JP2022124362A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can make an ejection direction of a recording medium from a transfer nip part constant and can ensure stability in conveyance of the recording medium at the transfer nip part.SOLUTION: An image forming apparatus 1 comprises: a photoreceptor drum 61; a transfer roller 71; a transfer roller moving mechanism 17; a drum cleaning roller 642; a driving unit 13; a torque detection unit 14; and a control unit 10. The control unit 10 can execute a polishing mode of polishing a surface of the photoreceptor drum 61 in a non-image forming period, predicts a change in coefficient of friction in association with a change in surface shape of the photoreceptor drum 61 based on the torque difference between initial torque in driving the photoreceptor drum 61 detected at the start of usage of the photoreceptor drum 61 and torque after polishing detected by executing the polishing mode after execution of image formation on a predetermined number of sheets S, and moves a contact position of the transfer roller 71 with the photoreceptor drum 61 in a circumferential direction according to a result of the prediction.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image forming apparatus.

2. Description of the Related Art In electrophotographic image forming apparatuses such as copiers and printers, it is known that discharge products generated by discharge during charging tend to adhere to the surface of an image bearing member such as a photosensitive drum. When this discharge product absorbs moisture, the electrical resistance of the surface of the photosensitive drum is lowered, which may cause a problem of image deletion that disturbs the electrostatic latent image.

Therefore, the toner adhering to the surface of the photosensitive drum is removed by mixing a small amount of abrasive in the toner and using a cleaning roller (abrasive member) and a cleaning blade in combination. At this time, a cleaning method is known in which toner (abrasive) is adhered to the surface of the cleaning roller, and the toner is used to polish discharge products adhering to the surface of the photosensitive drum. An example of conventional technology related to this is disclosed in Patent Document 1.

A conventional image forming apparatus disclosed in Patent Document 1 includes a cleaning member that cleans the surface of an image carrier, and a torque detection section that detects the torque of a drive device for the image carrier. When the surface of the image carrier is worn and smoothed, the frictional resistance between the image carrier and the cleaning member increases, and the torque increase coefficient of the driving device for the image carrier increases. This image forming apparatus can determine the degree of smoothness of the surface of the image carrier based on the torque increase coefficient from the start of printing until the torque of the driving device reaches the maximum value.

JP 2016-170384 A

However, in the prior art, there is a problem that no suitable consideration is given to the smoothing of the surface of the image carrier, in other words, to the increase in the coefficient of friction of the surface of the image carrier. As a result, for example, in a transfer nip portion where a toner image formed on the surface of the image carrier is transferred to the recording medium, the recording medium tends to adhere to the surface of the image carrier, and the conveyance of the recording medium becomes unstable. was concerned.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and can make the discharge direction of the recording medium constant from the transfer nip portion, and can ensure the stability of the conveyance of the recording medium at the transfer nip portion. An object of the present invention is to provide an image forming apparatus that is capable of

In order to solve the above problems, the image forming apparatus of the present invention includes an image carrier, a charging section, an exposure section, a development section, a transfer member, a transfer member moving mechanism, a voltage application section, and a polishing member. , a drive unit, a torque detection unit, and a control unit. The image carrier has a photosensitive layer on its surface. The charging section charges the surface of the image carrier. The exposure section forms an electrostatic latent image on the surface of the image carrier charged by the charging section. The developing section has a toner carrier that carries toner containing an abrasive, and supplies the toner from the toner carrier to the surface of the image carrier to develop the electrostatic latent image to form a toner image. do. The transfer member transfers the toner image formed on the surface of the image carrier onto a recording medium at a transfer nip formed in contact with the image carrier. The transfer member moving mechanism moves the contact position of the transfer member with respect to the circumferential direction of the image carrier. The voltage applying section applies a voltage to the charging section, the toner carrier, and the transfer member. The polishing member polishes the surface of the image carrier by rotating at a peripheral speed different from that of the image carrier while being in contact with the image carrier. The driving section rotationally drives the image carrier and the polishing member. The torque detection section detects the torque of the drive section when rotationally driving the image carrier. The control section controls the transfer member moving mechanism, the voltage application section, and the drive section, and predicts a change in the friction coefficient of the surface of the image carrier based on the torque detected by the torque detection section. . The control section is capable of executing a polishing mode for supplying toner from the developing section to the surface of the image carrier and polishing the surface of the image carrier using the polishing member during non-image formation. An initial torque detected by the torque detection unit when the image carrier is started to be used, and a post-polishing torque detected by the torque detection unit after executing the polishing mode after performing image formation on the recording medium for a predetermined number of sheets. A friction coefficient change due to a change in the surface shape of the image carrier is predicted based on the torque difference between and, and the contact position of the transfer member with respect to the circumferential direction of the image carrier is moved according to the prediction result.

According to the configuration of the present invention, a change in the friction coefficient associated with a change in the surface shape of the image carrier is predicted, and the contact position of the transfer member in the circumferential direction of the image carrier is moved according to the prediction result. As a result, the recording medium can be discharged from the transfer nip portion in a constant direction, and the stability of the recording medium transport in the transfer nip portion can be ensured.

1 is a schematic cross-sectional side view showing the configuration of an image forming apparatus according to an embodiment of the invention; FIG. 2 is a cross-sectional side view of the periphery of an image forming unit of the image forming apparatus of FIG. 1; FIG. 2 is a block diagram showing the configuration of the image forming apparatus of FIG. 1; FIG. 3 is a side view of the periphery of a transfer roller moving mechanism of the image forming unit of FIG. 2; FIG. FIG. 5 is a side view of the periphery of the transfer roller moving mechanism in FIG. 4, showing a state in which the transfer roller has been moved from the initial position; 2 is a flowchart showing an example of transfer roller movement processing in the image forming apparatus of FIG. 1; FIG. 5 is a partially enlarged side view of the vicinity of the transfer nip portion in FIG. 4, showing the transition of the discharge direction of the paper from the transfer nip portion; 5 is a graph showing the effect of the contact position of a transfer roller with respect to a photosensitive drum on the angle of paper discharge from the transfer nip portion in the image forming apparatuses of Examples and Comparative Examples.

Embodiments of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to the following contents.

FIG. 1 is a schematic cross-sectional side view showing the configuration of an image forming apparatus 1 according to an embodiment. FIG. 2 is a cross-sectional side view of the periphery of the image forming unit 6 of the image forming apparatus 1 of FIG. FIG. 3 is a block diagram showing the configuration of the image forming apparatus 1 of FIG. 1. As shown in FIG. An example of the image forming apparatus 1 of the present embodiment is a so-called printer that receives image data and a print command relating to a print job from an external computer and performs an image forming operation on a recording medium such as paper.

As shown in FIGS. 1, 2, and 3, the image forming apparatus 1 includes a paper feeding section 3, a paper conveying section 4, an exposure section 5, an image forming section 6, a transfer section 7, A fixing unit 8 , a paper ejection unit 9 , a control unit 10 and a storage unit 11 are provided.

The paper feed unit 3 accommodates a plurality of sheets (recording media) S, and separates and feeds out the sheets S one by one at the time of printing. The paper conveying unit 4 conveys the paper S fed from the paper feeding unit 3 to the transfer unit 7 and the fixing unit 8, and further discharges the paper S after fixing to the paper discharging unit 9 from the paper discharging port 4a. The exposure unit 5 irradiates the image forming unit 6 with laser light L controlled based on image data.

The image forming section 6 is arranged above the sheet feeding section 3 . The image forming section 6 includes a photosensitive drum (image carrier) 21 rotatably supported in a predetermined direction (counterclockwise in FIG. 2) as shown in FIG. The image forming section 6 further includes a charging section 62 , a developing section 63 , and a drum cleaning section 64 arranged around the photosensitive drum 61 along its rotational direction. A transfer section 7 is arranged between the developing section 63 and the drum cleaning section 64 .

The photosensitive drum 61 has a photosensitive layer 611 on its surface. The charging unit 62 has, for example, a charging roller 621 that is arranged to face and contact the photosensitive drum 61 . The charging section 62 charges the surface of the photosensitive drum 61 to a predetermined potential. The exposure unit 5 exposes the surface of the photosensitive drum 61 charged by the charging unit 62 to form an electrostatic latent image of the document image on the surface of the photosensitive drum 61 . The developing section 63 has, for example, a developing roller (toner carrier) 634 arranged to face the photosensitive drum 61 . The developing unit 63 attaches toner to the electrostatic latent image on the surface of the photoreceptor drum 61 and develops it to form a toner image.

The transfer section 7 is arranged above the paper feeding section 3 and below the image forming section 6 . The transfer unit 7 has a transfer roller (transfer member) 71 that is arranged to face and contact the photosensitive drum 61 . The transfer roller 71 transfers the toner image formed on the surface of the photoreceptor drum 61 onto the sheet S at the transfer nip formed in contact with the photoreceptor drum 61 . After the toner image is transferred onto the sheet S, the drum cleaning section 64 cleans the surface of the photosensitive drum 61 by removing residual toner and the like.

The fixing section 8 is arranged downstream of the sheet conveying section 4 relative to the image forming section 6 and the transfer section 7 in the sheet conveying direction. The fixing section 8 heats and presses the sheet S onto which the toner image has been transferred, thereby fixing the toner image onto the sheet S. As shown in FIG.

The control unit 10 includes a CPU, an image processing unit, and other electronic circuits and electronic components (all not shown). The CPU controls the operation of each component provided in the image forming apparatus 1 based on control programs and data stored in a storage unit (not shown), and performs processing related to the functions of the image forming apparatus 1. . The paper feeding unit 3, the paper conveying unit 4, the exposure unit 5, the image forming unit 6, the transfer unit 7, and the fixing unit 8 receive commands individually from the control unit 10 and form images on the paper S in conjunction with each other. I do.

The storage unit 11 is configured by a combination of a non-volatile storage device such as a program ROM (Read Only Memory) and a data ROM (not shown) and a volatile storage device such as a RAM (Random Access Memory).

3, the image forming apparatus 1 includes a voltage applying section 12, a driving section 13, a torque detecting section 14, a drum detecting section (image carrier detecting section) 16, and a transfer roller moving mechanism 17. And further comprising.

The voltage application unit 12 includes, for example, a power supply unit and a control circuit (both not shown). The voltage applying section 12 is electrically connected to the charging roller 621 of the charging section 62 , the developing roller 634 of the developing section 63 and the transfer roller 71 . The voltage applying section 12 applies voltage to the charging roller 621 , the developing roller 634 of the developing section 63 and the transfer roller 71 . The control unit 10 controls the timing, voltage value, polarity, application time, and the like of voltage application to the charging roller 621 , the developing roller 634 , and the transfer roller 71 via the voltage application unit 12 .

The drive unit 13 includes, for example, a motor and a control circuit (both not shown). The motor of the drive unit 13 is connected to the photosensitive drum 61 and a cleaning roller (abrasive member) 642 of the drum cleaning unit 64, which will be described later. The driving unit 13 can rotationally drive the photosensitive drum 61 and the drum cleaning roller 642 . The control unit 10 controls the timing, rotation speed (peripheral speed), rotation direction, rotation time, etc. of the photosensitive drum 61 and the drum cleaning roller 642 via the drive unit 13 .

The torque detection unit 14 detects the torque of the driving unit 13 when driving the photosensitive drum 61 to rotate. The torque of the driving section 13 when the photosensitive drum 61 is rotationally driven can be alternatively detected by detecting the output current of the motor of the driving section 13, for example. That is, in the present embodiment, the output current of the motor of the drive unit 13 is used as an index representing torque. The method of detecting the torque of the drive unit 13 is not limited to detecting the output current of the motor, and the torque of the rotating shaft of the motor may be directly detected by a torque sensor. A detection signal from the torque detection unit 14 is transmitted to the control unit 10 .

The drum detector 16 is arranged near the photosensitive drum 61 and includes, for example, an optical sensor and a control circuit (both not shown). The photosensitive drum 61 is detachable from the main body 2 of the image forming apparatus 1 and can be replaced. The drum detection unit 16 can detect the presence or absence of the photoreceptor drum 61 , that is, the attachment and detachment of the photoreceptor drum 61 , by means of an optical sensor arranged in the main body 2 . A detection signal from the drum detector 16 is transmitted to the controller 10 .

The transfer roller moving mechanism 17 is arranged near the photosensitive drum 61 and the transfer roller 71 . The transfer roller moving mechanism 17 can move the contact position of the transfer roller 71 with respect to the circumferential direction of the photosensitive drum 61 . The control unit 10 controls movement of the contact position of the transfer roller 71 with respect to the circumferential direction of the photosensitive drum 61 via the transfer roller moving mechanism 17 . Details of the transfer roller moving mechanism 17 will be described later.

Next, the configuration of the image forming section 6 will be described with reference to FIGS. 2 and 3. FIG. The image forming section 6 includes the photosensitive drum 61, the charging section 62, the developing section 63, and the drum cleaning section 64, as described above. The axes of rotating bodies such as the photosensitive drum 61, the charging roller 621, the developing roller 634, and the drum cleaning roller 642, which will be described later, extend parallel to each other along the depth direction of the paper surface of FIG.

The photoreceptor drum 61 has a cylindrical shape and is rotatably supported with its center axis horizontal, and is rotated around the center axis at a constant speed by the drive unit 13 . The drive unit 13 has, for example, a motor, and the rotation speed and rotation direction are controlled by the control unit 10 . The photoreceptor drum 61 has a photoreceptor layer 611 made of an inorganic photoreceptor such as amorphous silicon on the surface (peripheral surface) of a drum tube made of metal such as aluminum. An electrostatic latent image is formed on the surface of the photosensitive drum 61 .

The charging section 62 has, for example, a charging roller 621 and a charging cleaning roller 622 .

The charging roller 621 extends parallel to the axial direction of the photosensitive drum 61 and is rotatably supported with its central axis horizontal. The charging roller 621 rotates as the photoreceptor drum 61 rotates by contacting the surface of the photoreceptor drum 61 . The charging roller 621 has, for example, a conductive layer on the surface (outer peripheral surface) of the metal core, which is made of crosslinked rubber or the like containing an ion conductive material. When a predetermined charging voltage is applied to the charging roller 621, the surface of the photosensitive drum 61 is uniformly charged. The charging cleaning roller 622 contacts the surface of the charging roller 621 and cleans the surface of the charging roller 621 . Note that the charging unit 62 may be configured to have a corona discharge type corona wire instead of the charging roller 621 .

The developing section 63 has a developing container 631 , a first stirring and conveying member 632 , a second stirring and conveying member 633 , a developing roller (toner carrier) 634 , and a regulation member 635 .

The developer container 631 has an elongated shape extending along the axial direction of the photosensitive drum 61 and is arranged with its longitudinal direction horizontal. The developer container 631 accommodates, for example, a two-component developer containing toner and magnetic carrier as the developer to be supplied from the developing unit 63 to the surface of the photoreceptor drum 61 . Note that the developer may be a one-component developer.

The first agitating/conveying member 632 and the second agitating/conveying member 633 are supported by the developer container 631 so as to be rotatable around an axis extending parallel to the photosensitive drum 61 . The first agitating and conveying member 632 and the second agitating and conveying member 633 rotate about their axes, thereby agitating and conveying the developer in opposite directions along the axis of rotation.

The developing roller 634 is rotatably supported by the developing container 631 about an axis extending parallel to the axis of the photosensitive drum 61 . A part of the surface of the developing roller 634 is exposed from the developer container 631 and faces and approaches the photosensitive drum 61 . The developing roller 634 carries on its surface the toner to be supplied to the surface of the photoreceptor drum 61 in the area facing the photoreceptor drum 61 . The developing roller 634 supplies the toner in the developing container 631 to the surface of the photosensitive drum 61 to develop the electrostatic latent image and form a toner image.

The regulating member 635 is arranged on the upstream side in the rotation direction of the developing roller 634 in the area where the developing roller 634 and the photosensitive drum 61 face each other. The regulating member 635 faces and is close to the developing roller 634 and is arranged with a predetermined gap between its tip and the surface of the developing roller 634 . The regulating member 635 extends over the entire area of the developing roller 634 in the axial direction.

The toner in the developing container 631 is agitated and circulated by the first agitating and conveying member 632 and the second agitating and conveying member 633 , charged, and carried on the surface of the developing roller 634 . The layer thickness of the developer (toner) carried on the surface of the developing roller 634 is regulated by the regulating member 635 . When a predetermined development voltage is applied to the developing roller 634 , the toner carried on the surface of the developing roller 634 is exposed in the area facing the photosensitive drum 61 due to the potential difference between it and the potential of the surface of the photosensitive drum 61 . It flies to the surface of body drum 61 . Therefore, the electrostatic latent image on the surface of the photosensitive drum 61 is developed with toner.

The drum cleaning section 64 has a recovery container 641 , a drum cleaning roller (abrasive member) 642 , a drum cleaning blade 643 and a recovery spiral 644 .

The collection container 641 has an elongated shape extending along the axial direction of the photoreceptor drum 61 and is arranged with its longitudinal direction horizontal. The collection container 641 stores residues such as waste toner removed from the surface of the photosensitive drum 61 by the drum cleaning roller 642 and the drum cleaning blade 643 .

The drum cleaning roller 642 is rotatable around an axis extending parallel to the axis of the photosensitive drum 61 and supported by the collection container 641 . The drum cleaning roller 642 has, for example, an elastic layer made of foamed rubber (for example, carbon-containing conductive foamed EPDM) or the like on the surface (peripheral surface) of the metal core. A part of the surface of the drum cleaning roller 642 is exposed from the collection container 641 to face the photoreceptor drum 61 and contact the surface of the photoreceptor drum 61 with a predetermined pressure.

The drum cleaning roller 642 is in contact with the surface of the photoreceptor drum 61 and is rotated by the drive unit 13 in such a direction that the contact area with the photoreceptor drum 61 moves in the same direction as the photoreceptor drum 61 . The drum cleaning roller 642 rotates at a peripheral speed different from that of the photosensitive drum 61 . That is, the drum cleaning roller 642 rotates at a peripheral speed different from that of the photoreceptor drum 61 while being in contact with the photoreceptor drum 61 to polish the surface of the photoreceptor drum 61 .

The toner supplied from the developing section 63 to the surface of the photosensitive drum 61 contains an external additive (abrasive). The external additive is composed of materials such as titanium, copper, zinc, and aluminum. The toner not only adheres to the electrostatic latent image on the surface of the photosensitive drum 61 to form a toner image, but also uses residual toner (waste toner) remaining on the surface of the photosensitive drum 61 without being transferred. It is also used for polishing the surface of the photosensitive drum 61 .

The drum cleaning blade 643 is arranged downstream of the drum cleaning roller 642 in the drum rotation direction. The drum cleaning blade 643 has a plate shape extending along the axial direction of the photosensitive drum 61 . The drum cleaning blade 643 contacts the surface of the photosensitive drum 61 with a predetermined pressure. The drum cleaning blade 643 removes residues such as waste toner remaining on the surface of the photosensitive drum 61 after transfer.

The recovery spiral 644 is arranged in a region away from the photoreceptor drum 61 across the drum cleaning roller 642 . The recovery spiral 644 is supported by the recovery container 641 so as to be rotatable around an axis extending parallel to the axis of the photosensitive drum 61 . The collection spiral 644 conveys residual matter such as waste toner removed from the surface of the photosensitive drum 61 to a collected matter disposal container (not shown) provided outside the drum cleaning section 64 .

Next, the transfer roller moving mechanism 17 will be described in detail. FIG. 4 is a side view around the transfer roller moving mechanism 17 of the image forming section 6 of FIG. FIG. 5 is a side view around the transfer roller moving mechanism 17 in FIG. 4, showing a state in which the transfer roller 71 has been moved from the initial position. 4 and 5 are drawn such that the ejection angle of the sheet S at the transfer nip portion N is substantially horizontal when the transfer roller 71 is at the initial position for convenience of explanation.

The transfer roller moving mechanism 17 is arranged near the photosensitive drum 61 and the transfer roller 71, as shown in FIGS. The transfer roller moving mechanism 17 includes a support member 171 , a biasing member 172 , a swing gear 173 , an idle gear 174 , a drive gear 175 and a drive motor 176 .

The support member 171 is supported by the shaft portion 61x of the photosensitive drum 61 so as to be swingable around the axis of the shaft portion 61x. The support member 171 rotatably supports the transfer roller 71 .

The biasing member 172 is provided on the support member 171 . The biasing member 172 is composed of, for example, a compression spring, and is arranged between the transfer roller 71 and the support member 171 at a position separated from the photosensitive drum 61 across the transfer roller 71 . The biasing member 172 biases the transfer roller 71 toward the photosensitive drum 61 .

The swing gear 173 is fixed to the support member 171 and is rotatable around the axis of the shaft portion 61x of the photosensitive drum 61 . That is, the support member 171 rotates (rocks) together with the rocking gear 173 . The swing gear 173 meshes with the idle gear 174 .

Drive gear 175 meshes with idle gear 174 . The drive gear 175 is fixed to the rotary shaft 176x of the drive motor 176. As shown in FIG. When the drive motor 176 is driven, the swing gear 173 rotates via the drive gear 175 and the idle gear 174, and the transfer roller 71 rotates (swings) together with the support member 171 around the axis of the shaft portion 61x.

FIG. 4 shows the transfer roller 71 at its initial position. FIG. 5 shows a state in which the transfer roller 71 has been moved from the initial position. The transfer roller 71 is moved along the circumferential direction of the photosensitive drum 61 by the transfer roller moving mechanism 17 . The power for swinging the support member 171 may be obtained from the drive section 13 instead of the drive motor 176. FIG.

The control unit 10 of the image forming apparatus 1 of the present embodiment supplies toner from the developing unit 63 to the surface of the photoreceptor drum 61 during non-image formation as needed, and also uses the drum cleaning roller 642 to clean the photoreceptor drum. A polishing mode for polishing the surface of 61 can be performed.

Specifically, by applying a development voltage having the same polarity (positive) as that of the toner to the developing roller 634 of the developing unit 63 , the toner used for polishing the surface of the photoreceptor drum 61 is transferred from the developing unit 63 to the photoreceptor drum. 61 (toner supply step). While the toner is being supplied to the drum cleaning roller 642 , a voltage having the same polarity (positive) as the toner (transfer reverse voltage) is applied to the transfer roller 71 so that the toner does not adhere to the transfer roller 71 .

After the toner is supplied to the surface of the photoreceptor drum 61 , the surface of the photoreceptor drum 61 is polished by rotating the drum cleaning roller 642 at a peripheral speed different from that of the photoreceptor drum 61 . The discharge product is removed together with the toner (polishing step). Even after the supply of toner from the developing roller 634 is stopped, the photosensitive drum 61 and the drum cleaning roller 642 continue pre-rotating for a while.

A polishing mode including a toner supply process and a polishing process is executed for a preset time, or a cycle in which each of the toner supply process and the polishing process is performed once is executed for a preset number of times. Moisture and discharge products on the surface of the body drum 61 can be removed. This makes it possible to effectively prevent image deletion for a long period of time. Note that the execution time and the number of repetition cycles of the polishing mode are appropriately set according to the configuration of the photosensitive layer 611 of the photosensitive drum 61 to be used, the environment in which the image forming apparatus 1 is used, and the like.

Further, the control unit 10 controls the transfer roller moving mechanism 17, the voltage applying unit 12, and the driving unit 13, and the torque of the driving unit 13 when rotating the photosensitive drum 61 detected by the torque detecting unit 14 is controlled. Based on this, the change in the friction coefficient of the surface of the photosensitive drum 61 is predicted. If the surface shape of the photoreceptor drum 61 changes and the friction coefficient of the surface of the photoreceptor drum 61 changes, the torque when the photoreceptor drum 61 is rotationally driven is likely to change according to the amount of change, and the friction coefficient It becomes easier to pick up the fluctuation of That is, the coefficient of friction of the surface of the photoreceptor drum 61 can be grasped by monitoring the torque variation when the photoreceptor drum 61 is rotationally driven.

Then, the controller 10 detects the initial torque detected by the torque detector 14 at the start of use of the photoreceptor drum 61 and the torque detector 14 by executing the polishing mode after performing image formation on the predetermined number of sheets of paper S. A torque difference from the detected post-polishing torque is obtained. Further, the control unit 10 predicts a change in the friction coefficient associated with a change in the surface shape of the photoreceptor drum 61 based on the torque difference, and adjusts the contact position of the transfer roller 71 with respect to the circumferential direction of the photoreceptor drum 61 according to the prediction result. move.

Next, a process of moving the transfer roller 71 in the image forming apparatus 1 will be described. FIG. 6 is a flowchart showing an example of processing for moving the transfer roller 71 in the image forming apparatus 1 of FIG.

When the image forming apparatus 1 is operated for the first time and the use of the image forming apparatus 1 is started (start in FIG. 4), the control section 10 detects the initial torque of the driving section 13 when driving the photosensitive drum 61 to rotate. (step #101). The control unit 10 acquires the torque (initial torque) of the drive unit 13 when rotating the photoreceptor drum 61 detected by the torque detection unit 14 when the use of the photoreceptor drum 61 is started.

Next, the control unit 10 determines whether or not the photoreceptor drum 61 has been attached or detached since the friction coefficient lowering process for the surface of the photoreceptor drum 61 was performed last time (step #102). For example, when the photoreceptor drum 61 is replaced, the attachment/detachment of the photoreceptor drum 61 is detected by the drum detection unit 16, and information regarding the attachment/detachment of the photoreceptor drum 61 is stored in the storage unit 11 or the like. The control unit 10 determines whether or not the attachment/detachment of the photoreceptor drum 61 has been detected by the drum detection unit 16 after the friction coefficient lowering process for the surface of the photoreceptor drum 61 was executed last time.

For example, when the photoreceptor drum 61 is not attached or detached, such as immediately after the image forming apparatus 1 is started to be used (No in step #102), the operation flow proceeds to step #103.

Next, the control section 10 executes an image forming operation on the sheet S (step #103). The control unit 10 executes an image forming operation on the paper S based on the print job accepted by the image forming apparatus 1 .

Next, the control unit 10 determines whether or not the number of images formed on the sheet S exceeds a predetermined number (for example, 100,000 sheets) (step #104). If the number of images formed does not exceed the predetermined number (No in step #104), determination of attachment/detachment of the photosensitive drum 61 (step #102) and execution of the image forming operation (step #103) are repeated.

On the other hand, when the number of images formed exceeds the predetermined number (Yes in step #104), the control section 10 executes a polishing mode for the photosensitive drum 61 (step #105). That is, the control unit 10 supplies toner from the developing unit 63 to the surface of the photoreceptor drum 61 during non-image formation, and polishes the surface of the photoreceptor drum 61 using the drum cleaning roller 642 .

Subsequently, the control unit 10 acquires the torque (post-grinding torque) of the drive unit 13 when rotationally driving the photosensitive drum 61 detected by the torque detection unit 14 (step #106). Then, the control unit 10 acquires a torque difference between the initial torque acquired at step #101 and the post-polishing torque acquired at step #106 (step #107).

Next, the control unit 10 determines whether or not the torque difference between the initial torque and the post-polishing torque exceeds a predetermined threshold (step #108). When the torque difference exceeds the predetermined threshold value (Yes in step #108), the controller 10 moves the contact position of the transfer roller 71 with respect to the circumferential direction of the photosensitive drum 61 (step #109).

In other words, the control unit 10 predicts the friction coefficient change associated with the surface shape change of the photoreceptor drum 61 based on the torque difference, and adjusts the contact position of the transfer roller 71 with respect to the circumferential direction of the photoreceptor drum 61 according to the prediction result. move. As a result, the discharge direction of the paper S from the transfer nip portion N formed by the contact between the photosensitive drum 61 and the transfer roller 71 can be made constant, and the transport of the paper S in the transfer nip portion N can be stabilized. It is possible to ensure

Details of the process of moving the transfer roller 71 include the following configuration example.

As the torque difference increases, the control unit 10 moves the contact position of the transfer roller 71 with respect to the circumferential direction of the photosensitive drum 61 to the upstream side in the rotational direction of the photosensitive drum 61, as shown in FIGS. .

FIG. 7 is a partially enlarged side view of the vicinity of the transfer nip portion N in FIG. At the beginning of use of the photosensitive drum 61, the discharge direction D0 of the sheet S from the transfer nip portion N is substantially tangential to the exit of the transfer nip portion N, as shown in FIG. On the other hand, when the photoreceptor drum 61 is used for a long time and the friction coefficient of the surface of the photoreceptor drum 61 increases, the paper S tends to adhere to the surface of the photoreceptor drum 61 at the transfer nip portion N. As a result, the discharge direction D1 of the sheet S from the transfer nip portion N changes to approach the surface of the photoreceptor drum 61 when the period from the start of use of the photoreceptor drum 61 has elapsed.

FIG. 8 is a graph showing the influence of the contact position of the transfer roller with respect to the photosensitive drum on the paper discharge angle from the transfer nip portion in the image forming apparatuses of Examples and Comparative Examples. In each of the image forming apparatus 1 of the example and the image forming apparatus of the comparative example, after performing image formation on a predetermined number of sheets S (for example, 300,000 sheets), the sheet discharge angle from the transfer nip portion was measured. The paper discharge angle shown in FIG. 8 indicates that the tangential direction of the exit of the transfer nip portion is 0 degrees, and the angle increases as the photosensitive drum 61 is approached.

In the image forming apparatus 1 of the embodiment, the contact position of the transfer roller 71 with respect to the circumferential direction of the photoreceptor drum 61 is moved to the upstream side in the rotation direction of the photoreceptor drum 61 as the process of moving the transfer roller 71 . In the image forming apparatus of the comparative example, the contact position of the transfer roller with respect to the circumferential direction of the photosensitive drum is not changed. Other configuration and operating conditions of the image forming apparatus are as follows: image forming speed of 40 sheets/min; peripheral speed of photosensitive drum of 240.28 mm/sec; diameter of photosensitive drum of 30 mm; The distance is 0.3 mm, the photosensitive layer is an amorphous silicon layer, the surface potential of the photosensitive drum is 220 V, and the diameter of the transfer roller is 19 mm.

According to FIG. 8, in the case of the image forming apparatus of the comparative example, when the number of images formed on the sheet S increases, the coefficient of friction of the surface of the photosensitive drum greatly increases, causing the sheet to come closer to the photosensitive drum. It can be seen that the ejection angle is large.

On the other hand, in the case of the image forming apparatus 1 of the embodiment, by moving the contact position of the transfer roller 71 with respect to the circumferential direction of the photosensitive drum 61 to the upstream side in the rotational direction of the photosensitive drum 61, the paper discharge angle is set to the initial value. It can be seen that there is almost no change with respect to the state. According to the configuration of the embodiment, the discharge direction of the paper S from the transfer nip portion N can be easily made constant, and the stability of the paper S transport in the transfer nip portion N can be ensured.

The controller 10 also controls the transfer roller moving mechanism 17 to increase the amount of movement of the transfer roller 71 from the initial position in the circumferential direction of the photosensitive drum 61 as the torque difference increases. According to this configuration, it is possible to cope with the fact that the paper S tends to approach the photoreceptor drum 61 as the coefficient of friction of the surface of the photoreceptor drum 61 increases. That is, based on the magnitude of the torque difference, the ejection direction of the paper S from the transfer nip portion N can be made constant, and the stability of the transportation of the paper S in the transfer nip portion N can be ensured.

Further, the control unit 10 executes the polishing mode and acquires the torque difference every time image formation is performed on a predetermined number of sheets of paper S. FIG. According to this configuration, frequent execution of the polishing mode, which requires a certain amount of time, can be suppressed. Therefore, the torque difference can be obtained efficiently, and the contact position of the transfer roller 71 with respect to the circumferential direction of the photosensitive drum 61 can be effectively moved.

Further, the control unit 10 continuously detects the torque of the drive unit 13 by the torque detection unit 14, and when the torque exceeds a predetermined threshold value, executes the polishing mode and acquires the torque difference. According to this configuration, it is possible to constantly monitor the torque of the driving section 13 when rotating the photosensitive drum 61 . Therefore, when the torque exceeds a predetermined threshold, it is possible to quickly execute the polishing mode and acquire the torque difference.

On the other hand, if the torque difference between the initial torque and the post-grinding torque of the photoreceptor drum 61 does not exceed the predetermined threshold value (No in step #108), the control unit 10 sets the contact position of the transfer roller 71 to the initial position. return (step #110). Specifically, when the torque difference obtained after moving the contact position of the transfer roller 71 with respect to the circumferential direction of the photosensitive drum 61 is equal to or less than a predetermined threshold value, the control unit 10 changes the contact position of the transfer roller 71 to its initial position.

For example, when the control unit 10 moves the contact position of the transfer roller 71 with respect to the circumferential direction of the photoreceptor drum 61 to the upstream side in the rotation direction of the photoreceptor drum 61 in the previous process of moving the transfer roller 71, If the torque difference does not exceed the predetermined threshold in the operation flow, the contact position of the transfer roller 71 is returned to the initial position. According to this configuration, it is possible to prevent the discharge direction of the sheet S from the transfer nip portion N from being excessively separated from the surface of the photosensitive drum 61 . As a result, the direction of ejection of the sheet S from the transfer nip portion N can be made constant, and the stability of the transport of the sheet S in the transfer nip portion N can be ensured.

After moving the contact position of the transfer roller 71 with respect to the circumferential direction of the photosensitive drum 61 (step #109), or after the contact position of the transfer roller 71 is returned to the initial position (step #110), the operation flow is the photosensitive drum. The process returns to determination of attachment/detachment of the body drum 61 (step #102).

For example, when the photosensitive drum 61 is attached or detached due to replacement of the photosensitive drum 61 (Yes in step #102), the controller 10 returns the contact position of the transfer roller 71 to the initial position (step # 111). Specifically, when the drum detection unit 16 detects attachment/detachment of the photoreceptor drum 61 after moving the contact position of the transfer roller 71 with respect to the circumferential direction of the photoreceptor drum 61, the control unit 10 The contact position of 71 is returned to the initial position.

According to this configuration, it is possible to prevent the discharge direction of the sheet S from the transfer nip portion N from being excessively separated from the surface of the photosensitive drum 61 when the photosensitive drum 61 is new. As a result, the direction of ejection of the sheet S from the transfer nip portion N can be made constant, and the stability of the transport of the sheet S in the transfer nip portion N can be ensured.

Although the embodiment of the present invention has been described above, the scope of the present invention is not limited to this, and various modifications can be made without departing from the gist of the invention.

For example, in the above embodiment, the image forming apparatus 1 is an image forming apparatus for monochrome printing that forms a monochrome image, but is not limited to such a model. The image forming apparatus may be an image forming apparatus for color printing that forms a color image by superimposing a plurality of color images.

INDUSTRIAL APPLICABILITY The present invention can be used in image forming apparatuses.

REFERENCE SIGNS LIST 1 image forming apparatus 2 main body 5 exposure unit 6 image forming unit 7 transfer unit 8 fixing unit 10 control unit 11 storage unit 12 voltage application unit 13 driving unit 14 torque detection unit 16 drum detection unit (image carrier detection unit)
17 transfer roller moving mechanism (transfer member moving mechanism)
61 photoreceptor drum (image carrier)
62 charging section 63 developing section 64 drum cleaning section 71 transfer roller (transfer member)
611 photosensitive layer 621 charging roller 634 developing roller (toner carrier)
642 drum cleaning roller (abrasive member)
643 Drum cleaning blade S Paper (recording medium)

Claims (7)

an image carrier having a photosensitive layer on its surface;
a charging unit that charges the surface of the image carrier;
an exposure unit that forms an electrostatic latent image on the surface of the image carrier charged by the charging unit;
a developing unit having a toner carrier that carries a toner containing an abrasive, and supplying the toner from the toner carrier to the surface of the image carrier to develop the electrostatic latent image and form a toner image;
a transfer member that transfers the toner image formed on the surface of the image carrier onto a recording medium at a transfer nip formed in contact with the image carrier;
a transfer member moving mechanism for moving a contact position of the transfer member with respect to the circumferential direction of the image carrier;
a voltage applying unit that applies a voltage to the charging unit, the toner carrier, and the transfer member;
a polishing member that polishes the surface of the image carrier by rotating at a peripheral speed different from that of the image carrier while being in contact with the image carrier;
a drive unit that rotates the image carrier and the polishing member;
a torque detection unit that detects the torque of the driving unit when the image carrier is rotationally driven;
a control unit that controls the transfer member moving mechanism, the voltage application unit, and the drive unit, and predicts a change in the friction coefficient of the surface of the image carrier based on the torque detected by the torque detection unit;
with
The control unit
a polishing mode in which toner is supplied from the developing unit to the surface of the image carrier during non-image formation, and the surface of the image carrier is polished using the polishing member;
An initial torque detected by the torque detection unit when the image carrier is started to be used, and an after-polishing torque detected by the torque detection unit after executing the polishing mode after performing image formation on the recording medium for a predetermined number of sheets. A friction coefficient change associated with a surface shape change of the image carrier is predicted based on a difference between the torque and the torque, and the contact position of the transfer member with respect to the circumferential direction of the image carrier is moved according to the prediction result. image forming apparatus. 2. The method according to claim 1, wherein, as the torque difference increases, the control section moves the contact position of the transfer member with respect to the circumferential direction of the image carrier upstream in the rotational direction of the image carrier. image forming device. 3. The image forming apparatus according to claim 2, wherein, as the torque difference increases, the controller increases the amount of movement of the transfer member from the initial position in the circumferential direction of the image carrier. 4. The control unit according to any one of claims 1 to 3, wherein the control unit executes the polishing mode and acquires the torque difference each time image formation on the recording medium is performed for a predetermined number of sheets. image forming device. The control unit continuously detects the torque by the torque detection unit, and when the torque exceeds a predetermined threshold value, executes the grinding mode and acquires the torque difference. 4. The image forming apparatus according to any one of claims 1 to 3. The controller returns the contact position of the transfer member to an initial position when the torque difference acquired after moving the contact position of the transfer member in the circumferential direction of the image carrier is equal to or less than a predetermined threshold value. 6. The image forming apparatus according to claim 2, wherein: The image carrier is detachable with respect to the main body of the image forming apparatus,
The main body includes an image carrier detection unit that detects attachment and detachment of the image carrier,
The control section moves the contact position of the transfer member with respect to the circumferential direction of the image carrier when the image carrier detecting section detects the attachment and detachment of the image carrier after moving the contact position of the transfer member. 6. The image forming apparatus according to any one of claims 2 to 5, wherein the is returned to the initial position.

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