image. As described above, the image forming apparatus of this embodiment employs the reversal development method (negative / positive development method).

A transfer roller 7, which is an example of a transfer device, is disposed below the photoconductor 1. The transfer roller 7 rotates in the forward direction with respect to the rotation direction of the photoconductor 1, and toward the transfer portion 8 between the transfer roller 7 and the photoconductor 1 facing the transfer roller 7, a recording medium made of a transfer paper 16 is formed. Are transferred in the direction of arrow P, and the transfer roller 7 is pressed against the surface of the photoconductor 1 via the transfer paper 16 sent to the transfer unit 8, and at this time, the function of the transfer roller causes the photoconductor 1 to move. The toner image formed thereon is transferred onto the transfer paper 16. That is, the power source E _{3 is applied} to the transfer roller 7 so that
Positive (plus) polarity voltage opposite to the charge polarity of the above toner,
For example, a voltage of + 950V is applied, and at this time, the negative toner T on the photoconductor 1 is electrostatically attracted to the transfer paper 16 side and adheres to the transfer paper. It is also possible to use a transfer device separated from the photoconductor 1 such as a transfer device including a corona discharger.

The transfer paper 16 on which the toner image has been transferred is separated from the photoconductor 1 by a separating device (not shown), and is sent to a fixing device (not shown).
The toner image on 6 is fixed. In this way, the transfer paper 16 is ejected outside the image forming apparatus main body as copy paper.

As described above, the image forming apparatus of this embodiment has the image carrier composed of the photosensitive member 1 which is rotationally driven, the latent image forming means for forming an electrostatic latent image on the image carrier, and the latent image forming means. The developing device 4 visualizes the electrostatic latent image as a toner image, and the transfer device 7 includes a transfer roller 7 for transferring the toner image on the image carrier to a recording medium composed of the transfer paper 16. A cleaning member including a cleaning roller 12 described below is provided.

The toner image on the photoconductor 1 is transferred to the transfer paper 16 at the transfer portion 8. After the toner image is transferred, the photoconductor 1 is transferred.
The toner remaining on the photoconductor 1 without being transferred to the transfer paper 16 adheres to the surface of the. Transfer residual toner T ₁
When they reach the cleaning unit 14, they are temporarily collected by a cleaning roller 12 which is an example of a cleaning member.

The cleaning roller 12 has a core member 12a made of a rigid body, and a conductive or medium-resistance elastic body 12b fixed on the surface of the core member 12a. In the illustrated example, the core member 12a. Is made of a round shaft-shaped conductive metal, and the elastic body 12b is made of a foamed body formed in a cylindrical shape concentric with the core member 12a. The cleaning roller 12 is a cleaning case 17 shown in FIGS.
Each of the end portions of the core member 12a is rotatably supported by the front and rear side walls 17a and 17b of the cleaning case 17, but is supported immovably. The cleaning roller 12, together with the developing roller 5, the charging roller 2, and the transfer roller 7, is positioned substantially parallel to the photoconductor 1.

Here, in FIG. 1, most of the toner T of the toner image directed from the developing unit 6 to the transfer unit 8 is a toner having a charging polarity at the time of development, that is, a negative polarity toner in this example. On the other hand, when the toner image is transferred, a voltage having a polarity opposite to the toner charging polarity at the time of development, which is a positive polarity in this example, is applied to the transfer roller 7, so that the toner remains on the photoconductor 1 after the toner image is transferred. The adhered toner, that is, the transfer residual toner T ₁ is a toner in which positive and negative toners are mixed. The transfer residual toner is transferred to the cleaning unit 14 in a state in which both positive and negative polarity toners are mixed.

The cleaning roller 12 of the present embodiment, when recovering the residual toner T ₁ of the the photosensitive member 1, a clockwise direction in FIG. 1 (arrow a direction), i.e. in the counter direction with respect to the rotation direction of the photosensitive member 1 It is rotated by a drive control means (not shown) and rotates while rubbing against the surface of the photoconductor 1. The cleaning roller 12 is
The surface portion of itself is pressed against the photosensitive member 1 so that it is elastically deformed by the photosensitive member 1. As shown in FIG. 3, a nip region N is formed at this pressed portion. This nip area N becomes a cleaning area.

In the nip area N, the transfer residual toner T ₁ having both positive and negative polarities becomes a toner having the same polarity (negative polarity in this example) as the toner at the time of development while being in contact with the cleaning roller 12. It is frictionally charged. Transfer residual toner T ₁
However, the negative polarity, which is the charging polarity at the time of development, can be obtained.

Thus, the cleaning roller 1 of this example
2 is the transfer residual toner that is frictionally charged between the photosensitive member 1 and
It also performs the function of frictionally charging the toner so that the toner has a negative polarity, which is the original polarity. That is, the cleaning member including the cleaning roller 12 includes a toner whose transfer residual toner toward the cleaning roller 12 has a polarity opposite to the charging polarity of the toner at the time of development, and the toner has the charging polarity ( The toner is triboelectrically charged so that the toner can have the original polarity). The elastic body 12b of the cleaning roller 12 is composed of a charging series charging material capable of frictionally charging the toner to its original polarity, in this example, negative polarity.

Returning to FIG. 1, the transfer residual toner T ₁ on the photosensitive member 1 after the toner image is transferred onto the recording medium made of the transfer paper 16
Is collected by a cleaning member composed of a cleaning roller 12 that rotates while being pressed against the photoconductor 1, and at the time of collection, the core member 12 of the cleaning roller 12 is collected.
A voltage having a polarity opposite to the charging polarity of the toner frictionally charged by the roller 12, that is, a positive voltage in this example, for example, +200 V, is applied to a by the voltage power source E ₄ .
Therefore, the residual toner after the transfer of the toner image, which has passed through the transfer portion 8, that is, the residual transfer toner T ₁ is electrostatically attracted to the surface of the cleaning roller 12 to which the positive voltage is applied, and the residual toner of the roller 12 is transferred. It adheres to the surface and is temporarily collected by this roller. As a result, the surface of the photoconductor 1 is cleaned. As described above, the cleaning roller 12 rotating in contact with the photoconductor 1 has
Between the transfer residual toner T ₁ on the photosensitive member and the surface of the cleaning roller 12 to form an electric field that can be electrostatically attracted to the surface of the cleaning roller 12. Then, a positive polarity voltage is applied.

As described above, the cleaning roller 12
The toner collected on the surface of the toner is indicated by reference numeral T _{2 in} FIGS. 1 and 3. In FIG. 4, the toner image on the photoconductor 1 is transferred to the transfer paper 16, and the transfer residual toner T ₁
FIG. 6 is a schematic view showing a state where is collected on the surface of the cleaning roller 12. The surface portion of the photoconductor 1 that has been cleaned by the cleaning roller 12 is subjected to static elimination action by a static elimination lamp 13 which is an example of a static elimination device, and the surface potential thereof is lowered to a reference value. The charge eliminating lamp 13 continues to be turned on during the image forming operation. The surface of the photoconductor that has been subjected to the static elimination is continuously charged by the charging roller 2 as can be seen from FIG. 4, and the image forming operation described above is continued.

In this way, one sheet of toner image is formed on the photosensitive member 1 while the photosensitive member 1 is rotated several times, for example.
This is continuously transferred onto the transfer paper 16, and the circumferential area on the photoreceptor 1 where such a toner image is formed is the image forming area. In FIG. 4, the image forming area is denoted by a reference numeral X, and the leading end in the rotation direction of the photosensitive member is denoted by a reference numeral Y. Similarly, in FIG. 5, the symbol Z is attached to the rear end of the image forming area X in the rotation direction of the photoconductor.

When the leading edge Y of the image forming area X reaches the cleaning roller 12, the cleaning roller 1
The operation of collecting the transfer residual toner T _{1 on} the second transfer toner T 2 is started, and the operation of collecting the transfer residual toner T ₁ is continued until the rear end Z of the image forming area X reaches the cleaning roller 12. The portion of the image forming area X that has passed the cleaning roller 12 has already been cleaned by the cleaning roller.

As shown in FIG. 5, when the rear end Z of the image forming area X in the direction of rotation of the photosensitive member passes the charging roller 2, the charging roller 2 is separated from the surface of the photosensitive member 1 at this time. (See Figure 6). At the same time, the switch S ₁₀ shown in FIG. 1 is switched to turn off the voltage application to the charging roller 2.

[0030] When the image forming region trailing Z passes the developing roller 5 of the developing device 4 as shown in FIG. 6, is switched switch S ₁ shown in FIG. 1, the developing roller 5 is voltage source E ₂
A positive polarity voltage opposite to the charging polarity of the toner, for example, a voltage of +500 V is applied to the developing roller 5 so that the toner does not adhere to the photoconductor 1. Subsequently, as shown in FIG. 7, when the trailing edge Z of the image forming area passes through the transfer portion 8, at this time, the voltage application to the transfer roller 7 is stopped. At this time, in this example, the transfer roller 7 is separated from the photoconductor 1 (see FIG. 8).

As described above, the cleaning roller 12 temporarily collects the transfer residual toner T ₁ on the photoconductor 1 after the toner image transfer, and then collects the collected toner T ₂ on the photoconductor 1. It is redeposited on the surface portion that does not affect the formation of the next electrostatic latent image. That is, when the trailing edge Z of the image forming area after the toner image is transferred onto the transfer paper 16 passes through the cleaning roller 12 as shown in FIG. 8, the switch S ₂ shown in FIG. 12 is connected to the voltage power source E ₅ , and the core member 12a of the cleaning roller 12 has the same negative polarity as the charging polarity of the toner frictionally charged by the cleaning roller 12;
For example, a voltage of -3000 V is applied. In this way, the toner on the cleaning roller 12 is provided between the cleaning roller 12 and the non-image forming area W (FIG. 8) on the surface of the photosensitive member on the rear side of the rear end Z of the image forming area in the rotation direction of the photosensitive member 1. An electric field is formed in the direction in which T ₂ is emitted toward the photoconductor 1.

Due to the electric field, as shown in FIG.
The toner T ₂ temporarily collected on the cleaning roller 12 is reattached to the non-image forming area W on the photoconductor 1 and returned. At this time, the cleaning roller 12 of this example is
The photoconductor 1 is rotationally driven in the forward direction (counterclockwise in FIG. 1). Toner T redeposited on the photoconductor 1
_As shown in FIG. 10, the subsequent rotation of the photosensitive member 1 passes under the charge removing roller 13 and the charging roller 2 separated from the photosensitive member 1, and reaches the developing device 4 as shown in FIG. At this time, as described above, since the positive polarity voltage opposite to the charging polarity of the toner at the time of development is applied to the developing roller 5, the negative polarity toner T ₃ redeposited on the photoconductor 1 is applied. Are electrostatically transferred to the developing roller 5 side and are collected in the developer in the developing device.

As described above, the cleaning roller 12
Removes the toner T ₂ temporarily collected on the surface of the photoreceptor 1.
The toner T ₃ redeposited on the image carrier composed of the toner T ₃ and redeposited on the surface of the image carrier is electrostatically collected in the developing device 4. The toner collected in the developing device 4 is reused in the developing device 4. In this way,
It is possible to eliminate the waste toner, and it is not necessary to provide a toner conveying pipe for returning the toner collected by the cleaning roller 12 to the developing device 4.

The toner T ₂ collected on the cleaning roller 12 reattaches to the non-image forming area W in the vicinity of the trailing edge Z of the image forming area X on the photoconductor 1, so that the reattached toner T ₃ causes Not only the electrostatic latent image formed during the image forming operation but also the electrostatic latent image formed next is not affected. The collected toner is redeposited on the surface portion of the photoconductor 1 that does not affect the formation of the next latent image. It is also possible to re-adhere the toner from the cleaning roller 12 to the rear portion of the image forming area X.

As shown in FIG. 10, when the collected toner on the cleaning roller 12 has been redeposited on the photoconductor 1, the cleaning roller 12 has a polarity opposite to that of the toner during development. By applying a positive voltage and rotating the cleaning roller 12 in the counter direction with respect to the rotation direction of the photoconductor 1, even a very small amount of toner, which should not have originally adhered, adheres to the photoconductor. If so, it is preferable to control the cleaning roller 12 so as to collect the toner.

When the image forming operation is continued,
When the next image forming area X1 shown in FIG. 10 and FIG. 11 is continuously subjected to the static elimination action by the static elimination lamp 13, and the tip Y1 of the photoconductor rotating direction moves to the position of the charging roller 2, the charging roller 2 is exposed to light. By contacting the surface of the body 1 and negatively charging the next image forming area X1, an electrostatic latent image is formed on the next image forming area X1 in exactly the same manner as described above. As shown, it is visualized as a toner image in the developing device 4. At this time, of course, the negative voltage is applied to the developing roller 5. When the leading edge Y1 of the image forming area reaches the transfer section 8, the transfer roller 7 is pressed against the photoconductor 1, and the leading edge of the next transfer paper 16 reaches the transfer section 8, and the next image forming area X1 is reached.
The toner image formed on the transfer paper 16 is transferred to the transfer paper 16.
The transfer residual toner at this time is temporarily collected by the cleaning roller 12 as described above, and the above-described operation is repeated. In this way, the image forming operation is repeated a predetermined number of times.

In the state shown in FIG. 10, neither the electrostatic latent image nor the toner image has been formed in the next image forming area X1. To be exact, the area X1 shown in FIG. It can be said that the area is to be the next image forming area. Also,
1 and FIGS. 3 to 12, the toner T, T ₁ , T ₂ , on the photoconductor 1 or the cleaning roller 12 is
For T _3, T _4, is shown an enlarged view of these schematically.

As described above, the transfer residual toner on the image carrier is electrostatically transferred to the cleaning member by applying the bias voltage of the polarity opposite to the charging polarity of the toner at the time of development to the cleaning member. It is possible,
As a result, the transfer residual toner can be collected by the cleaning member. Further, after the collection, the polarity of the bias voltage applied to the cleaning member is switched, and the bias voltage having the same polarity as the charging polarity of the toner at the time of development is applied to the cleaning member, so that the toner collected on the cleaning member is carried as an image. It can be electrostatically transferred to the body. As a result, the collected toner can be reattached to the image carrier, and the reattached toner can be collected in the developing device.

Here, in the above-described image forming apparatus, the cleaning roller 12 is brought into pressure contact with the surface of the photoconductor 1 to collect the transfer residual toner and to reattach the collected toner to the photoconductor 1. However, as described above, in the conventionally proposed image forming apparatus of this type, the cleaning roller is constantly pressed against the photoconductor with a strong force so that the re-adhesion efficiency of the toner does not decrease. Adopted a configuration. For this reason, the burden on the cleaning roller is increased, and the service life of the cleaning roller is shortened.

By adopting the following structure, the above problems can be solved.

In FIG. 2, the cleaning case 17
Is rotatably supported by a pair of image forming apparatus main body side plates (not shown) by a pivot 19 whose axis is shown alone, and a tension spring 18 is provided between the cleaning case 17 and the main body side plate. Is hung. The central axis of both pivots 19, that is, the swing axis of the cleaning case 17 extends parallel to the center of rotation of the cleaning roller 12 and the photoconductor 1 (FIG. 1).

The cam shaft 21 extending substantially parallel to the cleaning roller 12 is rotatably supported around a central axis thereof by a pair of image forming apparatus main body side plates (not shown) facing each other. A pair of pressing force switching cams 22 is fixedly mounted on the shaft, and one shaft end of the cam is connected to a motor 23.

[0043] Figure 1 shows a state in which the recovery of residual toner T ₁ of the the photosensitive member 1 to the cleaning roller 12, this time, the cleaning case 17, rear wall surface of the photosensitive member 1 and the opposite side The cam surface portion 22a of the cam peripheral surface of the pressing force switching cam 22 is in pressure contact with the cam surface portion 22a by the elastic tension of the tension spring 18.

When the transfer residual toner is collected as shown in FIG. 8, the motor 23 shown in FIG. 2 is operated for a predetermined time, whereby the cam shaft 21 is rotated and the cam 22 is
It rotates clockwise from the position shown in FIG. 1 to the position shown in FIG.

At this position, the cam surface portion 22b of the cam peripheral surface of the pressing force switching cam 22 is pressed against the back wall surface of the cleaning case 17. In this state, the cleaning roller 12 rotates, for example, in the forward direction with respect to the rotation direction of the photosensitive member 1, that is, in the direction of the chain line arrow b in FIG. 13, and the toner collected on the roller surface is transferred to the surface of the photosensitive member 1. Reattach. The redeposited toner is collected by the developing device 4 (FIG. 1) as described above.

The pressing force switching cam 22 of this embodiment is constructed so that the cam surface portion 22b is set at a position farther from the axial center of the cam shaft 21 than the cam surface portion 22a. The pressing force on the cleaning case 17 is stronger than the pressing force when the cam surface portion 22a is in pressure contact. That is, the pressing force of the transfer residual toner is increased more than when the toner is collected.

On the other hand, although the cleaning roller 12 is rotatable with respect to the cleaning case 17, the cleaning roller 12 is provided in a fixed position. Therefore, the roller 12 also collects the collected toner photoconductor 1 more than when the transfer residual toner is collected. When redeposited onto the photoreceptor, the photoreceptor is strongly pressed against the photoreceptor. As described above, since the cleaning roller 12 is pressed against the photoconductor 1 with a strong force when the collected toner is re-adhered to the photoconductor, it is possible to prevent a decrease in toner reattachment efficiency. That is, the cleaning roller 12
The toner remains on the cleaning roller 1, and the toner is finally deposited on the image forming area of the photoconductor 1 to prevent the toner image formed on the photoconductor 1 from being stained. Of.

On the other hand, when the transfer residual toner on the photoconductor 1 is collected by the cleaning roller 12, as shown in FIG.
Since the cam surface portion 22a located closer to the cleaning case 17 comes into pressure contact with the cleaning case 17, the pressing force of the cleaning roller 12 against the photoconductor 1 becomes weaker than that when the collected toner is reattached to the photoconductor. By such pressure contact force setting,
The burden on the cleaning roller 12 is reduced, and it is possible to prevent the cleaning roller 12 from being permanently deformed and deteriorated over a long period of time, and to extend its life.

When the re-adhesion of the collected toner on the cleaning roller 12 to the photosensitive member is completed, the motor 23 shown in FIG. 2 operates for a predetermined time in the opposite direction to that described above, and as a result, the motor 23 shown in FIG. Pressing force switching cam 22
From the position shown in the figure to the counterclockwise direction in the figure.
Rotate to the position shown in and stop. As a result, the cleaning roller 12 is pressed against the surface of the photoconductor 1 with a weak pressing force, and is rotated clockwise in FIG.

As described above, in the illustrated image forming apparatus, the transfer residual toner T ₁ on the photoconductor 1 is cleaned by the cleaning roller 12 more than when the collected toner T ₂ on the cleaning roller 12 is reattached to the photoconductor 1. Since the pressing force of the cleaning roller 12 with respect to the photoconductor 1 is switched so that the pressure contact force of the cleaning roller 12 with respect to the photoconductor 1 becomes weaker when the toner is collected in 12, the efficiency of re-adhesion of toner to the photoconductor 1 is reduced. In addition, the cleaning roller 12 can be prevented from being constantly pressed against the photoconductor 1 with a large force, and the life of the cleaning roller 12 can be extended. Moreover, in this example, after the reattachment of the collected toner to the photoconductor 1 is completed and before the next transfer residual toner is collected, the cleaning roller 1
Since 2 is brought into contact with the photoconductor 1 with a weak pressure contact force, it is possible to more reliably prevent early deterioration of the cleaning roller 12.

As described above, in the image forming apparatus of this example, the pressure contact force of the cleaning member against the image carrier becomes weaker when the transfer residual toner is collected than when the collected toner is reattached to the image carrier. Although the pressing force switching means for switching the pressing force of the cleaning member with respect to the image carrier is provided, in the illustrated example, the cam shaft 21, the pressing force switching cam 22 and the motor 23 shown in FIG. An example of the pressing force switching means is configured.

As described above, with respect to the pressure contact force of the cleaning roller 12 with respect to the photosensitive member 1, if the pressure contact force is too weak, the re-adhesion efficiency of the toner decreases, and the toner adheres to the cleaning roller 12. This remains and accumulates on the cleaning roller, and finally the toner adheres to the photoconductor, and the toner image formed on the photoconductor 1 is smeared and the image quality is deteriorated.

According to the experiments conducted by the present inventors, the pressure contact force of the cleaning roller 12 with respect to the photosensitive member 1 is 500 g.
In contrast to /5.5 cm, when it was dropped to 300 g / 5.5 cm, the transfer amount of the toner from the cleaning roller to the photosensitive member decreased from 7 mg / 1 cm to 5 mg / 1 cm. Here, “5.5 cm” and “1 cm” mean the length of the cleaning roller 12 in the axial direction.

In view of this point, the cleaning roller 1
If 2 is constantly pressed against the photoconductor 1 with a strong force, for example, a force of 500 g / 5.5 cm, the re-adhesion efficiency of the toner can be prevented from being lowered, but the burden on the cleaning roller is increased and the life thereof is reduced. .

Therefore, the present inventors apply the cleaning roller 12 to the photoconductor 1 with a strong force as before in order to prevent the re-adhesion efficiency of the toner from being lowered when the collected toner is reattached to the photoconductor. Recalling a new technique of pressing the rollers and pressing the roller against the photoconductor 1 at the time of collecting the transfer residual toner, the image forming apparatus is configured as described above based on this technology. I did. According to the experiment, it is clear that even if the cleaning roller is pressed against the photoconductor with a weaker force than that when re-adhering the collected toner, the collection efficiency of the transfer residual toner to the cleaning roller, that is, the cleaning efficiency does not decrease. There is.

More specifically, according to the experiments conducted by the present inventors, the pressure contact force of the cleaning roller with respect to the photoconductor is 500 g / 5.
It has been confirmed that when set to 5 cm, the collected toner on the cleaning roller transfers to the photosensitive member without any problem. Further, if the pressure contact force is set to 300 g / 5.5 cm when the transfer residual toner is collected on the cleaning roller, the transfer residual toner is sufficiently frictionally charged between the cleaning roller and the photosensitive member, and the cleaning roller is It has been confirmed that there is no problem in transfer.

Note that when the image forming apparatus is not performing the image forming process, or when the image forming apparatus is not in operation, such as when the image forming apparatus is turned off,
If the cleaning roller 12 is separated from the photoconductor 1 as shown in FIG. 5, it is possible to more reliably prevent the cleaning roller 12 from being permanently deformed early.

For example, at the end of the image forming operation, after stopping the photoconductor 1, the motor 23 shown in FIG. 2 is operated to move the pressing force switching cam 22 from the position shown in FIG. When the cleaning case 17 shown in FIG. 1 is rotated to the position shown in FIG.
Rotate clockwise around in the figure. Then, as shown in FIG. 14, the cleaning case 17 is stopped by the stopper pin 24 provided on the main body side plate, and the cleaning roller 12 is held at a position separated from the photoconductor 1. That is, when the cam surface 22c of the cam peripheral surface of the pressing force switching cam 22 comes to a position facing the cleaning case 17, the cleaning roller 12 is completely separated from the photoconductor 1. The cam surface portion 22
c is set at a position closest to the shaft center of the cam shaft 21 on the cam peripheral surface. A configuration may be adopted in which the cleaning roller 12 is separated from the photoconductor 1 in a state where the cam surface portion 22c is in pressure contact with the cleaning case 17 without using the stopper pin 24.

Further, in order to start the image forming operation, the photosensitive member 1
Prior to rotating the cleaning roller 12, the motor 23 is operated to rotate the pressing force switching cam 22 from the position shown in FIG. 14 to the position shown in FIG.
Pressure contact.

The switching of the pressing force of the cleaning roller 12 with respect to the photosensitive member 1 and the separation of the roller from the photosensitive member may be performed by the displacement of the cleaning roller 12 itself instead of the displacement of the cleaning case 17. good. For example, the cleaning roller 12 shown in FIG.
It is provided in the cleaning case 17 so as to be movable in the radial direction of the photoconductor 1, that is, in the illustrated example, in the horizontal direction, has the same structure as the pressing force switching cam 22, and is provided inside or outside the cleaning case. The core member 1 of the cleaning roller 12 is provided by a pressing force switching cam that does not exist.
It is also possible to press and displace 2a. In this case,
This pressing force switching cam and the drive device that rotates it are
The aforementioned pressing force switching means is configured.

The transfer residual toner T ₁ on the photosensitive member 1 which has passed through the transfer portion 8 shown in FIG. 1 is the toner having a polarity opposite to the charging polarity of the toner at the time of development as described above. (Abnormal polarity toner) is mixed, and in this example, the abnormal polarity toner is used as the cleaning roller 1.
By frictional charging with No. 2, it is arranged to have the same polarity as the charging polarity of the toner at the time of development. However, it is difficult to completely align the charging polarities of the transfer residual toners existing in the nip area N shown in FIG. 3, and in some cases, the toners having the charging polarities opposite to the charging polarities of the toners at the time of development, that is, The abnormal polarity toner may exist.
At the time of toner recovery, a voltage having a polarity opposite to the charge polarity of the toner at the time of development is applied to the cleaning roller 12 as described above, and the toner having the charge polarity at the time of development is electrostatically transferred to the cleaning roller 12. The toner having a polarity opposite to the charging polarity at the time of development (abnormal polarity toner) is cleaned by the mechanical scraping force received from the cleaning roller 12 at this time. It adheres to the surface of the roller 12. If such abnormal polarity toner is transferred to the photoconductor 1 during the operation of collecting the toner from the photoconductor 1, background stains on the image and stains on the charging roller 2 are likely to occur.

Therefore, in the image forming apparatus of this embodiment, when the transfer residual toner T ₁ is collected from the photoconductor 1 to the cleaning roller 12 as shown in FIG. Contact area with the cleaning roller 12,
That is, the rotation direction of the cleaning roller 12 is controlled so that the two move in opposite directions (counter direction) in the nip region N where they are pressed against each other.
Further, the rotation of the cleaning roller 12 is controlled so that the transfer residual toner T ₁ on the photoconductor 1 is collected by the cleaning roller 12 with the rotation of the cleaning roller 12 less than one rotation. With the rotation of the cleaning roller 12 less than one rotation, the operation for collecting the transfer residual toner T ₁ on the photoconductor 1 is completed.

With this configuration, the cleaning roller 12
The toner T ₂ collected in the
It does not contact the photoreceptor 1 again. Moreover, it is possible to prevent the abnormal polarity toner collected on the cleaning roller 12 from being electrostatically transferred to the surface of the photoconductor 1 after cleaning during the toner collecting operation.

If the transfer residual toner T ₁ is collected, the cleaning roller 12 is rotated in the direction in which the cleaning roller 12 and the photoconductor 1 move in the same direction in the nip region N with the photoconductor 1, as shown by the chain line arrow b in FIG. If so, the collected toner T ₄ is present on the cleaning roller 12 on the downstream side in the rotation direction of the photoconductor 1, and if the toner T ₄ is an abnormal polarity toner that remains positively charged, cleaning is performed. Since the same positive voltage as that is applied to the roller 12 when the toner is collected, the toner T ₄ having the positive polarity is electrostatically attracted toward the photoconductor 1 and adheres to the surface of the photoconductor. . In this case, the cleaning failure of the photoconductor 1 occurs, and the toner adheres to the charging roller 2, so that the toner image formed subsequently has a background stain.

In order to eliminate such a problem, as described above, the cleaning roller 12 rotates so as to rotate in the counter direction with respect to the rotation direction of the photosensitive member 1, that is, in the direction of the solid arrow a in FIG. The direction is set.

At this time, if the cleaning roller 12 is rotated once or more to collect the transfer residual toner from the photosensitive member 1, the toner collected by the cleaning roller 12 has an abnormal polarity charged to the positive polarity. When the toner is present, when the toner approaches the photoconductor 1 again or comes in contact with the photoconductor 1, the toner adheres to the photoconductor 1 and cleaning failure of the photoconductor 1 occurs. Therefore, in this example, the toner collecting operation from the photoconductor 1 to the cleaning roller 12 is completed while the cleaning roller 12 is rotationally driven for less than one rotation.

According to the above construction, the cleaning roller 1
It is possible to make it difficult to transfer the toner (abnormal polarity toner) having a polarity opposite to the charge polarity at the time of development, which is collected in No. 2, to the photoconductor 1.

The cleaning roller 12 for reattaching the collected toner on the cleaning roller 12 to the photosensitive member 1
May rotate in any direction. In this example, as described above, in the nip region N with the photoconductor 1, the cleaning roller 12 and the photoconductor 1 are in the same direction (the direction of the chain line arrow b in FIG. 3). The rotation direction of the cleaning roller 12 is controlled so that the cleaning roller 12 rotates. Moreover, the rotation speed thereof is set higher than that at the time of toner recovery, and the photosensitive member 1 is rotated at a speed higher than the peripheral speed so that the toner can be reattached to the photosensitive member 1 efficiently in a short time.

The present invention is an image forming apparatus using not only a roller-shaped cleaning member but also an endless belt-shaped cleaning member, or an image formation using an endless belt-shaped member other than a drum-shaped image carrier. It can also be applied to devices. Further, the present invention can be applied to an image forming apparatus in which an intermediate transfer member is used as a recording medium, a toner image is transferred from the image carrier to the intermediate transfer member, and then the toner image is transferred to a transfer material. Further, according to the present invention, after the image bearing member is charged by the charging device, an electrostatic latent image is formed by a portion which is not irradiated with light at the time of image exposure on the surface of the image bearing member, and the latent image potential is charged to the opposite polarity. It can also be applied to a so-called positive / positive developing type image forming apparatus in which the generated toner is adhered to the electrostatic latent image to perform development.

[0070]

According to the image forming apparatus of the present invention, the transfer residual toner is collected by the cleaning member to the cleaning member, the collected toner is reattached to the image carrier, and then the reattached toner is attached. In the image forming apparatus that collects toner in the developing device, when the toner collected in the cleaning member is reattached to the image carrier, the cleaning member presses against the image carrier with a strong pressing force necessary for the reattachment. Therefore, it is possible to prevent a decrease in the re-adhesion efficiency of the toner, and it is possible to prevent a decrease in image quality due to this decrease. Further, when the transfer residual toner is collected by the cleaning member, the cleaning member is pressed against the image carrier with a weak pressing force as compared with when the toner is re-adhered, so that the burden on the cleaning member can be reduced. It is possible to prevent the life from decreasing.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional explanatory view of an image forming apparatus according to an exemplary embodiment of the present invention, in which the toner on a photoconductor and a cleaning roller is schematically illustrated and enlarged.

FIG. 2 is a perspective view showing a means for switching the pressing force of the cleaning roller with respect to the photosensitive member together with a cleaning case provided with the cleaning roller.

FIG. 3 is an enlarged schematic illustration of a toner and a frictional contact portion between the photoconductor and the cleaning roller, for explaining that the charging polarities of the toner are made uniform.

FIG. 4 is an explanatory diagram illustrating a relative positional relationship between a charging roller, a developing roller, a transfer roller, a cleaning roller, and a photoconductor, and illustrating a state in which transfer residual toner on the photoconductor is collected by the cleaning roller. Is.

FIG. 5 is an explanatory diagram similar to FIG. 4, showing a state in which the rear end of the image forming area reaches a portion facing the charging roller.

FIG. 6 is an explanatory view similar to FIG. 4, showing a state when the rear end of the image forming area reaches a portion facing the developing roller.

FIG. 7 is an explanatory diagram similar to FIG. 4, showing a state in which the rear end of the image forming area reaches a portion facing the transfer roller.

FIG. 8 is an explanatory diagram similar to FIG. 4, showing a state when the rear end of the image forming area reaches a portion facing the cleaning roller.

FIG. 9 is an explanatory view similar to FIG. 4, showing how the collected toner on the cleaning roller is reattached to the photoconductor.

FIG. 10 is an explanatory view similar to FIG. 4, showing a state in which the redeposited toner on the photoconductor is conveyed toward the developing device.

FIG. 11 is an explanatory view similar to FIG. 4, showing a state in which the redeposited toner on the photoconductor is collected by the developing device.

FIG. 12 is an explanatory diagram similar to FIG. 4, showing a state when the next image forming area reaches a portion facing the transfer roller.

FIG. 13 is a partial cross-sectional view of the peripheral configuration portion of the cleaning roller, the pressing force of which is switched by the operation of the pressing force switching cam.

FIG. 14 is a partial cross-sectional view of a peripheral configuration portion of a cleaning roller separated from a photoconductor by the action of a pressing force switching cam.

[Explanation of symbols]

4 Developing device T ₁ toner T ₂ toner

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masako Yoshii 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (1)

[Claims] 1. An image carrier that is driven to rotate, a latent image forming unit that forms an electrostatic latent image on the carrier, and a developing device that visualizes the electrostatic latent image as a toner image. A transfer device that transfers the toner image on the image carrier to the recording medium, and the transfer residual toner on the image carrier after the toner image transfer is temporarily collected, and then the collected toner is collected on the image carrier. A cleaning member for reattaching the surface of the image bearing member which does not affect the formation of the next electrostatic latent image. In an image forming apparatus that collects the transfer residual toner by pressure contact with the surface and redeposits the collected toner on the surface of the image carrier, Cleaning unit for the image carrier at the time of collection Of such pressure contact force is weakened, the image forming apparatus characterized in that a pressing force switching means for switching pressing force of the cleaning member against the image bearing member.