JP2013041178A - Position detection device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position detection device capable of highly accurately detecting a position of a sheet at low cost and with a simple construction, and to provide an image forming apparatus comprising the same.SOLUTION: A position detection device comprises: a movable holder 81 which has an upper surface 81a and a lower surface 81b disposed opposite each other and is reciprocally movable in the direction of sheet width; a driving unit 82 which drives the movable holder 81; and a sensor pair 85 which emits and receives light between the upper surface 81a and the lower surface 81b and detects presence/absence of a sheet. A sheet end detection part 8 for detecting the end position of a sheet which is passing through the movable holder 81 by moving in the direction of sheet width includes a plurality of sensor pairs each consisting of a light emitting element and a light receiving element respectively disposed on the upper surface 81a and the lower surface 81b arranged in a row in the direction of sheet width. Among the plurality of sensor pairs, a sensor pair 86 disposed within the irradiation area to which a light emitting element 85a of the adjacent sensor pair 85 emits light is arranged in such a manner that its light emitting element 86a and light receiving element 86b are disposed in the opposite direction in relation to those of the adjacent sensor pair 85.

Description

  The present invention relates to a position detection device that detects an end position of a sheet that is passing through a sheet conveyance path, and an image forming apparatus including the position detection device.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, after forming an image on a first surface of a sheet (hereinafter referred to as “single-sided printing”), the sheet is reversed and the first side opposite to the first surface is Some have a double-sided printing function that forms images on two sides (hereinafter referred to as “double-sided printing”).

  When performing double-sided printing with such an image forming apparatus, the sheet conveyance path leading to double-sided printing (for example, the path from reversing a sheet for which single-sided printing has been completed to sending it to the image forming unit) is compared to single-sided printing. Long. For this reason, the sheet gradually moves in the sheet width direction perpendicular to the sheet conveyance direction due to the slight misalignment of the conveyance roller and the distortion of the guide plate, and the image formed on the sheet moves in the sheet width direction. There was a risk of misalignment.

  For this, a position detection device has been proposed in which a line sensor detects the amount of positional deviation of the end position of the sheet in the sheet width direction in the sheet conveyance path, and determines the double-sided print start position based on the detection result. (See Patent Document 1). In the position detection device described in Patent Document 1, line sensors are arranged in a row so that the end position of the conveyed sheet from the minimum size to the maximum size can be detected, and light is irradiated from one side of the sheet to block the light. The end position in the sheet width direction is detected depending on the state.

  However, since the position detection device described in Patent Document 1 detects the end position in the sheet width direction of all sizes of sheets that can be conveyed, it detects the end position in the sheet width direction of all sizes of sheets. A possible line sensor is required. Therefore, there is a problem that the cost of the sensor itself increases, and as a result, the cost of the entire apparatus also increases.

  For this, a position detection device that detects an end position in the sheet width direction orthogonal to the sheet conveyance direction using a holder (for example, a photo interrupter) in which a pair of light emitting units and light receiving units are arranged to face each other is proposed. (See Patent Document 2). As shown in FIG. 5, the position detection device described in Patent Document 2 moves the holder 108 in the sheet width direction so that the end of the sheet crosses between a pair of light emitting units and a light receiving unit arranged to face each other. The end position in the sheet width direction is detected based on the distance from the reference position to the optical path blocking position.

  However, since the position detection device described in Patent Document 2 detects the position by a pair of light emitting units and light receiving units, when measuring the end position in the sheet width direction of a plurality of types of sheets, a holder It is necessary to increase the moving distance of 108. And in order to ensure the movement distance of the holder 108, it is necessary to enlarge a moving mechanism, for example. Thereby, there exists a possibility that apparatus itself may enlarge.

  In response to this, for example, the holder 108 is moved by arranging a plurality of pairs of light emitting units and light receiving units in the sheet width direction with respect to the holder so as to correspond to the end positions of a plurality of types of sheets. It is considered that the distance can be shortened to avoid an increase in the size of the moving mechanism or the like.

JP 2002-292960 A Japanese Patent Laid-Open No. 5-132193

  However, when a plurality of sensors are arranged side by side, the light receiving unit adjacent to the light receiving unit facing the light emitted from the light emitting unit may receive light, which may cause a detection error. Further, for example, when a plurality of sensors are arranged at positions corresponding to the size of the conveyed sheet and only the sensors at positions corresponding to the size of the conveyed sheet are moved, the number of sensors is equal to the number of sensors. A circuit and a driving unit are required. As a result, the cost increases and a space for placing wiring and the like is required, which may increase the size of the device itself.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a position detecting device capable of detecting a position of a sheet with high accuracy without increasing the size, and an image forming apparatus including the same.

  The present invention has a first holding surface and a second holding surface arranged to face each other so as to sandwich the end portion in the sheet width direction from both sides of the sheet passing through the sheet conveying path, and the first holding surface and the second holding surface A movable holder capable of reciprocally moving the holding surface in the sheet width direction; a holder driving unit that drives the moving holder in the sheet width direction; and the first holding surface and the second holding surface of the moving holder. Sensor means for detecting the presence or absence of a sheet by irradiating and receiving light between them, and driving the moving holder in the sheet width direction to scan the end portion of the passing sheet in the sheet width direction. In the position detection device for detecting the end position in the sheet width direction, the sensor means includes a pair of sensors each having a light emitting portion and a light receiving portion arranged on the first holding surface and the second holding surface, respectively. Multiple to align in the sheet width direction Of the plurality of sensor pairs, at least a sensor pair that overlaps within an irradiation range irradiated by a light emitting unit of the adjacent sensor pair is the first holding surface and the second holding with respect to the adjacent sensor pair. The light emitting portion and the light receiving portion are disposed so as to be opposite to each other on the surface.

  According to the present invention, the light emitting unit opposed to the light receiving unit of the adjacent sensor is arranged alternately in the opposite direction so that the light emitting unit is alternately arranged in the opposite direction, thereby increasing the size with an inexpensive and simple configuration. This makes it possible to detect the position of the sheet with high accuracy without doing so.

It is sectional drawing which shows typically the whole structure of the laser beam printer which concerns on embodiment of this invention. It is a perspective view which shows the sheet | seat edge part detection part of the laser beam printer which concerns on this embodiment. FIG. 3 is a partial enlarged cross-sectional view of a sensor unit of a sheet edge detection unit illustrated in FIG. 2. It is a figure which shows the irradiation range of the light emitting element of the sensor unit shown in FIG. It is a figure which shows the state which passes a sheet | seat to the sheet | seat edge part detection apparatus which concerns on a prior art example, and detects the edge part of a sheet | seat.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. An image forming apparatus according to an embodiment of the present invention includes a sheet edge detection unit capable of detecting the position of the sheet width direction edge of a sheet passing through a sheet conveyance path, such as a copying machine, a printer, a facsimile, and a composite device thereof. An image forming apparatus provided. In the following embodiments, a laser beam printer 1 will be described as an image forming apparatus.

  First, the overall structure of a laser beam printer 1 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing the overall structure of a laser beam printer according to an embodiment of the present invention.

  As shown in FIG. 1, the laser beam printer 1 includes an image on a sheet feeding unit 2 that feeds a sheet S, an image forming unit 3 that forms an image, and a sheet S fed from the sheet feeding unit 2. And a fixing unit 5 for fixing the image transferred to the sheet S. Further, the laser beam printer 1 includes a discharge unit 6 that discharges the sheet S on which an image is fixed, and a reverse conveyance unit 7 that reverses and conveys the sheet to perform double-sided printing on the sheet S on which single-sided printing is performed. And comprising.

  The sheet feeding unit 2 includes a feeding cassette 20 in which the sheet S is stored, a feeding roller pair 21 that feeds the sheet S stored in the feeding cassette 20 to the image forming unit 3, and one sheet S. And a separation unit (not shown) that separates each one. The sheet feeding unit 2 feeds the sheets S stored in the feeding cassette 20 toward the image forming unit 3 by the feeding roller pair 21 while separating the sheets S one by one by the separating unit.

  The image forming unit 3 includes a process cartridge 30 and an exposure unit 31, and the process cartridge 30 includes a photosensitive drum 32, a charging unit (not shown), and a developing unit (not shown). Configured. The photosensitive drum 32 is formed of a metal cylinder having a negatively charged photosensitive layer on the surface. The charging unit uniformly charges the drum surface of the photosensitive drum 32 which is an image carrier. The exposure unit 31 irradiates a laser beam based on the image information and forms an electrostatic latent image on the photosensitive drum 32. Note that the exposure unit 31 according to the present embodiment is configured to detect an electrostatic latent image formed on the photosensitive drum 32 according to the end position in the sheet width direction of the sheet detected by a sheet end detection unit 8 described later. A correction device (not shown) for correcting the position (image forming position) is provided. The developing unit attaches toner to the electrostatic latent image on the photosensitive drum 32 formed by the exposure unit 31 and visualizes it as a toner image.

  The transfer unit 4 is constituted by a transfer roller, and forms a nip with the photosensitive drum 32. The transfer unit 4 transfers the toner image formed on the photosensitive drum 32 to the sheet S sent to the nip with the photosensitive drum 32 at a predetermined timing by the registration roller pair 10.

  The fixing unit 5 includes a driving roller 50 and a fixing roller 51 with a built-in heater. The fixing unit 5 applies heat and pressure to the sheet S on which the unfixed toner image is transferred by the transfer unit 4 to fix the unfixed toner image on the sheet S.

  The discharge unit 6 includes an inner discharge roller pair 60, an outer discharge roller 61, and a discharge tray 62. The discharge unit 6 discharges the sheet S after single-sided printing or double-sided printing onto the discharge tray 62 via the inner discharge roller pair 60 and the outer discharge roller 61.

  The reversing conveyance unit 7 includes a reversing unit 70 that reverses the front and back (first and second surfaces) of the sheet S when performing double-sided printing, and an end position in the sheet width direction of the sheet S reversed by the reversing unit 70. And a sheet edge detection unit 8 as a position detection device for detecting the position. The laser beam printer 1 according to the present embodiment includes a double-sided print mode for performing double-sided printing in addition to the single-sided printing mode for performing single-sided printing. The reversing conveyance unit 7 mainly performs the double-sided printing mode. Used.

  The reversing unit 70 includes a switchback roller pair 71, a refeed path 72, a double-sided conveyance path 73, an intermediate tray 74, and a refeed roller pair 75. The sheet S on which duplex printing is performed is reversed by the inner discharge roller pair 60 or the switchback roller pair 71, and the reversed sheet S is placed on the intermediate tray 74 via the refeed path 72 and the duplex conveyance path 73. Temporarily stored. Then, the sheet S stored on the intermediate tray 74 is conveyed again toward the image forming unit 3 at a predetermined timing for image formation by the refeed roller pair 75, and thereafter, the same process as single-sided printing is performed. Then, it is discharged onto the discharge tray 62.

  The sheet end detection unit 8 is provided in the sheet conveyance path 11 located on the downstream side of the refeed roller pair 75. The sheet edge detection unit 8 refers to a direction (Y direction shown in FIG. 2) orthogonal to the sheet conveyance direction (X direction shown in FIG. 1 and hereinafter referred to as “sheet conveyance direction X”). The position of the edge in the sheet width direction Y where the positional deviation has occurred is detected.

  Here, the sheet edge detection unit 8 will be specifically described with reference to FIGS. 2 to 4. FIG. 2 is a perspective view showing the sheet edge detection unit 8 of the laser beam printer 1 according to the present embodiment. FIG. 3 is a partial enlarged cross-sectional view of the sensor unit 80 of the sheet edge detection unit 8 shown in FIG. FIG. 4 is a diagram showing an irradiation range of the light emitting elements of the sensor unit 80 shown in FIG. First, the configuration of the sheet edge detection unit 8 will be described with reference to FIGS.

  As shown in FIGS. 2 and 3, the sheet end detection unit 8 includes a moving holder 81 that can reciprocate in the sheet width direction Y, a drive unit 82 that serves as a holder driving unit that reciprocates the moving holder 81, and a pair. The conveyance guides 83 and 84 are configured. Further, the sheet edge detection unit 8 is arranged side by side in the sheet width direction, and includes a plurality of sensor pairs 85, 86, 87, and 88 that detect the presence or absence of a sheet (four sets in the present embodiment). Has been. The moving holder 81 and the four sensor pairs 85 to 88 constitute a sensor unit 80. The sensor unit 80 moves in the sheet width direction and scans in the sheet width direction Y, and ends in the sheet width direction Y. Detect position.

  The movable holder 81 has a substantially U-shaped cross section in the sheet width direction Y, and includes an upper surface 81a as a first holding surface and a lower surface 81b as a second holding surface. The upper surface 81a and the lower surface 81b are opposed to each other with a predetermined distance (so as to be sandwiched from both surfaces of the sheet) so that the sheet can pass between the upper surface 81a and the lower surface 81b. The moving holder 81 is configured to be reciprocally movable in the sheet width direction Y, and the upper surface 81a and the lower surface 81b are reciprocated in the sheet width direction Y integrally.

  The drive unit 82 includes a stepping motor 82a, a pinion 82b connected to the stepping motor 82a, and a drive train 82c that meshes with the pinion 82b. The drive train 82c is connected to the moving holder 81. By rotating the stepping motor 82a, the drive train 82c engaged with the pinion 82b is driven, and the movable holder 81 reciprocates in the sheet width direction Y.

  In the present embodiment, the drive unit 82 reciprocates the moving holder 81 with a predetermined stroke M necessary for detecting the end position in the sheet width direction Y of each of the plurality of types of sheets S1, S2, S3, and S4. . The predetermined stroke M refers to a reciprocating movement centered on a reference position, which will be described later, based on a preset maximum deviation width that allows each of the plurality of types of sheets S1, S2, S3, and S4 to be displaced in the sheet width direction Y. The amount of movement.

  The pair of conveyance guides 83 and 84 includes a first conveyance guide 83 having a rectangular plate shape and a second conveyance guide 84 having a rectangular plate shape. The first transport guide 83 is disposed on the upper surface 81a side of the moving holder 81 between the upper surface 81a and the lower surface 81b of the moving holder 81, and the second transport guide 84 is separated from the first transport guide 83 by a predetermined interval. Is arranged on the lower surface 81b side of the moving holder 81. Thus, the pair of conveyance guides 83 and 84 constitutes a sheet conveyance path 11 through which the sheet S can pass. The first transport guide 83 and the second transport guide 84 are made of a transparent material so as to transmit light from a light emitting element described later included in the four sensor pairs 85 to 88.

  The four pairs of sensors 85 to 88 include light emitting elements (LEDs) 85a, 86a, 87a, 88a as light emitting units and light receiving elements 85b, 86b, 87b, 88b as light receiving units, The moving holder 81 is held side by side in the sheet width direction Y. In addition, the four sensor pairs 85 to 88 have an upper surface 81a and a lower surface 81b so that the light emitting elements 85a to 88a do not interfere with the light receiving elements 85b to 88b of the adjacent sensor pairs 85 to 88 (not located within the irradiation range). Are held alternately in opposite directions. For example, in the light emitting element 85a of the sensor pair 85 and the light emitting element 86a of the sensor pair 86 adjacent to the sensor pair 85, the light emitting element 85a is held on the lower surface 81b, and the light emitting element 86a is opposite to the light emitting element 85a on the upper surface 81a. Is retained.

  Further, the four sensor pairs 85 to 88 can pass through end portions in the sheet width direction of a plurality of types (A size, B size, etc.) of sheets S1 to S4 having different predetermined lengths in the sheet width direction Y. It is arranged on the reference position. Note that the reference position is a position where a plurality of types of sheets S1 to S4 can pass through the sheet conveying path 11 without being displaced in the sheet width direction.

  In the present embodiment, as shown in FIG. 3, the broken line 89a is the reference position of the sheet S1, and the sensor pair 85 is disposed on the broken line 89a. A broken line 89b is the reference position of the sheet S2, and the sensor pair 86 is arranged on the broken line 89b. Similarly, the broken line 89c is the reference position of the sheet S3, and the sensor pair 87 is disposed on the broken line 89c. A broken line 89d is the reference position of the sheet S4, and the sensor pair 88 is disposed on the broken line 89d.

  As described above, in the present invention, a plurality of sensor pairs corresponding to usable sheet sizes are arranged at the respective reference positions, and in this embodiment, four sensor pairs 85 that can correspond to four sheet sizes. ~ 88 are arranged. Thereby, the edge part position of the sheet | seat width direction of four types of sheets S1-S4 is detectable. In the present embodiment, the light receiving elements 85b to 88b are covered with a cover member having a light receiving hole so as to receive light emitted from the pair of light emitting elements 85a to 88a, thereby improving the light receiving accuracy. ing.

  Next, the operation of the sheet edge detection unit 8 will be described. The sheet edge detection unit 8 reciprocates the moving holder (sensor unit 80) 81 in which the four sensor pairs 85 to 88 are arranged at a high speed in order to detect the light shielding state of the sheet S in a smaller operation region. It will be necessary. Therefore, the sensor unit 80 causes the drive unit 82 to reciprocate the moving holder 81 with a predetermined stroke M necessary for detecting the end position of one sheet in the sheet width direction.

  Due to the reciprocating motion of the moving holder 81, the four sensor pairs 85 to 88 fixedly arranged on the moving holder 81 also reciprocate simultaneously. Here, as shown in FIG. 3, the moving distance of the moving holder 81 covers the distance N from the maximum to the minimum size of the sheet conveyed from the reversing unit 70, and any of the optical paths received by the light receiving elements 85b to 88b. One of them is configured so as to cross the end of the conveyed sheet.

  Further, the position of the moving holder 81 during the reciprocating motion is controlled so as to be calculated from the initial position at the start of the motion by the number of pulses of the stepping motor 82a that drives the moving holder 81. For example, the position at which the light emitting element 85a and the light receiving element 85b detect the end position of the sheet S1 in the sheet width direction during the movement of the movable holder 81 from the reference initial position (for example, the position where the optical path is blocked by the sheet S1). The end position of the sheet S1 is calculated based on the distance up to. This is because the sheet S1 blocks the optical path formed by the light emitting element 85a and the light receiving element 85b, thereby causing light brightness and darkness, and the end position of the sheet S1 can be detected by the light receiving element 85b.

  At this time, as shown in FIG. 4, the light receiving element 85b of the sensor pair 85 and the light receiving element 86b of the sensor pair 86 adjacent to the sensor pair 85 are held on the upper surface 81a, and the light receiving element 86b is It is held on the lower surface 81b in the opposite direction to the light receiving element 85b. That is, the light receiving element 85b and the light receiving element 86b are not disposed adjacent to each other, but are disposed to face each other in an oblique direction. Therefore, the light receiving element 85b and the light receiving element 86b are not within the irradiation ranges L1 and L2 of the light emitted by the paired light emitting elements 85a and 86a, but the light emitted by the paired light emitting elements 85a and 86a There is no interference.

  As the control of the laser beam printer 1, for example, the initial position of the sensor pair 85 to 88 outside the sheet conveyance region and the initial value of the driving pulse of the stepping motor 82a are set. Then, the correction device of the exposure unit 31 uses the average position (average distance) of the end positions of the sheet S detected multiple times during conveyance of one sheet as the end position (distance to the end position) of the sheet S. The exposure position at which the photosensitive drum 32 of the image forming unit 3 is exposed is corrected. As a result, even when the sheet is displaced in the sheet width direction, an appropriate image with no displacement in the sheet width direction Y is formed on the sheet. When the conveyance of the sheet S is completed, the moving holder 81 is stopped by stopping the stepping motor 82a. The position of the stopped moving holder 81 is recognized by the number of pulses, and is set as an initial position when the next moving holder 81 starts reciprocating motion.

  As described above, the light emitting elements 85a to 88a and the light receiving elements 85b to 88b of the four sensor pairs 85 to 88 provided in the sheet edge detection unit 8 according to the present embodiment are provided on the upper surface 81a and the lower surface 81b of the moving holder 81. Are arranged alternately. Therefore, as shown in FIG. 4, the irradiation range (optical path) L1 of the light emitting element 85a that detects the sheet S reaches not only the light receiving element 85b but also the adjacent light emitting element 86a, but reaches the light receiving element 86b. do not do. Thereby, it is possible to prevent the optical path of the light emitting element from entering the light receiving element of the sensor pair adjacent to the light emitting element. As a result, it is possible to prevent a detection error due to the light receiving element, and it is possible to detect the edge position of the sheet with high accuracy without degrading the reading detection accuracy.

  Thereby, for example, based on the position information of the sheet by the sensor pair, the exposure position of the electrostatic latent image formed on the photosensitive drum 32 by the exposure unit 31 can be corrected by a correction device (not shown), and there is no proper lateral deviation. Can be obtained. Further, by correcting the exposure position based on the average of the edge position of the sheet detected a plurality of times, it is possible to form an image with higher accuracy.

  In addition, the sheet edge detection unit 8 according to the present embodiment reciprocates the moving holder 81 that holds the four pairs of sensors 85 to 88 to move the edge positions of the four types of sheets S1 to S4 in the sheet width direction Y. Is detected. Therefore, for example, the number of sensor pairs can be reduced as compared with the case of using a line sensor, and the cost can be reduced. Further, by moving the four pairs of sensors 85 to 88 with a predetermined stroke M, it is possible to detect by a simple reciprocating movement of a small stroke, and for example, the configuration of the drive unit 82 can be simplified. In addition, a complicated moving mechanism is not necessary. Furthermore, since the moving distance is short, the increase in size of the moving mechanism and the apparatus can be suppressed.

  In addition, for example, like a photo interrupter, it waits in a range where it does not overlap with the conveyed sheet in the sheet width direction, or stops before colliding with the end of the sheet after detecting the end position of the sheet, etc. Complex control is also unnecessary.

  In addition, the sheet edge detection unit 8 according to the present embodiment holds the four sensor pairs 85 to 88 in the moving holder 81 and moves them integrally, so that it is necessary to move each sensor pair individually. It is not necessary to secure a space for a plurality of electric circuits and wirings. As a result, the cost can be reduced and the size of the apparatus can be prevented from being increased.

  As described above, the sheet edge detection unit 8 according to the present embodiment can detect the position of the sheet with high accuracy without increasing the size with an inexpensive and simple configuration.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment mentioned above. In addition, the effects described in the embodiments of the present invention only list the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments of the present invention.

  For example, in the present embodiment, the description has been given using the LED as the light emitting element, but the present invention is not limited to this. The light emitting element may be any element that can receive light by the light receiving element. Further, although the stepping motor 82a is used for the drive unit 82 for moving the moving holder 81, the present invention is not limited to this. Any device that can drive the movable holder 81 may be used.

  Further, in the present embodiment, the sheet edge detection unit 8 is provided on the downstream side of the reversing unit 70, but the present invention is not limited to this. For example, the sheet edge detection unit 8 may be provided between the sheet feeding unit 2 and the image forming unit 3.

  Moreover, in this embodiment, all the light emitting elements 85a to 88a and the light receiving elements 85b to 88b of the four sensor pairs 85 to 88 are arranged so as to be opposite to each other. It is not limited to. The plurality of sensor pairs should be arranged such that the light emitting part and the light receiving part of the sensor pair in the position overlapping the irradiation range irradiated by the light emitting part of the adjacent sensor pair are opposite to the adjacent sensor pair. That's fine.

1 Laser beam printer (image forming device)
3 Image forming unit 8 Sheet edge detection unit (position detection device)
11 Sheet conveyance path 81 Moving holder 81a Upper surface (first holding surface)
81b Lower surface (second holding surface)
82 Drive unit (holder drive unit)
85 Sensor pairs (sensor means)
85a Light emitting element (light emitting part)
85b Light receiving element (light receiving part)
86 Sensor pair (sensor means)
86a Light emitting element (light emitting part)
86b Light receiving element (light receiving part)
87 Sensor pair (sensor means)
87a Light emitting element (light emitting part)
87b Light receiving element (light receiving part)
88 Sensor pair (sensor means)
88a Light emitting element (light emitting part)
88b Light receiving element (light receiving part)
S sheet M stroke

Claims (3)

The first holding surface and the second holding surface are provided so as to be opposed to each other so as to sandwich the end portion in the sheet width direction from both sides of the sheet passing through the sheet conveying path, and the first holding surface and the second holding surface are integrated. Light between the first holding surface and the second holding surface of the moving holder, a moving holder that can reciprocate in the sheet width direction, a holder driving unit that drives the moving holder in the sheet width direction, and Sensor means for detecting the presence or absence of a sheet by irradiating and receiving light, and driving the moving holder in the sheet width direction to scan the end of the passing sheet in the sheet width direction. In the position detection device that detects the end position of the
The sensor means includes a plurality of sensor pairs each having a light emitting portion and a light receiving portion arranged on the first holding surface and the second holding surface, respectively, so as to be aligned in the sheet width direction,
Among the plurality of sensor pairs, at least a sensor pair that overlaps within an irradiation range irradiated by a light emitting unit of the adjacent sensor pair is the first holding surface and the second holding surface with respect to the adjacent sensor pair. With the light emitting part and the light receiving part arranged in the opposite direction,
A position detection device characterized by that. The plurality of sensor pairs are arranged on the moving holder so as to be positioned on a plurality of reference positions that pass when the end portions in the sheet width direction of each of the plurality of types of sheets are not displaced in the sheet width direction,
By the reciprocating movement of the moving holder in the sheet width direction by the preset maximum deviation width, the holder driving unit is provided with a sensor pair disposed on a reference position corresponding to the type of the sheet being passed, Detect the edge position of the passing sheet,
The position detection device according to claim 1. The position detection device according to claim 1, and an image forming unit that forms an image on a sheet by correcting an image forming position according to an end position in a sheet width direction of the sheet detected by the position detection device. With
An image forming apparatus.

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