JP2014013359A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of load fluctuation of an intermediate transfer belt and a surface speed difference between the intermediate transfer belt and a secondary transfer roller during secondary transfer process so as to prevent the occurrence of transfer blur.SOLUTION: An image forming apparatus includes: an intermediate transfer belt 21 that has a surface on which a toner image formed on an image carrier by an image forming unit is primary-transferred, and secondary-transfers the toner image to a recording medium in a secondary transfer unit; a secondary transfer roller 30 that forms the secondary transfer unit between the intermediate transfer belt 21 and the secondary transfer roller 30; and an opposite secondary transfer roller 24 that is arranged opposite to the secondary transfer roller 30 to support the intermediate transfer belt 21 from the rear face. When a recording medium enters the secondary transfer unit, the image forming apparatus connects an electromagnetic clutch 80 to transmit rotation of a drive gear 81 so as to rotate and drive the secondary transfer roller 30. During periods other than the entry of the recording medium, the image forming apparatus disconnects the electromagnetic clutch 80 to allow the secondary transfer roller 30 to freely rotate so as to rotate along with the intermediate transfer belt 21.

Description

  The present invention relates to an image forming apparatus provided with an intermediate transfer member.

  As an electrophotographic image forming apparatus, a plurality of toner images sequentially formed on an image carrier such as a photoconductive drum are sequentially superposed on a rotating intermediate transfer member, which is another image carrier, for primary transfer. An intermediate transfer type image forming apparatus is known in which a primary transfer image (toner image) on the intermediate transfer body is secondarily transferred collectively onto a sheet such as transfer paper as a recording medium. This intermediate transfer type image forming apparatus is particularly popular as a color image forming apparatus because it is easy to reduce in size and has few restrictions on the type of recording medium onto which a visible image is finally transferred. Yes.

An intermediate transfer belt is often used as an intermediate transfer member in the intermediate transfer type image forming apparatus. In this case, generally, at the secondary transfer position, the back side of the intermediate transfer belt is supported by a secondary transfer counter roller (backup roller), and is a secondary transfer member that rotates in contact with the surface of the intermediate transfer belt. A secondary transfer nip (secondary transfer portion) is formed between the rollers. The toner image on the surface of the intermediate transfer belt is transferred onto the recording medium while the recording medium is sandwiched and conveyed by the secondary transfer nip.
In such an image forming apparatus, in order to transfer the toner image on the intermediate transfer belt onto the recording medium without expansion and contraction in the conveying direction, the surface speeds of the intermediate transfer belt and the secondary transfer roller are kept constant. There is a need.

  Further, in order to clean the adhering matter such as residual toner and paper powder adhering to the intermediate transfer belt after the toner image is transferred, it is necessary to press and contact a cleaning member such as a cleaning blade. . In this case, since the load for rotating the intermediate transfer belt becomes large, the secondary transfer roller is not rotated by the frictional force caused by the contact with the intermediate transfer belt. Some are driven to rotate by another drive source.

For example, in the image forming apparatus described in Patent Document 1, when performing secondary transfer while transporting a recording medium sandwiched between an intermediate transfer belt and a secondary transfer roller, a first drive unit for driving the intermediate transfer belt; The second transfer roller is rotationally driven by another second driving means. On the other hand, when the secondary transfer is not performed, the secondary transfer roller is rotated around the intermediate transfer belt while the second driving unit is shut off, and the rotation speed is detected. Then, the drive speed of the second drive means is controlled based on the detection result.
As a result, the surface speed of the secondary transfer roller that is rotationally driven by the second driving means during the secondary transfer is made to coincide with the surface speed of the intermediate transfer belt, and the intermediate transfer belt and the secondary transfer due to variations in component accuracy. A difference in surface speed between the roller and the roller is prevented.

  In the image forming apparatus described in Patent Document 2, in the non-secondary transfer process, the intermediate transfer belt and the secondary transfer roller are driven by different driving means, and the secondary transfer is performed by the electromagnetic clutch only during the secondary transfer process. The secondary transfer roller is driven to rotate by interrupting the power of the driving means from the transfer roller.

In the technique disclosed in Patent Document 1, the driving speed of the second driving unit is controlled based on the result of detecting the rotational speed due to the rotation of the secondary transfer roller while the second driving unit is shut off. However, if the diameter of the secondary transfer roller fluctuates due to environmental fluctuations during the period from the detection of the rotation speed to the next detection (during the secondary transfer process), the surface speed difference between the intermediate transfer belt Will occur.
Further, since the conveyance speed difference caused by the thickness of the recording medium corrects the rotational speed of the secondary transfer roller with a preset value, there is also a problem that a surface speed difference occurs due to variations in the thickness of the recording medium.

  On the other hand, in the technique disclosed in Patent Document 2, immediately after the recording medium enters the secondary transfer portion, the secondary transfer roller is driven and rotated by the power of its driving means, so that the recording is performed on the secondary transfer portion. When the medium enters, the load of the intermediate transfer belt increases rapidly, which is directly transmitted to the driving means of the intermediate transfer belt, and there is a problem that shock jitter occurs.

In the non-secondary transfer process, the secondary transfer roller and the intermediate transfer belt are both in contact with each other and are driven by different driving means. For this reason, a difference in linear velocity occurs due to variations in the diameter of the secondary transfer roller due to component variations and environmental variations. Due to the difference in linear velocity, there is a problem that transfer blur occurs in the primary transfer portion.
Such a problem also occurs in an image forming apparatus that uses an intermediate transfer drum that rotates while forming a secondary transfer portion between the intermediate transfer member and a secondary transfer member.

  The present invention has been made to solve the above-described problem, and prevents the load of the intermediate transfer member from rapidly increasing when the recording medium enters the secondary transfer portion, thereby changing the moving speed thereof. It is an object of the present invention to prevent the occurrence of transfer blur and the like by preventing a difference in surface speed between the intermediate transfer member and the secondary transfer member during the secondary transfer process.

  In order to achieve the above object, an image forming apparatus according to the present invention forms an image forming unit for forming a toner image on an image carrier, and a toner image formed on the image carrier by the image forming unit is primarily formed on the surface. An intermediate transfer member to which the toner image is secondarily transferred to a recording medium at the secondary transfer portion; a secondary transfer member that forms the secondary transfer portion between the intermediate transfer member; and the secondary transfer member. A secondary transfer member driving means for rotationally driving the member; a drive transmission releasing means for transmitting and releasing the driving force of the secondary transfer member driving means to the secondary transfer member; and a recording medium on the secondary transfer portion. When the leading edge enters, the driving force is transmitted to the secondary transfer member, and during the other periods, the transmission of the driving force to the secondary transfer member is canceled and the secondary transfer member can be rotated. Control for controlling the drive transmission release means Characterized by comprising a means.

  The image forming apparatus according to the present invention can greatly reduce the load of the intermediate transfer member when the recording medium enters the secondary transfer member and the movement speed thereof fluctuates, and during the secondary transfer process, Since the secondary transfer member is rotated by the movement of the intermediate transfer member, there is almost no risk of a surface speed difference between the intermediate transfer member and the secondary transfer member, and transfer blur or the like hardly occurs. Therefore, a high quality image can be formed.

1 is a diagram showing a schematic internal configuration of a color copying apparatus which is an electrophotographic apparatus of a tandem type indirect transfer system as an embodiment of an image forming apparatus according to the present invention. FIG. 2 is an enlarged cross-sectional view of a normal state of a mechanism portion related to a secondary transfer portion including a secondary transfer roller and a secondary transfer counter roller in FIG. 1. FIG. 6 is an enlarged cross-sectional view of a state before the gap is formed when the electromagnetic clutch is turned on just before the recording sheet enters the secondary transfer portion. Similarly, when the recording sheet enters the secondary transfer portion, the electromagnetic clutch is ON and an enlarged cross-sectional view in a state where a gap is formed. FIG. 3 is a schematic side view of a main part showing a state where an intermediate transfer belt and a secondary transfer roller are in contact with each other. FIG. 4 is a schematic side view of a main part showing a state where a gap is formed between an intermediate transfer belt and a secondary transfer roller.

FIG. 2 is a block diagram showing a control system of each drive motor and electromagnetic clutch according to the present invention by a control unit of the color copying apparatus shown in FIG. 1. FIG. 6 is a timing chart for explaining a first operation example in the illustrated embodiment. FIG. 10 is a timing diagram for explaining a second operation example in the illustrated embodiment. It is a timing diagram for demonstrating the 1st operation example in other embodiment of this invention. It is a timing diagram for demonstrating the 2nd operation example in other embodiment of this invention. FIG. 6 is an enlarged cross-sectional view showing portions related to a secondary transfer device and an intermediate transfer device in another embodiment of the image forming apparatus according to the present invention. It is the schematic front view seen from the left in FIG.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings.
[Embodiment of Image Forming Apparatus]
FIG. 1 shows a color copying apparatus which is an electrophotographic apparatus of a tandem type indirect transfer system as an embodiment of an image forming apparatus according to the present invention. This color copying apparatus includes a printer unit 100, a paper feed table 200 on which the printer unit 100 is placed, a scanner unit 300 mounted on the printer unit 100, and an automatic document mounted on the scanner unit 300. It is comprised by the conveying apparatus (ADF) 400 grade | etc.,.

  The printer unit 100 includes an endless belt-like intermediate transfer belt 21 as an intermediate transfer member. The intermediate transfer belt 21 has an inverted triangular shape as shown in FIG. 1 when viewed from the side, and includes a plurality of rollers, a driving roller 22, a driven roller 23, and a secondary transfer counter roller (backup roller) 24. It is supported by being hung around. Then, by the rotational driving of the driving roller 22, it is rotated (referred to as rotation) in the clockwise direction (arrow direction) in FIG.

  Above the intermediate transfer belt 21, four image forming units (image forming units) 1C and 1M for forming C (cyan), M (magenta), Y (yellow), and K (black) toner images are formed. , 1Y, 1K are arranged side by side along the moving direction of the intermediate transfer belt 21, and constitute the tandem image forming unit 10. This is an image forming unit that forms a toner image on an image carrier to be described later.

  The image forming units 1C, 1M, 1Y, and 1K are respectively photosensitive drums 2C, 2M, 2Y, and 2K as image carriers, developing units 3C, 3M, 3Y, and 3K, and photosensitive member cleaning devices 4C and 4M. , 4Y, 4K. The photosensitive drums 2C, 2M, 2Y, and 2K are in contact with the intermediate transfer belt 21 at positions facing the primary transfer rollers 25C, 25M, 25Y, and 25K, respectively, and primary transfer nips for C, M, Y, and K, respectively. 1 is rotated in the counterclockwise direction (arrow direction) in FIG. 1 by a driving means (not shown).

  The developing units 3C, 3M, 3Y, and 3K develop the electrostatic latent images formed on the photosensitive drums 2C, 2M, 2Y, and 2K with toners of C, M, Y, and K colors. Further, the photoreceptor cleaning devices 4C, 4M, 4Y, and 4K clean the transfer residual toner attached to the photoreceptor drums 2C, 2M, 2Y, and 2K after passing through the primary transfer nip.

  An optical writing unit 15 is disposed above the tandem image forming unit 10 in the printer unit 100. The optical writing unit 15 forms an electrostatic latent image by performing optical writing processing by scanning with laser light on the surfaces of the photosensitive drums 2C, 2M, 2Y, and 2K that are rotationally driven in the directions indicated by the arrows. To do. Prior to the optical writing process, the surfaces of the photosensitive drums 2C, 2M, 2Y, and 2K are uniformly charged by the respective chargers.

  The transfer unit 20 including the intermediate transfer belt 21 includes primary transfer rollers 25C, 25M, 25Y, and 25K inside the loop of the intermediate transfer belt 21. The primary transfer rollers 25C, 25M, 25Y, and 25K face the intermediate transfer belt 21 toward the photosensitive drums 2C, 2M, 2Y, and 2K on the back side of the primary transfer nip for each color of C, M, Y, and K, respectively. Pressing.

A secondary transfer roller 30 as a secondary transfer member is disposed below the intermediate transfer belt 21. The secondary transfer roller 30 presses and contacts the front surface side of the portion of the intermediate transfer belt 21 that is wound around the secondary transfer counter roller 24 to form a secondary transfer nip as a secondary transfer portion. Yes.
A recording sheet as a recording medium is fed into the secondary transfer nip by a positioning roller pair 95 at a predetermined timing. The four color superimposed toner images on the intermediate transfer belt 21 are collectively transferred onto the recording sheet at the secondary transfer nip.

The scanner unit 300 reads image information of a document placed on the contact glass 301 by the reading sensor 302 and sends the read image information to the control unit of the printer unit 100. A control unit (not shown) controls a light source such as a laser diode in the optical writing unit 15 of the printer unit 100 based on the image information received from the scanner unit 300, and performs laser writing for C, M, Y, and K. Light is emitted to optically scan the photosensitive drums 2C, 2M, 2Y, and 2K.
By this optical scanning, electrostatic latent images are formed on the surfaces of the photosensitive drums 2C, 2M, 2Y, and 2K, and the latent images are developed into toner images of C, M, Y, and K colors through a predetermined development process. Is done.

  A paper feed table 200 includes paper feed cassettes 202 arranged in multiple stages in the paper bank 201, a paper feed roller 203 that feeds a recording sheet as a recording medium from the paper feed cassette 202, and a separated recording sheet that is fed out. A separation roller 205 that leads to the paper path 204, a transport roller pair 206 that transports the recording sheet to the paper feed path 99 of the printer unit 100, and the like are provided.

In addition to the paper feed table 200, manual paper feed is also possible, and the manual feed tray 98 for manual feed and the recording sheets on the manual feed tray 98 are separated one by one toward the manual feed path 97. A separating roller 96 is also provided. In the printer unit 100, the manual paper feed path 97 joins the paper feed path 99.
A positioning roller pair 95 is disposed near the end of the paper feed path 99. The positioning roller pair 95 sandwiches a recording sheet conveyed in the paper feed path 99 or the manual paper feed path 97 between the rollers, and then feeds the recording sheet toward the secondary transfer nip at a predetermined timing.

  When a color image is copied by this color copying apparatus, the original is set on the original table 401 of the ADF 400, or the ADF 400 is opened, the original is set on the contact glass 301 of the scanner unit 300, and the ADF 400 is closed. Hold the manuscript.

When a start button (not shown) is pressed, if the document is set on the ADF 400, the document is conveyed onto the contact glass 301. Thereafter, the scanner unit 300 starts driving, and the first traveling body 303 and the second traveling body 304 start traveling along the document surface. The light emitted from the light source of the first traveling body 303 is reflected by the document surface, and the reflected light is turned back and directed toward the second traveling body 304. The folded light is further folded by the mirror of the second traveling body 304 and then enters the reading sensor 302 through the imaging lens 305.
As a result, the document content is read by the reading sensor 302 and a signal processing circuit (not shown), temporarily stored as image information, and sequentially sent to the printer unit 100.

  When the printer unit 100 receives the image information from the scanner unit 300, the printer unit 100 feeds a recording sheet having a size corresponding to the image information to the paper feed path 99. Along with this, the drive roller 22 is rotationally driven by a drive motor (not shown) to rotate the intermediate transfer belt 21 in the direction of the arrow. At the same time, after the photosensitive drums 2C, 2M, 2Y, and 2K of the image forming units 1C, 1M, 1Y, and 1K of the tandem image forming unit 10 start to rotate in the directions indicated by the arrows, their surfaces are uniformly charged. The

  Then, based on the image information received from the scanner unit 300, optical writing processing is performed by the optical writing unit 15, and electrostatic latent images are formed on the surfaces of the photosensitive drums 2C, 2M, 2Y, and 2K, respectively. The developing units 3C, 3M, 3Y, and 3K develop the toner with the respective color toners. The toner images of C, M, Y, and K colors formed on the surfaces of the photosensitive drums 2C, 2M, 2Y, and 2K by these processes are sequentially overlapped at the primary transfer nip for C, M, Y, and K. In addition, primary transfer is performed on the intermediate transfer belt 21 to form a full-color toner image in which four colors are superimposed.

  In the paper feed table 200, one of the paper feed rollers 203 is selectively rotated so as to feed a recording sheet having a size corresponding to the document size, and the recording sheet is sent out from one of the three paper feed cassettes 202. It is. The recording sheets sent out are separated one by one by the separation roller 205 and introduced into the paper feed path 204, and then conveyed by the conveyance roller pair 206 and sent to the paper feed path 99 in the printer unit 100.

  When the manual feed tray 98 is used, the paper feed roller 94 of the manual feed tray 98 rotates to feed the recording sheet on the tray, and is fed to the manual feed path 97 while being separated by the separation roller 96. Near the end of road 99. In the vicinity of the end of the paper feed path 99, the recording sheet stops by abutting the leading edge against the positioning roller pair 95.

  Thereafter, when the positioning roller pair 95 rotates at a timing that can be synchronized with the full-color toner image on the intermediate transfer belt 21, the recording sheet is fed into the secondary transfer nip, and the full-color toner image on the intermediate transfer belt 21. Close contact with. Then, the toner image is collectively transferred onto the recording sheet by the action of an electric field by the nip pressure and the secondary transfer bias voltage. The secondary transfer nip is a secondary transfer portion formed by the secondary transfer roller 30 facing the secondary transfer counter roller 24 and the intermediate transfer belt 21.

  The recording sheet on which the full-color toner image has been secondarily transferred in the secondary transfer portion is sent into the fixing device 71 by the paper conveyance belt 70. Then, the toner image is fixed on the surface by the pressurization and the heat treatment by the fixing device 71 being sandwiched in the fixing nip between the pressure roller 72 and the fixing belt 73.

The recording sheet on which the color image is formed in this manner is sent out by the discharge roller pair 74 and stacked on the discharge tray 75 outside the apparatus. When an image is also formed on the other side of the recording sheet, the recording sheet is discharged from the fixing device 71 and then sent to the sheet reversing device 77 by the path switching by the switching claw 76.
Then, after being turned upside down, it is returned again to the positioning roller pair 95, sent to the secondary transfer nip, where the full color toner image is secondarily transferred to the other surface, and the toner image is again passed through the fixing device 71. Are fixed on the paper discharge tray 75.

  After passing through the secondary transfer nip, the belt cleaning device 26 is in contact with the surface of the intermediate transfer belt 21 before entering the cyan primary transfer nip where the primary transfer process is the most upstream of the four colors. The belt cleaning device 26 cleans transfer residual toner adhering to the surface of the intermediate transfer belt 21.

[Details of secondary transfer part components]
Next, details of the constituent parts of the secondary transfer unit in the embodiment of the image forming apparatus described above will be described.
FIG. 2 is an enlarged cross-sectional view in a normal state (a state other than when the recording sheet enters and exits) of the mechanical portion related to the secondary transfer portion including the secondary transfer roller 30 and the secondary transfer counter roller 24 in FIG. is there. FIG. 3 shows a state before the gap is formed by turning on the electromagnetic clutch immediately before the recording sheet enters the secondary transfer portion, and FIG. 4 shows the electromagnetic clutch when the recording sheet enters the secondary transfer portion. It is an expanded sectional view of the state where a gap was formed with ON.

FIG. 5 is a schematic side view of a main part showing a state in which the intermediate transfer belt 21 and the secondary transfer roller 30 are in contact, and FIG. 6 is a state in which a gap is formed therebetween.
Each of these drawings shows the same embodiment, and the components are the same, so the configuration will be described mainly with reference to FIG. 2 and FIG.
A secondary transfer roller 30 is pressed and brought into contact with the front surface of the intermediate transfer belt 21 shown in FIG. 1 to form a secondary transfer nip as a secondary transfer portion. The secondary transfer counter roller 24 faces the secondary transfer roller and supports the intermediate transfer belt 21 from the back surface.

  The secondary transfer roller 30 includes a roller portion 31, a first shaft member 32 and a second shaft member 33 that protrude from the center portions of both end surfaces in the axial direction and extend in the rotational axis direction, and a first idling roller. 34 and a second idling roller 35. The roller portion 31 includes a cylindrical hollow core 31a, an elastic layer 31b made of an elastic material fixed to the outer peripheral surface, and a surface layer 31c covered on the outer peripheral surface. The first shaft member 32 and the second shaft member 33 are supported by a roller unit holder 40 also shown in FIG. 5 via ball bearings 41 (not shown in FIG. 5).

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, when the cleaning blade is brought into contact with the roller portion 31, there is a risk of causing a problem 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 from epichlorohydrin rubber having a certain degree of conductivity.

As the conductive rubber material, instead of the above-described conductive epichlorohydrin rubber, carbon-dispersed EPDM or Si rubber, NBR having an ion conductive function, urethane rubber, or the like may be used. Many rubber materials have good chemical affinity for the toner or have a relatively high coefficient of friction. For this reason, the surface of the elastic layer 31b made of rubber is covered with the surface layer 31c. As a result, toner adhesion to the surface of the roller portion 31 is suppressed, and the load of sliding friction with the cleaning blade is reduced.
As the material of 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 having a low friction coefficient and good toner releasability is suitable.

  When the cleaning blade is not brought into contact with the roller portion 31, an inexpensive foam material such as highly flexible foam rubber is used as the conductive rubber material constituting the elastic layer 31b of the secondary transfer roller 30, The surface layer 31c can be omitted. By configuring the elastic layer 31b with the foam material in this way, the elastic layer 31b can be flexibly deformed in the thickness direction in the secondary transfer nip, and the secondary layer having a certain extent in the recording sheet conveyance direction. A transfer nip can be formed. As the foamed rubber, for example, conductive foamed NBR can be used.

The secondary transfer roller 30 having such a configuration is applied with a pressing force toward the intermediate transfer belt 21 that is wound around the secondary transfer counter roller 24.
That is, the roller unit holder 40 that supports the secondary transfer roller 30 via the first and second shaft members 32 and 33 and the respective ball bearings 41 has one end in the longitudinal direction as shown in FIG. The support shaft 42 is rotatably supported by a device fixing portion (not shown). A compression coil spring 43 is interposed between the other end side in the longitudinal direction and the device fixing portion. By the restoring force of the compression coil spring 43, the roller unit holding body 40 is pressed around the support shaft 42 so as to rotate counterclockwise in FIG. Thereby, a pressing force is applied to the secondary transfer roller 30 toward the intermediate transfer belt 21.

  The secondary transfer counter roller 24 that is wound around the intermediate transfer belt 21 passes through a roller portion 24b that is a cylindrical main body portion and a rotation center portion of the roller portion 24b in the rotation axis direction, and the roller portion 24b is freely rotatable. And a through shaft member 24a. The through shaft member 24a is made of metal, and freely rotates the roller portion 24b on the outer peripheral surface thereof.

  The roller portion 24b, which is a main body portion, includes a drum-shaped hollow core metal 24c, an elastic layer 24d made of an elastic material fixed to the peripheral surface thereof, and ball bearings 24e press-fitted to both ends in the axial direction of the hollow core metal 24c. It is equipped with. The ball bearing 24e rotates on the penetrating 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 24a includes a first bearing 53a fixed to the first side plate 29a of the transfer unit 20 (FIG. 1) that stretches the intermediate transfer belt 21, and a second bearing 53b fixed to the second side plate 29b. It is supported rotatably. However, most of the time during the print job is stopped without being driven to rotate. Then, the roller portion 24b to be rotated with the endless movement of the intermediate transfer belt 21 is freely idled on its outer peripheral surface.

  The elastic layer 24d fixed on the outer 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 have a resistance of 7.5 [LogΩ] or more. ing. The electrical resistance of the elastic layer 24d is adjusted within a predetermined range because there is no recording sheet in the secondary transfer nip when a recording sheet having a relatively small size in the roller axial direction such as A5 size is used. This is to prevent the transfer current from being concentrated at a location where the intermediate transfer belt 21 and the secondary transfer roller 30 are in direct contact with each other. By making the electric resistance of the elastic layer 24d larger than the resistance of the recording sheet, it is possible to suppress such concentration of transfer current.

  In the penetrating shaft member 24a of the secondary transfer counter roller 24, the two end regions that are not located in the roller portion 24b in the entire longitudinal direction are respectively abutted against the secondary transfer roller 30. An eccentric cam as a member is fixed so as to rotate integrally with the through shaft member 24a.

  Specifically, the first eccentric cam 50 is fixed to one end region in the longitudinal direction of the penetrating shaft member 24a. In the first eccentric cam 50, an eccentric cam portion 50a and a true circular roller portion 50b are integrally formed side by side in the axial direction. The first eccentric cam 50 is fixed to the penetrating shaft member 24a by screwing the screw 52 penetrating the roller portion 50b into the penetrating shaft member 24a. Similarly to the first eccentric cam 50, a second eccentric cam 51 in which an eccentric cam portion 51a and a roller portion 51b are integrally formed is attached to the other end region in the longitudinal direction of the penetrating shaft member 24a by a screw 52. It is fixed.

A drive receiving gear 54 is fixed to a region outside the second eccentric cam 51 in the axial direction of the penetrating shaft member 24a. Further, a detected disk 59 formed of an insulating member such as resin is fixed to the outer side of the drive receiving gear 54.
On the other hand, a motor bracket 65 bent in a crank shape is fixed to the second side plate 29b of the transfer unit 20 (FIG. 1), and a cam drive motor 58 is attached and fixed thereto. Then, the rotating shaft of the cam drive motor 58 protrudes downward from the horizontal portion of the motor bracket 65, and the worm gear 57 is fitted and fixed to the rotating shaft.

A mounting plate 66 extending downward in parallel with the second side plate 29b is fixed to an upright portion of the motor bracket 65, and a worm wheel 55 integrally provided with a pinion 56 is rotatably supported. The worm wheel 55 meshes with the worm gear 57, and the pinion 56 meshes with the drive receiving gear 54.
Therefore, when the worm gear 57 is rotated by the cam drive motor 58, the worm wheel 55 meshed with the pinion 56 is rotated integrally with the pinion 56, and the drive receiving gear 54 meshed with the pinion 56 is rotated. The member 24a can be rotated.

When the through-shaft member 24a rotates, the first eccentric cam 50 and the second eccentric cam 51, which are respectively fixed to both ends in the axial direction of the through-shaft member 24a, rotate together, so that the through-shaft member 24a is driven. It is possible to rotate the first eccentric cam 50 and the second eccentric cam 51 on both ends only by providing a drive transmission mechanism for transmitting the signal on one end side in the axial direction.
At this time, even if the through-shaft member 24a is rotated, the roller portion 24b can freely idle on the through-shaft member 24a, so that the intermediate transfer belt 21 does not hinder the roller portion 24b from being rotated.

  When the penetrating shaft member 24a rotates within a predetermined rotation angle range, the first eccentric cam 50 and the second eccentric cam 51 are respectively connected to the first idling roller 34 and the second idling roller 34 of the secondary transfer roller 30 with the eccentric cam portions 50a and 51a. The secondary transfer roller 30 is pushed downward in FIG. 2 by contacting (contacting with) the idle roller 35. That is, it pushes back against the restoring force of the compression coil spring 43 that presses the roller unit holder 40 shown in FIG. As a result, the secondary transfer roller 30 is moved away from the secondary transfer counter roller 24 (and thus the intermediate transfer belt 21), and the distance between the axes of the secondary transfer counter roller 24 and the secondary transfer roller 30 can be increased. it can.

As a result, as shown in FIGS. 4 and 6, a gap is formed between the surface of the intermediate transfer belt 21 and the outer peripheral surface of the secondary transfer roller 30.
In this embodiment, the secondary transfer counter roller 24 and the secondary transfer are made by the first eccentric cam 50, the second eccentric cam 51, the cam drive motor 58, various gears, the through shaft member 24a, the roller unit holder 40 described above, and the like. A means for increasing the distance (distance between the shafts) with the roller 30 is configured. The first and second eccentric cams 50 and 51 are made of an insulating material such as resin.

  In this embodiment, the hollow cored bar 31a of the secondary transfer roller 30 is grounded, while 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. As a result, a secondary transfer electric field for electrostatically moving the toner from the secondary transfer counter roller 24 side toward the secondary transfer roller 30 side is formed between both rollers in the secondary transfer nip.

The first bearing 53a that rotatably receives the metal penetrating shaft member 24a of the secondary transfer counter roller 24 is formed of a conductive slide bearing. A high voltage power supply 61 that outputs a secondary transfer bias is connected to the conductive first bearing 53a.
The secondary transfer bias voltage output from the high-voltage power supply 61 is guided to the secondary transfer counter roller 24 via the conductive first bearing 53a. In the secondary transfer counter roller 24, the voltage is transmitted in sequence from the metal penetrating shaft member 24a to the metal ball bearing 24e, the metal hollow core metal 24c, and the conductive elastic layer 24d.

An insulating member 63 is interposed between the first bearing 53a and the first side plate 29a. The second bearing 53b is formed of an insulating member such as resin. Therefore, the secondary transfer bias voltage is not applied to the first side plate 29a and the second side plate 29b.
Further, since the drive receiving gear 54, the integral worm wheel 55 and pinion 56, and the worm gear 57 are all formed of an insulating member such as resin, the secondary transfer bias is also applied to the motor bracket 65 and the cam drive motor 58. No voltage is applied.

The detected 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, a transmissive optical sensor 60 is fixed to the mounting plate 66 fixed to the motor bracket 65. 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, it transmits a light reception signal to the control unit 110 described later with reference to FIG. The control unit 110 includes a first eccentric cam 50 and a second eccentric cam fixed to the penetrating shaft member 24a based on the timing when the light reception signal from the light receiving element is interrupted and the driving amount of the cam drive motor 58 from that timing. The rotational angle positions of the 51 eccentric cam portions 50a and 51a are grasped.

  As described above, the eccentric cam portions 50a and 51a are brought into contact with the first idling roller 34 and the second idling roller 35 of the secondary transfer roller 30 within a predetermined rotation angle range, thereby causing the secondary transfer roller 30 to be compressed coil springs. 43 (see FIGS. 5 and 6) is pushed back in the direction away from the secondary transfer counter roller 24 against the restoring force (hereinafter, this pushing back is referred to as “pushing down”). The amount of depression at this time is determined by the rotational angle positions of the first eccentric cam 50 and the second eccentric cam 51. Note that the greater the amount by which the secondary transfer roller 30 is pushed down, the greater the interaxial distance 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 rotatably provided on a first shaft member 32 that rotates integrally with the roller portion 31. The first idling roller 34 is a ball bearing (ball bearing) having a donut disk shape whose outer diameter is slightly larger than that of the roller portion 31, and can idle on the outer peripheral surface of the first shaft member 32. A second idling roller 35 having the same configuration as the first idling roller 34 is also rotatably provided on the second shaft member 33 of the secondary transfer roller 30.

As described above, the first eccentric cam 50 and the second eccentric cam 51 fixed to the penetrating shaft member 24a of the secondary transfer counter roller 24 have the eccentric cam portions 50a and 51a at the predetermined rotational angle positions. 30 abuts on the first idling roller 34 and the second idling roller 35, respectively.
The first and second idling rollers 34 and 35 that are in contact with the eccentric cam portions 50a and 51a are prevented from rotating, but the rotation of the secondary transfer roller 30 is not prevented thereby.

  Even if the first and second idling rollers 34 and 35 stop rotating, they are ball bearings, so the first and second shaft members 32 and 33 of the secondary transfer roller 30 are This is because the second idle rollers 34 and 35 can rotate freely independently. By stopping the rotation of the first and second idling rollers 34 and 35 with the contact of the eccentric cam portions 50a and 51a, the occurrence of sliding contact between them can be avoided. Thereby, it is possible to avoid an increase in load torque of the intermediate transfer belt drive motor and the secondary transfer roller drive motor.

In this embodiment, an electromagnetic clutch 80 and a drive gear 81 are further provided at the end of the first shaft member 32 of the secondary transfer roller 30. The drive gear 81 is rotationally driven by a secondary transfer drive motor via a transmission mechanism (wheel train, belt mechanism, etc.) not shown. These constitute secondary transfer roller driving means for rotationally driving the secondary transfer roller 30.
The fixed portion 80 a of the electromagnetic clutch 80 is fixed to the first shaft member 32, and the movable portion 80 b is fixed to the drive gear 81 and can slide on the first shaft member 32 together with the drive gear 81. The electromagnetic clutch 80 constitutes a drive transmission canceling unit that transmits and cancels the driving force of the secondary transfer roller driving unit.

When the electromagnetic clutch 80 is OFF, the fixed portion 80a and the movable portion 80b are separated as shown in FIG. 2, and the transmission of the rotational force of the drive gear 81 to the secondary transfer roller 30 is released. Yes. Therefore, the secondary transfer roller 30 is rotatable and is in a state where it can be rotated together.
When the electromagnetic clutch 80 is turned on, the electromagnetic coil in the fixed portion 80a is excited, and the fixed portion 80a adsorbs the movable portion 80b and becomes integrated as shown in FIG. Therefore, the rotational force of the drive gear 81 is transmitted to the secondary transfer roller 30 and rotationally drives the secondary transfer roller 30. At that time, the moving speed of the surface of the intermediate transfer belt 21 is made equal to the speed of the outer peripheral surface of the secondary transfer roller 30.

[Control system configuration example]
FIG. 7 is a block diagram showing a control system as a control means for each drive motor and electromagnetic clutch according to the present invention by the control unit of the color copying apparatus shown in FIG.
The control unit 110 includes a CPU that is a central processing unit, a ROM that is a program memory, a RAM that is a data memory, and the like, and controls the operation of each unit of the color copying apparatus shown in FIG. Have the image formed. However, FIG. 7 shows only the control system as the control means for each drive motor and electromagnetic clutch according to the present invention.

The controller 110 controls the motor drive circuits 27, 37, and 67 to drive and stop the intermediate transfer belt drive motor 28, the secondary transfer roller drive motor 38, and the cam drive motor 58, respectively, at predetermined timings. .
The intermediate transfer belt drive motor 28 is a motor for rotating the drive roller 22 in FIG. 1 to rotate the intermediate transfer belt 21 in a direction indicated by an arrow at a predetermined speed.
The secondary transfer roller drive motor 38 rotates the drive gear 81 in FIGS. 2 to 4 at a predetermined speed, and rotates the secondary transfer roller 30 at a predetermined speed when the electromagnetic clutch 80 is ON. It is a motor of the next transfer roller driving means.

  The cam drive motor 58 rotates the first eccentric cam 50 and the second eccentric cam 51 fixed to one end of the penetrating shaft member 24a of the secondary transfer counter roller 24 as described with reference to FIG. This is a motor that expands the distance (distance between the axes) between the opposing roller 24 and the secondary transfer roller 30.

The control unit 110 also controls the clutch drive circuit 87 to control ON (transmission) and OFF (release) of the electromagnetic clutch 80 shown in FIGS.
The light receiving signal from the light receiving element of the optical sensor 60 shown in FIGS. 2 to 4 is input, and the first eccentric cam is based on the driving amount of the cam driving motor 58 from the timing when the light receiving signal is interrupted. 50 and the rotational angle positions of the eccentric cam portions 50a and 51a of the second eccentric cam 51 are grasped.

  When starting image formation, the control unit 110 generates a trigger signal as a reference for the sequence operation, and controls the operation timing of each unit by time management (by counting the clock signal) based on the trigger signal. to decide. Therefore, the timing at which the leading edge of the recording sheet enters the secondary transfer portion and the timing at which the trailing edge escapes from the secondary transfer portion can also be determined or predicted.

[Example of operation of secondary transfer unit components]
1. First Operation Example of Illustrated Embodiment In the embodiment described with reference to FIGS. 2 to 7 (illustrated embodiment), the secondary transfer counter roller 24 and the secondary transfer roller 30 described above are in the middle during image formation. During the period other than the time when the leading edge of the recording sheet enters the secondary transfer portion that faces the transfer belt 21 across the transfer belt 21, the above-described secondary transfer portion constituting portion is in the state shown in FIG. This period is a period in which there is no recording sheet in the secondary transfer portion, or during the secondary transfer of the toner image on the intermediate transfer belt 21 to the recording medium.

  In the state shown in FIG. 2, the first and second eccentric cams 50 and 51 are opposed to the first and second idling rollers 34 and 35 at the portions where the dimension from the rotation center of the cam portions 50a and 51a is the shortest. Stopped at the rotation position. Accordingly, the eccentric cam portions 50a and 51a are separated from the first and second idling rollers 34 and 35, and the secondary transfer roller 30 is moved to the secondary transfer counter roller 24 side by the restoring force of the compression coil spring 43 shown in FIG. Is pressed against the surface of the intermediate transfer belt 21 to form a secondary transfer nip at the secondary transfer portion as shown in FIG.

At this time, the test part 59a of the disk 59 to be detected enters between the light emitting element and the light receiving element of the optical sensor 60 and blocks the optical path between them, and the light reception signal from the light receiving element is interrupted. It has become.
Further, since the electromagnetic clutch 80 is OFF and the fixed portion 80a and the movable portion 80b are not connected apart from each other, the secondary transfer roller 30 is driven by the rotational force of the drive gear 81 due to the rotation of the secondary transfer roller drive motor 38. Communication to is released. Therefore, the secondary transfer roller 30 is rotatable and is in a state where it can be rotated together.

  Therefore, when there is no recording sheet in the secondary transfer portion, the secondary transfer roller 30 is brought into direct contact with the surface of the intermediate transfer belt 21 and is moved along with the movement, and the secondary transfer portion having the recording sheet in the secondary transfer portion. In the middle, the secondary transfer roller 30 contacts the back surface of the recording medium, and rotates along with the recording medium being conveyed by the movement of the intermediate transfer belt 21.

  When the leading edge of the recording sheet enters the secondary transfer portion and when the trailing edge of the recording sheet escapes from the secondary transfer portion, as shown in FIG. 3, the electromagnetic clutch 80 is turned on and the fixing portion 80a is turned on. And the movable part 80b are connected. As a result, the rotational force of the drive gear 81 due to the rotation of the secondary transfer roller drive motor 38 is transmitted to the secondary transfer roller 30, and the secondary transfer roller 30 is rotationally driven at the aforementioned predetermined speed.

Further, in this embodiment, the cam drive motor 58 is operated at this time, and the first and second eccentric cams 50 and 51 are rotated 180 ° from the state of FIG. 2 by the driving force, and the eccentric cam portions 50a and 51a are rotated. The portion with the longest dimension from the center is set to the rotational position facing the first and second idling rollers 34 and 35.
Accordingly, the first and second idling rollers 34 and 35 are pushed downward, and as shown in FIGS. 4 and 6, the interval between the secondary transfer counter roller 24 and the secondary transfer roller 30 is widened, and the intermediate transfer belt. A gap is formed between 21 and the secondary transfer roller 30. Therefore, the secondary transfer roller 30 rotates alone in a state of being separated from the intermediate transfer belt 21.

  The operation flow when the recording medium (recording sheet) according to the first operation example passes through the secondary transfer portion will be described with reference to the timing chart of FIG. A predetermined time required for the operation for forming a gap between the intermediate transfer belt 21 and the secondary transfer roller 30 and the operation for eliminating the gap is defined as a time T. Since this time T depends on the operating speed of the image forming apparatus, it is set in advance according to the model. Further, t1 in FIG. 8 indicates a predicted time point when the leading end of the recording medium enters the secondary transfer portion, and t2 indicates a predicted time point when the trailing end of the recording medium exits the secondary transfer portion.

(A) Before the recording medium arrives just before the secondary transfer portion Both the cam drive motor 58 and the electromagnetic clutch 80 are OFF, and the secondary transfer roller 30 is in contact with the intermediate transfer belt 21 in a rotatable state. The intermediate transfer belt 21 rotates with the movement.

(B) Immediately before the leading edge of the recording medium enters the secondary transfer portion The cam drive motor 58 is turned on and the intermediate transfer belt 21 is turned on for a time T before the predicted time t1 when the leading edge of the recording medium enters the secondary transfer portion. And the secondary transfer roller 30 are started. At the same time, the electromagnetic clutch 80 is turned on to start driving the secondary transfer roller 30.

(C) Time point when the leading edge of the recording medium enters the secondary transfer portion After the time T (predicted time point t1), the gap formation is completed. Simultaneously with the completion, the electromagnetic clutch 80 is turned off to stop the driving of the secondary transfer roller 30 and to rotate freely.
(D) Immediately after the leading edge of the recording medium enters the secondary transfer portion The cam drive motor 58 is turned on and the clearance releasing operation is started immediately. After time T, the clearance is completed and the cam drive motor 58 is turned off. During this time T, the leading margin of the recording medium is passing through the secondary transfer nip, and the secondary transfer is not performed.

(E) During secondary transfer There is no gap, and the secondary transfer roller 30 rotates with the movement of the intermediate transfer belt 21 across the recording medium.
(F) The rear end of the recording medium is in the same state as (a) when and after exiting the secondary transfer portion.

In this way, the secondary transfer roller 30 rotates along with the intermediate transfer belt 21 when the toner image is transferred to the recording sheet and when there is no recording sheet in the secondary transfer portion. Therefore, even if the secondary transfer roller 30 changes in diameter due to component variations or environmental changes, no linear speed difference occurs between the intermediate transfer belt 21 and the secondary transfer roller 30.
Therefore, it is possible to prevent the occurrence of transfer blur at the primary transfer portion due to the linear velocity difference and image blur due to the looseness of the intermediate transfer belt 21.

In addition, since the detection toner image is formed on the intermediate transfer belt 21 and the density adjustment and position adjustment of the image are not caused, a difference in linear velocity is not generated, so that it is possible to prevent the detection accuracy from being deteriorated due to transfer blur. is there.
Further, when the recording sheet enters the secondary transfer portion, the first and second eccentric rollers 50 and 51 are pushed down by the first and second eccentric cams 50 and 51, and the secondary transfer roller 30 and the intermediate transfer belt 21 are pushed down. Since a gap is formed between the recording sheet and the recording sheet, the impact when the recording sheet enters the secondary transfer portion can be reduced, and the occurrence of shock jitter can be suppressed.

  At this time, since the secondary transfer roller 30 rotates alone by the driving force of the secondary transfer driving means, the secondary transfer roller 30 stops the speed difference between the intermediate transfer belt 21 and the secondary transfer roller 30. It can be made smaller than the case. Therefore, it is possible to reduce the load fluctuation when the intermediate transfer belt 21 and the secondary transfer roller 30 are in contact with each other, thereby suppressing the occurrence of shock jitter.

2. Second Operation Example of Illustrated Embodiment Next, with respect to the second operation example of the illustrated embodiment, the operation flow when the recording medium (recording sheet) passes through the secondary transfer unit is shown in the timing chart of FIG. Will be explained.
In the second operation example, when the leading edge of the recording sheet enters the secondary transfer portion and when the trailing edge of the recording sheet escapes from the secondary transfer portion, the state shown in FIG. A gap is formed between the intermediate transfer belt 21 and the secondary transfer roller 30, and the secondary transfer roller 30 is rotated alone. The time T and the time points t1 and t2 are the same as those in FIG.

During the other periods, the above-described secondary transfer portion constituent portions are in the state shown in FIG. This period is a period in which there is no recording sheet in the secondary transfer portion, or during the secondary transfer of the toner image on the intermediate transfer belt 21 to the recording medium.
The same operation as (a) to (e) described above is performed from before the recording medium arrives just before the secondary transfer portion until most of the period during the secondary transfer. The same operations as in (b) to (d) described above are performed immediately before the trailing edge of the recording medium escapes from the secondary transfer portion, that is, from the time point T before the predicted time t2 when the trailing edge of the recording medium escapes. To do.

(G) Immediately before the rear end of the recording medium escapes from the secondary transfer portion, the cam drive motor 58 is turned on and intermediate transfer is performed for a time T before the predicted time t2 when the rear end of the recording medium escapes from the secondary transfer portion. A gap forming operation between the belt 21 and the secondary transfer roller 30 is started. At the same time, the electromagnetic clutch 80 is turned on to start driving the secondary transfer roller 30.

(H) Time point at which the trailing edge of the recording medium escapes from the secondary transfer portion After the time T (predicted time point t2), the gap formation is completed. Simultaneously with the completion, the electromagnetic clutch 80 is turned off to stop the driving of the secondary transfer roller 30 and to rotate freely.
(I) Immediately after the trailing edge of the recording medium escapes from the secondary transfer portion, the clearance release operation is started immediately with the cam drive motor 58 turned on. After time T, the clearance is completed and the cam drive motor 58 is turned off. During this time T, the secondary transfer roller 30 is stopped because it is initially separated from the intermediate transfer belt 21, but immediately comes into contact with the intermediate transfer belt 21 and moves with it.

(J) After the passage of time T after the trailing edge of the recording medium escapes from the secondary transfer portion After the time T has elapsed from the predicted time t2 when the trailing edge of the recording medium escapes from the secondary transfer portion, the same state as (a) become.

Depending on the thickness of the recording medium and the process linear velocity, it is conceivable that the load fluctuation of the intermediate transfer belt 21 occurs even when the recording medium escapes from the secondary transfer portion.
However, according to the above, since the gap is formed between the secondary transfer roller 30 and the intermediate transfer belt 21 even when the recording sheet escapes from the secondary transfer portion, the recording sheet becomes the secondary transfer portion. It is also possible to reduce load fluctuations and shocks when escaping from the vehicle, and to suppress the occurrence of shock jitter.

  Also in this case, since the secondary transfer roller 30 rotates independently by the driving force of the secondary transfer driving means, the speed difference between the intermediate transfer belt 21 and the secondary transfer roller 30 can be reduced, and the intermediate transfer belt It is possible to reduce the load fluctuation when 21 and the secondary transfer roller 30 are in contact with each other, thereby suppressing the occurrence of shock jitter.

3. First Operation Example of Other Embodiments In the above-described embodiments, means for widening the interval between the secondary transfer counter roller 24 and the secondary transfer roller 30 (first and second eccentric cams rotated by the cam drive motor 58). 50, 51 etc.). Then, due to the action of the means, when the leading edge of the recording medium enters the secondary transfer section, or at that time and when the trailing edge of the recording medium escapes from the secondary transfer section, the above-mentioned interval is widened and intermediate transfer is performed. A gap was formed between the belt 21 and the secondary transfer roller 30.

However, the present invention can also be applied to an image forming apparatus of a type that does not include a means for widening the above-described interval and always contacts the secondary transfer roller 30 and the intermediate transfer belt 21 of the secondary transfer portion.
Another embodiment is an embodiment when the present invention is applied to such an image forming apparatus. This corresponds to a basic embodiment of the present invention.
Regarding the first operation example, the flow of the operation when the recording medium (recording sheet) passes through the secondary transfer portion will be described with reference to the timing chart of FIG.
The time points t1 and t2 in FIG. 10 are the same as those in FIGS. 8 and 9, but the time T that is a predetermined time is not necessarily the same as the time T in FIGS. 8 and 9, and can be arbitrarily set.

In the case of the first operation example shown in FIG. 10, when the recording medium enters the secondary transfer portion, that is, from the predicted time t1 when the leading edge of the recording medium enters the secondary transfer portion, from the time T to the predicted time t1. During this period, the electromagnetic clutch 80 is turned on and the secondary transfer roller 30 is driven to rotate.
During other periods, the electromagnetic clutch 80 is turned off and not connected, the transmission of the driving force of the secondary transfer roller drive motor 38 is released, and the secondary transfer roller 30 is made rotatable, and the intermediate transfer belt 21 is moved. Rotate around.

Also by doing so, the load fluctuation when the recording medium enters the secondary transfer portion can be suppressed by the rotation of the secondary transfer roller, and the occurrence of shock jitter can be suppressed.
In addition, when the toner image is transferred to the recording sheet and when there is no recording sheet in the secondary transfer portion, the secondary transfer roller 30 rotates along with the intermediate transfer belt 21, so that the intermediate transfer belt 21 is rotated. And a speed difference between the secondary transfer roller 30 does not occur.

  Therefore, it is possible to prevent the occurrence of transfer blur in the primary transfer portion and the occurrence of image rubbing due to the looseness of the intermediate transfer belt 21. Further, since the detection toner image is formed on the intermediate transfer belt 21 and the density adjustment or position adjustment of the image is not caused, a difference in linear velocity is not generated, so that deterioration of detection accuracy due to transfer blur can be prevented. is there.

4). Second Operation Example of Other Embodiment Next, regarding the second operation example of the other embodiment, the operation flow when the recording medium (recording sheet) passes through the secondary transfer portion is shown in the timing chart of FIG. Will be explained.
In the second operation example, when the leading edge of the recording medium enters the secondary transfer portion and when the trailing edge of the recording medium escapes from the secondary transfer portion, the secondary transfer roller 30 is moved to the secondary transfer roller 30. The driving force of the driving motor 38 is transmitted, and during the other period, the driving force is released to make the secondary transfer roller 30 rotatable, and the intermediate transfer belt 21 is rotated together.

That is, a period from a predicted time t1 before the predicted time t1 when the leading edge of the recording medium enters the secondary transfer portion to a predicted time t1 and a time T from the predicted time t2 when the trailing edge of the recording medium escapes from the secondary transfer portion. The secondary transfer roller 30 is rotationally driven by turning on the electromagnetic clutch 80 only during the period from the previous time to the prediction time t2.
In this way, load fluctuations and impacts when the recording medium escapes from the secondary transfer portion can be mitigated, and the occurrence of shock jitter at that time can also be suppressed.

[Other Embodiments of Image Forming Apparatus]
Next, another embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. The overall configuration of the image forming apparatus of this embodiment is the same as that of the image forming apparatus described above with reference to FIG. The configuration of the parts related to the secondary transfer device and the intermediate transfer device is also mostly the same as that of the above-described image forming apparatus.
Therefore, in FIG.12 and FIG.13, the same code | symbol is attached | subjected to the same part as FIGS. 1-7, and those description is abbreviate | omitted.

  FIG. 12 is an enlarged cross-sectional view showing portions related to the secondary transfer device and the intermediate transfer device in the image forming apparatus of this embodiment. The secondary transfer device including the secondary transfer roller 30 shown in FIG. 12 includes a secondary transfer roller gear 81 at the end of the secondary transfer roller shaft 32. Further, a coupling gear 82 that meshes with the secondary transfer roller gear 81 is provided on the secondary transfer unit side. The coupling gear 82 is configured to be fitted to the drive unit side coupling 83, and the drive unit side coupling 83 is rotated by the acting force of the secondary transfer drive unit.

  Further, the secondary transfer device includes support brackets 84 and 85 that support the secondary transfer roller 30. The support brackets 84 and 85 are engaged with positioning portions 18 a and 19 a provided on the side plates 18 and 19 of the intermediate transfer device including the intermediate transfer belt 21 to determine the position of the secondary transfer device. Yes.

FIG. 13 is a schematic front view of the secondary transfer device and the intermediate transfer device shown in FIG. 12 as viewed from the left. The positioning portions 19a are arranged in pairs at two positions with a gap in the left-right direction (recording medium transport direction) when viewed from the front (one is the main reference and the other is the sub-reference). 19a engages with the support bracket 85.
Although not shown in FIG. 13, the right side positioning portion 18 a and the support bracket 84 in FIG. 12 have the same configuration, and the positioning portions 18 a are arranged in pairs at two locations.
The places where the driving force of the driving means for driving the secondary transfer roller 30 is input to the secondary transfer device are the coupling gear 82 and the drive unit side coupling 83, which are secondary as shown in FIG. When viewed from the axial direction of the transfer roller, it is disposed in an extended region indicated by T between the two positioning portions 19a.

With this configuration, since the secondary transfer device is positioned with respect to the intermediate transfer device, the impact force generated when the secondary transfer roller 23 and the intermediate transfer belt come into contact with each other is set to the side plate 18 of the intermediate transfer device. It can be received by positioning portions 18a, 19a provided at 19.
Therefore, it is possible to prevent transfer blur that occurs due to the impact transmitted to the primary transfer portion.
At this time, the positions of the coupling gear 82 that couples the secondary transfer device and the secondary transfer drive device and the drive unit side coupling 83 are within the extension region between the two positioning portions 18a and at two locations. It exists in the extension area | region between the positioning parts 19a. Therefore, it is possible to ensure the positional accuracy of the coupling gear 82 and the drive unit side coupling 83.
Accordingly, it is possible to prevent uneven transfer due to the occurrence of uneven rotation of the secondary transfer roller due to the misalignment of the axes of both.

In addition, since there is a drive input section between the two positioning sections, the distance between the positioning section and the drive input section can be reduced, and the secondary transfer driving force can be applied to the secondary transfer apparatus and the intermediate transfer apparatus as a whole. The acting force to move can be reduced. For this reason, it is possible to prevent the occurrence of uneven transfer due to fluctuations in the positions of the secondary transfer device and the intermediate transfer device.
Also in this embodiment, it is preferable to combine the driving force transmission to the secondary transfer roller and the timing control of the release according to the above-described embodiment. In addition, the functions of the above-described embodiments can be combined as appropriate.

In the above-described embodiment, the secondary transfer device and the driving device are separate, and the driving force is transmitted by fitting the coupling gear 82 and the driving unit side coupling 83.
However, there is no problem even if the secondary transfer device and the driving device are integrated. In this case, the pulling gear 72 and the drive unit side coupling 73 are replaced with one gear, and the gear and the secondary transfer roller gear 71 are engaged with each other to drive the secondary transfer roller 30.
Even in this case, since the drive input unit is in the extension region between the two positioning units, the distance between the positioning unit and the drive input unit can be reduced. Therefore, the secondary transfer driving force can reduce the acting force to move the entire secondary transfer device and the intermediate transfer device, and the positions of the secondary transfer device and the intermediate transfer device fluctuate to cause transfer unevenness. It is possible to prevent this.

In any of the above-described embodiments, the secondary transfer roller 30 can be an inexpensive foam roller having at least a skin layer formed of a foam material, which is cost-effective.
However, since the friction coefficient of the surface is high when the foam roller is used, the load fluctuation generated when the secondary transfer roller 30 and the intermediate transfer belt 21 come into contact with each other becomes larger. Therefore, the effect by this invention appears more notably.

[Image forming apparatus and recording medium]
The present invention is not limited to the color copying apparatus shown in FIG. 1, but is a mechanism capable of executing the operation of the secondary transfer unit according to the present invention, such as a color printer, a color facsimile apparatus, and a multifunction machine having a plurality of functions thereof. The present invention can be applied to various image forming apparatuses including
An image forming unit that forms a toner image on an image carrier uses each color developing device by switching, and sequentially forms toner images of each color on an image carrier such as a single photosensitive drum or a photosensitive belt. It may be of a type. The present invention can also be applied to an image forming apparatus that uses an intermediate transfer drum as an intermediate transfer member. In this case, a secondary transfer portion is formed between the intermediate transfer drum and a secondary transfer roller as a secondary transfer member, but a secondary transfer counter roller is not necessary.

  The recording medium has been described as an example of a recording sheet, but is also referred to as transfer paper, plain paper, cut paper, transfer sheet, recording material, etc., and a sheet-like member that can transfer a toner image on paper, resin sheet, leather, cloth, etc If it is.

1C, 1M, 1Y, 1K: Image forming unit (image forming unit)
2C, 2M, 2Y, 2K: photosensitive drum 10: tandem image forming unit
15: Optical writing unit 18, 19: Side plate of intermediate transfer device
18a, 19a: positioning unit 20: transfer unit 21: intermediate transfer belt
22: Drive roller 23: Driven roller 24: Secondary transfer counter roller
24a: Through shaft member 24b: Roller portion
25C, 25M, 25Y, 25K: primary transfer roller 26: belt cleaning device 27, 37, 67: motor drive circuit 28: intermediate transfer belt drive motor 29a: first side plate 29b: second side plate

30: Secondary transfer roller 31: Roller portion 32: First shaft member 33: Second shaft member 34: First idling roller 35: Second idling roller 38: Secondary transfer roller drive motor 40: Roller unit holder 41: Ball bearing 42: Support shaft
43: Compression coil spring 50: First eccentric cam 51: Second eccentric cam
50a, 51a: Eccentric cam portion 53a: First bearing 53b: Second bearing
54: Drive receiving gear 55: Worm wheel 56: Pinion
57: Worm gear 58: Cam drive motor 59: Detected disk
59a: Test part 60: Optical sensor 61: High voltage power supply
65: Motor bracket 66: Mounting plate

70: Paper transport belt 71: Fixing device 77: Sheet reversing device 80: Electromagnetic clutch 81: Drive gear 82: Coupling gear
83: Drive unit side coupling 84, 85: Support bracket
87: Clutch drive circuit 95: Positioning roller pair 100: Printer unit 110: Control unit 200: Paper feed table
300 Scanner unit 400 Automatic document feeder (ADF)

JP 2010-134061 A JP 2006-106113 A

Claims (12)

An image forming unit for forming a toner image on the image carrier;
A toner image formed on the image carrier by the image forming unit is primarily transferred to the surface, and an intermediate transfer member for secondary transfer of the toner image to a recording medium by a secondary transfer unit;
A secondary transfer member for forming the secondary transfer portion between the intermediate transfer member;
Secondary transfer member driving means for rotationally driving the secondary transfer member;
Drive transmission release means for transmitting and releasing the drive force of the secondary transfer member drive means to the secondary transfer member;
When the leading edge of the recording medium enters the secondary transfer portion, the driving force is transmitted to the secondary transfer member, and during other periods, the transmission of the driving force to the secondary transfer member is canceled. Control means for controlling the drive transmission release means so as to make the secondary transfer member rotatable;
An image forming apparatus comprising: An image forming unit for forming a toner image on the image carrier;
A toner image formed on the image carrier by the image forming unit is primarily transferred to the surface, and an intermediate transfer member for secondary transfer of the toner image to a recording medium by a secondary transfer unit;
A secondary transfer member for forming the secondary transfer portion between the intermediate transfer member;
Secondary transfer member driving means for rotationally driving the secondary transfer member;
Drive transmission release means for transmitting and releasing the drive force of the secondary transfer member drive means to the secondary transfer member;
When the leading end of the recording medium enters the secondary transfer portion and when the trailing end of the recording medium escapes from the secondary transfer portion, the driving force is transmitted to the secondary transfer member, and the other period Control means for controlling the drive transmission releasing means so as to release the transmission of the driving force to the secondary transfer member and to make the secondary transfer roller rotatable.
An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, further comprising means for widening a distance between the intermediate transfer member and the secondary transfer member, and when the leading edge of the recording medium enters the secondary transfer portion by the action of the means. In the image forming apparatus, a gap is formed between the intermediate transfer member and the secondary transfer member by widening the interval.   3. The image forming apparatus according to claim 2, further comprising means for increasing a distance between the intermediate transfer member and the secondary transfer member, and when the leading edge of the recording medium enters the secondary transfer portion by the action of the means. When the trailing edge of the recording medium escapes from the secondary transfer unit, the gap is increased to form a gap between the intermediate transfer member and the secondary transfer member.   The image forming apparatus according to claim 1, wherein the driving force is transmitted to the secondary transfer member from a predetermined time before a predicted time point when a leading edge of a recording medium enters the secondary transfer unit. An image forming apparatus having only a period up to a time point.   5. The image forming apparatus according to claim 2, wherein the driving force is transmitted to the secondary transfer member from a predetermined time before a predicted time point when a leading edge of a recording medium enters the secondary transfer unit. An image forming apparatus comprising: a period up to a time point; and a period from a predetermined time before the predicted time point when the trailing edge of the recording medium escapes from the secondary transfer unit to the predicted time point.   The image forming apparatus according to claim 3, wherein the gap is formed between the surface of the intermediate transfer member and the secondary transfer member from a predicted time point when the leading edge of the recording medium enters the secondary transfer portion. An image forming apparatus characterized by being only within a period from a predetermined time before the predicted time to a predetermined time.   5. The image forming apparatus according to claim 4, wherein the gap is formed between the surface of the intermediate transfer member and the secondary transfer member from a predicted time point when the leading edge of the recording medium enters the secondary transfer portion. Within a period from a predetermined time before the predicted time to a predetermined time and within a period from a predetermined time before the predicted time when the trailing edge of the recording medium escapes from the secondary transfer portion to a predetermined time after An image forming apparatus.   The image according to any one of claims 1 to 8, wherein the secondary transfer member is a secondary transfer roller, and at least a skin layer of the secondary transfer roller is formed of a foam material. Forming equipment. The intermediate transfer member is an intermediate transfer belt supported by a plurality of rollers,
The one of the plurality of rollers is a secondary transfer opposing roller that faces the secondary transfer member and supports the intermediate transfer belt from the back surface thereof. The image forming apparatus described in the item. The image forming apparatus according to claim 1, wherein
An intermediate transfer device provided with an intermediate transfer belt as the intermediate transfer member;
A secondary transfer device including a secondary transfer roller as the secondary transfer member;
Positioning the secondary transfer device relative to the intermediate transfer device, provided at least two positioning portions,
The portion where the power of the drive portion of the secondary transfer member drive means is input to the secondary transfer device is in the extension region between the two positioning portions as seen from the axial direction of the secondary transfer roller. An image forming apparatus.   12. The image forming apparatus according to claim 11, wherein power of a driving unit of the secondary transfer member driving unit is input to the secondary transfer device by fitting of a coupling.

Images