JP2011248256A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a situation in which a movement of a registration roller exceeds a movable limit, and prevent reduction in productivity of image forming operation and a cost increase.SOLUTION: An image forming apparatus comprises an image forming part, a registration roller 32, a shift sensor 34, a registration roller position detection sensor 37, and a CPU 51. The CPU 51 carries out: executing a side-shift correction for the sheet P by moving the registration roller 32 to a first direction while holding the sheet P based on a side-edge position of the sheet P detected by the shift sensor 34; changing a setting of the image writing position to be performed by the image forming part 20 so that the registration roller 32 is moved in a second direction opposite to the direction in which the registration roller 32 has moved, if the position of the registration roller 32 is determined to have reached a predefined position after the side-shift correction; and causing the registration roller 32 to be moved in the second direction while holding the sheet P and causing an image to be formed on the sheep P at the image writing position that has been changed.

Description

  The present invention relates to an image forming apparatus.

  In the image forming apparatus, a latent image is written on an image carrier by an LD (Laser Diode) based on image data, developed with toner, and the obtained toner image is directly or via an intermediate transfer member. The image is formed by transferring to The paper is provided in a paper feed tray inside or outside the image forming apparatus, and the paper is transported for image formation.

  When transporting paper, the paper may be displaced in a direction orthogonal to the paper transport direction. For this reason, if an image is formed as it is, an image with poor positional accuracy is formed. In order to prevent this, a method for detecting the edge position of the paper in the main scanning direction in the middle of the conveyance by the offset sensor to obtain the deviation amount of the paper, and correcting the position for image formation based on the deviation amount of the paper It has been known.

  FIG. 6 is a diagram illustrating an example in which the deviation amount of the sheet is detected by the offset sensor. FIG. 6A is a diagram illustrating a state before a sheet conveyed in a direction perpendicular to the sheet conveyance direction, that is, a state shifted in the main scanning direction, is nipped by a registration roller. Here, the sheet center position indicates the position of the sheet when the center position of the sheet in the main scanning direction matches the mechanical center position of the sheet transport path. The paper offset correction range indicates a range in which the paper offset (displacement) in the main scanning direction can be corrected.

  As shown in FIG. 6A, when the sheet is shifted by 2.5 mm to the right with respect to the center position of the sheet and nipped by the registration roller, the position of the end of the sheet is detected by the offset sensor. Thereby, the offset detection amount 2.5 mm indicating the offset value of the sheet is calculated.

Then, as shown in FIG. 6B, the registration roller moves to the left by 2.5 mm based on the offset detection amount of 2.5 mm. As a result, the sheet shifts to the normal position, that is, the sheet center position.

  At this time, if the interval between the conveyed sheets is short, the next sheet immediately enters the registration roller. For this reason, the registration roller cannot be returned to the HP (home position) position. The HP position of the registration roller refers to the position of the registration roller when the mechanical center position of the registration roller in the main scanning direction matches the mechanical center position of the conveyance path.

  When the registration roller cannot be returned to the HP position, as shown in FIG. 6B, the edge position of the sheet is detected by the offset sensor with the registration roller displaced 2.5 mm to the left. At this time, if the next sheet is also moved 2.5 mm to the right from the center position of the sheet, as shown in FIG. 6C, the registration roller further moves 2.5 mm to the left from the state of FIG. 6B. . If the movement of the registration roller as shown in FIGS. 6B and 6C continues, the movement limit of the registration roller, that is, the movable range is exceeded, and the registration roller cannot be moved. For this reason, there has been a problem in that it is impossible to correct the misalignment of the sheet and the position accuracy of image formation cannot be improved.

  In view of this, there is known a method in which when the gap between the conveyed sheets is narrow, the gap is widened and the registration roller is returned to the HP position for each gap. In addition, when the movable range of the registration roller is wide, a method is also known in which the registration roller is returned to the HP position for each job from the end of the job to the start of the next job. Further, by providing a timing roller between the registration roller and the transfer unit, the sheet is transferred from the registration roller to the timing roller, and after the transfer, the registration roller is separated while the timing roller is transporting the sheet. A method of returning to a position is also known.

  Also, a correction amount of the image forming position with respect to the paper is obtained, the registration roller is moved by the difference between the correction amount and the deviation amount of the paper, and the image forming position is corrected based on the correction amount. A technique for aligning with accuracy is also known (see, for example, Patent Document 1).

JP 2009-143643 A

  However, the technique of returning the registration roller to the HP position for every sheet or every job has a problem that the productivity of the image forming operation is lowered. Further, in the technology for returning the registration roller to the HP position while the timing roller is transporting the sheet, the timing roller must be prepared separately, which increases the cost. Further, Patent Document 1 does not describe a technique for preventing the movement of the registration roller from exceeding the movable range.

  An object of the present invention is to prevent the movement of a registration roller from exceeding a movable range, and prevent a decrease in productivity and an increase in cost of an image forming operation.

In order to solve the above-described problem, an image forming apparatus according to claim 1 is provided.
An image forming unit for forming an image on paper;
A swinging roller movable along the main scanning direction while sandwiching a sheet in the middle of conveyance in preparation for the image formation;
A first detection unit that detects an end position in a main scanning direction of a sheet being conveyed in preparation for the image formation;
A second detector for detecting a position of the swing roller in the main scanning direction;
Based on the edge position of the paper detected by the first detection unit, the paper roller is moved in the first direction while sandwiching the paper to execute the paper offset correction, and the offset correction is executed. Later, when it is determined that the position of the swing roller detected by the second detection unit has reached a predetermined position, the swing roller is moved in a second direction opposite to the first direction. The image forming position of the image forming unit is changed so as to cause the image forming unit to move the swing roller in the second direction while sandwiching the paper, and the image is changed according to the changed writing position on the paper. A control unit for executing the formation;
Is provided.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
The predetermined position is
The position is within a movable range of the swing roller.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect,
The controller is
When the predetermined position is a limit position where the swing roller is movable, and the swing roller moves in the first direction and reaches the limit position, the swing position in the second direction. An image writing position by the image forming unit is changed to move the moving roller.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects,
The controller is
When the position of the swing roller in the main scanning direction returns to the center position of the moving range, the image writing position by the image forming unit is returned to the default position.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects,
The range in which the setting of the writing position of the image by the image forming unit can be changed is
This is beyond the possible range of paper offset correction.

  According to the present invention, it is possible to prevent the movement of the registration roller from exceeding the movable range, and it is possible to prevent a decrease in productivity and an increase in cost of the image forming operation.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present invention. It is a figure which shows a loop roller and a registration roller. FIG. 2 is a control block diagram of the image forming apparatus. It is the figure which showed the flow of control which concerns on this invention. It is a flowchart which shows a correction process. It is the figure which showed an example of the prior art which detects the deviation | shift amount of a sheet | seat with a offset sensor.

  Embodiments according to the present invention will be described below in detail with reference to the accompanying drawings. However, the scope of the invention is not limited to the illustrated examples.

  First, a schematic cross-sectional configuration diagram of the image forming apparatus 1 will be described with reference to FIG. The image forming apparatus 1 includes a copy function for reading an image from a document, forming the read image on paper P, and outputting it, page data including image data from an external device or the like, image forming conditions for each image data, and the like. It has a print function for receiving job job data, forming an image on paper P based on the received job data, and outputting the image. As shown in FIG. 1, the image forming apparatus 1 includes an image reading unit 10, an image forming unit 20, a paper feeding unit 25, and a conveyance unit 30.

  The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder) and a reading unit 12. The document d placed on the document tray of the automatic document feeder 11 is conveyed to a contact glass which is a reading location, an image on one or both sides of the document d is read by an optical system, and the document is scanned by a CCD (Charge Coupled Device). The image of d is read. Here, the image includes not only image data such as graphics and photographs but also text data such as characters and symbols.

An image (analog image signal) read by the image reading unit 10 is a CPU 51 described later.
3) and after various image processing such as analog processing, A / D conversion processing, shading correction, image compression processing, etc., Y (yellow), M (magenta), C (cyan), K (Black) is separated into colors and output to the image forming unit 20 as digital image data.

  The image forming unit 20 performs electrophotographic image forming processing based on the input image data. The image forming unit 20 includes exposure units 2Y, 2M, 2C, and 2K, developing units 3Y, 3M, 3C, and 3K, photosensitive drums 4Y, 4M, 4C, and 4K, and charging units 5Y, 5M, 5C, and 5K. , Cleaning units 6Y, 6M, 6C and 6K, primary transfer rollers 7Y, 7M, 7C and 7K, an intermediate transfer belt 8, a belt cleaning unit 9, a secondary transfer roller 21 and a fixing unit 22. Configured.

  The exposure units 2Y, 2M, 2C, and 2K include a laser light source such as an LD, a polygon mirror, and a plurality of lenses. The exposure units 2Y, 2M, 2C, and 2K scan and expose the surfaces of the photosensitive drums 4Y, 4M, 4C, and 4K with a laser beam based on image data sent from the CPU 51. By this laser beam scanning exposure, latent images are formed, that is, images are written at the image forming positions of the photosensitive drums 4Y, 4M, 4C, and 4K charged by the charging units 5Y, 5M, 5C, and 5K. The image forming positions of the photoconductor drums 4Y, 4M, 4C, and 4K are positions where a latent image is formed on the photoconductor drum. Hereinafter, the image forming position is referred to as an image writing position. Further, the image writing is executed based on an instruction from the CPU 51 for the start timing of image writing in the main scanning direction and the sub-scanning direction. Hereinafter, in the present embodiment, image writing in the main scanning direction will be described.

  The latent images formed on the photoconductive drums 4Y, 4M, 4C, and 4K are visualized by development by the corresponding developing units 3Y, 3M, 3C, and 3K, and are formed on the photoconductive drums 4Y, 4M, 4C, and 4K. A toner image is formed on.

  The toner images formed and carried on the photosensitive drums 4Y, 4M, 4C, and 4K are sequentially transferred to a predetermined position on the intermediate transfer belt 8 by the primary transfer rollers 7Y, 7M, 7C, and 7K, and are primarily transferred. .

  Residual toner is removed from the surfaces of the photosensitive drums 4Y, 4M, 4C, and 4K after the transfer of the toner image by the cleaning units 6Y, 6M, 6C, and 6K.

The intermediate transfer belt 8 is a semiconductive endless belt that is suspended and supported rotatably by a plurality of rollers, and is driven to rotate as the rollers rotate.
The intermediate transfer belt 8 is pressure-bonded to the respective photosensitive drums 4Y, 4M, 4C, and 4K by primary transfer rollers 7Y, 7M, 7C, and 7K. As a result, the toner developed on the surfaces of the photosensitive drums 4Y, 4M, 4C, and 4K is transferred (primary transfer) to the intermediate transfer belt 8 at the transfer positions by the primary transfer rollers 7Y, 7M, 7C, and 7K. At the transfer position by the secondary transfer roller 21, yellow, magenta, cyan, and black toners are sequentially transferred onto the paper P and transferred (secondary transfer). The intermediate transfer belt 8 transfers the toner image onto the paper P by the secondary transfer roller 21 and then separates the paper P from the curvature and electrostatically, and the residual toner is removed by the belt cleaning unit 9.

  The fixing unit 22 thermally fixes the toner image transferred onto the paper P. As a result, the toner image is fixed on the paper P and an image is formed. The paper P that has been subjected to the fixing process by the fixing unit 22 is discharged to the paper discharge tray 91.

  That is, image formation by the image forming unit 20 is a series of operations including an operation of forming latent images at the image writing positions of the photosensitive drums 4Y, 4M, 4C, and 4K by the exposure units 2Y, 2M, 2C, and 2K. That means. Specifically, the image formation by the image forming unit 20 is formed by forming latent images at the image writing positions of the photosensitive drums 4Y, 4M, 4C, and 4K by the exposure units 2Y, 2M, 2C, and 2K. This means a series of operations in which the toner image with the toner attached to the latent image is transferred to the intermediate transfer belt 8 and further transferred onto the paper P, and the toner image on the paper P is thermally fixed by the fixing unit 22.

  The paper feed unit 25 includes a plurality of paper feed trays 25a, 25b, and 25c and a paper feed unit 25d. In the paper feed trays 25a, 25b, and 25c, paper P such as standard paper and special paper such as tab paper and cutting paper identified based on the amount and size of the paper is stored for each preset type. Yes. The paper feed unit 25d feeds the paper P stored in each paper feed tray one by one from the top toward the transport unit 30.

  The transport unit 30 includes a transport roller mechanism for transporting the paper P fed from the paper feed unit 25 and a transport path that is a transport path of the paper P. The transport unit 30 includes a loop roller 31 and a registration roller 32 as a transport roller mechanism for transporting the paper P.

  Here, with reference to FIG. 2, the loop roller 31 and the registration roller 32 as a rocking roller will be described. Here, it is assumed that the transport direction of the paper P is from the bottom to the top of the paper (see the paper transport direction in FIG. 2).

  The loop roller 31 is rotationally driven by driving a loop roller driving unit 36 (see FIG. 3). The loop roller 31 has a function of correcting the bending of the paper P. Specifically, when the paper P passes through the loop roller 31, it strikes against the resist roller 32 in a stopped state. Then, when the paper P is further conveyed by the loop roller 31 from the state in which the paper P hits the registration roller 32, the paper P is bent and the bending is corrected.

  The registration roller 32 swings in the main scanning direction by driving a registration roller swing driving unit 33 (see FIG. 3) while sandwiching a sheet in the middle of conveyance in preparation for image formation. The main scanning direction refers to a direction orthogonal to the paper transport direction. The swinging means that the registration roller 32 reciprocates along the main scanning direction. Hereinafter, in the present embodiment, the movement of the registration roller 32 in one direction in the main scanning direction is referred to as movement in the main scanning direction. The registration roller 32 is driven to rotate by driving a registration roller rotation driving unit 35 (see FIG. 3).

  Further, as shown in FIG. 2, the offset sensor 34 is disposed immediately after the registration roller 32. The offset sensor 34 as the first detection unit includes a light emitting element composed of a light emitting diode array, and a light receiving element composed of a line CCD arranged at a position sandwiching the conveyance path or a position where light reflected by the paper P is received. The sheet P passing through, that is, the edge in the main scanning direction of the sheet P being conveyed is detected in preparation for image formation. It is possible to calculate the edge position of the paper P from the light receiving position by the light receiving element in the edge detection and the reference position of the transport path. The reference position of the conveyance path refers to the mechanical center position of the conveyance path. Since the paper P is normally conveyed so that the center of the paper is at the reference position, a reference position (edge reference position) of the edge of the paper P is assumed for each size, and the detected edge position of the paper and The difference in distance from the edge reference position is calculated as the amount of paper deviation.

  Next, a control block diagram of the image forming apparatus 1 will be described with reference to FIG. As shown in FIG. 3, the image forming apparatus 1 includes a control unit 50, an image forming unit 20, a offset sensor 34, a registration roller swing driving unit 33, a registration roller 32, and a registration roller rotation driving unit 35. , A loop roller driving unit 36, a loop roller 31, and a registration roller position detection sensor 37 as a second detection unit. In the following description, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals, the detailed description thereof is used, and different parts are mainly described.

  The control unit 50 includes a CPU (Central Processing Unit) 51, a ROM (Read Only Memory) 52, and a RAM (Random Access Memory) 53.

  The CPU 51 reads a specified program from the system programs and various application programs stored in the ROM 53, expands them in the RAM 52, executes various processes in cooperation with the programs expanded in the RAM 52, and forms an image. Centralized control of each part of the apparatus 1 is performed.

  Specifically, the CPU 51 moves the registration roller 32 in the first direction (for example, left shown in FIG. 5B) while holding the paper P based on the edge position of the paper P detected by the offset sensor 34. ) To perform the paper offset correction. When the CPU 51 determines that the position of the registration roller 32 detected by the registration roller position detection sensor 37 has reached a predetermined position after performing the offset correction, the CPU 51 reverses the direction in which the registration roller 32 has moved. The image writing position by the image forming unit 20 is changed so that the registration roller 32 is moved in the second direction (for example, the right direction shown in FIG. 5C). Then, the CPU 51 moves the registration roller 32 in the second direction while sandwiching the paper P, and executes image formation at the image writing position whose setting has been changed with respect to the paper P.

  The ROM 52 stores various programs executed by the CPU 51. The RAM 53 is a volatile memory, has a work area for storing various programs executed by the CPU 51, data related to these various programs, and the like, and temporarily stores the information.

  The registration roller swing drive unit 33 is a drive unit that drives the registration roller 32 in the main scanning direction. The registration roller swing drive unit 33 is configured by, for example, a pulse motor. The registration roller rotation drive unit 35 is a drive unit that rotates the registration roller. The loop roller driving unit 36 is a driving unit that rotationally drives the loop roller.

The registration roller position detection sensor 37 is a photosensor that optically detects the position of the registration roller 32 in the main scanning direction. Specifically, the registration roller position detection sensor 37 includes a light emitting element and a light receiving element, both of which are arranged so as to sandwich the registration roller 32 or a part thereof, and the registration roller 32 that passes between the two. The position of the registration roller 32 in the main scanning direction is detected on the basis of the light detection pattern corresponding to the position.
Alternatively, the current position of the registration roller 32 may be detected by counting the number of drive pulses of the registration roller swing driving unit 33. For example, the current position of the registration roller may be detected by setting the number of drive pulses at the HP position of the registration roller 32 to 0 and counting the number of drive pulses at the current position.
Further, the current position of the registration roller 32 may be detected by measuring the driving time of the registration roller swing driving unit 33. For example, the current position of the registration roller 32 may be detected by measuring time information such as 0.1 seconds or 0.2 seconds as the drive time of the registration roller swing drive unit 33.

Next, the operation of the image forming apparatus 1 will be described with reference to FIGS. 4 and 5.
FIG. 4 is a diagram illustrating a control process executed by the image forming apparatus 1. In the control process, the image writing position is set in the direction opposite to the moving direction of the registration roller 32, the image writing to the set image writing position is executed, and the registration roller 32 is moved in the direction of the set image writing position. It is processing.

In the image forming apparatus 1, job execution is started in response to reception of an input operation for starting job execution or reception of a command for starting job execution from an external device, Assume that the sheet P is being fed from the section 25.
Further, it is assumed that the paper P is transported in a state shifted from the central position of the paper, that is, offset. This deviation of the paper P is, for example, when the mechanical position of the paper feed tray is deviated from the normal position, when there is nip nonuniformity in the conveyance roller mechanism, or the position of the conveyance roller mechanism. This occurs when there is a difference in accuracy.

  First, the sheet P is nipped by the registration roller 32 in a state where the sheet P is offset (step S1). For example, as shown in FIG. 5A, the sheet P is nipped by the registration roller 32 in a state of being shifted to the right by 2.5 mm with respect to the center position of the sheet. Here, FIG. 5A is the same diagram as FIG. The sheet center position and the sheet offset correction range are the same as those described with reference to FIG. Hereinafter, a different part from FIG. 6A in FIG. 5A will be mainly described.

  The movable range refers to a range in which the registration roller 32 can move in the main scanning direction from the HP position. That is, the registration roller 32 moves in the main scanning direction with reference to the HP position that is the center position of the movable range. Hereinafter, the movable range is ± 10 mm in the main scanning direction with the HP position of the registration roller 32 as a reference. For example, as shown in FIG. 5A, if the registration roller 32 is at the HP position and the left direction on the paper is + and the right direction is −, the range of +10 mm and −10 mm from the HP position of the registration roller 32 is movable. Corresponds to the range.

  The image writing position changeable range refers to a range in which the setting of the image writing position in the main scanning direction can be changed. The image writing position changeable range is a range that is not less than the paper offset correction range and is within the movable range. For example, as shown in FIG. 5A, when the paper offset correction range is ± 5 mm in the main scanning direction from the paper center position, the image writing position changeable range is a range of ± 5 mm or more and ± 10 mm or less.

  Also, the paper center position and the default position for image writing coincide. The default position for image writing refers to an initial setting value set in advance as the image writing position.

  Returning to FIG. 4, after execution of step S1, the paper P is conveyed by the registration rollers 32 (step S2). After execution of step S2, the edge position of the paper is detected by the offset sensor 34, and based on the detected edge position, the CPU 51 calculates the amount and direction of deviation of the paper with respect to the paper center position (step S3). . For example, in the case of FIG. 5A, the edge position of the paper P is detected by the offset sensor 34, and based on the detected edge position of the paper P, the CPU 51 sets the amount of deviation of the paper from the paper center position to 2. .5 mm, and the deviation direction of the paper is calculated as right.

  After the execution of step S3, the registration roller 32 is moved based on the calculated sheet shift amount and direction (step S4). Specifically, a drive command including a movement amount and a direction for moving the registration roller 32 is transmitted from the CPU 51 to the registration roller swing drive unit 33 based on the deviation amount and direction of the paper, and based on the drive command. Thus, the registration roller 32 is moved. For example, if it is calculated in step S3 that the sheet displacement amount is 2.5 mm and the sheet displacement direction is right, a drive command for moving the registration roller 32 to the left by 2.5 mm in order to correct the sheet displacement. Is transmitted from the CPU 51 to the registration roller swing drive unit 33. Then, based on the drive command, the registration roller 32 moves to the left by 2.5 mm. At this time, the registration roller 32 moves 2.5 mm to the left while sandwiching the paper P. As a result, the position of the sheet P is corrected to the center position of the sheet.

  After execution of step S4, the position of the registration roller 32 is detected by the registration roller position detection sensor 37 based on an instruction from the CPU 51. Then, the CPU 51 determines whether or not the position of the registration roller 32 is a predetermined position, that is, whether or not the predetermined position has been reached (step S5). The predetermined position refers to a position of the registration roller 32 that does not exceed the movable range of the registration roller 32 in the main scanning direction, that is, the movable range. For this reason, the predetermined position is always within the movable range (within ± 10 mm) of the registration roller 32. For example, in the case of FIG. 5B, the predetermined position is ± 2.5 mm. The predetermined position is set by the user.

  Note that the user may set a predetermined range instead of the predetermined position. The predetermined range refers to an arbitrary range that does not exceed the movable range of the registration roller 32. For example, when a range of ± 2.5 mm to ± 10 mm is set as the predetermined range, when the position of the registration roller 32 reaches ± 2.5 mm, YES is determined in step S5. That is, when the registration roller 32 reaches the minimum position (± 2.5 mm) in the predetermined range, “YES” is determined in the step S5.

  In step S5, when it is determined that the position of the registration roller 32 is a predetermined position (step S5; YES), in order to prevent the registration roller 32 from moving too much in one direction and correcting the deviation of the sheet. The CPU 51 sets the image writing position opposite to the direction of the registration roller 32 (step S6).

  Here, the operation of step S6 will be described with reference to FIGS. FIG. 5B is a diagram showing that the registration roller 32 has moved to the left in the main scanning direction from the state of FIG. In this case, since the shift direction (movement direction) of the registration roller 32 is the left direction, the image writing position is set by the CPU 51 in the right direction, which is the opposite direction to the left direction. Specifically, the image writing position is set to the limit position of the sheet offset correction range. For example, as shown in FIG. 5B, when the registration roller 32 moves in the left direction, the image writing position is set at the limit position of the right-side sheet offset correction range that is opposite to the left direction.

  Then, image writing to the set image writing position is performed. Specifically, the CPU 51 sets the image writing timing in the main scanning direction based on the image writing position. Then, the CPU 51 outputs a command to execute image writing at the set image writing timing to the exposure units 2Y, 2M, 2C, and 2K of the image forming unit 20. Based on the command, a laser beam is output from the exposure units 2Y, 2M, 2C, and 2K, and the laser beam scans and exposes the surfaces of the photosensitive drums 4Y, 4M, 4C, and 4K, thereby forming a latent image. That is, image writing is executed.

  After the image writing is executed, development by the developing units 3Y, 3M, 3C, and 3K, primary transfer onto the intermediate transfer belt 8, and secondary transfer onto the paper P by the secondary transfer roller 21 are executed. For this reason, a certain time lag occurs after the image writing position is set until the secondary transfer onto the paper P is executed. In order to take this time lag into account, a sheet that has been detected several times after the end of the sheet is detected and the image writing position is set (hereinafter referred to as the sheet on which the image writing position is set) is conveyed. Then, the movement control of the registration roller 32 is executed by the CPU 51.

  For example, when the paper size is A3, the paper transported at an interval from the paper on which the image writing position has been set (that is, transported next to the paper on which image writing has been set) The movement control of the registration roller 32 is executed for the sheet to be printed). When the paper size is A4, the movement control of the registration roller 32 is executed with respect to the paper that is conveyed at an interval of two sheets from the paper on which the image writing position has been set. It is assumed that the movement control timing of the registration roller 32 in consideration of this time lag is set in advance according to the paper size.

  FIG. 5C is a diagram showing that the position of the registration roller 32 has moved (shifted) to the right, which is the direction in which the image writing position is set. For example, if the paper size is A3 and the setting to the image writing position shown in FIG. 5B is executed, the paper conveyed by the registration roller 32 shown in FIG. ), The sheet is transported at an interval from the sheet on which the image writing position has been set.

  As shown in FIG. 5C, when the registration roller 32 moves 2.5 mm to the right, the position of the paper P moves to the right. At this time, the registration roller 32 executes the movement of 2.5 mm by one operation. Thereafter, the registration roller 32 moves to the HP position. When the registration roller 32 returns to the HP position, the CPU 51 sets the image writing position to the default position.

  Returning to FIG. 4, after execution of step S6, the process proceeds to step S1. If it is determined in step S5 that the position of the registration roller 32 is not the predetermined position (step S5; NO), it is determined whether or not the job is completed based on the job data of the job (step S7). If it is determined in step S7 that the job has not ended (step S7; NO), the process proceeds to step S1. If it is determined in step S7 that the job has ended (step S7; YES), the control process ends.

  As described above, according to the present embodiment, when it is determined that the position of the registration roller 32 has reached the predetermined position after the offset correction of the paper P, the reverse of the left direction shown in FIG. The image writing position by the image forming unit 20 is changed so that the registration roller 32 is moved in the right direction, the registration roller 32 is moved in the right direction while holding the paper, and the image whose setting is changed with respect to the paper P is changed. Image formation is executed according to the writing position. For this reason, it is possible to prevent the registration roller 32 from exceeding the movable range. In addition, by executing the control process, it is not necessary to return the registration roller 32 to the HP position between sheets or between jobs, and it is not necessary to provide the image forming apparatus 1 with a timing roller. For this reason, it is possible to prevent a decrease in productivity and an increase in cost of the image forming operation.

  Further, when the registration roller 32 returns to the HP position, the image writing position can be returned to the default position.

  Further, the control process can be executed under the condition that the image writing position changeable range is equal to or greater than the paper offset correction range (condition of image writing position changeable range ≧ paper offset correction range).

  In addition, if the deviation of the conveyed paper P is within the paper offset correction range, the registration roller 32 is moved and controlled regardless of the position within the paper offset correction range. The position of the paper P in the scanning direction can be corrected so as to coincide with the image writing position in the main scanning direction.

  Note that the description in the above embodiment is an example of the image forming apparatus according to the present invention, and the present invention is not limited to this.

  For example, in the above embodiment, the predetermined position is described as ± 2.5 mm. However, the present invention is not limited to this. For example, the predetermined position may be the limit position (± 10 mm) of the movable range of the registration roller 32. In this case, when the registration roller 32 reaches the limit position of the movable range, the image writing position is automatically set in the direction opposite to the moving direction of the registration roller 32, and the registration roller is set in the direction of the set image writing position. 32 moves.

  Further, for example, in FIG. 5B, the registration roller 32 is moved to the left side 5 mm which is the limit range of the paper correction range, and the image writing position is set to the right side 5 mm which is the limit range of the paper correction range. In this case, the registration roller 32 moves 10 mm to the right in one operation. As a result, even if the current position of the registration roller 32 and the image writing position are separated to some extent, the paper P can be moved to the image writing position while the paper P is conveyed by the registration roller 32.

  As described above, one or two sheets are spaced from the sheet on which the image writing position has been set depending on the time lag from when the image writing position is set to when the secondary transfer onto the sheet P is performed. The movement of the registration roller 32 is controlled with respect to the sheet conveyed. That is, one or two sheets are conveyed to the registration roller 32 from the sheet on which the image writing position is set to the sheet on which the movement control of the registration roller 32 is performed. In order to make sure that the registration roller 32 does not exceed the movable range while the one or two sheets are conveyed, the predetermined position or the predetermined range has a certain margin (a value larger than the movable range). It is desirable that the value be a small value.

  In addition, the detailed structure and detailed operation of the image forming apparatus in the present embodiment can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2Y, 2M, 2C, 2K Exposure unit 3Y, 3M, 3C, 3K Development unit 4Y, 4M, 4C, 4K Photosensitive drum 5Y Charging part 6Y Cleaning part 7Y Primary transfer roller 8 Intermediate transfer belt 9 Belt cleaning part DESCRIPTION OF SYMBOLS 10 Image reading part 11 Automatic document feeding part 12 Reading part 20 Image forming part 21 Secondary transfer roller 22 Fixing part 25 Paper feeding part 25a, 25b, 25c Paper feeding tray 25d Paper feeding means 30 Conveying part 31 Loop roller 32 Registration roller 33 Registration roller swing drive unit 34 Offset sensor 35 Registration roller rotation drive unit 36 Loop roller drive unit 37 Registration roller position detection sensor 50 Control unit

Claims (5)

An image forming unit for forming an image on paper;
A swinging roller movable along the main scanning direction while sandwiching a sheet in the middle of conveyance in preparation for the image formation;
A first detection unit that detects an end position in a main scanning direction of a sheet being conveyed in preparation for the image formation;
A second detector for detecting a position of the swing roller in the main scanning direction;
Based on the edge position of the paper detected by the first detection unit, the paper roller is moved in the first direction while sandwiching the paper to execute the paper offset correction, and the offset correction is executed. Later, when it is determined that the position of the swing roller detected by the second detection unit has reached a predetermined position, the swing roller is moved in a second direction opposite to the first direction. The image forming position of the image forming unit is changed so as to cause the image forming unit to move the swing roller in the second direction while sandwiching the paper, and the image is changed according to the changed writing position on the paper. A control unit for executing the formation;
An image forming apparatus comprising: The predetermined position is
The image forming apparatus according to claim 1, wherein the position is within a movable range of the swing roller. The controller is
When the predetermined position is a limit position where the swing roller is movable, and the swing roller moves in the first direction and reaches the limit position, the swing position in the second direction. The image forming apparatus according to claim 1, wherein an image writing position by the image forming unit is set and changed so as to move a moving roller. The controller is
4. The image formation according to claim 1, wherein when the position of the swing roller in the main scanning direction returns to the center position of the moving range, the image writing position by the image forming unit is returned to the default position. 5. apparatus. The range in which the setting of the writing position of the image by the image forming unit can be changed is
The image forming apparatus according to any one of claims 1 to 4, wherein the image forming apparatus is within a possible range of correction of the offset of the sheet.

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