JP6653075B2 - Transfer device and image forming device - Google Patents

Description

  The present invention relates to a transfer device and an image forming device.

  2. Description of the Related Art Conventionally, as a transfer device of an image forming apparatus, a transfer device that sandwiches a recording medium in a transfer nip formed by an image carrier and a nip forming member and transfers a toner image from the image carrier is known.

  The image forming apparatus described in Patent Literature 1 is provided with such a transfer device, which is a secondary transfer device that performs a secondary transfer of a toner image primary-transferred from a photoconductor to an intermediate transfer belt to a sheet as a recording medium. ing. This secondary transfer device has a secondary transfer roller that contacts the front surface of the intermediate transfer belt, and a secondary transfer opposing roller that faces the secondary transfer roller and contacts the back surface of the intermediate transfer belt. Further, the secondary transfer device includes a contact / separation mechanism for bringing the intermediate transfer belt and the secondary transfer roller into and out of contact with each other. In the secondary transfer device, before the leading end of the sheet enters the secondary transfer unit from a state where the intermediate transfer belt and the secondary transfer roller are in contact with each other and there is no sheet in the secondary transfer unit, the intermediate transfer belt and the secondary transfer roller contact the intermediate transfer belt. Separate from the next transfer roller. As a result, a gap is formed between the intermediate transfer belt and the secondary transfer roller, thereby reducing shock jitter when the leading edge of the sheet enters the secondary transfer portion. Then, in a state where the leading end of the sheet enters the gap and the sheet is present in the secondary transfer portion, the intermediate transfer belt and the secondary transfer roller are brought into contact with each other via the sheet, so that a sufficient transfer pressure is obtained in the secondary transfer portion. And the occurrence of transfer failure is suppressed. Also, when the trailing edge of the sheet comes out of the secondary transfer section, the intermediate transfer belt and the secondary transfer roller are separated by the contact / separation mechanism with the sheet in the secondary transfer section, and the secondary transfer section is Shock jitter when the rear end comes off is reduced.

  However, the magnitude of the speed fluctuation of the intermediate transfer belt that can be caused by the contact / separation operation between the intermediate transfer belt and the secondary transfer roller by the contact / separation mechanism differs depending on the presence or absence of the sheet in the secondary transfer unit. For this reason, there is a problem that a speed fluctuation is generated in the intermediate transfer belt in one of the case where the sheet is present in the secondary transfer portion and the case where the sheet is not present, and a shock jitter due to the speed fluctuation is generated. Occurs.

In order to solve the above-described problems, the present invention provides a rotatable transfer member that forms a transfer unit that sandwiches a recording medium between a rotatable image carrier and transfers an image from the image carrier to the recording medium. A transfer device provided with contact / separation means for bringing the image carrier and the transfer member into and out of contact with each other, wherein the speed of contact / separation between the image carrier and the transfer member is determined by the presence or absence of a recording medium in the transfer unit; Unlike in accordance with, as contact and separation operation speed when no recording medium is slower than and away operation speed when the recording medium is present, and wherein the control means for controlling said moving means I do.

  As described above, according to the present invention, there is an excellent effect that it is possible to reduce the shock jitter caused by the speed variation of the image carrier that can be caused by the contact / separation operation between the image carrier and the transfer member.

4 is a timing chart of a contact / separation operation. FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 3 is a diagram illustrating an example of a layout of an intermediate transfer unit and a secondary transfer unit in the image forming apparatus. FIG. 4 is an enlarged cross-sectional view illustrating a configuration around a secondary transfer unit of the transfer unit. 9 is a flowchart illustrating an example of an operation of moving the secondary transfer roller toward and away from the intermediate transfer belt by the contacting and separating mechanism. FIG. 7A is a diagram illustrating a state of sheet conveyance when a sheet is present in a secondary transfer unit, and FIG. 7B is a diagram illustrating a state of sheet conveyance when a sheet is not present in a secondary transfer unit. (A) A graph showing the fluctuation of the intermediate transfer belt speed during the contact / separation operation when there is paper in the secondary transfer unit, and (b) the intermediate transfer belt speed during the contact / separation operation when there is no paper in the secondary transfer unit. Graph showing fluctuation. 7 is a graph showing the rank (good or bad) of a shock jitter when the contact / separation speed is changed. FIG. 4 is an enlarged cross-sectional view illustrating a configuration around a secondary transfer unit of a transfer unit when a paper detection sensor is installed on an upstream side in a sheet conveyance direction with respect to the secondary transfer unit. FIG. 3 is an enlarged cross-sectional view illustrating a configuration around a secondary transfer unit of a transfer unit when a torque detection sensor that detects a torque of a secondary transfer drive motor or an intermediate transfer drive motor is provided.

  Hereinafter, an embodiment of an image forming apparatus to which the present invention is applied will be described. FIG. 2 is a schematic configuration diagram of a copying machine 1 which is an image forming apparatus according to the present embodiment. The copier 1 includes a copier main body 100, a paper feed table 200 on which the copier main body 100 is mounted, a scanner 300 mounted on the copier main body 100, and an automatic document feeder mounted on the scanner 300. And an ADF (ADF) 400.

  In the scanner 300, the first traveling body 302 equipped with a light source and a mirror for document illumination and the second traveling body 303 equipped with a plurality of reflection mirrors are placed on the contact glass 301 as the reciprocating movement. The scanning of the read original is performed. The scanning light sent from the second traveling body 303 is condensed by an imaging lens 304 on an image forming surface of a reading sensor 305 provided behind the scanning light, and is read as an image signal by the reading sensor 305.

  A tandem image forming unit 10 is arranged in the copying machine main body 100. The tandem-type image forming section 10 includes image forming units 11Y, 11C, 11M, and 11K corresponding to toners of yellow, cyan, magenta, and black, respectively. Each image forming unit 11 is provided with photosensitive drums 12Y, 12C, 12M, and 12K that are image carriers that carry a toner image formed with a toner image formed by a developing device on which an electrostatic latent image is formed. Have been. Around the photosensitive drum 12, a charging device for uniformly charging the photosensitive drum, a developing device for developing a latent image on the photosensitive drum, a photosensitive member cleaning device for removing residual toner on the photosensitive drum, and the like Each means for executing the electrophotographic process is disposed.

  An exposure device 18 is provided above the tandem type image forming unit 10 to form a latent image by exposing the photosensitive drum 12 with laser light or LED light based on image information. At the lower position of the tandem type image forming unit 10 facing each photoconductor drum 12, an image carrier which is formed of an endless belt member and carries a toner image which is primarily transferred from each photoconductor drum 12 sequentially. An intermediate transfer belt 21 as an intermediate transfer member is disposed. The intermediate transfer belt 21 is supported by a driving roller 14, a driven roller 15, and a secondary transfer opposing roller 24, and is conveyed clockwise in FIG. The image forming units are arranged in the order of yellow, cyan, magenta, and black from the upstream side along the moving direction on the extension surface of the intermediate transfer belt 21 stretched between the driving roller 14 and the driven roller 15. 11Y, 11C, 11M and 11K are arranged side by side. A transfer roller that constitutes a transfer unit that transfers a toner image of each color formed on each photosensitive drum 12 onto the intermediate transfer belt 21 at an adjacent position facing each photosensitive drum 12 via the intermediate transfer belt 21 The primary transfer roller 13 is disposed. Further, a cleaning device 17 for removing the toner remaining on the surface of the intermediate transfer belt 21 is provided on the downstream side in the moving direction of the intermediate transfer belt 21 supported by the secondary transfer facing roller 24.

  On the opposite side of the tandem-type image forming unit 10 with the intermediate transfer belt 21 interposed therebetween, a transfer device as a transfer device that collectively transfers a toner image formed by being superimposed on the surface of the intermediate transfer belt onto a sheet P as a recording medium. A unit 20 is arranged. The transfer unit 20 mainly includes a secondary transfer facing roller 24, a secondary transfer roller 30 that is a transfer roller that comes into contact with the secondary transfer facing roller 24 via the intermediate transfer belt 21, and a secondary transfer roller 30 described in detail below. It comprises a moving means for moving with respect to the intermediate transfer belt 21. With this moving means, the secondary transfer roller 30 can be moved so as to come into contact with or separate from the intermediate transfer belt 21. The transfer unit 20 transfers the sheet P conveyed from the sheet feeding cassette 44 of the sheet feeding table 200 by causing the secondary transfer roller 30 to contact the intermediate transfer belt 21 by moving means. The sheet is nipped by the secondary transfer nip, which is the nip. In this manner, the secondary transfer pressure is applied to the paper P sandwiched by the secondary transfer nip portion, and the secondary transfer bias is applied to transfer the toner image carried on the intermediate transfer belt 21 to the paper P. .

  At a position adjacent to the secondary transfer roller 30 on the downstream side in the paper transport direction, two stretch rollers 23 and a transport belt 22 stretched over these are configured to transport the secondary-transferred paper P. A belt conveying device is provided. A fixing device 25 is provided at a position adjacent to the transport belt 22 on the downstream side in the sheet transport direction. The fixing device 25 fixes the toner image on the sheet P transported by the transport belt 22. The fixing device 25 mainly includes a fixing belt 26 which is an endless belt, and a pressure roller 27 pressed against the fixing belt 26. Below the transfer unit 20 and the fixing device 25, a sheet reversing device 80 that reverses the sheet P so as to record images on both sides of the sheet P is disposed in parallel with the tandem-type image forming unit 10. .

  Next, an operation when color copying is performed by the copying machine 1 having the above configuration will be described. First, the original is set on the original platen 401 of the automatic document feeder 400 in FIG. 2 or the original is set on the contact glass 301 of the scanner 300 by opening the automatic document feeder 400 and the automatic document feeder 400 is moved. Close and hold the original. When the start switch is pressed in this state, when the original is set in the automatic document feeder 400, the original is conveyed and moved onto the contact glass 301, and then, when the original is set on the contact glass 301. Immediately, the scanner 300 is driven. Then, the vehicle travels on the first traveling body 302 and the second traveling body 303, emits light from the light source at the first traveling body 302, receives reflected light from the document surface, and reflects the reflected light toward the second traveling body 303. Then, the reflected light is further reflected by the mirror of the second traveling body 303. The reflected light enters the reading sensor 305 through the imaging lens 304, and the reading sensor 305 reads the contents of the document.

  By pressing a start switch provided on the copying machine 1, the driving roller 14 among the driving roller 14, the driven roller 15, and the secondary transfer facing roller 24 that rotatably supports the intermediate transfer belt 21 is driven. I do. As a result, the intermediate transfer belt 21 rotates, and the driven roller 15 and the secondary transfer facing roller 24 rotate following the intermediate transfer belt 21. At the same time, the rotation of the photosensitive drum 12 is started in each image forming unit 11, and the photosensitive drum 12 is uniformly charged by the charging device. Next, based on the content read by the scanner 300, the exposure device 18 irradiates the photosensitive drums 12 charged with the writing light L by a laser, an LED, or the like, corresponding to the respective colors of yellow, cyan, magenta, and black. An electrostatic latent image is formed. A toner is supplied from the developing device to each photosensitive drum 12 on which the electrostatic latent image is formed, and the electrostatic latent image is visualized, and yellow, cyan, magenta, and black are respectively supported on each photosensitive drum 12. Thus, a monochrome toner image is formed.

  Each single-color toner image is sequentially primary-transferred by the primary transfer bias applied from each primary transfer roller 13 so as to overlap the intermediate transfer belt 21, and the color toner image synthesized on the intermediate transfer belt 21 is formed. It is formed. After the primary transfer, the surface of each photoconductor drum 12 is cleaned of the residual toner by the photoconductor cleaning device, and is discharged by the discharging device to prepare for the next image formation.

  When the start switch is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selected and rotated, and the paper P is fed out from one of the paper feed cassettes 44 provided in the paper bank 43 in multiple stages and separated. The sheets are separated one by one by a roller 45 and introduced into a sheet feeding path 46. The paper P introduced into the paper feed path 46 is transported by the transport rollers 47, guided to the paper feed path 48 in the copying machine main body 100, and stopped against the registration rollers 49. On the other hand, when the paper P is to be manually fed, the manual paper feed roller 70 is rotated to feed out the paper P on the manual feed tray 71, separated by the manual feed roller 72 one by one, and introduced into the manual paper feed path 73. It is stopped by abutting against the roller 49. Next, the registration roller 49 is rotated in synchronization with the color toner image synthesized on the intermediate transfer belt 21, and the paper P is fed between the intermediate transfer belt 21 and the secondary transfer roller 30, and the transfer unit 20 is moved. And the color toner image is transferred onto the paper P.

  The sheet P carrying an unfixed toner image passing through a secondary transfer nip formed by the intermediate transfer belt 21 and the secondary transfer roller 30 is composed of two stretching rollers 23 and a transport belt 22. The sheet is conveyed to the fixing device 25 by the belt conveying device. Then, the toner image transferred onto the paper P by applying heat and pressure by the fixing device 25 is fixed as a permanent image.

  The paper P on which the toner image is fixed is switched by the switching claw 74 to the transport destination, is discharged by the discharge roller 75, and is stacked on the discharge tray 76. On the other hand, in the case of double-sided copying, the paper P on which an image is formed on one side is switched by the switching claw 74 and is introduced into the paper reversing device 80, where it is reversed and guided again to the transfer position. An image is also formed on the sheet, and then the sheet is discharged onto a sheet discharge tray 76 by a discharge roller 75. At this time, the residual toner remaining on the intermediate transfer belt 21 after the secondary transfer is removed by the cleaning device 17, and the tandem image forming unit 10 prepares for the second image formation.

  FIG. 3 is a diagram illustrating an example of a layout of the transfer unit 20 provided in the copying machine 1. A cam drive motor 58, which is a stepping motor for driving the contact / separation mechanism 500, is disposed in the transfer unit 20. The cam drive motor 58 is driven by the control driver 4 to rotate the first cam 50. The first cam 50 contacts the bearing of the secondary transfer roller 30. The cam rotation changes the cam radius and moves the secondary transfer roller 30 in the direction of the arrow in the figure. The secondary transfer roller 30 and the intermediate transfer belt 21 come into contact with each other by the upward movement of the secondary transfer roller 30 (contact operation), and the secondary transfer roller 30 is moved from the intermediate transfer belt 21 by the downward movement of the arrow. Are separated (separation operation).

  FIG. 4 is an enlarged cross-sectional view illustrating a configuration around the secondary transfer portion N of the transfer unit 20. The secondary transfer roller 30 includes a roller portion 31 extending in the width direction orthogonal to the sheet conveying direction, a first shaft member 32 and a second shaft member 32 projecting from both end surfaces in the axial direction and extending in the rotation axis direction. The shaft member 33 includes a first idle roller 34 and a second idle roller 35 described later. The roller unit 31 includes a cylindrical hollow cored bar 31a, an elastic layer 31b made of an elastic body fixed to the peripheral surface thereof, and a surface layer 31c fixed to the peripheral surface of the elastic layer 31b.

  Examples of the metal constituting the hollow cored bar 31a include stainless steel and aluminum, but are not limited to these materials. The elastic layer 31b preferably has a JIS-A hardness of 70 [°] or less. However, since the cleaning blade 39 is in contact with the roller portion 31, various problems are caused if the elastic layer 31b is too soft. Therefore, it is desirable that the elastic layer 31b has a JIS-A hardness of 40 [°] or more. The elastic layer 31b having a JIS-A hardness of about 50 [°] may be formed of epichlorohydrin rubber exhibiting a certain degree of conductivity. As the rubber material exhibiting conductivity, EPDM or Si rubber in which carbon is dispersed, NBR having an ion conductive function, urethane rubber, or the like may be used instead of the above-mentioned conductive epichlorohydrin rubber. Since most rubber materials exhibit good chemical affinity for the toner or exhibit a relatively large friction coefficient, the surface of the elastic layer 31b made of rubber material is covered with a surface layer 31c. ing. As a result, the adhesion of the toner to the surface of the roller unit 31 is suppressed, and the load of sliding with the cleaning blade 39 is reduced. As the material of the surface layer 31c, a material in which a resistance adjusting material such as carbon or an ion conductive agent is added to a fluororesin-based resin having a low friction coefficient and exhibiting good toner releasability is preferable.

  When the secondary transfer roller 30 rotates while being in contact with the belt surface 21a of the intermediate transfer belt 21, the secondary transfer roller 30 may have a slight linear velocity difference from the belt surface 21a. In order to prevent the belt from slipping due to the difference in linear speed, the friction coefficient of the surface layer 31c is adjusted to 0.3 or less. The intermediate transfer belt 21 is required to be driven at a constant speed in order to transfer the images of the respective colors in a superimposed manner without color shift. Therefore, it is not possible to reduce the surface friction resistance of the surface layer 31c of the secondary transfer roller 30. is important. The secondary transfer roller 30 having such a configuration is urged by an urging spring toward the intermediate transfer belt 21 wrapped around the secondary transfer opposing roller 24.

  The secondary transfer opposing roller 24 around the intermediate transfer belt 21 includes a roller portion 24b, which is a cylindrical main body portion, and a roller portion 24b that penetrates the rotation center of the roller portion 24b in the rotation axis direction. On its own surface. The penetrating shaft member 24a is made of a metal member, and the roller portion 24b is rotatably supported on the peripheral surface thereof so as to be able to idle. The roller portion 24b as a main body portion includes a drum-shaped hollow core 24c, an elastic layer 24d made of an elastic body fixed on the peripheral surface thereof, and balls pressed into both ends of the hollow core 24c in the axial direction. And a bearing 24e. Thus, the ball bearing 24e rotates on the through shaft member 24a together with the hollow core 24c while supporting the hollow core 24c. The elastic layer 24d is pressed into the outer peripheral surface of the hollow core 24c.

  The through shaft member 24 a is rotatably supported by a first bearing 52 fixed to the first side plate 28 of the transfer unit 20 that stretches the intermediate transfer belt 21 and a second ball bearing 53 fixed to the second side plate 29. Have been. However, most of the time during the print job, the penetrating shaft member 24a is stopped without being driven to rotate. The penetrating shaft member 24a freely rotates the roller portion 24b, which tends to follow the endless movement of the intermediate transfer belt 21, on its own peripheral surface.

  The elastic layer 24d fixed on the peripheral surface of the hollow metal core 24c is made of a conductive rubber material whose resistance value is adjusted by adding an ionic conductive agent so as to exhibit a resistance of 7.5 [Log Ω] or more. Have been. The reason why the electric resistance of the elastic layer 24d is adjusted to a predetermined range is as follows. That is, when a recording medium having a relatively small size in the roller axis direction such as A5 size is used, the belt surface 21a directly contacts the roller surface without the recording medium P in the secondary transfer portion N. This is because the purpose is to prevent the transfer current from being concentrated on the portion where the transfer current exists. By setting the electric resistance of the elastic layer 24d to a value larger than the resistance of the recording medium P, it is possible to suppress such concentration of the transfer current.

  As the conductive rubber material forming the elastic layer 24d, foamed rubber is used so as to exhibit elasticity of about 40 [°] in Asker-C hardness. By forming the elastic layer 24d with such a foamed rubber, the elastic layer 24d is flexibly deformed in the thickness direction in the secondary transfer portion N, and the secondary transfer portion having a certain width in the recording medium conveyance direction. N can be formed.

  In the penetrating shaft member 24a of the secondary transfer opposing roller 24, a pair of cams constituting a part of the contact / separation means is provided at both end regions not located in the roller portion 24b of the entire region in the longitudinal direction. 50, 51 are fixed so as to rotate integrally with the through shaft member 24a. That is, the first cam 50 is fixed to one end region in the longitudinal direction of the through shaft member 24a. In the first cam 50, a cam portion 50a and a true circular roller portion 50b are integrally formed side by side in the axial direction. The first cam 50 is fixed to the penetrating shaft member 24a by screwing a screw 62 penetrating the roller portion 50b to the penetrating shaft member 24a. A second cam 51 having the same configuration as the first cam 50 is fixed to the other end region in the longitudinal direction of the through shaft member 24a. A drive receiving pulley 54 is fixed to a region outside the second cam 51 in the axial direction of the through shaft member 24a. A detected disk 59 is fixed further outside the drive receiving pulley 54.

  On the second side plate 29 of the transfer unit 20, a cam drive motor 58 serving as a cam drive means for rotating the cams 50 and 51 in the normal rotation direction and the reverse rotation direction is fixedly arranged. The cam drive motor 58 rotates a motor pulley 57 provided on its output shaft, and transmits a driving force to a drive receiving pulley 54 fixed to the through shaft member 24a via a timing belt 56. With such a configuration, it is possible to rotate the through shaft member 24a by operating the cam drive motor 58. At this time, even if the penetrating shaft member 24a is rotated, the roller portion 24b can be freely rotated on the penetrating shaft member 24a, so that the rotation of the roller portion 24b by the intermediate transfer belt 21 is prevented. There is no. Further, by using a stepping motor as the cam drive motor 58, the motor rotation angle can be freely set without providing a rotation angle detecting means such as an encoder. Of course, a rotation angle detecting means may be provided to detect the rotation angle of the cam drive motor 58.

  When the penetrating shaft member 24a stops at a predetermined rotation angle, the first cam 50 and the second cam 51 push the cam portions 50a and 51a against the secondary transfer roller 30 to bias the secondary transfer roller 30. Outer peripheral surfaces 50c and 51c are formed so as to be pushed back against the urging force of the spring. In other words, by controlling the rotational positions of the cams 50 and 51 and moving the secondary transfer roller 30 in a direction approaching the secondary transfer opposing roller 24 and, consequently, the intermediate transfer belt 21, the secondary transfer roller 30 The distance L between the shaft and the secondary transfer roller 30 is adjusted. By adjusting the axial distance L between the secondary transfer opposing roller 24 and the secondary transfer roller 30, the gap between the surface 30 a of the secondary transfer roller 30 and the belt surface 21 a of the intermediate transfer belt 21 in the secondary transfer section N is adjusted. X can be adjusted.

  In the present embodiment, the inter-axis distance L between the secondary transfer facing roller 24 and the secondary transfer roller 30 is adjusted by at least the cams 50 and 51 and the cam drive motor 58. That is, the contact / separation mechanism 500 that contacts / separates the surface 30a of the secondary transfer roller 30 and the belt surface 21a of the intermediate transfer belt 21 is configured. The secondary transfer opposing roller 24 as a rotatable support member freely rotates the roller portion 24b on a penetrating shaft member 24a penetrating the cylindrical roller portion 24b. When the penetrating shaft member 24a rotates, the cams 50 and 51 fixed to both ends in the axial direction of the penetrating shaft member 24a rotate integrally. Therefore, the cams 50 and 51 at both ends can be rotated only by providing a drive transmission mechanism for transmitting the drive to the through shaft member 24a at one end in the axial direction.

  In the copying machine 1, while the hollow core 31a of the secondary transfer roller 30 is electrically grounded, a secondary transfer bias having the same polarity as the toner is applied to the hollow core 24c of the secondary transfer opposing roller 24. Apply. Thus, in the secondary transfer portion N, a secondary transfer electric field for electrostatically moving the toner from the secondary transfer opposing roller 24 toward the secondary transfer roller 30 is formed between the two rollers. That is, the first bearing 52 rotatably receiving the metal through shaft member 24a of the secondary transfer opposed roller 24 is formed of a conductive sliding bearing. The conductive first bearing 52 is connected to a high-voltage power supply 61 serving as a transfer unit that outputs a secondary transfer bias. The secondary transfer bias output from the high voltage power supply 61 is supplied to the secondary transfer opposing roller 24 via the conductive first bearing 52. Then, in the secondary transfer opposing roller 24, a metal through shaft member 24a, a metal ball bearing 24e, a metal hollow core 24c, and a conductive elastic layer 24d are sequentially transmitted.

  The detection disk 59 fixed to one end of the through shaft member 24a has a test portion 59a that rises in the axial direction at a predetermined position in the rotation direction of the through shaft member 24a. On the other hand, an optical sensor 60 serving as a detecting unit is fixed to a sensor bracket 501 fixed to the second side plate 29 of the transfer unit 20. During the rotation of the penetrating shaft member 24a, when the penetrating shaft member 24a is positioned within a predetermined rotation angle range, the test portion 59a of the detection disk 59 enters between the light emitting element and the light receiving element of the optical sensor 60. Block the optical path between them. When the light receiving element of the optical sensor 60 receives light from the light emitting element, the light receiving element transmits a light receiving signal to the control unit 600.

  The control unit 600 is constituted by a known computer, and here, in particular, the optical sensor 60 and the cam drive motor 58 are connected. The control unit 600 operates the cam drive motor 58 by calculating the timing when the light receiving signal from the light receiving element of the optical sensor 60 is interrupted and the drive amount of the cam drive motor 58 from that timing. At the same time, based on the calculated drive amount, the rotation angle positions of the cam portions 50a, 51a of the cams 50, 51 fixed to the through shaft member 24a are detected, and the cams 50, 51 are stopped at predetermined positions. It has a function to make it work.

  The cams 50 and 51 abut against the secondary transfer roller 30 at a predetermined rotation angle and push the secondary transfer roller 30 back in a direction away from the secondary transfer opposing roller 24 against the urging force of the urging spring (hereinafter, referred to as the cam 50 or 51). This pushback is referred to as "push down"). The pushing back amount (hereinafter, referred to as “pressing amount”) at this time is determined by the rotational angle positions of the cams 50 and 51. As the amount by which the cams 50 and 51 push down the secondary transfer roller 30 increases, the axial distance L between the secondary transfer opposing roller 24 and the secondary transfer roller 30 increases.

  In the secondary transfer roller 30, a first idler roller 34 is provided on a first shaft member 32 that rotates integrally with the roller portion 31 so as to be idle. The first idling roller 34 has a donut disk shape whose outer diameter is slightly larger than that of the roller portion 31. And, itself has a function as a ball bearing, and can idle on the peripheral surface of the first shaft member 32. A second idler roller 35 having the same configuration as the first idler roller 34 is provided on the second shaft member 33 of the secondary transfer roller 30 so as to idle.

  In the secondary transfer opposing roller 24, the cams 50, 51 fixed to the penetrating shaft member 24a have their outer peripheral surfaces 50c, 51c abutted against the idle rollers 34, 35 at a predetermined rotation angle position. Is formed. Specifically, the cam portion 50a of the first cam 50 fixed to one end of the through shaft member 24a abuts on the first idle roller 34 of the secondary transfer roller 30. At this time, at the same time, the cam portion 51a of the second cam 51 fixed to the other end of the through shaft member 24a strikes the second idle roller 35 of the secondary transfer roller 30. The idle rollers 34 and 35 abutted against the cams 50 and 51 are prevented from rotating with the abutment, however, the rotation of the secondary transfer roller 30 is not hindered. Even if the idle rollers 34, 35 stop rotating, the idle rollers are ball bearings, so that the shaft members 32, 33 of the secondary transfer roller 30 rotate freely independently of the idle rollers 34, 35. Because you can do it. By stopping the rotation of the idle rollers 34 and 35 in accordance with the abutment of the cams by the cam portions 50a and 51a, it is possible to avoid rubbing between the two.

  FIG. 5 is a flowchart showing an example of the operation of the contact / separation mechanism 500 for contacting / separating the secondary transfer roller from / to the intermediate transfer belt 21. First, before the sheet P enters the secondary transfer section N, the secondary transfer roller is separated from the intermediate transfer belt 21 (S1). When the sheet P enters the secondary transfer section N (S2), the secondary transfer roller and the intermediate transfer belt 21 are brought into contact with each other (S3), and the image is transferred from the intermediate transfer belt 21 to the sheet P at the secondary transfer section N. Is transferred (S4). When the transfer of the image to the sheet P is completed (S5), the secondary transfer roller is separated from the intermediate transfer belt 21 before the trailing edge of the sheet passes through the secondary transfer portion N (S6). Thereafter, the trailing edge of the sheet passes through the secondary transfer portion N (S7).

  FIG. 6A shows the state of sheet conveyance when the sheet P is in the secondary transfer section N. FIG. 6B shows the state of sheet conveyance when the sheet P is not in the secondary transfer section N. When the surface linear velocity of the intermediate transfer belt is Vt, the linear velocity of the paper surface is Vs', the linear velocity of the surface of the secondary transfer roller is Vs, the thickness of the paper is t, and the radius of the secondary transfer roller is r, Equation 1 holds.

  Therefore, a linear velocity difference on the surface of the intermediate transfer belt corresponding to the right side of Equation 1 occurs depending on the presence or absence of the sheet P in the secondary transfer portion N. Further, since the relationship of Vs ′> Vs is satisfied and the paper surface linear velocity Vs ′ and the intermediate transfer belt surface linear velocity Vs are different, when the contact / separation operation is performed, depending on the presence or absence of the paper P in the secondary transfer portion N, The speed fluctuation amount generated in the intermediate transfer belt 21 changes.

  FIG. 7A is a graph illustrating a change in the speed of the intermediate transfer belt during the contact / separation operation when the paper P is present in the secondary transfer portion N. FIG. 7B is a graph showing the fluctuation of the intermediate transfer belt speed during the contact / separation operation when the paper P is not present in the secondary transfer portion N. 7A and 7B, the horizontal axis represents time, and the vertical axis represents the intermediate transfer belt speed. 7 (a) and 7 (b), the contact / separation operation in the case where the sheet P is not present in the secondary transfer portion N is compared with the contact / separation operation in the case where the sheet P is present in the secondary transfer portion N. A large speed fluctuation may occur in the intermediate transfer belt 21. Therefore, at the time of the contact / separation operation when the paper P is not present in the secondary transfer portion N, a problem such as deterioration of shock jitter may occur. Therefore, in the copying machine 1 according to the present embodiment, the speed of the contact / separation operation between the intermediate transfer belt 21 and the secondary transfer roller 30 by the contact / separation mechanism 500 is switched according to the presence or absence of the sheet P in the secondary transfer portion N. To improve shock jitter.

  FIG. 8 is a graph showing the rank (good or bad) of the shock jitter when the contact / separation operation speed is changed. As shown in FIG. 8, it can be seen that the shock jitter is improved by reducing the contact / separation operation speed. Therefore, the contact / separation operation speed when the sheet P is not present in the secondary transfer unit N is switched to a low-speed mode in which the contact / separation operation speed is lower than when the sheet P is present in the secondary transfer unit N. Thereby, the speed fluctuation of the intermediate transfer belt 21 that may be caused by the contact / separation operation when the sheet P is not present in the secondary transfer portion N is reduced, and the shock jitter can be improved.

  FIG. 1 is a timing chart showing the timing of the contact / separation operation between the intermediate transfer belt 21 and the secondary transfer roller 30 by the contact / separation mechanism 500. In the copying machine 1 according to the present embodiment, before the start of the printing operation, the intermediate transfer belt 21 and the secondary transfer roller 30 are separated from each other. When the printing operation is started, the intermediate transfer belt 21 and the secondary transfer roller 30 are brought into contact by the contact / separation mechanism 500 in a state where the sheet P is not present in the secondary transfer portion N. The contact operation at this time is a contact operation when there is no paper P in the secondary transfer portion N ((1) in the figure). Then, a cleaning voltage is applied to the secondary transfer opposing roller 24 so that an electric field is formed such that toner adhered to the surface of the secondary transfer roller 30 moves on the surface of the intermediate transfer belt 21 by electrostatic force. By applying the voltage, the surface of the secondary transfer roller 30 is cleaned. Accordingly, it is possible to prevent the paper P that has passed through the secondary transfer unit N from being stained by the toner attached to the surface of the secondary transfer roller 30. In particular, in a configuration in which the surface of the secondary transfer roller 30 is cleaned using a cleaning member such as the cleaning blade 39 as in the copying machine 1 according to the present embodiment, the cleaning property of the surface of the secondary transfer roller 30 is further improved. be able to. Further, even in a configuration that does not include a cleaning unit that cleans the surface of the secondary transfer roller 30 with a cleaning member such as a cleaning blade, the surface of the secondary transfer roller 30 can be cleaned. It is a target.

  Here, the rotational positions of the cams 50 and 51 of the contact / separation mechanism 500 in the separated state between the intermediate transfer belt 21 and the secondary transfer roller 30 before the start of the printing operation are used as the reference of the preset rotational position. There is a possibility that it is out of position. If the rotational positions of the cams 50 and 51 in the separated state are deviated from the home position, the rotation of the cams 50 and 51 cannot be accurately controlled. Therefore, once the printing operation is started and before the first sheet P reaches the secondary transfer portion N, the intermediate transfer belt 21 and the secondary transfer roller 30 are once brought into contact with each other, and the cams 50 and 51 are moved. Recognize the rotational position of. Then, an operation of rotating the cams 50 and 51 by a predetermined amount so that the cams 50 and 51 are moved to the home position from the contact state is performed. Thereby, rotation control of the cams 50 and 51 can be performed with high accuracy.

  After the intermediate transfer belt 21 and the secondary transfer roller 30 are brought into contact with each other and the secondary transfer roller 30 is rotated at least once after the cleaning voltage is applied, the first sheet P reaches the secondary transfer portion N. Before the transfer, the intermediate transfer belt 21 and the secondary transfer roller 30 are separated from each other. As a result, a gap is formed between the intermediate transfer belt 21 and the secondary transfer roller 30, and it is possible to reduce shock jitter when the sheet enters the secondary transfer portion N. The separating operation at this time is a separating operation when there is no sheet P in the secondary transfer portion N ((2) in the figure). After the leading edge of the sheet P enters the secondary transfer section N, the intermediate transfer belt 21 and the secondary transfer roller 30 are brought into contact with each other via the sheet P. As a result, a sufficient transfer pressure can be exerted in the secondary transfer portion N, and occurrence of transfer failure can be suppressed. The contact operation at this time is a contact operation when the sheet P is present in the secondary transfer portion N ((3) in the figure). The intermediate transfer belt 21 and the secondary transfer roller 30 are separated by the separating operation of the contact / separation mechanism 500 before the trailing edge of the previous sheet P passes through the secondary transfer portion N. Accordingly, it is possible to reduce the shock jitter when the rear end of the sheet P comes out of the secondary transfer portion N. The separating operation at this time is a separating operation when the sheet P is present in the secondary transfer portion N ((4) in the figure). The above-described contact / separation operation is repeatedly performed on the subsequent sheets P.

  In the present embodiment, as can be seen from FIG. 1, the separating operation speed when the sheet P is not present in the secondary transfer unit N is lower than the separating operation speed when the sheet P is present in the secondary transfer unit N. are doing. As a result, it is possible to improve the shock jitter caused by the speed fluctuation of the intermediate transfer belt 21 which may be caused by the separating operation between the intermediate transfer belt 21 and the secondary transfer roller 30.

  In the present embodiment, the contact operation speed when the paper P is not present in the secondary transfer unit N is higher than the separation operation speed when the paper P is not present in the secondary transfer unit N. This makes it possible to increase the speed of the first sheet when the contact operation speed when the sheet P is not present in the secondary transfer unit N is equal to or lower than the separation operation speed when the sheet P is not present in the secondary transfer unit N. , The time until the start of printing on the paper P can be shortened, and the productivity of printed matter can be increased.

  The separation operation speed and the contact operation speed when the paper P is not present in the secondary transfer portion N can be determined by using the detection result of the speed detection means of the intermediate transfer belt 21 or the drive roller 14. For example, an experiment or the like is performed in advance, and the speed detection unit detects and records a change in the speed of the intermediate transfer belt due to the separating operation or the contact operation when the sheet P is present in the secondary transfer unit N. Next, the separating operation speed or the contact operation speed when the sheet P is not present in the secondary transfer portion N is reduced until the absolute value of the intermediate transfer belt speed variation becomes equal to or less than the maximum value. Then, the separation operation speed or the contact operation speed when the separation operation speed or the contact operation speed is reduced to the maximum value or less is determined as the separation operation speed or the contact operation speed when the sheet P is not present in the secondary transfer unit N.

  FIG. 9 is an enlarged cross-sectional view illustrating a configuration around the secondary transfer unit N of the transfer unit 20 when the paper detection sensor 90 is installed upstream of the secondary transfer unit N in the paper transport direction. In FIG. 1, the presence or absence of a sheet in the secondary transfer unit N is determined for the first image and thereafter, but as shown in FIG. It is also possible to determine the presence or absence of a sheet in the secondary transfer unit N by using a sheet detection sensor 90 installed at a position separated by L.

  First, the timer 91 provided in the copying machine 1 starts a timer count together with the start of the printing operation, and the time after the start is t. Further, after the timer count is started, the i-th sheet P reaches the detection position of the sheet detection sensor 90 provided at a position separated by the distance L on the upstream side in the sheet conveyance direction with respect to the secondary transfer portion N. Let ti be the time at which it was performed. The paper size can be acquired at the time of printing, for example, by inputting the paper P to be used by a user from an operation panel provided in the copying machine 1. The paper length in the paper transport direction is set to Lp, and the transport of the paper P is performed. Let V be the linear velocity. Then, when the time t satisfies the relationship of the following expression 2, it is determined that “paper is present”, and when the time t does not satisfy the relationship of the following expression 2, it is determined that there is no paper.

  FIG. 10 is an enlarged cross-sectional view showing the configuration around the secondary transfer portion N of the transfer unit 20 when the torque detection sensors 93 and 94 for detecting the torque of the secondary transfer drive motor 38 and the intermediate transfer drive motor 92 are provided. It is. The torque of the secondary transfer drive motor 38 for driving the secondary transfer roller 30 and the torque of the intermediate transfer drive motor 92 for driving the drive roller 14 for rotating the intermediate transfer belt 21 depend on the presence or absence of the sheet P in the secondary transfer portion N. fluctuate. Therefore, the torque of at least one of the secondary transfer drive motor 38 and the intermediate transfer drive motor 92 is detected by the torque detection sensors 93 and 94, and the paper P in the secondary transfer portion N is detected based on the detected torque information. It is also possible to detect the presence or absence. As the torque detection sensors 93 and 94, for example, those that detect the drive torque from the drive current of the secondary transfer drive motor 38 and the intermediate transfer drive motor 92 can be used.

  In the above-described embodiment, an image forming apparatus of an intermediate transfer system has been described. For example, a toner image formed on a photosensitive belt is transferred to a transfer unit formed by the photosensitive belt and a transfer roller. The present invention is also applicable to an image forming apparatus of a direct transfer type for transferring the image on P.

What has been described above is merely an example, and each embodiment has a specific effect.
(Aspect A)
A secondary transfer roller that forms a transfer unit such as a secondary transfer unit N that sandwiches a recording medium such as paper P between an image carrier such as the intermediate transfer belt 21 and transfers an image from the image carrier to the recording medium. In a transfer apparatus such as a transfer unit 20 including a transfer member such as 30 and a contacting / separating unit such as a contact / separation mechanism 500 for bringing the image carrier and the transfer member into and out of contact, the image carrier and the transfer member Control for controlling the contact / separation means such that at least one of a separation operation speed between the transfer unit and the image bearing member and the transfer member is different depending on the presence or absence of a recording medium in the transfer unit. It has control means such as a driver 4.
For example, when the surface speed of the image carrier at the transfer unit is set to be substantially the same as the surface speed of the recording medium nipped and transported by the image carrier and the transfer member at the transfer unit. think of.
When the transfer unit has a recording medium, the surface speed of the image carrier and the surface speed of the recording medium in a state where the image carrier and the transfer member are in contact with each other via the recording medium are substantially the same. The rotation load is hardly applied to the image carrier. For this reason, even when the separating operation between the image carrier and the transfer member is performed abruptly when the recording medium is in the transfer section, a large speed fluctuation does not occur in the image carrier.
On the other hand, when there is no recording medium in the transfer section, in the contact state between the image carrier and the transfer member, the surface speed of the transfer member becomes slower than the surface velocity of the image carrier by the thickness of the recording medium, and the speed difference is increased. The resulting rotational load is applied to the image carrier. Therefore, if the separating operation between the image carrier and the transfer member is performed abruptly when there is no recording medium in the transfer section, the rotational load is suddenly lost, and a large speed fluctuation occurs in the image carrier. Therefore, control means controls the contact / separation means so as to slow down the separation operation speed when there is no recording medium in the transfer unit as compared to when the recording medium is present in the transfer unit. In accordance with the presence or absence of a recording medium. Accordingly, when there is no recording medium in the transfer unit, the separation operation between the image carrier and the transfer member can be performed while gradually reducing the rotational load, and accordingly, a large speed fluctuation occurs in the image carrier. This can be suppressed.
Further, control means controls the contact / separation means so that the contact operation speed when the recording medium is not present in the transfer unit is slower than when the recording medium is present in the transfer unit, and the contact operation speed is controlled by the transfer unit. In accordance with the presence or absence of a recording medium. This prevents the rotational load from being suddenly applied to the image carrier by the contact operation between the image carrier and the transfer member when there is no recording medium in the transfer section, and causes a large speed fluctuation in the image carrier. Can be suppressed.
Therefore, in (Aspect A), it is possible to reduce the shock jitter caused by the fluctuation in the speed of the image carrier, which may be caused by the contact / separation operation between the image carrier and the transfer member.
(Aspect B)
In (Aspect A), the control unit controls the contact / separation mechanism so that a separation operation speed when the transfer unit has no recording medium is lower than a separation operation speed when the transfer unit has a recording medium. Control. According to this, as described in the above-described embodiment, the speed fluctuation of the image carrier that can be caused by the separating operation when there is no recording medium in the transfer unit is reduced, and the shock jitter can be improved.
(Aspect C)
In (Aspect A) or (Aspect B), the contact / separation means operates at timings before and after the leading end of the recording medium or the trailing end of the recording medium respectively pass through the transfer section. According to this, as described in the above embodiment, it is possible to reduce the shock jitter that may occur when the leading end or the trailing end of the recording medium passes through the transfer unit.
(Aspect D)
In any one of (Aspect A) to (Aspect C), the image forming apparatus further includes a speed fluctuation detecting unit configured to detect information on a speed fluctuation of the image carrier, and performs a contact / separation operation when there is no recording medium in the transfer unit. The contact / separation operation is performed based on the detection result of the speed variation detection unit so that the speed variation of the image carrier is equal to or less than the speed variation of the image carrier due to the contact / separation operation when the recording medium is present in the transfer unit. Adjust speed. According to this, as described in the above embodiment, the shock jitter can be improved.
(Aspect E)
In any one of (Aspect A) to (Aspect D), a recording medium presence / absence detection unit such as a paper detection sensor 90 for detecting the presence / absence of a recording medium in the transfer unit is provided. According to this, as described in the above embodiment, it is possible to determine the presence or absence of the recording medium in the transfer unit.
(Aspect F)
In any one of (Aspect A) to (Aspect D), an image carrier driving means such as an intermediate transfer drive motor for driving the image carrier to rotate, and a secondary transfer drive motor 38 for rotating the transfer member. A transfer member driving unit, and a torque detecting unit that detects a driving torque of at least one of the image carrier driving unit and the transfer member driving unit, and based on a detection result of the torque detecting unit, The presence or absence of a recording medium at the transfer unit is determined. According to this, as described in the above embodiment, it is possible to determine the presence or absence of the recording medium in the transfer unit.
(Aspect G)
An image forming apparatus such as a copying machine 1 having a transfer unit for transferring a toner image carried on the surface of the image carrier to a recording medium sandwiched between transfer portions by contact between the image carrier and the transfer member In the above, the transfer device according to any one of (Aspect A) to (Aspect F) was used as the transfer unit. According to this, as described in the above embodiment, it is possible to reduce the shock jitter due to the speed fluctuation of the image carrier that can be caused by the contact / separation operation between the image carrier and the transfer member, and perform good image formation. Can be.

REFERENCE SIGNS LIST 1 copier 4 control driver 10 tandem image forming unit 11 image forming unit 12 photosensitive drum 13 primary transfer roller 14 drive roller 15 driven roller 17 cleaning device 18 exposure device 20 transfer unit 21 intermediate transfer belt 21a belt surface 22 transport belt 23 Stretch roller 24 Secondary transfer facing roller 24a Penetrating shaft member 24b Roller part 24c Hollow core 24d Elastic layer 24e Ball bearing 25 Fixing device 26 Fixing belt 27 Pressure roller 28 First side plate 29 Second side plate 30 Secondary transfer roller 30a Front surface 31 Roller portion 31a Hollow core metal 31b Elastic layer 31c Surface layer 32 First shaft member 33 Second shaft member 34 First idle roller 35 Second idle roller 38 Secondary transfer drive motor 39 Cleaning blade 40 Roller unit holder 42 Supply Paper roller 43 Paper bank 44 Paper feed cassette 45 Separation roller 46 Paper feed path 47 Transport roller 48 Paper feed path 49 Registration roller 50 First cam 50a Cam portion 50b Roller portion 50c Outer surface 51 Second cam 51a Cam portion 51b Roller portion 51c Outer surface 52 First bearing 53 Second ball bearing 54 Drive receiving pulley 56 Timing belt 57 Motor pulley 58 Cam drive motor 59 Detected disk 59a Tested part 60 Optical sensor 61 High voltage power supply 62 Screw 70 Feed roller 71 Manual feed tray 72 Separation roller 73 Manual feed Paper feed path 74 Switching claw 75 Discharge roller 76 Discharge tray 80 Paper reversing device 90 Paper detection sensor 91 Timer 92 Intermediate transfer drive motor 93 Torque detection sensor 94 Torque detection sensor 100 Copier body 200 Feed table 300 Scanner 3 01 contact glass 302 first traveling body 303 second traveling body 304 imaging lens 305 reading sensor 400 automatic document feeder 401 original table 500 contact / separation mechanism 501 sensor bracket 600 control unit

JP 2014-178660 A

Claims (6)

A rotatable transfer member that sandwiches a recording medium between the rotatable image carrier and forms a transfer unit that transfers an image from the image carrier to the recording medium;
A transfer device comprising: a contact / separation unit configured to contact / separate the image carrier and the transfer member;
Contact at contact and separation operation speed of the transfer member and the image bearing member, said varies depending on the presence or absence of the recording medium in the transfer portion, and away from the operating speed when no recording medium is found that the recording medium is present A transfer device comprising a control means for controlling the contact / separation means so as to be slower than a separation operation speed . The transfer device according to 請 Motomeko 1,
The transfer device, wherein the contacting / separating means operates at timings before and after a leading end of the recording medium or a trailing end of the recording medium respectively pass through the transfer section. The transfer device according to claim 1 , wherein
It has a speed fluctuation detecting means for detecting information on the speed fluctuation of the image carrier,
The speed variation of the image carrier due to the contact / separation operation when there is no recording medium in the transfer unit is equal to or less than the speed variation of the image carrier due to the contact / separation operation when the recording unit is present in the transfer unit, A transfer device for adjusting a contact / separation operation speed based on a detection result of the speed fluctuation detection unit. The transfer device according to any one of claims 1 to 3 ,
A transfer device comprising a recording medium presence / absence detecting means for detecting the presence / absence of a recording medium in the transfer unit. The transfer device according to any one of claims 1 to 3 ,
Image carrier driving means for rotationally driving the image carrier,
Transfer member driving means for rotating the transfer member,
A torque detecting unit that detects a driving torque of at least one of the image carrier driving unit and the transfer member driving unit;
A transfer device, wherein the presence or absence of a recording medium in the transfer unit is determined based on a detection result of the torque detection unit. An image forming apparatus comprising: a transfer unit that transfers a toner image carried on a surface of an image carrier to a recording medium sandwiched by a transfer unit formed by contact between an image carrier and a transfer member;
As the transferring unit, the image forming apparatus characterized by using a transfer apparatus according to any one of claims 1 to 5.

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