JP2017105625A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent sheet skew at the time of bias correction.SOLUTION: A control part of an image formation device, in a case where sheet type of a sheet P is a thick sheet and it is determined that sheet size is A3, three register roller pairs 200, a loop roller pair 240 and an ADU transportation roller pair 300 are selected as a transportation roller pair for an object that is swung. The control part, at the time of bias correction, based on a bias amount detected with a bias detection sensor 280, the register roller pair 200, the loop roller pair 240, and the ADU transportation roller pair 300 pinching the sheet P are swung at the same timing, in the same swing direction (sheet width direction D2) and at the same movement amount. Thus, at the time of bias correction, sheet skew and occurrence of a wrinkle are prevented.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, image forming apparatuses such as printers and copiers that employ an electrophotographic method have been widely used. In general image forming apparatuses, the direction of the paper is the direction of conveyance due to various types and properties of the paper used, the characteristics of parts such as the conveyance rollers, and the usage environment of temperature and humidity during conveyance. In some cases, the sheet is conveyed in a direction that is perpendicular to the sheet (hereinafter referred to as a sheet width direction or a main scanning direction). If the printing process is executed in this state, there is a problem that the printing position accuracy is lowered.

  Therefore, conventionally, the position of the paper relative to the image is detected by detecting the amount of deviation in the paper width direction by the deviation sensor and moving the paper in the paper width direction while being sandwiched between the registration roller pairs based on the detection result. So-called offset correction (registration swing correction) is performed to adjust the relationship. Patent Document 1 relates to a sheet aligning apparatus for performing sheet registration, and describes that a pre-registration roller disposed in an upstream portion of the sheet aligning function is provided with an aligning function without performing sheet alignment only by a registration roller. Has been.

JP 05-124752 A

  However, the paper aligning device described in Patent Document 1 described above has the following problems. For example, when there is a bend in the reversal path for reversing the front and back of the paper, and the resist swing correction is performed in a state where the rear end of the paper does not pass through the bend, the guide plate is caused by the stiffness of the paper. May cause sliding resistance. In particular, since the stiffness of cardboard is very large, the problem of sliding resistance becomes significant. As a result, when paper such as thick paper is used, the trailing edge of the paper cannot follow the swinging operation due to the increased sliding resistance, and the amount of swinging of the trailing edge of the paper is insufficient, causing the paper to be bent or wrinkled. It was. If the image forming process is executed in these states, there is a problem that a problem such as a bent image position occurs.

  SUMMARY An advantage of some aspects of the invention is to provide an image forming apparatus that can prevent paper skew at the time of deviation correction.

  The image forming apparatus according to the present invention moves the first transport roller pair in a second direction perpendicular to the first direction of the paper transport direction in a state where the paper is sandwiched between the first transport roller pair. The sheet is sandwiched between the first moving unit, at least one second conveying roller pair provided upstream of the first conveying roller pair in the sheet conveying direction, and the second conveying roller pair. A second moving unit that moves in the second direction in a state in which the sheet is moved, a detection unit that is provided on the downstream side of the first conveyance roller pair in the sheet conveyance direction and detects a shift of the sheet, A control unit that corrects the misalignment of the sheet based on the amount of misalignment of the sheet detected by the detection unit, and the control unit includes the first and second moving units at the time of the misalignment correction. Controlling the first and second Same timing conveying roller pair, and moves in the same direction and the same amount of movement.

  In the present invention, the second conveyance roller pair may be a single conveyance roller pair or two or more conveyance roller pairs. When providing the 2nd conveyance roller pair, the 2nd moving part can also be provided with two or more according to this. Examples of the second transport roller pair include a loop roller for forming a loop on the paper, and a transport roller provided on a reversing path for reversing the front and back of the paper. Further, the paper type includes the thickness and basis weight of the paper.

  According to the present invention, since the paper is moved by the first and second transport roller pairs at the same timing, in the same direction, and with the same movement amount, it is possible to reliably prevent the paper from being bent during the deviation correction.

1 is a diagram illustrating a configuration example of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the structural example of a resist part. 2 is a block diagram illustrating an example of a functional configuration of the image forming apparatus. FIG. It is a figure for demonstrating the rocking | fluctuation operation | movement at the time of deviation correction which concerns on the 1st Embodiment of this invention. It is a figure for demonstrating the rocking | fluctuation operation | movement at the time of the deviation correction in the past. FIG. 10 is a diagram for explaining a swinging operation when a pair of conveyance rollers is selected according to a paper size and the like. It is a figure which shows the conveyance pressure of each conveyance roller pair according to paper types. It is a figure for demonstrating rocking | fluctuation operation | movement in the case of selecting a conveyance roller pair according to deviation | shift amount. FIG. 10 is a flowchart illustrating an example of an operation of the image forming apparatus at the time of deviation correction. 6 is a flowchart illustrating an operation example of the image forming apparatus during a conveyance roller pair control process. It is a figure for demonstrating the rocking | fluctuation operation | movement at the time of the deviation correction in the past. It is a figure for demonstrating the rocking | fluctuation operation | movement at the time of deviation correction which concerns on the 2nd Embodiment of this invention. 6 is a flowchart illustrating an operation example of the image forming apparatus during a conveyance roller pair control process. It is a figure for demonstrating the rocking | fluctuation operation | movement at the time of deviation correction which concerns on 3rd Embodiment of this invention. 6 is a flowchart illustrating an operation example of the image forming apparatus during a conveyance roller pair control process.

  Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, the dimension ratio of drawing is expanded on account of description and may differ from an actual ratio.

<First Embodiment>
[Configuration Example of Image Forming Apparatus 100]
FIG. 1 shows an example of the configuration of an image forming apparatus 100 according to the present invention. As shown in FIG. 1, the image forming apparatus 100 is called a tandem type image forming apparatus, and includes an automatic document feeder 80 and an apparatus main body 102. The automatic document conveyance unit 80 is attached to the upper part of the apparatus main body 102 and sends out the paper set on the conveyance table to the image reading unit 90 of the apparatus main body 102 by a conveyance roller or the like.

  The apparatus main body 102 includes an operation display unit 70, an image reading unit 90, an image forming unit 10, an intermediate transfer belt 8, a paper feeding unit 20, a registration unit 400, a fixing unit 44, and an automatic paper reversing conveyance unit. 60 (Auto Duplex Unit: hereinafter referred to as ADU).

  The operation display unit 70 includes a touch panel in which a display unit and an input unit are combined, and operation keys including a start key and a determination key provided in a peripheral part of the touch panel. The operation display unit 70 displays an operation screen or the like on the screen, or receives an image forming condition related to a paper size or the like input by a touch operation on the operation screen or an operation of an operation key.

  The image reading unit 90 scans and exposes the document placed on the document table or the document transported by the automatic document transport unit 80 by the optical system of the scanning exposure device, and the image of the scanned document is CCD (Charge Coupled Device). ) Photoelectric conversion is performed by an image sensor to generate an image information signal. The image information signal is output to the image forming unit 10 after being subjected to analog processing, analog / digital (hereinafter referred to as A / D) conversion processing, pseudo correction, image compression processing, and the like by an image processing unit (not shown).

  The image forming unit 10 forms an image by electrophotography, and includes an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) image, The image forming unit 10C forms a cyan (C) color image, and the image forming unit 10K forms a black (K) color image. In this example, common function names, for example, Y, M, C, and K indicating colors to be formed are added to the back of the reference numeral 10.

  The image forming unit 10Y includes a photosensitive drum 1Y, a charger 2Y, an exposure unit (optical writing unit) 3Y, a developing unit 4Y, and a cleaning unit 6Y arranged around the photosensitive drum 1Y. The image forming unit 10M includes a photosensitive drum 1M, a charger 2M, an exposure unit 3M, a developing unit 4M, and a cleaning unit 6M disposed around the photosensitive drum 1M. The image forming unit 10C includes a photosensitive drum 1C, and a charger 2C, an exposure unit 3C, a developing unit 4C, and a cleaning unit 6C disposed around the photosensitive drum 1C. The image forming unit 10K includes a photosensitive drum 1K, a charger 2K, an exposure unit 3K, a developing unit 4K, and a cleaning unit 6K disposed around the photosensitive drum 1K.

  Respective photosensitive drums 1Y, 1M, 1C, and 1K in the image forming units 10Y, 10M, 10C, and 10K, chargers 2Y, 2M, 2C, and 2K, exposure units 3Y, 3M, 3C, and 3K, and developing units 4Y, 4M, and 4C and 4K, cleaning units 6Y, 6M, 6C, and 6K, and primary transfer rollers 7Y, 7M, 7C, and 7K have the same configuration. In the following description, Y, M, C, and K are not used unless particularly distinguished.

  The charger 2 charges the surface of the photosensitive drum 1 almost uniformly. The exposure unit 3 is composed of, for example, an LPH (LED Print Head) having an LED array and an imaging lens, or a polygon mirror type laser exposure scanning device, and the photosensitive drum 1 is irradiated with laser light based on an image information signal. Scan to form an electrostatic latent image. The developing device 4 develops the electrostatic latent image formed on the photosensitive drum 1 with toner. As a result, a toner image which is a visible image is formed on the photosensitive drum 1.

  The intermediate transfer belt 8 is stretched by a plurality of rollers and is rotatably supported. Along with the rotation of the intermediate transfer belt 8, the primary transfer roller 7 and the photosensitive drum 1 rotate, and a predetermined voltage is applied between the primary transfer roller 7 and the photosensitive drum 1, whereby the photosensitive member. The toner image formed on the drum 1 is transferred onto the intermediate transfer belt 8 (primary transfer).

  The paper feed unit 20 has a plurality of paper feed trays 20A and 20B in which paper P such as A3 and A4 is accommodated. The paper P transported from the paper feed trays 20A, 20B by the transport rollers 22, 24, 26, 28, etc. is transported to the registration unit 400. Note that the number of paper feed trays is not limited to two. Further, a single or a plurality of large-capacity paper feeders that can accommodate a large-capacity paper P may be connected as necessary.

  The registration unit 400 corrects the bending of the sheet P by creating a loop by abutting the leading end of the sheet conveyed from the sheet feeding unit 20 or the like, or swings in the sheet width direction D2 while holding the sheet P ( The offset of the paper P is corrected. The paper P in which the deviation of the paper P is corrected is conveyed to the secondary transfer unit 34 at a predetermined timing.

  In the secondary transfer unit 34, the Y, M, C, and K color toner images transferred onto the intermediate transfer belt 8 are collectively transferred onto the surface of the paper P conveyed from the registration unit 400 (secondary transfer). Next transfer). The second-transferred paper P is conveyed to the fixing unit 44 on the downstream side in the paper conveyance direction D1. The fixing unit 44 includes a pressure roller and a heating roller. The fixing unit 44 fixes the toner image on the surface of the paper P to the paper P by performing pressure and heat treatment on the paper P on which the toner image has been transferred by the secondary transfer unit 34.

  The transport path switching unit 48 switches the transport path of the paper P to the discharge path side or the ADU 60 side based on the selected printing mode (single-sided printing mode, double-sided printing mode, etc.). The paper P on which single-sided printing has been completed in the single-sided printing mode or the paper P on which double-sided printing has been completed in the double-sided printing mode is discharged onto the paper discharge tray by the paper discharge roller 46.

  Further, when an image is formed on the back side of the paper P in the duplex printing mode, the paper P on which the image is formed on the front side is conveyed to the ADU 60 via the conveyance roller 62 and the like. In the switchback path of the ADU 60, the reverse rotation control of the ADU roller 64 transports the paper P to the U-turn path part with the rear end of the sheet P as the leading edge, and the front and back sides of the ADU 60 by the transport rollers 66, 68, 300, etc. provided in the U-turn path part. The paper is fed again to the registration unit 400 in the inverted state.

[Configuration Example of Resist Unit 400]
FIG. 2 shows an example of the configuration of the resist unit 400. As shown in FIG. 2, the registration unit 400 includes a registration roller pair 200, a loop roller pair 240, a deviation detection sensor 280, and an ADU transport roller pair 300. Hereinafter, the registration roller pair 200, the loop roller pair 240, and the ADU transport roller pair 300 may be collectively referred to as a transport roller pair.

  The registration roller pair 200 is arranged on the transport path R1 upstream of the secondary transfer unit 34 in the paper transport direction D1. The registration roller pair 200 includes a driving roller 202 that rotates and a driven roller 204 that rotates following the rotation of the driving roller 202. The registration roller pair 200 corrects the bending of the paper P by creating a loop by abutting the leading edge of the paper, corrects the alignment between the leading edge of the paper after re-conveying the paper and the leading edge of the image, or sandwiches the paper P. The offset of the paper P is corrected by swinging in the paper width direction D2.

  The loop roller pair 240 is disposed on the transport path R1 upstream of the registration roller pair 200 in the paper transport direction D1. The loop roller pair 240 includes a driving roller 242 that rotates and a driven roller 244 that rotates following the rotation of the driving roller 242. The loop roller pair 240 adjusts the feed amount of the paper P to create a loop by abutting the front end of the paper P against the nip portion of the registration roller pair 200.

  The deviation detection sensor 280 is disposed downstream of the registration roller pair 200 in the paper transport direction D1. The deviation detection sensor 280 can be configured by a line sensor in which a plurality of photoelectric conversion elements are linearly arranged along the paper width direction D2, or an image sensor in which photoelectric conversion elements are arranged in a matrix. As the line sensor and the image sensor, a CCD type image sensor or a CMOS type (including MOS type) image sensor can be used.

  The ADU transport roller pair 300 is disposed in a bending path R2 curved in a substantially U shape of the ADU 60. For example, the bending path R2 includes a pair of guide plates arranged to face each other. The ADU transport roller pair 300 includes a driving roller 302 that rotates and a driven roller 304 that rotates following the rotation of the driving roller 302.

[Block Configuration Example of Image Forming Apparatus 100]
FIG. 3 is a block diagram illustrating an example of a functional configuration of the image forming apparatus 100. As shown in FIG. 3, the image forming apparatus 100 includes a control unit 50 for controlling the operation of the entire apparatus. The control unit 50 includes a CPU (Central Processing Unit) 52, a ROM (Read Only Memory) 54, and a RAM (Random Access Memory) 56.

  The CPU 52 implements functions related to image forming processing by executing software (program) read from the ROM 54. In this embodiment, the pair of conveying rollers to be swung is selected according to the paper size and the type of paper, the pair of conveying rollers to be swung is selected according to the conveying path, and the detected deviation amount is selected. Set the number of oscillations accordingly.

  The control unit 50 includes a registration roller driving unit 210, a registration roller swinging unit 220, a registration roller press release unit 230, a deviation detection sensor 280, a loop roller driving unit 250, and a loop roller swinging unit 260. The loop roller pressure release unit 270, the ADU conveyance roller driving unit 310, the ADU conveyance roller rocking unit 320, and the ADU conveyance roller pressure release unit 330 are connected to each other.

  The registration roller driving unit 210 includes a registration roller driving motor and the like, and is driven based on a driving signal supplied from the control unit 50 to drive the registration roller pair 200 forward or backward. The registration roller swing unit 220 includes a registration roller swing motor, a rack, a pinion gear, and the like, and is driven based on a drive signal supplied from the control unit 50 to swing the registration roller pair 200 in the paper width direction D2. Let The registration roller press release unit 230 includes a registration roller press release motor, a cam, a cam follower, and the like, and is driven based on a drive signal supplied from the control unit 50 to press and separate the registration roller pair 200.

  The loop roller driving unit 250 includes a loop roller driving motor, and is driven based on a driving signal supplied from the control unit 50 to rotationally drive the loop roller pair 240. The loop roller swing unit 260 includes a loop roller swing motor, a rack, a pinion gear, and the like, and is driven based on a drive signal supplied from the control unit 50 to swing the loop roller pair 240 in the paper width direction D2. Let The loop roller press release unit 270 includes a loop roller press release motor, a cam, a cam follower, and the like, and is driven based on a drive signal supplied from the control unit 50 to press and separate the loop roller pair 240.

  The ADU transport roller drive unit 310 includes a transport roller drive motor and the like, and is driven based on a drive signal supplied from the control unit 50 to rotate the ADU transport roller pair 300. The ADU transport roller rocking unit 320 includes a transport roller rocking motor, a rack and a pinion gear, and the like, and is driven based on a drive signal supplied from the control unit 50 to move the ADU transport roller pair 300 in the sheet width direction D2. Rocks. The ADU transport roller press release unit 330 includes a transport roller press release motor, a cam, a cam follower, and the like, and is driven based on a drive signal supplied from the control unit 50 to press and separate the ADU transport roller pair 300.

[Basic swinging motion of transport roller pair during offset correction]
When only one conventional registration roller pair 200 is swung, the trailing edge of the sheet cannot follow due to the resistance of the bending path R2 of the ADU transport roller pair 300 or the ADU 60. Bending occurred. In particular, thick paper with high rigidity has high resistance and paper bending becomes prominent. In this embodiment, this problem is dealt with as follows.

  FIG. 4 is a diagram for explaining the swinging operation of the transport roller pair at the time of deviation correction. As shown in FIG. 4, for example, during double-sided printing, the registration roller pair 200, the loop roller pair 240, and the ADU conveyance roller in a state where the paper P is sandwiched between the registration roller pair 200, the loop roller pair 240, and the ADU conveyance roller pair 300. The pair 300 is swung with the same timing (synchronization), the same swinging direction, and the same swinging amount. Further, even when the pair of conveyance rollers, for example, the registration roller pair 200 and the loop roller pair 240 are swung, the registration roller pair 200 and the loop roller pair 240 are moved at the same timing, in the same swing direction, and in the same swing amount. Rock.

  In the following, based on this basic swing operation, the optimum transport roller pair to be swung is selected according to the paper size, paper type, transport route, etc., and the selected transport roller pair is swung at the same timing and at the same time. Deviation correction is performed by swinging in the same direction and with the same swing amount. Hereinafter, each swing operation will be described in detail.

[When selecting a transport roller pair that swings according to the paper size and type]
When the paper size is large, particularly when thick paper is used, it is necessary to swing a plurality of transport roller pairs such as the registration roller pair 200, the loop roller pair 240, and the ADU transport roller pair 300. However, when using plain paper or thin paper having a small paper size, the paper can be swung only by the registration roller pair 200, and the upstream ADU transport roller pair 300 or the like may not be used. In this case, for example, it is necessary to leave a gap between the loop roller pair 240 and the ADU transport roller pair 300 until the next sheet can be transported, leading to a decrease in productivity. Therefore, in this embodiment, by selecting a pair of conveying rollers to be swung according to the paper size and paper type, it is possible to prevent the gap between the next paper and the paper from spreading even a little.

(Conventional case)
FIG. 5A to FIG. 5E are diagrams for explaining a conventional deviation correction operation. Note that the paper P on which an image is to be formed has a size that can be sandwiched between the two registration roller pairs 200 and the loop roller pair 240. In FIG. 5, in the paper width direction D2, the front side of the paper is called the front side of the apparatus, and the back side of the paper is called the back side of the apparatus.

  As shown in FIG. 5A, the deviation amount of the paper P is detected by the deviation detection sensor 280 (see FIG. 2) as the paper P1 is re-conveyed after the registration correction of the paper P. The registration roller pair 200 and the loop roller pair 240 swing, for example, toward the front side of the apparatus (in the direction of the arrow), with the paper P being sandwiched based on the detected deviation amount. The ADU transport roller pair 300 swings without holding the paper P. The swing time at this time is defined as ty.

  As shown in FIG. 5B, when the leading edge of the paper P reaches the secondary transfer portion 34, the registration roller pair 200, the loop roller pair 240, and the ADU transport roller pair 300 are separated from each other. Let the separation time at this time be tr.

  As shown in FIG. 5C, the registration roller pair 200, the loop roller pair 240, and the ADU transport roller pair 300 are moved away from each other (arrow direction) in order to return to the home position after being separated. Move. The swing time at this time is defined as ty.

  As shown in FIG. 5D, when the registration roller pair 200, the loop roller pair 240, and the ADU transport roller pair 300 return to the home position, they are brought into a press-bonded state. Let the separation time at this time be tr.

  As shown in FIG. 5E, when the registration roller pair 200, the loop roller pair 240, and the ADU transport roller pair 300 are brought into the pressure-bonded state and ready to receive the next paper P2, the transport of the next paper P2 is started. The As described above, when three transport roller pairs are used for the small-sized paper P, it takes (ty × 2 + tr × 2) as the waiting time Ta for the offset correction.

(In the case of this embodiment)
FIG. 6A to FIG. 6D are diagrams for explaining the deviation correction operation in the present invention. Note that the paper P on which an image is to be formed has a size that can be sandwiched between the two registration roller pairs 200 and the loop roller pair 240. In FIG. 6, in the paper width direction D2, the front side of the paper is called the front side of the apparatus, and the back side of the paper is called the back side of the apparatus.

  As shown in FIG. 6A, when the registration correction of the paper P1 is completed, the pressure bonding of the loop roller pair 240 and the ADU transport roller pair 300 is released, and the paper P1 is separated. Further, the deviation amount of the paper P is detected by the deviation detection sensor 280 along with the re-conveyance of the paper P1. The registration roller pair 200 swings, for example, toward the front side of the apparatus (in the direction of the arrow) in a state where the sheet P1 is sandwiched based on the deviation amount. The loop roller pair 240 and the ADU transport roller pair 300 do not swing. Let the separation time at this time be tr.

  As shown in FIG. 6B, when the leading edge of the paper P1 reaches the secondary transfer portion 34, the registration roller pair 200 is brought into a separated state, and the loop roller pair 240 and the ADU transport roller pair 300 are brought into a pressure-bonded state. The The pressure bonding time at this time is tr.

  As shown in FIG. 6C, the registration roller pair 200 swings toward the back of the apparatus (arrow direction) in order to return to the home position. Further, the conveyance of the next sheet P2 is started by the loop roller pair 240 and the ADU conveyance roller pair 300 that are already in the pressure-bonded state.

  As shown in FIG. 6D, when the conveyance of the next sheet P2 is started by the loop roller pair 240 and the ADU conveyance roller pair 300, the registration roller pair 200 is brought into a pressure-bonded state, and the registration correction of the sheet P2 is performed. . In the present embodiment, since one transport roller pair is used for the small-sized paper P, it takes (tr × 2) as the waiting time Tb at the time of deviation correction. Therefore, the deviation correction waiting time is conventionally: Ta> this embodiment: Tb, and the deviation correction of the present embodiment can narrow the pitch between the next sheet P2 and the production. It is possible to improve the performance.

[When transport pressure of transport roller pair is controlled according to paper type]
When offset correction is performed in a state where thick paper having a large frictional resistance is sandwiched between a pair of conveyance rollers, a large conveyance force (conveyance pressure) is required. Generally, the transport pressure of the transport roller pair is set according to the paper type that requires the most transport pressure. However, with thin paper with low frictional resistance, the transport pressure exceeds the frictional resistance, and wrinkles and buckling are likely to occur on the thin paper. Become. Therefore, in this embodiment, by providing a mechanism for adjusting the conveyance pressure depending on the paper type, it is possible to prevent insufficient swing due to paper slipping or paper bending and damage to the paper.

  As an adjustment mechanism for adjusting the conveyance pressure of the conveyance roller pair, for example, a registration roller pressure release unit 230, a loop roller pressure release unit 270, and an ADU conveyance roller pressure release unit 330 can be used. Since the adjustment mechanism can employ a known technique, a detailed description thereof will be omitted. By adjusting the rotational position of the cam by driving the motor of the adjustment mechanism, the conveyance pressure (nip pressure) of the conveyance roller pair such as the registration roller pair 200 can be adjusted.

  FIG. 7 shows an example of the relationship between the paper type and the conveyance pressure among the registration roller pair 200, the loop roller pair 240, and the ADU conveyance roller pair 300. As shown in FIG. 7, the registration roller pair 200 that requires image position accuracy is set to have a higher conveyance pressure than the upstream loop roller pair 240 and the like. Further, the conveyance pressure is set to be higher as the thickness of the paper P is larger. Further, the transport pressure of the upstream loop roller pair 240 and the ADU transport roller pair 300 should be set smaller than the transport pressure of the resist roller pair 200 for the purpose of extending the life when the distance to the resist roller pair 200 is short. Can do. Further, by setting the transport pressure of the upstream transport roller pair in this way, it is possible to suppress the occurrence of wrinkles and the like when the paper P swings.

[When the offset amount exceeds the swinging movable range]
At present, the center of the paper is easily shifted from the design value due to operations such as inserting / removing the paper feed tray or ADU frame during jam processing, and it is a piece exceeding the range of single swing movement of the transport roller pair. There is a case where the amount of deviation occurs. In this case, there is a problem that the deviation cannot be corrected by only one swing and the image forming position is shifted. Therefore, in the present embodiment, the offset correction exceeding the upper limit value of the swing movable range is enabled by performing the swing a plurality of times using at least two pairs of transport rollers.

  FIGS. 8A to 8H are diagrams for explaining the shift correction when the detected shift amount exceeds the swing movable range. Hereinafter, the maximum value of the swing movable range of the transport roller pair such as the registration roller pair 200 is set to ± 5 mm. Further, the paper P indicated by the solid line is the current paper position, and the paper P indicated by the broken line is the ideal paper position. Further, the upper side of the page is the back side of the apparatus, and the lower side of the page is the front side of the apparatus.

  As shown in FIG. 8A, when the registration correction is completed, the re-conveyance of the sheet P is started by the registration roller pair 200, the loop roller pair 240, and the ADU conveyance roller pair 300 that are brought into the press-bonded state. Along with the re-conveyance of the paper P, the deviation detection sensor 280 detects the deviation amount of the paper P. In this example, the offset amount is 10 mm. Therefore, it is necessary to perform the swing operation twice.

  As shown in FIG. 8B, the registration roller pair 200, the loop roller pair 240, and the ADU transport roller pair 300 have the same swinging direction and the same based on the detected deviation amount in the state where the paper P is sandwiched. Swings at the same timing and swing amount. The swing direction is the front side of the apparatus (in the direction of the arrow), and the swing amount is a maximum value of 5 mm.

  As shown in FIG. 8C, when the swinging of the paper P is completed, the loop roller pair 240 maintains the pressure-bonded state to hold the paper P, and the other two registration roller pairs 200 and the ADU transport roller pair. 300 is released from the pressure bonding and is in a separated state.

  As shown in FIG. 8D, the registration roller pair 200 and the ADU transport roller pair 300 that are separated from each other swing to the back side of the apparatus (arrow direction) in order to return to the home position. The swing amount is 5 mm which is the maximum value.

  As shown in FIG. 8E, the registration roller pair 200 and the ADU transport roller pair 300 that have returned to the home position are brought into the press-bonded state again. As a result, the leading end portion and the trailing end portion (or their peripheral portions) of the sheet P are held by the registration roller pair 200 and the ADU transport roller pair 300. Further, as shown in FIG. 8F, the loop roller pair 240 is in a separated state.

  As shown in FIG. 8 (G), the registration roller pair 200 and the ADU transport roller pair 300 have the paper P sandwiched between them, with the same swinging direction, the same timing, and the same swinging amount toward the front side (arrow direction). Swing. The swinging direction is the front side of the apparatus, and the swinging amount is 5 mm, which is the maximum value. By the two swings, the paper P swings 10 mm, which is the target value, toward the front side of the apparatus.

  As shown in FIG. 8 (H), when the swinging is finished, the loop roller pair 240 is brought into a pressure-bonded state. In this way, by performing the two-stage swing, it is possible to cope with a deviation amount exceeding the swing movable range of the transport roller pair.

[Operation Example of Image Forming Apparatus 100]
FIG. 9 is a flowchart illustrating an example of the operation of the image forming apparatus 100 according to the first embodiment. The control unit 50 (CPU 52) of the image forming apparatus 100 implements the processing shown in the flowchart shown below by executing the software read from the ROM 254.

  In step S100, when the job is transmitted, the control unit 50 executes the conveyance roller pair control process. In the present embodiment, the conveyance roller pair control process is a process of changing the conveyance roller pair to be swung according to the paper size and the paper type. FIG. 9 is a subroutine of the conveyance roller pair selection process.

  As shown in FIG. 9, in step S200, the control unit 50 determines whether the paper type of the job is plain paper or thick paper based on the image forming conditions included in the job. Note that the paper type information can also be acquired by input from the operation display unit 70. If the control unit 50 determines that the paper type of the job to be executed is plain paper, the control unit 50 proceeds to step S210.

  In step S210, the control unit 50 determines whether the plain paper is A4 size or A3 size. When the control unit 50 determines that the plain paper is A4 size, the control unit 50 selects only the registration roller pair 200 as the conveying roller pair that performs the swinging. When step S220 ends, the subroutine ends and the process proceeds to step S110 shown in FIG.

  On the other hand, when determining that the plain paper is A3 size, the control unit 50 proceeds to step S230, and selects the registration roller pair 200 and the upstream conveyance roller pair as the conveyance roller pair to be swung. For example, the ADU transport roller pair 300 can be selected as the upstream transport roller pair. When step S230 ends, the subroutine ends and the process proceeds to step S110 shown in FIG.

  In step S200, when the control unit 50 determines that the paper type of the job to be executed is thick paper, the process proceeds to step S240.

  In step S240, the control unit 50 determines whether the cardboard is A4 size or A3 size. When determining that the cardboard is A4 size, the control unit 50 proceeds to step S230, and selects the registration roller pair 200 and the upstream conveyance roller pair as the conveyance roller pair to be swung. When step S240 ends, the subroutine ends and the process proceeds to step S110 shown in FIG.

  On the other hand, if the control unit 50 determines that the cardboard is A3 size, the control unit 50 proceeds to step S250, and sets the three registration roller pairs 200, the loop roller pair 240, and the ADU transport roller pair 300 as the transport roller pairs that swing. select. When step S250 ends, the process proceeds to step S110 shown in FIG.

  In step S110 shown in FIG. 9, when the control unit 50 selects a pair of transport rollers to be swung at the time of deviation correction, the control unit 50 starts transport of the paper P. With the start of conveyance of the paper P, the paper P taken out from the paper supply unit 20 is registered in a state in which the image is formed on the front surface by the secondary transfer unit 34 and then reversed through the ADU 60. The paper is fed again to the section 400.

  In step S <b> 120, the deviation detection sensor 280 detects the deviation amount of the paper P that is re-conveyed after the registration correction by the registration roller pair 200 is completed. When step S120 ends, the process proceeds to step S130.

  In step S130, the control unit 50 determines whether or not the deviation amount of the paper P detected by the deviation detection sensor 280 exceeds a preset reference value (the deviation amount is excessive). When the control unit 50 determines that the amount of deviation of the paper P does not exceed the reference value and is equal to or less than the reference value, the process proceeds to step S180. Here, the reference value of the deviation amount means the maximum value of the swing movable range of each transport roller pair.

  In step S180, the control unit 50 swings the paper P in the paper width direction D2 in a state where the paper P is held by the pair of transport rollers selected as the swing target, according to the detected deviation amount of the paper P. For example, when the conveyance roller pair selected as the swing target is the registration roller pair 200 and the loop roller pair 240 (S230), the registration roller pair 200 and the loop roller pair 240 are brought into a pressure-bonded state, and the ADU conveyance roller pair 300 is separated. The registration roller pair 200 and the loop roller pair 240 are swung with the same timing, the same swinging direction, and the same movement amount.

  On the other hand, when the control unit 50 determines in step S130 that the amount of deviation of the paper P detected by the deviation detection sensor 280 exceeds the reference value, the process proceeds to step S140.

  In step S <b> 140, the control unit 50 calculates the number of swings N according to the detected amount of deviation. For example, when the maximum value of the swing movable range of the transport roller pair is 5 mm and the detected deviation amount is 12 mm, the control unit 50 calculates 3 times as the number of swings. When step S140 ends, the process proceeds to step S150.

  In step S150, the control unit 50 swings the sheet P by the maximum value of the swing movable range, for example, 5 mm in a state where the paper P is held by the pair of transport rollers selected as the swing target. When step S150 ends, the process proceeds to step S160.

  In step S160, the control unit 50 determines whether or not the conveyance roller pair has been swung N-1 times. When it is determined that the swing of the transport roller pair has not been performed N-1 times, the control unit 50 returns to step S150 and swings the transport roller pair by the maximum value of the swing movable range.

  On the other hand, when it is determined that the swing of the transport roller pair has been performed N-1 times, the control unit 50 proceeds to step S170 and swings the transport roller pair by the remaining offset amount. In this example, since the remaining offset amount is 2 mm, the conveying roller pair is swung by 2 mm as the third swinging operation. In addition, when the amount of deviation detected is a multiple of the maximum value of the swing movable range, this step S170 can be omitted. In this example, such processing is repeatedly executed.

  As described above, according to the first embodiment, at the time of deviation correction, the registration roller pair 200, the loop roller pair 240, and the ADU transport roller pair 300 are set to the same timing, the same swinging direction, and the same swinging amount. Therefore, it is possible to suppress paper bending and wrinkles. Thereby, it is possible to prevent the image position from being shifted during image printing, and to prevent the image quality from deteriorating.

<Second Embodiment>
The second embodiment is different from the first embodiment in that the pair of conveyance rollers that swing is changed according to the conveyance path of the paper P. Since the other configurations and operations of the image forming apparatus 100 are the same as those in the first embodiment, common constituent elements are denoted by the same reference numerals, and detailed description thereof is omitted.

[When selecting a transport roller pair that swings according to the transport path of the paper P]
In the second embodiment, when a paper feeding method using alternating circulation paper feeding is adopted, control is performed so that the loop roller pair 240 does not swing during double-sided conveyance. Thereby, compared with the case where the loop roller pair 240 is swung at the time of double-sided conveyance, the gap between the next paper P to be conveyed on one side is shortened by the rocking time for the loop roller pair 240 to return to the home position after the rocking. be able to.

(Conventional case)
FIG. 11A to FIG. 11F are diagrams for explaining a conventional deviation correction operation. In FIG. 11, in the paper width direction D2, the front side of the paper is called the front side of the apparatus, and the back side of the paper is called the back side of the apparatus.

  As shown in FIG. 11A, the deviation amount of the paper P1 is detected by the deviation detection sensor 280 (see FIG. 2) during duplex printing. The registration roller pair 200, the loop roller pair 240, and the ADU transport roller pair 300 swing, for example, toward the front side of the apparatus in a state where the sheet P1 is held based on the detected deviation amount. The swing time at this time is defined as ty.

  As shown in FIG. 11B, when the leading edge of the paper P1 reaches the secondary transfer portion 34, the registration roller pair 200, the loop roller pair 240, and the ADU transport roller pair 300 are separated from each other. Let the separation time at this time be tr.

  As shown in FIG. 11C, when the registration roller pair 200, the loop roller pair 240, and the ADU transport roller pair 300 are in the separated state, they swing to the back of the apparatus in order to return to the home position. The swing time at this time is defined as ty.

  As shown in FIG. 11D, when the registration roller pair 200 and the loop roller pair 240 return to the home position, they are brought into a press-bonded state. The pressure bonding time at this time is tr.

  As shown in FIG. 11E, when the registration roller pair 200 and the loop roller pair 240 are brought into the pressure-bonded state, the conveyance of the next sheet P2 on which single-side printing is performed by these conveyance roller pairs is started.

  As shown in FIG. 11F, the deviation amount of the paper P2 is detected by the deviation detection sensor 280 during single-sided printing. The registration roller pair 200 and the loop roller pair 240 swing to the front side of the apparatus, for example, in a state where the sheet P2 is held based on the detected deviation amount. At this time, the transport roller pair 290 is in a separated state. As described above, when three pairs of transport rollers are used, it takes (ty × 2 + tr × 2) as the waiting time Tc for the swing correction.

(In the case of this embodiment)
FIG. 12A to FIG. 12E are diagrams for explaining the shift correction operation according to the present embodiment. In FIG. 12, in the paper width direction D2, the front side of the paper is called the front side of the apparatus, and the back side of the paper is called the back side of the apparatus.

  As shown in FIG. 12A, the deviation amount of the paper P1 is detected by the deviation detection sensor 280 during duplex printing. The registration roller pair 200 and the ADU transport roller pair 300 swing to the front side of the apparatus, for example, in a state where the sheet P1 is held based on the detected deviation amount. The loop roller pair 240 is in a separated state and does not swing. Let the separation time at this time be tr.

  As shown in FIG. 12B, when the leading edge of the paper P reaches the secondary transfer portion 34 and the trailing edge of the paper P passes through the loop roller pair 240, the registration roller pair 200 and the ADU transport roller pair 300. Are separated from each other, and the loop roller pair 240 is brought into a press-bonded state. The pressure bonding time at this time is tr.

  As shown in FIG. 12C, after the leading edge of the paper P2 is sandwiched by the loop roller pair 240, the conveyance of the next paper P2 is started by the loop roller pair 240 and the conveyance roller pair 290. When single-sided printing is started, the registration roller pair 200 and the ADU transport roller pair 300 move to the back side of the apparatus in order to return to the home position.

  As shown in FIG. 12D, when the registration roller pair 200 and the ADU transport roller pair 300 return to the home position, they are brought into a press-bonded state. In addition, the registration roller pair 200 performs registration correction by creating a loop on the paper P <b> 2 conveyed by the loop roller pair 240.

  As shown in FIG. 12E, the deviation amount of the paper P2 is detected by the deviation detection sensor 280 during single-sided printing. The registration roller pair 200 and the loop roller pair 240 swing to the front side of the apparatus, for example, in a state where the sheet P2 is held based on the detected deviation amount. The conveyance roller pair 290 is in a separated state. As described above, when two pairs of transport rollers are used, a time of (tr × 2) is required as the waiting time Td during the swing correction. Therefore, the waiting time for the swing correction is conventional: Tc> this embodiment: Td, and the swing correction according to the present embodiment can narrow the pitch between the next paper P2 and the production. It is possible to improve the performance.

[Operation Example of Image Forming Apparatus 100]
FIG. 13 is a flowchart illustrating an example of the operation of the image forming apparatus 100 according to the second embodiment. The control unit 50 (CPU 52) of the image forming apparatus 100 implements the processing shown in the flowchart shown below by executing the software read from the ROM 254. In the following, only the contents of the subroutine are different from the flowchart shown in FIG. 9 and the other contents are common, so only the subroutine will be described.

  In step S100 illustrated in FIG. 9, when the job is transmitted, the control unit 50 executes a conveyance roller pair control process. In the present embodiment, the conveyance roller pair control process is a process of changing the conveyance roller pair to be swung according to the conveyance path (paper feeding method). FIG. 13 is a subroutine of the conveyance roller pair selection process.

  In step S300, the control unit 50 determines whether or not the paper P feeding method is set to alternate circulation paper feeding. If the control unit 50 determines that the paper P feeding method is alternating circulation paper feeding, the control unit 50 proceeds to step S310.

  In step S <b> 310, the control unit 50 selects the two registration roller pairs 200 and the ADU transport roller pair 300 as transport roller pairs that swing during double-sided printing. The loop roller pair 240 is not a swing target. Further, the control unit 50 selects the registration roller pair 200 and the loop roller pair 240 as the conveyance roller pair that swings during single-sided printing. When step S310 ends, the subroutine ends and the process proceeds to step S110 shown in FIG.

  On the other hand, when the control unit 50 determines that the alternating circulation sheet feeding is not set as the sheet feeding method, the process proceeds to step S320. In step S320, the control unit 50 selects the three registration roller pairs 200, the loop roller pair 240, and the ADU transport roller pair 300 as the transport roller pairs that swing during double-sided printing. Further, the control unit 50 selects the registration roller pair 200 and the loop roller pair 240 as the conveyance roller pair that swings during single-sided printing. When step S310 ends, the subroutine ends and the process proceeds to step S110 shown in FIG.

  In the second embodiment, the function of selecting a pair of conveyance rollers according to the paper size and paper type described in the first embodiment can be combined. For example, when the paper P is thin and A4 size during duplex printing, the paper P is swung only by one registration roller pair 200 without swinging the ADU transport roller pair 300. Also good.

  As described above, according to the second embodiment, in the case of alternating circulation feeding, control is performed so that the loop roller pair 240 does not swing during double-sided conveyance. Compared with the case of moving, it is possible to shorten the interval between the next paper P to be conveyed on one side only by the swing time for the loop roller pair 240 to return to the home position after swinging.

<Third Embodiment>
The third embodiment is different from the first and second embodiments in that the conveyance roller pair can be moved according to the paper size. Since the other configurations and operations of the image forming apparatus 100 are the same as those in the first embodiment, common constituent elements are denoted by the same reference numerals, and detailed description thereof is omitted.

[When sliding the transport roller pair according to the paper size]
Conventionally, for example, the position of the loop roller pair 240 or the like is fixed, but there are cases where the paper cannot be clamped at an optimal position depending on the paper size. In this case, if the misalignment correction is performed, the paper may be bent. Therefore, in the third embodiment, the conveyance roller pair provided on the upstream side of the registration roller pair 200 in the paper conveyance direction D1 is configured to be slidable in the paper conveyance direction D1 or in the opposite direction.

  FIGS. 14A to 14C are diagrams for explaining the deviation correction in the case where the loop roller pair 240 is moved to the optimum position according to the paper size. In FIG. 14, in the paper width direction D2, the front side of the paper is called the front side of the apparatus, and the back side of the paper is called the back side of the apparatus. In the following, the loop roller pair 240 is exemplified as the slidable transport roller pair, but the present invention is not limited to this, and if the upstream side in the paper transport direction D1 with respect to the registration roller pair 200, the ADU is used. The present invention can also be applied to a transport roller pair such as the transport roller pair 300.

  As shown in FIG. 14A, the loop roller pair 240 is disposed on the upstream side of the registration roller pair 200 in the paper transport direction D1. In the present embodiment, the position where the loop roller pair 240 of FIG. The loop roller pair 240 is configured to be movable in the paper transport direction D1 or in the opposite direction by a moving mechanism (adjustment unit) including a motor, a gear, and the like not shown. Since a known technique can be adopted for the moving mechanism, a detailed description of the moving mechanism is omitted.

  When the rear end portion of the paper P is positioned at the installation position of the loop roller pair 240, the front end portion of the paper P is sandwiched between the registration roller pair 200, and the rear end portion of the paper P is sandwiched between the loop roller pair 240. In this case, it is not necessary to move the loop roller pair 240. Therefore, the deviation correction is performed without sliding the loop roller pair 240.

  As shown in FIGS. 14B and 14C, the paper size is large (long in the paper transport direction D1), and the position where the paper P is sandwiched by the loop roller pair 240 does not become the rear end portion of the paper P, for example. In this case, the loop roller pair 240 is slid to the upstream side in the paper transport direction D1. As a result, the paper P can be clamped at an optimum position, and the paper can be prevented from being bent during conveyance.

[Operation Example of Image Forming Apparatus 100]
FIG. 15 is a flowchart illustrating an example of the operation of the image forming apparatus 100 according to the third embodiment. The control unit 50 (CPU 52) of the image forming apparatus 100 implements the processing shown in the flowchart shown below by executing the software read from the ROM 254. In the following, only the contents of the subroutine are different from the flowchart shown in FIG. 9 and the other contents are common, so only the subroutine will be described.

  In step S100 illustrated in FIG. 15, when the job is transmitted, the control unit 50 executes a conveyance roller pair control process. In the present embodiment, the transport roller pair control process is a process of moving the transport roller pair to be swung to an optimal position according to the paper size. FIG. 15 is a subroutine of the conveyance roller pair control process.

  As shown in FIG. 15, in step S <b> 400, the control unit 50 determines the trailing edge of the paper P when the leading edge of the paper P is sandwiched by the registration roller pair 200 based on the paper size of the image forming condition included in the job. Calculate the position. For the position of the trailing edge of the paper P, a table in which the paper size is associated with the position of the trailing edge of the paper P is prepared in advance, and when the paper size is input, the table corresponds to the paper size. The position of the trailing edge of the sheet P may be read out. When step S400 ends, the process proceeds to step S410.

  In step S <b> 410, the control unit 50 determines whether or not the upstream-side transport roller pair that sandwiches the rear end portion of the paper P is in the optimum position. For example, when the upstream conveying roller pair is the loop roller pair 240, the control unit 50 compares the installation position of the loop roller pair 240 acquired in advance with the calculated position of the rear end of the paper P, Judgment is made based on whether the comparison result exceeds a preset allowable range. Further, when the control unit 50 determines that the upstream transport roller pair is at the optimum position, it is not necessary to move the upstream transport roller pair, so the subroutine is terminated and the process proceeds to step S110 shown in FIG. move on.

  On the other hand, when the control unit 50 determines that the upstream conveying roller pair is not at the optimum position, the control unit 50 proceeds to step S420. In step S420, the control unit 50 controls the moving mechanism to move the loop roller pair 240 to the position corresponding to the rear end portion of the paper P along the paper transport direction D1 or the opposite direction. When step S420 ends, the subroutine ends and the process proceeds to step S110 shown in FIG.

  When performing misalignment correction, the registration roller pair 200 and the conveyance roller pair are moved at the same timing, in the same swinging direction, and in the same movement while the sheet P is sandwiched between the registration roller pair 200 and the moved upstream conveyance roller pair. Swing with the amount. When the upstream conveying roller pair is not moved, the normal deviation correction as described above is performed. In the third embodiment, the function of selecting a pair of transport rollers according to the paper size and paper type described in the first embodiment can also be combined.

  As described above, according to the third embodiment, the registration roller pair 200 is configured to be slidable in the paper transport direction D1 or in the opposite direction according to the paper size. It can be held by a pair of conveying rollers such as the loop roller pair 240, and the occurrence of paper bending and wrinkles during swinging can be reliably prevented.

  It should be noted that the technical scope of the present invention is not limited to the above-described embodiments, and includes those in which various modifications are made to the above-described embodiments without departing from the spirit of the present invention. Although the image forming apparatus 100 shown in FIG. 1 forms a color image, the present invention is not limited to an image forming apparatus that forms a color image, but can be applied to an image forming apparatus that forms a monochrome image.

50 Control unit 200 Registration roller pair (first transport roller pair)
220 Registration roller swinging part (first moving part)
230 Registration roller pressure release part (first transport pressure adjustment part)
240 Loop roller pair (second transport roller pair)
260 Loop roller swinging part (second moving part)
270 Loop roller pressure release part (second transport pressure adjustment part)
280 Offset sensor (detector)
300 ADU transport roller pair (second transport roller pair)
320 ADU transport roller swinging part (second moving part)
330 ADU transport roller pressure release part (second transport pressure adjustment part)

Claims (8)

A first pair of transport rollers;
A first moving unit configured to move in a second direction perpendicular to the first direction of the paper conveyance direction in a state where the paper is sandwiched by the first conveyance roller pair;
At least one or more second transport roller pairs provided upstream of the first transport roller pair in the paper transport direction;
A second moving unit configured to move in the second direction in a state where the sheet is sandwiched between the second conveying roller pair;
A detection unit that is provided downstream of the first transport roller pair in the paper transport direction and detects a shift of the paper;
A control unit that corrects the deviation of the sheet based on the amount of deviation of the sheet detected by the detection unit,
The control unit controls the first and second moving units to move the first and second transport roller pairs at the same timing, in the same direction, and with the same movement amount during the deviation correction. An image forming apparatus. 2. The image formation according to claim 1, wherein the control unit selects the second transport roller pair to be moved at the time of the deviation correction based on at least one condition of a paper type and a paper size. apparatus. When the paper size is less than a predetermined size and the paper thickness is less than a predetermined value, the control unit selects only the first transport roller pair, and the paper size is equal to or larger than the predetermined size. The image forming apparatus according to claim 2, wherein when the thickness of the sheet is equal to or greater than the predetermined value, the first and second transport roller pairs are selected. The image forming apparatus according to claim 1, wherein the control unit selects the second transport roller pair to be moved at the time of the deviation correction according to a transport path of the sheet. An adjustment unit capable of moving the second conveyance roller pair in a paper conveyance direction or in a direction opposite to the direction;
The control unit controls the adjustment unit to move the second transport roller pair to the predetermined position when the sheet cannot be clamped at the predetermined position by the second transport roller pair. Item 5. The image forming apparatus according to any one of Items 1 to 4. A first transport pressure adjusting unit for adjusting the transport pressure of the first transport roller pair;
A second transport pressure adjusting unit that adjusts the transport pressure of the second transport roller pair,
The control unit controls at least one of the first and second transport pressure adjusting units to adjust the pressure of the first transport roller pair or the second transport roller pair according to the paper type. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The controller adjusts the transport pressure of at least one of the first and second transport roller pairs according to the distance between the first transport roller pair and the second transport roller pair. The image forming apparatus according to claim 6. When the deviation amount of the sheet detected by the detection unit exceeds the maximum movable range in at least one of the first and second moving units, the control unit includes a plurality of first and second transport roller pairs. The image forming apparatus according to claim 1, wherein the image forming apparatus is moved in divided steps.

Images