JP5923455B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to a sensor positioning technique for reading a toner image of a reference pattern formed on an intermediate transfer belt.

  There is known a tandem type image forming apparatus in which image forming units of respective colors are arranged in parallel to a position facing the intermediate transfer belt, and toner images of the respective colors are superimposed on the intermediate transfer belt to form a color image. In this image forming apparatus, for example, as disclosed in Japanese Patent Application Laid-Open No. 2004-228561, the image forming apparatus faces the intermediate transfer belt in order to detect the position and density of each color toner image transferred from the image forming unit onto the intermediate transfer belt. An optical sensor is disposed at the position. In this image forming apparatus, the density adjustment and toner image formation timing adjustment of each image forming unit are performed based on the detection result by the optical sensor, so that the tint is optimized and color misregistration is prevented at the time of color image formation.

JP 2001-175126 A

  In the image forming apparatus, the detection result of the optical sensor is used for density adjustment and toner image formation timing adjustment. Therefore, accuracy is required for the detection result by the optical sensor. In order to obtain an accurate detection result by the optical sensor, the distance between the intermediate transfer belt on which the toner image is formed and the optical sensor is an important factor. Therefore, accuracy is required for positioning of the optical sensor with respect to the intermediate transfer belt. Here, if the optical sensor is integrated with the intermediate transfer unit, the positioning problem is solved. However, the optical sensor has a longer life than the intermediate transfer unit and satisfies the entire life of the image forming apparatus. Arrangement not on the unit side but on the apparatus main body side is preferable. When the optical sensor is provided on the apparatus main body side in this way, the positioning of the optical sensor with respect to the intermediate transfer belt when the intermediate transfer unit is attached to the apparatus main body is performed through many parts, so that it is difficult to obtain accuracy. For example, the optical sensor is attached to the intermediate transfer belt, the belt drive roller, the roller bearing, the intermediate transfer unit housing, the intermediate transfer position unit determining member on the apparatus frame side, the main body frame, and the main body frame. Relative positioning with the intermediate transfer belt is performed via the optical sensor.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to suppress unnecessary replacement of the optical sensor and to accurately position the optical sensor with respect to the intermediate transfer belt.

An image forming apparatus according to an aspect of the present invention includes an intermediate transfer unit and an intermediate transfer unit that includes a roller that allows the intermediate transfer belt to run endlessly, and is detachable from the apparatus main body.
A secondary transfer roller that forms a nip portion paired with a roller that runs the intermediate transfer belt endlessly;
A registration roller for conveying a recording medium toward the nip portion;
A pre-transfer guide that is rotatably mounted about the axis of the registration roller and guides a recording medium conveyed from the registration roller to the nip portion;
A sensor for reading a toner image formed on the intermediate transfer belt;
A holding member for holding the sensor;
A mounting member for movably holding the contact and separation direction, attached to the pre-transfer guide relative to the intermediate transfer unit and the holding member,
A restricting portion that is provided on the holding member and restricts a movement limit position of the sensor in the contact / separation direction by contact with a part of the intermediate transfer unit;
A contact portion that is provided in the pre-transfer guide and restricts a rotation limit position of the pre-transfer guide in a direction toward the intermediate transfer unit.

  According to the present invention, even if the sensor for reading the toner image formed on the intermediate transfer belt is not provided on the intermediate transfer unit side but is provided on the apparatus main body side, the contact and separation directions with respect to the intermediate transfer unit are also provided. Since the sensor can be positioned with a relatively small number of parts, unnecessary replacement of the optical sensor can be suppressed and the sensor can be accurately positioned with respect to the intermediate transfer belt.

1 is a front sectional view showing a structure of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view illustrating an appearance of an intermediate transfer unit. It is a figure which shows opening and closing of the door part provided in the image forming apparatus. FIG. 3 is a perspective view showing an external appearance of an intermediate transfer unit, a registration roller, and a pre-transfer guide portion mounted on the apparatus main body. It is a perspective view which shows the structure of a registration roller, a pre-transfer guide, and a sensor unit. It is a perspective view which shows the structure of a registration roller, a pre-transfer guide, and a sensor unit part. It is an expansion perspective view of the guide groove part of an attachment member. It is a perspective view which shows the pre-transfer guide of the state attached to the rotating shaft of a registration roller. It is a perspective view which shows the press spring attached between the holding member and the attachment member. (A) is a cross-sectional view of the intermediate transfer unit (part), the registration roller, the pre-transfer guide, and the sensor unit at the position where the optical sensor is disposed when the door of the apparatus main body is open. FIG. 4B is a cross-sectional view of the pre-transfer guide and the sensor unit at a position where the optical sensor is not disposed when the door portion of the apparatus main body is open. FIG. 6C is a cross-sectional view of the pre-transfer guide and the sensor unit at the position where the push spring is disposed when the door portion of the apparatus main body is open. (A) is a cross-sectional view of the intermediate transfer unit (part), the registration roller, the pre-transfer guide, and the sensor unit at the position where the optical sensor is disposed when the door portion of the apparatus main body is closed. FIG. 5B is a cross-sectional view of the pre-transfer guide and the sensor unit at a position where the optical sensor is not disposed when the door portion of the apparatus main body is closed. (C) is a cross-sectional view of the pre-transfer guide and the sensor unit at the position where the push spring is disposed when the door of the apparatus main body is closed.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a front sectional view showing the structure of an image forming apparatus 1 according to an embodiment of the present invention.

  An image forming apparatus 1 according to an embodiment of the present invention is a multifunction machine having a plurality of functions such as a copy function, a printer function, a scanner function, and a facsimile function. The image forming apparatus 1 is configured to include an operation unit 47, an image forming unit 12, a fixing unit 13, a paper feeding unit 14, a document feeding unit 6, and an image reading unit 5 in the apparatus main body 11.

The operation unit 47 receives instructions such as an image forming operation execution instruction and a document reading operation execution instruction from the operator regarding various operations and processes that can be executed by the image forming apparatus 1.

  When the image forming apparatus 1 performs a document reading operation, the image reading unit 5 optically reads a document fed by the document feeding unit 6 or a document placed on the document placing glass 161. Generate image data. The image data generated by the image reading unit 5 is stored in a built-in HDD or a computer connected to a network.

  When the image forming apparatus 1 performs an image forming operation, based on image data generated by a document reading operation, image data received from a computer connected to a network, image data stored in a built-in HDD, or the like, The image forming unit 12 forms a toner image on a recording paper (an example of a recording medium) P as a recording medium fed from the paper feeding unit 14. The image forming units 12M, 12C, 12Y, and 12Bk of the image forming unit 12 include a photosensitive drum 121, a developing device 122 that supplies toner to the photosensitive drum 121, a toner cartridge (not shown) that stores the toner, A charging device 123, an exposure device 124, and a primary transfer roller 126 are provided.

  When performing color printing, the magenta image forming unit 12M, the cyan image forming unit 12C, the yellow image forming unit 12Y, and the black image forming unit 12Bk of the image forming unit 12 each receive image data. A toner image is formed on the photosensitive drum 121 by charging, exposure, and development processes based on the image composed of each color component, and the toner image is transferred to the driving roller 125a and the driven roller 125b by the primary transfer roller 126. The image is transferred onto the intermediate transfer belt 125 that is stretched.

  The intermediate transfer belt 125 is driven by a driving roller 125 a in a state where an image carrying surface on which a toner image is transferred is set on the outer peripheral surface thereof and in contact with the peripheral surface of the photosensitive drum 121. The intermediate transfer belt 125 travels endlessly between the driving roller 125a and the driven roller 125b while being synchronized with each photosensitive drum 121. The intermediate transfer belt 125 is supported from the inside by a tension roller 125c disposed in the vicinity of the drive roller 125a.

  The intermediate transfer belt 125, the primary transfer roller 126, the driving roller 125a, the driven roller 125b, and the tension roller 125c are mounted on the intermediate transfer unit 50.

  The toner images of the respective colors transferred onto the intermediate transfer belt 125 are superimposed on the intermediate transfer belt 125 with the transfer timing adjusted to become a color toner image. The secondary transfer roller 210 transfers a color toner image formed on the surface of the intermediate transfer belt 125 from the paper supply unit 14 to the plurality of transport rollers 19 at a nip N between the intermediate transfer belt 125 and the driving roller 125a. As a result, the transfer path 190 is transferred to the recording paper P that has been transported. The registration roller 19a adjusts the leading end position of the recording paper P conveyed to the nip portion N, and the pre-transfer guide 190a guides the recording paper P from the registration roller 19a to the nip portion N. A sensor unit 500 described later is attached to the pre-transfer guide 190a. After the transfer of the toner image onto the recording paper P, the fixing unit 13 fixes the toner image on the recording paper P to the recording paper P by thermocompression bonding. The recording paper P on which the color image has been formed after completion of the fixing process is discharged to a discharge tray 151.

  Next, the intermediate transfer unit 50 will be described. FIG. 2 is a perspective view showing the appearance of the intermediate transfer unit 50. FIG. 3 is a view showing opening and closing of a door portion provided in the image forming apparatus 1.

The intermediate transfer unit 50 is configured to be detachable from the apparatus main body 11. As described above, the intermediate transfer unit 50 mounts the intermediate transfer belt 125, the primary transfer roller 126, the driving roller 125a, the driven roller 125b, and the tension roller 125c.

  The intermediate transfer unit 50 includes a casing 54. Each mechanism included in the intermediate transfer unit 50 is attached to the casing 54. The casing 54 includes an upper surface portion 54c and side surface portions 54a and 54b provided at the edge of the upper surface portion 54c. A driving roller 125a is rotatably supported at one end of the casing 54, and a driven roller 125b is supported at the other end.

  The intermediate transfer belt 125 is stretched between the driving roller 125a and the driven roller 125b supported in this manner, and the upper and both sides thereof are covered with a casing 54 including an upper surface portion 54c and side surface portions 54a and 54b. ing. A lower portion of the intermediate transfer belt 125 in FIG. 2 is exposed from the casing 54. In a state where the intermediate transfer unit 50 is loaded in the apparatus main body 11, an image forming unit for each color is disposed in the apparatus main body 11 below the exposed intermediate transfer belt 125 portion.

  As shown in FIG. 3, a door 11 a that can be opened and closed is provided on the side of the apparatus main body 11. A part of the side part of the apparatus main body 11 is a door part 11a, and the door part 11a rotates in the contact / separation direction D1 with respect to the image forming part 12 in the apparatus main body 11 with the rotation shaft 11b as a rotation axis. One side portion of the transport path 190 is disposed on the door portion 11a, and the transport roller 19 and the secondary transfer roller 210 disposed on the one side portion of the transport path 190 are also disposed on the door portion 11a. For this reason, when the operator rotates the door portion 11a in the direction away from the apparatus main body 11, the secondary transfer roller 210 provided on the door portion 11a is separated from the driving roller 125a of the intermediate transfer unit 50, and the conveyance path 190. The intermediate transfer unit 50 in the apparatus main body 11 is exposed.

  When the door portion 11a is rotated in the state shown in FIG. 3, the intermediate transfer unit 50 exposes the drive roller 125a and the casing 54 portion where the drive roller 125a is disposed. A grip portion 540 (FIG. 2) is provided in the exposed casing 54 portion. When the operator grasps the grip portion 540 and pulls out the intermediate transfer unit 50 in the drawing direction D2 shown in FIGS. 2 and 3, the intermediate transfer unit 50 is detached from the apparatus main body 11 and pulled out from the apparatus main body 11 to the outside.

  When the intermediate transfer unit 50 is mounted in the apparatus main body 11, the operator can move the intermediate transfer unit 50 in the state shown in FIG. 3 in which the door 11 a is rotated to open the apparatus main body 11. Is inserted into the apparatus main body 11 in the insertion direction D3 shown in FIG. 3 from the end 50a on the side where the driven roller 125b is attached. A protrusion 541 is provided at the end 50a. Although FIG. 2 shows an example in which there are two protrusions 541, only one of the protrusions 541 may be provided. In the vicinity of the inner surface 11c in the apparatus main body 11, a recess into which the protrusion 541 is fitted is formed. When the operator inserts the intermediate transfer unit 50 into the apparatus main body 11 by a predetermined amount, the protrusion The intermediate transfer unit 50 is fixed in the apparatus main body 11, and positioning and mounting of the intermediate transfer unit 50 with respect to the apparatus main body 11 are completed.

  FIG. 4 is a perspective view showing the external appearance of the intermediate transfer unit 50, the registration roller 19a, and the pre-transfer guide 190a mounted on the apparatus main body 11. As shown in FIG. FIG. 5 is a perspective view showing structures of the registration roller 19a, the pre-transfer guide 190a, and the sensor unit 500. FIG. 6 is a perspective view showing the structure of the registration roller 19a, the pre-transfer guide 190a, and the sensor unit 500.

  The registration roller 19a is disposed on the upstream side in the transport direction of the recording P with respect to the nip portion N between the intermediate transfer belt 125 and the secondary transfer roller 210 stretched around the driving roller 125a. The registration roller 19 a adjusts the timing at which the leading end of the recording paper P transported by the transport roller 19 toward the nip N through the transport path 190 reaches the nip N.

  The pre-transfer guide 190a is a member that forms part of the transport path 190 and guides the transport direction of the recording paper P transported from the registration roller 19a to the nip portion N.

  The pre-transfer guide 190a includes a connecting portion 190b, a base portion 190c, a guide tip portion 190d, and a contact portion 190e.

  The connecting portion 190b is connected to each of the bearing portions 19c at both ends of the registration roller 19a. The base portion 190c is an elongated plate-like member that extends between the connection portions 190b. The guide front end 190d is a long plate-like member that extends from the end of the base 190c on the intermediate transfer unit 50 side toward the nip portion N and has a length that spans the width of the intermediate transfer belt 125 in the length direction. is there. The abutting portion 190e is formed on both outer sides of the longitudinal end portion of the guide front end portion 190d in the base portion 190c, protrudes toward the intermediate transfer unit 50, abuts against a part of the intermediate transfer unit 50, and contacts the pre-transfer guide 190a. The rotation limit position is regulated.

  The pre-transfer guide 190a is attached to the bearing portions 19c at both ends of the registration roller 19a by the connecting portion 190b so as to be rotatable in the contact / separation direction with respect to the intermediate transfer unit 50 with the shaft 19b of the registration roller 19a as a rotation axis. Yes.

  A torsion coil spring (described later) is attached to the connecting portion 190b attached to the bearing portion 19c. The torsion coil spring urges the pre-transfer guide 190a away from the intermediate transfer unit 50 when rotating. When the intermediate transfer unit 50 is attached to the apparatus main body 11, the pre-transfer guide 190a is directed to the intermediate transfer unit 50 by a protrusion provided on the conveyance path 190 provided on the door portion 11a side. It is pressed in the direction and held in the posture shown in FIG.

  When the operator removes the intermediate transfer unit 50 from the apparatus main body 11, when the operator opens the door portion 11a provided on the side portion of the apparatus main body 11, the pre-transfer guide 190a is moved to the conveyance path 190 portion on the door portion 11a side. The pre-transfer guide 190a is released from being pressed by the provided protrusion, and is biased by the torsion coil spring. The pre-transfer guide 190a moves around the shaft 19b of the registration roller 19a when the intermediate transfer unit 50 is pulled out from the apparatus main body 11. It is rotated in a direction away from the intermediate transfer unit 50 to a position below it. Thus, the operator can pull out the intermediate transfer unit 50 without the pre-transfer guide 190a becoming an obstacle.

  The sensor unit 500 is a unit having two optical sensors (an example of a sensor in claims) 51. Each optical sensor 51 reads the toner image of the reference pattern formed on the intermediate transfer belt 125 by the image forming unit 12. The detection result by each optical sensor 51 is used for density adjustment (calibration) at the time of toner image formation by the image forming unit 12 and adjustment of toner image formation timing. The sensor unit 500 includes an optical sensor 51, a holding member 52, and an attachment member 510.

  The optical sensor 51 is held by the holding member 52 so that light can be irradiated onto the peripheral surface of the intermediate transfer belt 125. The attachment member 510 attaches the sensor unit 500 to the pre-transfer guide 190a. The attachment member 510 is made of a flat plate-like member and has a storage portion 5101 for storing the holding member 52. Further, both ends of the mounting member 510 in the length direction are screwed to the base portion 190c of the pre-transfer guide 190a. The holding member 52 has a size that is the same as or slightly smaller than the storage portion 5101 of the holding member 52 in plan view. The mounting member 510 can move the holding member 52 up and down in the storage portion 5101 that is a gap between the pre-transfer guide 190 a and the mounting member 510, that is, can move in the contact and separation direction with respect to the intermediate transfer unit 50. Hold.

  The optical sensor 51 is provided in the holding member 52 at two different positions in the rotation axis direction of the registration roller 19a. Further, the optical sensor 51 is located at a position facing the intermediate transfer belt 125 and in the vicinity of both ends in the width direction (rotational axis direction of the driving roller 125a) with respect to the intermediate transfer belt 125. And the mounting position of the sensor unit 500 with respect to the apparatus main body 11 are set. The optical sensor 51 is electrically connected to a control unit (not shown), and outputs the detected toner image to the control unit.

The optical sensor 51 includes a light emitting unit and a light receiving unit.

  The light emitting unit irradiates light to an arbitrary point on the circumferential surface of the intermediate transfer belt 125, that is, a position where the toner image is transferred for density adjustment or toner image formation timing adjustment by the image forming unit 12. The light receiving unit receives light reflected from the circumferential surface of the intermediate transfer belt 125 by the light emitted from the light emitting unit. The light receiving unit splits the reflected light and receives, for example, light of the first and second polarization components.

  The reflected light on the circumferential surface of the intermediate transfer belt 125 includes specularly reflected light in the vicinity of the same angle as the incident angle of the light from the light emitting portion and other diffused light, and the toner transferred to the circumferential surface of the intermediate transfer belt 125. Depending on the amount, the ratio of the diffused light component increases and the ratio of the first and second polarization components changes. The optical sensor 51 outputs an analog voltage corresponding to the ratio of the first and second polarization components received by the light receiving unit to a control unit (not shown). When there is no toner on the peripheral surface of the intermediate transfer belt 125, the first polarization component becomes maximum and the output voltage becomes the maximum value. As the amount of toner on the peripheral surface of the intermediate transfer belt 125 increases, the first polarization component increases. The amount of light decreases and the output voltage decreases. Based on the output voltage of the optical sensor 51, the controller calculates the amount of toner constituting the toner image on the circumferential surface of the intermediate transfer belt 125, that is, the toner density of the toner image.

  The holding member 52 is a member for holding the optical sensor 51. The holding member 52 is a long member extending in the rotation axis direction of the registration roller 19a. At both ends in the longitudinal direction of the holding member 52, restricting portions 52 a that come into contact with a part of the intermediate transfer unit 50 are provided. The regulating portion 52a has a shape protruding toward the intermediate transfer unit 50 in the posture shown in FIG. The restricting portion 52a is held by the holding member 52 and the holding member 52 by contact with a part of the intermediate transfer unit 50, in this embodiment, a bearing portion 125d (FIG. 11C described later) of the tension roller 125c. When the optical sensor 51 moves in the contact / separation direction with respect to the intermediate transfer unit 50, the movement limit position is regulated. The tension roller 125c is a roller that applies tension by pressing the intermediate transfer belt 125 stretched around the drive roller 125a from the inside.

  Further, the attachment member 510 guides the movement of the holding member 52 in the contact / separation direction, and in the contact / separation direction, at a position closer to the intermediate transfer unit 50 than the movement limit position regulated by the regulating portion 52a. A guide groove 512 that restricts the movement of the holding member 52 is formed. The guide groove 512 is a notch that extends and opens in the contact / separation direction. The holding member 52 is formed with a claw portion 52b that slidably fits in the guide groove 512.

  FIG. 7 is an enlarged perspective view of the guide groove 512 portion of the mounting member 510. The holding member 52 is prevented from moving in the direction of the shaft 19b of the registration roller 19a by the claw portion 52b, which is a part of the holding member 52, being fitted in the guide groove 512 of the mounting member 510, and the contact and separation described above. The sliding movement along the guide groove 512 is possible only in the direction.

  FIG. 8 is a perspective view showing the pre-transfer guide 190a attached to the rotating shaft 19b of the registration roller 19a. A torsion coil spring 53 as a first urging member is attached to the longitudinal end portion of the pre-transfer guide 190a, that is, the pre-transfer guide 190a attached to the rotating shaft 19b of the registration roller 19a. The torsion coil spring 53 is attached around the bearing portion 19c of the rotary shaft 19b. The torsion coil spring 53 is an elastic member that urges the pre-transfer guide 190 a so that the pre-transfer guide 190 a rotates in a direction away from the intermediate transfer unit 50 attached to the apparatus main body 11.

  FIG. 9 is a perspective view showing a pressing spring attached between the holding member 52 and the attaching member 510. At the upper bottom portion 52d of the holding member 52 held by the mounting member 510, the upper end portion of the pressing spring 55 that presses the holding member 52 in the direction toward the intermediate transfer unit 50 in the posture shown in FIG. The spring 55 is attached as a second urging member. The lower end of the push spring 55 is attached to the inner bottom 513 of the attachment member 510. Accordingly, the holding member 52 and the optical sensor 51 are pressed toward the intermediate transfer unit 50 (upward in FIG. 9) by the pressing spring 55, and the holding member 52 is moved to the intermediate transfer unit 50 side (in FIG. 9). When a pressure is applied from above (upward), it can slide in a direction away from the intermediate transfer unit 50 (downward in FIG. 9).

  Next, positioning of the optical sensor 51 in the present embodiment will be described.

  10A shows the intermediate transfer unit 50 (part), the registration roller 19a, the pre-transfer guide 190a, and the sensor unit 500 at the position where the optical sensor 51 is disposed when the door 11a of the apparatus main body 11 is open. FIG. FIG. 10B is a cross-sectional view of the pre-transfer guide 190a and the sensor unit 500 at a position where the optical sensor 51 is not disposed when the door portion 11a of the apparatus main body 11 is open. FIG. 10C is a cross-sectional view of the pre-transfer guide 190a and the sensor unit 500 at the position where the pressing spring 55 is disposed when the door portion 11a of the apparatus main body 11 is open.

  When the door portion 11a of the apparatus main body 11 is open, the pre-transfer guide 190a and the sensor unit 500 are separated from the intermediate transfer unit 50 mounted in the apparatus main body 11 by the urging force of the torsion coil spring 53, that is, the apparatus. The intermediate transfer unit 50 is rotated in the pulling direction from the main body 11. Here, the pre-transfer guide 190a and the sensor unit 500 are set to rotate to a position that does not exist on the path where the intermediate transfer unit 50 is pulled out from the apparatus main body 11 by the biasing force of the torsion coil spring 53. As a result, the intermediate transfer unit 50 can be pulled out (moved leftward in FIG. 10) from the apparatus main body 11 without receiving interference between the pre-transfer guide 190a and the sensor unit 500.

  FIG. 11A shows the intermediate transfer unit 50 (part), the registration roller 19a, the pre-transfer guide 190a, and the sensor unit 500 at the position where the optical sensor 51 is disposed when the door 11a of the apparatus main body 11 is closed. FIG. FIG. 11B is a cross-sectional view of the pre-transfer guide 190a and the sensor unit 500 at a position where the optical sensor 51 is not disposed when the door portion 11a of the apparatus body 11 is closed. FIG. 11C is a cross-sectional view of the pre-transfer guide 190a and the sensor unit 500 at the position where the push spring 55 is disposed when the door portion 11a of the apparatus main body 11 is closed.

  When the door portion 11a of the apparatus main body 11 is closed, the intermediate transfer unit 50 is mounted in the apparatus main body 11. At this time, as described above, the pre-transfer guide 190a resists the biasing force of the torsion coil spring 53 by the above-described protrusion provided on the conveyance path 190 provided on the door portion 11a side of the apparatus main body 11. For example, at the position near the both ends of the rotation axis direction of the driving roller 125a in the base 190c and out of the conveyance area of the recording paper P, the pressure is received so as to rotate in the direction toward the intermediate transfer unit 50. Accordingly, when the pre-transfer guide 190a and the sensor unit 500 are rotated to a position where the contact portion 190e of the pre-transfer guide 190a contacts the part 542 of the intermediate transfer unit 50, the rotation stops. Accordingly, the pre-transfer guide 190a and the sensor unit 500 are positioned with respect to the intermediate transfer unit 50 in the rotation direction.

  The protrusions provided on the conveyance path 190 preferably have flexibility or elasticity in the contact / separation direction with respect to the intermediate transfer unit 50 when the pre-transfer guide 190a and the sensor unit 500 are rotated. In this case, the accuracy required at the time of positioning by the contact between the contact portion 190e and the part 542 of the intermediate transfer unit 50 can be reduced.

  As described above, when the pre-transfer guide 190 a and the sensor unit 500 are positioned with respect to the intermediate transfer unit 50 in the rotation direction, the holding member 52 and the optical sensor 51 approach the intermediate transfer unit 50 by the pressing spring 55. It is energized in the direction to do. At this time, the amount of movement of the holding member 52 and the optical sensor 51 due to the pressing of the pressing spring 55 is the direction in which the restricting portion 52a provided on the holding member 52 approaches the intermediate transfer unit 50, as indicated by the arrow in FIG. Is set to an amount sufficient to contact the bearing portion 125d of the tension roller 125c. Due to the contact between the restriction portion 52a and the bearing portion 125d, the holding member 52 and the optical sensor 51 are positioned in the contact / separation direction with respect to the intermediate transfer unit 50, and the distance of the optical sensor 51 to the intermediate transfer belt 125 is accurately determined.

  The restricting portion 52a has an arcuate cross-sectional shape (arc 52c) along the circumferential shape of the bearing portion 125d of the tension roller 125c. The restricting portion 52a abuts on the bearing portion 125d at the arc 52c portion.

  When the pre-transfer guide 190a rotates from the position state of FIG. 10C to the position state of FIG. 11C to change the posture, first, the end 52d or 52e of the arc 52c is the bearing of the tension roller 125c. It abuts on the portion 125d. Thereby, the holding member 52 and the optical sensor 51 move in the expansion / contraction direction of the push spring 55, that is, the contact / separation direction of the intermediate transfer unit 50 (vertical direction in FIG. 11C). Thereafter, the bearing portion 125d of the tension roller 125c is fitted into the arc 52c of the restricting portion 52a, so that the position of the holding member 52 in the contact / separation direction with respect to the bearing portion 125d is easily determined, and the optical sensor 51 and the intermediate portion in the direction are intermediate. The distance from the transfer belt 125 is determined more accurately.

  The torsion coil spring 53 and the push spring 55 absorb positioning errors in the rotation direction and the contact / separation direction of the optical sensor 51 with respect to the intermediate transfer unit 50 when the bearing portion 125d is in contact with the restriction portion 52a. The optical sensor 51 can be accurately positioned with respect to the intermediate transfer unit 50 each time the intermediate transfer unit 50 is attached to the apparatus main body 11.

  As described above, in this embodiment, even if the optical sensor 51 is provided on the apparatus main body 11 side without being provided on the intermediate transfer unit 50 side, the optical sensor 51 in the contact / separation direction with respect to the intermediate transfer unit 50 is provided. This positioning can be performed with a relatively small number of parts. Thus, according to the present embodiment, the optical sensor 51 is provided on the apparatus main body 11 side so that the optical sensor 51 can be used until the lifetime of the image forming apparatus 1. Positioning can be performed with higher accuracy than in the past. That is, according to the present embodiment, the optical sensor 51 can be accurately positioned with respect to the intermediate transfer belt 125 while suppressing unnecessary replacement of the optical sensor.

The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. In the above-described embodiment, the multifunction apparatus is used as an embodiment of the image forming apparatus according to the present invention. However, this is only an example, and other image forming apparatuses such as a printer, a copier, and a facsimile apparatus are used. Other image forming apparatuses may be used.

  Moreover, in the said embodiment, the structure and process which were shown by the said embodiment using FIG. 1 thru | or FIG. 11 are only one Embodiment of this invention, and are not the meaning which limits this invention to the said structure and process.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Apparatus main body 50 Intermediate transfer unit 125 Intermediate transfer belt 125a Drive roller 125c Tension roller 125d Tension roller bearing part 210 Secondary transfer roller 19a Registration roller 19b Registration roller axis N Nip part 190a Pre-transfer guide 190e Contact Part 500 sensor unit 51 optical sensor 52a regulating part 510 mounting member 53 torsion coil spring (first biasing member)
55 Push spring (second biasing member)

Claims (5)

An intermediate transfer unit that includes an intermediate transfer belt and a roller that moves the intermediate transfer belt endlessly, and is detachable from the apparatus body;
A secondary transfer roller that forms a nip portion paired with a roller that runs the intermediate transfer belt endlessly;
A registration roller for conveying a recording medium toward the nip portion;
A pre-transfer guide that is rotatably mounted about the axis of the registration roller and guides a recording medium conveyed from the registration roller to the nip portion;
A sensor for reading a toner image formed on the intermediate transfer belt;
A holding member for holding the sensor;
A mounting member for movably holding the contact and separation direction, attached to the pre-transfer guide relative to the intermediate transfer unit and the holding member,
A restricting portion that is provided on the holding member and restricts a movement limit position of the sensor in the contact / separation direction by contact with a part of the intermediate transfer unit;
An image forming apparatus comprising: an abutting portion provided on the pre-transfer guide, wherein the pre-transfer guide regulates a rotation limit position in a direction toward the intermediate transfer unit. A first urging member that urges the pre-transfer guide away from the intermediate transfer unit during the rotation;
The image forming apparatus according to claim 1, further comprising: a second urging member that urges the holding member in a direction approaching the intermediate transfer unit. The mounting member guides the movement of the holding member in the contact / separation direction, and in the contact / separation direction, the holding member is located at a position closer to the intermediate transfer unit than the movement limit position regulated by the regulating unit. The image forming apparatus according to claim 1, wherein a guide groove that restricts movement of the image forming portion is formed. The intermediate transfer unit is disposed in the vicinity of the roller, and includes a tension roller that supports the intermediate transfer belt from the inside and applies tension.
The image forming apparatus according to claim 1, wherein the restricting portion is configured to abut against a bearing portion of the tension roller. The image forming apparatus according to claim 4, wherein the restricting portion has a shape in which a contact portion of the tension roller with the bearing portion follows a peripheral surface shape of the bearing portion.