JP2013195875A - Image forming apparatus - Google Patents

Abstract

When a drive source of a contact / separation mechanism is in a non-energized state during a period of maintaining the contact / separation state between an image carrier and a transfer member, the switching timing of the contact / separation state in the contact / separation operation performed after that period It is an object to control with high accuracy.
An optical sensor for detecting a filler that moves integrally with the operation of an eccentric cam is provided, and the cam drive motor is energized during a contact maintaining period in which the contact state between the intermediate transfer belt and the secondary transfer roller is maintained. In the separation operation after the abutting maintenance period, the cam drive motor starts to be driven at a predetermined drive start timing, and then determined in advance based on the sensor output switching timing of the optical sensor. The cam drive motor is temporarily stopped so that the eccentric cam moves to a predetermined target position at a predetermined target time.
[Selection] Figure 8

Description

  The present invention relates to a copying machine, a facsimile, a printer, or the like that forms an image by transferring an image on the surface of the image carrier to the recording material in a state where the recording material is sandwiched between the surface of the image carrier and the surface of the transfer member. The present invention relates to an image forming apparatus.

  As this type of image forming apparatus, for example, each color toner image formed on a plurality of latent image carriers for the purpose of high image quality and high reliability is primarily transferred to an intermediate transfer member so as to overlap with each other, and then intermediate transfer is performed. A toner image that is secondarily transferred onto a recording material is known. In this image forming apparatus, a transfer bias is applied while the recording material sandwiched between the secondary transfer roller (transfer member) and the intermediate transfer member (image carrier) (transfer region) passes through the transfer region, As a result, the toner image on the intermediate transfer member is secondarily transferred to the recording material. In such an image forming apparatus, secondary transfer is not performed during standby for image forming operation or image quality adjustment operation (process control). Therefore, for the purpose of suppressing deterioration of the secondary transfer roller, Some have contact / separation means (opposing state switching means) for separating the transfer roller and the intermediate transfer member.

  Further, when the image carrier and the transfer member are always in contact with each other in the transfer area, for example, a recording material having high rigidity such as cardboard may be caused by an impact generated when the recording medium enters the transfer area or comes out of the transfer area. Shock jitter occurs on the image. In order to prevent this shock jitter, the transfer member is brought into contact with the image carrier at the timing immediately after the recording material enters the transfer area, and the transfer member is imaged at the timing immediately before the recording material comes out of the transfer area. There is also an image forming apparatus provided with contact / separation means for separating from a carrier (for example, Patent Document 1).

  Not only the image forming apparatus exemplified above, but also a moving mechanism that operates with a driving force from a driving source is operated to apply the facing state between the surface of the image carrier and the surface of the transfer member with a predetermined contact pressure. There are various known image forming apparatuses including a facing state switching unit that switches between a contacting state and a contact state that is smaller than a corresponding contact pressure or a non-contact state that separates both surfaces. As the facing state switching means, from the viewpoint of space saving and cost reduction of the apparatus, for example, by rotating the cam by a rotational driving force from a driving source such as a stepping motor, the surface of the image carrier and the transfer member Many use a cam mechanism that switches the state of opposition to the surface. Hereinafter, the problem of the present invention will be described by taking the case of using a cam mechanism as an example.

  When switching the facing state between the surface of the image carrier and the surface of the transfer member, the facing state between the surface of the image carrier and the surface of the transfer member is maintained constant except during the switching operation of the facing state. The source is not driven and is placed on standby. Conventionally, not only during the switching operation of the facing state but also during the period in which the facing state is maintained constant, the drive source continues to be energized. There was a problem of an increase in.

  In order to solve this problem, it is preferable to stop energization of the drive source during a period in which the facing state is kept constant. However, since the cam connected to the drive source is easy to rotate (non-fixed state) during the period when the energization to the drive source is stopped, the rotation angle of the cam is driven by the vibration of the image forming apparatus. It may change from the rotation angle before stopping energization to the source. For this reason, as described below, there arises a problem that the switching timing of the facing state between the surface of the image carrier and the surface of the transfer member cannot be controlled with high accuracy.

The facing state switching timing control is generally performed as follows from the viewpoint of cost reduction by simplification of the configuration and simplification of control.
First, a detection member that moves integrally with the rotation of the cam is provided, and detection means that detects the detection member when the rotation angle of the cam reaches a predetermined rotation angle is provided. And the said opposing state is switched by controlling the drive of the said drive source based on the detection timing which the detection means detected the to-be-detected member. The contents of control at this time will be described below by taking as an example a case of switching from the contact state to the non-contact state.

  In order to complete the switching to the non-contact state accurately at the time when the switching to the non-contact state should be completed (target time), the target time is started after the drive source is started and the cam is rotated. On the other hand, it is necessary to perform control so that the rotation angle of the cam becomes a target angle (target position) corresponding to the completion of switching to the non-contact state at a highly accurate timing. The time from the start of driving of the drive source until the cam rotation angle reaches a predetermined rotation angle can be grasped in advance with high accuracy.

  Therefore, in many cases, at the time of the previous facing state switching operation for switching from the non-contact state to the contact state, the control is performed such that the cam is stopped at the predetermined rotation angle and maintained at the rotation angle. It is normal. Specifically, the control is performed so that the cam is stopped based on the detection timing at which the detection unit detects the detected member during the previous facing state switching operation, and the cam is stopped at a predetermined rotation angle. It is normal. According to this control, the rotation angle when the cam is stopped can be controlled with high positional accuracy. Therefore, the rotation angle of the cam at the start of the next facing state switching operation is a specified rotation angle with high accuracy. As a result, at the time of the next facing state switching operation, driving of the driving source is started at a driving start timing that is calculated in advance from the target timing and is grasped in advance, so that the cam rotation angle is accurately set to the target angle at the target timing. Can be operated as follows. Therefore, the switching timing of the facing state between the surface of the image carrier and the surface of the transfer member can be controlled with high accuracy.

  However, even if the stop position of the cam at the previous switching operation is controlled with high positional accuracy, if the energization to the driving source is subsequently stopped as described above, driving of the driving source is started at the next switching operation. In some cases, the rotation angle of the cam changes from the stop position. In this case, in the normal switching timing control as described above, the cam cannot be accurately set to the target angle at the target time when the switching to the non-contact state should be completed.

  If a dedicated sensor that detects the cam rotation angle at the start of driving of the drive source at the next switching operation is provided, the cam rotation angle is adjusted by correcting the drive start timing from the detection result of the sensor. It is possible to set the target angle at the target time. However, the amount by which the cam rotation angle changes due to the vibration of the image forming apparatus during the state maintaining period is very small. For this reason, the drive start timing cannot be corrected with high accuracy unless a high-resolution sensor capable of detecting such a small amount of change is employed. Adding such a high resolution sensor increases the cost. Moreover, adding the arithmetic processing for correcting the drive start timing according to the detection result of such a dedicated sensor complicates the control contents.

Further, the above problem is not limited to stopping energization to the drive source during the state maintenance period, and the cam mechanism can be operated by applying an external force other than the drive force of the drive source during the state maintenance period. If there is a non-fixed period, the problem can occur as well.
In addition, the above problem can occur in the same manner even when another moving mechanism different from the cam mechanism is used.

  The present invention has been made in view of the above problems, and the object thereof is to provide a state in which a moving mechanism such as a cam is in a non-fixed state in the state maintaining period, even after the state maintaining period. An object of the present invention is to provide an image forming apparatus capable of controlling the switching timing with high accuracy in the switching operation in the facing state.

  To achieve the above object, the present invention provides an image carrier, image forming means for forming an image on the surface of the image carrier, and a recording material between the surface of the image carrier and the surface of a transfer member. In a state where the image carrier is sandwiched, a transfer means for transferring an image on the surface of the image carrier onto the recording material, and a moving mechanism is operated by a driving force from a driving source, whereby the surface of the image carrier and the image carrier Opposing state switching means for switching between a contact state in which the surface of the transfer member is contacted with a predetermined contact pressure and a non-contact state in which the contact surface is contacted with a contact pressure smaller than the contact pressure or both surfaces are separated from each other. Detecting means for detecting a detected member that moves integrally with the operation of the moving mechanism, and controlling the driving of the drive source based on a detection timing at which the detecting means detects the detected member. The surface of the image carrier and the surface of the transfer member An external force other than the driving force of the driving source is applied in a state maintaining period in which the facing state between the surface of the image carrier and the surface of the transfer member is maintained. When there is a non-fixed period in which the moving mechanism can operate and the control means switches the facing state after the state maintaining period in which the non-fixed period exists, Based on the detection timing at which the detection means detects the detected member, the moving mechanism is determined in advance at a predetermined target time based on the start of driving of the drive source at a predetermined drive start timing. The drive of the drive source is controlled so as to move to the target position.

  In the present invention, in the case where the facing state is switched after the non-fixed period in which the moving mechanism of the facing state switching means is in the non-fixed state has elapsed, the detecting means is the member to be detected after the driving of the drive source is started. Is detected. Based on the detection timing after the drive of the drive source is started, the drive of the drive source is controlled so that the moving mechanism operates to a predetermined target position at a predetermined target time. With such control, even if the operating position of the moving mechanism is unknown at the start of driving of the driving source, the operating position of the moving mechanism can be grasped by detection after the driving of the driving source is started. The target position can be moved with high accuracy at the target time.

  According to the present invention, even when a non-fixed period exists in the state maintenance period, an excellent effect is obtained that the switching timing can be controlled with high accuracy in the switching operation of the facing state performed after the state maintenance period.

1 is a configuration diagram illustrating an example of an image forming apparatus according to an embodiment. FIG. 2 is an enlarged schematic diagram illustrating a secondary transfer region and a surrounding configuration in a copying machine main body of the image forming apparatus. FIG. 6 is an enlarged cross-sectional view showing a peripheral configuration of a secondary transfer region. FIG. 6 is an enlarged schematic diagram illustrating a state of a secondary transfer region immediately before plain paper enters. FIG. 6 is an enlarged schematic diagram illustrating a state of a secondary transfer region immediately before entering a thick paper. It is an expansion schematic diagram which shows the state of the secondary transfer area | region which concerns on the other example just before making thick paper approach. It is explanatory drawing which shows an example of the relationship between the profile of an eccentric cam, and the axial distance L of a secondary transfer opposing roller and a secondary transfer roller. 6 is a flowchart illustrating a flow of contact / separation timing control during a print job for forming an image on a thick sheet. 6 is a timing chart when the facing state of the intermediate transfer belt and the secondary transfer roller is switched from a contact state to a separated state.

Hereinafter, an embodiment of an image forming apparatus to which the present invention is applied will be described.
FIG. 1 is a configuration diagram illustrating an example of an image forming apparatus according to the present embodiment.
The image forming apparatus includes a copying machine main body 100, a paper feed table 200 on which the copying machine main body 100 is placed, a scanner 300 attached on the copying machine main body 100, and an automatic document attached on the scanner 300. It is mainly composed of a transfer device (ADF) 400.

  The scanner 300 is placed on the contact glass 32 as the first traveling body 33 equipped with a document illumination light source or mirror and the second traveling body 34 equipped with a plurality of reflecting mirrors reciprocate. Scanning of a document (not shown) is performed. The scanning light sent out from the second traveling body 34 is condensed on the imaging surface of the reading sensor 36 installed behind the imaging lens 35 and then read as an image signal by the reading sensor 36.

  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 image forming unit 11 is provided with photosensitive drums 12Y, 12C, 12M and 12K which are latent image carriers. 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 21 that exposes the photosensitive drum 12 with laser light or LED light based on the image information to form a latent image is provided above the tandem image forming unit 10.

  Further, an intermediate transfer belt 20 as an image carrier made of an endless belt member is disposed at a lower position facing the photosensitive drum 12 of the tandem image forming unit 10. The intermediate transfer belt 20 is supported by support rollers 14, 15 and 16. A primary transfer roller 13 for transferring the toner images of the respective colors formed on the photosensitive drum 12 to the intermediate transfer belt 20 is disposed at a position adjacent to the photosensitive drum 12 via the intermediate transfer belt 20. Further, the intermediate transfer belt 20 is provided with a cleaning device 17 for removing toner remaining on the surface thereof.

  Under the intermediate transfer belt 20, secondary transfer is performed in which the toner images formed on the surface of the intermediate transfer belt 20 are collectively transferred onto a sheet as a transfer medium conveyed from the paper feed cassette 44 of the paper feed table 200. A roller 22 is arranged. The secondary transfer roller 22 contacts the support roller 16 via the intermediate transfer belt 20, and transfers the toner image on the intermediate transfer belt 20 to a sheet (not shown). Hereinafter, the support roller 16 is referred to as a secondary transfer counter roller 16.

  At a position adjacent to the secondary transfer roller 22, a conveyance belt 24 stretched around the two rollers 23 is provided to convey the secondary transferred sheet. A fixing device 25 is provided at a position adjacent to the conveyance belt 24. The fixing device 25 fixes the image on the sheet conveyed by the conveyance belt 24. 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. Below the secondary transfer roller 22 and the fixing device 25, a sheet reversing device 28 for reversing the sheet is disposed. The sheet reversing device 28 reverses the sheet to record images on both sides of the sheet.

Next, the operation of the image forming apparatus having the above configuration will be described.
First, a document is set on the document table 30 of the automatic document feeder 400 shown in FIG. 1, or the automatic document feeder 400 is opened and a document is set on the contact glass 32 of the scanner 300. close up. In this state, when a start switch (not shown) is pressed, when the document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 32, and then the document is set on the other contact glass 32. When this occurs, the scanner 300 is immediately driven to cause the first traveling body 33 and the second traveling body 34 to travel. The first traveling body 33 emits light from the light source and receives reflected light from the document surface, reflects the reflected light toward the second traveling body 34, and further reflects the reflected light by the mirror of the second traveling body 34. Then, the light enters the reading sensor 36 through the imaging lens 35, and the reading sensor 36 reads the content of the document.

  Further, by pushing a start switch of the apparatus, a drive motor (not shown) is driven to rotate one of the support rollers 14, 15, and 16 and the other two support rollers are driven to rotate, thereby performing intermediate transfer. The belt 20 is rotated. At the same time, in each image forming unit 11, the photosensitive drum 12 is uniformly charged by the charging device, and then charged by irradiating the writing light L from the exposure device 21 with a laser, LED, or the like according to the reading content of the scanner 300 An electrostatic latent image is formed on each photosensitive drum 12. Toner is supplied from the developing device to the photosensitive drum 12 on which the electrostatic latent image is formed, the electrostatic latent image is visualized, and black, yellow, magenta, and cyan single-color images are respectively formed on the photosensitive drums 12. Form. A single color image is sequentially primary transferred by the primary transfer roller 13 so as to overlap the intermediate transfer belt 20, and a composite color image is formed on the intermediate transfer belt 20. Residual toner is removed from the surface of the photoconductive drum 12 after image transfer by a photoconductor cleaning device, and the charge is removed by a static eliminator to prepare for image formation again.

  By pressing the start switch, one of the paper feed rollers 42 of the paper feed table 200 is selected and rotated, and the sheet is fed out from one of the paper feed cassettes 44 provided in multiple stages in the paper bank 43, and the separation roller 45. Then, the sheets are separated one by one and inserted into the sheet feeding path 46, conveyed by the conveying roller 47, guided to the sheet feeding path 48 in the copying machine main body 100, and abutted against the registration roller 49 and stopped. On the other hand, when the sheet is manually fed, the sheet feeding roller 50 is rotated to feed the sheet on the manual tray 51, and the sheet is separated one by one by the separation roller 52 and inserted into the manual sheet feeding path 53. Similarly, the registration roller Stop at 49. Next, the registration roller 49 is rotated in synchronization with the composite color image on the intermediate transfer belt 20, the sheet is fed between the intermediate transfer belt 20 and the secondary transfer roller 22, and transferred by the secondary transfer roller 22. Transfer the color image onto the sheet.

  The sheet carrying the unfixed toner image that has passed through the secondary transfer region between the intermediate transfer belt 20 and the secondary transfer roller 22 is conveyed to the fixing device 25, and the fixing device 25 applies heat and pressure to transfer the sheet. Fix the image as a permanent image. The sheet after image fixing is switched by the switching claw 55 and discharged by the discharge roller 56 and stacked on the paper discharge tray 57, or switched by the switching claw 55 and introduced into the sheet reversing device 28, where it is reversed. The image is again guided to the transfer position, an image is recorded on the back side, and then discharged onto the discharge tray 57 by the discharge roller 56. At this time, residual toner remaining on the intermediate transfer belt 20 after the image transfer is removed by the cleaning device 17 to prepare for the image formation by the tandem image forming unit 10 again.

FIG. 2 is an enlarged schematic view showing a secondary transfer region and its peripheral configuration in the copying machine main body 100 of the image forming apparatus according to the embodiment.
In the same figure, the secondary transfer counter roller 16 that partially wraps the belt around its own peripheral surface on the inner peripheral surface side of the intermediate transfer belt 20 backs up the deformable intermediate transfer belt 20 on its peripheral surface. It is responsible for maintaining the shape along a certain curvature. The secondary transfer roller 22 comes into contact with the secondary transfer counter roller 16 on the intermediate transfer belt 20 from the outer peripheral surface side of the intermediate transfer belt 20 to form a secondary transfer nip.

  The secondary transfer roller 22 is rotatably held by the roller unit holder 60 via a bearing (not shown). The roller unit holding body 60 is configured to be rotatable about a rotation shaft 60 a disposed so as to take a posture parallel to the rotation axis of the secondary transfer roller 22. When the roller unit holding body 60 rotates counterclockwise around the rotation shaft 60a in the drawing, the secondary transfer roller 22 held by the roller unit holding body 60 is pressed against the intermediate transfer belt 20 and applied. Then, a secondary transfer nip is formed. Further, when the roller unit holding body 60 rotates in the clockwise direction in the drawing around the rotation shaft 60 a, the secondary transfer roller 22 held by the roller unit holding body 60 is separated from the intermediate transfer belt 20. Get in contact. In the image forming apparatus according to the embodiment, the biasing coil spring 65 always biases the end of the roller unit holding body 60 opposite to the rotation shaft 60 a toward the intermediate transfer belt 20. The urging coil spring 65 always applies a force to the roller unit holding body 60 to rotate counterclockwise in the drawing around the rotation shaft 60a, thereby causing the secondary transfer roller 22 to move to the intermediate transfer belt 20. It is energizing towards.

  The secondary transfer roller 22 is rotationally driven in the counterclockwise direction in the figure by transmitting the rotational driving force of a roller driving motor (not shown) via a drive transmission means such as a gear (not shown). These roller drive motors and drive transmission means are also held by the roller unit holder 60 and rotated together with the secondary transfer roller 22 and the roller unit holder 60. The roller unit holder 60 also holds a cleaning blade 64, a solid lubricant 61, a lubricant pushing device 63, and the like.

  The toner on the intermediate transfer belt adheres to the surface of the secondary transfer roller 22 that is in contact with the outer peripheral surface of the intermediate transfer belt 20 that carries the toner image. If this adhering toner is left as it is, it is transferred to the back surface of the recording sheet in the secondary transfer region, and so-called back contamination occurs. Therefore, in this copying machine, the toner is mechanically removed from the surface of the secondary transfer roller 22 by bringing the edge of the cleaning blade 64 into contact with the surface of the secondary transfer roller 22. In such a configuration, a load impeding the rotation is applied to the secondary transfer roller 22 due to the contact of the cleaning blade 64, so that the secondary transfer roller 22 is driven to rotate along with the intermediate transfer belt 20. I can't. For this reason, the secondary transfer roller 22 is rotationally driven by the roller drive motor described above.

  The lubricant pressing device 63 applies the lubricant powder to the secondary transfer roller 22 by pressing the solid lubricant 61 made of a zinc stearate lump or the like against the secondary transfer roller 22 by the biasing coil spring 62. By applying the lubricant in this way, an increase in rotational load due to contact between the cleaning blade 64 and the secondary transfer roller 22 is suppressed. In addition, occurrence of blade edge entrainment is also suppressed. Instead of pressing the solid lubricant 61 against the secondary transfer roller 22, a rotary application brush for applying the lubricant to the secondary transfer roller 22 while scraping the lubricant from the solid lubricant 61 may be provided.

Next, a characteristic configuration of the image forming apparatus according to the embodiment will be described.
FIG. 3 is an enlarged cross-sectional view showing a peripheral configuration of the secondary transfer region.
In the figure, the secondary transfer roller 22 includes a roller portion 22A, first and second shaft members 22B and 22C that protrude from both axial end surfaces of the roller portion 22A and extend in the rotational axis direction. It has a first idling roller 22D and a second idling roller 22E. The roller portion 22A includes a cylindrical hollow cored bar 22a, an elastic layer 22b made of an elastic material fixed to the peripheral surface thereof, and a surface layer 22c fixed to the peripheral surface thereof. .

  Examples of the metal constituting the hollow metal core 22a include stainless steel and aluminum, but are not limited to these materials. The elastic layer 22b is preferably 70 [°] or less in terms of JIS-A hardness. However, since the cleaning blade 64 is in contact with the roller portion 22A, if the elastic layer 22b is too soft, various problems are caused. Therefore, it is desirable that the elastic layer 22b has a JIS-A hardness of 40 [°] or more. An elastic layer 22b having a JIS-A hardness of about 50 [°] is 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 friction coefficient, the surface of the elastic layer 22b made of rubber is covered with the surface layer 22c. ing. As a result, toner adhesion to the surface of the roller portion 22A is suppressed, and the rubbing load with the blade is reduced. As a material for the surface layer 22c, 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 22 rotates in contact with the intermediate transfer belt 20, the secondary transfer roller 22 may have a slight linear velocity difference from the intermediate transfer belt 20. The surface layer 22c is adjusted so that the friction coefficient with the intermediate transfer belt 20 is 0.3 or less so that the intermediate transfer belt 20 does not slip due to this linear speed difference. The intermediate transfer belt 20 is required to be driven at a constant speed in order to transfer the toner images of the respective colors without color misregistration, so that the surface friction resistance of the surface layer 22c of the secondary transfer roller 22 is reduced. Is important.

  The secondary transfer roller 22 having such a configuration is biased toward the intermediate transfer belt 20 that is wound around the secondary transfer counter roller 16. The secondary transfer counter roller 16 that is wound around the intermediate transfer belt 20 passes through the roller portion 16B, which is a cylindrical main body portion, and the rotation center portion of the roller portion 16B in the rotation axis direction, while passing through the roller portion 16B. And a penetrating shaft member 16A that idles on its surface. The penetrating shaft member 16A is made of metal, and freely rotates the roller portion 16B on its peripheral surface. The roller portion 16B includes a drum-shaped hollow core 16a, an elastic layer 16b made of an elastic material fixed on the peripheral surface thereof, and ball bearings 16c press-fitted to both ends in the axial direction of the hollow core 16a. It has. The ball bearing 16c rotates on the through shaft member 16A together with the hollow core metal 16a while supporting the hollow core metal 16a. The elastic layer 16b is press-fitted into the outer peripheral surface of the hollow cored bar 16a.

  The through shaft member 16 </ b> A is rotatable by a first bearing 73 fixed to the first side plate 71 of the transfer unit that stretches the intermediate transfer belt 20 and a second ball bearing 74 fixed to the second side plate 72. It is supported. However, most of the time during the print job is stopped without being driven to rotate. Then, the roller portion 16 </ b> B that is to be rotated along with the endless movement of the intermediate transfer belt 20 is freely idled on its own peripheral surface.

  The elastic layer 16b fixed on the peripheral surface of the hollow core metal 16a is made of a conductive rubber material whose resistance value is adjusted by adding an ionic conductive agent so as to exhibit a resistance of 7.5 [LogΩ] or more. Has been. The reason why the electric resistance of the elastic layer 16b is adjusted within a predetermined range is that when a recording sheet having a relatively small size in the roller axial direction, such as A5 size, is used, the recording sheet is moved in the secondary transfer nip. This is for the purpose of preventing the transfer current from being concentrated at a location where the intermediate transfer belt 20 and the secondary transfer roller 22 are in direct contact without intervention. By making the electric resistance of the elastic layer 16b larger than the resistance of the recording sheet, it is possible to suppress such concentration of transfer current.

  In addition, as the conductive rubber material constituting the elastic layer 16c, foamed rubber is used so as to exhibit elasticity of about 40 [°] in Asker-C hardness. By forming the elastic layer 16c with such foamed rubber, the elastic layer 16c is flexibly deformed in the thickness direction in the secondary transfer nip to form a secondary transfer nip having a certain size in the sheet conveying direction. can do. In this image forming apparatus, as described above, for the convenience of bringing the cleaning blade 64 into contact with the secondary transfer roller 22, a material having high elasticity is used as the material of the roller portion of the secondary transfer roller 22. Is difficult. Therefore, instead of the secondary transfer roller 22, the roller portion 16B of the secondary transfer counter roller 16 is elastically deformed.

  In the penetrating shaft member 16A of the secondary transfer counter roller 16, the both end regions that are not located in the roller portion 16B in the entire longitudinal region are abutted against the secondary transfer roller 22, respectively. The eccentric cams 75 and 76 as members are fixed so as to rotate integrally with the through shaft member 16A. Specifically, the first eccentric cam 75 is fixed to one end region in the longitudinal direction of the penetrating shaft member 16A. In the first eccentric cam 75, an eccentric cam portion 75a and a true circular roller portion 75b are integrally formed side by side in the axial direction. The first eccentric cam 75 is fixed to the penetrating shaft member 16A by screwing the screw 75c penetrating the roller portion 75b into the penetrating shaft member 16A. A second eccentric cam 76 having the same configuration as the first eccentric cam 75 is fixed to the other end region in the longitudinal direction of the through shaft member 16A.

  A drive receiving pulley 77B is fixed to a region outside the second eccentric cam 76 in the axial direction of the through shaft member 16A. On the other hand, a cam drive motor 79 comprising a stepping motor is fixed to the second side plate 72 of the transfer unit. A drive output pulley 77A is fixed to the motor shaft of the cam drive motor 79. A timing belt 78 is stretched between the drive output pulley 77A and the drive receiving pulley 77B. Therefore, by driving the cam drive motor 79, the through shaft member 16A can be rotated, and thereby the first eccentric cam 75 and the second eccentric cam 76 fixed on the through shaft member 16A can be rotated. At this time, even if the penetrating shaft member 16A is rotated, the roller portion 16B can be freely idled on the penetrating shaft member 16A, so that the intermediate transfer belt 20 is prevented from rotating along with the roller portion 16B. There is no.

  When the facing state of the intermediate transfer belt 20 and the secondary transfer roller 22 is switched from the contact state shown in FIG. 3 to the non-contact state, the first eccentric cam 75 and the second eccentric cam are driven by the cam drive motor 79. By rotating 76, the respective cam surfaces abut against the idle rollers 22 </ b> D and 22 </ b> E of the secondary transfer roller 22, and push the idle rollers 22 </ b> D and 22 </ b> E against the urging force of the urging coil spring 65 of the roller unit holder. As a result, the secondary transfer roller 22 moves away from the secondary transfer counter roller 16, and the intermediate transfer belt 20 and the secondary transfer roller 22 are finally brought into a non-contact state.

  On the other hand, when the facing state of the intermediate transfer belt 20 and the secondary transfer roller 22 is switched from the non-contact state to the contact state shown in FIG. 3, the first eccentric cam 75 and the second eccentric cam 75 are driven by the drive of the cam drive motor 79. By rotating the eccentric cam 76, the idling rollers 22D and 22E are pushed down against the urging force of the urging coil spring 65 of the roller unit holding member in contact with the respective cam surfaces. As a result, the secondary transfer roller 22 moves in a direction approaching the secondary transfer counter roller 16, and finally, the intermediate transfer belt 20 and the secondary transfer roller 22 are in contact with each other by the biasing force of the biasing coil spring 65. become. At this time, the idle rollers 22 </ b> D and 22 </ b> E of the secondary transfer roller 22 are separated from the cam surfaces of the first eccentric cam 75 and the second eccentric cam 76.

  In such a configuration, the first eccentric cam 75, the second eccentric cam 76, the cam drive motor 79, the idling rollers 22D and 22E, the pulleys 77A and 77B, the timing belt 78, and the like are used to connect the intermediate transfer belt 20 and the secondary transfer roller 22. Opposing state switching means for switching the facing state is configured.

  In this image forming apparatus, the hollow cored bar 22a of the secondary transfer roller 22 is grounded, while a secondary transfer bias having the same polarity as the toner is applied to the hollow cored bar 16a of the secondary transfer counter roller 16. . As a result, a secondary transfer electric field for electrostatically moving the toner from the secondary transfer counter roller 16 side toward the secondary transfer roller 22 side is formed between both rollers in the secondary transfer nip.

  The first bearing 73 that rotatably receives the metal penetrating shaft member 16A of the secondary transfer counter roller 16 includes a conductive sliding bearing. The conductive first bearing 73 is connected to a high voltage power source (not shown) that outputs a secondary transfer bias. The secondary transfer bias output from the high voltage power source is guided to the secondary transfer counter roller 16 via the conductive first bearing 73. In the secondary transfer counter roller 16, a metal penetrating shaft member 16A, a metal ball bearing 16c, a metal hollow core 16a, and a conductive elastic layer 16b are sequentially transmitted.

  Further, a detected disk 81 as a detected member is fixed to one end of the penetrating shaft member 16A so that the center of the disk and the center of the rotating shaft of the penetrating shaft member 16A are coaxial. Therefore, the detected disk 81 rotates integrally with the first eccentric cam 75 and the second eccentric cam 76 fixed on the penetrating shaft member 16A. The detected disk 81 has a filler 81a that rises in the axial direction at a predetermined position in the rotation direction of the penetrating shaft member 16A.

  On the other hand, an optical sensor 80 is fixed to a device side plate (not shown). In the process of rotating the through-shaft member 16A, when the eccentric cams 75 and 76 are positioned within a predetermined rotation angle range, the filler 81a of the detected disk 81 enters between the light emitting element and the light receiving element of the optical sensor 80. To block the optical path between the two. When the light receiving element of the optical sensor 80 receives light from the light emitting element, it transmits a light receiving signal to a control unit (not shown). The control unit grasps the rotational angle positions of the eccentric cams 75 and 76 in accordance with the switching timing of the light reception signal from the light receiving element. In this embodiment, the sensor output is turned on when the intermediate transfer belt 20 and the secondary transfer roller 22 are in contact with each other, and the sensor output is turned off when in the non-contact state.

  As described above, the eccentric cams 75 and 76 abut against the idling rollers 22 </ b> D and 22 </ b> E of the secondary transfer roller 22 at a predetermined rotation angle, so that the secondary transfer roller 22 is against the urging force of the urging coil spring 65 and the secondary cam 22. Push down in a direction away from the transfer counter roller 16. The amount of depression at this time is determined by the rotational angle position of the eccentric cams 75 and 76. Note that the greater the amount by which the secondary transfer roller 22 is pushed down, the greater the distance between the axes of the secondary transfer counter roller 16 and the secondary transfer roller 22.

  In the secondary transfer roller 22, a first idling roller 22 </ b> D is provided on the first shaft member 22 </ b> B that rotates integrally with the roller portion 22 </ b> A so as to be idling. A second idling roller 22E having the same configuration as the first idling roller 22D is provided on the second shaft member 22C of the secondary transfer roller 22 so as to be idling. The idling rollers 22D and 22E against which the eccentric cams 75 and 76 of the secondary transfer counter roller 16 are abutted are prevented from rotating along with the abutment, but the rotation of the secondary transfer roller 22 is thereby prevented. There is no. This is because even if the idling rollers 22D and 22E stop rotating, the idling rollers are ball bearings, so that the shaft members 22B and 22C of the secondary transfer roller 22 freely rotate independently of the idling rollers. . By stopping the rotation of the idling rollers 22D and 22E in accordance with the abutment of the eccentric cams 75 and 76, the occurrence of friction between them is avoided, and the belt drive motor and the drive motor for the secondary transfer roller 22 due to the friction are avoided. It is also possible to avoid the occurrence of torque increase.

Figure 4 is an enlarged schematic view showing a state of the secondary transfer region immediately before advancing the plain paper P ₁ as a recording sheet.
In the image forming apparatus, plain paper P ₁ when to enter the secondary transfer area, as shown, the eccentric cam 75 and 76 of the secondary transfer counter roller 16, idle rollers 22D of the secondary transfer roller 22 , 22E is stopped at a position where it does not abut against 22E. That is, when the plain paper P ₁ is used, the secondary transfer roller 22 is not pushed down by the eccentric cams 75 and 76. Even if the secondary transfer roller 22 is not pushed down on the relatively thin plain paper P ₁ , a large load fluctuation on the intermediate transfer belt 20 and the secondary transfer roller 22 when entering the secondary transfer region does not occur. This is because problems such as shock jitter are unlikely to occur.

Figure 5 is an enlarged schematic view showing a state of the secondary transfer region immediately before advancing the cardboard P ₂ as a recording sheet.
Figure 6 is an enlarged schematic view showing a state of the secondary transfer region according to another embodiment immediately before advancing the cardboard P ₂ as a recording sheet.
In the image forming apparatus, when advancing the cardboard P ₂ to the secondary transfer region, the eccentric cam 75 and 76 of the secondary transfer counter roller 16, idle rollers 22D of the secondary transfer roller 22, abut against the 22E position Thus, the rotation of the through shaft member 16A of the secondary transfer counter roller 16 is stopped. That is, when using the thick paper _{P 2} performs a depression of by the eccentric cam 75 and 76 the secondary transfer roller 22. In relatively large cardboard P ₂ of thickness, if not carried out depression of the secondary transfer roller 22, to generate a large load fluctuations on the intermediate transfer belt 20 and the secondary transfer roller 22 during secondary transfer area entry, the shock jitter etc. This is because it is easy for problems to occur.

If to reduce the problem of shock jitter, etc. with the cardboard P _2, as shown in FIG. 5, to the contact pressure while keeping contact with the intermediate transfer belt 20 and the secondary transfer roller 22 may be reduced, As shown in FIG. 6, the intermediate transfer belt 20 and the secondary transfer roller 22 may be separated from each other.

Comparing FIG. 4 with FIG. 5, the length Wb of the secondary transfer nip in the intermediate transfer belt moving direction when the secondary transfer roller 22 is pushed down by the eccentric cams 75 and 76 is as follows. It becomes shorter than the length Wa. On the other hand, the inter-axis distance Lb between the secondary transfer opposing roller 16 and the secondary transfer roller 22 when the pressing is performed is larger than the inter-axis distance La when the pressing is not performed. When the distance between the axes is increased, the pressing force of the secondary transfer roller 22 against the intermediate transfer belt 20 is weakened, and the secondary transfer nip pressure is reduced. Accordingly, to suppress the occurrence of a sudden increase in the load to the intermediate transfer belt 20 and the secondary transfer roller 22 upon entering the cardboard P ₂ to the secondary transfer region, it is possible to suppress the occurrence of trouble such as shock jitter.

Further, referring to the example of FIG. 6, the inter-axis distance Lc between the secondary transfer counter roller 16 and the secondary transfer roller 22 when the pressing is performed is further larger than the inter-axis distance Lb in the example of FIG. In the example of FIG. 6, the pressing force against the intermediate transfer belt 20 of the secondary transfer roller 22 because it is zero, the sudden load increase for the intermediate transfer belt 20 and the secondary transfer roller 22 when the thick paper P ₂ enters Occurrence can be greatly suppressed, and problems such as shock jitter can be more effectively suppressed.

As described above, the example of FIG. 6 has a higher effect of reducing shock jitter and the like than the example of FIG. 5, so in this embodiment, as shown in FIG. 6, the intermediate transfer belt 20 and the secondary transfer roller 22 The structure which separates is adopted. However, in the example of FIG. 6, to the tip of the cardboard P ₂ into the secondary transfer region enters is the intermediate transfer belt 20 and the secondary transfer roller 22 and the separation state, but to reduce the shock jitter or the like, cardboard image region distal portion of the P ₂ needs to be able to realize an appropriate second transfer to form a secondary transfer nip between the intermediate transfer belt 20 and the secondary transfer roller 22 before entering. That is, from the tip of the cardboard P ₂ is enters the secondary transfer area, within a very short period until the image area the tip portion of the cardboard P ₂ enters the secondary transfer region, the intermediate transfer belt 20 secondary It is necessary to switch the facing state to the transfer roller 22 from the separated state to the contact state.

Further, in the present embodiment, in order to reduce even failure of shock jitter, etc. when the rear end of the cardboard P ₂ comes out from the secondary transfer region, after the image area rear end portion of the thick paper P ₂ has passed through the secondary transfer region The intermediate transfer belt 20 and the secondary transfer roller 22 are separated from the contact state to reduce shock jitter and the like. At this time, achieve an appropriate second transfer to form a secondary transfer nip between the up image area rear end portion of the thick paper P ₂ passes through the secondary transfer region to the intermediate transfer belt 20 and the secondary transfer roller 22 It needs to be possible. That is, the image area rear end portion of the thick paper P ₂ is passed through the secondary transfer region, in a very short period until the trailing edge of the cardboard P ₂ passes through the secondary transfer region, the intermediate transfer belt 20 secondary It is necessary to switch the facing state to the transfer roller 22 from the contact state to the separated state.

As described above, in the present embodiment, when forming an image on thick paper P _2, to switch the opposite state of the intermediate transfer belt 20 and the secondary transfer roller 22 with high precision timing is required.

  Here, in the present embodiment, in order to reduce a problem due to a temperature rise inside the copying machine and a problem of an increase in power consumption due to heat generation of the cam drive motor 79, a period during which the rotational drive of the cam drive motor 79 is stopped, That is, a non-energization period in which the energization to the cam drive motor 79 is stopped is provided in a period in which the intermediate transfer belt 20 and the secondary transfer roller 22 are maintained in the facing state (opposing state maintaining period). Specifically, a non-energization period is provided in at least one of a contact maintaining period in which the contact state is maintained and a separation maintaining period in which the separated state is maintained.

At this time, abutment sustain period and may be a non-energized period provided in both the period of spaced sustain period, but in the case of forming images continuously into cardboard P _2, in this embodiment, the secondary transfer region less time between paper between the cardboard P ₂ and thick paper P ₂ passes, thus also spaced sustain period short. In such a short period, the above-described problems of heat generation and increase in power consumption of the cam drive motor 79 are small. Conversely, if a non-energization period is provided in such a short period, the energization to the cam drive motor 79 is stopped. Energization is resumed soon afterwards, and the effect of reducing the problem is small just by making the control complicated. Therefore, in this embodiment, the non-energization period is provided only in the contact maintaining period.

  As described above, in this embodiment, a stepping motor is employed as the cam drive motor 79. Therefore, if energization is stopped while the cam drive motor 79 is stopped, the excitation of the stepping motor is released, and the rotation angle of the stepping motor can be changed by vibration of the image forming apparatus or the like. That is, the eccentric cams 75 and 76 are in a non-fixed state where the eccentric cams 75 and 76 can rotate due to vibration of the image forming apparatus. Therefore, during the contact maintaining period, the rotational positions of the eccentric cams 75 and 76 may change due to vibrations of the image forming apparatus.

  In the present embodiment, as described below, even if the rotational positions of the eccentric cams 75 and 76 change due to vibration of the image forming apparatus during the contact maintaining period, the contact is made at the end of the contact maintaining period. The timing for switching from the state to the separated state can be controlled with high accuracy.

FIG. 7 is an explanatory diagram showing an example of the relationship between the profile of the eccentric cams 75 and 76 and the inter-axis distance L between the secondary transfer opposing roller 16 and the secondary transfer roller 22.
FIG. 7 is a graph in which the rotation angle positions of the eccentric cams 75 and 76 are taken on the horizontal axis, and the inter-axis distance L between the secondary transfer opposing roller 16 and the secondary transfer roller 22 is taken on the vertical axis. The inter-axis distance L in this graph is set to zero when the opposing state of the secondary transfer opposing roller 16 and the secondary transfer roller 22 is actually switched. In FIG. 7, when the rotational angle positions of the eccentric cams 75 and 76 are within the angle range of 30 ° to 60 °, the intermediate transfer belt 20 and the secondary transfer roller 22 are in contact with each other. In the present embodiment, the control target value (stop position at the time of contact) of the rotation stop angle of the eccentric cams 75 and 76 in the contact maintaining period is set to 49 °.

  When switching from the separated state to the contact state, drive control of the cam drive motor 79 is performed to rotate the eccentric cams 75 and 76, and the eccentric cams 75 and 76 are cams at a rotation angle position at which the control target value is 49 °. The drive of the drive motor 79 is stopped. The rotational angles of the eccentric cams 75 and 76 at the time of stopping coincide with the control target value 49 ° with high accuracy. However, in this embodiment, energization to the cam drive motor 79 is stopped after the eccentric cams 75 and 76 are stopped, and no standby current is applied to the cam drive motor 79. Therefore, since the cam drive motor 79 is not in an excited state, the rotation angle of the eccentric cams 75 and 76 is a control target value (a stop target position at the time of contact) due to vibration of the image forming apparatus or the like during the contact maintaining period. There is a risk of slight change from 49 °.

  Therefore, when the contact state is switched from the contact state to the separated state after the contact maintaining period has elapsed, the rotation angles of the eccentric cams 75 and 76 at the start of driving of the cam drive motor 79 slightly change from the stop target position at the time of contact. The actual rotation stop angle is unknown. Therefore, the contact is made on the assumption that the rotation angle of the eccentric cams 75 and 76 at the start of driving of the cam drive motor 79 after the contact maintaining period has elapsed coincides with the contact stop target position (49 °). When the control to switch from the state to the separated state is performed, there is a possibility that the timing at which the intermediate transfer belt 20 and the secondary transfer roller 22 should be separated from each other exceeds the allowable range. is there.

  Therefore, in the present embodiment, during the operation of switching from the contact state to the separation state, specifically, the rotation angle of the eccentric cams 75 and 76 changes from the contact stop target position (49 °) to the separation stop target position (314). .. 5 °), the filler 81a is provided so that the sensor output of the optical sensor 80 changes from ON to OFF. In the present embodiment, the state in which the secondary transfer roller 22 faces the intermediate transfer belt 20 is actually switched when the rotational angles of the eccentric cams 75 and 76 are approximately 180 °. In the present embodiment, the sensor output is changed from ON to OFF before the time point at which the secondary transfer roller 22 is actually switched to the intermediate transfer belt 20. Specifically, for example, when the rotation angle of the eccentric cams 75 and 76 is about 80 °, the sensor output of the optical sensor 80 is set to be turned from ON to OFF.

Figure 8 is a flowchart showing the flow of and away from the timing control when a print job for forming an image to the thick paper P _2.
When a print job for forming an image to the thick paper P ₂ is inputted, first, it executes the home position detection of the rotation angle of the eccentric cam 75 and 76 (S1). This is because the cam drive motor 79 is in a non-energized state in the image forming operation standby state before job input, and the accurate rotation angles of the eccentric cams 75 and 76 are unknown. Note that the intermediate transfer belt 20 and the secondary transfer roller 22 are in a separated state in an image forming operation standby state before job input. In home position detection, the cam drive motor 79 is driven in reverse, and the cam drive motor 79 is stopped according to the timing at which the sensor output of the optical sensor 80 is switched from OFF to ON. Thereby, the eccentric cams 75 and 76 can be stopped with high accuracy at a position where the rotation angle becomes the separation target stop position (314.5 °).

  When the home positions of the eccentric cams 75 and 76 are thus detected, the cam drive motor 79 is kept energized and waits until the contact operation start timing arrives (S2). The contact operation start timing is determined by the process timing of the image forming operation, and is synchronized with, for example, the rotation timing of the registration roller 49. When the contact operation start timing arrives (Yes in S2), the reverse drive of the cam drive motor 79 is started (S3). As a result, the eccentric cams 75 and 76 rotate in the reverse direction from 314.5 ° toward the contact stop target position 49 °, and as shown in FIG. The inter-axis distance L with the roller 22 gradually decreases.

Then, the reverse drive of the cam drive motor 79 is stopped (S5) at a timing when a predetermined time determined in advance from the time of the contact operation start timing (S4). As a result, the eccentric cams 75 and 76 can be stopped at a position where the rotation angle becomes the stop target position (49 °) during contact, and the intermediate transfer belt 20 and the secondary transfer roller 22 are brought into contact with each other. Maintained. By such control, the rotation angle of the eccentric cams 75 and 76 can be set to the contact stop target position (49 °) at a highly accurate timing with respect to a predetermined target timing. Therefore, from the tip of the cardboard P ₂ is enters the secondary transfer area, within a very short period until the image area the tip portion of the cardboard P ₂ enters the secondary transfer region, the intermediate transfer belt 20 secondary The state of facing the transfer roller 22 can be appropriately switched from the separated state to the contact state.

  After switching to the contact state in this way, energization to the cam drive motor 79 is stopped (S6). Thereby, the heat generation of the cam drive motor 79 can be suppressed, and the power consumption can be reduced. Thereafter, a separation operation start timing calculated backward from a target timing at which the forward drive of the cam drive motor 79 should be stopped (a timing at which the rotation angle of the eccentric cams 75 and 76 should be set as a separation stop target position (314.5 °)). (S7), the forward drive of the cam drive motor 79 is started (S8). As a result, the eccentric cams 75 and 76 start rotating, and the sensor output of the optical sensor 80 is switched from ON to OFF when the rotation angle reaches approximately 80 ° (S9).

  If this switching is detected (Yes in S9), the drive of the cam drive motor 79 is temporarily stopped according to the detection timing (S10). As a result, the eccentric cams 75 and 76 can be stopped with high positional accuracy at a position where the rotation angle becomes the standby target position (94 °) before the separation operation.

  However, the rotation angle of the eccentric cams 75 and 76 at the time when the forward drive of the cam drive motor 79 is started is the relationship where the energization to the cam drive motor 79 is stopped, and the contact stop target position (49 ° ) Has an error ε. Therefore, the length of the period from the start of normal rotation driving of the cam drive motor 79 to the temporary stop of driving of the cam drive motor 79 according to the detection timing varies depending on the error ε. . Therefore, when the forward drive stop timing of the cam drive motor 79 is controlled in accordance with the forward drive start timing of the cam drive motor 79, the time is shifted from the target time at which the forward drive of the cam drive motor 79 should be stopped. Thus, the forward drive of the cam drive motor 79 stops.

Therefore, in this embodiment, the drive of the cam drive motor 79 is temporarily stopped according to the detection timing of the sensor output after the start of forward rotation drive of the cam drive motor 79, and the eccentric cams 75, 76 are set to the standby target positions before the separation operation ( 94 °) with a high positional accuracy, and waits while the energized state of the cam drive motor 79 is maintained. Then, the forward drive of the cam drive motor 79 is restarted (S12) in accordance with the arrival of the drive restart timing calculated backward from the target time at which the forward drive of the cam drive motor 79 should be stopped (S11). The target timing is that the image area rear end portion of the thick paper P ₂ is passed through the secondary transfer region, the rear end of the cardboard P ₂ is determined according to the very short time to exit the secondary transfer region Thus, it is obtained from the process timing of the image forming operation.

  Then, in accordance with the arrival of the separation operation stop timing that is calculated backward from the target time (S13), the forward drive of the cam drive motor 79 is stopped (S14). Accordingly, the eccentric cams 75 and 76 can be stopped at a position where the rotation angle becomes the stop target position (314.5 °) at the time of separation, and the intermediate transfer belt 20 and the secondary transfer roller 22 are separated from each other. Maintained.

The rotation angles of the eccentric cams 75 and 76 at the time when the normal rotation drive of the cam drive motor 79 is resumed are the standby target position (94 °) before the separation operation with high positional accuracy. Therefore, the forward drive of the cam drive motor 79 is resumed in accordance with the arrival of the drive resumption timing that is calculated backward from the target time at which the forward drive of the cam drive motor 79 is to be stopped, and the separation operation is stopped that is calculated backward from this target time. By stopping the forward drive of the cam drive motor 79 at the timing, the rotational angle of the eccentric cams 75 and 76 is set to the separation target stop position (314.5 °) at a highly accurate timing with respect to the target timing. can do. Therefore, the image area rear end portion of the thick paper P ₂ is passed through the secondary transfer region, in a very short period until the trailing edge of the cardboard P ₂ passes through the secondary transfer region, the intermediate transfer belt 20 secondary The state of facing the transfer roller 22 can be appropriately switched from the contact state to the separated state.

  When printing on the next thick paper remains (No in S15), the above-described steps S2 to S14 are repeated again. When printing on the next thick paper is lost (Yes in S15), the job is ended.

FIG. 9 is a timing chart when the facing state of the intermediate transfer belt 20 and the secondary transfer roller 22 is switched from the contact state to the separated state.
In this timing chart, the horizontal axis is time t, the motor speed of the cam drive motor 79, the sensor output of the optical sensor 80, and the time change of the inter-axis distance L between the secondary transfer counter roller 16 and the secondary transfer roller 22. It is shown. Time t is the time when the trailing edge of the thick paper P ₂ passes through the secondary transfer region to zero (t = 0), one graduation of the horizontal axis has a 10 [ms] units. Time the trailing edge of the thick paper P ₂ passes through the secondary transfer area (t = 0) is being grasped by the process timing of the image forming operation.

In the present embodiment, while the cardboard P ₂ is passing through the secondary transfer area, i.e., abutment sustain period contact between the intermediate transfer belt 20 and the secondary transfer roller 22 is maintained, 9 As shown in FIG. 3, the cam drive motor 79 is stopped for the most part, and the energization to the cam drive motor 79 is stopped for most of the stop period of the cam drive motor 79. Then, the cam drive motor 79 starts to rotate forward at the separation operation start timing (t = −120 [ms]) calculated backward from the timing when the rear end of the thick paper P ₂ passes through the secondary transfer region (t = 0). (Start of separation preliminary operation).

  In the process of the separation preliminary operation, the filler 81a is detected by the optical sensor 80, and the sensor output of the optical sensor 80 is switched from ON to OFF. This switching timing varies due to a slight change in the rotation angle of the eccentric cams 75 and 76 when the cam drive motor 79 is not energized. Here, it is assumed that the sensor output is switched from ON to OFF at time t = −60 ms. The drive of the cam drive motor 79 is temporarily stopped (t = −50 ms) after a predetermined time (here, 10 [ms]) has elapsed from the timing at which this sensor output switching is detected.

Thereafter, the eccentric cams 75 and 76 from the standby target position before the separation operation (94 °) to the rotational position (about 180 °) at which the facing state of the intermediate transfer belt 20 and the secondary transfer roller 22 switches from the contact state to the separation state. The drive of the cam drive motor 79 is resumed (t = −40 ms) at the timing (drive resume timing) before t = 0 by the time required to rotate the motor (here, 40 [ms]). Thus, as shown in FIG. 9, the time immediately before t = 0 the trailing edge of the thick paper P ₂ passes through the secondary transfer region, the intermediate transfer belt 20 and the secondary transfer roller 22 becomes the separated state. More specifically, the time immediately before t = 0 the trailing edge of the thick paper P ₂ passes through the secondary transfer region, the intermediate transfer belt 20 and the secondary transfer roller 22 becomes the separated state. Specifically, the image area rear end portion of the thick paper P ₂ is passed through the secondary transfer region, extremely short period until the trailing edge of the cardboard P ₂ passes through the secondary transfer region (in this case 10 [ms] ), The intermediate transfer belt 20 and the secondary transfer roller 22 are separated from each other. Then, 50 [ms] after the intermediate transfer belt 20 and the secondary transfer roller 22 are separated from each other, when the rotational angle of the eccentric cams 75 and 76 reaches the separation target stop position (314.5 °). Then, the drive of the cam drive motor 79 is stopped.

In the present embodiment, since the stops energizing the cam driving motor 79, the start of the spaced preliminary operation in the separating operation start timing from while the cardboard P ₂ is passing through the secondary transfer area, the optical sensor There is a variation in the time until the sensor output of 80 switches from ON to OFF. Therefore, the temporary stop timing of the cam drive motor 79 corresponding to the sensor output switching timing also varies. However, the drive resumption timing for resuming the drive of the cam drive motor 79 that has been paused is predetermined according to the target time, and therefore does not vary. Then, the rotation angle of the eccentric cam 75 and 76 at the time to restart the actuation of cam drive motor 79 is paused is controlled with high positional accuracy in the separation operation before the standby target position (94 °), the cardboard P ₂ images from the area rear end portion leaves the secondary transfer region, extremely short period until the trailing edge of the cardboard P ₂ passes through the secondary transfer region in the (10 [ms] in this case), and the intermediate transfer belt 20 two The state of facing the next transfer roller 22 can be appropriately switched from the contact state to the separated state.

According to this embodiment, the relationship that stops energizing the cam driving motor 79 while the thick paper P ₂ is passing through the secondary transfer area, the rotation stop angle of the eccentric cam 75 and 76 when abutting Although it deviates from the target stop position (error ε), the period during which the cam drive motor 79 is temporarily stopped changes according to the error ε. The state of facing the next transfer roller 22 does not affect the timing of switching from the contact state to the separated state.

  As shown in FIG. 9, in the present embodiment, the motor speed during the separation preliminary operation from the start of the forward rotation drive of the cam drive motor 79 to the temporary stop is determined by restarting the drive of the cam drive motor 79. From the motor speed during the separation main operation until the stop at the stop target position at the time of separation. This is because the separation preliminary operation has time, so the motor speed is reduced to reduce the influence of vibration on the secondary transfer during motor acceleration, while the separation main operation is rotated accurately in a short time. This is because it is necessary.

  In the present embodiment, during the operation of switching from the contact state to the separated state, an operation for temporarily stopping the cam drive motor 79 based on the sensor output switching timing (detection timing) is added to thereby determine a predetermined target. Although the eccentric cams 75 and 76 are moved to a predetermined target position at the time, a method in which such a pause operation is not performed may be used. For example, the motor speed of the cam drive motor 79 is changed based on the sensor output switching timing (detection timing) so that the eccentric cams 75 and 76 operate to a predetermined target position at a predetermined target time. Also good.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
An image carrier such as an intermediate transfer belt 20, an image forming unit such as a tandem image forming unit 10 that forms an image on the surface of the image carrier, a transfer of the surface of the image carrier and the secondary transfer roller 22, etc. The recording material is sandwiched between the surface of the member and a transfer means for transferring the image on the surface of the image carrier onto the recording material, and the drive force from a drive source such as a cam drive motor 79 is eccentric. A contact state in which the surface of the image carrier and the surface of the transfer member are contacted with a predetermined contact pressure by operating a moving mechanism such as cams 75 and 76, and a contact pressure smaller than the contact pressure. Detecting a detected member such as a contact state switching means such as a contact / separation means for switching to a non-contact state in which they are brought into contact with each other or separated from both surfaces, and a filler 81a that moves integrally with the operation of the moving mechanism. Detection means such as the optical sensor 80 and the detection means By controlling the drive of the drive source based on the detection timing at which the detected member is detected (timing at which the sensor output is switched from OFF to OFF), the facing state between the surface of the image carrier and the surface of the transfer member is changed. In an image forming apparatus having a control means for switching, during a state maintaining period (abutting maintaining period) in which the facing state of the surface of the image carrier and the surface of the transfer member is maintained, a driving force other than the driving force of the driving source There is a non-fixed period in which the moving mechanism can operate by applying an external force (vibration of the image forming apparatus, etc.), and the control means has the state maintaining period in which the non-fixed period exists. When the facing state is switched after the abutting maintenance period has elapsed, driving of the driving source is started at a predetermined driving start timing, and then the detection means is Based on the detection timing of detecting the detection member, as the moving mechanism to a target timing predetermined operates to predetermined target position, and controls the driving of the drive source.
According to this, even if the operating position of the moving mechanism is unknown at the time of starting the driving of the driving source, the operating position of the moving mechanism can be grasped by detection after the driving of the driving source is started. It can be moved to the target position with high accuracy.

(Aspect B)
In the aspect A, the control unit starts driving the drive source at the predetermined drive start timing, and then drives the drive source based on the detection timing at which the detection unit detects the detected member. Is then temporarily stopped, and then, a predetermined re-drive timing (a time earlier than the target time by a predetermined time required for the moving mechanism to operate from the temporary stop position to the target position) The driving of the driving source is controlled so that the driving of the driving source is resumed at the driving resumption timing).
According to this, as compared with control such as changing the motor speed of the cam drive motor 79 based on the sensor output switching timing (detection timing), the moving mechanism is moved to the target position at the target timing by simple control. It can be operated with accuracy.

(Aspect C)
In the aspect A or the aspect B, the control unit performs control to stop energization to the drive source during the state maintaining period, and the energization to the drive source is stopped to be in the non-fixed state. It is characterized by.
According to this, it is possible to alleviate the problem caused by the temperature rise inside the image forming apparatus and the problem of increased power consumption due to the heat generated by the drive source.

(Aspect D)
In any one of the above aspects A to C, the control means is after the image area on the recording material has passed through the transfer area between the surface of the image carrier and the surface of the transfer member. At a time before the trailing edge of the recording material passes, the surface of the image carrier and the surface of the transfer member are switched from a contact state to a non-contact state, and the leading edge of the next recording material is moved to the transfer region. Control is performed to switch the surface of the image carrier and the surface of the transfer member from the non-contact state to the contact state after entering, but before the image area of the recording material enters the transfer region. The non-fixed period exists in a state maintaining period in which the surface of the image carrier and the surface of the transfer member are maintained in contact with each other.
The contact maintaining period in which the surface of the image carrier and the surface of the transfer member are maintained in contact with each other is usually longer than the separation maintaining period in which the surface of the image carrier and the surface of the transfer member are maintained in a separated state. Since it is long, a high defect reduction effect can be obtained by providing the non-fixed period at least in the contact maintaining period.

(Aspect E)
In any one of the above aspects A to D, the drive source is a stepping motor.
According to this, the moving position of the moving mechanism can be controlled with high accuracy with a simple configuration.

(Aspect F)
In any one of the above aspects A to E, the moving mechanism is a cam mechanism that drives a cam by a driving force from the driving source.
According to this, the facing state between the surface of the image carrier and the surface of the transfer member can be switched with a simple configuration.

DESCRIPTION OF SYMBOLS 10 Tandem type image forming part 11 Image forming unit 12 Photosensitive drum 16 Secondary transfer counter roller 17 Cleaning device 20 Intermediate transfer belt 21 Exposure device 22 Secondary transfer roller 22D, 22E Rolling roller 24 Conveying belt 25 Fixing device 60 Roller unit holding Body 60a Rotating shaft 75, 76 Eccentric cam 77A, 77B Pulley 78 Timing belt 79 Cam drive motor 80 Optical sensor 81 Detected disk 81a Filler

JP 2010-122D142 A

Claims (6)

An image carrier;
An image forming means for forming an image on the surface of the image carrier;
Transfer means for transferring an image on the surface of the image carrier onto the recording material in a state where the recording material is sandwiched between the surface of the image carrier and the surface of the transfer member;
A contact state in which the surface of the image carrier and the surface of the transfer member are in contact with each other with a predetermined contact pressure by operating a moving mechanism with a driving force from a drive source, and a contact smaller than the contact pressure. Opposing state switching means for switching to a non-contact state in which the two surfaces are contacted or separated by pressure,
Detecting means for detecting a detected member that moves integrally with the movement mechanism;
An image having control means for switching the facing state between the surface of the image carrier and the surface of the transfer member by controlling the drive of the drive source based on the detection timing at which the detection means detects the detected member. In the forming device,
During the state maintaining period in which the surface of the image carrier and the surface of the transfer member are maintained, an external force other than the driving force of the driving source is applied, and the moving mechanism is in a non-fixed state. There is a non-fixed period,
The control means starts driving the drive source at a predetermined drive start timing when the facing state is switched after the state maintaining period in which the non-fixed period exists, and then the detection means An image forming apparatus that controls driving of the driving source so that the moving mechanism operates to a predetermined target position at a predetermined target time based on a detection timing at which a detected member is detected. . The image forming apparatus according to claim 1.
The control means starts driving the drive source at the predetermined drive start timing, and then temporarily stops driving the drive source based on the detection timing when the detection means detects the detected member. After that, at a predetermined re-drive timing that is a time before the target time by a predetermined time required for the moving mechanism to operate from the temporary stop position to the target position, An image forming apparatus that controls driving of the driving source so as to resume driving. The image forming apparatus according to claim 1 or 2,
The control means performs control to stop energization to the drive source during the state maintenance period,
An image forming apparatus, wherein the non-fixed state is achieved by stopping energization of the drive source. The image forming apparatus according to any one of claims 1 to 3,
The control means is the time after the image area on the recording material passes through the transfer area between the surface of the image carrier and the surface of the transfer member and before the trailing edge of the recording material passes. , After the surface of the image carrier and the surface of the transfer member are switched from a contact state to a non-contact state, and after the leading edge of the next recording material enters the transfer region, the image region of the recording material Is a control to switch the surface of the image carrier and the surface of the transfer member from a non-contact state to a contact state before entering the transfer region,
An image forming apparatus, wherein the non-fixed period exists in a state maintaining period in which the surface of the image carrier and the surface of the transfer member are maintained in contact with each other. The image forming apparatus according to any one of claims 1 to 4, wherein:
An image forming apparatus, wherein the drive source is a stepping motor. The image forming apparatus according to any one of claims 1 to 5,
The image forming apparatus according to claim 1, wherein the moving mechanism is a cam mechanism that drives a cam by a driving force from the driving source.

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