Sheet conveying device and image forming apparatus

Abstract

To provide a sheet carrier device suppressed in lowering of detection performance of a sensor due to paper powder generated from a sheet.SOLUTION: A sheet carrier device has carrier means for carrying the sheet, a guide member forming a carrier route of the sheet carried by the carrier means, and a sensor arranged on the same side of the guide member in relation to the carrier route. In the guide member, a part overlapping a detection position of the sensor in the sheet width direction perpendicular to the sheet carrier direction is provided with a retreating form retreated in the separating direction from a sheet passing position in the carrier route, compared to a non-overlapping part with the detection position of the sensor.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to a sheet conveying device that conveys a sheet and an image forming apparatus that forms an image on a sheet. [Background technology]

[0002] Image forming devices such as printers, copiers, and multifunction peripherals are equipped with a sheet conveying device for conveying sheets used as recording media. In such sheet conveying devices, fine particles of foreign matter (so-called paper dust) may be generated as paper fibers, fillers, etc., fall off from the sheet during sheet conveyance. Patent Document 1 describes a method of suppressing degradation of conveyance performance due to adhesion of paper dust to the registration roller by arranging a cleaning member that cleans the surface of the registration roller. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-006950 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in sheet conveying devices and image forming devices, various sensors such as optical sensors and ultrasonic sensors are used to detect the density of an image to be formed (or formed) on a sheet and to automatically determine the material of the sheet used for image formation. However, if paper dust generated from the sheet inside the device adheres to the sensor, it may degrade the detection performance of the sensor.

[0005] The present invention provides a sheet conveying device and an image forming apparatus that can prevent a decrease in the detection performance of a sensor due to paper dust generated from a sheet. [Means for solving the problem]

[0006] One aspect of the present invention is a sheet conveying device including: a conveying unit that conveys a sheet; a guide member that forms a conveying path for the sheet conveyed by the conveying unit; and a sensor that is disposed on the same side as the guide member with respect to the conveying path. a detected member to be detected by the sensor; A sheet conveying device having: When the position of the detected member that is detected by the sensor is defined as the detection position, In the guide member, in the sheet width direction perpendicular to the sheet conveying direction, The aforementioned In the area that overlaps with the detection position, The aforementioned A retracted shape is provided on a side away from a passing position of the sheet in the conveying path compared to a portion that does not overlap with the detection position. The detection position is located outside the conveying path as viewed in the sheet width direction and on the same side as the sensor with respect to the conveying path. The sheet conveying device is characterized in that

[0007] Another aspect of the present invention is a toner image forming unit having an image carrier and forming a toner image on the image carrier; an intermediate transfer body that transports the toner image transferred from the image carrier; a transfer member that forms a secondary transfer unit between the intermediate transfer body and the intermediate transfer body and that transfers the toner image from the intermediate transfer body to a sheet; transport means that transports the sheet; and a transfer member that is disposed on the same side as the intermediate transfer body with respect to a transport path of the sheet and that transports the sheet to the intermediate transfer body. secondary a guide member for guiding the image carrier to the transfer portion, and a guide member for guiding the image carrier to the intermediate transfer member in the conveying direction of the intermediate transfer member; The aforementioned an optical sensor that is disposed downstream of a primary transfer unit where a toner image is transferred and upstream of the secondary transfer unit, and that detects a pattern image formed on the intermediate transfer body by the toner image forming unit, wherein the guide member protrudes toward the opposite side of the conveying path as it goes downstream in the sheet conveying direction when viewed in a sheet width direction perpendicular to the sheet conveying direction, When the position on the intermediate transfer body where the pattern image is detected by the optical sensor is defined as a detection position, The downstream edge of the guide member in the sheet conveying direction is The aforementioned In the area overlapping with the detection position, The aforementioned A recessed shape recessed toward the upstream side in the sheet conveying direction is provided compared to a portion that does not overlap with the detection position. The detection position is located outside the conveying path as viewed in the sheet width direction and on the same side as the optical sensor with respect to the conveying path. The image forming apparatus is characterized in that Yet another aspect of the present invention is A sheet conveying device having a conveying means for conveying a sheet, a guide member that forms a conveying path for the sheet conveyed by the conveying means, and a sensor arranged on the same side as the guide member with respect to the conveying path, the sensor detecting an object to be detected at a detection position, wherein a portion of the guide member that overlaps with the detection position in the sheet width direction perpendicular to the sheet conveying direction has a retracted shape that is retracted away from the position where the sheet passes in the conveying path compared to a portion that does not overlap with the detection position, and the sensor has an emitter that emits light or sound to the object to be detected, and the retracted shape is located outside the area through which the light or sound emitted by the emitter passes before reaching the object to be detected. [Effects of the Invention]

[0008] According to the present invention, it is possible to prevent the detection performance of the sensor from being reduced due to paper dust generated from the sheet. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a perspective view of an intermediate transfer unit according to the first embodiment. [Figure 3] FIG. 2 is a perspective view of a secondary transfer unit according to the first embodiment. [Figure 4] FIG. 2 is a cross-sectional view showing the configuration of the periphery of a secondary transfer unit of the image forming apparatus according to the first embodiment. [Figure 5] FIG. 2 is a schematic diagram illustrating the arrangement of patch sensors according to the first embodiment. [Figure 6] 10A and 10B are diagrams illustrating the positional relationship between a notch portion of a first pre-transfer guide and a patch sensor according to the first embodiment. [Figure 7] FIG. 4 is an enlarged view of an edge portion of a first pre-transfer guide according to the first embodiment. [Figure 8] FIG. 10 is a perspective view of a first pre-transfer guide according to a modified example of the first embodiment. [Figure 9] FIG. 10 is a perspective view of a secondary transfer unit according to a second embodiment. [Figure 10] FIG. 10 is a perspective view showing a part of a second pre-transfer guide according to a second embodiment. [Figure 11] 10 is a diagram showing the positional relationship between a drawn portion of a second pre-transfer guide and a sheet material discrimination sensor according to the second embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. [Example]

[0011] 1 is a schematic diagram showing the cross-sectional configuration of an image forming apparatus 1 according to a first embodiment (Example 1). The image forming apparatus 1 of this example is an electrophotographic, intermediate transfer color printer that forms an image on a sheet P as a recording material based on image information input from an external device. A variety of sheet materials of different sizes and materials can be used as the recording material, including paper such as plain paper and cardboard, surface-treated sheet materials such as plastic film, cloth, and coated paper, and sheet materials of special shapes such as envelopes and index paper.

[0012] The image forming apparatus 1 has an image forming section 1B including first, second, third, and fourth process units SY, SM, SC, and SK as a plurality of toner image forming sections. The first to fourth process units SY to SK are for forming images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. These four process units SY, SM, SC, and SK are arranged in a line at regular intervals, and furthermore, in this embodiment, each process unit SY to SK is arranged below the intermediate transfer belt 26 in the direction of gravity.

[0013] In this embodiment, the first to fourth process units SY to SK are substantially identical in configuration, except for the toner colors they use. Each process unit SY, SM, SC, and SK is provided with a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum 6) as a rotatable image carrier that carries a toner image. Around the photosensitive drum 6, a charging roller 61 as a charging member that charges the photosensitive drum 6, a developing unit as developing means, and a cleaning unit are provided. Furthermore, an exposure unit that irradiates laser light from a laser scanner 7 as exposure means is provided downstream of the charging roller 61 in the rotation direction of the photosensitive drum 6 and upstream of the developing unit where development is performed by the developing unit.

[0014] The developing unit has a developing roller 63 as a developing member (developer carrier) and a container that contains developer including toner. The developing roller 63 is rotatable by receiving a driving force from a driving source (not shown). The cleaning unit has a cleaning blade 65 as a cleaning member that contacts the photosensitive drum 6 and contains the toner collected by the cleaning blade 65.

[0015] As shown in FIG. 1, an intermediate transfer belt 26, which is an intermediate transfer body made of an endless belt member, is disposed opposite the photosensitive drum 6 of each of the process units SY to SK. The intermediate transfer belt 26 is stretched around a plurality of roller members serving as tension members. More specifically, the intermediate transfer belt 26 is stretched by having its inner circumferential surface supported by three tension rollers: a drive roller 30, a driven roller 28, and a tension roller 22. The intermediate transfer belt 26 is transported (rotationally moved) in the direction of arrow R1 in the drawing by the rotation of the drive roller 30, which rotates by receiving a driving force from a drive source (not shown).

[0016] Four primary transfer rollers 16 serving as primary transfer members are arranged on the inner circumferential surface side of the intermediate transfer belt 26 at positions facing the respective photosensitive drums 6. The primary transfer rollers 16 are biased with a predetermined pressure against the photosensitive drums 6 with the intermediate transfer belt 26 sandwiched therebetween, and form a primary transfer portion N1 as a nip portion where the intermediate transfer belt 26 and the photosensitive drums 6 come into contact. A primary transfer power supply (not shown) is connected to the primary transfer rollers 16, and the primary transfer power supply can apply a voltage of a predetermined polarity to the primary transfer rollers 16.

[0017] A secondary transfer roller 10 serving as a transfer member (secondary transfer member) is disposed on the outer peripheral surface side of the intermediate transfer belt 26, facing the drive roller 30. The secondary transfer roller 10 is biased with a predetermined pressure against the drive roller 30 by a transfer spring 38 serving as a biasing member, with the intermediate transfer belt 26 sandwiched therebetween, and a secondary transfer portion N2 is formed as a nip portion where the intermediate transfer belt 26 and the secondary transfer roller 10 come into contact. A secondary transfer power source (not shown) is connected to the secondary transfer roller 10, and the secondary transfer power source can apply a voltage of a predetermined polarity to the secondary transfer roller 10.

[0018] A cleaning unit 20 that collects toner remaining on the intermediate transfer belt 26 after secondary transfer (hereinafter referred to as residual toner) is provided upstream of the four primary transfer units N1 and downstream of the secondary transfer unit N2 in the movement direction of the intermediate transfer belt 26. The cleaning unit 20 has a cleaning blade 20a that comes into contact with the intermediate transfer belt 26.

[0019] A sheet feeding unit including a cassette 2 that stores sheets P, a feeding roller 3 for feeding the sheets P, and a separation roller pair 4 for transporting the sheets P to the secondary transfer unit N2 is provided at the bottom of the image forming apparatus 1. The separation roller pair 4 has a transport roller that transports the sheets P received from the feeding roller 3, and a separation roller that is pressed against the transport roller to form a separation nip and separates the sheets P by friction. A registration roller pair 5 is disposed downstream of the separation roller pair 4 and upstream of the secondary transfer unit N2 in the transport direction of the sheets P.

[0020] A thermal fixing type fixing device 9, a pair of discharge rollers 12 for discharging the sheet P from the image forming apparatus 1, and a stacking tray 15 for stacking the discharged sheet P are provided downstream of the secondary transfer portion N2 in the conveying direction of the sheet P. The fixing device 9 has a pair of rollers for nipping and conveying the sheet P, and a heating means such as a halogen lamp for heating the image on the sheet P.

[0021] In addition, a reversing roller pair 51 for reversing the first and second sides of the sheet P is provided above the discharge roller pair 12, and a switching guide 49 for switching the conveying path of the sheet P between the discharge roller pair 12 and the reversing roller pair 51 is provided downstream of the fixing device 9. In addition, the image forming apparatus 1 is provided with a double-sided conveying path 52 extending from the reversing roller pair 51 toward the registration roller pair 5, and a plurality of conveying roller pairs are arranged on the double-sided conveying path 52. The rollers (pairs) including the registration roller pair 5 arranged along the conveying path in the image forming apparatus 1 described above are an example of a conveying means for conveying the sheet P.

[0022] [Image formation operation] When image information and an execution command for an image forming operation are sent from an external device (not shown) to the controller 50 of the image forming apparatus 1, the controller 50 controls each part of the image forming apparatus 1 to start the following image forming operation. First, the photosensitive drum 6 and developing roller 63 of each process unit SY to SK, as well as the drive roller 30 that drives the intermediate transfer belt 26, are driven at a predetermined rotational speed. The surface of the rotating photosensitive drum 6 is charged approximately uniformly to a predetermined polarity (negative polarity in this embodiment) by the charging roller 61. At this time, a predetermined charging voltage is applied to the charging roller 61 from a charging power source. Then, the photosensitive drum 6 is exposed by irradiating it with a laser beam from the laser scanner 7 that is modulated based on image information (signals corresponding to each color component of the image information) corresponding to each process unit SY to SK. As a result, an electrostatic latent image according to the image information is formed on the surface of the photosensitive drum 6.

[0023] The developing roller 63 carries toner charged to the normal charging polarity of the toner (negative polarity in this embodiment), and a predetermined developing voltage is applied from a developing power supply. As a result, the latent image formed on the photosensitive drum 6 is visualized by negative toner at the opposing portion (developing portion) between the photosensitive drum 6 and the developing roller 63, and a toner image is formed on the photosensitive drum 6.

[0024] Next, the toner image formed on the photosensitive drum 6 is transferred (primary transfer) to the intermediate transfer belt 26, which is being rotated, at the primary transfer portion N1 by a current (hereinafter referred to as the primary transfer current) flowing from the primary transfer roller 16 to the photosensitive drum 6. At this time, a voltage of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the primary transfer roller 16 from the primary transfer power supply. In this embodiment, the toner image is primarily transferred from the photosensitive drum 6 to the intermediate transfer belt 26 by constant current control, which controls the output of the primary transfer power supply so that a predetermined primary transfer current flows from the primary transfer roller 16 to the photosensitive drum 6.

[0025] When a full-color image is formed, an electrostatic latent image is formed on each photosensitive drum 6 in each of the process units SY to SK, and this is developed into a toner image of each color. The toner images of each color formed on the photosensitive drum 6 of each of the process units SY to SK are then transferred to the intermediate transfer belt 26 in each primary transfer portion N1 so as to be superimposed one on top of the other, and a full-color image made of toners of four colors is formed on the intermediate transfer belt 26.

[0026] Meanwhile, sheets P loaded in cassette 2, which serves as a storage unit, are fed from cassette 2 by feed roller 3 and conveyed one by one by separation roller pair 4. The leading edge of sheet P abuts against registration roller pair 5, which is stationary, to correct skew. Then, registration roller pair 5 conveys sheet P to secondary transfer unit N2 in synchronization with the image formation process in image forming unit 1B. The toner image carried on intermediate transfer belt 26 is transferred (secondarily transferred) to conveyed sheet P by a current (hereinafter referred to as the "secondary transfer current") flowing from secondary transfer roller 10 to intermediate transfer belt 26 at secondary transfer unit N2. At this time, a secondary transfer voltage of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to secondary transfer roller 10 from a secondary transfer power source. In this embodiment, the toner image is secondarily transferred from intermediate transfer belt 26 to sheet P by constant current control, which controls the output of the secondary transfer power source so that a predetermined secondary transfer current flows from secondary transfer roller 10 to intermediate transfer belt 26.

[0027] Thereafter, the sheet P onto which the toner image has been transferred is conveyed to the fixing unit 9, where the toner image is fixed onto the surface of the sheet P, and then the sheet P is discharged by the pair of discharge rollers 12 to the outside of the main body of the image forming apparatus 1 and stacked on the stacking tray 15. When double-sided printing is performed, the sheet P onto which the toner image has been transferred onto the first side and which has passed through the fixing unit 9 is guided to the pair of reversing rollers 51, where it is switchback-conveyed and conveyed to the double-sided conveying path 52. Then, the sheet P, on which an image has been formed on the second side opposite to the first side by passing through the secondary transfer unit N2 and the fixing unit 9 again, is discharged by the pair of discharge rollers 12 to the outside of the main body of the image forming apparatus 1 and stacked on the stacking tray 15.

[0028] Note that the toner remaining on the photosensitive drum 6 after the primary transfer is removed from the surface of the photosensitive drum 6 by a cleaning blade 65. Furthermore, the untransferred toner remaining on the intermediate transfer belt 26 after passing through the secondary transfer portion N2 is removed from the surface of the intermediate transfer belt 26 by a cleaning blade 20a. Thereafter, the removed toner passes through a toner transport path 29 and is stored in a toner recovery container 24.

[0029] [Calibration operation] As described above, during image formation, toner images are formed on the photosensitive drums 6 in each of the process units SY to SK, and then transferred to the intermediate transfer belt 26 so that they are superimposed on each other. However, there is a possibility that the position of the toner images of each color transferred to the intermediate transfer belt 26 may be misaligned, or that the density of the toner images created by the process units SY to SK may deviate from the set value or tolerance range. Examples of factors that can cause such deviations include component tolerances of the image forming apparatus 1, changes in the resistance value of the intermediate transfer belt 26 due to changes in the installation environment, and wear on the photosensitive drums 6.

[0030] As shown in FIG. 1, the image forming apparatus 1 is equipped with a patch sensor 13, which is a sensor for automatically correcting (calibrating) deviations in the position and density of such toner images. A controller 50 of the image forming apparatus 1 causes the process units SY to SK to create pattern images for measurement to adjust the images, and causes the patch sensor 13 to read the pattern images transferred to the intermediate transfer belt 26. The controller 50 then adjusts the position and density (gradation) of the images formed by the process units SY to SK based on the reading results of the patch sensor 13. In such adjustment control, data obtained as a result of reading the pattern images by the patch sensor 13 is sent to the controller 50 and processed by the controller 50, and the timing and exposure time for exposing the photosensitive drum 6 to light by the laser scanner 7 are adjusted based on the results.

[0031] The patch sensor 13 is an optical sensor that has a light-emitting element (light-emitting element) such as an LED and a light-receiving element (light-receiving element) such as a phototransistor, and detects the amount of light reflected by the toner image on the intermediate transfer belt 26 using the light-receiving element. An example of a pattern image for measurement is one in which toner images of each color, each consisting of line segments in the main scanning direction (X direction), are arranged in the sub-scanning direction. In this case, the toner images detected by the patch sensor Between The color shift of the color image can be corrected by adjusting the exposure start timing of the laser scanner 7 for each process unit SY to SK based on the difference between the interval and a predetermined interval. The pattern image is not limited to this, and may be, for example, a patch image for adjusting the density of the image.

[0032] [Configuration of the secondary transfer unit] Next, the secondary transfer unit N2 and its peripheral configuration and the sheet transport path in the image forming apparatus will be described with reference to Figures 2 to 7. In the drawings, the vertical upward direction when the image forming apparatus 1 is installed on a horizontal surface is defined as the Z direction (arrow Z). The direction parallel to the rotation axis direction of the photosensitive drum 6 is defined as the X direction (arrow X). The X direction is the sheet width direction perpendicular to the sheet transport direction in the image forming apparatus 1, and is also the main scanning direction during image formation. The X direction is a direction intersecting the Z direction, and preferably perpendicular to it. The horizontal direction perpendicular to the Z direction and the X direction is defined as the Y direction (arrow Y).

[0033] Fig. 2 is a perspective view showing the intermediate transfer unit 8. Fig. 3 is a perspective view showing the secondary transfer unit 17. Fig. 4 is a cross-sectional view of the periphery of the secondary transfer portion N2 cut along a plane perpendicular to the X direction.

[0034] 2, the intermediate transfer unit 8 includes side frames 8a, 8b, and a first pre-transfer guide 11 in addition to the intermediate transfer belt 26, drive roller 30, driven roller 28, and tension roller 22 described above. The side frames 8a, 8b are provided on both sides of the intermediate transfer unit 8 in the X direction and are elongated members that extend substantially in the Y direction. The drive roller 30, driven roller 28, and tension roller 22 are rotatably held at both ends in the axial direction (X direction) by the side frames 8a, 8b. The side frames 8a, 8b are connected to each other by a frame member (not shown) that extends in the X direction, thereby constituting the frame body of the intermediate transfer unit 8.

[0035] The first pre-transfer guide 11 is supported at both ends in the X direction by the side frames 8a and 8b. The first pre-transfer guide 11 is connected to a second pre-transfer guide 21 (see FIG. 3) of the secondary transfer unit 17, which will be described later. )The first pre-transfer guide 11 is a guide member that faces the pair of registration rollers 5. The first pre-transfer guide 11, together with the second pre-transfer guide 21, forms part of the sheet transport path (transport space) between the registration roller pair 5 and the secondary transfer portion N2 (FIG. 4). The first pre-transfer guide 11 is a guide member that faces the sheet surface (image surface, first surface) of the sheet P that is transported toward the secondary transfer portion N2, on the side where the toner image is transferred at the secondary transfer portion N2.

[0036] As shown in FIG. 2, the first pre-transfer guide 11 is supported by the side frames 8a and 8b of the intermediate transfer unit 8. The first pre-transfer guide 11 is a plate-like member that is elongated in the X direction, which is the sheet width direction. The first pre-transfer guide 11 extends in the X direction over a range that encompasses the entire sheet passing area. The "sheet passing area" refers to the area through which the sheet P passes when the image forming apparatus 1 conveys a sheet P with the maximum sheet width (length of the sheet in the X direction) on which an image can be formed. As shown in FIG. 4, the downstream end of the first pre-transfer guide 11 in the sheet conveyance direction (approximately upward in the figure) is located between the portion of the intermediate transfer belt 26 that is supported by the driven roller 28 and the sheet conveyance path 14. The "sheet conveyance path 14" refers to a typical passage path of the sheet P conveyed inside the image forming apparatus 1 (the designed position through which the sheet P passes). The "sheet conveyance direction" refers to the movement direction of the sheet P conveyed along the sheet conveyance path 14.

[0037] Next, the secondary transfer unit 17 will be described. As shown in FIG. 3, the secondary transfer unit 17 has a secondary transfer roller 10 and a second pre-transfer guide 21. Both ends of the secondary transfer roller 10 in the axial direction (X direction) are rotatably held by the frame of the secondary transfer unit 17. The second pre-transfer guide 21 is a guide member that faces a sheet surface (non-image surface, second surface) of the sheet P conveyed toward the secondary transfer portion N2 opposite to a sheet surface (image surface, first surface) on which a toner image is transferred at the secondary transfer portion N2. The second pre-transfer guide 21 is a plate-shaped member that extends in the X direction, which is the sheet width direction. The second pre-transfer guide 21 extends in the X direction over a range that encompasses the entire sheet passing area.

[0038] 4 shows the positional relationship between the sheet transport path 14 and peripheral components near the secondary transfer portion N2. On the upstream side of the secondary transfer portion N2, the sheet P is guided so that its posture is determined by the edge (downstream end in the sheet transport direction) of the first pre-transfer guide 11 of the intermediate transfer unit 8 and the second pre-transfer guide 21 provided in the secondary transfer unit 17. This configuration stabilizes the transport of the sheet P by guiding it close to the secondary transfer portion N2, preventing image defects caused by an unstable posture of the sheet P before transfer. The first pre-transfer guide 11 prevents the sheet P from accidentally coming into contact with the intermediate transfer belt 26 on the upstream side of the secondary transfer portion N2, thereby contributing to the prevention of image defects.

[0039] In this embodiment, the guide surfaces of the first pre-transfer guide 11 and the second pre-transfer guide 21, which face each other, are inclined so that they approach each other downstream in the sheet conveyance direction. That is, when viewed in the sheet width direction, the first pre-transfer guide 11, which serves as a guide member in this embodiment, is inclined toward the opposite side of the conveyance path as it moves downstream in the sheet conveyance direction. The second pre-transfer guide 21 also has a similar inclination. Furthermore, the guide surface of the first pre-transfer guide 11 is inclined so as to protrude toward the opposite side of the conveyance path as it moves downstream in the sheet conveyance direction, relative to an extension line of the upstream guide 11A that guides the sheet P upstream of the first pre-transfer guide 11. Similarly, the guide surface of the second pre-transfer guide 21 is inclined so as to protrude toward the opposite side of the conveyance path as it moves downstream in the sheet conveyance direction, relative to an extension line of the upstream guide 21A that guides the sheet P upstream of the second pre-transfer guide 21.

[0040] [Sensor placement] The following describes the placement of patch sensor 13, which measures the pattern image on intermediate transfer belt 26. Because patch sensor 13 measures intermediate transfer belt 26, which is a flexible belt member, it is desirable to place patch sensor 13 at a location where the running position of intermediate transfer belt 26 is stable so that the distance from the outer circumferential surface of intermediate transfer belt 26 to patch sensor 13 is constant. Therefore, it is preferable to place patch sensor 13 at a position where the inner circumferential surface of intermediate transfer belt 26 is supported by a roller member (a position facing the roller member across intermediate transfer belt 26).

[0041] As shown in FIG. 5, the patch sensor 13 in this embodiment is disposed in a position facing the driven roller 28 across the intermediate transfer belt 26. The driven roller 28 is a second roller located upstream in the sheet conveyance direction of the drive roller 30, which serves as a first roller disposed in the secondary transfer unit N2. As shown in FIG. 1, the driven roller 28 is also a roller located downstream of the primary transfer unit N1 of the process units SY to SK and upstream of the drive roller 30 in the conveyance direction of the intermediate transfer belt 26. In this embodiment, the process units SY to SK are disposed below the intermediate transfer belt 26, which is stretched approximately in the Y direction. Therefore, the patch sensor 13 faces the intermediate transfer belt 26 on its upper surface 39. Furthermore, as viewed in the X direction as shown in FIG. 5, the patch sensor 13 is adjacent to the surface of the first pre-transfer guide 11 opposite the surface facing the sheet conveyance path 14. In other words, the optical sensor in this embodiment is disposed on the opposite side of the conveyance path across the guide member when viewed in the sheet width direction, facing the second roller across the belt member.

[0042] 5 is a cross-sectional view showing the arrangement of the patch sensor 13 and the intermediate transfer belt 26, and is a schematic representation of a cross section of the device taken along a plane passing through the rotation axis of the driven roller 28 and the optical axis of the patch sensor 13. As shown in FIG. 5, the patch sensors 13 of this embodiment are provided near both ends of the intermediate transfer belt 26 in the X direction, one on each side.

[0043] Hereinafter, the center position of the intermediate transfer belt 26 in the X direction is referred to as the center reference position X0. The center reference position X0 is also a reference for the center position in the sheet width direction of the sheet P being transported through the sheet transport path 14. In other words, the image forming apparatus 1 is configured to transport the sheet P while aligning the center in the sheet width direction with the center reference position X0.

[0044] For the patch sensor 13 on one side in the X direction (the right side in the figure), the end position of the surface of the patch sensor 13 facing the intermediate transfer belt 26 that is closest to the central reference position X0 in the X direction is designated as X1, and the end position farther from the central reference position X0 is designated as X3. The detection position (the reflection position of the representative light path from the light-emitting unit to the light-receiving unit) at which the patch sensor 13 on one side in the X direction detects the image on the intermediate transfer belt 26 is designated as X2. The detection position X2 is a position between the end positions X1 and X3. The distances from the central reference position X0 to each position (X1, X2, X3) of the patch sensor 13 on one side in the X direction are designated as L1 [mm], L2 [mm], and L3 [mm], respectively.

[0045] Similarly, for the patch sensor 13 on the other side in the X direction (left side in the figure), the end position of the surface of the patch sensor 13 facing the intermediate transfer belt 26 that is closest to the central reference position X0 in the X direction is designated X1', and the end position of the surface farthest from the central reference position X0 is designated X3'. The detection position at which the patch sensor 13 on the other side in the X direction detects the image on the intermediate transfer belt 26 is designated X2'. The detection position X2' is a position between the end positions X1' and X3'. The distances from the central reference position X0 to each position (X1', X2', X3') of the patch sensor 13 on the other side in the X direction are designated L1' [mm], L2' [mm], and L3' [mm], respectively.

[0046] The two patch sensors 13 are preferably arranged so that at least the detection positions X2 and X2' are symmetrical in the X direction with respect to the central reference position X0. In other words, excluding unavoidable positional deviations due to component tolerances and the like, L2=L2'.

[0047] [Pre-transcription guide details] Next, the first pre-transfer guide 11 will be described in detail. The first pre-transfer guide 11 can be formed from a resin material or a metal material, with a metal plate being preferred in terms of rigidity and wear resistance. The first pre-transfer guide 11 is a guide member located immediately before the secondary transfer portion N2 and rubs against the sheet P each time an image is formed. Therefore, by constructing the first pre-transfer guide 11 from a highly wear-resistant metal plate, wear on the guide can be reduced, thereby contributing to a longer lifespan of the image forming apparatus 1. Furthermore, since contact between the sheet P and the intermediate transfer belt 26 before entering the secondary transfer portion N2 can lead to image distortion, it is particularly preferred to form the first pre-transfer guide 11 from a highly rigid material to more reliably prevent such contact. A preferred material for the first pre-transfer guide 11 is, for example, a rolled steel plate.

[0048] Here, it will be explained that the first pre-transfer guide 11 is provided with a retraction shape to suppress the influence of paper dust generated from the sheet P on the patch sensor 13. In this disclosure, "paper dust" is not necessarily limited to what was part of the paper (paper fibers, fillers, etc.), but also includes dust that was attached to the sheet P and what was part of an image that had already been printed or written on the sheet P. FIG. 6 shows the intermediate transfer unit 8 and the first pre-transfer guide 11 as seen from the sheet transport path 14 side (the right side in FIG. 4). In FIG. 6, the position of the upper surface 39 of the patch sensor 13, which is the surface that faces the intermediate transfer belt 26, is indicated by hatching. In FIG. 6, the patch sensor 13 is hidden by the upstream guide 11A.

[0049] 6, the first pre-transfer guide 11 is provided with a notch 18, which is a recessed portion that is recessed toward the upstream side in the sheet conveying direction in the X direction (sheet width direction) of a downstream end 19 in the sheet conveying direction. The range in the X direction where the notch 18 is provided overlaps at least with the detection positions X2 and X2' of the patch sensor 13.

[0050] FIG. 7 is a schematic diagram of the vicinity of the downstream end of the first pre-transfer guide 11 as viewed in the X direction. As shown in FIG. 7, the first pre-transfer guide 11 is disposed so that the guide surface 11a is inclined at an angle of approximately 20 degrees with respect to the sheet transport path 14. Therefore, by providing the notch 18, the edge 18p in the range where the notch 18 is provided among the edges 18p and 19p of the first pre-transfer guide 11 is retracted away from the sheet transport path 14 compared to the edge 19p in the range other than the notch 18. The edges 18p and 19p are downstream edges in the sheet transport direction of the guide surface 11a of the first pre-transfer guide 11 facing the sheet transport path 14. The "side away from the sheet transport path 14" refers to the side away from the sheet transport path 14 in the sheet transport direction (the sheet transport direction at a position in the sheet transport path 14 closest to the downstream end of the first pre-transfer guide 11) and the direction perpendicular to the sheet width direction. In this way, in the guide member of this embodiment, the portion that overlaps with the sensor's detection position in the sheet width direction perpendicular to the sheet conveying direction has a retracted shape that is retracted away from the sheet passing position in the conveying path compared to the portion that does not overlap with the sensor's detection position.

[0051] During conveyance of the sheet P, paper dust is generated from the sheet P mainly due to friction between the sheet P and the guide member. In this embodiment, by providing the cutout portion 18 as the above-described retracted shape, the first pre-transfer guide 11 and the sheet P are less likely to come into contact in the range where the cutout portion 18 is provided, thereby suppressing the generation of paper dust. In particular, the first pre-transfer guide 11, which is a guide member that protrudes downstream in the sheet conveyance direction to the opposite side of the conveyance path, tends to rub strongly against the sheet P at the downstream edge of the guide surface 11a, generating paper dust. In this embodiment, by providing the cutout portion 18, it is possible to suppress the generation of paper dust at the edge 18p in the range that overlaps with the detection positions X2 and X2' of the patch sensor 13 in the X direction (sheet width direction).

[0052] It has been found that the generation of paper dust can be effectively suppressed even if the depth of the notch 18 (the distance from the edge 18p of the notch 18 to the extension of the edge 19p other than the notch 18) is shallow, for example, about 1 mm (preferably about 1.5 mm). Furthermore, as the retraction shape, a concave portion (see the drawn portion 23 in Example 2) in which a portion of the guide surface 11a is recessed can be provided instead of the notch 18 of this embodiment. However, because the first pre-transfer guide 11 faces the intermediate transfer belt 26 on the side opposite the conveyance path, providing a concave portion ensures a necessary clearance to prevent the first pre-transfer guide 11 from contacting the intermediate transfer belt 26. In this embodiment, the retraction shape is the notch 18 rather than the concave portion, so the first pre-transfer guide 11 can be positioned closer to the intermediate transfer belt 26 than in the above-described modified example, and the first pre-transfer guide 11 can guide the sheet P to a position closer to the secondary transfer portion N2.

[0053] The relationship between the notch portion 18 and the side edge position of the sheet will be further explained using FIG. 6. In FIG. 6, the double-dashed line indicates the width of a standard-sized sheet on which the image forming apparatus 1 can form an image. For the notch portion 18 on one side in the X direction (the right side in the figure), the distance from the central reference position X0 to the end 18a of the notch portion 18 on the side closest to the central reference position X0 is defined as La. For the notch portion 18 on one side in the X direction (the right side in the figure), the distance from the central reference position X0 to the end 18b of the notch portion 18 on the side farther from the central reference position X0 is defined as Lb. Similarly, for the notch portion 18 on the other side in the X direction (the left side in the figure), the distance from the central reference position X0 to the end 18a of the notch portion 18 on the side closer to the central reference position X0 is defined as La'. For the notch portion 18 on the other side in the X direction (the left side in the figure), the distance from the central reference position X0 to the end 18b of the notch portion 18 on the side farther from the central reference position X0 is defined as Lb'. The ends 18a and 18b indicate the positions of the openings of the notch shape (the upper end positions in the drawing).

[0054] In this embodiment, the notch 18 on one side in the X direction (the right side in the figure) is arranged so as to satisfy the relationship of La < L1 < L3 < Lb. Similarly, the notch 18 on the other side in the X direction (the left side in the figure) is arranged so as to satisfy the relationship of La' < L1' < L3' < Lb'. In other words, the range (18a to 18b) where the retreat shape is provided in the sheet width direction includes the entire range (X1 to X3, X1' to X3') in the sheet width direction of the surface (upper surface 39) where the sensor faces the detection object. Thereby, the possibility that paper dust reaches the surface (object surface) where the sensor faces the detection object can be effectively reduced.

[0055] Also, in this embodiment, a plurality of sensors are arranged, and a plurality of retreat shapes are provided corresponding to the plurality of sensors. Each of the plurality of retreat shapes is provided over the range in the sheet width direction that includes the entire area of the surface where the corresponding sensor faces the detection object. With such an arrangement, the influence of paper dust on each patch sensor 13 can be more reliably reduced. Further, in this embodiment, a notch 18 is provided above the patch sensor 13 in the Z direction (vertical direction). That is, in a configuration where the guide member where paper dust is generated is located above the sensor, a retreat shape for suppressing the generation of paper dust is provided in the guide member, so that the arrival of paper dust at the sensor can be effectively reduced.

[0056] Moreover, among standard sizes, the image forming apparatus 1 of this embodiment can form an image on sheets P of at least A5 size (sheet width 149 mm), B5 size (sheet width 182 mm), A4 size (sheet width 210 mm), and LTR size (sheet width 216 mm). As shown in FIG. 6, the inner end 18a of each notch 18 in the X direction (sheet width direction) is outside the side end position of the A5 size and inside the side end position of the B5 size. Also, the outer end 18b of each notch 18 in the X direction (sheet width direction) is outside the side end position of the B5 size and inside the side end positions of the A4 size and the LTR size.

[0057] Due to the above positional relationship, for A5-, A4-, and LTR-sized sheets P, the side edges of the sheet P are guided by the portion of the first pre-transfer guide 11 where the notched portion 18 is not provided. In other words, the side edges of the sheets P of these sizes are guided by the edge 19p (FIG. 7) in the range where the notched portion 18 is not provided, so the side edges of the sheet P are prevented from accidentally contacting the intermediate transfer belt 26 upstream of the secondary transfer portion N2. Furthermore, during the transport of sheets P of these sizes, the sheet P does not normally rub against the edge 18p of the notched portion 18, and paper dust due to rubbing between the edge 18p and the sheet P is unlikely to be generated.

[0058] On the other hand, for a B5-sized sheet P, the side edge is located inside the notch 18 in the X direction (sheet width direction). However, because the inside edge 18a of the notch 18 is located outside the side edge position of at least the A5-sized sheet, the distance from the inside edge 18a of the notch 18 to the side edge of the B5-sized sheet P is usually a short distance of 17 mm or less. Therefore, even during transport of the B5-sized sheet P, the side edge of the sheet P is unlikely to come into contact with the edge 18p of the notch 18, and the generation of paper dust due to friction between the edge 18p and the sheet P is suppressed.

[0059] If the notch 18 were not provided and the edge 19p of the first pre-transfer guide 11 were linearly continuous over the entire area in the X direction, paper dust would be generated near the detection positions X2 and X2' of the patch sensor 13 due to friction between the sheet P and the edge 19p. Some of this paper dust would drift in the space inside the image forming apparatus 1 and reach the top surface 39 of the patch sensor 13. If the amount of paper dust adhering to the top surface 39 of the patch sensor 13 increases, the detection performance of the patch sensor 13 would deteriorate. Specifically, the detection light would be diffused by the paper dust, preventing the amount of received light from changing in accordance with the image density, which could result in a decrease in detection sensitivity or erroneous detection.

[0060] In contrast, in this embodiment, notch portions 18 are provided as a retraction shape at positions overlapping with detection positions X2 and X2' of patch sensor 13, thereby suppressing the generation of paper dust near detection positions X2 and X2'. The shorter the distance from the paper dust generation position to patch sensor 13, the higher the probability that the generated paper dust will reach patch sensor 13. Therefore, by suppressing the generation of paper dust near detection positions X2 and X2', the amount of paper dust that reaches patch sensor 13 is reduced, making it less likely that the sensor's detection performance will be degraded by paper dust.

[0061] In particular, the patch sensor 13 in this embodiment is located on the opposite side of the sheet transport path 14 across the first pre-transfer guide 11, and is positioned adjacent to the surface of the first pre-transfer guide 11 on the opposite side from the transport path. In this way, even if the first pre-transfer guide 11 and the patch sensor 13 are configured to be close to each other when viewed in the X direction, the generation of paper dust near the detection positions X2 and X2' of the patch sensor 13 in the X direction can be suppressed, thereby suppressing a decrease in the detection performance of the sensor due to paper dust.

[0062] As described above, in this embodiment, the guide member has a retracted shape in the portion of the guide member that overlaps with the sensor detection position in the sheet width direction, which is retracted further away from the sheet passage position in the conveyance path than the portion that does not overlap with the sensor detection position. This makes it less likely that the guide member will come into contact with the sheet around the sensor detection position, reducing the possibility that paper dust generated by friction between the guide member and the sheet will reach the sensor. This reduces the impact of paper dust on the sensor's detection performance, allowing the sensor to exhibit stable detection performance over a long period of time.

[0063] (Variation) A modified example of this embodiment will be described below with reference to FIG. 8. FIG. 8 is a perspective view of the first pre-transfer guide 11 according to this modified example. In the first embodiment, the first pre-transfer guide 11 is configured using a metal plate. However, in this modified example, the first pre-transfer guide 11 is configured by attaching a resin sheet material 27 to a plate-shaped guide main body 11B. The leading edge of the sheet material 27 is the downstream end of the first pre-transfer guide 11 in the sheet conveyance direction. In this configuration, a notch 18 is provided in which the downstream end (edge of the guide surface) of the sheet material 27 is recessed toward the upstream side in the sheet conveyance direction at a position in the X direction that overlaps with the detection positions X2 and X2' of the patch sensor 13. This configuration also suppresses the generation of paper dust near the detection positions X2 and X2' and reduces the amount of paper dust that reaches the patch sensor 13, thereby suppressing degradation of the sensor's detection performance due to paper dust. [Example]

[0064] Next, a second embodiment (Example 2) will be described with reference to Figures 9 to 11. Hereinafter, elements with the same reference numerals as Example 1 will be considered to have substantially the same configurations and functions as those described in Example 1, and differences from Example 1 will be mainly described.

[0065] FIG. 9 is a perspective view showing the secondary transfer unit 17 of this embodiment. The secondary transfer unit 17 includes a sheet material discrimination sensor 33 as a sensor according to this embodiment. The sheet material discrimination sensor 33 is a sensor that uses ultrasonic waves to discriminate the material of a sheet. The sheet material discrimination sensor 33 includes a transmitter that is located on the secondary transfer unit 17 side and emits ultrasonic waves, and a receiver (not shown) that is located on the opposite side of the conveyance path and outputs a signal corresponding to the intensity of the received ultrasonic waves. The controller 50 of the image forming apparatus 1 can automatically discriminate the type of sheet P based on the signal output by the receiver of the sheet material discrimination sensor 33, taking advantage of the fact that the transmittance of ultrasonic waves varies depending on the material (e.g., basis weight) of the sheet P. Based on the discrimination result, the controller 50 controls the image forming operation (e.g., current control in the secondary transfer unit N2 and temperature control in the fixing unit 9) according to the material of the sheet P.

[0066] 10 is an enlarged perspective view of the center of the second pre-transfer guide 21 in the X direction (sheet width direction) of this embodiment. As shown in FIGS. 9 and 10, the pre-transfer guide 21 is provided with a drawn portion 23 as a retracted shape in which a portion of the guide surface 21a facing the conveyance path is retracted to a side away from the sheet conveyance path 14. The pre-transfer guide 21 in this embodiment is made of a plate-shaped metal, and the drawn portion 23 is formed as a concave portion recessed from the surrounding guide surface 21a by drawing. In other words, the retracted shape in this embodiment is a concave portion in which a portion of the surface of the guide member facing the conveyance path is retracted to a side away from the sheet passing through the conveyance path in a direction perpendicular to the surface.

[0067] By providing the drawn portion 23 as a retracted shape in this manner, the generation of paper dust due to friction between the second pre-transfer guide 21 and the sheet P is suppressed at a position that overlaps with the detection position of the sheet material discrimination sensor 33 in the X direction. If paper dust adheres to the transmitter or receiver of the sheet material discrimination sensor 33, the propagation of ultrasonic waves may be hindered, which may reduce the accuracy of sheet material discrimination. According to this embodiment, the generation of paper dust at a position that overlaps with the detection position of the sheet material discrimination sensor 33 in the X direction is suppressed, thereby suppressing the adhesion of paper dust to the sheet material discrimination sensor 33. This makes it possible to prevent the detection performance (discrimination accuracy) of the sheet material discrimination sensor 33 from being reduced due to paper dust.

[0068] In the first embodiment, the guide member has a notched edge as a retracted shape. However, in the present embodiment, a concave portion is formed by recessing a portion of the surface of the guide member, which has the advantage of making it easier to ensure the strength of the guide member. Also, as in the first embodiment, the drawn portion 23 as a retracted shape is located above the sheet material discrimination sensor 33 in the direction of gravity (Z direction). It is believed that some of the paper dust generated by the friction between the second pre-transfer guide 21 and the sheet P falls due to gravity. If the amount of paper dust generated above the sheet material discrimination sensor 33 is small, the amount of paper dust reaching the sheet material discrimination sensor 33 can be reduced. Thus, even if the sensor and a guide member that is prone to generating paper dust are located far apart, if the sensor is in a position where paper dust is likely to reach the sensor due to the influence of gravity, air currents within the device, or the like, it is preferable to provide the guide member with a retracted shape to suppress the generation of paper dust.

[0069] 11 is a view of the secondary transfer unit 17 of this embodiment as seen from the sheet conveying path side. The sheet material discrimination sensor 33 is disposed only on one side of the central reference position X0 in the X direction. In other words, the sensor of this embodiment is disposed asymmetrically with respect to the reference center position of the sheet in the sheet width direction. On the other hand, the drawing sections 23 are disposed on both sides of the central reference position X0 in the X direction, symmetrically with respect to the central reference position X0, and such that one drawing section 23 encompasses the detection position of the sheet material discrimination sensor 33 in the X direction. In other words, the retracted shape of this embodiment encompasses the detection position of the sensor in the sheet width direction and is disposed symmetrically with respect to the reference center position.

[0070] Hereinafter, the edge position of the surface of the sheet material discrimination sensor 33 facing the conveyance path (the opening area provided in the guide for emitting ultrasonic waves) that is closest to the central reference position X0 will be referred to as X4, and the edge position farthest from the central reference position X0 will be referred to as X6. The detection position X5 of the sheet material discrimination sensor 33 will be referred to as the midpoint between the edge positions X4 and X6. Furthermore, the distances from the central reference position X0 to each position (X4, X5, X6) of the sheet material discrimination sensor 33 will be referred to as L4 [mm], L5 [mm], and L6 [mm], respectively.

[0071] Regarding the drawing part 23 on one side in the X direction (the left side in the figure), let the distance from the central reference position X0 to the end 23a on the side closer to the central reference position X0 of the drawing part 23 be Lc. Regarding the drawing part 23 on one side in the X direction (the left side in the figure), let the distance from the central reference position X0 to the end 23a on the side farther from the central reference position X0 of the drawing part 23 be Ld. Similarly, regarding the drawing part 23 on the other side in the X direction (the right side in the figure), let the distance from the central reference position X0 to the end 23a on the side closer to the central reference position X0 of the drawing part 23 be Lc'. Regarding the drawing part 23 on the other side in the X direction (the right side in the figure), let the distance from the central reference position X0 to the end 23a on the side farther from the central reference position X0 of the drawing part 23 be Ld'.

[0072] The drawing part 23 on the same side as the sheet material discrimination sensor 33 is arranged so as to satisfy the relationship of Lc < L4 < L5 < Ld. In other words, the range in which the retracted shape is provided in the sheet width direction includes the entire area in the sheet width direction of the surface where the sensor faces the detection object. Thereby, the influence of paper dust on the sheet material discrimination sensor 33 can be more effectively reduced.

[0073] In particular, in this embodiment, the sensor is disposed asymmetrically with respect to the reference center position of the sheet in the sheet width direction, and the retracted shape encompasses the sensor detection position and is disposed symmetrically with respect to the reference center position in the sheet width direction. This arrangement reduces the influence of paper dust on the sheet material discrimination sensor 33 and reduces the possibility of the sheet P being skewed compared to when the drawing unit 23 is disposed asymmetrically. In other words, when the drawing unit 23 is disposed asymmetrically, the frictional resistance that the sheet P receives from the second pre-transfer guide 21 is distributed asymmetrically with respect to the X direction, which may cause the sheet P to rotate during transport. In contrast, in this embodiment, the drawing unit 23 (the drawing unit 23 on the right side in FIG. 11 ), which is not essential from the perspective of reducing the influence of paper dust on the sheet material discrimination sensor 33, is added and disposed symmetrically, thereby reducing the possibility of the sheet P rotating. Note that when the sheet material discrimination sensor 33 or other sensors are disposed asymmetrically in the sheet width direction but the number or positions of the sensors are different, the drawing units 23 are disposed symmetrically while incorporating the number and positions of the sensors.

[0074] (Variation) Although the sheet material discrimination sensor 33 using ultrasonic waves has been exemplified in the second embodiment, a sheet material discrimination sensor that discriminates the sheet material by irradiating light onto the sheet and detecting the intensity of the reflected light and / or the intensity of the transmitted light may also be used. Even in this case, if paper dust adheres to the sensor, it will lead to a decrease in detection performance, so the configuration described in this embodiment can suppress the influence of paper dust on the sensor.

[0075] (Other embodiments) Providing a retracted shape to a guide member is effective in reducing the influence of paper dust on sensors in sheet conveying devices that handle sheets, including the patch sensor 13 and the sheet material discrimination sensor 33 described in the first and second embodiments. As an example, the image forming apparatus 1 shown in FIG. 1 has a color sensor 62 disposed in the duplex conveying path 52. The color sensor 62 is an example of an optical sensor that detects a toner image formed on a sheet by an image forming unit. The controller 50 of the image forming apparatus 1 can adjust the color and density of the image formed on the sheet P by the image forming unit 1B using the color sensor 62. In this case, providing a retracted shape, such as the notch 18 or the drawn portion 23 described in the first and second embodiments, in a guide member that constitutes the duplex conveying path 52 and is located near the color sensor 62 can reduce the adhesion of paper dust to the color sensor 62. Other examples of sensors include an optical sensor that detects a sheet on the sheet transport path to monitor the sheet transport status (presence or absence of jam), and an optical sensor that detects the amount of slack (loop amount) when correcting skew of the sheet or the amount of slack (loop amount) between transfer and fixation.

[0076] In addition, in the above-described first and second embodiments, an electrophotographic image forming apparatus equipped with an intermediate transfer type image forming unit 1B is exemplified, but the present technology may be applied to a direct transfer type electrophotographic image forming apparatus in which an image is directly transferred from an image carrier (photosensitive member) to a sheet. Also, the present technology may be applied to an image forming apparatus other than the electrophotographic type, for example, an inkjet type or an offset printing type. [Explanation of symbols]

[0077] 5... Conveying means (pair of registration rollers) / 11, 21... Guide members (first pre-transfer guide, second pre-transfer guide) / 13, 33... Sensors (patch sensor, sheet material discrimination sensor) / 18, 23... Retraction shapes (notch portion, drawn portion)

Claims

1. a conveying means for conveying a sheet; a guide member that forms a conveyance path for the sheet conveyed by the conveyance means; a sensor disposed on the same side of the conveying path as the guide member; a detected member to be detected by the sensor; A sheet conveying device having: When the position of the detected member that is detected by the sensor is defined as the detection position, a portion of the guide member that overlaps with the detection position in a sheet width direction perpendicular to the sheet conveying direction has a retracted shape that is retracted to a side away from a passing position of the sheet in the conveying path compared to a portion that does not overlap with the detection position; The sheet conveying device according to claim 1, wherein the detection position is located outside the conveying path as viewed in the sheet width direction and on the same side as the sensor with respect to the conveying path.

2. 2. The sheet conveying device according to claim 1, When viewed in the sheet width direction, the guide member protrudes toward the opposite side of the conveyance path as it goes downstream in the sheet conveyance direction, The sheet conveying device, wherein the retracted shape is a concave shape in which a part of an edge of the guide member on a downstream side in the sheet conveying direction in the sheet width direction is concave toward the upstream side in the sheet conveying direction.

3. 2. The sheet conveying device according to claim 1, A sheet conveying device characterized in that the retracted shape is a concave portion in which a portion of the surface of the guide member facing the conveying path is recessed toward the side away from the position where the sheet passes in the conveying path in a direction perpendicular to the surface.

4. 4. The sheet conveying device according to claim 1, The sensor is arranged in plurality, The sheet conveying device is characterized in that a plurality of the retracted shapes are arranged corresponding to a plurality of the sensors.

5. 4. The sheet conveying device according to claim 1, the sensors are arranged asymmetrically with respect to a reference of a center position of the sheet in the sheet width direction, The sheet conveying device, wherein the retracted shape includes the detection position in the sheet width direction and is disposed symmetrically with respect to the reference center position.

6. 6. The sheet conveying device according to claim 1, The sheet conveying device according to claim 1, wherein the range in which the retracted shape is provided in the sheet width direction includes the entire area in the sheet width direction of the surface of the sensor facing the detected member.

7. 7. The sheet conveying device according to claim 1, The sheet conveying device, wherein the retracted shape is provided above the sensor.

8. The sheet conveying device according to any one of claims 1 to 7, an image forming means for forming an image on the sheet conveyed by the sheet conveying device; An image forming apparatus comprising:

9. 9. The image forming apparatus according to claim 8, the image forming means includes a toner image forming unit having an image carrier and forming a toner image on the image carrier, an intermediate transfer member that conveys the toner image that has been primarily transferred from the image carrier, and a transfer member that forms a secondary transfer unit between the intermediate transfer member and the intermediate transfer member and that transfers the toner image from the intermediate transfer member to a sheet, the detected member is the intermediate transfer body, The image forming apparatus is characterized in that the sensor is an optical sensor that detects the pattern image formed on the intermediate transfer body by the toner image forming unit.

10. 10. The image forming apparatus according to claim 9, the conveying unit includes a pair of registration rollers that convey the sheet toward the secondary transfer unit, the guide member is disposed between the pair of registration rollers and the secondary transfer unit in the sheet conveying direction, and is disposed so as to prevent the sheet from contacting the intermediate transfer body; The image forming apparatus is characterized in that the guide member is made of a metal plate.

11. 11. The image forming apparatus according to claim 9, The image forming apparatus is characterized in that the optical sensor is adjacent to a surface of the guide member opposite to a surface facing the conveying path when viewed in the sheet width direction.

12. 12. The image forming apparatus according to claim 9, the intermediate transfer body is an endless belt member, The roller member supports the inner circumferential surface of the belt member. The image forming apparatus is characterized in that the guide member and the optical sensor are both provided at positions facing the roller member with the belt member interposed therebetween.

13. a toner image forming unit having an image carrier and forming a toner image on the image carrier; an intermediate transfer member that conveys the toner image transferred from the image carrier; a transfer member that forms a secondary transfer portion between the intermediate transfer member and the transfer member, and that transfers the toner image from the intermediate transfer member to a sheet; a conveying means for conveying the sheet; a guide member disposed on the same side as the intermediate transfer body with respect to a conveyance path of the sheet, the guide member guiding the sheet to the secondary transfer unit; an optical sensor that is disposed downstream of a primary transfer unit where the toner image is transferred from the image carrier to the intermediate transfer body and upstream of the secondary transfer unit in a transport direction of the intermediate transfer body, and that detects a pattern image formed on the intermediate transfer body by the toner image forming unit; An image forming apparatus having When viewed in a sheet width direction perpendicular to a sheet conveying direction, the guide member protrudes toward the opposite side of the conveying path as it goes downstream in the sheet conveying direction, When the position on the intermediate transfer body where the pattern image is detected by the optical sensor is defined as a detection position, a portion of an edge of the guide member on a downstream side in the sheet conveying direction that overlaps with the detection position in the sheet width direction has a recessed shape that is recessed toward an upstream side in the sheet conveying direction compared to a portion of the edge that does not overlap with the detection position, The image forming apparatus is characterized in that the detection position is located outside the conveying path as viewed in the sheet width direction and on the same side of the conveying path as the optical sensor.

14. 14. The image forming apparatus according to claim 13, The optical sensor is arranged in plurality, The image forming apparatus is characterized in that a plurality of the concave portions of the guide member are arranged corresponding to a plurality of the optical sensors.

15. 15. The image forming apparatus according to claim 13, The image forming apparatus according to claim 1, wherein the concave portion of the guide member is provided above the optical sensor.

16. 16. The image forming apparatus according to claim 13, the conveying unit includes a pair of registration rollers that convey the sheet toward the secondary transfer unit, the guide member is disposed between the pair of registration rollers and the secondary transfer unit in the sheet conveying direction, and is disposed so as to prevent the sheet from contacting the intermediate transfer body; The image forming apparatus is characterized in that the guide member is made of a metal plate.

17. 17. The image forming apparatus according to claim 13, the intermediate transfer body is a belt member, The roller member supports the inner circumferential surface of the belt member. The image forming apparatus is characterized in that the guide member and the optical sensor are both provided at positions facing the roller member with the belt member interposed therebetween.

18. A conveying means for conveying a sheet; a guide member that forms a conveyance path for the sheet conveyed by the conveyance means; a sensor disposed on the same side of the conveying path as the guide member, the sensor detecting an object to be detected at a detection position; A sheet conveying device having: a portion of the guide member that overlaps with the detection position in a sheet width direction perpendicular to the sheet conveying direction has a retracted shape that is retracted to a side away from a passing position of the sheet in the conveying path compared to a portion that does not overlap with the detection position; The sensor includes a transmitter that emits light or sound toward the object to be detected, the retracted shape is located outside a region through which the light or the sound emitted by the transmitter passes from the transmitter to the detection object; A sheet conveying device characterized by:

Images