Image reading device and image forming device

Abstract

To reduce false detection due to thermal expansion of a reading member.SOLUTION: An image reading device 500 comprises: a first reading member 610 that reads a sheet in a main scanning direction with a light transmissive member 602 therebetween; a second reading member 611 that is arranged shifted with respect to the first reading member in a sub scanning direction and reads the sheet; and a housing 605 that holds the first reading member and the second reading member. One end of the first reading member in the main scanning direction is located at a first positioning position A with respect to the housing. The other end of the second reading member opposite to one end of the first reading member in the main scanning direction is located at a second positioning position B with respect to the housing. In the main scanning direction, the first positioning position is outside the middle position 610C of the first reading member with respect to the middle position C of the housing. In the main scanning direction, the second positioning position is outside the middle position 611C of the second reading member with respect to the middle position of the housing.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an image reading device and an image forming device. [Background technology]

[0002] Conventionally, there is known a device that reads an image on a sheet by an image sensor while the sheet is being transported. For example, as disclosed in Patent Document 1, a contact glass facing the image surface of the sheet is arranged in a transport path along which the sheet is transported, and an image formed on the sheet is read by an image sensor through the contact glass. A reference member (backing) that serves as a reference for reading is arranged on the opposite side of the contact glass, and the backing is formed as a part of the sheet reading transport path.

[0003] Furthermore, as in Patent Document 2, in a reading device, by using multiple inexpensive image sensors, the component cost can be reduced compared to using one wide image sensor. When multiple image sensors are used, a configuration is known in which the ends of adjacent image sensors are staggered so that they partially overlap in the main scanning direction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-184863 A [Patent Document 2] JP 2011-55344 A Summary of the Invention [Problem to be solved by the invention]

[0005] The toner is fixed, and the image sensor heats up as the heated sheet passes through. If the image sensor is positioned on the inside of the center of the housing in the main scanning direction, the sensor position will expand from the center of the housing to the outside due to thermal expansion as the image sensor heats up. If the image width is read with a sensor that has expanded outward, it may erroneously read the image as smaller than it actually is. This erroneous detection poses the problem of correcting the image width to be larger than it actually is.

[0006] Also, Patent Document 2 discloses a configuration in which the linear expansion coefficients of the image sensor and base member are made the same, and the distance and direction of the positioning of the overlapping image sensor and sensor housing, and the positioning of the sensor housing and base member are aligned to reduce misalignment of the image sensor joint. In this configuration, the positioning position on one side is placed near the sensor joint, far from the detection position. Even with this, the erroneous detection caused by thermal expansion on one side cannot be solved.

[0007] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to reduce erroneous detection caused by thermal expansion of a reading member. [Means for solving the problem]

[0008] An image reading device according to an embodiment of the present invention comprises: A light-transmitting member; A plurality of light receiving elements are arranged in the main scanning direction, The sheet is formed by passing the light transmitting member through the sheet. Read the image a first reading member for reading the a first reading member that is shifted in a sub-scanning direction perpendicular to the main scanning direction; and a plurality of light receiving elements arranged in the main scanning direction and arranged so as to overlap the first reading member when viewed from the sub-scanning direction, The sheet Read the image a second reading member for reading the a housing that holds the first reading member and the second reading member; Equipped with The first reading member and the second reading member has an elongated shape in the main scanning direction, the first reading member and the second reading member are disposed such that, in the main scanning direction, a center position of the first reading member is located on one side of a center position of the housing, and a center position of the second reading member is located on the other side of the center position of the housing; of the first reading member in the main scanning direction One of the two ends is located on the one side with respect to the center position of the housing.the end portion is positioned at a first position relative to the housing; and an end portion of the first reading member that is located on the other side with respect to a center position of the housing, among both ends of the first reading member in the main scanning direction, is not positioned with respect to the housing, In the main scanning direction Before The second reading member One of the two ends is located on the other side with respect to the center position of the housing. the end portion is positioned at a second position relative to the housing; and an end portion of the second reading member that is located on the one side with respect to a center position of the housing, among both ends of the second reading member in the main scanning direction, is not positioned with respect to the housing, the first positioning position is located outside a center position of the first reading member with respect to a center position of the housing in the main scanning direction; The second positioning position is located outside a central position of the second reading member with respect to the central position of the housing in the main scanning direction. Effect of the Invention

[0009] According to the present invention, it is possible to reduce erroneous detection caused by thermal expansion of the reading member. [Brief description of the drawings]

[0010] [Figure 1] FIG. [Diagram 2] FIG. [Diagram 3] An explanatory diagram of the front and back registration section. [Figure 4] An explanatory diagram of the front and back registration section. [Diagram 5] FIG. 2 is a block diagram of an image forming apparatus and an adjustment unit. [Figure 6] FIG. 4 is a diagram showing a screen displayed on the operation unit. [Figure 7] 4A and 4B are diagrams showing patch images formed on a sheet. [Figure 8] 4 is a flow chart of the control operation of sheet transport and front-to-back registration. [Figure 9] FIG. 4 is an explanatory diagram of sheet transport to a through path. [Figure 10] FIG. 4 is an explanatory diagram of sheet conveyance to a discharge path. [Figure 11] FIG. 4 is an explanatory diagram of thermal expansion of the back side reading unit. [Figure 12] 5A to 5C are diagrams illustrating thermal expansion of the image sensor according to the first reference example. [Figure 13] 13A to 13C are diagrams illustrating thermal expansion of an image sensor according to a second reference example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (Image forming system) FIG. 1 is a partial cross-sectional view of an image forming system 100. The image forming system 100 includes an image forming apparatus 101, an operation unit (user interface) 180, an adjustment unit (automatic adjustment device) 400, and a post-processing device (finisher) 1200. The image forming apparatus 101 forms an image on a recording medium (hereinafter referred to as a sheet) P. The operation unit 180 is operated by a user to set image formation conditions, and also displays the state of the image forming apparatus 101. The adjustment unit 400 performs front-back registration to adjust the positional deviation between an image formed on the front side of the sheet P by the image forming apparatus 101 and an image formed on the back side. The post-processing device 1200 discharges the sheet P on which the image has been formed to a discharge tray 1201, and performs post-processing such as stapling, punching, and sorting.

[0012] (Image forming device) The image forming apparatus 101 is an electrophotographic laser beam printer. The image forming apparatus 101 forms an image on a sheet using an electrophotographic image forming process. In addition to a laser beam printer, the image forming apparatus 101 may be, for example, an electrophotographic copying machine (e.g., a digital copying machine), a color LED printer, an MFP (multifunction machine), a facsimile machine, or a printing machine. The image forming apparatus 101 is not limited to a color image forming apparatus that forms a color image, but may also be a monochrome image forming apparatus that forms a monochrome image. The image forming apparatus 101 is not limited to an electrophotographic image forming apparatus, but may also be an inkjet printer, a dye-sublimation printer, or a thermal printer using a thermal drying method.

[0013] The image forming apparatus 101 will be described with reference to Fig. 1 and Fig. 5. Fig. 5 is a block diagram of the image forming apparatus 101 and the adjustment unit 400. The image forming apparatus 101 has a printer controller 103, an engine control unit 312, and an engine unit 140. The printer controller 103 has a sheet library 900 and an image shape correction unit 320. The printer controller 103 is electrically connected to the operation unit 180, the engine control unit 312, and a communication unit 250 of the adjustment unit 400.

[0014] The engine control unit 312 is electrically connected to the conveying roller drive motor 311 and the flapper drive unit 141. The flapper drive unit 141 drives the flappers 131, 132, 133, and 134. The engine control unit 312 is further electrically connected to the first post-fixing sensor 153, the second post-fixing sensor 163, the inversion sensor 137, and the engine unit 140. The engine control unit 312 controls the engine unit 140 to execute the image forming process (including the sheet feeding process). The engine unit 140 has a yellow image forming unit 120, a magenta image forming unit 121, a cyan image forming unit 122, and a black image forming unit 123. The engine unit 140 further has a feed cassette 113, an intermediate transfer body 106, a secondary transfer roller 114, a first fixing unit 150, and a second fixing unit 160.

[0015] The yellow image forming unit 120 forms a yellow (Y) toner image. The magenta image forming unit 121 forms a magenta (M) toner image. The cyan image forming unit 122 forms a cyan (C) toner image. The black image forming unit 123 forms a black (K) toner image. The yellow image forming unit 120, the magenta image forming unit 121, the cyan image forming unit 122, and the black image forming unit 123 have almost the same structure except for the color of the toner, so the yellow image forming unit 120 will be described below.

[0016] The yellow image forming unit 120 has a rotating photosensitive drum 105. Around the photosensitive drum 105, a charger 111, a laser scanner 107, a developing unit 112, and a primary transfer roller 118 are arranged. The charger 111 uniformly charges the surface of the photosensitive drum 105. The laser scanner 107 has a laser driver (not shown) that turns on / off a laser beam emitted from a semiconductor laser 108 according to image data supplied from the printer controller 103. The laser beam emitted from the semiconductor laser 108 is deflected in the main scanning direction by a rotating polygon mirror (not shown). The laser beam deflected in the main scanning direction is guided to the surface of the photosensitive drum 105 by a reflecting mirror 109, and exposes the uniformly charged surface of the photosensitive drum 105 in the main scanning direction. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 105 according to the image data.

[0017] The developing device 112 develops the electrostatic latent image on the surface of the photosensitive drum 105 with yellow (Y) toner to form a yellow (Y) toner image. A voltage of the opposite polarity to that of the toner image is applied to the primary transfer roller 118, which transfers the yellow (Y) toner image on the surface of the photosensitive drum 105 onto the intermediate transfer body 106. Similarly, a magenta (M) toner image, a cyan (C) toner image, and a black (K) toner image formed by a magenta image forming unit 121, a cyan image forming unit 122, and a black image forming unit 123 are sequentially transferred onto the intermediate transfer body 106. The yellow (Y), magenta (M), cyan (C), and black (K) toner images are transferred onto the intermediate transfer body 106 in a superimposed manner to form a full-color toner image.

[0018] Meanwhile, the sheets P stored in the feeding cassette 113 are conveyed one by one to the secondary transfer roller 114. The secondary transfer roller 114 presses the sheet P against the intermediate transfer body 106 and simultaneously applies a bias of the opposite polarity to the toner. The secondary transfer roller 114 transfers the toner image on the intermediate transfer body 106 to the sheet P. The photosensitive drum 105 and the developing device 112 are detachable. A feeding timing sensor 116 for timing the feeding of the sheet P is disposed in the sheet conveying path in front of the secondary transfer roller 114. In addition, an image formation start position detection sensor 115 for determining the print start position when forming an image and a density sensor 117 for measuring the density of a patch image during density control are disposed around the intermediate transfer body 106. When performing density control, the density sensor 117 measures the density of each patch image.

[0019] The image forming apparatus 101 has a first fixing device 150 and a second fixing device 160 that heat and pressurize the toner image transferred to the sheet P to fix the toner image to the sheet P. The first fixing device 150 includes a fixing roller 151 having an internal heater, a pressure belt 152 that presses the sheet P against the fixing roller 151, and a first post-fixing sensor 153 that detects the completion of fixing. The fixing roller 151 and the pressure belt 152 hold the sheet P between them and heat and pressurize it to fix the toner image to the sheet P, while conveying the sheet P. The second fixing device 160 is disposed downstream of the first fixing device 150 in the conveying direction of the sheet P. The second fixing device 160 is provided to increase the gloss of the image fixed to the sheet P by the first fixing device 150 and ensure fixability. The second fixing device 160 includes a fixing roller 161, a pressure roller 162, and a second post-fixing sensor 163.

[0020] Depending on the type of sheet P, it may not be necessary to use the second fixing device 160. In this case, in order to reduce energy consumption, the sheet P is conveyed to the conveying path 130 without passing through the second fixing device 160. The flapper 131 switches the conveying destination of the sheet P between the second fixing device 160 and the conveying path 130. The flapper 132 switches the conveying destination of the sheet P between the conveying path 135 and the discharge path 139. For example, in the face-up discharge mode, the flapper 132 switches the conveying destination of the sheet P to the discharge path 139 in order to convey the sheet P having an image formed on its first side to the discharge path 139. For example, in the face-down discharge mode, the flapper 132 switches the conveying destination of the sheet P to the conveying path 135 in order to convey the sheet P having an image formed on its first side to the conveying path 135. When the trailing end of the sheet P passes the flapper 134 , the conveying direction of the sheet P is reversed, and the conveying destination of the sheet P is switched to a discharge path 139 by the flapper 134 .

[0021] For example, in a double-sided printing mode, in order to print an adjustment chart (measurement test pattern) on the second side of the sheet P after the adjustment chart (measurement test pattern) is printed on the first side of the sheet P, the flapper 132 switches the conveyance destination of the sheet P to the conveyance path 135. The sheet P conveyed to the conveyance path 135 is conveyed to the inversion unit 136. After the rear end of the sheet P conveyed to the inversion unit 136 is detected by the inversion sensor 137, the conveyance direction of the sheet P is reversed. The flapper 133 switches the conveyance destination of the sheet P to the conveyance path 138. This inverts the front and back of the sheet P. The sheet P is conveyed from the conveyance path 138 to the secondary transfer nip between the intermediate transfer body 106 and the secondary transfer roller 114. The adjustment chart is transferred to the second side of the sheet at the secondary transfer nip. The sheet P with the adjustment charts printed on both sides is conveyed from the discharge path 139 to the adjustment unit 400.

[0022] (Adjustment unit) The adjustment unit 400 is disposed downstream of the image forming apparatus 101 in the conveying direction of the sheet P. Fig. 2 is a cross-sectional view of the adjustment unit 400. The adjustment unit 400 has a conveying roller pair 401 that receives a sheet from the image forming apparatus 101, an image reading device (hereinafter referred to as a front and back registration unit) 500 that reads an image of the sheet conveyed from the conveying roller pair 401, and a flapper 422 located downstream thereof. The adjustment unit 400 has a through path 430 that delivers the sheet P to the post-processing device 1200 disposed downstream of the adjustment unit 400, a discharge tray 431 provided on the upper surface, and a discharge path 432 that continues from the front and back registration unit 500 to the discharge tray 431.

[0023] The flapper 422 can switch between a through path 430 and a discharge path 432. When passing the sheet P through the through path 430, the flapper 422 is moved to an upper position. The sheet P is discharged to the post-processing device 1200 by a pair of conveying rollers 406. On the other hand, when passing the sheet P through the discharge path 432, the flapper 422 is moved to a lower position. The sheet P is conveyed through the discharge path 432 by discharge conveying rollers 415, 416, and 417, and is discharged to the discharge tray 431 by tray discharge rollers 418.

[0024] In this way, the discharge destination of the sheet P can be switched by the flapper 422. A user job sheet on which an image has been formed according to a normal user job is discharged to the post-processing device 1200 via a through path 430. An adjustment sheet read by the front and back registration unit 500 is discharged to a discharge tray 431 through a discharge path 432. In this way, by switching the user job sheet and the adjustment sheet to different trays, it is possible to prevent the adjustment sheet, which is an unnecessary deliverable for the user, from being included in the user job sheet.

[0025] As shown in FIG. 5, the adjustment unit 400 includes a communication unit 250, an image processing unit 260, and a control unit (control means) 251. The communication unit 250 is electrically connected to the image processing unit 260 and the control unit 251. The communication unit 250 is electrically connected to the printer controller 103 of the image forming apparatus 101. The adjustment unit 400 further includes a conveying motor 252, a timer 310, a flapper switching motor 240, a sheet sensor 522, a sheet sensor 523, a backing motor 834, an image sensor 610, and an image sensor 611. The conveying motor 252, the timer 310, the flapper switching motor 240, the sheet sensor 522, the sheet sensor 523, the backing motor 834, the image sensor 610, and the image sensor 611 are electrically connected to the control unit 251. The conveying motor 252 drives the conveying roller pairs 401, 501, 502, 503, and 406. The flapper switching motor 240 drives the flapper 422. The image processing unit 260 is electrically connected to the image sensor 610 and the image sensor 611.

[0026] (Front and back registration section) Next, the inside of the front and back register section 500 will be described with reference to FIG. 3. FIG. 3 is an explanatory diagram of the front and back register section 500. FIG. 3(a) is a cross-sectional view of the front and back register section 500. FIG. 3(b) is a plan view of the front and back register section 500. In the front and back register section 500, a sheet is conveyed in a conveying direction CD shown in FIG. 3(a) by conveying roller pairs 501, 502, and 503. The front and back register section 500 also has a back reading section 600-1 that reads the edge of the conveyed sheet and a patch on the back surface of the sheet, and a front reading section 600-2 that similarly reads the front surface. Furthermore, the front and back register section 500 is provided with a biasing roller 510-12 that biases the sheet facing the back reading section 600-1, and biasing rollers 510-11-1 and 510-11-2 that bias the sheet upstream of the biasing roller 510-12. Similarly, a biasing roller 510-22 that biases the sheet against the front surface reading unit 600-2, and biasing rollers 510-21-1 and 510-21-2 that bias the sheet upstream of the biasing roller 510-22 are provided. The biasing rollers 510 (510-12, 510-11-1, 510-11-2) are arranged with a predetermined gap (space) between them and the glass 602 that is a part of the back surface reading unit 600-1. Similarly, the biasing rollers 510 (510-22, 510-21-1, 510-21-2) are arranged with a predetermined gap between them and the glass 602 that is a part of the front surface reading unit 600-2. In other words, the biasing rollers 510 and the glass 602 are not nipped. Furthermore, the six biasing rollers 510 are rotationally driven by a backing motor 834 (FIG. 5).

[0027] (Image sensor positioning configuration) The positioning configuration of contact image sensors (hereinafter referred to as image sensors) 610 and 611 in the back surface reading unit 600-1 will be described with reference to FIG. 4. FIG. 4(a) is a plan view of the back surface reading unit 600-1. FIG. 4(b) is a cross-sectional view of the back surface reading unit 600-1. As shown in FIG. 4(a), the back surface reading unit 600-1 is provided with image sensors 610 and 611 as reading members for reading the back surface of a sheet. Based on the reading results of the image sensors 610 and 611, the edge of the sheet and a patch formed on the sheet are detected. Based on the reading results of the image sensors 610 and 611, the absolute magnification of the image can be adjusted. The back surface reading unit 600-1 has a sensor holding member (first holding member) 601-1 for holding the image sensor 610 and a sensor holding member (second holding member) 601-2 for holding the image sensor 611. The back side reading unit 600-1 has glass (transparent member) 602 as a light transmitting member that transmits light. The back side reading unit 600-1 has a sub-scanning restricting spring 603 that restricts the positions of the image sensors 610 and 611 in the sub-scanning direction, and a height restricting spring 604 that restricts the positions of the image sensors 610 and 611 in the height direction H. The front side reading unit 600-2 has a similar structure to the back side reading unit 600-1, so a description thereof will be omitted.

[0028] In the housing 605 of the back surface reading unit 600-1, an image sensor (first reading member) 610 is disposed upstream (front side) in the main scanning direction with respect to a center position C of the housing 605. An image sensor (second reading member) 611 is disposed downstream (rear side) in the main scanning direction with respect to the center position C. The main scanning direction is a direction perpendicular to the conveying direction CD. The image sensor 610 and the image sensor 611 are disposed offset in the sub-scanning direction (conveying direction CD). The image sensor 610 and the image sensor 611 are disposed offset in the main scanning direction, and when viewed along the sub-scanning direction, the two overlap and are disposed in a staggered manner. The image sensor 610 and the image sensor 611 read the sheet in a line shape in the main scanning direction through the glass 602. The image sensor 610 and the image sensor 611 have an elongated shape extending in the main scanning direction.

[0029] The image sensor 610 is biased in the sub-scanning direction by the sub-scanning restricting spring 603 to come into contact with the sensor holding member 601-1, and the position of the image sensor 610 in the sub-scanning direction is restricted. The image sensor 611 is biased in the sub-scanning direction by the sub-scanning restricting spring 603 to come into contact with the sensor holding member 601-2, and the position of the image sensor 611 in the sub-scanning direction is restricted. The image sensor 610 is biased in the height direction H toward the glass 602 by the height restricting spring 604 to come into contact with the sensor holding member 601-1, and the position of the image sensor 610 in the height direction H is restricted. The image sensor 611 is biased in the height direction H toward the glass 602 by the height restricting spring 604 to come into contact with the sensor holding member 601-2, and the position of the image sensor 611 in the height direction H is restricted.

[0030] The image sensor 610 has a rectangular parallelepiped protrusion (first convex portion) 616 at one end in the main scanning direction. The protrusion 616 of the image sensor 610 fits into a rectangular hole (first concave portion) 618 provided in the sensor holding member 601-1, and the image sensor 610 is positioned at a positioning position A in the main scanning direction with respect to the sensor holding member 601-1. The positioning position A is located on the opposite side of the central position C of the housing 605 (outside the central position 610C) with respect to the central position 610C of the image sensor 610 in the main scanning direction. The image sensor 610 can read the sheet between the positioning position A and the central position C. The image sensor 611 has a rectangular parallelepiped protrusion (second convex portion) 617 at the other end in the main scanning direction. A protrusion 617 of the image sensor 611 fits into a rectangular hole (second recess) 619 provided in the sensor holding member 601-2, and the image sensor 611 is positioned at positioning position B in the main scanning direction relative to the sensor holding member 601-2. Positioning position B is located on the opposite side of center position C of the housing 605 (outside center position 611C) with respect to center position 611C of the image sensor 611 in the main scanning direction. The image sensor 611 is capable of reading a sheet between positioning position B and center position C.

[0031] (Front and back registration feedback configuration) Next, the measurement by the front and back registration unit 500 and the feedback destination of the measurement result will be described. FIG. 6 is a diagram showing a screen displayed on the operation unit 180. FIG. 6(a) is a diagram showing a sheet library editing screen 1001 displayed on the operation unit 180. The user can select and set the sheet type 910 from the sheet library editing screen 1001. When the user operates the operation unit 180 to select print position adjustment 1002 in the sheet library editing screen 1001 shown in FIG. 6(a), a correction method selection screen 1003 shown in FIG. 6(b) is displayed on the operation unit 180. When the user selects "Read test page and adjust" 1105, the image forming apparatus 101 forms a patch image 820 (FIG. 7) as an adjustment chart on the sheet P. The patch image 820 is formed at a predetermined distance from the edge of the sheet P and is detected to adjust the image width.

[0032] 7 is a diagram showing a patch image 820 formed on a sheet P. While conveying the sheet P by conveying roller pairs 501, 502, and 503, the front and back registration section 500 continuously reads the back surface of the sheet P on which the patch image 820 as an adjustment chart is formed by the image sensors 610 and 611 of the back surface reading section 600-1. Similarly, the front surface of the sheet P on which the patch image 820 as an adjustment chart is formed is continuously read by the image sensors 610 and 611 of the front surface reading section 600-2. The image processing section 260 combines the read line images to synthesize image data, and performs measurement from the combined image.

[0033] 7(a) is a diagram showing a surface measurement pattern image 822 obtained by reading the surface of a sheet P on which a patch image 820 is formed, by the image sensors 610 and 611 of the surface reading unit 600-2. The four patch images 820 are formed in the four corner areas of the surface measurement pattern image 822. The surface measurement pattern image 822 includes a leading edge 822a and a trailing edge 822b in the conveying direction CD of the sheet P, and a left edge 822c and a right edge 822d along the conveying direction CD. The conveying direction CD of the sheet P is defined as the sub-scanning direction Y, and the direction perpendicular to the sub-scanning direction Y is defined as the main scanning direction X.

[0034] The image processing unit 260 detects the detection coordinates (X 01 ,Y 01 ), (X 11 ,Y 11 ), (X 21 ,Y 21 ) and (X 31 ,Y 31 The image processing unit 260 calculates the detection coordinates (X 41 ,Y 41 ), (X 51 ,Y 51 ), (X 61 ,Y 61 ) and (X 71 ,Y 71 The image processor 260 calculates the detection coordinates (X 01 ,Y 01 )~(X 71 ,Y 71 ), the image processing unit 260 measures the amount of distortion of the image on the front side and the amount of misalignment between the sheet P and the image. Based on the amount of distortion and the amount of misalignment of the image on the front side, the image processing unit 260 calculates a first geometric adjustment value that can instruct the image shape correction unit 320 to correct the shape. The first geometric adjustment value includes the lead position, side position, main scanning magnification, sub-scanning magnification, perpendicularity, rotation amount, and absolute magnification.

[0035] 7(b) is a diagram showing a back surface measurement pattern image 823 obtained by reading the back surface of the sheet P on which the patch images 820 are formed by the image sensors 610 and 611 of the back surface reading unit 600-1. The four patch images 820 are formed in the four corner areas of the back surface measurement pattern image 823. The back surface measurement pattern image 823 includes a leading edge 823a and a trailing edge 823b in the conveying direction CD of the sheet P, and a left edge 823c and a right edge 823d along the conveying direction CD.

[0036] The image processing unit 260 detects the detection coordinates (X 02 ,Y 02 ), (X 12 ,Y 12 ), (X22 ,Y 22 ) and (X 32 ,Y 32 The image processing unit 260 calculates the detection coordinates (X 42 ,Y 42 ), (X 52 ,Y 52 ), (X 62 ,Y 62 ) and (X 72 ,Y 72 The image processor 260 calculates the detection coordinates (X 02 ,Y 02 )~(X 72 ,Y 72 ), the amount of distortion of the image on the back side and the amount of misalignment between the sheet P and the image are measured. Based on the amount of distortion and the amount of misalignment of the image on the back side, the image processing unit 260 calculates second geometric adjustment values ​​that enable shape correction instructions to be given to the image shape correction unit 320. The second geometric adjustment values ​​include the lead position, side position, main scanning magnification, sub-scanning magnification, perpendicularity, rotation amount, and absolute magnification.

[0037] The first and second geometric adjustment values ​​calculated by the image processing unit 260 are transmitted to the sheet library 900 in the image forming apparatus 101 through the communication unit 250. The first and second geometric adjustment values ​​are stored in the sheet library 900 as front and back parameters. In this manner, a set value is stored in the sheet library 900 for each sheet type 910. By reading out the set value from the sheet library 900 according to the sheet type 910 for which a print job is executed and correcting the image position and image distortion, it is possible to output a print image in which the front and back printing positions are corrected with high accuracy. Here, the front surface measurement pattern image 822 and the back surface measurement pattern image 823 exemplified in this description may be measured before the execution of a print job, or may be automatically measured at a predetermined timing as calibration during the execution of a print job.

[0038] (Control Action) The control operations of sheet transport and front-back registration in the image forming apparatus 101 and the adjustment unit 400 will be described below with reference to Figs. 8, 9 and 10. Fig. 8 is a flow chart of the control operations of sheet transport and front-back registration. The control unit 251 executes the control operations according to a program stored in an internal memory (not shown). Fig. 9 is an explanatory diagram of sheet transport to the through path 430. Fig. 10 is an explanatory diagram of sheet transport to the discharge path 432.

[0039] When a job is input by a user from the operation unit 180, the control unit 251 starts a control operation. The control unit 251 judges whether the job is a normal print job or not (S1101). If the job is a normal print job (YES in S1101), the control unit 251 makes the image forming apparatus 101 and each member of the adjustment unit 400 wait at a home position (HP) (S1102). At this time, in order to guide the sheet P to the through path 430 in the adjustment unit 400, the control unit 251 makes the flapper 422 wait in an upward direction (through path position) (S1102).

[0040] The image forming apparatus 101 forms an image on the sheet P (S1103). As shown in FIG. 9A, the adjustment unit 400 receives the sheet P on which the image has been formed from the image forming apparatus 101 (S1104). The control unit 251 controls the conveying motor 252 to convey the sheet P to the through path 430 by the conveying roller pairs 401, 501, 502, 503, and 406. As shown in FIG. 9B, the sheet P is discharged to the post-processing apparatus 1200 (S1105) and is stacked on the discharge tray 1201 of the post-processing apparatus 1200. The control unit 251 determines whether the sheet P is the last sheet (S1106). If the sheet P is not the last sheet (NO in S1106), the control unit 251 returns the process to S1101. If the sheet P is the last sheet (YES in S1106), the control unit 251 ends the control operation.

[0041] On the other hand, when the user selects the sheet type 910 from the sheet library 900 by the operation unit 180 and selects the print position adjustment 1002, a front and back registration job is input. If the job is a front and back registration job (NO in S1101), the control unit 251 makes the image forming apparatus 101 and the adjustment unit 400 wait at the home position (HP) (S1107). At this time, in order to guide the sheet P to the discharge path 432 in the adjustment unit 400, the control unit 251 makes the flapper 422 wait with the flapper facing downward (discharge path position) (S1107). The image forming apparatus 101 forms patch images 820 as adjustment charts on both sides of the sheet P (S1108). The adjustment unit 400 receives the sheet P on which the patch images 820 have been formed (S1109).

[0042] The sheet P conveyed to the adjustment unit 400 is conveyed to the front and back registration section 500 (S1110), as shown in Fig. 10(a), where the print position deviation of the patch image 820 on the sheet P and the shape of the sheet P are measured. At this time, the back side reading section 600-1 starts reading after a predetermined time set by the timer 310 after the leading edge of the sheet P passes the sheet sensor 522 (Fig. 5) (S1111). Also, the front side reading section 600-2 starts reading after a predetermined time set by the timer 310 after the leading edge of the sheet P passes the sheet sensor 523 (Fig. 5) (S1111). The image processing section 260 calculates a first geometric adjustment value and a second geometric adjustment value from the front side measurement pattern image 822 and the back side measurement pattern image 823. The image processing unit 260 stores the first geometric adjustment values ​​and the second geometric adjustment values ​​in the sheet library 900 of the image forming apparatus 101 through the communication unit 250 (S1112). This completes the print position adjustment for front-to-back registration.

[0043] As shown in FIG. 10(b), the sheet P is conveyed by the flapper 422 to the discharge path 432 and discharged to the discharge tray 431 (S1113). The control unit 251 determines whether the sheet P is the last sheet (S1106), and if the sheet P is the last sheet (YES in S1106), the control unit 251 ends the control operation. The control unit 251 determines whether the sheet P is the last sheet (S1106). If the sheet P is not the last sheet (NO in S1106), the control unit 251 returns the process to S1101. If the sheet P is the last sheet (YES in S1106), the control unit 251 ends the control operation.

[0044] In this embodiment, it is determined whether each sheet in a job is a print job or a front-to-back registration job. However, it may be determined for each job whether the job is a print job (user job) or a front-to-back registration job (job dedicated to adjustment).

[0045] (Explanation of thermal expansion of the back side reading section) FIG. 11 is an explanatory diagram of thermal expansion of the back surface reading unit 600-1. FIG. 11(a) is a plan view of the back surface reading unit 600-1 before thermal expansion. The image sensor 610 is positioned at a position A (first position) in the main scanning direction with respect to the sensor holding member 601-1, at one end of the image sensor 610 in the longitudinal direction (main scanning direction) on the side far from the center position C of the housing 605. The sensor holding member 601-1 is positioned at a position D (third position) in the main scanning direction with respect to the housing 605. The image sensor 611 is positioned at a position B (second position) in the main scanning direction with respect to the sensor holding member 601-2, at one end of the image sensor 610 in the longitudinal direction (main scanning direction) on the side far from the center position C of the housing 605. The position B is on the opposite side of the position A with respect to the center position C of the housing 605. The sensor holding member 601-2 is positioned at a position E (fourth position) in the main scanning direction with respect to the housing 605. The reading width L in the main scanning direction of the image sensors 610 and 611 is set to the distance between positioning positions A and B. The image sensors 610 and 611 are shorter than the reading width L. The image width L3 is set to the distance between the left register mark RM1 and the right register mark RM2.

[0046] The image sensor 610 is a line image sensor having a plurality of light receiving elements (pixels) arranged in the main scanning direction. Before the thermal expansion of the image sensor 610, the light receiving element 610-1 of the image sensor 610 reads the register mark RM1. The distance from the positioning position A of the image sensor 610 to the light receiving element 610-1 that reads the register mark RM1 is a distance L1. The image sensor 611 is a line image sensor having a plurality of light receiving elements (pixels) arranged in the main scanning direction. Before the thermal expansion of the image sensor 611, the light receiving element 611-1 of the image sensor 611 reads the register mark RM2. The distance from the positioning position B of the image sensor 611 to the light receiving element 611-1 that reads the register mark RM2 is a distance L2. The image width L3 is expressed by the following formula. L3=L-L2-L1

[0047] FIG. 11(b) is a plan view of the back side reading unit 600-1 after thermal expansion. As shown in FIG. 11(b), when the image sensor 610 thermally expands, the light receiving element that reads the register mark RM1 moves from the light receiving element 610-1 to the light receiving element 610-2. The shift amount (movement amount) ΔL1 of the light receiving element that reads the register mark RM1 is the distance between the light receiving element 610-1 and the light receiving element 610-2. When the image sensor 611 thermally expands, the light receiving element that reads the register mark RM2 moves from the light receiving element 611-1 to the light receiving element 611-2. The shift amount (movement amount) ΔL2 of the light receiving element that reads the register mark RM2 is the distance between the light receiving element 611-1 and the light receiving element 611-2. The deviations ΔL1 and ΔL2 are expressed by the following equations using the thermal expansion coefficients S and the temperature rise ΔT of the image sensors 610 and 611, respectively. ΔL1=L1×S×ΔT ΔL2=L2×S×ΔT

[0048] Even if the image sensors 610 and 611 thermally expand, the positioning position A of the image sensor 610 and the positioning position B of the image sensor 611 are not shifted. In other words, the reading width L is not changed. In this case, the shift amount ΔL3 of the image width L3 when the image sensors 610 and 611 thermally expand is expressed by the following formula. ΔL3=-ΔL2-ΔL1

[0049] (1st reference example) A first reference example will be described with reference to FIG. 12. FIG. 12 is an explanatory diagram of thermal expansion of an image sensor 710 of the first reference example. In the first reference example, one image sensor 710 capable of covering an image width L3 is used instead of the image sensors 610 and 611 of this embodiment. FIG. 12(a) is a plan view of the image sensor 710 before thermal expansion. The image sensor 710 is positioned at a positioning position A in the main scanning direction with respect to the sensor holding member 701. The image sensor 710 is composed of a plurality of light receiving elements (pixels). In a state before the thermal expansion of the image sensor 710, the light receiving element 710-1 of the image sensor 710 reads the register mark RM1, and the light receiving element 710-2 reads the register mark RM2. The distance from the positioning position A of the image sensor 710 to the light receiving element 710-1 that reads the register mark RM1 is the distance L1. The distance from the positioning position A of the image sensor 710 to the light receiving element 710-2 that reads the register mark RM2 is the distance L4. The image width L3 is expressed by the following formula: L3=L4-L1

[0050] Fig. 12(b) is a plan view of the image sensor 710 after thermal expansion. As shown in Fig. 12(b), when the image sensor 710 thermally expands, the light receiving element that reads the register mark RM1 moves from the light receiving element 710-1 to the light receiving element 710-3. The shift amount (movement amount) ΔL1 of the light receiving element that reads the register mark RM1 is the distance between the light receiving element 710-1 and the light receiving element 710-3. The light receiving element that reads the register mark RM2 moves from the light receiving element 710-2 to the light receiving element 710-4. The shift amount (movement amount) ΔL4 of the light receiving element that reads the register mark RM2 is the distance between the light receiving element 710-2 and the light receiving element 710-4.

[0051] It is assumed that the positioning position A of the image sensor 710 does not shift even if the image sensor 710 thermally expands. In this case, the amount of shift ΔL3 of the image width L3 when the image sensor 710 thermally expands is expressed by the following formula. ΔL3=ΔL4-ΔL1 The amount of deviation ΔL4 is expressed by the following formula. ΔL4=L4×S×ΔT

[0052] Here, the deviation amount ΔL3=-ΔL2-ΔL1 of the image width L3 in this embodiment is compared with the deviation amount ΔL3=ΔL4-ΔL1 of the image width L3 in the first reference example. The distance L2 in this embodiment is much smaller than the distance L4 in the first reference example. Therefore, the deviation amount ΔL2 in this embodiment is much smaller than the deviation amount ΔL4 in the first reference example. Therefore, the deviation amount ΔL3 of the image width L3 in this embodiment is smaller than that in the first reference example. This is because the distance L4 from the positioning position A of the image sensor 710 in the first reference example to the right register mark RM2 is large, so the deviation amount ΔL3 of the image width L3 of the image sensor 710 in the first reference example is large.

[0053] (2nd reference example) A second reference example will be described with reference to FIG. 13. FIG. 13 is an explanatory diagram of thermal expansion of image sensors 810 and 811 of the second reference example. In the second reference example, a plurality of image sensors 810 and 811 arranged in a staggered pattern are used instead of the image sensors 610 and 611 of this embodiment. FIG. 13(a) is a plan view of the image sensors 810 and 811 before thermal expansion. One end of the image sensor 810 in the longitudinal direction (main scanning direction) on the side farther from the central position C is positioned at position A in the main scanning direction with respect to the sensor holding member 801-1. One end of the image sensor 811 in the longitudinal direction (main scanning direction) on the side closer to the central position C is positioned at position F in the main scanning direction with respect to the sensor holding member 801-2.

[0054] The distance between the end position G of the reading width of the image sensor 811 opposite the positioning position F is set as distance L6. The reading width L in the main scanning direction of the image sensors 810 and 811 is set to the distance between the positioning position A and the end position G of the reading width of the image sensor 811. The image width L3 is set to the distance between the left register mark RM1 and the right register mark RM2.

[0055] The image sensor 810 is made up of a plurality of light receiving elements (pixels). Before the thermal expansion of the image sensor 810, the light receiving element 810-1 of the image sensor 810 reads the register mark RM1. The distance from the positioning position A of the image sensor 810 to the light receiving element 810-1 that reads the register mark RM1 is the distance L1. The image sensor 811 is made up of a plurality of light receiving elements (pixels). Before the thermal expansion of the image sensor 811, the light receiving element 811-1 of the image sensor 811 reads the register mark RM2. The distance from the positioning position F of the image sensor 811 to the light receiving element 811-1 that reads the register mark RM2 is the distance L5. The image width L3 is expressed by the following formula. L3=L-L1-(L6-L5)

[0056] Fig. 13(b) is a plan view of the image sensors 810 and 811 after thermal expansion. As shown in Fig. 13(b), when the image sensor 810 thermally expands, the light receiving element that reads the register mark RM1 moves from the light receiving element 810-1 to the light receiving element 810-2. The shift amount (movement amount) ΔL1 of the light receiving element that reads the register mark RM1 is the distance between the light receiving element 810-1 and the light receiving element 810-2. When the image sensor 811 thermally expands, the light receiving element that reads the register mark RM2 moves from the light receiving element 811-1 to the light receiving element 811-2. The shift amount (movement amount) ΔL5 of the light receiving element that reads the register mark RM2 is the distance between the light receiving element 811-1 and the light receiving element 811-2.

[0057] Even if the image sensors 810 and 811 thermally expand, the positioning position A of the image sensor 810 and the positioning position F of the image sensor 811 are not shifted. The reading width L in the main scanning direction of the image sensors 810 and 811 changes. The shift amount ΔL3 of the image width L3 when the image sensors 810 and 811 thermally expand is expressed by the following formula. ΔL3=ΔL5+ΔL6-ΔL1 The deviation amounts ΔL5 and ΔL6 are respectively expressed by the following equations. ΔL5=L5×S×ΔT ΔL6=L6×S×ΔT

[0058] Here, the deviation amount ΔL3=-ΔL2-ΔL1 of the image width L3 in this embodiment is compared with the deviation amount ΔL3=ΔL5+ΔL6-ΔL1 of the image width L3 in the second reference example. The distance L2 in this embodiment is much smaller than the distances L5 and L6 in the second reference example. Therefore, the deviation amount ΔL2 in this embodiment is much smaller than the deviation amounts ΔL5 and ΔL6 in the second reference example. Therefore, the deviation amount ΔL3 of the image width L3 in this embodiment is smaller than that in the second reference example. This is because the distance L5 from the positioning position F of the image sensor 811 to the right register mark RM2 in the second reference example is large, and the deviation amount ΔL3 of the image width L3 in the second reference example is large due to the fluctuation of the reading width L in the second reference example due to thermal expansion.

[0059] The front and back registration unit 500 of this embodiment is configured to automatically perform front and back registration in-line. Positioning positions A and B of the image sensors 610 and 611 that detect the image width L3 are located outside the central positions 610C and 611C of the image sensors 610 and 611 with respect to the central position C of the housing 605 in the main scanning direction. This makes it possible to reduce the influence of reading errors caused by thermal expansion of the image sensors 610 and 611. According to this embodiment, it is possible to reduce deviation in the absolute magnification of the image, and a product on which front and back registration has been performed with high accuracy can be automatically provided to the user.

[0060] According to this embodiment, the positioning positions A and B of the multiple image sensors 610 and 611 are disposed on the outer side opposite the central position C of the housing 605 with respect to the central positions 610C and 611C of the image sensors 610 and 611 in the main scanning direction. This makes it possible to employ a contact image sensor (CIS), which is less expensive than a CCD, while reducing the effect of reading errors due to thermal expansion. In other words, it is possible to reduce costs while suppressing image reading errors.

[0061] According to this embodiment, it is possible to reduce erroneous detection caused by thermal expansion of the image sensors 610 and 611.

[0062] In this embodiment, the image forming apparatus 101 is configured to be detachable from the adjustment unit 400. However, the image forming apparatus 101 may be provided integrally with the adjustment unit 400. The combination of the image forming apparatus 101 and the adjustment unit 400 may also be referred to as the image forming apparatus. [Explanation of symbols]

[0063] 500 ···Front and back registration section 602...Glass 605···Housing 610, 611...Image sensor 610C, 611C...center position P···Sheet A: First positioning position B: Second positioning position C...center position

Claims

1. A light-transmitting member; a first reading member having a plurality of light receiving elements arranged in a main scanning direction and reading an image on a sheet through the light transmitting member; a second reading member that is arranged offset from the first reading member in a sub-scanning direction perpendicular to the main scanning direction and that is arranged to overlap a portion of the first reading member when viewed from the sub-scanning direction, the second reading member having a plurality of light receiving elements aligned in the main scanning direction, and that reads an image on the sheet through the light transmitting member; a housing that holds the first reading member and the second reading member; Equipped with the first reading member and the second reading member have an elongated shape in the main scanning direction, the first reading member and the second reading member are disposed such that, in the main scanning direction, a center position of the first reading member is located on one side of a center position of the housing, and a center position of the second reading member is located on the other side of the center position of the housing; an end portion of the first reading member in the main scanning direction that is located on one side with respect to a center position of the housing is positioned at a first position with respect to the housing, and an end portion of the first reading member in the main scanning direction that is located on the other side with respect to the center position of the housing is not positioned with respect to the housing, an end portion of the second reading member in the main scanning direction that is located on the other side with respect to a center position of the housing is positioned at a second position with respect to the housing, and an end portion of the second reading member in the main scanning direction that is located on the one side with respect to a center position of the housing is not positioned with respect to the housing, the first positioning position is located outside a center position of the first reading member with respect to a center position of the housing in the main scanning direction; an image reading device, characterized in that the second positioning position is located outside a central position of the second reading member with respect to the central position of the housing in the main scanning direction;

2. the first reading member reads the sheet between the first positioning position and the central position of the housing in the main scanning direction; 2. The image reading device according to claim 1, wherein the second reading member reads the sheet between the second positioning position and the central position of the housing in the main scanning direction.

3. a first holding member that holds the first reading member; a second holding member that holds the second reading member; Further comprising: the first reading member is positioned at the first position relative to the first holding member; the second reading member is positioned at the second position relative to the second holding member, the first holding member is positioned at a third position relative to the housing in the main scanning direction; the second holding member is positioned at a fourth position relative to the housing in the main scanning direction, the third positioning position is located outside the central position of the first reading member with respect to the central position of the housing in the main scanning direction; 3. The image reading device according to claim 1, wherein the fourth positioning position is located outside the central position of the second reading member with respect to the central position of the housing in the main scanning direction.

4. the first reading member is provided with a first protrusion, The first holding member is provided with a first recess, the first protrusion is fitted into the first recess, whereby the first reading member is positioned at the first positioning position with respect to the first holding member; the second reading member is provided with a second protrusion, the second holding member is provided with a second recess; 4. The image reading device according to claim 3, wherein the second reading member is positioned at the second position relative to the second holding member by fitting the second convex portion into the second concave portion.

5. 5. The image reading device according to claim 1, wherein the first reading member and the second reading member are each a line image sensor in which the plurality of light receiving elements are arranged in the main scanning direction.

6. an image forming unit that forms an image on a sheet; The image reading device according to claim 1 , which reads the sheet on which the image is formed by the image forming unit; An image forming apparatus comprising:

Images