JP5999494B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that transfers a toner image carried on an image carrier onto the surface of a belt member that moves endlessly or the surface of a recording member on the belt member.

  Conventionally, as this type of image forming apparatus, an intermediate transfer belt, which is a belt member supported by a plurality of stretching rollers, and a plurality of photoconductors arranged in parallel so as to contact and face the intermediate transfer belt, An intermediate transfer type tandem type color image forming apparatus is known (for example, Patent Document 1). In this apparatus, toner images of respective colors formed on the respective photoconductors are transferred onto the intermediate transfer belt that moves endlessly (primary transfer), and the toner images on the intermediate transfer belt are collectively transferred to the transfer material (secondary transfer). Transfer), a color image can be formed on the transfer material.

Some image forming apparatuses including an intermediate transfer belt are configured to selectively execute a single color mode and a multi-color mode. The single color mode is a mode in which one photoconductor is used to form an image composed of a single color toner image. The multiple color mode is a mode in which a plurality of photoconductors are used so as to form a color image in which a plurality of color toner images are superimposed.
In such an apparatus, in the single-color mode using one photoconductor, the other photoconductors are not used and are generally separated from the intermediate transfer belt. This is for the purpose of extending the life by suppressing the consumption of the photosensitive member, the parts around the photosensitive member, and the primary transfer member facing the photosensitive member across the intermediate transfer belt. In order to extend the service life, it is desirable that all the photoconductors are separated from the intermediate transfer belt when image formation is not performed.

  In the image forming apparatus described in Patent Document 1, the trajectory of the intermediate transfer belt is changed by changing the position of the stretching roller that supports the intermediate transfer belt, and the intermediate transfer belt is brought into contact with and separated from the photosensitive member. Specifically, in the monochrome mode which is the monochrome mode, the intermediate transfer belt is separated from the other photoconductors, and when no image is formed, the intermediate transfer belt is separated from all the photoconductors.

  The image forming apparatus disclosed in Patent Document 1 has a configuration capable of suppressing the occurrence of color misregistration due to the speed variation of the intermediate transfer belt. In this image forming apparatus, a scale having a plurality of marks arranged at a predetermined pitch in the belt circumferential direction is provided on the intermediate transfer belt. Then, the speed of the intermediate transfer belt is detected based on the time interval at which each mark on the scale is detected by the scale sensor. Feedback control of the driving speed of the belt driving motor based on the detection result reduces the speed fluctuation of the intermediate transfer belt.

  Patent Document 1 discloses a holding member that holds an upstream tension roller and a downstream tension roller in the moving direction of the intermediate transfer belt with respect to a detection position where the scale sensor detects a mark. A configuration in which a scale sensor is fixed is described. That is, the position of the scale sensor, the upstream tension roller, and the downstream tension roller is fixed to one holding member.

In this configuration, by moving the holding member, the position of the stretching roller held by the holding member is changed, the trajectory of the intermediate transfer belt is changed, and the intermediate transfer belt is brought into contact with and separated from the photoreceptor. In addition, since the scale sensor is fixed to the holding member that holds the tension roller on the upstream side and the tension roller on the downstream side of the detection position, even if the holding member moves, the tension sensor is stretched on the two tension rollers. The positional relationship between the tension surface of the intermediate transfer belt and the scale sensor does not change. In the configuration described in Patent Document 1, since the detection position is set on the tension surface between the upstream tension roller and the downstream tension roller, the intermediate transfer belt is moved when the contact / separation operation is performed. Even if the trajectory changes, the positional relationship between the intermediate transfer belt and the scale sensor in the portion including the detection position does not change.
Regardless of the contact / separation operation, the positional relationship between the intermediate transfer belt in the part including the detection position and the scale sensor does not change, so the scale sensor can detect the mark in either the contact state or the separation state. Can be done.

In the configuration of Patent Document 1, the holding member rotates about a rotation shaft so that an intermediate portion including a tension surface on which an upstream tension roller and a downstream tension roller are stretched is stretched. The contact / separation operation of the transfer belt with respect to the photosensitive member is performed. In addition, the distance from the rotation shaft is such that the downstream tension roller is separated from the upstream tension roller, and the displacement when the holding member is rotated is the downstream tension roller. Is larger.
In such a configuration, if the movement range due to the rotation of the holding member is small, the movement amount of the upstream tension roller near the rotation shaft becomes small, and the separation amount between the separated photosensitive member and the intermediate transfer belt Becomes smaller. If the separation amount is small, when the toner image is transferred to the intermediate transfer belt by the photosensitive member upstream of the separated photosensitive member, the photosensitive member and the intermediate transfer belt that should have been separated may have a tolerance or fluctuation. There is a risk of image rubbing due to contact due to the like.

  On the other hand, if the range of movement due to the rotation of the holding member is set to be large, the amount of movement of the upstream tension roller is also large, and contact between the photosensitive member and the intermediate transfer belt that should have been separated can be prevented. It is possible to prevent image blurring. However, if the movement range by the rotation of the holding member is set to be large so that the movement amount of the upstream tension roller is sufficiently large, the downstream side is located farther from the rotation shaft than the upstream tension roller. The amount of movement of the tension roller is greater than the amount of movement of the upstream tension roller. As a result, the trajectory of the intermediate transfer belt at the portion stretched by the downstream stretch roller changes greatly. In this way, if the track of the intermediate transfer belt changes greatly, a significant change in the belt tension force can be avoided only by urging by the tension roller provided to suppress the belt tension force change caused by the track change. It may not be possible.

In order to solve the problem that the movement amount of the other stretching roller is further increased when the movement amount of one stretching roller is set to be large in this way, the stretching roller on the upstream side of the detection position and the downstream side thereof are solved. The tension roller is held by a separate holding member, and a structure for performing contact and separation operations is required.
In such a configuration, the positional relationship between the holding member of the stretching roller upstream of the detection position and the intermediate transfer belt in the portion including the detection position is changed by the contact / separation operation. Similarly, the positional relationship between the holding member of the tension roller on the downstream side of the detection position and the intermediate transfer belt in the portion including the detection position is also changed by the contact / separation operation. For this reason, even if the scale sensor is fixed to either the upstream tension roller holding member and the downstream tension roller holding member, the intermediate transfer belt and the scale including the detection position are included. The positional relationship with the sensor cannot be kept constant.
Therefore, even if the positional relationship between the upstream tension roller holding member or the downstream tension roller holding member and the intermediate transfer belt in the portion including the detection position is changed by the contact / separation operation, the scale There is a need for a configuration that can keep the positional relationship between the sensor and the detection position of the intermediate transfer belt constant regardless of the contact / separation operation.

Such a problem is not limited to the intermediate transfer belt, but may also occur in other belt members such as a transfer conveyance belt that conveys a recording material to a transfer position where the belt surface faces the image carrier.
Further, the detection means for detecting the detection target on the surface of the belt member is not limited to a scale sensor that detects a plurality of marks on the belt member. Similar problems may occur even with other detection means such as detection means for detecting scratches on the surface and detection means used for detecting the toner adhesion amount.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a tension member on the upstream side of the detection position, a holding member for the tension member on the downstream side, and a belt member in a portion including the detection position. It is an object of the present invention to provide an image forming apparatus capable of maintaining the positional relationship between the detection means and the detection position of the belt member constant regardless of the contact / separation operation even when the positional relationship is changed by the contact / separation operation.

In order to achieve the above object, an invention according to claim 1 is directed to an image carrier that carries a toner image, and an endless belt that moves endlessly while forming a transfer nip with an outer peripheral surface being in contact with the image carrier. A member, contact / separation means for contacting / separating the belt member with respect to the image carrier, detection means for detecting a detection target on the surface of the belt member, and holding the detection means, with the rotation axis as a center An image forming apparatus having a rotatable detection means holding member, comprising: a detection means rotation shaft moving means for moving the rotation shaft of the detection means holding member relative to the apparatus body , wherein the detection means rotation The shaft moving means is configured such that the distance from the plane of the belt member including the detection position where the detection means detects the detection target to the rotation shaft of the detection means holding member is the same in the contact state and the separated state. Next, the rotation shaft of the detection means holding member is moved. Positioning of the detection means holding member in the rotational direction so that the inclination of the detection means holding member with respect to the plane of the belt member including the detection position is the same in the contact state and the separated state is characterized in Rukoto includes a sensing means rotating direction positioning means for performing.

To keep the positional relationship between the detection means and the detection position of the belt member constant, the distance between the belt member tension surface including the detection position and the detection means, and the inclination of the detection means relative to the tension surface including the detection position And must be kept constant.
In the conventional image forming apparatus such as the configuration described in Patent Document 1, the rotation shaft of the detection unit holding member that holds the detection unit is fixed to the apparatus main body. When the orbit of the belt member in the portion including the detection position is changed by the contact / separation operation, the positional relationship between the belt member in the portion including the detection position and the apparatus main body is changed. In order to keep the positional relationship between the belt member whose positional relationship with respect to the apparatus main body changes in this way and the detection means in which the rotation shaft of the holding member is fixed to the apparatus main body, the following configuration is required.

That is, the detection means and the belt member at the portion including the detection position rotate together around the same rotation axis. In order to realize such a configuration, the tension member on the upstream side of the detection position, the tension member on the downstream side of the detection position, and the detection means are configured to be held by one holding member.
If it is this structure, since the two tension members of the upstream and downstream of a detection position are hold | maintained at the same holding member, these two tension members, the belt member of the part containing a detection position, The positional relationship of is not changed by the contact / separation operation. For this reason, the positional relationship between the detection means, which is held by the same holding member as the two stretching members and the positional relationship between the two stretching members is fixed, and the belt member of the portion including the detection position is also determined by the contact / separation operation. It does not change and can be kept constant regardless of the contact / separation operation.

  However, this configuration is a configuration in which two tension members are held by the same holding member, and if the movement amount of one tension member is set to be large, the movement amount of the other tension member is further increased. Can occur.

On the other hand, in the present invention, the rotation shaft of the detection means holding member can be moved with respect to the apparatus main body by the detection means rotation shaft moving means. The rotation shaft of the detection means holding member can be moved. Then, in accordance with the displacement of the belt member including the detection position, the rotational axis is moved and the detection means holding member is rotated, thereby connecting the positional relationship between the detection means and the detection position of the belt member. It becomes possible to keep constant regardless of the separation operation.
Further, since the rotation shaft is moved and the detection means holding member is rotated in accordance with the displacement of the belt member, the belt member and the detection means in the portion including the detection position rotate around the same rotation axis. It doesn't have to move. For this reason, the structure in which the positional relationship between the tension member on the upstream side of the detection position or the holding member of the tension member on the downstream side and the belt member in the portion including the detection position may be changed by the contact / separation operation.

  According to the present invention, the positional relationship between the tension member on the upstream side of the detection means or the holding member of the tension member on the downstream side and the belt member in the portion including the detection position is changed by the contact / separation operation. In addition, there is an excellent effect that the positional relationship between the detection means and the detection position of the belt member can be kept constant regardless of the contact / separation operation.

The enlarged explanatory view of the belt unit in the vicinity of the belt speed detecting device, (a) is a contact state, (b) is a separated state. 1 is a schematic configuration diagram showing a copying machine. Explanatory drawing of shape factor SF-1. Explanatory drawing of shape factor SF-2. FIG. 4 is a partially enlarged explanatory view of an intermediate transfer belt. FIG. 3 is a schematic explanatory diagram of an intermediate transfer belt driving device. Explanatory drawing of the arrangement state of a scale mark and a scale sensor. Explanatory drawing about the detection of the scale mark by a scale sensor, (a) is a top view of a scale mark, (b) is a side perspective drawing, (c) is a top view of the detection surface of a scale sensor. Explanatory drawing of a scale sensor and a sensor holding member, (a) is explanatory drawing of the sensor board | substrate which provided two scale sensors integrally, (b) is explanatory drawing of the state which hold | maintained the sensor board | substrate in the sensor holding member. The perspective enlarged view of the sensor holding member vicinity. Explanatory drawing of the change of the locus of the intermediate transfer belt in each mode, (a) is the mode in which the intermediate transfer belt is in contact with all the photoconductors, (b) is the K photoconductor on the most downstream side of the intermediate transfer belt. FIG. 7C is an explanatory diagram of a mode in which only the uppermost S is in contact with the intermediate transfer belt, and FIG. FIG. 3 is an enlarged perspective view of the vicinity of a primary transfer roller for K of the belt unit. Explanatory drawing which looked at the back side separation slider from the near side. Explanatory drawing which looked at each member hold | maintained at the back side contact / separation slider from the back side contact / separation slider side. FIG. 14 is an enlarged explanatory view of the positional relationship between the contact / separation stud provided on the contact / separation slider and each roller bracket, (a) is an enlarged view of a region indicated by α in FIG. 14, and (b) is an enlarged view of FIG. The enlarged view of the area | region shown by (beta), (c) is the enlarged view of the area | region shown by (gamma) in FIG. Explanatory drawing of the part shown in FIG. 13 in a separation state. Explanatory drawing of the part shown in FIG. 14 in a separation state. FIG. 6 is an explanatory diagram of a conventional example in a state where an intermediate transfer belt is in contact with all four photoconductors. FIG. 7 is an explanatory diagram of a conventional example in a state where an intermediate transfer belt is in contact with only a K photoconductor among four photoconductors. FIG. 6 is an explanatory diagram of a conventional example in a state where an intermediate transfer belt is separated from all the photoconductors. Explanatory drawing of the structure which fixed the K nip upstream roller, the K primary transfer roller, and the scale sensor to the 1st bracket, (a) is a contact state, (b) is a separation state. FIG. 22 is an enlarged view of the vicinity of a contact portion between the C photoconductor and the C primary transfer roller having the configuration illustrated in FIG. 21.

Hereinafter, an embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter simply referred to as a copying machine 500) will be described.
First, the basic configuration of the copying machine 500 will be described.
FIG. 2 is a schematic configuration diagram showing the copying machine 500. In the following, an image forming apparatus according to an embodiment of the present invention will be described. The copying machine 500 is a tandem color image forming apparatus, and includes a printer unit 150 that is a main body of the image forming apparatus, a paper feeding device 200, a scanner 300, and an automatic document feeder (ADF) 400.

The printer unit 150 includes a belt unit 510 having an intermediate transfer belt 50 that is an endless belt member at the center. As shown in FIG. 2, the intermediate transfer belt 50 is wound around three support rollers (14, 15 and 16), and in this state, the intermediate transfer belt 50 can move endlessly in the clockwise direction in FIG. The printer unit 150 includes an intermediate transfer body cleaning device 17 at a position (on the left side of the cleaning counter roller 15 in the drawing) that faces the cleaning counter roller 15 with the intermediate transfer belt 50 interposed therebetween among the three support rollers. . The intermediate transfer body cleaning device 17 removes residual toner remaining on the intermediate transfer belt 50 after the image is transferred to the transfer paper S.
A tandem image forming unit 120 is disposed at a position facing the stretched surface of the intermediate transfer belt 50 stretched between the belt driving roller 14 and the cleaning facing roller 15 among the three support rollers. ing. The tandem type image forming unit 120 includes four image forming units 18 that are black, magenta, cyan, and yellow image forming units along the surface movement direction of the stretched surface of the opposing intermediate transfer belt 50. It is juxtaposed facing the frame.

  Each of the four image forming units 18 includes a photoconductor 10 (K, M, C, Y), a charging device that forms a toner image on the photoconductor 10, a developing device, a photoconductor cleaning device, and a static eliminator. Further, four primary transfer rollers 62 are provided with the intermediate transfer belt 50 interposed therebetween so as to face the four photoconductors 10 respectively.

  An exposure device 21 is disposed above the tandem type image forming unit 120. The secondary transfer device 22 is disposed on the opposite side (below the intermediate transfer belt 50) to the side where the tandem image forming unit 120 is disposed with the intermediate transfer belt 50 interposed therebetween. In the secondary transfer device 22, a transfer conveyance belt 24 that is an endless belt is stretched around a pair of transfer conveyance support rollers 23, and one of the pair of transfer conveyance support rollers 23 is rotationally driven as a drive roller. The transfer / conveying belt 24 is driven to rotate counterclockwise in FIG. In addition, the right transfer conveyance support roller 23 and the secondary transfer counter roller 16 in FIG. 2 are in contact with each other with the intermediate transfer belt 50 and the transfer conveyance belt 24 interposed therebetween. A contact portion between the intermediate transfer belt 50 and the transfer conveyance belt 24 due to the contact serves as a secondary transfer nip for transferring an image on the intermediate transfer belt 50 onto the transfer sheet S.

A fixing device 25 for fixing the toner image on the transfer paper S is disposed on the downstream side (left side in FIG. 2) of the transfer paper S of the secondary transfer device 22 in the printer unit 150. The fixing device 25 includes a heating roller 26 provided with a heater (not shown) serving as a heating unit therein, and a pressure roller that is pressed by a spring (not shown) and presses against the heating roller 26 to form a nip portion as a pressure contact portion. 27.
The secondary transfer device 22 described above also has a sheet conveying function for conveying the transfer sheet S after image transfer to the fixing device 25. As the secondary transfer device 22, a non-contact charger may be disposed. In such a case, it is difficult for the secondary transfer device 22 to have this sheet conveying function.
Below the secondary transfer device 22 and the fixing device 25 in the printer unit 150, a reversing device that inverts the transfer sheet S when performing image formation on both sides of the transfer sheet S in parallel with the tandem image forming unit 120 described above. 28 is arranged.

  Next, formation of a full color image (color copy) using the copying machine 500 will be described. First, a document is set on a document table 430 of an automatic document feeder (ADF) 400, or the automatic document feeder 400 is opened and a document is set on the contact glass 32 of the scanner 300. Is closed and the document is held by the automatic document feeder 400.

  When the user presses the start switch on the operation panel (not shown), 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 scanner 300 is driven. The first traveling body 33 and the second traveling body 34 travel. On the other hand, when the document is set on the contact glass 32, the scanner 300 is driven immediately and the first traveling body 33 and the second traveling body 34 travel. At this time, the light from the light source is irradiated by the first traveling body 33, and this light is reflected by the document surface, and the reflected light is reflected by the mirrors in the first traveling body 33 and the second traveling body 34. The light is received by the reading sensor 36 through the imaging lens 35. As a result, a color original (color image) is read and used as black, yellow, magenta, and cyan image information.

When the user presses a start switch (not shown), the belt drive roller 14 is rotationally driven by a drive motor (not shown), the other two support rollers (15 and 16) are driven to rotate, and the intermediate transfer belt 50 is moved. Move endlessly.
At the same time, the photosensitive members 10 of the four image forming units 18 in the tandem type image forming unit 120 are driven to rotate. The above-described image information of black, magenta, cyan, and yellow is transmitted to the exposure device 21, and exposure light corresponding to each image information is emitted toward each photoconductor 10 of each image forming unit 18. As a result, toner images of respective colors of black, magenta, cyan, and yellow are formed on the respective photoreceptors 10 of the respective image forming units 18.
The color toner images thus formed are sequentially superimposed and transferred (primary transfer) onto the intermediate transfer belt 50 moving on the surface, and a composite color image is formed on the intermediate transfer belt 50.

On the other hand, when the user presses a start switch (not shown), one of the paper feeding rollers 142 is selectively rotated in the paper feeding device 200. As a result, the transfer paper S is fed out from one of the paper cassettes 144 provided in multiple stages in the paper bank 143, separated one by one by the separation roller 145, and sent to the paper feed path 146. The transfer sheet S that has reached the paper feed path 146 is transported by the transport roller 147 and guided to the main body side paper feed path 148 in the printer unit 150, and abuts against the registration roller 49 to stop.
Alternatively, when the user presses a start switch (not shown), the manual feed roller 51 is rotated to feed out the transfer sheet S on the manual feed tray 54. Then, the sheets are separated one by one by the manual separation roller 52 and put into the manual sheet feed path 53, and abutted against the registration roller 49 and stopped as described above.
The registration roller 49 is generally used while being grounded, but may be used in a state where a bias is applied to remove the paper dust of the transfer paper S.

  After abutting against the registration roller 49 and stopping, the registration roller 49 is rotated in synchronization with the synthesized color image formed on the intermediate transfer belt 50, and the transfer sheet S is fed toward the secondary transfer nip described above. The composite color image on the intermediate transfer belt 50 is transferred onto the transfer sheet S by a transfer electric field formed between the transfer conveyance support roller 23 on the secondary transfer device 22 side and the secondary transfer counter roller 16 in the secondary transfer nip. Then, a color image is formed on the transfer paper S. The transfer residual toner on the intermediate transfer belt 50 after passing through the secondary transfer nip is removed by the intermediate transfer body cleaning device 17 to prepare for the image formation by the tandem image forming unit 120 again.

  The transfer sheet S on which the color image is formed is conveyed by the secondary transfer device 22 and sent to the fixing device 25. In the fixing device 25, a color image is fixed on the transfer sheet S by applying heat and pressure at a nip portion formed by the heating roller 26 and the pressure roller 27.

  The transfer sheet S that has passed through the fixing device 25 is given a conveyance force by the conveyance roller pair 56 after fixing and reaches the position of the switching claw 55. The transfer sheet S is discharged by the discharge roller pair 156 when the switching claw 55 switches the transport direction and is stacked on the discharge tray 57. Alternatively, the switching claw 55 switches to the conveying direction to reach the reversing device 28, where it is reversed and guided to a position where it abuts against the registration roller 49 again. An image is also formed on the back surface at the secondary transfer nip and fixed by the fixing device 25, and then discharged by the discharge roller pair 156 and stacked on the discharge tray 57.

The intermediate transfer belt 50 is composed of single layer or multiple layers of PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), and the like. A conductive material such as carbon black is dispersed therein, and the volume resistivity is in the range of 10 ⁸ to 10 ¹² [Ω · cm] and the surface resistivity is in the range of 10 ⁹ to 10 ¹³ [Ω · cm]. It has been adjusted. If necessary, a release layer may be coated on the surface of the intermediate transfer belt 50. Materials used for the coating include ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluorocarbon resin), FEP (four-fluorocarbon). Fluorine resin such as ethylene fluoride-propylene hexafluoride copolymer) or PVF (vinyl fluoride) can be used, but is not limited thereto.

The method of manufacturing the intermediate transfer belt 50 includes a casting method, a centrifugal molding method, and the like, and the surface thereof may be polished if necessary.
If the volume resistivity of the intermediate transfer belt 50 exceeds the above-described range, the bias necessary for transfer increases, which increases the power supply cost, which is not preferable. Further, since the charging potential of the intermediate transfer belt 50 becomes high and the self-discharge becomes difficult in the transfer process, the transfer paper peeling process, etc., it is necessary to provide a static elimination means. Also, if the volume resistivity and surface resistivity are below the above ranges, the charge potential decays faster, which is advantageous for static elimination by self-discharge, but toner scatter occurs because the current during transfer flows in the surface direction. Resulting in. Accordingly, the volume resistivity and surface resistivity of the intermediate transfer belt 50 are preferably within the above-described ranges.

The volume resistivity and surface resistivity were measured by connecting an HRS probe (inner electrode diameter 5.9 [mm], ring electrode inner diameter 11 [mm]) to a high resistivity meter (Mitsubishi Chemical Corporation: Hiresta IP). Do. Then, a voltage of 100 [V] (surface resistivity of 500 [Ω · cm]) was applied to the front and back of the intermediate transfer belt 50, and the measured value after 10 [seconds] was used.
The transfer roller (roller forming the secondary transfer nip) is obtained by applying a foamed resin agent to a metal core (iron, stainless steel, aluminum, etc.). The thickness of the foamed resin agent is 2 [mm] to 10 [mm], but is not limited thereto.

Next, toner that is preferably used in the copying machine 500 will be described.
As the toner used in the copying machine 500, it is desirable that the shape factor SF-1 is in the range of 100 to 180 and the shape factor SF-2 is in the range of 100 to 180.
FIG. 3 is a diagram schematically showing the shape of the toner for explaining the shape factor SF-1. The shape factor SF-1 indicates the ratio of the roundness of the toner shape and is represented by the following formula (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-1 = {(MXLNG) ² / AREA} × (100π / 4) (1)
When the value of SF-1 is 100, the shape of the toner becomes a true sphere, and becomes larger as the value of SF-1 increases.

FIG. 4 is a diagram schematically showing the shape of the toner in order to explain the shape factor SF-2. The shape factor SF-2 indicates the ratio of unevenness in the shape of the toner, and is represented by the following formula (2). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane by the figure area AREA and multiplying by 100 / 4π.
SF-2 = {(PERI) ² / AREA} × 100 / (4π) (2)
When the value of SF-2 is 100, there is no unevenness on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.

  Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. Calculated. When the shape of the toner is close to a sphere, the contact state between the toner and the toner or between the toner and the photoconductor becomes a point contact. For this reason, the attractive force between the toners becomes weak and the fluidity becomes high. Further, the attracting force between the toner and the photoreceptor is weakened, and the transfer rate is increased. If either of the shape factors SF-1 or SF-2 exceeds 180, the transfer rate is lowered, and cleaning properties when toner adheres to the photoreceptor 10 or the intermediate transfer belt 50 are also not preferable.

  The toner particle size is preferably in the range of 4 to 10 [μm] in terms of volume average particle size. When the particle diameter is smaller than this range, it becomes a cause of background staining during development, fluidity is deteriorated, and aggregation tends to occur, so that voids are likely to occur. Conversely, when the particle diameter is larger than this range, a high-definition image cannot be obtained due to toner scattering and resolution deterioration. In the copying machine 500, toner having a volume average particle diameter of 6.5 [μm] is used.

FIG. 5 is a partially enlarged explanatory view of the intermediate transfer belt 50, and is an explanatory view of the positional relationship between the locus of the intermediate transfer belt 50 and the sensor holding member 130.
The intermediate transfer belt 50 moves on the surface in the direction of arrow F in FIG. A tension roller 19 that presses the intermediate transfer belt 50 from the outer peripheral surface side is provided between the secondary transfer counter roller 16 and the cleaning counter roller 15. The tension roller 19 is pressed toward the outer peripheral surface of the intermediate transfer belt 50 by a belt tension spring (not shown) that is an urging member, and is configured to suppress fluctuations in the belt tension of the intermediate transfer belt 50. .
Further, a belt speed provided with a scale sensor 6 described later on the upstream side of the surface of the intermediate transfer belt 50 in the K nip where the primary transfer roller 62K for K comes into contact with the photosensitive member 10K with the intermediate transfer belt 50 interposed therebetween. A detection device 110 is arranged.

FIG. 6 is a schematic explanatory diagram of the intermediate transfer belt driving device 105 that controls the driving of the intermediate transfer belt 50.
As shown in FIG. 6, the intermediate transfer belt 50 is stretched around the belt driving roller 14, the cleaning facing roller 15, and the secondary transfer facing roller 16. In FIG. 6, a predetermined tension is applied along the surface movement direction (the direction of arrow F in the figure) by the tension roller 19 (not shown). In this state, when the belt driving motor 7 is driven and rotational driving is transmitted to the reduction gear 8 attached to the belt driving roller 14, the belt driving roller 14 is rotationally driven, and the intermediate transfer belt 50 moves on the surface at a predetermined speed. .

Further, a predetermined interval (pitch) is provided along one side edge of the front surface or the back surface of the intermediate transfer belt 50 (the inner peripheral surface which is the back surface in the configuration shown in FIG. 6) in the endless movement direction. A plurality of scale marks SM are continuously provided.
The plurality of scale marks SM are formed to have the same length, are arranged at equal intervals in parallel with each other, and are arranged at an extremely small pitch along the endless movement direction, and are provided on the entire circumference of the intermediate transfer belt 50. The scale 5 of the intermediate transfer belt 50 is configured as a whole.
In the configuration shown in FIG. 6, the scale mark SM is formed in a scale of a predetermined color, for example, printed with ink having a higher reflectance than the surface of the intermediate transfer belt 50. As another example, there may be mentioned a person who has attached a tape printed with a scale mark SM having a reflectance different from the reflectance of the ground over the entire circumference of the intermediate transfer belt 50.

The drive control device 70 that controls the driving of the intermediate transfer belt 50 includes a control device 71, a motor drive circuit 81, and a scale sensor 6 that detect the scale mark SM, which are connected to each other. The scale sensor 6 is arranged at a slight distance above the formation position of the scale mark SM on the intermediate transfer belt 50.
A plurality of scale sensors 6 (two downstream sensors 6A and 6B in the configuration shown in FIG. 6) are arranged at predetermined intervals along the surface movement direction of the intermediate transfer belt 50, and each intermediate transfer is performed. The scale marks SM on the belt 50 are sequentially detected and a detection signal is output to the control device 71.

  As will be described later, the control device 71 acquires position data for correcting the pitch of the scale mark SM from the detection signal and inputs the target position data to the motor drive circuit 81 to move the intermediate transfer belt 50. Control the speed. As described above, the control device 71 appropriately outputs a signal to the motor drive circuit 81 based on the position information of the intermediate transfer belt 50 detected by the downstream sensor 6A and the upstream sensor 6B. Then, the belt drive motor 7 is driven by the motor drive circuit 81 to feedback control the surface moving speed of the intermediate transfer belt 50.

FIG. 7 is an explanatory diagram of the arrangement state of the scale mark SM and the scale sensor 6.
In the drive control device 70 of the present embodiment, as shown in FIG. 7, the upstream sensor 6B and the downstream sensor 6A are all arranged along the surface movement direction of the intermediate transfer belt 50 indicated by the arrow F in the drawing. The scale mark SM is arranged so that it can be detected.
Further, as shown in FIG. 7, when the detection point interval between the upstream sensor 6B and the downstream sensor 6A is the detection interval D and the design value of the pitch of the scale mark SM is the scale pitch P0, the following is performed. Is set. That is, the detection interval D is set to an integral multiple of the scale pitch P0 (D = N · P0 (N = 1, 2, 3,...)).

  When the intermediate transfer belt 50 is not expanded or contracted, the center portions of the two scale marks SM pass through the detection points of the upstream sensor 6B and the downstream sensor 6A simultaneously. When the intermediate transfer belt 50 moves, the upstream sensor 6 </ b> B and the downstream sensor 6 </ b> A sequentially detect the scale marks SM and output detection signals to the control device 71. Then, as will be described later, the control device 71 feedback-controls the motor drive circuit 81 based on the phase difference of the detection signal (input signal) or the like.

FIG. 8 is an explanatory diagram regarding the detection of the scale mark SM by the scale sensor 6. 8A is a plan view of the scale mark SM viewed from the inside of the intermediate transfer belt 50, FIG. 8B is a side perspective view showing the configuration of the optical system and the optical path of the scale sensor 6, and FIG. c) is a plan view (top view) of the detection surface of the scale sensor 6. FIG.
The scale mark SM of the present embodiment is a reflective mark, and, as shown in FIG. 8A, a reflecting portion (scale) is formed on the outer peripheral surface of the intermediate transfer belt 50 along the surface movement direction indicated by the arrow F in the drawing. The marks SM) and the light shielding portions SB are alternately formed.

  As shown in FIGS. 8B and 8C, the scale sensor 6 includes a light emitting element 121 such as an LED, a collimating lens 122, and a slit mask 123. Furthermore, the scale sensor 6 includes a light receiving window 124 made of a transparent cover such as glass or a transparent resin film, and a light receiving element 125 such as a phototransistor. These members are fixed to each part of the sensor housing 140.

When the light emitting element 121 which is the light source of the scale sensor 6 emits light, the light passes through the collimating lens 122 and becomes a parallel light flux. Then, the light passes through a plurality of slits 123 a parallel to the scale mark SM of the slit mask 123, is divided into a plurality of light beams LB, and is irradiated onto the scale 5 on the intermediate transfer belt 50.
A part of the plurality of light beams LB is reflected by the scale mark SM, and the reflected light is received by the light receiving element 125 through the light receiving window 124, and the light receiving element 125 detects the change (strength) of the brightness of the reflected light as an electric signal. Convert to
As described above, the scale sensor 6 detects the scale mark SM by sensing the intensity of the reflected light by the light receiving element 125, and the presence / absence of the scale mark SM accompanying the movement of the intermediate transfer belt 50 is continuously modulated to the analog. Output as an alternating signal.

  FIG. 9 is an explanatory diagram of the scale sensor 6 and the sensor holding member 130 in the belt speed detection device 110. FIG. 9A is an explanatory view of the sensor substrate 127 in which the two scale sensors 6 (6A and 6B) are integrally provided, and FIG. 9B is an explanatory view of a state in which the sensor substrate 127 is held by the sensor holding member 130.

As shown in FIG. 9B, the belt speed detection device 110 is mainly composed of a sensor substrate 127 and a sensor holding member 130.
As shown in FIG. 9A, the sensor substrate 127 is arranged so that the detection surfaces 126 of the two scale sensors 6 (6A and 6B) including the light emitting element 121 and the light receiving element 125 are directed upward in the drawing. ing. In addition, a harness connector 128 fixed so as to protrude upward in the figure is disposed in the vicinity of the end of the sensor substrate 127 opposite to the side where the two scale sensors 6 (6A and 6B) are provided. Yes.

The sensor holding member 130 holds the sensor substrate 127 as shown in FIG. 9B. And it fixes to the sensor bracket 161 mentioned later, and the one end side of the belt movement direction upstream of the sensor bracket 161 is rotatably supported by the sensor rotating shaft 162 mentioned later.
Two sensor windows 132 are formed on the belt facing surface 131 of the sensor holding member 130. The two sensor windows 132 are for exposing part of the detection surfaces 126 of the two scale sensors 6 fixed to the sensor substrate 127 held by the sensor holding member 130 to the intermediate transfer belt 50.
Since the belt facing surface 131 is in contact with the intermediate transfer belt 50, the surface is subjected to a flocking process or the like to reduce the frictional force. In addition, the sensor holding member 130 of the present embodiment is made of resin, but may be made of metal as long as there are no restrictions due to other design conditions.

FIG. 10 is an enlarged perspective view of the vicinity of the sensor holding member 130, and the intermediate transfer belt 50 and the sensor bracket 161 are partially sectional views.
In this embodiment, as shown in FIG. 10, in order to suppress the detection error of the scale sensor 6 due to the flapping of the intermediate transfer belt 50, the intermediate transfer belt 50 is moved by the sensor holding member 130 and the belt upper pressing member 135. It is sandwiched.
The contact surface of the upper pressing contact portion 136 where the upper pressing member 135 is in contact with the intermediate transfer belt 50 is also preferably reduced by a flocking process.
Further, it is preferable to reduce the friction coefficient of the belt facing surface 131 where the sensor holding member 130 comes into contact with the intermediate transfer belt 50 by, for example, performing a flocking process.

In the configuration in which the upper pressing member 135 is provided, the scale sensor 6 is preferably installed at the end of the intermediate transfer belt 50 in the width direction (direction orthogonal to the surface movement direction indicated by the arrow). Since the upper pressing member 135 is provided at a position facing the scale sensor 6 with the intermediate transfer belt 50 interposed therebetween, the following problems occur when the scale sensor 6 is provided on the center side in the width direction of the intermediate transfer belt 50. That is, the back side of the intermediate transfer belt 50 at the position where the scale sensor 6 faces is within the image range on the intermediate transfer belt 50, and the upper pressing member 135 cannot be installed. The upper pressing member 135 is positioned by screwing with respect to the sensor holding member 130, and moves together with the sensor holding member 130 when the sensor holding member 130 moves.
As shown in FIG. 14, by bringing the sensor holding member 130 and the intermediate transfer belt 50 into contact with each other, the variation in the distance between the scale sensor 6 and the scale mark SM can be reduced.

FIG. 11 is an explanatory diagram of changes in the trajectory of the intermediate transfer belt 50 in each mode. FIG. 11A is an explanatory diagram of a mode in which the intermediate transfer belt 50 is in contact with all the photoconductors 10, and FIG. 11B is a diagram illustrating the intermediate transfer belt 50 connected to the most downstream K photoconductor 10K. It is explanatory drawing of the mode which is contacting only. FIG. 11C is an explanatory diagram of a mode in which the intermediate transfer belt 50 is in contact only with the most upstream S photoconductor 10S.
In FIG. 2, the configuration including the four photoconductors 10 is illustrated. However, as illustrated in FIG. 11, the configuration including the five photoconductors 10 may be used. Examples of the S photoconductor 10S that is the fifth photoconductor 10 include a configuration in which development is performed with transparent clear toner.
The number of photoreceptors 10 that the intermediate transfer belt 50 contacts and the locus of the intermediate transfer belt 50 shown in FIG. 11 are examples. For example, a mode in which the intermediate transfer belt 50 is in contact with only the central three-color (Y, C, M) photoreceptor 10 may be set.

  The copying machine 500 forms a K nip that is a primary transfer portion for K where the K photoconductor 10K and the K primary transfer roller 62K are in contact with the intermediate transfer belt 50 interposed therebetween. As shown in FIG. 11, a belt speed detection device 110 is disposed upstream of the surface of the intermediate transfer belt 50 in the surface movement direction (hereinafter referred to as “belt movement direction”) with respect to the K nip. Further, a K nip upstream roller 153 is further provided on the upstream side in the belt movement direction with respect to the belt speed detection device 110, and a K nip downstream roller 154 is provided on the downstream side in the belt movement direction with respect to the K nip.

Next, the characteristic part of this invention is demonstrated using FIG.
FIG. 1 is an enlarged explanatory view of the vicinity of the belt speed detection device 110 in FIG. FIG. 1A is an explanatory diagram in a mode (the mode of FIG. 11A or FIG. 11B) in which the most downstream K photoconductor 10K and the intermediate transfer belt 50 are in contact with each other. FIG. 1B is an explanatory diagram for the mode (mode of FIG. 11C) in which the most downstream K photoconductor 10K and the intermediate transfer belt 50 are separated from each other.

The K nip upstream roller 153 is held by the upstream roller bracket 702, and the K nip upstream roller 153 moves up and down as the upstream roller bracket 702 rotates around the upstream roller rotation shaft 172. The upstream roller rotation shaft 172 is fixed to the apparatus main body (intermediate transfer belt frame or the like), and this upstream roller rotation shaft 172 is a main reference for the movement of the upstream roller bracket 702 in the rotation direction.
The upstream roller bracket 702 is pulled upward (in the direction of the arrow E1 in FIG. 1) by the upstream roller biasing spring 750 schematically shown by a two-dot chain line at the end on the side away from the upstream roller rotation shaft 172. Yes. In the contact state shown in FIG. 1A, the upstream roller drive cam 703 is not in contact with the upstream roller bracket 702. For this reason, the upstream roller bracket 702 biased by the upstream roller biasing spring 750 hits the upstream roller secondary reference member 705 fixed to the apparatus main body (intermediate transfer belt frame or the like). Accordingly, the upstream roller bracket 702 and the K nip upstream roller 153 are positioned with respect to the apparatus main body.

When the contact state shown in FIG. 1A is changed to the separated state shown in FIG. 1B, a drive motor (not shown) is driven and the upstream roller drive cam 703 is rotated, so that the upstream roller bracket 702 has an upstream roller. The drive cam 703 hits. At this time, the upstream roller drive cam 703 presses the upstream roller bracket 702 downward. Accordingly, the left end side of the upstream roller bracket 702 in FIG. 1 is lowered downward against the biasing force of the upstream roller biasing spring 750, and the upstream roller bracket 702 is separated from the upstream roller slave reference member 705. In this state, the upstream roller drive cam 703 that abuts the upstream roller bracket 702 serves as a secondary reference for the upstream roller bracket 702, and positions the upstream roller bracket 702 with respect to the apparatus main body.
In the configuration shown in FIG. 1, the K nip upstream roller 153 is separated from the intermediate transfer belt 50 in the separated state shown in FIG.

The sensor bracket 161 that holds the scale sensor 6 described above via the sensor holding member 130 is rotatably supported at its upstream end in the belt movement direction by a sensor rotation shaft 162 that is a rotation shaft.
A sensor rotation shaft 162 serving as a main reference of the sensor bracket 161 is installed on the upstream roller bracket 702. With such a configuration, the position of the sensor rotation shaft 162 relative to the apparatus main body is moved by the rotation operation of the upstream roller bracket 702.

  The sensor bracket 161 is pulled downward (in the direction of arrow E2 in FIG. 1) from the sensor rotation shaft 162 by a sensor bracket biasing spring 751 schematically shown by a two-dot chain line. The upstream roller bracket 702 is provided with a contact reference member 704 that supports the sensor bracket 161 from below as a reference for the sensor bracket 161 in the contact state shown in FIG. On the other hand, a separation reference member 713 for supporting the sensor bracket 161 from below is provided as a reference for the sensor bracket 161 in the separated state shown in FIG. In other words, in the separated state, the sensor bracket 161 is abutted against a slave reference that is provided on the main body of the apparatus such as the intermediate transfer belt frame and that is abutted against the sensor bracket 161.

  In the contact state shown in FIG. 1A, the sensor bracket 161 urged downward by the sensor bracket urging spring 751 abuts against the separated reference member 713 located above the contacted reference member 704. The sensor bracket 161 is positioned by being biased by the sensor bracket biasing spring 751 and abutting against the slave reference member 704 at the time of contact.

  When the upstream roller drive cam 703 rotates from the contact state shown in FIG. 1A and hits the upstream roller bracket 702, the upstream roller bracket 702 rotates in the clockwise direction in FIG. 1 about the upstream roller rotation shaft 172. Rotate. As a result, the contact reference member 704 fixed to the upstream roller bracket 702 moves downward. In accordance with the movement of the secondary reference, the sensor bracket 161 also rotates in the clockwise direction in FIG. 1 about the sensor rotation shaft 162. Thereafter, when the sensor bracket 161 abuts against the slave reference member 713 that is fixed to the apparatus main body, the rotation of the sensor bracket 161 about the sensor rotation shaft 162 stops. As a result, the contact reference member 704 is separated from the sensor bracket 161. When the rotation of the upstream roller drive cam 703 stops, the position of the upstream roller bracket 702 is determined, and the position of the sensor rotation shaft 162 provided on the upstream roller bracket 702 is also determined. At this time, the sensor bracket 161 is biased by the sensor bracket biasing spring 751 and abuts against the slave reference member 713 at the time of separation, whereby the sensor bracket 161 is positioned.

In addition, the sensor rotation in the upstream roller bracket 702 is performed so that the distance W between the intermediate transfer belt 50 including the detection position and the sensor rotation shaft 162 is the same in the contact state and the separation state. The position of the axis 162 is set. Further, the position of the slave reference member 704 at the time of contact and the position of the slave reference member 713 at the time of separation are set so that the inclination of the sensor bracket 161 with respect to the stretched surface of the intermediate transfer belt 50 in the portion including the detection position is constant. doing.
In the present embodiment, the distance W from the sensor rotation shaft 162 to the stretching surface of the intermediate transfer belt 50 including the detection position and the inclination of the sensor bracket 161 with respect to this stretching surface are constant regardless of the contact / separation operation. . For this reason, the positional relationship between the tension surface of the intermediate transfer belt 50 including the detection position and the scale sensor 6 fixed to the sensor bracket 161 can be kept constant regardless of the contact / separation operation.

As described above, the sensor bracket 161 and the upstream roller bracket 702 are positioned by being urged by the spring and abutting against the respective abutting members (705, 703, 704, 713). If the two brackets are positioned only by gravity or the like, the resonance point cannot be adjusted. On the other hand, the resonance point can be adjusted by adjusting the spring constant by using an elastic member such as a spring.
The belt upper holding member 135 is positioned on the sensor holding member 130, and the sensor holding member 130 is fixed to the sensor bracket 161. That is, the belt upper holding member 135 is fixed to the sensor bracket 161 via the sensor holding member 130. For this reason, even if the sensor bracket 161 is displaced by the contact / separation operation, the positional relationship of the belt upper pressing member 135 with respect to the sensor holding member 130 and the sensor bracket 161 is maintained.

Here, a configuration of an image forming apparatus provided with a conventional intermediate transfer belt will be described.
In an image forming apparatus provided with an intermediate transfer belt, even if a drive motor that drives the intermediate transfer belt is driven at a constant speed, speed fluctuation may occur in the intermediate transfer belt. The causes of the speed fluctuation include eccentricity of the stretching roller that stretches the intermediate transfer belt, eccentricity of the drive gear, uneven thickness in the circumferential direction of the intermediate transfer belt, and the like. During the transfer of the toner image on the intermediate transfer belt, when the speed fluctuation of the intermediate transfer belt occurs, the shape of the toner image resulting from the speed fluctuation appears as a color shift. Image quality degradation is very noticeable.

  The image forming apparatus disclosed in Patent Document 1 has a configuration capable of suppressing the occurrence of color misregistration due to the speed variation of the intermediate transfer belt. In this image forming apparatus, a scale having a plurality of marks arranged at a predetermined pitch in the belt circumferential direction is provided on the intermediate transfer belt. Then, the speed of the intermediate transfer belt is detected based on the time interval at which each mark on the scale is detected by the scale sensor. Feedback control of the driving speed of the belt driving motor based on the detection result reduces the speed fluctuation of the intermediate transfer belt.

  In the case of a structure in which contact and separation operations are performed by changing the track of the intermediate transfer belt, even if the track of the intermediate transfer belt changes, the surface of the intermediate transfer belt (hereinafter, “ It is required that the positional relationship with the “detection position” does not change. Patent Document 1 describes a configuration in which a tension roller on the upstream side in the moving direction of the intermediate transfer belt, a tension roller on the downstream side, and a scale sensor are fixed to a single holding body with respect to the scale sensor. . Hereinafter, the configuration described in Patent Document 1 will be described with reference to FIGS.

  18 to 20 are explanatory views showing the positional relationship between the intermediate transfer belt 50 stretched around a plurality of stretch rollers and the four photoconductors 10 (Y, M, C, K). FIG. 18 is an explanatory diagram of a state in which the intermediate transfer belt 50 is in contact with all of the four photoconductors 10 (Y, M, C, K), and corresponds to the above-described multi-color mode. FIG. 19 is an explanatory diagram of a state in which the intermediate transfer belt 50 is in contact with only the K photoconductor 10K among the four photoconductors 10 (Y, M, C, and K), and corresponds to the single color mode. . FIG. 20 is an explanatory diagram of a state in which the intermediate transfer belt 50 is separated from all the photoreceptors 10 (Y, M, C, K), and corresponds to a state in which the above-described image formation is not performed.

The K primary transfer roller 62K that is in contact with the K photoconductor 10K with the intermediate transfer belt 50 interposed therebetween is held by the first bracket 72. Three primary transfer rollers 62 (Y, M, C) other than the primary transfer roller 62K for K are held by a second bracket (not shown). The three primary transfer rollers 62 (Y, M, C) are separated from the three photoreceptors 10 (Y, M, C) by rotating the second bracket from the state of FIG. To do. As a result, the intermediate transfer belt 50 is separated from the three photoconductors 10 (Y, M, C), and the state shown in FIG. 19 is obtained. Further, by rotating the first eccentric cam 73 from the state of FIG. 19, the first bracket 72 is rotated about the first rotation shaft 72a, and the K primary transfer roller 62K is moved to the K photoconductor 10K. Separate from. As a result, the intermediate transfer belt 50 is separated from the K photoconductor 10K and is in a state indicated by a solid line in FIG.
Such a contact / separation operation changes the stretched shape of the intermediate transfer belt 50. However, the tension roller 19 that is slidably held by a bracket (not shown) and urged toward the outer peripheral surface of the belt moves flexibly according to the change, thereby avoiding a significant change in the belt tension force. ing.

  18 to 20 includes a scale sensor 6 that detects a mark provided on the surface of the intermediate transfer belt 50 on the upstream side in the movement direction of the intermediate transfer belt 50 with respect to the K primary transfer roller 62K. Further, a K nip upstream roller 153 is provided upstream of the scale sensor 6 in the belt movement direction, and a K nip downstream roller 154 is provided downstream of the K primary transfer roller 62K in the belt movement direction. The K nip upstream roller 153, the K primary transfer roller 62K, the scale sensor 6, and the K nip downstream roller 154 are all held by the first bracket 72. That is, the K nip upstream roller 153, which is a tension roller on the upstream side with respect to the scale sensor 6, the K primary transfer roller 62K, which is a tension roller on the downstream side, and the scale sensor 6 are one holding body. The first bracket 72 is fixed. For this reason, the positional relationship between the surface of the intermediate transfer belt 50 and the scale sensor 6 between the K nip upstream roller 153 and the K primary transfer roller 62K for which the scale sensor 6 detects the mark depends on the rotation of the first bracket 72. Regardless of movement.

  In this configuration, by rotating the first bracket 72, the trajectory of the intermediate transfer belt 50 is changed, and the contact and separation operation of the intermediate transfer belt 50 with respect to the K photoconductor 10K is performed. The positional relationship between the scale sensor 6 and the detection position of the intermediate transfer belt 50 is constant regardless of the rotation of the first bracket 72 and does not change. Therefore, it is possible to realize a configuration in which the positional relationship between the scale sensor 6 and the portion of the intermediate transfer belt 50 including the detection position does not change even when the trajectory of the intermediate transfer belt 50 changes in the configuration in which the contact / separation operation is performed.

However, as shown in FIGS. 18 to 20, the tension roller on the upstream side in the moving direction of the intermediate transfer belt 50, the tension roller on the downstream side, and the scale sensor 6 are connected to the scale sensor 6. The configuration fixed to the holder may cause the following problems.
FIG. 21 shows that the K nip upstream roller 153 that is a tension roller on the upstream side of the scale sensor 6, the K primary transfer roller 62K that is a tension roller on the downstream side, and the scale sensor 6 are attached to the first bracket 72. It is explanatory drawing of the fixed structure. FIG. 21A is an explanatory view showing a state in which the intermediate transfer belt 50 is in contact with all the photoconductors 10, and FIG. 21B is the most upstream photoconductor among the plurality of photoconductors 10. 10 is an explanatory diagram of a state in which the intermediate transfer belt 50 is in contact with only 10. FIG. 22 is an enlarged view of the vicinity of the contact portion between the C photoconductor 10C and the C primary transfer roller 62C on the upstream side of the scale sensor 6, and the state of FIG. The state of FIG. 21B is shown by a solid line.

The first bracket 72 is rotatable about a first rotation shaft 72a, and a first bracket 72 includes a spring (not shown) that biases the right side of the first bracket 72 in the drawing downward and a first eccentric cam 73. 72 is positioned in the rotational direction. Then, as the first eccentric cam 73 moves up and down, the first bracket 72 also moves up and down. In FIG. 21A and FIG. 21B, the locus of the intermediate transfer belt 50 changes. In either locus, the K nip upstream roller 153 and the K primary transfer roller 62K are intermediate transfer belt 50. , The scale sensor 6 forms a locus of the intermediate transfer belt 50 including a detection position where the mark is detected. With such a configuration, the positional relationship between the intermediate transfer belt 50 including the detection position and the scale sensor 6 is kept constant.
In this configuration, since the K nip upstream roller 153 and the K primary transfer roller 62K are fixed to the same bracket, the respective positions cannot be positioned independently. If one position is moved, the other position is also changed. It will move.

With such a configuration, the following problem occurs when the movement range by the rotation of the first bracket 72 is small. As shown in FIG. 21B, when the intermediate transfer belt 50 is in contact with only the most upstream photoconductor 10, the intermediate transfer belt 50 is opposed to the most upstream photoconductor 10. And the K nip upstream roller 153 are stretched so as to form a linear stretching surface. For this reason, even if the primary transfer roller 62 on the upstream side of the K nip upstream roller 153 is sufficiently separated from the intermediate transfer belt 50, the distance between each photoconductor 10 and the intermediate transfer belt 50 is equal to the K nip upstream roller. It is smaller than the movement amount 153 (“D” in FIG. 22). When the movement range by the rotation of the first bracket 72 is small, the movement amount of the K nip upstream roller 153 is small, and the separation amount between the separated photosensitive member 10 and the intermediate transfer belt 50 is small.
If the separation amount is small, the intermediate transfer belt 50 to which the toner image has been transferred from the most upstream photoreceptor 10 contacts the downstream photoreceptor 10 that should have been separated due to tolerance, flapping of the intermediate transfer belt 50, or the like. There is a risk of image rubbing.

In order to prevent such a problem, it is conceivable to set a large movement range by the rotation of the first bracket 72. In this case, the following problem occurs.
First, in order to solve the above problem, the moving range by the rotation of the first bracket 72 is set large so that the moving amount of the K nip upstream roller 153 becomes sufficiently large. With this setting, the amount of movement of the K primary transfer roller 62K at a position where the distance from the first rotation shaft 72a is further away from the K nip upstream roller 153 is set to a sufficiently large K nip upstream roller 153. The amount of movement is greater than the amount of movement.
For example, it is assumed that the distance from the first rotation shaft 72a to the K nip upstream roller 153 is 30 [mm] and the distance from the first rotation shaft 72a to the K primary transfer roller 62K is 60 [mm]. At this time, if the K nip upstream roller 153 is set to be lowered by 3 [mm], the K primary transfer roller 62K is lowered by 6 [mm].

  In the configuration shown in FIG. 21, the position of the K nip downstream roller 154 that is located farther from the first rotation shaft 72a than the K primary transfer roller 62K is also fixed to the first bracket 72. Therefore, the movement amount of the K nip downstream roller 154 is larger than that of the K primary transfer roller 62K. As a result, the trajectory of the intermediate transfer belt 50 in the portion stretched around the primary transfer roller 62 and the K nip downstream roller 154 changes greatly. At this time, the distance from the contact point between the most upstream photoconductor 10 and the intermediate transfer belt 50 to the end of winding of the belt driving roller 14 is shorter than the state shown in FIG.

When the tension roller 19 moves, the locus of the intermediate transfer belt 50 is formed by the movement of the tension roller 19, but when the tension roller 19 moves, the spring load of the belt tension spring decreases. A large change in the belt tension force cannot be avoided only by the urging by the tension roller 19.
Since the belt tension force is reduced, the fluttering of the belt is increased and the image is rubbed, or the drive control is adversely affected due to a change in drive characteristics.
Further, if the amount of movement of the first eccentric cam 73 is increased in order to set a large movement range by the rotation of the first bracket 72, the torque when the first eccentric cam 73 is rotated increases. If the torque of the first eccentric cam 73 is increased, the cost of the motor is increased, and gear wear, cam wear, etc. are likely to occur.

  As described above, as a configuration for preventing problems caused by holding a plurality of driven rollers (153, 62K, and 154) in one bracket, a configuration in which each driven roller is fixed by separate brackets can be considered. As a result, each lowering position of each driven roller can be freely determined independently. Therefore, if the movement amount of one tension roller is set large, the movement amount of the other tension roller is set larger. Can be prevented from occurring.

In such a configuration, the positional relationship between the holding member of the stretching roller on the upstream side of the scale sensor and the intermediate transfer belt in the portion including the detection position is changed by the contact / separation operation. Similarly, the positional relationship between the holding member of the stretching roller on the downstream side of the scale sensor and the intermediate transfer belt at the portion including the detection position is also changed by the contact / separation operation. As a result, the angle formed between the sensor surface of the scale sensor and the stretched surface of the belt member including the detection position changes.
Thus, in the configuration in which the trajectory of the tension surface of the belt member including the detection position is changed, and the two tension rollers forming the tension surface are held by independent holding members, the scale sensor is It is impossible to hold the two tension rollers on the same holding member. Therefore, either the same holding member as one of the stretching rollers or the holding member only of the scale sensor is used.

In this case, theoretically, unless the rotation axis of the sensor bracket is near the position where the uppermost belt member where the belt member bends and the photosensitive member are in contact with each other, the positional relationship between the belt member and the sensor surface is maintained. It cannot be kept constant.
Examples of the configuration that keeps the positional relationship between the belt member and the sensor surface constant include the following configurations (1) and (2).

(1) The rotation axis of the sensor bracket is brought close to the contact between the most upstream photoconductor and the belt member (the belt bends).
(2) The positioning reference of the sensor bracket is changed not only by the sub-reference but also by the main reference at the time of contact and separation.
When trying to implement the configuration (1), the sensor bracket becomes very large, and it is necessary to provide a space for arranging the large sensor bracket.
Therefore, although the configuration of (2) is used, the configuration corresponding to the configuration of (2) is the configuration described with reference to FIG.

  In the configuration shown in FIG. 1, the upstream tension roller and the downstream tension roller can be separate holding members with respect to the scale sensor. For this reason, the position at the time of separation of the stretching roller can be independently positioned so as to prevent the belt tension from being lowered as much as possible while ensuring the separation amount. In the configuration shown in FIG. 1, the positional relationship between the intermediate transfer belt 50 and the scale sensor 6 can be kept constant.

Next, a configuration example in which the K nip upstream roller 153, the K primary transfer roller 62K, and the K nip downstream roller 154 are held by individual holding members in the copier 500 of the present embodiment to perform the contact / separation operation will be described.
FIG. 12 is an enlarged perspective view of the vicinity of the K primary transfer roller 62K of the belt unit 510 with the intermediate transfer belt 50 removed.

The belt unit 510 includes two transfer frames 501 (a front transfer frame 501a and a back transfer frame 501b) as intermediate transfer belt frames.
A back side contact / separation slider 550b is slidably held with respect to the back side transfer frame 501b, and a front side contact / separation slider 550a (not shown) is slidably held with respect to the front side transfer frame 501a.

  FIG. 13 is an explanatory view of the rear side contact / separation slider 550b as viewed from the front side (the direction of arrow G in FIG. 12), and each roller is a sectional view. FIG. 14 is an explanatory view of each member held by the back side contact / separation slider 550b as viewed from the back side contact / separation slider 550b side (in the direction of arrow H in FIG. 12). FIGS. 13 and 14 are explanatory views of the K primary transfer roller 62K in contact with the K photoconductor 10K with the intermediate transfer belt 50 interposed therebetween.

  As shown in FIG. 12, the belt unit 510 includes a front upstream roller bracket 702a and a back upstream roller bracket 702b as two upstream roller brackets 702 that hold the K nip upstream roller 153. Further, as the two K roller brackets 802 for holding the K primary transfer roller 62K, a front K roller bracket 802a and a back K roller bracket 802b are provided. Further, as the two downstream roller brackets 902 that hold the K-nip downstream roller 154, a front-side downstream roller bracket 902a and a back-side upstream roller bracket 902b are provided.

  In addition, a contact / separation cam 503 that slides the contact / separation slider 550 left and right by abutting against the contact / separation slider 550 and an contact / separation cam drive shaft 504 are provided. Further, a pulley 505 and a timing belt 506 that transmit driving to the contact / separation cam drive shaft 504 are provided, and a cam drive motor 508 that is a drive source of the contact / separation cam drive shaft 504 is provided. Further, a cam drive member holding bracket 507 that holds a cam drive motor 508, a drive gear (not shown), and the like is fixed to the front transfer frame 501a.

The contact / separation slider 550 is configured to slide in the left-right direction in FIG. 13 with respect to the transfer frame 501. The contact / separation slider 550 is positioned in the vertical direction by a first slider positioning ball bearing 551 and a second slider positioning ball bearing 552.
The contact / separation slider 550 is positioned by the contact / separation cam 503 in the left-right direction. The contact / separation slider 550 is pulled in the right direction in FIG. 13 (in the direction of arrow E3 in the figure) by a slider tension spring 560 having one end fixed to the transfer frame 501. The contact / separation cam receiving ball bearing 513 is positioned by abutting against the contact / separation cam 503 in a state where the contact / separation slider 550 is pulled by the slider tension spring 560.

  As shown in FIG. 13, the upstream roller bracket 702 is rotatable about an upstream roller rotation shaft 172 fixed to the transfer frame 501. The upstream roller bracket 702 is urged in the direction of arrow E4 in the figure by an upstream roller bracket tension spring 723 having one end fixed to the contact / separation slider 550. Further, as shown in FIG. 14, the upstream roller bracket 702 includes an upstream roller abutting reference member 706. In the contact state, the upstream roller abutting reference member 706 abuts against an upstream roller positioning stud 707 provided on the transfer frame 501, thereby positioning the upstream roller bracket 702.

  The downstream roller bracket 902 is rotatable about a downstream roller rotation shaft 192 fixed to the transfer frame 501. The downstream roller bracket 902 is biased in the direction of arrow E6 in the figure by a downstream roller bracket tension spring 903 having one end fixed to the contact / separation slider 550. As shown in FIG. 14, the downstream roller bracket 902 includes a downstream roller abutting reference member 906. In the contact state, the downstream roller abutting reference member 906 abuts the downstream roller positioning stud 907 provided on the transfer frame 501, thereby positioning the downstream roller bracket 902.

  The K roller bracket 802 is rotatable about a K roller rotation shaft 182 fixed to the transfer frame 501. The K roller bracket 802 is urged in the direction of arrow E5 in the figure by a K roller bracket tension spring 803 having one end fixed to the contact / separation slider 550. The K roller bracket 802 is positioned in the contact state when the K primary transfer roller 62K abuts against the K photoconductor 10K with the intermediate transfer belt 50 interposed therebetween.

  FIG. 15 is an enlarged explanatory view of the positional relationship between the contact / separation studs (715, 805 and 905) provided on the contact / separation slider 550 and the roller brackets (702, 802 and 902). 15 (a) is an enlarged view of the region indicated by α in FIG. 14, FIG. 15 (b) is an enlarged view of the region indicated by β in FIG. 14, and FIG. 15 (c) is an enlarged view of γ in FIG. It is an enlarged view of the area | region shown by.

In the contact state, as shown in FIG. 15A, the downstream roller bracket separation contact surface 952 of the downstream roller bracket 902 is separated from the downstream roller contact / separation stud 905. Further, as shown in FIG. 15B, the K roller bracket separating contact surface 852 of the K roller bracket 802 is separated from the K roller contact / separation stud 805. Furthermore, the upstream roller bracket separation surface 752 of the upstream roller bracket 702 is separated from the upstream roller contact / separation stud 715.
As described above, in the contact state, positioning is performed by abutting the abutting slave reference or the primary transfer roller. For this reason, it arrange | positions so that the abutting surface (752,852,952) at the time of separation of each bracket may not contact each contact / separation stud (715,805,905).

FIG. 16 is an explanatory diagram of the part shown in FIG. 13 in the separated state, and FIG. 17 is an explanatory diagram of the part shown in FIG. 14 in the separated state.
When the cam drive motor 508 is driven from the contact state and the contact / separation cam 503 is displaced from the state shown in FIG. 13 to the state shown in FIG. 16, the contact / separation cam receiving ball bearing 513 is pushed by the contact / separation cam 503. The contact / separation slider 550 slides in the direction of arrow I in the drawing.
Thereby, as shown in FIG. 14, each contacting / separating stud (715, 805 and 905) contacts the abutting surface (752, 852 and 952) of each bracket, and each roller bracket (702, 802 and 902) is pressed.

Each roller bracket (702, 802 and 902) is rotated by being pressed, and each roller (153, 62K and 154) is moved downward, and the K primary transfer roller 62K is moved relative to the K photoconductor 10K. Are separated.
In the contact state, the abutting reference members (706 and 906) that are in contact with the positioning studs (707 and 907) included in the transfer frame 501 are separated from the positioning studs (707 and 907) in the separated state. It becomes.
In the separated state, the roller brackets (702, 802 and 902) biased by the tension springs (723, 803 and 903) abut against the contact studs (715, 805 and 905). Thereby, each roller bracket (702, 802 and 902) is positioned.

  The contact / separation cam 503 in the configuration described with reference to FIGS. 12 to 17 corresponds to the upstream roller drive cam 703 in the configuration of FIG. The upstream roller bracket tension spring 723 in the configuration described with reference to FIGS. 12 to 17 corresponds to the upstream roller biasing spring 750 in the configuration of FIG.

  In the configuration described with reference to FIG. 1, the member constituting the detecting means rotating shaft moving means that holds and moves the sensor rotating shaft 162 of the sensor bracket 161 that constitutes the detecting means holding member is the upstream roller bracket. 702. The member that moves while holding the sensor rotation shaft 162 is not limited to the upstream roller bracket 702, and may be a holding member (roller bracket) of another stretching roller. Furthermore, the sensor rotation shaft 162 that is the detection device rotation shaft may be held by a support member that is independent of the holding member of the stretching roller. That is, the distance between the intermediate transfer belt 50 including the detection position and the sensor rotating shaft 162 may be kept constant in the contact state and the separated state.

  The intermediate transfer belt 50 of this embodiment is supported by stretching rollers (14, 15, 16 and the like) that are a plurality of stretching members, and the outer peripheral surface of the intermediate transfer belt 50 is brought into contact with the photosensitive member 10 that is an image carrier. An endless belt member that moves endlessly while forming a nip. The belt unit 510 is a transfer unit that transfers the toner image on the surface of the photoreceptor 10 on the outer peripheral surface of the intermediate transfer belt 50 at the transfer nip. The transfer means is not limited to the one that transfers the toner image to the outer peripheral surface of the intermediate transfer belt 50, but is one that is carried by the transfer conveyance belt and transfers the toner image superimposed on the surface of the transfer material sandwiched between the transfer nips. May be.

The contact / separation slider 550 and the roller brackets (702, 802, 902) described with reference to FIGS. 12 to 17 are contact / separation means for contacting / separating the intermediate transfer belt 50 with respect to the K photoconductor 10K. The scale sensor 6 is a detection target on the surface (in the present embodiment, the inner peripheral surface) of the intermediate transfer belt 50 at the detection position of the intermediate transfer belt 50 where the trajectory changes due to the contact / separation operation of the contact / separation means. This is a detecting means for detecting the scale mark SM.
The sensor holding member 130 and the sensor bracket 161 are detection means holding members that hold the scale sensor 6 that is a detection means in a fixed state and can rotate around a sensor rotation shaft 162 that is a detection means rotation shaft. .

The upstream roller drive cam 703 and the upstream roller bracket 702 are detection unit rotation shaft moving units that move the sensor rotation shaft 162 in accordance with the above-described contact / separation operation. Further, the position of the sensor rotation shaft 162 in the upstream roller bracket 702 is set so that the distance from the intermediate transfer belt 50 including the detection position to the sensor rotation shaft 162 is the same as the contact state and the separation state. doing.
The contact-time slave reference member 704 and the separation-time slave reference member 713 are detection means rotation direction positioning means for positioning the rotation direction of the sensor bracket 161 that is a detection means holding member. The positions of the contact reference member 704 and the contact reference member 713 are set so that the inclination of the sensor bracket 161 with respect to the tension surface of the intermediate transfer belt 50 including the detection position is the same in the contact state and the separation state. ing.

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 a photoreceptor 10 that carries a toner image, a belt member such as an endless intermediate transfer belt 50 that moves endlessly while forming a transfer nip with an outer peripheral surface in contact with the image carrier, and a belt member Contact / separation means such as a contact / separation slider 550 and roller brackets (702, 802 and 902) that contact and separate the image carrier, and a scale sensor 6 that detects a detection target such as a scale mark SM on the surface of the belt member. Copier 500 having a detection means such as a sensor holding member 130 that holds the detection means and is rotatable about a rotation shaft such as a sensor rotation shaft 162 and a detection means holding member such as a sensor bracket 161. In the image forming apparatus such as the upstream roller drive cam 703 and the upstream roller bracket 702 that move the rotation shaft of the detection unit holding member with respect to the apparatus main body, Provided with the means.
According to this, as described in the above embodiment, the tension member such as the K nip upstream roller 153 on the upstream side of the detecting means such as the scale sensor 6 and the tension member such as the downstream K nip downstream roller 154 on the downstream side. Even if the positional relationship between the holding member (upstream roller bracket 702, downstream roller bracket 902, etc.) and the belt member including the detection position is changed by the contact / separation operation, the detection means and the detection position of the belt member It is possible to keep the positional relationship constant regardless of the contact / separation operation.
(Aspect B)
In the aspect A, the detecting means rotating shaft moving means such as the upstream roller driving cam 703 and the upstream roller bracket 702 is a belt member such as the intermediate transfer belt 50 including a detection position where the detecting means such as the scale sensor 6 detects the detection target. The rotation axis of the detection means holding member is moved so that the distance from the flat surface to the rotation axis of the detection means holding member such as the sensor rotation axis 162 is the same in the contact state and the separated state. Positioning of the detection means holding member in the rotation direction so that the inclination of the detection means holding members such as the sensor holding member 130 and the sensor bracket 161 with respect to the plane of the belt member including the detection position is the same in the contact state and the separated state. Detecting means rotation direction positioning means such as a contact-time slave reference member 704 and a separation-time slave reference member 713 are provided.
According to this, since the distance and inclination of the detection means holding member with respect to the plane of the belt member including the detection position can be kept constant as described in the above embodiment, the detection held by the detection means holding member The positional relationship between the means and the plane of the belt member including the detection position can be kept constant regardless of the contact / separation operation.
(Aspect C)
In the aspect A or the aspect B, a plurality of image carriers such as the photoconductor 10 are provided, and among the plurality of image carriers, the K photoconductor disposed on the most downstream side in the endless movement direction of the belt member such as the intermediate transfer belt 50. Only the image carrier such as the body 10K has the most downstream contact mode in which the belt member is brought into contact.
According to this, as described in the above embodiment, the positional relationship between the detection means and the plane of the belt member including the detection position can be maintained even in the monochrome mode such as the monochrome mode.
(Aspect D)
In any one of the aspects A to C, a plurality of image carriers such as the photoconductor 10 are provided, and among the plurality of image carriers, the belt member such as the intermediate transfer belt 50 is disposed on the most upstream side in the endless movement direction. Only the image carrier such as the S photoconductor 10S has the most upstream contact mode in which the belt member is brought into contact.
According to this, as described in the above embodiment, the positional relationship between the detection means and the plane of the belt member including the detection position is maintained even in the single color mode such as when only clear toner is transferred to the recording medium. Can do.
(Aspect E)
In any one of the aspects A to D, the detecting means such as the scale sensor 6 contacts the detecting means contact surface such as the belt facing surface 131 with the surface of the belt member such as the intermediate transfer belt 50, and the like. A belt sandwiching member such as a belt upper pressing member 135 that sandwiches the belt member with the detection means contact surface is provided for detecting a detection target.
According to this, as described in the above embodiment, the belt member at the detection position is sandwiched and pressed, so that the belt member can be prevented from flapping and the detection accuracy of the detection means can be increased.
(Aspect F)
In any of the aspects A to E, the abutting members such as the contact reference member 704 and the slave reference member 713 at the time of contact with which the detection means holding member such as the sensor bracket 161 abuts, and the detection means toward the abutment member An urging means such as a sensor bracket urging spring 751 for urging the holding member is provided, and the detecting means holding member is positioned in the rotational direction by the abutting member and the urging means.
According to this, as described in the above embodiment, the resonance frequency of the detection means holding member can be adjusted by adjusting the biasing force such as the spring constant, and the detection means holding member when vibration is input. Can reduce the vibration.
(Aspect G)
In any of the aspects A to F, the detecting means such as the scale sensor 6 contacts the detecting means contact surface such as the belt facing surface 131 with the surface of the belt member such as the intermediate transfer belt 50, and the like. The detection target is detected, and a flocking process is performed on the contact surface of the detection means.
According to this, as described in the above embodiment, the belt member and the detection target can be prevented from being damaged.

5 Scale 6 Scale sensor 7 Belt drive motor 8 Reduction gear 10 Photoreceptor 14 Belt drive roller 15 Cleaning facing roller 16 Secondary transfer facing roller 18 Image forming unit 19 Tension roller 21 Exposure device 22 Secondary transfer device 25 Fixing device 50 Intermediate transfer Belt 62 Primary transfer roller 70 Drive control device 71 Control device 105 Intermediate transfer belt drive device 110 Belt speed detection device 120 Tandem type image forming unit 130 Sensor holding member 131 Belt facing surface 132 Sensor window 135 Belt upper pressing member 136 Upper pressing contact portion 140 Sensor housing 150 Printer unit 153 K nip upstream roller 154 K nip downstream roller 156 Discharge roller pair 161 Sensor bracket 162 Sensor rotating shaft 200 Paper feeder 300 Scanner 400 Automatic document feeder 43 Document table 500 Copier 501 Transfer frame 501a Front transfer frame 501b Back transfer frame 503 Contact / separation cam 508 Cam drive motor 510 Belt unit 513 Contact / separation cam receiving ball bearing 550 Contact / separation slider 550a Front side contact / separation slider 550b Back Contact / separation slider 551 First slider positioning ball bearing 552 Second slider positioning ball bearing 560 Slider tension spring 702 Upstream roller bracket 702a Front upstream roller bracket 702b Back upstream roller bracket 703 Upstream roller drive cam 704 Contact reference member 705 Upstream roller follower reference member 706 Upstream roller abutting follower reference member 707 Upstream roller positioning stud 713 Separated follower reference member 715 Upstream roller contact / separation stud 723 Upstream roller bracket pull Pulling 751 Sensor bracket biasing spring 750 Upstream roller biasing spring 752 Abutting surface 802 when the upstream roller bracket is separated 802 K roller bracket 802a Front side K roller bracket 802b Back side K roller bracket 803 K roller bracket tension spring 805K Roller contacting / separating stud 852 K roller bracket separating contact surface 902 Downstream roller bracket 902a Front downstream roller bracket 902b Back downstream roller bracket 903 Downstream roller bracket tension spring 905 Downstream roller contacting stud 906 Downstream roller abutting reference Member 907 Downstream roller positioning stud 952 Abutting surface when downstream roller bracket is separated

JP 2010-256459 A

Claims (6)

An image carrier for carrying a toner image;
An endless belt member that moves endlessly while forming a transfer nip by bringing the outer peripheral surface into contact with the image carrier;
Contacting / separating means for contacting / separating the belt member to / from the image carrier;
Detecting means for detecting a detection target on the surface of the belt member;
An image forming apparatus having a detection means holding member that holds the detection means and is rotatable about a rotation axis;
E Bei sensing means rotating shaft moving means for moving the rotary shaft of said detecting means holding member relative to the apparatus main body,
The detecting means rotating shaft moving means is configured such that the distance from the plane of the belt member including the detection position where the detecting means detects the detection target to the rotating shaft of the detecting means holding member is a contact state and a separated state. The rotation axis of the detection means holding member is moved so as to be the same at
A detection means circuit for positioning the detection means holding member in the rotational direction so that the inclination of the detection means holding member with respect to the plane of the belt member including the detection position is the same in the contact state and the separated state. An image forming apparatus comprising a moving direction positioning unit. The image forming apparatus according to claim 1 .
The most downstream contact mode in which the belt member is brought into contact only with the image carrier disposed on the most downstream side in the endless movement direction of the belt member among the plurality of image carriers. An image forming apparatus comprising: The image forming apparatus according to claim 1 or 2 ,
The most upstream contact mode in which the belt member is brought into contact only with the image carrier disposed on the most upstream side in the endless movement direction of the belt member among the plurality of image carriers. An image forming apparatus comprising: The image forming apparatus according to any one of claims 1 to 3 ,
The detection means detects the detection target by bringing the detection means contact surface into contact with the surface of the belt member,
An image forming apparatus comprising: a belt pinching member that pinches the belt member with the detection unit contact surface. The image forming apparatus according to any one of claims 1 to 4 ,
The abutting member with which the detecting means holding member abuts, and an urging means for urging the detecting means holding member toward the abutting member, are held by the abutting member and the urging means. An image forming apparatus that positions a member in a rotation direction. The image forming apparatus according to claim 1 to 5,
The detection means detects the detection target by bringing the detection means contact surface into contact with the surface of the belt member,
An image forming apparatus, wherein a flocking process is performed on the contact surface of the detection means.

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