JP2017076079A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer device that can reduce shock jitter caused by a variation in speed of an image carrier occurring due to a contact/separation operation between the image carrier and a transfer member, and an image forming apparatus including the transfer device.SOLUTION: There is provided a transfer device 20 comprising: a transfer member 30 that sandwiches a recording medium P with a rotatable image carrier 21 to transfer an image from the image carrier to the recording medium; and contact/separation means 500 that brings the transfer member 30 into contact with the image carrier 21 or separates the transfer member 30 from the image carrier 21, the transfer device 20 including control means 4 that controls the contact/separation means so that at least one of the speed of an operation to separate the transfer member from the image carrier and the speed of an operation to bring the transfer member into contact with the image carrier is made different according to the presence or absence of a recording medium at the transfer part.SELECTED DRAWING: Figure 1

Description

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

  2. Description of the Related Art Conventionally, a transfer device for an image forming apparatus is known in which a recording medium is sandwiched in a transfer nip formed by an image carrier and a nip forming member, and a toner image is transferred from the image carrier.

  The image forming apparatus described in Patent Document 1 is provided with a secondary transfer device that is a transfer device that transfers a toner image that is primarily transferred from a photosensitive member to an intermediate transfer belt to a sheet that is a recording medium. ing. The secondary transfer device includes a secondary transfer roller that contacts the front surface of the intermediate transfer belt, and a secondary transfer counter roller that faces the secondary transfer roller and contacts the back surface of the intermediate transfer belt. The secondary transfer device includes a contact / separation mechanism for contacting and separating the intermediate transfer belt and the secondary transfer roller. In the secondary transfer device, the intermediate transfer belt and the secondary transfer roller come into contact with each other, and the intermediate transfer belt and the secondary transfer roller come into contact with the intermediate transfer belt before the leading edge of the paper enters the secondary transfer portion from the state where there is no paper in the secondary transfer portion. The next transfer roller is separated. As a result, a gap is formed between the intermediate transfer belt and the secondary transfer roller to reduce shock jitter when the leading edge of the paper enters the secondary transfer portion. When the leading edge of the paper enters the gap and the paper is in the secondary transfer section, the intermediate transfer belt and the secondary transfer roller are brought into contact with each other through the paper, so that the secondary transfer section has a sufficient transfer pressure. To suppress the occurrence of transfer defects. Also, when the trailing edge of the sheet comes out of the secondary transfer unit, the intermediate transfer belt and the secondary transfer roller are separated by the contact / separation mechanism with the sheet in the secondary transfer unit, and the secondary transfer unit is moved to the sheet. Reduces shock jitter when the rear end comes off.

  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 paper in the secondary transfer unit. For this reason, there is a problem that shock jitter due to the speed fluctuation may occur due to a larger speed fluctuation in the intermediate transfer belt than in the case where the sheet is present in the secondary transfer portion or not. Arise.

  In order to solve the above problems, the present invention provides a rotatable transfer member that sandwiches a recording medium with a rotatable image carrier and forms a transfer portion for transferring an image from the image carrier to the recording medium. In the transfer apparatus comprising a contact / separation means for contacting and separating the image carrier and the transfer member, the separation operation speed between the image carrier and the transfer member, and the image carrier and the transfer member It has a control means for controlling the contact / separation means so that at least one of the contact operation speeds differs depending on the presence or absence of a recording medium in the transfer section.

  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 fluctuation of the image carrier that can be caused by the contact / separation operation between the image carrier and the transfer member.

Timing chart of contact / separation operation. 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 an image forming apparatus. FIG. 3 is an enlarged cross-sectional view showing a configuration around a secondary transfer portion of a transfer unit. 6 is a flowchart showing an example of the contact / separation operation of the secondary transfer roller with respect to the intermediate transfer belt by the contact / separation mechanism. (A) The figure which showed the mode of paper conveyance when a paper exists in a secondary transfer part, (b) The figure which showed the mode of paper conveyance when a paper does not exist in a secondary transfer part. (A) A graph showing the intermediate transfer belt speed fluctuation at the time of contact / separation operation when paper is present in the secondary transfer unit, (b) Intermediate transfer belt speed at the time of contact / separation operation when no paper is present in the secondary transfer unit Graph showing fluctuations. A graph showing the shock jitter rank (good or bad) when the contact / separation speed is changed. FIG. 4 is an enlarged cross-sectional view illustrating a peripheral configuration of a secondary transfer unit of a transfer unit when a sheet detection sensor is installed on the upstream side in the sheet conveyance direction with respect to the secondary transfer unit. FIG. 3 is an enlarged cross-sectional view illustrating a peripheral configuration of a secondary transfer unit of a transfer unit when a torque detection sensor that detects torque of a secondary transfer drive motor and 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 the copying machine 1 which is the 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 placed, a scanner 300 mounted on the copier main body 100, and an automatic document transport mounted on the scanner 300. The apparatus (ADF) 400 is mainly configured.

  The scanner 300 is placed on the contact glass 301 as the first traveling body 302 equipped with a document illumination light source or mirror and the second traveling body 303 equipped with a plurality of reflecting mirrors reciprocate. The scanned original is scanned. The scanning light sent out from the second traveling body 303 is condensed on the imaging surface of the reading sensor 305 installed behind the imaging lens 304 and then read as an image signal by the reading sensor 305.

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

  An exposure device 18 is provided above the tandem image forming unit 10 to expose the photosensitive drum 12 with laser light or LED light based on image information to form a latent image. In addition, an image carrier which is made of an endless belt member and which carries a toner image which is sequentially primary-transferred from each photosensitive drum 12 at a lower position facing each photosensitive drum 12 of the tandem type image forming unit 10. An intermediate transfer belt 21 as an intermediate transfer member is disposed. The intermediate transfer belt 21 is supported by the driving roller 14, the driven roller 15, and the secondary transfer counter roller 24, and is conveyed clockwise in the drawing at the time of image formation. Further, on the extended surface of the intermediate transfer belt 21 stretched between the driving roller 14 and the driven roller 15, an image forming unit is arranged in the order of yellow, cyan, magenta, and black from the upstream side along the moving direction. 11Y, 11C, 11M, and 11K are arranged side by side. At adjacent positions facing the respective photosensitive drums 12 via the intermediate transfer belt 21, transfer rollers constituting transfer means for transferring the toner images of the respective colors formed on the respective photosensitive drums 12 onto the intermediate transfer belt 21. The primary transfer roller 13 is disposed. The intermediate transfer belt 21 is provided with a cleaning device 17 for removing the toner remaining on the surface thereof on the downstream side in the moving direction of the intermediate transfer belt 21 supported by the secondary transfer counter roller 24.

  On the opposite side of the tandem image forming unit 10 with the intermediate transfer belt 21 interposed therebetween, a transfer device that is a transfer device that collectively transfers toner images formed 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 counter roller 24, a secondary transfer roller 30 that is a transfer roller that contacts the secondary transfer counter roller 24 via the intermediate transfer belt 21, and a secondary transfer roller 30, which will be described in detail later. The moving unit moves the intermediate transfer belt 21. With this moving means, the secondary transfer roller 30 can be moved toward and away from the intermediate transfer belt 21. In the transfer unit 20, the transfer is formed on the sheet P conveyed from the sheet feeding cassette 44 of the sheet feeding table 200 so that the secondary transfer roller 30 is brought into contact with the intermediate transfer belt 21 by a moving unit. It is clamped at the secondary transfer nip portion which is a nip portion. In this way, a secondary transfer pressure is applied to the paper P sandwiched at the secondary transfer nip portion, and a secondary transfer bias is applied to transfer the toner image carried on the intermediate transfer belt 21 onto the paper P. .

  In a position adjacent to the downstream side of the secondary transfer roller 30 in the paper transport direction, the secondary transfer roller 30 includes two tension rollers 23 and a conveyor belt 22 stretched between them to convey the secondary-transferred paper P. A belt conveying device is provided. A fixing device 25 is provided at a position adjacent to the conveyance belt 22 on the downstream side in the sheet conveyance direction. The fixing device 25 fixes the toner image on the paper P conveyed by the conveyance belt 22. The fixing device 25 mainly includes a fixing belt 26 that is an endless belt and a pressure roller 27 that is pressed against the fixing belt 26. Also, below the transfer unit 20 and the fixing device 25, a paper reversing device 80 for reversing the paper P so as to record images on both sides of the paper P is disposed in parallel with the tandem image forming unit 10 described above. .

  Next, an operation when color copying is performed by the copying machine 1 having the above configuration will be described. First, a document is set on the document table 401 of the automatic document feeder 400 shown in FIG. 2, or the automatic document feeder 400 is opened and a document is set on the contact glass 301 of the scanner 300. Close and hold down the document. When the start switch is pressed in this state, when a document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 301, and on the other hand, when the document is set on the contact glass 301 The scanner 300 is immediately driven. The first traveling body 302 and the second traveling body 303 travel, and the first traveling body 302 emits light from the light source and receives reflected light from the document surface, and reflects this 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 is incident on the reading sensor 305 through the imaging lens 304 and the reading sensor 305 reads the document content.

  Further, by pressing a start switch provided in the copying machine 1, the drive roller 14 among the drive roller 14, the driven roller 15, and the secondary transfer counter roller 24 that rotatably supports the intermediate transfer belt 21 is driven to rotate. To do. As a result, the intermediate transfer belt 21 rotates, and the driven roller 15 and the secondary transfer counter 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, on the photosensitive drums 12 that are charged by irradiating the writing light L from the exposure device 18 with a laser, an LED, or the like based on the reading contents of the scanner 300, the colors corresponding to yellow, cyan, magenta, and black, respectively. An electrostatic latent image is formed. 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 each of the photosensitive drums 12 corresponds to yellow, cyan, magenta, and black. A single color toner image is formed.

  The single color toner images are sequentially primary transferred so as to be superimposed on the intermediate transfer belt 21 by the primary transfer bias applied from the primary transfer rollers 13, and the combined color toner images on the intermediate transfer belt 21 are obtained. It is formed. Residual toner is removed from the surface of each photoconductive drum 12 after the primary transfer by the photoconductor cleaning device, and the charge is removed by the static eliminator to prepare for image formation again.

  Also, by pressing the start switch, 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 multiple stages in the paper bank 43 and separated. The paper is separated one by one by the rollers 45 and introduced into the paper feed path 46. The paper P introduced into the paper feed path 46 is transported by the transport roller 47, guided to the paper feed path 48 in the copying machine main body 100, and abutted against the registration roller 49 and stopped. On the other hand, when manually feeding the paper P, the manual paper feed roller 70 is rotated to feed the paper P on the manual tray 71, separated one by one by the manual separation roller 72, and introduced into the manual paper feed path 73. It stops 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 sheet P is fed between the intermediate transfer belt 21 and the secondary transfer roller 30. And a color toner image is transferred onto the paper P.

  The sheet P carrying the unfixed toner image that has passed through the 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 conveying belt 22. It is conveyed to the fixing device 25 by the belt conveying device. 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 has been fixed is switched by the switching claw 74 and is discharged by the discharge roller 75 and stacked on the discharge tray 76. On the other hand, in the case of duplex copying, the sheet P on which an image is formed on one side is switched to the conveyance destination by the switching claw 74 and is introduced into the sheet reversing device 80 where it is reversed and guided to the transfer position again. An image is also formed on the sheet, and is then discharged onto the discharge tray 76 by the 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 to prepare for another image formation by the tandem type image forming unit 10.

  FIG. 3 is a diagram showing an example of the layout of the transfer unit 20 provided in the copying machine 1. A cam drive motor 58, which is a stepping motor that drives 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. As the cam rotates, the cam radius changes and the secondary transfer roller 30 is moved 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 movement of the secondary transfer roller 30 in the upward direction of the arrow (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 showing 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 a width direction orthogonal to the sheet conveyance 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 rotational axis direction. The shaft member 33 includes a first idling roller 34 and a second idling roller 35 described later. The roller portion 31 includes a cylindrical hollow core 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 core 31a include stainless steel and aluminum, but are not limited to these materials. The elastic layer 31b is preferably 70 [°] or less in terms of JIS-A hardness. 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 a rubber material exhibiting conductivity, EPDM or Si rubber in which carbon is dispersed, NBR having an ionic conductivity function, urethane rubber, or the like may be used instead of the above-described conductive epichlorohydrin rubber. Since many rubber materials exhibit good chemical affinity for the toner or exhibit a relatively large coefficient of friction, the surface of the elastic layer 31b made of a rubber material is covered with the surface layer 31c. ing. As a result, toner adhesion to the surface of the roller portion 31 is suppressed, and the rubbing load with the cleaning blade 39 is reduced. As a material for the surface layer 31c, a material in which a resistance adjusting material such as carbon or an ionic conductive agent is contained in a fluororesin resin that exhibits a low coefficient of friction and good toner releasability is suitable.

  When the secondary transfer roller 30 rotates 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. The friction coefficient of the surface layer 31c is adjusted to 0.3 or less so that the belt does not slip due to this linear speed difference. The intermediate transfer belt 21 is required to be driven at a constant speed in order to transfer the images of each color in a superimposed manner without color misregistration. Therefore, the surface friction resistance of the surface layer 31c of the secondary transfer roller 30 can be reduced. is important. The secondary transfer roller 30 having such a configuration is urged by an urging spring toward the intermediate transfer belt 21 wound around the secondary transfer counter roller 24.

  The secondary transfer counter roller 24 that is wound around the intermediate transfer belt 21 passes through the roller portion 24b, which is a cylindrical main body portion, and the rotation center portion of the roller portion 24b in the rotation axis direction, while passing through the roller portion 24b. And a through shaft member 24a that idles on its surface. The penetrating shaft member 24a is made of a metal member, and the roller portion 24b is rotatably supported on its peripheral surface so as to be idled. The roller portion 24b as the main body includes a drum-shaped hollow cored bar 24c, an elastic layer 24d made of an elastic body fixed on the peripheral surface thereof, and balls press-fitted to both ends in the axial direction of the hollow cored bar 24c. And a bearing 24e. For this reason, the ball bearing 24e rotates on the through shaft member 24a together with the hollow core metal 24c while supporting the hollow core metal 24c. The elastic layer 24d is press-fitted into the outer peripheral surface of the hollow cored bar 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. Has been. However, most of the time during the print job, the through shaft member 24a is stopped without being driven to rotate. The penetrating shaft member 24a freely idles the roller portion 24b to be rotated along with the endless movement of the intermediate transfer belt 21 on its peripheral surface.

  The elastic layer 24d fixed on the peripheral surface of the hollow core metal 24c is composed 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 [LogΩ] or more. Has 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 axial direction such as A5 size is used, the belt surface 21a and the roller surface are in direct contact with each other without the recording medium P in the secondary transfer portion N. This is because the aim is to prevent the transfer current from being concentrated on the existing location. By making the electric resistance of the elastic layer 24d larger than the resistance of the recording medium P, it becomes possible to suppress such concentration of transfer current.

  As the conductive rubber material constituting 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 foamed rubber, the elastic layer 24d is flexibly deformed in the thickness direction in the secondary transfer portion N, and the secondary transfer portion has a certain extent 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 contacting / separating means is provided in both end regions that are not located in the roller portion 24b in the entire region in the longitudinal direction. 50 and 51 are fixed so as to rotate together with the penetrating 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 into the penetrating shaft member 24a. A second cam 51 having the same configuration as that of 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 penetrating shaft member 24a. A detected disk 59 is fixed on the further outside of 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 driving the cams 50 and 51 to rotate in the forward direction and the reverse direction is fixed. 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 penetrating shaft member 24a via a timing belt 56. With such a configuration, the penetrating shaft member 24a can be rotated by operating the cam drive motor 58. At this time, even if the through-shaft member 24a is rotated, the roller portion 24b can be freely idled on the through-shaft member 24a, thereby inhibiting the intermediate transfer belt 21 from rotating the roller portion 24b. There is no. In addition, by using a stepping motor as the cam drive motor 58, the motor rotation angle can be freely set without providing a rotation angle detection means such as an encoder. Of course, a rotation angle detection means may be provided to detect the rotation angle of the cam drive motor 58.

  The first cam 50 and the second cam 51 urge the secondary transfer roller 30 by abutting the cam portions 50a and 51a against the secondary transfer roller 30 when the penetrating shaft member 24a stops at a predetermined rotation angle. The outer peripheral surfaces 50c and 51c are formed so as to push back against the urging force of the spring. That is, by controlling the rotational positions of the cams 50 and 51, the secondary transfer roller 30 is moved in the direction closer to the secondary transfer counter roller 24 and thus the intermediate transfer belt 21. The distance L between the axes with the secondary transfer roller 30 is adjusted. A gap between the surface 30a of the secondary transfer roller 30 and the belt surface 21a of the intermediate transfer belt 21 in the secondary transfer portion N is adjusted by adjusting the inter-axis distance L between the secondary transfer counter roller 24 and the secondary transfer roller 30. X can be adjusted.

  In the present embodiment, the inter-axis distance L between the secondary transfer counter 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, a contact / separation mechanism 500 that contacts and 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 counter roller 24 as a rotatable support member freely idles the roller portion 24b on the penetrating shaft member 24a penetrated through 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 together. Therefore, the cams 50 and 51 on both ends can be rotated by merely providing a drive transmission mechanism for transmitting drive to the penetrating shaft member 24a on one end in the axial direction.

  In the copying machine 1, while the hollow cored bar 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 cored bar 24c of the secondary transfer counter roller 24. Apply. Thereby, in the secondary transfer portion N, a secondary transfer electric field for electrostatically moving the toner from the secondary transfer counter roller 24 side to the secondary transfer roller 30 side is formed between both rollers. That is, the first bearing 52 that rotatably receives the metal penetrating shaft member 24a of the secondary transfer counter roller 24 is composed of a conductive slide bearing. The conductive first bearing 52 is connected to a high voltage power supply 61 serving as transfer means for outputting a secondary transfer bias. The secondary transfer bias output from the high-voltage power supply 61 is supplied to the secondary transfer counter roller 24 via the conductive first bearing 52. In the secondary transfer counter roller 24, a metal penetrating shaft member 24a, a metal ball bearing 24e, a metal hollow cored bar 24c, and a conductive elastic layer 24d are sequentially transmitted.

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

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

  The cams 50 and 51 abut against the secondary transfer roller 30 at a predetermined rotation angle, and push back the secondary transfer roller 30 in a direction away from the secondary transfer counter roller 24 against the urging force of the urging spring (hereinafter, referred to as “the second transfer roller 30”). This pushback is referred to as “push down”). The amount of pushing back at this time (hereinafter referred to as “the amount of pushing down”) is determined by the rotational angle position of the cams 50 and 51. The greater the amount by which the secondary transfer roller 30 is pushed down by the cams 50 and 51, the greater the inter-axis distance L between the secondary transfer opposing roller 24 and the secondary transfer roller 30.

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

  In the secondary transfer counter roller 24, the cams 50 and 51 fixed to the penetrating shaft member 24a have outer peripheral surfaces 50c and 51c of the cam portions 50a and 51a so as to abut against the idle rollers 34 and 35 at a predetermined rotational angle position. Is formed. Specifically, the cam portion 50 a of the first cam 50 fixed to one end side of the penetrating shaft member 24 a hits the first idling roller 34 of the secondary transfer roller 30. At the same time, the cam portion 51 a of the second cam 51 fixed to the other end side of the penetrating shaft member 24 a hits the second idling roller 35 of the secondary transfer roller 30. The idling rollers 34 and 35 abutted against the cams 50 and 51 are prevented from rotating along with the abutment, but the rotation of the secondary transfer roller 30 is not prevented thereby. Even if the idling rollers 34 and 35 stop rotating, the idling rollers are ball bearings, so that the shaft members 32 and 33 of the secondary transfer roller 30 freely rotate independently of the idling rollers 34 and 35. Because it can. By stopping the rotation of the idling rollers 34 and 35 in accordance with the abutment by the cam portions 50a and 51a of the cam, it is possible to avoid the occurrence of friction between them.

  FIG. 5 is a flowchart showing an example of the contact / separation operation of the secondary transfer roller with respect to the intermediate transfer belt 21 by the contact / separation mechanism 500. First, before the sheet P enters the secondary transfer portion N, the secondary transfer roller is separated from the intermediate transfer belt 21 (S1). When the paper P enters the secondary transfer portion 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 paper P at the secondary transfer portion N. Is transferred (S4). When the transfer of the image onto the paper P is completed (S5), the secondary transfer roller is separated from the intermediate transfer belt 21 before the trailing edge of the paper passes through the secondary transfer portion N (S6). Thereafter, the trailing edge of the sheet leaves the secondary transfer portion N (S7).

  FIG. 6A shows a state of paper conveyance when the paper P is in the secondary transfer portion N. FIG. FIG. 6B shows how the paper is conveyed when the paper P is not in the secondary transfer portion N. When the intermediate transfer belt surface linear velocity is Vt, the paper surface linear velocity is Vs ′, the surface linear velocity of the secondary transfer roller is Vs, the paper thickness is t, and the radius of the secondary transfer roller is r, The relationship of Formula 1 is established.

  Accordingly, the linear speed difference on the surface of the intermediate transfer belt is generated by the presence or absence of the paper P in the secondary transfer portion N by the right side of the above equation (1). Further, since the relationship Vs ′> Vs is satisfied and the sheet surface linear velocity Vs ′ is different from the intermediate transfer belt surface linear velocity Vs, when the contact / separation operation is performed, depending on the presence or absence of the sheet P in the secondary transfer portion N The speed fluctuation amount generated in the intermediate transfer belt 21 changes.

  FIG. 7A is a graph showing a change in the intermediate transfer belt speed during the contact / separation operation when the sheet P is present in the secondary transfer portion N. FIG. FIG. 7B is a graph showing the speed variation of the intermediate transfer belt during the contact / separation operation when the sheet P is not present in the secondary transfer portion N. 7A and 7B, the horizontal axis indicates time, and the vertical axis indicates the intermediate transfer belt speed. From FIG. 7A and FIG. 7B, the contact / separation operation when the sheet P is not present in the secondary transfer portion N is compared with the contact / separation operation when the sheet P is present in the secondary transfer portion N. A large speed fluctuation can occur in the intermediate transfer belt 21. Accordingly, there may be a problem that shock jitter is deteriorated during the contact / separation operation when the sheet P is not present in the secondary transfer portion N. Therefore, in the copying machine 1 according to the present embodiment, the contact / separation operation speed between the intermediate transfer belt 21 and the secondary transfer roller 30 by the contact / separation mechanism 500 is switched depending on the presence / absence of the sheet P in the secondary transfer unit N. To improve shock jitter.

  FIG. 8 is a graph showing the shock jitter rank (good or bad) when the contact / separation operation speed is changed. As shown in FIG. 8, it can be seen that 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 the low speed mode where the contact / separation operation speed is slower than when the sheet P is present in the secondary transfer unit N. Thereby, the speed fluctuation of the intermediate transfer belt 21 that can be caused by the contact / separation operation when there is no paper P in the secondary transfer portion N is reduced, and 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, the intermediate transfer belt 21 and the secondary transfer roller 30 are separated from each other before the printing operation is started. When the printing operation is started, the intermediate transfer belt 21 and the secondary transfer roller 30 are brought into contact with each other by the contact / separation mechanism 500 in a state where there is no paper P in the secondary transfer portion N. The contact operation at this time is a contact operation when there is no sheet P in the secondary transfer portion N ((1) in the figure). Then, a cleaning voltage is applied to the secondary transfer counter roller 24 so that an electric field is formed so that the toner attached to the surface of the secondary transfer roller 30 moves to the surface of the intermediate transfer belt 21 by electrostatic force. This is applied to clean the surface of the secondary transfer roller 30. As a result, it is possible to prevent the paper P that has passed through the secondary transfer portion N from being contaminated by the toner adhering to the surface of the secondary transfer roller 30. In particular, in the 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, which is effective in suppressing toner contamination on the paper P. Is.

  Here, the rotation position 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 is a home of a preset rotation position. May be out of position. As described above, when the rotation position of the cams 50 and 51 in the separated state is deviated from the home position, the rotation control of the cams 50 and 51 cannot be performed with high accuracy. Therefore, 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 before the first sheet P reaches the secondary transfer portion N after the printing operation is started. Recognize the rotation position. Then, the cams 50 and 51 are rotated by a predetermined amount so as to change from the contact state to the separated state, and the rotation position of the cams 50 and 51 is set to the home position. Thereby, the 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 cleaning voltage is applied, the secondary transfer roller 30 is rotated at least once, and then 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. As a result, a gap is formed between the intermediate transfer belt 21 and the secondary transfer roller 30, and shock jitter at the time of paper entry into the secondary transfer portion N can be reduced. The separation operation at this time is a separation operation when there is no sheet P in the secondary transfer portion N ((2) in the figure). After the leading edge of the paper P enters the secondary transfer portion N, the intermediate transfer belt 21 and the secondary transfer roller 30 are brought into contact with each other through the paper P. Thereby, it is possible to exert a sufficient transfer pressure at the secondary transfer portion N and suppress the occurrence of transfer failure. 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). Then, before the trailing edge of the previous sheet P passes through the secondary transfer portion N, the intermediate transfer belt 21 and the secondary transfer roller 30 are separated by a separation operation by the contact / separation mechanism 500. As a result, shock jitter when the trailing edge of the paper P passes through the secondary transfer portion N can be reduced. The separation operation at this time is a separation operation when the sheet P is present in the secondary transfer portion N ((4) in the figure). The contact / separation operation described above is repeated for subsequent sheets P.

  In this embodiment, as can be seen from FIG. 1, the separation operation speed when the sheet P is not present in the secondary transfer portion N is slower than the separation operation speed when the sheet P is present in the secondary transfer portion N. doing. As a result, it is possible to improve shock jitter caused by speed fluctuations of the intermediate transfer belt 21 that may occur due to the separation operation of the intermediate transfer belt 21 and the secondary transfer roller 30.

  Further, in the present embodiment, the contact operation speed when there is no paper P in the secondary transfer portion N is faster than the separation operation speed when there is no paper P in the secondary transfer portion N. Thereby, the contact operation speed when there is no paper P in the secondary transfer portion N is the same as or slower than the separation operation speed when there is no paper P in the secondary transfer portion N. The time to start 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 there is no paper P in the secondary transfer portion N can be determined using the detection result of the intermediate transfer belt 21 or the speed detection means of the drive roller 14. For example, an experiment or the like is performed in advance, and the intermediate transfer belt speed fluctuation due to the separation operation or the contact operation when the paper P is present in the secondary transfer portion N is detected and recorded by the speed detection unit. Next, the separation operation speed or the contact operation speed when the sheet P is not present in the secondary transfer portion N is lowered until the absolute value of the intermediate transfer belt speed fluctuation is equal to or less than the maximum value. Then, the separation operation speed or the contact operation speed when it is lowered 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 portion N.

  FIG. 9 is an enlarged cross-sectional view showing the peripheral configuration of 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 / absence of a sheet at the secondary transfer unit N is determined for the first image and the subsequent images. However, as shown in FIG. It is also possible to determine the presence / absence of a sheet at the secondary transfer unit N using a sheet detection sensor 90 or the like installed at a location separated by L.

  First, the timer 91 provided in the copying machine 1 starts the timer count as soon as the printing operation starts, and the time from the start is set to t. In addition, after the timer count is started, the i-th sheet P reaches the detection position of the sheet detection sensor 90 provided at a distance L from the secondary transfer portion N on the upstream side in the sheet conveyance direction. Let ti be the time. The user can input the paper P to be used from the operation panel provided in the copying machine 1 to obtain the paper size at the time of printing. The paper length in the paper transport direction is Lp, and the paper P is transported. Let V be the linear velocity. Then, it is determined that “paper is present” when the time t satisfies the relationship of the following equation 2, and “no paper” is determined when the time t does not satisfy the relationship of the following equation 2.

  FIG. 10 is an enlarged cross-sectional view showing the peripheral configuration of the secondary transfer portion N of the transfer unit 20 in the case where 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. Depending on the presence or absence of the paper P in the secondary transfer portion N, the torque of the secondary transfer drive motor 38 that drives the secondary transfer roller 30 and the intermediate transfer drive motor 92 that drives the drive roller 14 that rotates the intermediate transfer belt 21 are increased. 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 based on the detected torque information, the sheet P at the secondary transfer portion N is detected. It is also possible to detect the presence or absence. As the torque detection sensors 93 and 94, for example, a sensor that detects the drive torque from the drive current of the secondary transfer drive motor 38 or the intermediate transfer drive motor 92 can be employed.

  In the above-described embodiment, the intermediate transfer type image forming apparatus has been described. For example, a toner image formed on a photosensitive belt is transferred to a sheet at a transfer portion formed by the photosensitive belt and a transfer roller. The present invention can also be applied to an image forming apparatus of a direct transfer type that transfers onto P.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
(Aspect A)
A secondary transfer roller that forms a transfer portion such as a secondary transfer portion N that sandwiches a recording medium such as paper P between the image carrier such as the intermediate transfer belt 21 and transfers an image from the image carrier to the recording medium. 30. A transfer device such as a transfer unit 20 including a transfer member such as 30 and a contact / separation unit such as a contact / separation mechanism 500 that contacts and separates the image carrier and the transfer member. Control for controlling the contact / separation means so that at least one of the separation operation speed of the image carrier and the contact operation speed of the transfer member differs depending on the presence or absence of a recording medium in the transfer unit Control means such as a driver 4 is provided.
For example, when the surface speed of the image carrier is set to be approximately the same as the surface speed of the recording medium held and conveyed by the image carrier and the transfer member at the transfer portion regardless of the presence or absence of the recording medium at the transfer portion. think of.
When there is a recording medium in the transfer portion, the surface speed of the image carrier and the surface speed of the recording medium in the state where the image carrier and the transfer member are in contact with each other through the recording medium are substantially the same, and therefore, due to the speed difference. Almost no rotational load is applied to the image carrier. For this reason, even if the image carrier and the transfer member are abruptly moved when a recording medium is present in the transfer portion, a large speed fluctuation does not occur in the image carrier.
On the other hand, when there is no recording medium in the transfer portion, the surface speed of the transfer member is slower than the surface speed of the image carrier by the thickness of the recording medium in the contact state between the image carrier and the transfer member. The rotational load due to the generation is applied to the image carrier. For this reason, if the image carrier and the transfer member are suddenly separated when there is no recording medium in the transfer portion, the rotational load is lost at once, and a large speed fluctuation occurs in the image carrier. Therefore, the control unit controls the contact / separation unit so that the separation operation speed when there is no recording medium in the transfer unit is slower than when the transfer unit has a recording medium. Depending on the presence or absence of the recording medium in As a result, when there is no recording medium in the transfer unit, the image carrier and the transfer member can be separated while gradually reducing the rotational load. It can be suppressed from occurring.
Further, the contact operation speed is controlled by the control means so that the contact operation speed when there is no recording medium in the transfer section is slower than when the transfer section has a recording medium. Depending on the presence or absence of the recording medium in As a result, the contact operation between the image carrier and the transfer member when there is no recording medium in the transfer unit prevents the rotational load from being applied suddenly to the image carrier, and a large speed fluctuation occurs in the image carrier. Can be suppressed.
Therefore, in (Aspect A), it is possible to reduce the shock jitter caused by the speed fluctuation of the image carrier that can be caused by the contact / separation operation between the image carrier and the transfer member.
(Aspect B)
In (Aspect A), the control means controls the contact / separation mechanism so that a separation operation speed when there is no recording medium in the transfer unit is slower than a separation operation speed when there is a recording medium in the transfer unit. Control. According to this, as described in the above embodiment, the speed fluctuation of the image carrier that can be caused by the separation operation when there is no recording medium in the transfer portion is reduced, and shock jitter can be improved.
(Aspect C)
In (Aspect A) or (Aspect B), the contact / separation means operates at a timing before and after the leading end of the recording medium or the trailing end of the recording medium passes through the transfer portion. According to this, as described in the above embodiment, shock jitter that may occur when the leading end of the recording medium or the trailing end of the recording medium passes through the transfer portion can be reduced.
(Aspect D)
In any one of (Aspect A) to (Aspect C), it has speed fluctuation detecting means for detecting information relating to speed fluctuation of the image carrier, and is based on the contact / separation operation when there is no recording medium in the transfer section. The contact / separation operation based on the detection result of the speed variation detection means 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 transfer unit has a recording medium. Adjust the 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 detecting unit such as a paper detection sensor 90 that detects 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 a recording medium in the transfer unit.
(Aspect F)
In any one of (Aspect A) to (Aspect D), an image carrier driving unit such as an intermediate transfer driving motor that rotationally drives the image carrier, a secondary transfer driving motor 38 that rotationally drives the transfer member, and the like. 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 / absence of a recording medium in the transfer unit is determined. According to this, as described in the above embodiment, it is possible to determine the presence or absence of a recording medium in the transfer unit.
(Aspect G)
Image forming apparatus such as copier 1 provided with transfer means for transferring a toner image carried on the surface of the image carrier to a recording medium sandwiched in a transfer portion by contact between the image carrier and a transfer member 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 caused by the speed fluctuation of the image carrier that can be caused by the contact and separation operation of the image carrier and the transfer member, and to perform good image formation. Can do.

DESCRIPTION OF SYMBOLS 1 Copier 4 Control driver 10 Tandem type image forming part 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 Conveying belt 23 Stretch roller 24 Secondary transfer counter roller 24a Through shaft member 24b Roller portion 24c Hollow cored bar 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 Surface 31 Roller part 31a Hollow core 31b Elastic layer 31c Surface layer 32 First shaft member 33 Second shaft member 34 First idling roller 35 Second idling 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 Separating roller 46 Paper feed path 47 Transport roller 48 Paper feed path 49 Registration roller 50 First cam 50a Cam part 50b Roller part 50c Outer peripheral surface 51 Second cam 51a Cam part 51b Roller part 51c Outer peripheral surface 52 First Bearing 53 Second Ball Bearing 54 Drive Accepting Pulley 56 Timing Belt 57 Motor Pulley 58 Cam Drive Motor 59 Detected Disk 59a Detected Part 60 Optical Sensor 61 High Voltage Power Supply 62 Screw 70 Paper Feeding Roller 71 Manual Tray 72 Separating Roller 73 Manual Feeding Paper feed path 74 Switching claw 75 Paper discharge roller 76 Paper 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 main body 200 Paper 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 (7)

A rotatable transfer member that forms a transfer portion that sandwiches a recording medium with a rotatable image carrier and transfers an image from the image carrier to the recording medium;
In a transfer apparatus provided with contact / separation means for contacting and separating the image carrier and the transfer member,
At least one of the separation operation speed between the image carrier and the transfer member and the contact operation speed between the image carrier and the transfer member are different depending on the presence or absence of a recording medium in the transfer unit, A transfer apparatus comprising control means for controlling the contact / separation means. The transfer device according to claim 1,
The control means controls the contact / separation mechanism so that a separating operation speed when there is no recording medium in the transfer unit is slower than a separating operation speed when there is a recording medium in the transfer unit. Transfer device. In the transfer device according to claim 1 or 2,
The transfer device is characterized in that the contact / separation means operates at a timing before and after the leading end of the recording medium or the trailing end of the recording medium passes through the transfer portion. The transfer device according to any one of claims 1 to 3,
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 transfer unit has a recording medium. A transfer apparatus, wherein a contact / separation operation speed is adjusted based on a detection result of the speed fluctuation detecting means. The transfer apparatus according to any one of claims 1 to 4,
A transfer apparatus comprising: a recording medium presence / absence detecting means for detecting the presence / absence of a recording medium in the transfer unit. The transfer apparatus according to any one of claims 1 to 4,
Image carrier driving means for rotationally driving the image carrier;
Transfer member driving means for rotationally driving the transfer member;
A torque detecting means for detecting a driving torque of at least one of the image carrier driving means and the transfer member driving means;
6. A transfer apparatus, wherein the presence or absence of a recording medium in the transfer unit is determined based on a detection result of the torque detection means. In an image forming apparatus provided with a transfer unit that transfers a toner image carried on the surface of an image carrier to a recording medium sandwiched between transfer parts formed by contact between the image carrier and a transfer member.
An image forming apparatus using the transfer device according to claim 1 as the transfer unit.

Images