JP2017145142A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in which accuracy of lateral deviation correction and skew correction is reduced if a shift amount on a second face becomes large.SOLUTION: An image formation apparatus includes: a movement unit which moves a sheet in a width direction orthogonal to a conveyance direction; a re-conveyance unit which conveys a sheet again to a transfer unit by reversing the front and back of the sheet with a toner image transferred to the first face by a transfer unit; and a detection unit which detects the position of the sheet in the width direction. The control unit controls the movement unit so as to move the conveyed sheet to the position corresponding to first image position or the second image position in the width direction on the basis of the detection result of the detection unit. The center in the width direction of the toner image formed at the second image position is displaced with respect to the center in the width direction of the toner image formed at the first image position.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet.

  Generally, in an image forming apparatus such as a copying machine, a sheet may be laterally shifted in the width direction of the sheet while being conveyed. If an image is formed on a sheet with the sheet shifted laterally, the image is printed out of the center of the sheet, and the quality of the sheet is not good. For this reason, there is known a shift mechanism that detects the position of the end in the width direction of the sheet and corrects the lateral shift (position shift) of the sheet before forming an image on the sheet.

  Conventionally, the position of the edge of the first page in the width direction is detected, and the image forming position of the third page relative to the photoconductor is corrected based on the amount of deviation from the reference position of the edge of the first page. A forming apparatus has been proposed (see Patent Document 1). In this image forming apparatus, in order to correct the image forming position in advance based on the shift amount of the sheet two pages before, the shift amount of the sheet is reduced to improve the image quality and the production of the image forming apparatus. ing.

JP 2009-143643 A

  However, the image forming apparatus described in Patent Document 1 adds the detection result of the position of the end of the preceding sheet to the image forming position of the succeeding sheet. The formation position is not changed. In general, the position of the end in the width direction of the sheet may be shifted during the double-sided conveyance after the image is formed on the first surface of the sheet until the sheet reaches the registration roller pair again.

  For this reason, in the image forming apparatus described in Patent Document 1, the shift amount on the second side is increased by the amount of deviation in the width direction of the sheet during double-sided conveyance, leading to a decrease in productivity and image quality. .

  Therefore, the present invention provides an image forming apparatus that solves the above-described problems by reducing the shift amount on the second surface.

  In the image forming apparatus, an image carrier, an image forming unit that forms a toner image on the image carrier, and a toner image on the image carrier formed by the image forming unit are transferred to a sheet. A transfer unit, a moving unit that is provided upstream of the transfer unit in the sheet conveyance direction and moves the sheet in a width direction orthogonal to the conveyance direction, and a sheet on which the toner image is transferred on the first surface by the transfer unit. A re-conveying unit that conveys the sheet again to the transfer unit with the front and back reversed, a detection unit that detects the position of the sheet in the width direction, and a toner image transferred on the first surface to the image carrier The image forming unit is controlled to form a toner image that is formed at the first image position and transferred to the second surface at the second image position with respect to the image carrier, and the detection result of the detection unit is On the basis of, A control unit that controls the moving unit so that the fed sheet moves to the position corresponding to the first image position or the second image position in the width direction, and is formed at the second image position. The center of the toner image in the width direction is shifted from the center of the toner image formed at the first image position in the width direction.

  According to the present invention, it is possible to reduce the shift amount of a sheet when an image is formed on the second surface, thereby improving productivity and obtaining a high-quality product.

1 is an overall schematic diagram illustrating a printer according to a first embodiment. The perspective view which shows a sheet conveying apparatus. The block diagram which shows a control part. 6 is a flowchart illustrating sheet shift processing. (A) is a plan view showing a state where the sheet is skewed, (b) is a plan view showing a state where the skew of the sheet is corrected, and (c) is a state where the sheet is sandwiched by a pair of registration rollers. FIG. FIG. 5A is a plan view showing a state in which the first side of the sheet is corrected for lateral deviation, and FIG. 5B is a plan view showing a state in which the second side of the sheet is corrected for lateral deviation. The graph which shows the shift amount of a comparative example and a 1st Example. 10 is a table for determining an offset value of the printer according to the second embodiment. 10 is a timing chart of a printer according to a third embodiment. 10 is a flowchart illustrating control for determining an offset value of a printer according to a fourth embodiment. The flowchart which shows the process in the adjustment mode which concerns on 5th Embodiment. FIG. 3 is a schematic diagram illustrating a positional relationship between a first-side toner image and a second-side toner image.

<First Embodiment>
First, a first embodiment of the present invention will be described. The printer 1 (image forming apparatus) according to the first embodiment is an electrophotographic laser beam printer. As shown in FIG. 1, the printer 1 includes a cassette feeding unit 1B, a manual feeding unit 64, a sheet conveying device 100, an image forming unit 1C, an intermediate transfer belt 31 as an image carrier, and a re-conveying. A double-sided conveyance unit 1D as a unit, and a control unit 200.

  When an image formation command is output to the printer 1, an image forming process by the image forming unit 1 </ b> C is started based on image information input from an external computer or the like connected to the printer 1. The image forming unit 1C includes four exposure apparatuses 13Y, 13M, 13C, and 13K, and four process cartridges that form four color images of yellow (Y), magenta (M), cyan (C), and black (K). 10Y, 10M, 10C, and 10K. The four process cartridges 10Y, 10M, 10C, and 10K have the same configuration except that the colors of the images to be formed are different. Only the image forming process of the process cartridge 10Y will be described, and the process cartridges 10M, 10C, and 10K will be described. Description is omitted.

  The exposure device 13Y irradiates laser light toward the photosensitive drum 11Y of the process cartridge 10Y based on the input image information. At this time, the photosensitive drum 11Y is charged in advance by the charger 12Y, and an electrostatic latent image is formed on the photosensitive drum 11Y by irradiation with laser light. Thereafter, the electrostatic latent image is developed by the developing device 14Y, and a yellow (Y) toner image is formed on the photosensitive drum 11Y. The toner remaining on the photosensitive drum 11Y after the toner image is transferred to the intermediate transfer belt 31 is collected by the cleaner 15Y.

  Similarly, magenta (M), cyan (C), and black (K) toner images are formed on the photosensitive drums of the process cartridges 10M, 10C, and 10K. Each color toner image formed on each photosensitive drum is transferred to the intermediate transfer belt 31 by the primary transfer rollers 35Y, 35M, 35C, and 35K, and is conveyed to the secondary transfer inner roller 32 by the rotating intermediate transfer belt 31. . Note that the image forming process for each color is performed at the timing when the toner image is superimposed on the upstream toner image primarily transferred onto the intermediate transfer belt 31. The intermediate transfer belt 31 is stretched by a drive roller 33, a tension roller 34, and a secondary transfer inner roller 32, and rotates in the direction of arrow B.

  In parallel with the above-described image forming process, the sheet P is fed from the cassette feeding unit 1B or the manual feeding unit 64. The cassette feeding unit 1B has a plurality of cassettes 61, 62, and 63 (three in the present embodiment). These cassettes 61, 62, and 63 are respectively picked up by pickup rollers 61a, 62a, and 63a. Sheet P is fed. The manual feed unit 64 has a manual feed tray 64b that is rotatably supported, and the sheets P stacked on the manual feed tray 64b are fed by a pickup roller 64a.

  The sheet P fed from these pickup rollers 61a, 62a, 63a, 64a is corrected for skew of the sheet and displacement in the width direction by a sheet conveying device 100 described later. On the first surface of the sheet P that has passed through the sheet conveying apparatus 100, a predetermined pressure and electrostatic bias are applied to the transfer nip 1E as a transfer portion formed by the secondary transfer inner roller 32 and the secondary transfer outer roller 41. Given. As a result, the full-color toner image on the intermediate transfer belt 31 is transferred onto the sheet P on the first surface. The residual toner remaining on the intermediate transfer belt 31 is collected by the cleaner 36.

  The sheet P to which the toner image has been transferred is conveyed to the fixing device 5 by the air adsorption belt 42, and a predetermined pressure and heat are applied to melt and fix the toner image. The sheet P that has passed through the fixing device 5 is reversed by the fixing conveyance roller pair 52 to the discharge conveyance path 82 when being discharged onto the discharge tray 66 as it is, and when the image is formed on both sides of the sheet P, etc. It is conveyed to the guide path 83.

  A guide member 81 is rotatably provided at a branch portion between the discharge conveyance path 82 and the reverse guide path 83. The guide member 81 corresponds to a discharge mode in which the sheet P is discharged onto the discharge tray 66, a reverse discharge mode in which the sheet P is reversed and discharged, or a re-transport mode in which the sheet P is conveyed again to the image forming unit 1C. It is for switching paths. Then, by the path switching by the guide member 81, the sheet is guided to the discharge conveyance path 82 or the reverse guide path 83 according to the set mode.

  For example, in the discharge mode, the guide member 81 rotates downward and moves to a discharge position for discharging the sheet. Accordingly, the sheet P conveyed by the fixing conveyance roller pair 52 is conveyed along the upper surface of the guide member 81 to the discharge conveyance path 82 and is discharged to the discharge tray 66 by the discharge roller pair 77.

  Further, in the re-conveyance mode, the guide member 81 rotates upward and moves to a pull-in position where the sheet is guided to the reverse guide path 83. As a result, the sheet P conveyed by the fixing conveyance roller pair 52 is guided to the reverse guide path 83 along the lower surface of the guide member 81, and is drawn into the switchback path 84 by the first reverse roller pair 79. Then, the front and rear ends and the front and back sides of the sheet P are exchanged by a switchback operation in which the rotation direction of the second reversing roller pair 86 is rotated forward and backward, and the sheet P is conveyed to the duplex conveyance path 85. Thereafter, the sheet P conveyed to the double-sided conveyance path 85 is sent to the transfer nip 1E through the sheet conveying apparatus 100. The double-sided conveyance unit 1D includes a reverse guide path 83, a switchback path 84, a double-sided conveyance path 85, a first reverse roller pair 79, a second reverse roller pair 86, and another conveyance roller pair. Have. The subsequent image forming process for the back surface (second surface) is the same as the image forming process for the front surface (first surface) described above.

  Also in the reverse discharge mode, the guide member 81 rotates upward and moves to the retracted position. As a result, the sheet P is conveyed to the reverse guiding path 83 by the fixing conveyance roller pair 52, and is drawn into the switchback path 84 by the first reverse roller pair 79. Then, the leading and trailing ends of the sheet P are exchanged by a switchback operation in which the rotation direction of the first reversing roller pair 79 is forward and reverse, and the sheet P is conveyed to the reverse conveying path 89. Thereafter, the sheet P is conveyed to the discharge roller pair 77 by the reverse conveyance roller pair 78 provided in the reverse conveyance path 89, and is discharged to the discharge tray 66 by the discharge roller pair 77. In the printer 1 according to the present embodiment, as an example, a central reference sheet conveyance that conveys a sheet by matching the center in the width direction orthogonal to the sheet conveyance direction in the sheet conveyance path and the center in the width direction of the sheet. The explanation will be made assuming that the method is adopted.

  The cassettes 61, 62, and 63 are provided with size detection mechanisms 61d, 62d, and 63d for detecting the sizes of the sheets P accommodated therein. Since these size detection mechanisms 61d, 62d, and 63d have the same configuration, only the size detection mechanism 61d provided in the cassette 61 will be described, and the other description will be omitted.

  The size detection mechanism 61d includes a side regulation plate (not shown) that regulates the position of the sheet P in the width direction, and a rotatable size detection lever (not shown) that slides and interlocks with the side regulation plate. The side regulating plate is configured to be movable in accordance with the side end portion of the sheet P. In addition, when the side regulating plate is moved in accordance with the side end portion of the sheet P, the size detection lever is configured to rotate in conjunction with this.

  The size detection mechanism 61d has a plurality of sensors or switches that can detect the position of the size detection lever in a state where the cassette 61 is mounted on the printer main body 1A (device main body). That is, when the cassette 61 is mounted on the printer main body 1A, the size detection lever selectively turns on / off the sensor or the detection element of the switch. Accordingly, the printer 1 receives signals of different patterns output from the sensors or switches according to the sheets P stored in the cassette 61. The printer 1 can recognize the size of the sheet P stored in the cassette 61 based on the received signal.

  Further, the size detection mechanism 61d detects attachment / detachment of the cassette 61. For example, when the cassette 61 is removed, all the sensors or switch detection elements by the size detection lever are turned off. In the present embodiment, the manual feeding unit 64 is also provided with a size detection mechanism 64d similar to the size detection mechanism 61d.

  Note that the side regulating plate is for suppressing the skew of the sheet P and the positional deviation in the width direction that occur at the time of feeding the sheet P and at each of the conveying rollers arranged on the downstream side of the pickup roller. However, in practice, a slight gap may be generated between the side regulating plate and the sheet P. Due to this gap, when the sheet P is fed / conveyed, the sheet P may be skewed or misaligned in the width direction.

  As described above, when the sheet P is set in the cassettes 61, 62, 63, the center position of the sheet P is affected by the influence of the play of the side regulating plate or the vibration caused by inserting and removing the cassettes 61, 62, 63. Is generally shifted toward the front or back. Further, there may be a case where the size of the sheet P itself is slightly different from the nominal size. In such a case, the sheet continues to be offset by a certain value with respect to a reference position such as the center of the sheet conveyance path.

  In an image forming apparatus in a comparative example to be described later, since the sheet is controlled to be shifted in the width direction by the same distance as the fixed value, the sheet must be largely shifted. In addition, the sheet P fed from the cassette may be skewed during conveyance and further fed obliquely while moving in the width direction. In order to avoid such a state, the skew feeding correction and the like are performed by the sheet conveying apparatus 100. Hereinafter, this point will be described in detail.

  The sheet conveying apparatus 100 is provided in a conveying path 90 that connects the cassette feeding unit 1B and the manual feeding unit 64 to the transfer nip 1E. In addition, the sheet conveying apparatus 100 includes a registration roller pair 110, a pre-registration roller pair 120, a registration sensor 140, and a CIS (Contact Image Sensor) 141 as a moving unit. The pre-registration roller pair 120 is disposed upstream of the registration roller pair 110 in the sheet conveyance direction, and the registration sensor 140 and the CIS 141 are provided between these roller pairs.

  As shown in FIG. 2, the registration roller pair 110 that is a pair of rotating bodies includes an upper roller 110a and a lower roller 110b that is fixed to the rotating shaft 110S. An input gear 112 is fixed to the rotating shaft 110 </ b> S, and the input gear 112 is driven by the first drive motor 111 via the idler gear 113. The pre-registration roller pair 120 is driven by the second drive motor 121.

  A rack 153 is supported on the rotation shaft 110S so as to be relatively rotatable with respect to the rotation shaft 110S and not movable in the axial direction. The rack 153 receives a driving force from the shift motor 151 via the pinion gear 152 and shifts the rotating shaft 110S in the axial direction. Further, the upper roller 110a shifts in the axial direction in conjunction with the lower roller 110b by sandwiching a flange portion 114 provided integrally with the upper roller 110a by the input gear 112 of the lower roller 110b. When the registration roller pair 110 holding the sheet P moves in the width direction, the sheet moves in the width direction, and the position in the width direction of the sheet is corrected.

  Note that the idler gear 113 has a wider tooth width than the input gear 112. This is for maintaining the meshing of the gears and allowing the registration roller pair 110 to rotate even when the registration roller pair 110 and the input gear 112 move in the width direction.

  The CIS 141 serving as a detection unit detects the position of the end in the width direction of the conveyed sheet P (hereinafter referred to as the end position). The end position of the sheet on which the toner image is formed on the first surface detected by the CIS 141 is defined as the end position of the first surface, and the end position of the sheet on which the toner image is formed on the second surface detected by the CIS 141 is defined on the second surface. The end position of When the control unit 200 forms an image on the first surface of the sheet, the reference position in the sheet design (for example, the position where the center of the conveyance path 90 coincides with the center of the sheet) and the end position detected by the CIS 141 The amount of deviation is calculated. Then, the control unit 200 shifts the registration roller pair 110 by the calculated amount of deviation. Thereby, the position in the width direction of the sheet P matches the transfer position in the image forming unit 1C, and a high-quality product is obtained.

  The CIS 141 is arranged at a position that is biased to one side with respect to the center position of the transport path 90 in the width direction. This is because in the position correction of the sheet P, it is only necessary to detect the end position of only one side of the sheet P. Further, the CIS 141 is configured to be able to detect the end positions of the sheet P having the smallest width and the sheet P having the largest width among the sheet sizes permitted to be used by the printer 1. Further, the CIS 141 is arranged as close as possible to the registration roller pair 110 so as not to lower the detection accuracy of the CIS 141.

  Further, in the sheet conveying apparatus 100, the leading end of the conveyed sheet P is abutted against the nip portion of the stopped registration roller pair 110 and bent, and the leading end of the sheet P is caused to follow the nip portion. To correct skew. After the registration sensor 140 detects the leading edge of the sheet P and is fed by a predetermined amount by the pre-registration roller pair 120, the sheet P is conveyed by the registration roller pair 110 and is conveyed to the transfer nip 1E. Further, the gap between the CIS 141 and the lower guide 90a facing the CIS 141 is kept at a fixed distance, and the conveyance path 90 is predetermined by the lower guide 90a and the upper guides 90b and 90c so that the sheet is bent. A space is formed.

  FIG. 3 is a control block diagram showing the control unit 200 of the printer 1. The control unit 200 includes a 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 registration shift control unit 208. The CPU 201 implements various processes performed by the printer 1 by executing a predetermined control program and the like. The memory 202 is composed of, for example, a RAM or a ROM, and stores various programs and various data in a predetermined storage area. The operation unit 203 accepts input of various pieces of information (for example, sheet size, sheet basis weight, sheet surface property, etc.), job execution and cancellation, and the like.

  The image formation control unit 205 issues an instruction to the image forming unit 1C including the exposure devices 13Y, 13M, 13C, and 13K, and controls the image forming operation. The sheet conveyance control unit 206 instructs the feeding motor 65, the second drive motor 121, the first drive motor 111, and the like that drive the pickup rollers 61a, 62a, and 63a, and controls the conveyance operation of the sheet P. The sensor control unit 207 issues instructions to start and stop detection of the sensors provided in the size detection mechanisms 61d, 62d, 63d, and 64d, the registration sensor 140, and the like, and receives detection results of these sensors.

  The registration shift control unit 208 receives the detection result of the CIS 141 and issues an instruction to start and stop driving the shift motor 151 and controls the shift operation in the width direction of the registration roller pair 110. Further, the CPU 201 can be connected to, for example, an external computer 204 connected via a network, and can receive various information regarding a sheet, a print job, and the like from the computer 204.

  Next, the sheet P shifting process in the present embodiment will be described with reference to the flowchart shown in FIG. First, when a print instruction is input from the operation unit 203 or the computer 204, the control unit 200 starts a print job (step S1). Note that the user can specify the number of copies to be printed from the operation unit 203 or the computer 204 and can also specify the type of sheet to be used for printing. In addition, the control unit 200 acquires sheet information of sheets stored in the cassettes 61, 62, 63 and the manual feed tray 64b via the size detection mechanisms 61d, 62d, 63d, 64d.

The control unit 200 starts feeding the sheet P (step S2), and determines whether the printing is for the first side or the second side of the sheet in the print job (step S3). When it is determined that the printing is performed on the first surface of the sheet, the control unit 200 forms a toner image at the image writing position g ₁ on the first surface as the first image position determined in advance with respect to the intermediate transfer belt 31. Then, the image forming unit 1C is controlled to do so (step S4). Specifically, the control unit 200, process cartridges 10Y, 10M, 10C, exposure unit 13Y to form an electrostatic latent image at a position corresponding to the image writing position _{g 1} relative to the photosensitive drum 10K, 13M , 13C, 13K are controlled. As described above, the electrostatic latent images formed on the respective photosensitive drums are developed as toner images by the developing device, and these toner images are transferred to the intermediate transfer belt 31 by the primary transfer rollers 35Y, 35M, 35C, and 35K. Is done. The image writing position g1 on the _{first surface} is a value based on the adjustment result performed at the time of factory shipment or the like, and is stored in the memory 202 as a fixed value unique to the apparatus main body.

  On the other hand, the sheet P is conveyed to the pre-registration roller pair 120. Here, as shown in FIG. 5A, the conveyed sheet P rotates in a clockwise direction with respect to the arrow A direction, which is the conveyance direction, and skews to the left with respect to the arrow A direction. It is assumed that 5A to 6B indicate a state in which the leading edge of the sheet P conveyed without being skewed or laterally abutted against the nip portion of the registration roller pair 110. This is shown schematically. The end position in the width direction of the sheet at this time is defined as a zero point, and the left side is defined as a plus direction.

  Next, based on the detection result of the registration sensor 140 (step S5), the control unit 200 feeds the sheet P by the set feeding amount by the pre-registration roller pair 120. Accordingly, as shown in FIG. 5B, the sheet P is abutted against the stopped registration roller pair 110, and a predetermined amount of bending is formed (step S6). In this manner, the skew correction of the sheet P is performed, and the sheet P is nipped and conveyed by the registration roller pair 110 that has started to rotate as shown in FIG. 5C (step S7). ).

Then, the end position of the sheet P after the skew correction is detected by the CIS 141 (step S8), and the control unit 200 moves the movement distance in the sheet width direction based on the detection result (L ₁ ). The sheet shift amount is determined. The shift amount in this case can be obtained by subtracting (L ₁ −g ₁ ) the image writing position (g ₁ ) from the detection result (L ₁ ) of the CIS 141. In addition, the detection result by CIS141 is memorize | stored in the memory 202, for example.

The control unit 200 controls the shift motor 151 to move the registration roller pair 110 with the sheet P held therebetween in the width direction by the shift amount (L ₁ −g ₁ ) (step S 9). As a result, the sheet P is in a state in which the lateral displacement is corrected on the first surface, as shown in FIG. The toner image on the intermediate transfer belt 31 is transferred by the transfer nip 1E on the sheet P shifted by the shift amount (L ₁ -g ₁ ) by the registration roller pair 110 (step S10). This toner image is melted and fixed to the sheet P by the fixing device 5 (step S11).

  In the case of a single-sided job, the sheet P on which the toner image is fixed is discharged to the discharge tray 66 and the job is completed. However, in the case of a double-sided job, the sheet P is subjected to a reversal process for image formation on the second side. Performed (step S12). Next, the control unit 200 determines whether there is a subsequent sheet (step S13). If the control unit 200 determines that there is no subsequent sheet, the print job is terminated (step S14). If the control unit 200 determines that there is a subsequent sheet, the control unit 200 returns the registration roller pair 110 to the home position (center position) (step S15). Thereafter, the process returns to step S3.

  In step S3, when the control unit 200 determines that the printing is performed on the second side of the print job, the sheet P is conveyed again to the pre-registration roller pair 120 by the duplex conveying unit 1D. The switchback conveyance in the double-sided conveyance unit 1D is performed by sandwiching the sheet P only by the second reversing roller pair 86, and thus the sheet P is sometimes sent obliquely with respect to the conveyance direction. In particular, when the alignment of the second reversing roller pair 86 is broken, or when the conveyance resistance received from the conveyance guide is large, skew feeding is likely to occur. Further, the sheet may be laterally shifted in the width direction while the sheet is being conveyed on the duplex conveyance path 85. In many cases, the lateral deviation generated in the second reversing roller pair 86 and the double-sided conveyance path 85 is determined by the mechanical configuration of the apparatus main body. In the present embodiment, this lateral deviation amount is used as the offset value d unique to the apparatus main body. I remember it.

  The offset value d can be determined by adjustment during manufacturing. For example, an operator or a maintenance worker (hereinafter simply referred to as an operator) can execute the following adjustment mode, and acquires the offset value d by this adjustment mode. The operator first loads the adjustment sheets on the cassettes 61, 62, 63 or the manual feed tray 64b and feeds the adjustment sheets. Then, the offset value d is calculated from the difference between the position of the first surface of the adjustment sheet after the lateral deviation is corrected by the sheet conveying apparatus 100 and the end position of the second surface of the adjustment sheet detected by the CIS 141. . In addition, it is desirable to use a sheet for adjustment with good cutting accuracy. For example, in the case of a sheet formed in a parallelogram with poor cutting accuracy, an error occurs in the offset value d by the amount of deviation due to cutting.

  Further, after the offset value d is determined at the time of manufacturing the printer 1, it is not necessary to set the offset value d as it is. For example, there are cases where it is necessary to readjust the offset value d, for example, when parts of the duplex conveying unit 1D are replaced, when the wear of the second reversing roller pair 86 progresses, or when the installation environment of the apparatus main body changes. In view of such a case, the offset value d can be updated by the operator using the adjustment mode described above to readjust the offset value d.

When the second face printing of the sheet P is started, the control unit 200 reads the offset value d (step S16), and the image writing position g ₂ of the second surface of the second image position, image writing on the first side Obtained by adding the offset value d to the position g ₁ (g ₂ = g ₁ + d). The control unit 200 controls the image forming unit 1C to form a toner image at the image writing position g2 on the _second side (step S17). Specifically, the control unit 200, process cartridges 10Y, 10M, 10C, exposure unit 13Y to form an electrostatic latent image on the image writing position _{g 2} relative to the photosensitive drum 10K, 13M, @ 13 C, 13K To control. As described above, the electrostatic latent images formed on the respective photosensitive drums are developed as toner images by the developing device, and these toner images are transferred to the intermediate transfer belt 31 by the primary transfer rollers 35Y, 35M, 35C, and 35K. Is done. The sheet skew correction operation by the registration roller pair 110 on the second side is the same as that on the first side, and the description thereof is omitted (steps S18 to S20).

Here, FIG. 12 shows the positional relationship between the toner image PS1 on the first surface formed on the intermediate transfer belt 31 and the toner image PS2 on the second surface. Actually, the toner image PS1 and the toner image PS2 are not simultaneously formed on the intermediate transfer belt 31, but FIG. 12 shows both the toner image PS1 and the toner image PS2 for explanation. . Toner images PS1 is formed against the intermediate transfer belt 31 in the image writing position _{g 1,} toner images PS2 is formed on the image writing position _{g 2} with respect to the intermediate transfer belt 31. At this time, the center C2 in the width direction W of the toner image PS2 is shifted from the center C1 in the width direction W of the toner image PS1 by the offset value d in the width direction W.

Next, the sheet P after the skew correction is detected by the CIS 141 to detect the end position of the second surface (step S21), and the control unit 200, as shown in FIG. The shift amount of the sheet is determined based on the detection result (L ₂ ). The shift amount at this time can be obtained by subtracting the image writing position (g ₂ ) of the second surface from the detection result (L ₂ ) of the CIS 141.

In the example shown in FIG. 6 (b), for simplicity, the end position of the sheet corresponding to the image writing position g ₁ on the first side is to be the reference position _{(0) (g 1 = 0} ). In addition, the sheet tends to shift toward the back side of the main body during the double-sided conveyance by the double-sided conveyance unit 1D. In this case, after the sheet P is moved to the reference position (0) by the above-described lateral deviation correction on the first surface, the offset value (d) is displaced by a time until the end position of the second surface is detected by the CIS 141. It is predicted. In the present embodiment, the image writing position _{g 2} of the second surface, was determined by adding the offset value d in the image writing position _{g 1} on the first side _{(g 2 =} g 1 + d = d), so the second side The shift amount at is L ₂ −g ₂ = L ₂ −d (step S22). That is, the image writing position g ₂ is a position shifted by the offset value d from the reference position (0).

On the other hand, as shown in FIG. 6B, in the case of the comparative example in which the image writing positions on the first side and the second side are the same, the shift amount on the second side is L ₂ (> L ₂ -d). It becomes larger than the shift amount in the form. As described above, in the present embodiment, by taking the offset value d into account, the shift amount of the sheet on the second surface can be reduced, and the productivity can be improved. Further, by reducing the shift amount of the sheet by the registration roller pair 110, it is possible to reduce the skew of the sheet due to the shift operation. After the lateral deviation correction of the second surface of the sheet is completed, the toner image on the intermediate transfer belt 31 is transferred by the transfer nip 1E (step S23). Since the subsequent processing is the same as the processing on the first surface, the description thereof is omitted.

FIG. 7 is a graph in which the detection result of CIS 141, the image writing position, and the shift amount are plotted on the second surface of the present example and the comparative example when ten sheets are continuously passed through the printer 1. Here, the offset value d during double-sided conveyance is set to d = 1.5 mm. Although there is no particular mention regarding the first side, the image writing position g1 on the _{first side} is set to the reference position (0), and the shift operation is ideally performed on the detection result by the CIS 141 on the first side, and the shift is performed. It is assumed that the end position of the sheet immediately after the operation is the reference position (0).

In the present embodiment, the detection result of the CIS 141 on the second surface is in the range of −1.1 mm to −1.6 mm, and this value is close to the absolute value of the set offset value d = 1.5 mm. Yes. Therefore, in this embodiment, the second surface of the image writing position g ₂ With -d which is a difference between the first side image writing position g ₁ of ₍₌ 0), the image writing of the second side shift amount of the sheet The difference between the position g ₂ and the detection result of the CIS 141 on the second surface can be reduced. In the present embodiment, the shift amount (L ₂ −d) on the second surface is −0.4 mm to +0.1 mm. On the other hand, in the case of the comparative example, since the image writing position on the second surface is the same as the image writing position on the first surface, it can be seen that the shift amount greatly increases from +1.1 mm to +1.6 mm. As described above, in the present embodiment, it is possible to reduce the shift amount of the sheet when forming an image on the second surface, thereby improving productivity and obtaining a high-quality product. Further, by reducing the shift amount, it is possible to reduce the skew caused by the shift movement of the sheet.

  In the present embodiment, the CIS 141 is disposed upstream of the registration roller pair 110 in the transport direction, but may be disposed downstream of the registration roller pair 110. Further, instead of the CIS 141, a CCD sensor or a CMOS sensor may be used. If these sensors can detect the position in the width direction of the sheet, the positions of the end portions in the width direction of the sheet need not be detected.

  Further, instead of the method of correcting the skew of the sheet by abutting the sheet against the registration roller pair 110, a method of abutting the sheet against the shutter member provided upstream in the conveyance direction of the registration roller pair 110 is applied. May be. Further, the sheet may be shifted in the width direction by another roller pair without shifting the registration roller pair 110 for correcting the skew of the sheet in the width direction.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. In the second embodiment, the offset value d of the first embodiment is not a single eigenvalue but a variable according to sheet information. . For this reason, about the structure similar to 1st Embodiment, illustration is abbreviate | omitted or attaches | subjects the same code | symbol to a figure and demonstrates.

  There are various factors that cause the offset value d to change for the same model. In the present embodiment, as an example, the offset value d is determined according to the basis weight of the sheet P and the length in the transport direction. Hereinafter, the length in the sheet conveyance direction is simply referred to as a sub-scanning length. In particular, from the viewpoint of the size and cost of the apparatus main body, the number of transport rollers mounted on the printer 1 may be minimized, and the switchback operation is often performed with a pair of reverse rollers. Generally, when a sheet is nipped by a pair of rollers, the nipping pressure is lower when a pair is used than by a plurality of pairs. Therefore, the sheet P is easily affected by the frictional force and the like that the sheet P receives from the guide member during conveyance. In particular, when the basis weight of the sheet P is high and the rigidity is high, the sheet P is skewed or skewed, and the deviation of the end position of the second surface of the sheet becomes large. Further, the longer the distance conveyed by the pair of reverse rollers, that is, the longer the sub-scanning length of the sheet P, the larger the amount of skew feeding. For example, it is known that the skew feeding amount becomes larger when the reversing roller pair is misaligned.

  In the present embodiment, in view of such a tendency, the memory 202 stores a table of offset values d as shown in FIG. This table has a two-dimensional array, and an offset value d is determined according to the basis weight of the sheet and the sub-scanning length of the sheet. The offset value d is set to -0.8 mm to -2.0 mm depending on the combination of the basis weight of the sheet and the sub-scanning length of the sheet.

  The control unit 200 determines the offset value d in accordance with the sheet basis weight and the sub-scanning length information input from the operation unit 203 and the computer 204. Further, the basis weight of the sheet and the sub-scanning length of the sheet may be detected by the size detection mechanisms 61d to 64d.

  In this embodiment, the offset value d is determined according to the basis weight of the sheet and the sub-scanning length of the sheet. However, the present invention is not limited to this, and for example, the main scanning length that is the length in the width direction of the sheet, The offset value d may be determined from the sheet type, surface properties, and the like. In any case, the offset value d is determined by the information regarding the sheet.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. In the third embodiment, the offset value d is determined based on the detection result detected by the CIS 141. For this reason, about the structure similar to 1st Embodiment, illustration is abbreviate | omitted or attaches | subjects the same code | symbol to a figure and demonstrates.

FIG. 9 is a timing chart displaying image writing timings and CIS detection timings for three sheets in the middle of continuous image formation. For example, g _{1. n-1} represents an image writing signal for the first surface of the (n-1) th sheet, and L2 _{. n} represents the CIS detection signal on the second surface of the nth sheet.

Referring to the timing chart shown in FIG. 9, the image writing on the second sheet of the nth sheet has already been performed by time t ₁ before the end position of the second sheet surface is detected by the CIS 141. Therefore, the offset value d cannot be determined based on the detection result of the nth sheet itself.

Therefore, in the present embodiment, the offset value d that affects the image forming position on the second surface of the nth sheet (second sheet) is set to the value of the preceding (n−1) th sheet (first sheet). It sets based on the edge part position of the 2nd surface. Specifically, the end position of the (n−1) th sheet second surface by the CIS 141 is detected by a time t ₂ before the image writing timing of the nth sheet second surface. The image writing timing of the (n−1) th sheet first surface is a time t ₃ before the end position detection of the (n−1) th sheet second surface by the CIS 141. For this reason, the offset value d can be updated from the amount of lateral deviation during the double-sided conveyance of the (n-1) th sheet, and this can be reflected when writing the image on the second side of the nth sheet. The amount of lateral misalignment during the conveyance of both sides of the (n-1) th sheet is obtained by subtracting the end position of the (n-1) th sheet from the end position of the (n-1) th sheet. You can ask for it.

  In addition to the phenomenon specific to the apparatus main body as described above, the cause of the lateral deviation of the sheet is assumed to be a case caused by the sheet. For example, when the right angle of the sheet is shifted, it is known that the position of the second sheet in the width direction is shifted with respect to the first sheet. In the printer 1 according to the present embodiment, the offset value d can be sequentially updated during a continuous job. Therefore, even when characteristics such as the right angle of the sheet P change, the displacement of the second surface is more accurately detected. The amount can be predicted. Thereby, the shift amount of the registration roller pair 110 can be reduced, and the productivity can be improved and a high-quality product can be obtained.

  If the image writing timing for the nth sheet and the second sheet is in time, the offset value d may be updated using the (n-2) th sheet CIS detection result in addition to the (n-1) th sheet. Good. Further, in order to reduce the influence on the sudden lateral deviation of the sheet, the offset value d is updated by using a weighting α multiplied by the deviation amount in the width direction of the (n−1) th sheet. May be. For example, the weighting α is set to 0.7. In addition, the offset value d may be calculated while averaging the CIS detection results of a plurality of sheets before the (n−1) th sheet.

  Further, the detection of the end position of the sheet by the CIS 141 may be performed either before or after completion of the sheet shift operation. For this reason, the CIS 141 may be arranged either upstream or downstream of the registration roller pair 110 in the transport direction.

<Fourth embodiment>
Next, a fourth embodiment of the present invention will be described. The fourth embodiment has three modes for determining the offset value d after the cassette to be used is switched. In addition, about the structure similar to 1st Embodiment, illustration is abbreviate | omitted or attaches | subjects the same code | symbol to a figure and demonstrates.

  As described above, an appropriate value of the offset value d varies depending on the conveyance path length, the sheet length, and the like. Therefore, for example, consider a case where the cassette to be used is switched from the upper cassette 61 (first sheet support portion) to the lower cassette 63 (second sheet support portion). If the offset value used in the cassette 61 is applied to the cassette 63, the sheet shift amount may not be reduced appropriately. Further, the cassettes 61, 62, and 63 (sheet support portions) are configured to be detachable from the printer main body 1A, and the same cassette is the same depending on whether the cassettes 61, 62, and 63 are detached and reattached. Whether or not to use the offset value is different. This is because there is a possibility that the sheets in the cassette have been replenished or replaced when the cassette is detached and remounted. In the following, the case where the same cassette is detached and remounted is described, but the same control is performed when the cassette to be used is switched to another cassette.

  Therefore, in the present embodiment, the following three modes can be set as the initial setting mode of the printer 1. The first mode is a mode (high productivity mode) in which the offset value d is not always updated for the sheet regardless of whether the cassette is detached or reattached. The second mode is a mode (high accuracy mode) in which the offset value d is always updated for the sheet regardless of whether the cassette is detached and reattached. In the third mode, it is determined whether or not to update the offset value d for the first first sheet after the cassette is remounted, depending on whether or not the cassette is detached and remounted. Mode (automatic mode). These initial settings are set using the operation unit 203.

  FIG. 10 is a flowchart for explaining the control of these three modes. First, when the cassette to be used is switched, the control unit 200 determines which of the first mode, the second mode, and the third mode is selected as the control mode (step S31). When the control mode is set to the first mode, the control unit 200 does not update the offset value d regardless of the removal and remounting of the cassette. Then, an image writing position for the second surface of the first sheet is used by using an offset value d that is either a value unique to the apparatus main body or a value determined in a previous print job using the same cassette. Is determined (step S32). That is, when writing the image on the second side of the first sheet, the image writing is not delayed after waiting for the update of the offset value d, and the productivity is high.

  When the second mode is set in step S31, the control unit 200 updates the offset value d regardless of the removal and remounting of the cassette. Specifically, the CIS 141 detects the edge of the first and second sides of the first sheet, thereby determining the offset value d for the image writing position on the first side. After the offset value d is determined, the second image of the first sheet is written on each photosensitive drum based on the offset value d (step S33). In the second mode, since it is necessary to form the second image on the image forming unit 1C after the offset value d is determined, the second surface is detected before the end position of the second surface is detected by the CIS 141. Cannot be written on each photosensitive drum. For this reason, in the second mode, high-precision printing is possible, but productivity is lowered. On the other hand, the first mode is highly productive, but the shift amount increases, so that the accuracy such as skew is slightly reduced.

When the third mode is set in step S31, the control unit 200 determines whether or not the switched cassette is detached and reattached and is the first sheet feeding after the reattachment (step S31). S34). When the cassette is detached and reattached, and when it is the first feeding after reattachment, the control unit 200 updates the offset value d for the first sheet, and one sheet is based on the result. determining the image writing position _{g 2} of the second surface of the eye of the sheet (step S35). On the other hand, in step S34, if it is not the first sheet feeding after remounting, the control unit 200 does not update the offset value d for the first sheet, but determines it in the previous print job using the same cassette. An offset value is used (step S36). That is, the control unit 200 does not update the offset value d for the second and subsequent sheets fed from the same cassette. Then, the control unit 200 causes the image forming unit 1 </ b> C to form the image of the second surface before the detection of the end position of the second surface by the CIS 141 is completed. That is, in the third mode, it is determined whether or not the offset value d is automatically updated depending on whether or not the cassette is detached and remounted. Thereby, the mode switching operation by the user does not occur, and printing that achieves both high productivity and high accuracy is possible.

  In this way, in the present embodiment, having three control modes makes it possible to finely set which of the productivity and high accuracy is to be controlled. For this reason, usability can be improved.

<Fifth embodiment>
Next, a fifth embodiment of the present invention will be described. The fifth embodiment is configured so that the shift operation becomes invalid in the adjustment mode described in the first embodiment. Yes. For this reason, about the structure similar to 1st Embodiment, illustration is abbreviate | omitted or attaches | subjects the same code | symbol to a figure and demonstrates.

FIG. 11 is a flowchart illustrating a procedure for acquiring the offset value d in the printer 1. First, as shown in FIG. 11, the control unit 200 starts the adjustment mode (step S41), and invalidates the shift operation by the sheet conveying apparatus 100 (step S42). Then, after starting the sheet feeding (step S43), the control unit 200 determines whether the sheet is the first side or the second side in the print job (step S44). If it is determined that the first side in step S44, detects the edge position of the sheet in CIS141 one face, the control unit 200 obtains a detection result _{L 1} (step S45).

  Then, the toner image is transferred to the sheet P by the transfer nip 1E (step S46), and the toner image is melted and fixed by the fixing device 5 (step S47). In the case of a single-sided job, the sheet P on which the toner image is fixed is discharged to the discharge tray 66 and the job is completed. However, in the case of a double-sided job, the sheet P is subjected to a reversal process for image formation on the second side. Performed (step S48). Next, the control unit 200 determines whether there is a subsequent sheet (step S49).

Thereafter, when it is determined that the second side in step S44, detects the edge position of the sheet in CIS141 two face, the control unit 200 obtains a detection result _{L 2} (step S50). Then, 1 proceeds to the control similarly to step S49 of face, if it is determined that the subsequent sheet is not, the control unit 200 subtracts the detection result L ₂ from detection result L _1, the offset value d is calculated (D = L ₁ −L ₂ , step S51). This completes the adjustment mode (step S52).

  Thus, in the present embodiment, the offset value d is acquired in a state where the shift operation by the sheet conveying apparatus 100 is invalidated. This is because the sheet may be skewed by the shift operation of the first surface, and if the sheet is skewed, an accurate offset value d cannot be acquired. For this reason, in the present embodiment, an accurate offset value d can be obtained, and the shift amount can be further reduced.

1: image forming apparatus (printer) / 1A: apparatus main body (printer main body) / 1C: image forming unit / 1D: re-conveying unit (double-sided conveying unit) / 1E: transfer unit (transfer nip) / 61, 62, 63: Sheet support part (cassette) / 61: First sheet support part (upper cassette) / 63: Second sheet support part (lower cassette) / 110: Moving part, pair of rotating bodies (registration roller pair) / 141: Detection unit (CIS) / 200: Control unit / C1, C2: Center / d: Offset value / g ₁ : First image position / g ₂ : Second image position

Claims (16)

An image carrier;
An image forming unit for forming a toner image on the image carrier;
A transfer unit that transfers a toner image on the image carrier formed by the image forming unit to a sheet;
A moving unit that is provided upstream of the transfer unit in the conveyance direction of the sheet and moves the sheet in a width direction orthogonal to the conveyance direction;
A re-conveying unit that reverses the front and back of the sheet on which the toner image is transferred to the first surface by the transfer unit, and conveys the sheet to the transfer unit again;
A detection unit for detecting the position of the sheet in the width direction;
The toner image transferred on the first surface is formed at the first image position with respect to the image carrier, and the toner image transferred on the second surface is formed at the second image position with respect to the image carrier. The movement is performed so that a sheet to be conveyed moves to a position corresponding to the first image position or the second image position in the width direction based on a detection result of the detection unit, while controlling the image forming unit. A control unit for controlling the unit,
The center in the width direction of the toner image formed at the second image position is shifted from the center in the width direction of the toner image formed at the first image position.
An image forming apparatus. The second image position is a position deviated from the first image position by an offset value corresponding to the amount of deviation of the sheet in the width direction as the sheet is conveyed by the re-conveyance unit.
The image forming apparatus according to claim 1. The control unit corresponds to the position in the width direction of the sheet to which the toner image is transferred to the second surface detected by the detection unit and the second image position before the toner image is transferred to the second surface of the sheet. The sheet is moved by the moving unit by an amount based on a difference between the position of the sheet to be performed,
The image forming apparatus according to claim 2. The offset value is a preset fixed value.
The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. The offset value is set based on information about the sheet.
The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. The information on the sheet is information on at least one of the length of the sheet in the transport direction, the length of the sheet in the width direction, the basis weight of the sheet, and the surface property of the sheet.
The image forming apparatus according to claim 5. The control unit includes a position in the width direction of the sheet on which the toner image is transferred on the first surface detected by the detection unit, and a position in the width direction of the sheet on which the toner image is transferred on the second surface detected by the detection unit. And an adjustment mode in which the offset value can be updated based on the position.
The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. The control unit does not move the moving unit in the width direction when a sheet on which a toner image is transferred on the first surface passes through the moving unit in the adjustment mode.
The image forming apparatus according to claim 7. The control unit includes: a position in the width direction of the first sheet on which the toner image is transferred to the first surface detected by the detection unit; and the first sheet on which the toner image is transferred to the second surface detected by the detection unit. The offset value is obtained based on the position in the width direction, and the second image position of the second sheet subsequent to the first sheet is determined from the first image position of the second sheet. Set to a position shifted by the offset value obtained in
The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. The control unit includes: a position in the width direction of the first sheet on which the toner image is transferred to the first surface detected by the detection unit; and the first sheet on which the toner image is transferred to the second surface detected by the detection unit. The offset value is obtained based on the position in the width direction, and after the offset value is obtained, a toner image to be transferred to the second surface of the first sheet is formed on the image forming unit.
The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. A first sheet support part and a second sheet support part for supporting the sheet;
The control unit switches from a state in which a sheet is fed from the first sheet support unit to a state in which a sheet is fed from the second sheet support unit, and then from the second sheet support unit. The offset value is obtained based on the positions in the width direction of the first and second surfaces of the first sheet, which is the first sheet to be fed, and after the offset value is obtained, 2 of the first sheet is obtained. A toner image to be transferred to the surface is formed on the image forming unit;
The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. For the second sheet that is the second and subsequent sheets fed from the second sheet support unit, the control unit uses the offset value obtained for the first sheet to perform the second image position. And a toner image transferred on the second surface of the second sheet before the position in the width direction of the second sheet on which the toner image is formed on the second surface is detected by the detection unit. Forming in the image forming unit;
The image forming apparatus according to claim 11. An apparatus main body having the image forming unit;
A sheet support part that supports the sheet and is detachable from the apparatus main body,
The control unit is a first sheet that is fed from the sheet support unit after being reattached when the sheet support unit is detached and reattached to the apparatus main body. The offset value is obtained based on the positions of the first and second surfaces of the sheet in the width direction, and after the offset value is obtained, a toner image transferred to the second surface of the first sheet is transferred to the image forming unit. To form,
The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. For the second and subsequent sheets fed from the sheet support unit, the control unit sets the second image position using the offset value obtained for the first sheet. In addition, before the detection unit detects the position in the width direction of the second sheet on which the toner image is formed on the second surface, the toner image transferred on the second surface of the second sheet is formed on the image. Let the part form,
The image forming apparatus according to claim 13. The detection unit is disposed upstream of the moving unit in the transport direction.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The moving unit has a rotating body pair that abuts the leading edge of the sheet and corrects the skew of the sheet,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

Images