Image forming apparatus

Abstract

The invention relates to an image forming apparatus. The image forming apparatus includes an apparatus main body, an opening / closing unit, an image forming unit, an inverting unit configured to invert a sheet, a detecting unit configured to detect a position of the sheet in a sheet width direction orthogonal to a sheet conveying direction, and a control unit configured to control the image forming unit based on a detection result of the detection unit. A conveyance path is provided in the opening / closing unit through which the sheet reversed by the reversing unit is conveyed toward the image forming unit. The detection unit is disposed on the transfer path.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus for forming an image on a sheet. Background Art

[0002] JP 2009-51579A describes that an openable and closable duplex unit is provided on the right side surface portion of an image forming apparatus, and when a user performs jam clearing, a sheet conveying path is opened by opening the duplex unit.

[0003] In the configuration of the above document, the position of the sheet is shifted in the sheet width direction when the sheet is conveyed by the duplex unit as an openable and closable unit, and thus the image position accuracy of the image formed on the sheet may deteriorate. Summary of the invention

[0004] According to one aspect of the present invention, an image forming device includes: a device body; an opening / closing unit, which is provided on a side surface portion of the device body and is configured to be opened and closed relative to the device body; an image forming unit, which is configured to form an image on a sheet; a reversing unit, which is configured to reverse a sheet having a first surface on which a first image is formed to form a second image on a second surface opposite to the first surface; a detection unit, which is configured to detect a position of the sheet in a sheet width direction orthogonal to a sheet conveying direction; and a control unit, which is configured to control the image forming unit based on a detection result of the detection unit, wherein a conveying path is provided in the opening / closing unit, the sheet reversed by the reversing unit is conveyed toward the image forming unit through the conveying path, and the detection unit is deployed on the conveying path.

[0005] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a schematic diagram of the image forming apparatus according to the first embodiment.

[0007] Figure 2 is a block diagram illustrating a control system according to the first embodiment.

[0008] Figure 3 is an explanatory diagram of a contact image sensor (CIS) detection unit according to the first embodiment.

[0009] Figure 4A is an explanatory diagram of the door unit according to the first embodiment.

[0010] Figure 4Bis an explanatory diagram of the door unit according to the first embodiment.

[0011] Figure 4C is an explanatory diagram of the door unit according to the first embodiment.

[0012] Figure 5A is an explanatory diagram of the door unit according to the first embodiment.

[0013] Figure 5B is an explanatory diagram of the door unit according to the first embodiment.

[0014] Figure 6 are graphs and timing charts illustrating control according to the first embodiment.

[0015] Figure 7 is a flowchart illustrating control according to the first embodiment.

[0016] Figure 8 is a schematic diagram of an image forming apparatus according to a second embodiment.

[0017] Fig. 9A is an explanatory diagram of a CIS detection unit according to the second embodiment.

[0018] Fig. 9B is an explanatory diagram of a CIS detection unit according to the second embodiment.

[0019] Fig. 9C is an explanatory diagram of a CIS detection unit according to the second embodiment.

[0020] Fig.10 are graphs and timing charts illustrating control according to the second embodiment.

[0021] Fig.11 is a flowchart illustrating control according to the second embodiment.

[0022] Fig.12 : is a diagram illustrating a change in the side end position according to the second embodiment.

[0023] Fig.13A is a diagram illustrating a change in the image writing position according to the second embodiment.

[0024] Fig. 13B : is a diagram illustrating a change in the image printing position according to the second embodiment. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments according to the present disclosure will be described with reference to the accompanying drawings.

[0026] First embodiment

[0027] Figure 1is a schematic diagram of an image forming apparatus 1 according to the first embodiment. Figure 1 The cross section of the image forming apparatus 1 when the image forming apparatus 1 is viewed from the front is illustrated. The image forming apparatus 1 forms an image on a sheet P as a recording material (recording medium). As the sheet P, various sheet materials having different sizes and materials such as paper (such as plain paper or thick paper), sheet materials subjected to surface treatment (such as coated paper), sheet materials having a special shape (such as envelopes or index paper), plastic films, and cloth can be used.

[0028] The image forming apparatus 1 is an electrophotographic color image forming apparatus. More specifically, the image forming apparatus 1 includes an intermediate transfer type / tandem type electrophotographic mechanism in which four process units PY, PM, PC, and PK are arranged along an intermediate transfer belt 21 as an intermediate transfer member. The intermediate transfer type / tandem type is excellent in adaptability to a wide variety of recording materials, productivity of the image forming apparatus 1 (the number of printed sheets per unit time), and the like.

[0029] In the following, Figure 1 The front side or viewer side (the front side of the image forming device 1) is referred to as the “front side” or the “device front side”, and Figure 1 The rear side or far side of the image forming apparatus 1 (the rear side of the image forming apparatus 1 ) is referred to as the “rear side” or the “apparatus rear side”.

[0030] Image forming device

[0031] like Figure 1 As shown in FIG. 1 , the image forming apparatus 1 includes an image forming unit 1B, a secondary transfer roller 44 serving as a transfer member, and a fixing device 50 serving as a fixing unit. The image forming unit 1B, the secondary transfer roller 44, and the fixing device 50 form an intermediate transfer type / tandem type electrophotographic mechanism.

[0032] The image forming unit 1B includes four process units PY, PM, PC and PK, an intermediate transfer belt 21, a primary transfer roller 25, a secondary transfer inner roller 22, a driving roller 23 and a tension roller 24. The process units PY, PM, PC and PK have substantially the same configuration except that the color of the toner used for development is different. That is, each of the process units PY to PK includes a photosensitive drum 11 serving as an image bearing member (photosensitive member), a charging roller 12 serving as a charging unit, an exposure device 13 serving as an exposure unit and a developing device 14 serving as a developing unit.

[0033] The intermediate transfer belt 21 is stretched around the secondary transfer inner roller 22, the driving roller 23, and the tension roller 24. The intermediate transfer belt 21 is rotated in the direction of the arrow B in the figure by the driving roller 23 which is rotationally driven by the driving source. The tension roller 24 applies an appropriate tension to the intermediate transfer belt 21. The primary transfer roller 25 is disposed on the inner peripheral side of the intermediate transfer belt 21, and forms a primary transfer portion with the photosensitive drum 11.

[0034] The secondary transfer roller 44 contacts the outer peripheral surface of the intermediate transfer belt 21 and sandwiches the intermediate transfer belt 21 together with the secondary transfer inner roller 22. As a sandwiched portion between the intermediate transfer belt 21 and the secondary transfer roller 44, a transfer portion (secondary transfer portion) for transferring the toner image to the sheet P is formed.

[0035] The fixing device 50 is an image heating device that heats the toner image on the sheet P to fix the toner image on the sheet P. The fixing device 50 includes, for example, a fixing roller (heating roller), a pressure roller that forms a nip portion (fixing nip) together with the fixing roller, and a halogen lamp used as a heating unit for heating the fixing roller. The heating unit may be, for example, a ceramic heater having a pattern of a heating resistor printed on a ceramic substrate, or may be a coil unit for heating a conductive layer in the fixing roller by electromagnetic induction. Instead of the fixing roller, an endless (tubular) film or a belt may be used as a fixing member.

[0036] The image forming apparatus 1 includes a sheet feeding unit 30 and a pre-transfer conveying unit 40. The image forming apparatus 1 also includes a registration sensor 43, a discharge conveying unit 60, discharge trays 80 and 82, and a duplex conveying unit 70.

[0037] The sheet conveying device 100 of the present embodiment includes a sheet feeding unit 30, a pre-transfer conveying unit 40, a discharge conveying unit 60, a duplex conveying unit 70, and elements involved in conveying control of the sheet P in the conveying units. The elements involved in conveying control of the sheet P include a motor as a driving source of each conveying unit, a sensor for detecting the position of the sheet P on the conveying path or the side end position of the sheet P, and the like.

[0038] The sheet feeding unit 30 is a conveying unit that feeds the sheets P one by one toward the image forming unit 1B. The image forming apparatus 1 of the present embodiment includes cassette feeding units 31 and 32 and a manual feeding unit 33 as the sheet feeding unit 30 .

[0039] The cassette feeding unit 31 includes a cassette 31b serving as a sheet loading portion (sheet container or sheet supporting portion) for storing sheets P in a stacked state and a feeding unit 31a serving as a feeding unit, and the cassette feeding unit 32 includes a cassette 32b serving as a sheet loading portion (sheet container or sheet supporting portion) for storing sheets P in a stacked state and a feeding unit 32a serving as a feeding unit. Each of the feeding units 31a and 32a includes, for example, a pickup roller provided on the upper side of the cassette 31b or 32b and a separation roller pair that separates and conveys the sheets P. The separation roller pair is a roller pair including a conveying roller that is rotationally driven in the sheet feeding direction and a retard roller to which a driving force in a direction opposite to the sheet feeding direction is input via a torque limiter. The retard roller is an example of a separation member that separates the sheets P by frictional force, and, for example, a pad-shaped elastic member (separation pad) that contacts the conveying roller may be used as the separation member.

[0040] The manual feed unit 33 includes a manual feed tray 33b (multipurpose tray) serving as a sheet loading portion (sheet supporting portion) and a feed unit 33a serving as a feed unit. The manual feed tray 33b protrudes toward the outside of the image forming apparatus 1 so that a user can set the sheet P from the outside of the image forming apparatus 1. The feed unit 33a may have the same configuration as that of the feed units 31a and 32a of the cassette feed units 31 and 32.

[0041] The cassettes 31b and 32b and the manual feed tray 33b (hereinafter, collectively referred to as a sheet loading portion) include a side adjustment plate 31c and a size detection sensor 31d, a side adjustment plate 32c and a size detection sensor 32d, and a side adjustment plate 33c and a size detection sensor 33d, respectively.

[0042] The side adjustment plates 31c, 32c and 33c are adjustment members that adjust the end position (sheet side end position) of the sheet P in the sheet width direction orthogonal to the sheet conveying direction. The side adjustment plates 31c, 32c and 33c are a pair of adjustment plates provided to be movable in the sheet width direction. The side adjustment plates 31c, 32c and 33c are moved to contact the side ends of the sheets P according to the size of the sheets P set in the sheet loading portion, and adjust the side end positions of the sheets P.

[0043] The size detection sensors 31d, 32d, and 33d are detection units for detecting the size of the sheet P set in the sheet loading portion. The size detection sensors 31d, 32d, and 33d are, for example, detection units for detecting the size of the sheet P set in the sheet loading portion. Figure 1 More specifically, as the size detection sensors 31d, 32d, and 33d, a variable resistor using a pinion of a rack and pinion mechanism that moves a pair of adjustment plates in conjunction with each other can be used.

[0044] The image forming apparatus 1 according to the present embodiment uses a center-based sheet conveying method. The center-based sheet conveying method is a method of conveying a sheet P so that the center position of the sheet P in the sheet width direction is aligned with the center position of the sheet conveying path in the sheet width direction. Among the side adjustment plates 31c, 32c, and 33c provided in the sheet loading portion, the side adjustment plate on one side and the side adjustment plate on the other side in the sheet width direction move in conjunction with each other so as to maintain a symmetrical positional relationship with respect to the center position of the sheet conveying path.

[0045] The pre-transfer conveying unit 40 is a conveying unit that conveys the sheet P fed from the sheet feeding unit 30 toward the secondary transfer portion. The pre-transfer conveying unit 40 includes a pre-registration roller pair (hereinafter, referred to as a pre-registration roller pair 41) and a registration roller pair (hereinafter, referred to as a registration roller pair 42).

[0046] The discharge transport unit 60 is a transport unit that transports the sheet P that has passed through the fixing device 50 toward the discharge tray 80 or 82 or the double-sided transport unit 70. The discharge transport unit 60 includes a transport roller pair 61 and 63, a switching guide 64, and a discharge roller pair 62. The discharge roller pair 62 is an example of a discharge unit that discharges the sheet P to the outside of the image forming apparatus 1. In the present embodiment, the reverse transport roller pair 71 described below also serves as a discharge unit. The discharge trays 80 and 82 are stacking portions on which the sheets P serving as products are stacked.

[0047] The duplex transport unit 70 is a transport unit that reverses the sheet P having the first surface on which the image (first image) is formed by the image forming unit 1B and transports (re-feeds) the sheet P toward the image forming unit 1B again when duplex printing is performed. The duplex transport unit 70 includes a reversing transport roller pair 71 and duplex transport roller pairs 72, 73, and 74 arranged along a sheet transport path. The reversing transport roller pair 71 is an example of a reversing unit that reverses the sheet P having the first surface on which the image (first image) is formed to form an image (second image) on a second surface opposite to the first surface.

[0048] A contact image sensor (CIS) detection unit 2 is disposed in the double-sided conveying unit 70. The CIS detection unit 2 is a detection unit that detects the position of the sheet P in the sheet width direction (particularly, the side end position of the sheet P). The CIS detection unit 2 is a line sensor having a configuration of a contact image sensor. The CIS detection unit 2 includes a plurality of light receiving elements arranged in the sheet width direction, a light source that emits light toward the sheet P, a transparent member (reading glass) exposed to the double-sided path CP2, and a lens array that forms an equal-magnification optical system that guides reflected light from the sheet P to the plurality of light receiving elements. The CIS detection unit 2 emits light from the light source toward the double-sided path CP2, and converts an optical image formed on the light receiving element via the reading glass and the lens array into an electrical signal.

[0049] The sheet conveying path from the cassette feed units 31 and 32 or the manual feed unit 33 via the secondary transfer portion and the fixing device 50 to the discharge roller pair 62 or the reverse conveying roller pair 71 is an image forming path CP1 in which an image is formed on the sheet P. The sheet conveying path from the reverse conveying roller pair 71 via the double-sided conveying roller pairs 72, 73, and 74 to the registration roller pair 42 is a double-sided path CP2 that branches from the image forming path and merges with the image forming path upstream of the secondary transfer portion. The reverse conveying roller pair 71 can perform a reverse operation of turning back the sheet P conveyed through the image forming path and sending the sheet P to the double-sided path CP2 and a discharge operation of discharging the sheet P conveyed through the image forming path to the discharge tray 82.

[0050] The image forming apparatus 1 of the present embodiment adopts a configuration (also referred to as a vertical conveying type or a vertical passing type) in which an image forming path CP1 extends in a substantially vertical direction through the side of the image forming unit 1B when viewed from the front side of the apparatus body. The image forming path CP1 is a path through which the sheet P is conveyed upward, and the double-sided path CP2 is a path through which the sheet P is conveyed downward. As a result, there is an advantage that the installation area of ​​the image forming apparatus 1 can be reduced compared with, for example, a configuration (referred to as a horizontal conveying type or a horizontal passing type) in which the image forming path CP1 extends in a substantially horizontal direction through below the image forming unit 1B. In addition, since the door unit 101 described below is provided on the side surface portion of the image forming apparatus 1, the user can easily perform jam clearing.

[0051] Image forming operation

[0052] The control unit 200 ( Figure 2) performs a series of operations (image forming operation and printing operation) of forming an image on a sheet P based on image information according to an execution instruction from a user. The image information is input from, for example, an external computer connected to the image forming apparatus 1 via a network. In this embodiment, as a mode of the image forming operation (printing mode), single-sided printing in which an image is formed only on one side of the sheet P and double-sided printing in which an image is formed on both sides of the sheet P can be switched.

[0053] When the image forming operation is started, the photosensitive drums 11 of the processing units PY to PK and the intermediate transfer belt 21 are rotationally driven at a predetermined circumferential speed (processing speed). The charging roller 12 uniformly charges the surface of each photosensitive drum 11. Each exposure device 13 is driven by a video signal generated based on image information, irradiates the corresponding photosensitive drum 11 with light, and forms an electrostatic latent image on the surface of the photosensitive drum 11. The exposure device 13 can be a laser scanner using a laser beam or an LED exposure device using a light emitting diode (LED) as a light source. The developing device 14 supplies a developer containing a toner to the photosensitive drum 11 to develop the electrostatic latent image into a toner image. The toner image is transferred from the photosensitive drum 11 to the intermediate transfer belt 21 by the pressing force and electrostatic bias applied to the primary transfer portion by the primary transfer roller 25.

[0054] In the processing units PY to PK, the forming process of the toner images for yellow, magenta, cyan and black is performed in parallel. In addition, the forming process is performed at the timing that the toner images of the respective colors overlap each other on the intermediate transfer belt 21. Therefore, a full-color toner image is formed on the intermediate transfer belt 21 while passing through the four primary transfer parts. The full-color toner image is conveyed to the secondary transfer part by the rotation of the intermediate transfer belt 21.

[0055] At the same time, the sheets P are fed one by one from the cassette feeding units 31 and 32 and the manual feeding unit 33. The fed sheets P are conveyed to the registration roller pair 42 via the pre-registration roller pair 41, and skew feeding correction is performed by the registration roller pair 42. Specifically, even after the leading edge of the sheet P contacts the clamping portion of the stopped registration roller pair 42, the pre-registration roller pair 41 conveys the sheet P by a predetermined distance to deflect (bend) the sheet P. As a result, skew feeding correction of the sheet P is performed so that the leading edge of the sheet P follows the clamping portion of the registration roller pair 42. The registration roller pair 42 conveys the sheet P to the secondary transfer portion according to the timing at which the toner image carried by the intermediate transfer belt 21 reaches the secondary transfer portion.

[0056] In the secondary transfer section, the toner image is secondarily transferred from the intermediate transfer belt 21 to the sheet P by the pressing force and the electrostatic bias applied to the secondary transfer section by the secondary transfer roller 44. The sheet P having passed through the secondary transfer section is subjected to an image fixing process by the fixing device 50. The fixing device 50 fixes the toner image on the sheet P by heating and pressing the toner image on the sheet P while gripping the sheet P at the fixing nip and conveying the sheet P.

[0057] The sheet P having passed through the fixing device 50 is conveyed by the discharge conveying unit 60. In the discharge conveying unit 60, the conveying path of the sheet P is switched by the switching guide 64 depending on whether the mode of the image forming operation is single-sided printing or double-sided printing.

[0058] In the case of single-sided printing, when the discharge destination is set to the discharge tray 80 at the lower part, the sheet P is guided to the discharge roller pair 62 by the switching guide 64. The discharge roller pair 62 discharges the sheet P to the discharge tray 80. In the case of single-sided printing, when the discharge destination is set to the discharge tray 82 at the upper part, the sheet P is guided to the reverse conveying roller pair 71 by the switching guide 64. The reverse conveying roller pair 71 discharges the sheet P to the discharge tray 82.

[0059] In the case of double-sided printing, the sheet P having the first surface on which the image (first image) is formed is guided by the switching guide 64 to the reversing conveying roller pair 71. The reversing conveying roller pair 71 performs a series of operations (reversing) of conveying the sheet P in the discharge direction, reversing the conveying direction before the trailing edge of the sheet P passes through the reversing conveying roller pair 71 in the discharge direction, and conveying the sheet P toward the double-sided path CP2. The sheet P reversed by the reversing conveying roller pair 71 is conveyed through the double-sided path CP2 by the double-sided conveying roller pairs 72, 73, and 74, and reaches the registration roller pair 42 again. Then, when the sheet P passes through the secondary transfer portion and the fixing nip again, an image (second image) is formed on the second surface of the sheet P opposite to the first surface. Thereafter, depending on whether the discharge destination is the lower discharge tray 80 or the upper discharge tray 82, the sheet P is guided by the switching guide 64 to the discharge roller pair 62 or the reversing conveying roller pair 71, and discharged by the discharge roller pair 62 or the reversing conveying roller pair 71.

[0060] Control System

[0061] Hereinafter, the control unit 200 of the image forming apparatus 1 will be described. The control unit 200 is a control unit that controls the operation of the image forming apparatus 1. In the present embodiment, the control unit 200 functions as a control unit that controls the image forming unit based on the detection result of the detection unit.

[0062] Figure 22 is a block diagram illustrating a control unit 200 of the image forming apparatus 1. The control unit 200 includes a central processing unit (CPU) 201, a memory 202, an operation unit 203, an image formation control unit 205, a sheet conveyance control unit 206, a sensor control unit 207, and a sheet side end position control unit 208.

[0063] The CPU 201 operates the image forming apparatus 1 by executing a predetermined control program. The memory 202 is, for example, a random access memory (RAM), a read-only memory (ROM), etc., and stores various programs and various data in a predetermined storage area. The operation unit 203 receives various types of information (size information, grammage information, surface property information, etc.) related to a sheet used by a user for printing and various types of operations performed by the user (such as an instruction to execute or interrupt printing).

[0064] The image forming control unit 205 issues instructions to the image forming unit 1B including the exposure device 13 to control the toner image forming process. The sheet transport control unit 206 issues instructions to the feed motor M1, the registration motor M2, the double-sided motor M3, etc. to control the transport of the sheet P. The feed motor M1 is one or more motors that drive the feed units 31a, 32a, and 33a. The registration motor M2 is a motor that drives the registration roller pair 42. The double-sided motor M3 is a motor that drives the double-sided transport unit 70.

[0065] The sensor control unit 207 controls various sensors such as the size detection sensors 31d, 32d, and 33d ( Figure 1 ) and the start and end of detection of the alignment sensor 43), and receive the detection results of the sensor.

[0066] The sheet side end position control unit 208 is connected to the CIS detection unit 2. The sheet side end position control unit 208 receives the detection signal of the CIS detection unit 2 and converts the detection signal into the side end position of the sheet P.

[0067] The control unit 200 may also be configured to be able to receive data from, for example, a computer connected via a network (e.g., Figure 2 The computer 204 shown in FIG. 2 receives various types of information about sheets used for image forming operation. The various types of information about sheets include, for example, the size, grammage, and brand of the sheets P.

[0068] Configuration for detecting the side end position of a sheet

[0069] Hereinafter, a configuration for detecting the side end position of the sheet P in the sheet conveying apparatus 100 according to the present embodiment and a specific configuration of the sheet conveying apparatus 100 will be described.

[0070] The sheets P as recording materials are stacked on the sheet loading portion (cassette 31b or 32b or manual feed tray 33b) in each size. In order to record an image in an appropriate range on the sheet P, it is necessary to make the control unit 200 recognize the size of the sheet P set in the sheet loading portion. In the present embodiment, the control unit 200 acquires the size of the sheet P set in each sheet loading portion based on information input by the user via the operation unit 203 or information acquired by the sensor control unit 207 from the size detection sensors 31d, 32d, and 33d.

[0071] The side ends of the sheets P stacked in each sheet loading portion are regulated by the above-mentioned side regulating plates 31c, 32c or 33c. In the state where the sheets P are stacked in each sheet loading portion, the side regulating plates 31c, 32c and 33c suppress misalignment of the sheets P in the sheet width direction and skewed feeding of the sheets P.

[0072] Due to positioning errors of the side adjustment plates 31c, 32c, and 33c when setting the sheet P, vibration of the apparatus accompanying the image forming operation, and the like, a gap is generated between the side adjustment plates 31c, 32c, and 33c and the sheet P. Due to the generated gap, there is a possibility that misalignment or skew feeding of the sheet P occurs when the sheet P is fed and conveyed.

[0073] However, the length of the conveying path of the sheet P from the sheet loading portion to the secondary transfer portion is relatively short. For example, the cassettes 31b and 32b and the image forming unit 1B are in a positional relationship of vertically overlapping each other. Figure 1 The cassettes 31b and 32b and one side of the image forming unit 1B extend in a substantially vertical direction in the horizontal direction, so the length of the conveying path from the feeding units 31a and 32a to the secondary transfer portion is relatively short. In addition, since the manual feeding unit 33 is disposed in Figure 1 The sheet P is provided on a side surface portion of one side where the image forming path CP1 is provided in the horizontal direction of the sheet P, and therefore the conveying path length from the feeding unit 33a to the secondary transfer portion is relatively short. Therefore, misalignment and skew feeding of the sheet P occurring during the period from when the sheet P is fed from the sheet loading portion to when the sheet P reaches the secondary transfer portion and transfer of the toner image to the first surface of the sheet P starts is relatively small.

[0074] On the other hand, in the case of double-sided printing, the sheet P is turned back by the reverse conveying roller pair 71 after passing through the secondary transfer portion for the first time, and is conveyed to the secondary transfer portion again via the double-sided conveying unit 70 and the registration roller pair 42. At this time, there is a possibility that misalignment or skew feeding of the sheet P occurs when the sheet P is turned back by the reverse conveying roller pair 71. Since the reverse conveying roller pair 71 clamps the sheet P alone when the sheet P is turned back, misalignment or skew feeding of the sheet P tends to occur easily compared to the case where a plurality of conveying roller pairs separated in the sheet conveying direction clamp the sheet P at the same time. In addition, misalignment or skew feeding of the sheet P may occur when the sheet P is conveyed from the reverse conveying roller pair 71 to the registration roller pair 42 via a plurality of double-sided conveying roller pairs 72, 73, and 74. Since misalignment of the conveying rollers causes misalignment or skew feeding of the sheet P, misalignment or skew feeding of the sheet P tends to occur easily when the sheet P is delivered and conveyed by a large number of conveying roller pairs.

[0075] When misalignment or skew of the sheet P occurs during the period from when the sheet P first passes through the secondary transfer portion to when the sheet P reaches the secondary transfer portion again, there is a possibility that the image position accuracy on the second surface of the sheet P decreases.

[0076] Furthermore, when misalignment or skew feeding of the sheet P occurs during a period from when the sheet P first passes through the secondary transfer portion to when the sheet P reaches the secondary transfer portion again, a difference in the margin width from the side end of the sheet P to the image occurs between the image of the first surface and the image of the second surface formed by duplex printing. In terms of the quality of a duplex-printed product, it is desirable that the difference in the margin width between the first surface and the second surface is small.

[0077] As described above, in both the first and second surfaces of the sheet P, there is a possibility that the image position accuracy is reduced due to misalignment or skew feeding of the sheet P, but it is particularly necessary to improve the image position accuracy of the second surface compared with the image position accuracy of the first surface.

[0078] In the present embodiment, the CIS detection unit 2 is used to improve the image position accuracy on the second surface of the sheet P. As described above, the CIS detection unit 2 is disposed on the conveying path (duplex path CP2) of the duplex conveying unit 70. In the present embodiment, in the sheet conveying direction (arrow C) of the duplex conveying unit 70, the CIS detection unit 2 is disposed between the most upstream duplex conveying roller pair 72 and the second upstream duplex conveying roller pair 73 ( Figure 1 ).

[0079] like Figure 3As shown in , the CIS detection unit 2 is disposed at a position biased to one side in the sheet width direction relative to the center position Wc of the conveying path (double-sided path CP2) in the sheet width direction orthogonal to the sheet conveying direction (arrow C). This is because it is sufficient to detect the position of the sheet P in the sheet width direction if at least one side end position of the sheet P is detected. In the present embodiment, the CIS detection unit 2 is disposed on the rear side of the image forming apparatus 1. In this case, the control unit 200 can control the position of the image to be formed on the second surface of the sheet P with reference to the left side end PL when the sheet P is viewed in the sheet conveying direction (arrow C).

[0080] The CIS detection unit 2 is disposed so as to be able to detect the side end positions of a sheet P of a first size having a small width and a sheet P of a second size having a width greater than the first size among sheet sizes sufficient for image formation by the image forming apparatus 1. The first size and the second size may be a size having the smallest width (minimum size) and a size having the largest width (maximum size), respectively, among sheet sizes sufficient for image formation by the image forming apparatus 1.

[0081] The control unit 200 calculates the deviation amount between the nominal position (designed target position) of the side end PL of the sheet P and the position of the side end PL actually detected based on the detection result of the CIS detection unit 2. In the present embodiment, the image writing position when the exposure device 13 exposes the photosensitive drum 11 to form an image on the second surface of the sheet P is corrected based on the deviation amount. That is, the control unit 200 corrects the position of the image to be formed on the second surface of the sheet P based on the detection result of the CIS detection unit 2. As a result, the image position accuracy on the second surface of the sheet P can be improved.

[0082] Door unit

[0083] Next, the door unit 101 (right door) serving as an opening / closing unit provided on a side surface portion of the apparatus body 1A will be described. Figure 4A 1 is a cross-sectional view illustrating a portion of the image forming apparatus 1 in a state where the door unit 101 is closed. Figure 4B 1 is a cross-sectional view illustrating a portion of the image forming apparatus 1 in a state where the door unit 101 is opened. Figure 4C 1 is a cross-sectional view illustrating a portion of the image forming apparatus 1 in a state where the door unit 101 is open and the inner door 102 is open. FIG. 4A to FIG. 4C The diagram shows Figure 1 A cross section of the image forming apparatus 1 when viewed from the front side to the rear side of the image forming apparatus 1 as shown in FIG.

[0084] like FIG. 4A to FIG. 4CAs shown in , the image forming apparatus 1 includes an apparatus body 1A (a main body frame or a main housing) and a door unit 101, which is an opening / closing unit that is openable / closable relative to the apparatus body 1A. The above-mentioned image forming unit 1B and the fixing device 50 are mainly disposed in the apparatus body 1A. The double-sided conveying unit 70 is mainly disposed in the door unit 101. The pre-transfer conveying unit 40 and the discharge conveying unit 60 are separately disposed in the apparatus body 1A and the door unit 101 per element.

[0085] The door unit 101 can be moved to the closed position ( Figure 4A ) and open position ( Figure 4B and Figure 4C ). In the present embodiment, the rotation center 111 is provided at the lower end portion of the door unit 101 with reference to the posture when the door unit 101 is in the closed position. The rotation axis of the door unit 101 extends in the sheet width direction.

[0086] like Figure 4C As shown in FIG. 1 , the door unit 101 includes an outer door 101A rotatably supported by the device body 1A, and an inner door 102 rotatably supported by the outer door 101A. In other words, the opening / closing unit includes a first frame supported by the device body, a second frame supported by the first unit so as to be openable and closable, and a pair of conveying rollers that convey the sheet via the conveying path. In a state where the door unit 101 is in the open position, the inner door 102 can be moved relative to the outer door 101A to an inner door closed position ( Figure 4A and Figure 4B ) and inner door open position ( Figure 4C ). The rotation axis of the inner door 102 extends in the sheet width direction. That is, the rotation axis of the inner door 102 is parallel to the rotation axis of the door unit 101.

[0087] When the door unit 101 is in the closed position, the outer door 101A forms a right side surface portion (an outer surface on the right side when the image forming apparatus 1 is viewed from the front) of the image forming apparatus 1. When the door unit 101 is in the closed position, the inner door 102 is accommodated in a space between the apparatus body 1A and the outer door 101A.

[0088] The outer door 101A includes a conveying guide 123 that guides the second surface of the sheet P conveyed through the double-sided path CP2. The inner door 102 includes a conveying guide 121 that guides the first surface of the sheet P conveyed through the double-sided path CP2. Figure 4A ) or in a state where the door unit 101 is in the open position and the inner door 102 is in the inner door closed position ( Figure 4B), at least a portion of the double-sided path CP2 is formed between the conveying guides 121 and 123.

[0089] Hereinafter, a portion of the double-sided path CP2 provided in the door unit 101 is referred to as “in-door double-sided path CP2a.” The entire double-sided path CP2 may be the in-door double-sided path CP2a.

[0090] In a state where the door unit 101 is in the open position and the inner door 102 is in the inner door open position ( Figure 4C ), the conveying guide 121 is separated from the conveying guide 123, and the in-door double-sided path CP2a is opened.

[0091] One roller 72a, 73a or 74a of each double-sided conveying roller pair 72, 73 or 74 is disposed on the outer door 101A ( Figure 4C The other roller 72b, 73b or 74b of each double-sided conveying roller pair 72, 73 or 74 is disposed on the inner door 102. Figure 4A and Figure 4B As shown in FIG. 1 , in a state where the inner door 102 is not opened, one roller 72a, 73a or 74a of the double-sided conveying roller pair 72, 73 or 74 contacts the other roller 72b, 73b or 74b, so that a clamping portion of each roller pair is formed. Figure 4C In the state in which the inner door 102 is open as shown in FIG, one roller 72a, 73a or 74a of the double-sided conveying roller pair 72, 73 or 74 is separated from the other roller 72b, 73b or 74b so that the nip portion of each roller pair is released.

[0092] An urging member 125 (such as a spring member) for pressurizing the nip portion of the double-sided conveying roller pair 72, 73, or 74 is disposed in at least one of the outer door 101A or the inner door 102. Figure 4A ).exist Figure 4A , a pushing member 125 corresponding to one double-sided conveying roller pair 73 is illustrated, but a pushing member 125 corresponding to the other double-sided conveying roller pair 73 is also provided. The pushing member 125 pushes the roller provided on one of the outer door 101A and the inner door 102 toward the roller provided on the other of the outer door 101A and the inner door 102 to pressurize the clamping portion of the roller pair.

[0093] The inner door 102 of the present embodiment further includes a conveying guide for guiding the sheet P conveyed through the image forming path CP1, one roller 42a of the registration roller pair 42, the secondary transfer roller 44, and one roller 61a and 63a of the conveying roller pair 61 and 63 ( Figure 4B). The other roller 42b of the registration roller pair 42 and the other rollers 61b and 63b of the conveying roller pair 61 and 63 are supported by the device body 1A. A pushing member 125 for pressurizing the clamping portion of each roller pair (42, 61 or 63) is provided on at least one of the inner door 102 or the device body 1A. The pushing member 125 pushes the roller provided on one of the inner door 102 and the device body 1A toward the roller provided on the other of the inner door 102 and the device body 1A to pressurize the clamping portion of the roller pair.

[0094] In the state where the door unit 101 is closed, the roller (first roller) supported by the inner door 102 is pressed against the roller (second roller) supported by the device body 1A due to the urging force of the urging member 125. In this way, the door unit 101 receives a force in the direction to open the door unit from the device body 1A.

[0095] When the door unit 101 is in the closed position ( Figure 4A ), the conveying guide of the inner door 102 faces the conveying guide of the apparatus body 1A to form the image forming path CP1. In the state where the door unit 101 is in the closed position ( Figure 4A ), the secondary transfer roller 44 contacts the intermediate transfer belt 21 to form a secondary transfer portion. In addition, when the door unit 101 is in the closed position ( Figure 4A ), the registration roller pair 42 and one roller 42a, 61a and 63a and the other roller 42b, 61b and 63b of the conveying roller pairs 61 and 63 contact each other so that a clamping portion of each roller pair is formed.

[0096] When the door unit 101 is in the open position ( Figure 4B and Figure 4C ), the conveying guide of the inner door 102 is separated from the conveying guide of the apparatus body 1A, and the image forming path CP1 is opened. In the state where the door unit 101 is in the open position ( Figure 4B and Figure 4C ), the secondary transfer roller 44 is separated from the intermediate transfer belt 21, and the secondary transfer portion is released. In the state where the door unit 101 is in the open position ( Figure 4B and Figure 4C ), the clamping portions of the registration roller pair 42 and the conveying roller pair 61 and 63 are released.

[0097] When a conveyance abnormality (paper jam) of the sheet P occurs during the execution of the image forming operation and the image forming operation stops, the user can perform an operation (jam clearing) of removing the sheet P staying in the image forming apparatus 1 by opening the door unit 101. Specifically, Figure 4AThe diagram shows a state where a paper jam occurs in a state where the sheet P1 is nipped by the secondary transfer portion and the registration roller pair 42 and the sheet P2 is nipped by the double-sided conveying roller pair 73. The user can Figure 4B As shown in FIG. 1 , the door unit 101 is moved from the closed position to the open position to release the gripping portion of the secondary transfer portion and the registration roller pair 42 and remove the sheet P1. Figure 4C As shown in , the user can also move the inner door 102 from the inner door closed position to the inner door open position to release the nipped portions of the double-sided conveying roller pairs 72 , 73 , and 74 and remove the sheet P2 .

[0098] In the present embodiment, when the door unit 101 moves from the closed position to the open position, the clamping parts and the secondary transfer parts of the plurality of roller pairs deployed on the image forming path CP1 are uniformly released. In addition, in the present embodiment, when the inner door 102 moves from the inner door closed position to the inner door open position, the clamping parts of the plurality of roller pairs deployed on the inner door double-sided path CP2a are uniformly released. Therefore, the workability of the jam clearing by the user can be improved.

[0099] The image forming apparatus 1 includes a locking mechanism for locking the door unit 101 to a closed position. Figure 4B As shown in , a hook 113 is provided on the door unit 101, and a fixed shaft 115 is provided on the device body 1A. The hook 113 is rotatable around a hook shaft 114 extending substantially parallel to the sheet width direction. The hook 113 also has an engagement surface 116 that engages with the fixed shaft 115. The fixed shaft 115 is fixed to a frame member (sheet metal, etc.) of the device body 1A. A set of hooks 113 and fixed shafts 115 are disposed on each of the front and rear sides of the image forming device 1 (see also Figure 5A ). The two hooks 113 are connected to each other and rotate jointly with each other.

[0100] The hook 113 is connected to a handle portion provided on the outer door 101A via a link mechanism. When the user operates the handle portion, the hook 113 rotates around the hook shaft 114 so that the engagement between the hook 113 and the fixed shaft 115 is released.

[0101] like Figure 4A As shown in FIG. 1 , when the door unit 101 is in the closed position, the hook 113 serving as the engaging portion is engaged with the fixed shaft 115 serving as the engaged portion. In this case, the engaging surface 116 of the hook 113 contacts the fixed shaft 115, thereby restricting the movement of the door unit 101 from the closed position to the open position. That is, the door unit 101 is locked to the closed position.

[0102] As described above, the pushing member 125 for pressurizing the clamping portion of each roller pair deployed on the double-sided path CP2a inside the door is deployed on at least one of the outer door 101A or the inner door 102. The force of the rollers pressing each other at the clamping portion of each roller pair is transmitted to the frame of the outer door 101A via the bearing portion of the roller on the outer door 101A. Therefore, when the door unit 101 is in the closed position, the outer door 101A continuously receives the force in the right direction in the figure (the force for moving the door unit 101 from the closed position to the open position). When the engaging surface 116 contacts the fixed shaft 115, the hook 113 and the fixed shaft 115 overcome the force received by the door unit 101 due to the pushing force of the pushing member 125 for pressurizing the clamping portion of the roller pair to keep the door unit 101 in the closed position.

[0103] The fixed shaft 115 serving as the engaging portion may be disposed on the outer door 101A, and the rotatable hook 113 serving as the engaged portion may be disposed on the inner door 102 .

[0104] Relationship between sheet misalignment and door unit

[0105] As described above, the image forming apparatus 1 of the present embodiment includes the door unit 101 provided on the side surface portion of the apparatus body 1A so as to be openable and closable. With such a configuration, during the period from when the sheet P is reversed by the reverse conveying roller pair 71 in duplex printing to when the sheet P reaches the secondary transfer portion for the second time, misalignment or skew feeding (collectively referred to as misalignment, etc.) of the sheet P in the sheet width direction is likely to occur.

[0106] First, since the door unit 101 is openable and closable relative to the apparatus body 1A, positional misalignment of the door unit 101 may occur due to recoil of a support mechanism (hinge, etc.) that enables movement of the door unit 101. For this reason, when the sheet P is delivered and conveyed between the sheet conveying path of the apparatus body 1A and the sheet conveying path in the door unit 101, misalignment of the sheet P or the like may occur.

[0107] Furthermore, as a reference example, a horizontal transfer type image forming apparatus in which a part of a duplex transfer unit in the image forming apparatus is configured as a pull-out unit that can be pulled out (slidable) to the front side of the apparatus will be described with the difference from the door unit 101. In the reference example, the pull-out unit is pulled out and inserted in the sheet width direction, whereas the door unit 101 of the present embodiment is opened and closed in the direction in which the sheet transfer path inside the image forming apparatus 1 is opened (a direction intersecting the sheet width direction and the sheet transfer direction). That is, in the present embodiment, the opening / closing operation of the door unit 101 is performed so as to pressurize and separate the rollers of the transfer roller pair disposed on the sheet transfer path. Here, the opening / closing operation of the door unit 101 includes the opening / closing of the inner door 102 in a state in which the entire door unit 101 is opened.

[0108] For this reason, compared with the pull-out unit of the reference example, destruction of the roller pressure balance of the conveying roller pair, misalignment of the busbar of the conveying roller pair, front-to-back difference in the guide gap, etc. tend to occur easily with the opening and closing of the door unit 101. The destruction of the roller pressure balance means that the clamping pressure on the sheet at the clamping portion of the roller pair becomes uneven between one side and the other side in the sheet width direction. The busbar misalignment of the conveying roller pair means that the parallelism between the rotation axis of one roller in the conveying roller pair and the rotation axis of the other roller becomes low (misaligned) due to the backlash of the bearing, etc. The front-to-back difference in the guide gap means that the gap width between the conveying guides that face each other in the sheet width direction (front-to-back direction of the device) and form the sheet conveying path is different between one side and the other side in the sheet width direction.

[0109] In the present embodiment, a part of the image forming path CP1 and the double-sided path CP2 can be opened by the opening / closing operation of the door unit 101. Therefore, compared with the pull-out unit of the reference example that can open only a part of the double-sided path, the opening / closing frequency of the door unit 101 becomes high, and each of the above changes associated with the opening / closing of the door unit 101 is likely to be accumulated.

[0110] Due to these factors, in the configuration including the gate unit 101, misalignment or skew feeding of the sheet P in the sheet width direction may occur during the period from when the sheet P is reversed by the reversing conveying roller pair 71 to when the sheet P reaches the secondary transfer portion for the second time in duplex printing.

[0111] In order to improve the accuracy of the image position on the second surface of the sheet P, it is conceivable to arrange the detection unit for detecting the side end position of the sheet P somewhere in the conveying path through which the sheet P reaches the secondary transfer portion for the second time, and correct the image writing position on the second surface based on the detection result. For example, the vicinity of the reverse conveying roller pair 71, the in-door double-sided path CP2a, and the vicinity of the registration roller pair 42 can be considered as the arrangement position of the detection unit, but in the present embodiment, the CIS detection unit 2 used as the detection unit is deployed on the in-door double-sided path CP2a. The reason is as follows.

[0112] First, in the case where the detection unit is disposed near the reverse conveying roller pair 71, the conveying path length of the sheet P from the detection unit via the double-sided path CP2 to reach the secondary transfer portion for the second time becomes longer. Therefore, the error between the side end position detected by the detection unit and the actual side end position when the sheet P reaches the secondary transfer portion for the second time tends to be large. In addition, since the reverse conveying roller pair 71 clamps the sheet P alone during the switchback conveyance, the posture of the sheet P is difficult to stabilize, which is disadvantageous in terms of the detection accuracy of the side end position.

[0113] Furthermore, in the case where the detection unit is disposed near the registration roller pair 42, when the image writing position is to be changed using the detection result of the detection unit, the productivity of the image forming apparatus 1 deteriorates. That is, since the detection unit is close to the secondary transfer portion, when exposure is performed at the image writing position corrected based on the detection result of the detection unit, the start of exposure is delayed until the sheet P reaches the detection unit.

[0114] On the other hand, since the CIS detection unit 2 used as the detection unit is disposed on the in-door double-sided path CP2a as in the present embodiment, the detection accuracy of the side end position can be enhanced compared with the case where the detection unit is disposed in the vicinity of the reverse conveying roller pair 71. In addition, by ensuring the conveying path length from the detection unit to the secondary transfer portion, the degradation of the productivity of the image forming apparatus 1 can be avoided.

[0115] Positioning configuration of CIS detection unit

[0116] The positioning configuration of the CIS detection unit 2 will be described. The CIS detection unit 2 is disposed on one of the conveying guides 121 and 123 facing each other to form the double-sided path CP2. In the present embodiment, the CIS detection unit 2 is disposed on the conveying guide 123 of the outer door 101A.

[0117] In the present embodiment, the CIS detection unit 2 is disposed in the door unit 101. That is, the CIS detection unit 2 is disposed on the door inner double-sided path CP2a in the door unit 101 as an openable / closable opening / closing unit. For this reason, when the position of the CIS detection unit 2 is displaced due to the opening / closing of the door unit 101, an error occurs in the correction of the image position using the CIS detection unit 2, and the accuracy of the corrected image position deteriorates.

[0118] In the door unit 101, a plurality of conveying roller pairs (double-sided conveying roller pairs 72, 73, and 74) are arranged along the inner-door double-sided path CP2a. When misalignment of the rollers occurs due to the openable and closable configuration of the door unit 101, misalignment and skewed feeding of the sheet P that occurs when the sheet P is conveyed through the inner-door double-sided path CP2a tend to increase. The misalignment of the rollers caused by the openable and closable configuration of the door unit 101 includes, for example, a recoil of a support portion (rotation center 111) that rotatably supports the outer door 101A. In addition, since the door unit 101 is repeatedly opened and closed, the rotation center 111 and the locking mechanism (hook 113 and fixed shaft 115) are worn or deformed, and thereby the positioning accuracy of the door unit 101 when it is in the closed position is deteriorated.

[0119] Therefore, in the present embodiment, the positioning accuracy of the CIS detection unit 2 and the gate unit 101 is improved by the configuration described below.

[0120] like Figure 4A As shown in , the CIS detection unit 2 is disposed between the rotation center 111 of the outer door 101A and the hook 113. That is, the CIS detection unit 2 is disposed between the rotation center of the door unit 101 and the engaging portion (hook 113) for holding the door unit 101 in the closed position against the force caused by the urging force of the urging member 125 for pressurizing the clamping portion of the roller pair. In other words, when viewed in the sheet width direction in a state where the door unit 101 is in the closed position, the CIS detection unit 2 is disposed between the position of the rotation center 111 and the position of the hook shaft 114 in the direction along the straight line connecting the rotation center 111 and the hook shaft 114.

[0121] A case where the CIS detection unit 2 is positioned farther from the rotation center 111 than the hook 113 will be described. In this case, the portion of the door unit 101 farther from the rotation center 111 than the hook 113 is moved by the urging force of the urging member 125. Figure 4A For this reason, the position of the CIS detection unit 2 disposed on the outer door 101A slightly moves in a direction away from the conveying guide 121 facing the inner door 102, and therefore, there is a possibility that the position of the CIS detection unit 2 is displaced.

[0122] On the other hand, due to the engagement between the hook 113 and the fixed shaft 115, the portion of the door unit 101 closer to the rotation center 111 than the hook 113 is less likely to be Figure 4A In the present embodiment, since the CIS detection unit 2 is disposed between the rotation center 111 of the outer door 101A and the hook 113, positional misalignment of the CIS detection unit 2 due to the urging force of the urging member 125 can be suppressed.

[0123] In the present embodiment, the CIS detection unit 2 is used as a detection unit for detecting the side end position of the sheet P. However, it is known that the CIS has a shallow depth of field. The focus position of the CIS is often set near the reading surface of the CIS (the front surface of the reading glass). Therefore, it is preferred that the sheet P to be read passes through a position in close contact with the reading surface of the CIS as much as possible. At the same time, the gap between the reading surface of the CIS detection unit 2 and the conveying guide 121 facing the reading surface is set to approximately 2 to 3 mm so as to achieve stable sheet conveyance regardless of the thickness of the sheet P, etc. Therefore, strictly speaking, the sheet P is allowed to pass through a position shifted from the focus position of the CIS detection unit 2.

[0124] When the gap between the reading surface of the CIS detection unit 2 and the conveying guide 121 fluctuates, there is a possibility that the deviation of the sheet P from the focused position increases. In this case, the image acquired by the CIS detection unit 2 is blurred, and the error of the result of detecting the side end position of the sheet P increases. Therefore, it is desirable to minimize the fluctuation of the gap between the reading surface of the CIS detection unit 2 and the conveying guide 121.

[0125] Therefore, in the present embodiment, the protrusion 122 is provided on at least one of the inner door 102 or the outer door 101A and contacts the other of the inner door 102 or the outer door 101A, thereby stabilizing the gap between the reading surface of the CIS detection unit 2 and the conveying guide 121. That is, the opening / closing unit includes a first conveying guide and a second conveying guide that forms a conveying path with the first conveying guide. The protrusion is provided on one of the first conveying guide and the second conveying guide and is configured to contact the other of the first conveying guide and the second conveying guide when the opening / closing unit is closed. In the present embodiment, as Figure 4A As shown in FIG. 1 , a protrusion 122 is provided on a conveying guide 121 of the inner door 102 .

[0126] In a state where the door unit 101 is in the closed position, the protrusion 122 contacts the conveying guide 123 of the outer door 101A. As a result, the gap between the reading surface of the CIS detection unit 2 and the conveying guide 121 is adjusted with reference to the protruding height of the protrusion 122 from the conveying guide 121. That is, in a configuration in which the conveying guides 121 and 123 forming the inner-door double-sided path CP2a are opened and closed, the gap between the reading surface of the CIS detection unit 2 and the conveying guide 121 can be stabilized. Thus, the detection accuracy of the side end position of the sheet P can be improved.

[0127] In order to improve the detection accuracy, it is preferred that the protrusion 122 is disposed at a position close to the CIS detection unit 2. For example, the protrusion 122 is preferably disposed between the double-sided conveying roller pair 72 positioned upstream of the CIS detection unit 2 in the sheet conveying direction (arrow C) on the in-door double-sided path CP2a and the double-sided conveying roller pair 73 positioned downstream of the CIS detection unit 2. In other words, the opening / closing unit includes a first conveying roller pair disposed upstream of the detection unit in the sheet conveying direction on the conveying path, and a second conveying roller pair disposed downstream of the detection unit in the sheet conveying direction. The protrusion is disposed between the first conveying roller pair and the second conveying roller pair in the sheet conveying direction.

[0128] The pressing force of the protrusion 122 in contact with the conveying guide 123 is determined by the sum of the reaction forces received by the rollers disposed on the inner door 102 from the rollers disposed on the device body 1A or the outer door 101A. The reaction forces received by the roller 42a in the registration roller pair 42, the secondary transfer roller 44, and the rollers 61a and 63a in the conveying roller pair 61 and 63 from the rollers (42b, 22, 61b, and 63b) of the device body 1A are generated around the rotation center 112. Figure 4A The reaction force received by the rollers 72b, 73b and 74b of the double-sided conveying roller pair 72, 73 and 74 from the rollers 72a, 73a and 74a of the outer door 101A generates a torque in the clockwise direction around the rotation center 112. Figure 4A If the sum of the clockwise moment and the counterclockwise moment acting on the inner door 102 is in the direction in which the inner door 102 approaches the outer door 101A (clockwise direction), the protrusion 122 can be stably brought into contact with the conveying guide 123.

[0129] Next, we will refer to Figure 5A and Figure 5B The positioning configuration of the gate unit 101 in the sheet width direction is described. Figure 5A 1 is a perspective view illustrating the door unit 101 and a portion of the apparatus body 1A in an open position (the inner door 102 is in an inner door closed position). Figure 5B1 is a perspective view illustrating a state in which a projection 134 and a groove 133 described below are engaged with each other.

[0130] like Figure 5A and Figure 5B As shown in , shafts 131a and 131b are provided on the front and rear sides of the door unit 101. The shafts 131a and 131b are part of the outer door 101A. A hole 132a into which the shaft 131a is fitted and a hole 132b into which the shaft 131b is fitted are provided in the device body 1A. When the shafts 131a and 131b are fitted with the holes 132a and 132b, the door unit 101 is supported so as to be rotatable around the rotation center 111. The arrangement of the shafts and the arrangement of the holes can be interchanged, and the shafts can be provided in the device body 1A and the holes can be provided in the door unit 101.

[0131] In addition, a protrusion 134 is provided on the rear side of the door unit 101. The protrusion 134 is provided at a position away from the rotation center 111 and is a protruding portion that protrudes in a direction intersecting the sheet width direction (a direction along an arc centered on the rotation center 111). A groove 133 is provided in the device body 1A as a recessed portion to be engaged with the protrusion 134. The inner surface of the groove 133 faces both side surfaces of the protrusion 134 in the sheet width direction.

[0132] When the door unit 101 is in the closed position, the projection 134 engages with the groove 133. The engagement between the projection 134 and the groove 133 limits the positional misalignment of the door unit 101 relative to the device body 1A in the sheet width direction. That is, the positional misalignment of the door unit 101 relative to the device body 1A in the sheet width direction can be reduced to the size of the play between the projection 134 and the groove 133. Therefore, in a state where the door unit 101 is in the closed position, the positional accuracy of the CIS detection unit 2 in the sheet width direction can be improved. Thus, the detection accuracy of the side end position of the sheet P can be improved.

[0133] Furthermore, the projection 134 and the groove 133 are disposed on the rear side of the image forming apparatus 1 similarly to the CIS detection unit 2. That is, the projection 134, the groove 133, and the CIS detection unit 2 are arranged with respect to the center position Wc ( Figure 3 ) are all deployed on the same side (see also Figure 5A As a result, the projection 134 and the groove 133 and the CIS detection unit 2 are less likely to be affected by the intersecting components therebetween, compared with the case where the projection 134 and the groove 133 and the CIS detection unit 2 are disposed on opposite sides with the center position Wc therebetween. Therefore, the positioning accuracy of the CIS detection unit 2 can be further improved, and the detection accuracy of the side end position of the sheet P can be further improved.

[0134] Control Example

[0135] Reference Figure 6 and Figure 7 A method of controlling image position correction in this embodiment is described. Figure 6 The upper part of is a diagram illustrating changes in the leading edge position of one sheet P during a job (continuous print job) in which image forming operations are continuously performed on a plurality of sheets P. Figure 6 The lower part of FIG. 1 is a timing chart illustrating control timing related to the conveyance of the sheet P. Figure 7 It is a graphic with Figure 6 Flow chart of the control contents related to the sheet P. Each step of this process is performed by the control unit 200 ( Figure 2 )'s CPU 201 reads and executes the program from the memory 202 to execute.

[0136] Figure 6 The vertical axis in the upper part of the figure indicates in an overlapping manner the position on the conveying path before the sheet P is reversed and the position on the conveying path after the sheet P is reversed. The conveying path before the sheet P is reversed is from the leading edge position of the sheet P set in the sheet loading section (feeding start) through the feeding path and the image forming path CP1 ( Figure 1 ) to the reversing conveying roller pair 71. The conveying path after the sheet P is reversed is a conveying path from the reversing conveying roller pair 71 through the double-sided path CP2 and the image forming path CP1 to the discharge roller pair 62 or the reversing conveying roller pair 71. Since the leading edge of the sheet P is positioned at the downstream end of the sheet P in the sheet conveying direction, the leading edge and the trailing edge of the sheet P are switched before and after the turn-back by the reversing conveying roller pair 71.

[0137] In a continuous print job, repeatedly execute Figure 6 and Figure 7 The processing shown in is continued until the image formation on the number of sheets P specified by the user is completed. In addition, part of the processing for the preceding sheet and part of the processing for the succeeding sheet may be executed in parallel.

[0138] First, the control unit 200 causes the image forming unit 1B to start exposure for forming an image on the first surface of the sheet P ( Figure 6 The time t1 and Figure 7 Each exposure device 13 is based on the image formation control unit 205 ( Figure 2 ) transmits an image writing signal to illuminate the corresponding photosensitive drum 11 with light to write an electrostatic latent image on the corresponding photosensitive drum 11. In this embodiment, before the feeding of the sheet P is started, the process unit PY ( Figure 1) starts exposure of the photosensitive drum 11. Hereinafter, the photosensitive drum 11 of the process unit PY is referred to as the "most upstream photosensitive drum 11".

[0139] The reference position of the electrostatic latent image to be written on the photosensitive drum 11 by the exposure device 13 in the main scanning direction of the photosensitive drum 11 is referred to as an "image writing position". The control unit 200 can correct the image writing position by adjusting the timing of the image writing signal transmitted from the image formation control unit 205 to the exposure device 13. By correcting the image writing position, the position of the image relative to the reference side end of the sheet P in the sheet width direction is corrected.

[0140] In the present embodiment, the image writing position Ia on the first surface is a preset position. Information on the image writing position Ia is stored in the memory 202 ( Figure 2 ) and is read by the CPU 201. The image writing position 1a is set in advance with reference to, for example, a nominal position of the side end PL of the sheet P.

[0141] In the present embodiment, exposure of the most upstream photosensitive drum 11 is started before starting feeding of the sheet P. Therefore, in the present embodiment, control for correcting the image writing position Ia on the first surface based on the first detection result Xa is not performed.

[0142] After the exposure of the most upstream photosensitive drum 11 is started, the feeding of the sheet P is started ( Figure 6 The time t2 and Figure 7 When the sheet P reaches the secondary transfer portion, the transfer of the toner image from the intermediate transfer belt 21 to the first surface of the sheet P begins ( Figure 6 The time t3 and Figure 7 S103 in FIG. 10). Thereafter, the sheet P passes through the fixing device 50 to undergo a toner image fixing process. The length of the interval (t1 to t3) is the time required for the toner image to reach the secondary transfer portion after the exposure of the most upstream photosensitive drum 11 is started. The feeding and conveying of the sheet P are controlled so that the leading edge of the sheet P reaches the secondary transfer portion at time t3.

[0143] When the leading edge of the sheet P reaches the reverse conveying roller pair 71, the reverse conveying roller pair 71 performs switchback conveyance ( Figure 7 The timing at which the leading edge of the sheet P reaches a predetermined reversing position in the sheet conveying direction of the image forming path CP1 by the reversing conveying roller pair 71 ( S104 in FIG. 1 ) Figure 6 The rotation direction is reversed at time t4) in the double-sided path CP2, and the sheet P is conveyed toward the double-sided path CP2.

[0144] Thereafter, during the conveyance of the sheet P through the in-gate double-sided path CP2a, the CIS detection unit 2 detects the side end position ( Figure 6 The time t5 and Figure 7 The sensor control unit 207 converts the detection signal (image signal) of the CIS detection unit 2 into the side end position of the sheet P, whereby the control unit 200 acquires the side end position of the sheet P.

[0145] The control unit 200 calculates the correction amount ( ) of the image writing position Ib on the second surface of the sheet P by using the side end position of the sheet P detected by the CIS detection unit 2. Figure 7 Then, the control unit 200 causes the image forming unit 1B to start exposure for forming an image on the second surface of the sheet P based on the corrected image writing position Ib ( Figure 6 The time t6 and Figure 7 Thereafter, when the sheet P reaches the secondary transfer portion, the transfer of the toner image from the intermediate transfer belt 21 to the second surface of the sheet P starts ( Figure 6 The time t7 and Figure 7 , and the sheet P passes through the fixing device 50 to undergo a toner image fixing process.

[0146] The timing (time t5) at which the CIS detection unit 2 detects the side end position of the sheet P is earlier than the timing (time t6) at which exposure for forming an image on the second surface of the sheet P is started. The length of the interval (t6 to t7) is the time required for the toner image to reach the secondary transfer portion after the exposure of the most upstream photosensitive drum 11 is started. That is, the interval (t1 to t3) for the first surface and the interval (t6 to t7) for the second surface have the same time length.

[0147] The arrangement of the CIS detection unit 2 is set so that the side end position of the sheet P can be detected by the exposure start timing (time t6) which is a predetermined time before the transfer start timing (time t7). As a result, the control unit 200 can determine the correction amount of the image writing position Ib of the second surface of the sheet P based on the result of the detection of the side end position of the sheet P by the CIS detection unit 2 for each sheet.

[0148] exist Figure 3 , the nominal position of the side end PL of the sheet P is "0", and the displacement amount of the position of the side end PL detected by the CIS detection unit 2 relative to the nominal position is Yb. In this embodiment, with the image writing position Ia of the first surface as a reference, the image writing position Ib of the second surface is determined as a position shifted in the same direction and the same distance as the displacement amount (Yb) of the side end position (S106). In other words, the control unit determines the writing position based on the difference between the preset target position of the sheet and the position of the sheet detected by the detection unit. For example, when the sheet P is relative to Figure 3In the case where the nominal position shown in is shifted toward the rear side of the device, the image writing position Ib of the second surface is also shifted toward the rear side of the device.

[0149] As described above, misalignment or skew feeding of the sheet P is more likely to occur during the period from when the sheet P first passes through the secondary transfer portion to when the sheet P arrives at the secondary transfer portion again than during the period from when the feeding of the sheet P is started to when the sheet P arrives at the secondary transfer portion. According to the present embodiment, by correcting the image writing position Ib of the second surface based on the detection result of the CIS detection unit 2, the positional accuracy of the image formed on the second surface of the sheet P can be improved.

[0150] As described above, according to the present embodiment, in a configuration in which the in-door double-sided path CP2a is provided in the door unit 101 openable and closable relative to the apparatus body 1A of the image forming apparatus 1, the CIS detection unit 2 disposed on the in-door double-sided path CP2a is provided. In other words, a conveying path for conveying the sheet reversed by the reversing unit toward the image forming unit is provided in the opening / closing unit, and the detection unit is disposed on the conveying path. As a result, the image position accuracy on the second surface of the sheet P can be improved.

[0151] Modified Example

[0152] In the description of the first embodiment, the description has been made in which the side end PL ( Figure 3 The image position is controlled by the CIS detection unit 2 at the left side of the image detection unit 2 and the image position is controlled by the CIS detection unit 2 at the rear side of the device. The present technology is not limited to this, and for example, at the side end ( Figure 3 In the case of controlling the image position by the right side end in the image, the CIS detection unit 2 can be deployed on the front side of the device. In this case, by arranging the protrusion 134 and the groove 133 on the front side of the device, the same advantages as the above advantages can be expected.

[0153] In the first embodiment, an example has been described in which the CIS detection unit 2 is disposed downstream of the duplex conveying roller pair 72, but the CIS detection unit 2 may be disposed, for example, upstream of the duplex conveying roller pair 72 or downstream of the duplex conveying roller pair 73. The arrangement of the CIS detection unit 2 is determined so that the CIS detection unit 2 can detect the side end position of the sheet P before starting exposure of the photosensitive drum 11 for forming an image on the second surface of the sheet P. The arrangement of the CIS detection unit 2 is determined in consideration of factors such as the path length from the exposure position of the most upstream photosensitive drum 11 to the secondary transfer portion, the process speed, the sheet conveying speed in the duplex path CP2, and the stop time of the leading edge of the sheet in the registration roller pair 42.

[0154] The timing at which the CIS detection unit 2 detects the side end position of the sheet P may be the timing at which the leading edge of the sheet P reaches the detection position of the CIS detection unit 2, or may be the timing after the leading edge of the sheet P passes the detection position and is conveyed a predetermined distance. In addition, the CIS detection unit 2 may detect the side end position of one sheet P a plurality of times, and obtain an average value of a plurality of side end position data as a detection result indicating the side end position of the sheet P.

[0155] In addition, the CIS detection unit 2 is an example of a detection unit that detects the position of the sheet P in the sheet width direction, and, for example, a charge coupled device (CCD) image sensor can be used. As the detection unit, a mechanism can be used in which a sensor (for example, a reflective photoelectric sensor) that detects the presence or absence of a sheet is moved in the sheet width direction by a motor and the side end position of the sheet P is detected based on the driving amount of the motor.

[0156] In the first embodiment, a configuration has been described in which the door unit 101 is supported to be rotatable around the rotation center 111 provided at the lower end of the outer door 101A, but the support configuration of the door unit 101 is not limited thereto. For example, the door unit 101 may be supported by the device body 1A so that the door unit 101 rotates around the rotation center provided at the end of the door unit 101 on the rear side of the device and extending in a substantially vertical direction. In addition, as another example, the door unit 101 may be supported by the device body 1A via a slide rail, and may be moved along the slide rail. Figure 1 Also in these examples, the door unit 101 is movable between a closed position in which the door unit 101 covers a side surface portion of the apparatus body 1A and an open position in which a space is formed between the door unit 101 and the apparatus body 1A so that at least a portion of the sheet conveying path is opened.

[0157] The arrangement of the rollers in the door unit 101 and the device body 1A is not limited to the arrangement described in the first embodiment. For example, the registration roller pair 42 and / or the secondary transfer roller 44 may be disposed in an additional opening / closing unit independent of the door unit 101, or may be disposed in the device body 1A. In the former case, the gripping portion of the registration roller pair 42 and / or the secondary transfer portion may be released by opening the additional opening / closing unit after opening the door unit 101.

[0158] In the case where the registration roller pair 42 and / or the secondary transfer roller 44 are not disposed in the gate unit 101, there are advantages that the positioning accuracy of the rollers is not affected by the positioning accuracy of the gate unit 101 and that the clamping pressure of the registration roller pair 42 or the secondary transfer portion can be increased. Such advantages also apply to the fixing device 50 which is not disposed in the gate unit 101 in this embodiment.

[0159] Second embodiment

[0160] As a second embodiment, a mode will be described in which the registration roller pair 42 includes a detection unit that detects the side end position of the sheet P in addition to the CIS detection unit 2 of the duplex transport unit 70. Hereinafter, unless otherwise specified, elements denoted by reference numerals common to those of the first embodiment will have substantially the same configuration and function as those described in the first embodiment, and portions different from the first embodiment will be mainly described.

[0161] Figure 8 1 is a cross-sectional view illustrating a portion of an image forming apparatus 1 according to a second embodiment. Figure 8 As shown in FIG. 4 , the CIS detection unit C1 is disposed near the registration roller pair 42. The CIS detection unit C1 is a line sensor having a configuration of a contact image sensor similar to the CIS detection unit 2 disposed on the in-door double-sided path CP2a. The CIS detection unit C1 is an example of a first detection unit disposed on the conveying path from the sheet feeding unit 30 to the image forming unit 1B. The CIS detection unit 2 is an example of a second detection unit.

[0162] like Fig. 9A As shown in FIG. 1 , the CIS detection unit C1 detects the side end position of the sheet P fed from the sheet feeding unit 30 before it reaches the secondary transfer portion (secondary transfer roller 44). The side end position of the sheet P detected by the CIS detection unit C1 before the sheet P passes through the secondary transfer portion for the first time is a first detection result Xa. Arrow A indicates the sheet conveying direction in the image forming path CP1.

[0163] like Fig. 9B As shown in FIG. 1 , the CIS detection unit 2 detects the side end position of the sheet P during the sheet P reversed by the reverse conveying roller pair 71 is conveyed through the in-gate duplex path CP2a. The side end position of the sheet P detected by the CIS detection unit 2 before the sheet P reaches the secondary transfer portion again after passing through the secondary transfer portion for the first time is the second detection result Yb.

[0164] like Fig. 9C As shown in FIG. 1 , the CIS detection unit C1 detects the side end position of the sheet P before the sheet P conveyed through the duplex path CP2 reaches the secondary transfer portion (secondary transfer roller 44) again. The side end position of the sheet P detected by the CIS detection unit C1 before the sheet P passes the secondary transfer portion for the second time is the third detection result Xb.

[0165] As described above, in the present embodiment, the side end position of one sheet P is acquired three times using the two CIS detection units C1 and 2 .

[0166] The two CIS detection units C1 and 2 are disposed on the rear side of the device. That is, the two CIS detection units C1 and 2 are disposed on the same side relative to the center position Wc of the conveying path in the sheet width direction. Since the two CIS detection units C1 and 2 are disposed on the same side in the sheet width direction, the same side end of the sheet P becomes the detection target, which is advantageous from the viewpoint of detection accuracy.

[0167] Control Example

[0168] Reference Fig.10 and Fig.11 A method of controlling image position correction in this embodiment is described. Fig.10 The upper part of is a diagram illustrating changes in the leading edge position of one sheet P in a continuous print job. Fig.10 The lower part of FIG. 1 is a timing chart illustrating control timing related to the conveyance of the sheet P.

[0169] Fig.11 It is a graphic with Fig.10 Flow chart of the control contents related to the sheet P. Each step of this process is performed by the control unit 200 ( Figure 2 )'s CPU 201 reads and executes the program from the memory 202 to execute.

[0170] First, the control unit 200 causes the image forming unit 1B to start exposure for forming an image on the first surface of the sheet P ( Fig.10 The time t1 and Fig.11 Each exposure device 13 is based on the image formation control unit 205 ( Figure 2 ) transmits an image writing signal to illuminate the corresponding photosensitive drum 11 with light to write an electrostatic latent image on the corresponding photosensitive drum 11.

[0171] The image writing position Ia on the first surface is a preset position. Information about the image writing position Ia is stored in the memory 202 ( Figure 2 ) and is read by the CPU 201. The image writing position Ia is preset with reference to, for example, a nominal position of the side end PL of the sheet P. In the present embodiment, the exposure of the most upstream photosensitive drum 11 starts before the feeding of the sheet P is started. Therefore, in the present embodiment, the control of correcting the image writing position Ia on the first surface based on the first detection result Xa is not performed. That is, the control unit determines the first writing position Ia based on the preset target position (nominal position) of the sheet, regardless of the first detection result Xa.

[0172] After the exposure of the most upstream photosensitive drum 11 is started, the feeding of the sheet P is started ( Fig.10 The time t2 and Fig.11Thereafter, before the sheet P reaches the secondary transfer portion, the CIS detection unit C1 detects the side end position of the sheet P ( Fig.10 The time ta and Fig.11 When the sheet P reaches the secondary transfer portion, the transfer of the toner image from the intermediate transfer belt 21 to the first surface of the sheet P begins ( Fig.10 The time t3 and Fig.11 Thereafter, the sheet P passes through the fixing device 50 to undergo a toner image fixing process.

[0173] When the leading edge of the sheet P reaches the reverse conveying roller pair 71, the reverse conveying roller pair 71 performs switchback conveyance ( Fig.11 The timing at which the leading edge of the sheet P reaches a predetermined reversing position in the sheet conveying direction of the image forming path CP1 by the reversing conveying roller pair 71 ( S205 in FIG. 1 ) Fig.10 The rotation direction is reversed at time t4) in the double-sided path CP2, and the sheet P is conveyed toward the double-sided path CP2.

[0174] Thereafter, during the conveyance of the sheet P through the in-gate double-sided path CP2a, the CIS detection unit 2 detects the side end position ( Fig.10 The time t5 and Fig.11 (S206 in).

[0175] The control unit 200 calculates the correction amount ( xa , yb ) of the image writing position Ib on the second surface of the sheet P by using the side end position (the first detection result Xa and the second detection result Yb) of the sheet P detected by the CIS detection units C1 and 2. Fig.11 Then, the control unit 200 causes the image forming unit 1B to start exposure for forming an image on the second surface of the sheet P based on the corrected image writing position Ib ( Fig.10 The time t6 and Figure 7 (S208 in ).

[0176] Thereafter, before the sheet P reaches the secondary transfer portion again, the CIS detection unit C1 detects the side end position ( Fig.10 When the sheet P reaches the secondary transfer portion, the transfer of the toner image from the intermediate transfer belt 21 to the second surface of the sheet P begins ( Fig.10 The time t7 and Fig.11 , and the sheet P passes through the fixing device 50 to undergo a toner image fixing process.

[0177] The timing of the first detection by the CIS detection unit C1 and the timing of the detection by the CIS detection unit 2 (times t a and t 5 ) are earlier than the timing (time t 6 ) of starting exposure for forming an image on the second surface of the sheet P. Therefore, in the present embodiment, the first detection result Xa and the second detection result Yb are acquired for each sheet, and the image writing position Ib on the second surface is determined for the sheet P based on the first detection result Xa and the second detection result Yb.

[0178] In this embodiment, the second detection (time tb) of the CIS detection unit C1 is performed after the exposure (time t6) of the most upstream photosensitive drum 11 is started. Therefore, in this embodiment, control for correcting the image writing position Ib on the second surface based on the third detection result Xb is not performed.

[0179] In addition, Fig.10 In the process, the control unit 200 performs a standby process of making the sheet P stand by upstream of the registration roller pair 42 between time t6 and time tb. This is to make the sheet P stand by when exposure for forming an image cannot be started on the current sheet P whose side end position has been detected by the CIS detection unit 2 (for example, in the case where an image forming operation is performed on another sheet in a continuous print job).

[0180] Fig.12 1 is a diagram illustrating changes in the first detection result Xa, the second detection result Yb, and the third detection result Xb for each sheet in a continuous print job in which double-sided printing is performed on 30 sheets P. FIG.

[0181] The value of the first detection result Xa not only varies for each sheet but also gradually increases during the continuous printing job due to the generation of a gap between the side regulating plate and the sheet P in each sheet loading portion.

[0182] The value of the second detection result Yb shows a change in which the change for each sheet is added to the first detection result Xa. This is because the misalignment of the sheet P and the shape error (change in orthogonality) of the sheet P that occurs when the reverse conveying roller pair 71 individually clamps the sheet P and performs switchback conveyance are different for each sheet.

[0183] The value of the third detection result Xb shows a change in value relative to the second detection result Yb, which is offset from a substantially constant value. It is known that the difference between the third detection result Xb and the second detection result Yb occurs during the transfer process from the detection position of the CIS detection unit 2 to the detection position of the CIS detection unit C1 in the double-sided transfer unit 70.

[0184] Reference Fig.13A and Fig. 13BA method of determining the image writing position Ib on the second surface using the first detection result Xa and the second detection result Yb is described in detail. The side end of the sheet P in the following description is the side end used as a reference for the image position ( Fig. 9A The lateral end PL in the middle).

[0185] In the present embodiment, the image writing position Ia on the first surface is a preset position and is fixed to, for example, 0 (mm). On the other hand, the image writing position Ib on the second surface is calculated by the following formula.

[0186] Ib=Yb-Xa+Ia

[0187] In other words, in the present embodiment, the writing position at which the exposure unit writes the electrostatic latent image on the image bearing member to form an image (first image) on the first surface of the sheet is the first writing position (Ia). The writing position at which the exposure unit writes the electrostatic latent image on the image bearing member to form an image (second image) on the second surface of the sheet is the second writing position (Ib). The control unit determines the second writing position (Ib) based on the first writing position (Ia), the position (Xa) of the sheet detected by the first detection unit, and the position (Yb) of the sheet detected by the second detection unit.

[0188] Fig.13A Pictured Fig.12 0046] In the example of FIG. 10, the image writing position Ia on the first surface and the image writing position Ib on the second surface of each sheet are changed.

[0189] Next, when the first detection result Xa is considered to be the same as the side end position of the sheet P when the colorant image is transferred to the first surface of the sheet P, the position of the image formed on the first surface of the sheet P relative to the side end of the sheet P (the image printing position on the first surface) La can be expressed by the following formula.

[0190] La=Xa-Ia

[0191] Similarly, when the third detection result Xb is considered to be the same as the side end position of the sheet P when the colorant image is transferred to the second surface of the sheet P, the position of the image formed on the second surface of the sheet P relative to the side end of the sheet P (the image printing position on the second surface) Lb can be expressed by the following formula.

[0192] Lb=Xb-Ib=Xb-(Yb-Xa+Ia)

[0193] The difference between the image printing position La on the first surface and the image printing position Lb on the second surface is defined as the front-back difference ΔL of the image. From the above formulas of La and Lb, ΔL is expressed as follows.

[0194] ΔL=Lb-La

[0195] ={Xb-(Yb-Xa+Ia)}-{Xa-Ia}

[0196] =Xb-Yb

[0197] Fig. 13B Pictured Fig.12 The changes in the image printing position La on the first surface, the image printing position Lb on the second surface, and the front-back difference ΔL of the image in the example.

[0198] As can be seen from the above results, according to the present embodiment, the front-to-back difference ΔL of the image in duplex printing is substantially equal to the magnitude of the misalignment of the sheet P occurring on the conveying path from the CIS detection unit 2 to the CIS detection unit C1. Fig.12 and Fig. 13B It can be seen that the misalignment (Xb-Yb) of the sheet P occurring on the conveying path from the CIS detection unit 2 to the CIS detection unit C1 is relatively small. Therefore, by the method of this embodiment in which the correction amount of the image writing position Ib on the second surface is determined based on the misalignment (Yb-Xa) of the sheet P occurring on the conveying path from the CIS detection unit C1 to the CIS detection unit 2 without correcting the image writing position Ib on the first surface, the front-to-back difference ΔL of the image can be effectively reduced. In other words, the control unit of this embodiment determines the second writing position (Ib) based on the difference (Yb-Xa) between the second detection result (Yb) and the first detection result (Xa), so that the difference (front-to-back difference ΔL) between the position of the image on the first surface relative to the side end of the sheet and the position of the image on the second surface relative to the side end in the width direction of the sheet is close to 0.

[0199] Preferably, as expressed by the formula Ib-Ia=Yb-Xa obtained by modifying the calculation formula of the second writing position (Ib), the control unit determines the second writing position (Ib) so that the difference (Ib-Ia) between the second writing position (Ib) and the first writing position (Ia) is equal to the difference (Yb-Xa) between the second detection result (Yb) and the first detection result (Xa). As a result, the front-to-back difference ΔL of the image can be more effectively reduced. However, if the second writing position (Ib) is determined so that at least the positive or negative sign of the difference (Ib-Ia) between the second writing position (Ib) and the first writing position (Ia) and the sign of the difference (Yb-Xa) between the second detection result (Yb) and the first detection result (Xa) are consistent, then the front-to-back difference ΔL of the image can be close to 0.

[0200] As described above, according to the present embodiment, the image position accuracy during double-sided printing can be further improved.

[0201] Modified Example

[0202] exist Fig.13A and Fig. 13B In the example shown in , the image writing position Ib on the first surface is fixed to "0", but the image writing position Ib may have a value other than 0. For example, before factory shipment, the image printing position La on the first surface when the image writing position Ib on the first surface is set to 0 may be measured, and the value of Ib determined so that the value of La is close to 0 may be stored in the memory 202. As a result, the tendency of the image printing position La on the first surface caused by individual differences of the image forming apparatus 1 or the like can be improved.

[0203] In addition, Fig.13A and Fig. 13B In the example shown in , the misalignment (Xb-Yb) of the sheet P occurring on the conveying path from the CIS detection unit 2 to the CIS detection unit C1 is retained as the front-to-back difference ΔL of the image, but the front-to-back difference ΔL of the image can be eliminated by adjustment before factory shipment. That is, before factory shipment, a continuous print job can be executed by the method of this embodiment to obtain the value of the front-to-back difference ΔL of the image, and the value of the adjustment item of the image writing positions Ia and Ib can be determined so that ΔL is close to 0 and stored in the memory 202. The adjustment item is a constant to be added to the calculation formula of the image writing positions Ia and Ib described in this embodiment.

[0204] In the adjustment before factory shipment, Ib or the value of the adjustment item may be stored in the memory 202 as a table value corresponding to information such as the type and size of the sheet P.

[0205] In the present embodiment, the first detection result Xa for a certain sheet P is not reflected on the image writing position Ia on the first surface of the sheet P. However, in a continuous printing job, the first detection result Xa for the previous sheet can be reflected on the image writing position Ia on the first surface of the next sheet. For example, the image writing position Ia on the first surface of the next sheet can be set to a value obtained by subtracting the first detection result Xa for the previous sheet from the value described in the present embodiment. In addition, the image writing position Ib on the second surface can be calculated by the calculation formula of the present embodiment based on the image writing position Ia on the first surface calculated in this way. As a result, the image position accuracy on the first surface and the second surface can be further improved.

[0206] Other Examples

[0207] In the above-described embodiment, the control has been described in which detection is performed on each sheet by the CIS detection unit 2 and the image writing position Ib on the second surface of the sheet P is corrected based on the detection result. Alternatively, for example, the image writing position on the first surface or the second surface of the next sheet may be corrected in a continuous print job using the detection result of the previous sheet by the CIS detection unit 2. Furthermore, in a case where the detection result of the CIS detection unit 2 is equal to or greater than a predetermined threshold value, it may be determined that the image cannot be formed at an appropriate position using the correction of the image writing position, and the image forming operation may be interrupted.

[0208] According to the present disclosure, it is possible to provide an image forming apparatus capable of improving image position accuracy.

[0209] Other embodiments

[0210] Embodiments of the present invention may also be implemented by reading and executing computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be more completely referred to as a 'non-transitory computer-readable storage medium') to perform one or more of the functions of the above-mentioned embodiments and / or a computer of a system or device including one or more circuits (e.g., an application-specific integrated circuit (ASIC)) for performing one or more of the functions of the above-mentioned embodiments, and by a computer of the system or device, for example, reading and executing computer executable instructions from a storage medium to perform one or more of the functions of the above-mentioned embodiments and / or controlling one or more circuits to perform one or more of the functions of the above-mentioned embodiments. The computer may include one or more processors (e.g., a central processing unit (CPU), a microprocessing unit (MPU)), and may include a network of separate computers or separate processors to read and execute computer executable instructions. Computer executable instructions may be provided to the computer, for example, from a network or a storage medium. The storage medium may include, for example, a hard disk, a random access memory (RAM), a read-only memory (ROM), a storage device of a distributed computing system, an optical disk (such as a compact disk (CD), a digital versatile disk (DVD), or a Blu-ray disk (BD)) TM ), one or more of flash memory devices, memory cards, etc.

[0211] The embodiments of the present invention may also be implemented by providing software (program) for performing the functions of the above-described embodiments to a system or device via a network or various storage media, and a computer or a central processing unit (CPU) or a microprocessing unit (MPU) of the system or device reads and executes the program.

[0212] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An image forming device, comprising: Device body; an opening / closing unit provided on a side surface portion of the device body and configured to be opened and closed relative to the device body; an image forming unit configured to form an image on a sheet; a reversing unit configured to reverse a sheet having a first surface on which a first image is formed to form a second image on a second surface opposite to the first surface; a detection unit configured to detect a position of a sheet in a sheet width direction orthogonal to a sheet conveying direction; as well as a control unit configured to control the image forming unit based on the detection result of the detection unit, wherein A conveying path is provided in the opening / closing unit, through which the sheet reversed by the reversing unit is conveyed toward the image forming unit, and The detection unit is disposed on the conveying path.

2. The image forming apparatus according to claim 1, wherein The image forming unit includes an image bearing member and an exposure unit configured to expose the image bearing member to light, and The control unit is configured to determine a writing position at which the exposure unit writes the electrostatic latent image on the image bearing member to form the second image on the second surface of the sheet whose position has been detected by the detection unit, based on a detection result of the detection unit.

3. The image forming apparatus according to claim 2, wherein The control unit is configured to determine the writing position based on a difference between a preset target position of the sheet and a position of the sheet detected by the detection unit.

4. The image forming apparatus according to claim 2, further comprising: a sheet feeding unit including a sheet supporting portion configured to support a sheet, the sheet feeding unit configured to feed the sheet from the sheet supporting portion toward the image forming unit; as well as a first detection unit disposed on a conveying path from the sheet feeding unit toward the image forming unit and configured to detect a position of the sheet in the sheet width direction, wherein The detection unit is a second detection unit, and In a case where the position at which the exposure unit writes the electrostatic latent image on the image bearing member to form the first image on the first surface of the sheet is a first writing position, the writing position is a second writing position, the position of the sheet detected by the first detection unit before the first image is formed on the first surface is a first detection result, and the position of the sheet detected by the second detection unit is a second detection result, the control unit is configured to determine the second writing position based on the first writing position, the first detection result, and the second detection result.

5. The image forming apparatus according to claim 4, wherein The control unit is configured to cause the exposure unit to start writing the electrostatic latent image on the image bearing member to form the first image on the first surface of the sheet before the first detection unit detects the sheet fed from the sheet feeding unit, and The control unit is configured to determine the first writing position based on a preset target position of the sheet regardless of the first detection result.

6. The image forming apparatus according to claim 4, wherein The control unit is configured to determine the second writing position based on the difference between the second detection result and the first detection result, so that the difference between the position of the first image on the first surface relative to the side end of the sheet in the width direction of the sheet and the position of the second image on the second surface relative to the side end of the sheet is close to 0.

7. The image forming apparatus according to claim 4, wherein The control unit is configured to determine the second writing position so that a difference between the second writing position and the first writing position is equal to a difference between the second detection result and the first detection result.

8. The image forming apparatus according to claim 4, further comprising: a registration roller pair configured to convey the sheet fed from the sheet feeding unit to the image forming unit, wherein The first detection unit is disposed upstream of the registration roller pair in the sheet conveying direction, and The control unit is configured to make the sheet stand by upstream of the registration roller pair if exposure by the exposure unit has not started after the detection unit detects the position of the sheet.

9. The image forming apparatus according to claim 1, further comprising: a sheet feeding unit including a sheet supporting portion configured to support a sheet, the sheet feeding unit configured to feed the sheet from the sheet supporting portion toward the image forming unit, wherein The image forming unit includes a plurality of image bearing members, an exposure unit configured to expose the plurality of image bearing members, and an intermediate transfer member to which toner images are transferred from the plurality of image bearing members, and The control unit is configured to cause the exposure unit to start writing an electrostatic latent image for forming the first image on the first surface of the sheet on the image bearing member most upstream in the rotation direction of the intermediate transfer member among the plurality of image bearing members, and then cause the sheet feeding unit to start feeding the sheet.

10. The image forming apparatus according to any one of claims 1 to 9, wherein an image forming path is provided in the apparatus body, the image forming unit is configured to form an image on a sheet when the sheet is conveyed through the image forming path, The image forming path is a path in which sheets are conveyed upward, and The conveying path of the opening / closing unit is a path in which the sheet is conveyed downward.

11. The image forming apparatus according to any one of claims 1 to 9, wherein The opening / closing unit includes a first frame supported by the apparatus body, a second frame supported by the first frame so as to be openable and closable, and a pair of conveying rollers configured to convey a sheet via the conveying path, and The transport roller pair includes a roller supported by the first frame and a roller supported by the second frame, and is configured such that a clamping portion of the transport roller pair is released when the second frame is opened relative to the first frame.

12. The image forming apparatus according to any one of claims 1 to 9, wherein The opening / closing unit includes an engaging portion, The device body includes an engaged portion to be engaged with the engaging portion, and The opening / closing unit is held in a closed position by engagement between the engaging portion and the engaged portion.

13. The image forming apparatus according to claim 12, wherein The opening / closing unit is configured to rotate about a rotation axis relative to the device body, and The detection unit is disposed between the rotation shaft and the engagement portion.

14. The image forming apparatus according to claim 12, further comprising: a conveying roller pair including a first roller and a second roller and configured to nip a sheet at a nip portion between the first roller and the second roller to convey the sheet, the first roller being supported by the opening / closing unit and the second roller being supported by the apparatus main body; as well as a pushing member configured to push one of the first roller and the second roller toward the other of the first roller and the second roller, wherein When the first roller is pressed against the second roller by the urging force of the urging member in a state in which the opening / closing unit is closed, the opening / closing unit receives a force in a direction to open the opening / closing unit from the device body.

15. The image forming apparatus according to any one of claims 1 to 9, wherein The opening / closing unit includes a first conveying guide and a second conveying guide, the second conveying guide and the first conveying guide forming the conveying path, The second conveying guide is configured to move relative to the first conveying guide so that the conveying path is opened, and A protrusion is provided on one of the first conveying guide and the second conveying guide, and is configured to come into contact with the other of the first conveying guide and the second conveying guide in a state in which the opening / closing unit is closed.

16. The image forming apparatus according to claim 15, wherein The opening / closing unit includes a first conveying roller pair and a second conveying roller pair, the first conveying roller pair being disposed upstream of the detection unit in the sheet conveying direction, the second conveying roller pair being disposed downstream of the detection unit in the sheet conveying direction, and The protrusion is disposed between the first conveying roller pair and the second conveying roller pair in the sheet conveying direction.

17. The image forming apparatus according to any one of claims 1 to 9, further comprising: a protruding portion provided on one of the opening / closing unit and the device body and protruding in a direction intersecting with the sheet width direction; as well as a recessed portion provided on the other of the opening / closing unit and the device main body and configured to engage with the protruding portion, wherein in a state where the opening / closing unit is closed, movement of the opening / closing unit in the sheet width direction is restricted by engagement between the protruding portion and the recessed portion.

18. The image forming apparatus according to claim 17, wherein The detection unit, the protruding portion, and the recessed portion are disposed on the same side with respect to a center position of the conveying path in the sheet width direction.

Images