JP2009282118A - Image forming apparatus, control method for image forming apparatus, and control program for the image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for appropriately aligning an image formed on paper. <P>SOLUTION: The image forming apparatus is equipped with a photoreceptor 4A for carrying an image to be transferred to the paper; a transfer belt 412A provided to be opposed to the photoreceptor 4A; a leading edge detection sensor 14A for detecting the conveyed state of the paper on an upstream side of a nip part between the photoreceptor 4A and the transfer belt 412A in a paper conveyance path; and a printing head 20, which serves as an image writing part for writing the image on the photoreceptor 4A, and starts to writing the image before detection by the leading edge detection sensor 14A. By moving the photoreceptor 4A positionally, based on the result of detection by the leading edge detection sensor 14A, the position of the nip part is corrected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, an image forming apparatus control method, and an image forming apparatus control program, and more particularly to an image forming apparatus capable of correcting a position at which an image is formed on a sheet, an image forming apparatus control method, and The present invention relates to a control program for an image forming apparatus.

  In an electrophotographic image forming apparatus (an MFP (Multi Function Peripheral), a facsimile apparatus, a copier, a printer, etc.) having a scanner function, a facsimile function, a copying function, a function as a printer, a data communication function, and a server function, Registration control for adjusting the printing position on the paper is performed. This is for maintaining a good positional relationship between the toner image and the paper in the image forming apparatus. In order to perform registration control, an image forming apparatus is known that includes a sensor that detects the leading edge of a sheet and a mechanism that detects the timing at which a toner image reaches a transfer point.

  Typical color printing methods include a 4-cycle method, an intermediate transfer tandem method using an intermediate transfer belt, and a direct transfer tandem method using a direct transfer belt. The apparatus has a transfer belt in the 4-cycle system and the intermediate transfer tandem system, and a paper transport belt in the direct transfer tandem system. Each of these belt units is a major part of the cost of the machine. In the process of cost reduction, it is necessary to supplement the role of these belts with the functions of other units.

  From such a point of view, a configuration called a tandem system (beltless tandem system) that does not use a belt can be considered. However, in the beltless tandem system, there are many problems regarding stabilizing the conveyance of the paper, and there is a concern that the image writing position deviation on the paper and the color deviation may be worsened.

  FIG. 6 is a diagram illustrating the configuration around the image forming unit in the first conventional image forming apparatus.

  The image forming unit of the image forming apparatus forms yellow (Y), magenta (M), cyan (C), and black (BK) toner images. The image forming unit is provided with image forming units 108A to 108D for each color. Image forming units 108 </ b> A to 108 </ b> D are arranged in the order of Y → M → C → BK from the upstream side in the sheet conveyance direction (left side in the drawing). The paper P is conveyed from the left side to the right side of the drawing. This image forming apparatus employs a belt-less tandem system that does not have a belt for conveying paper or an intermediate transfer belt.

  A timing sensor 113 that detects the leading edge of the paper P sent from the paper feeding unit is attached to the uppermost stream in the paper conveyance direction of the image forming unit.

  Each of the image forming units 108A to 108D includes photoreceptors (photoreceptor drums) 104A to 104D, transfer rollers 105A to 105D disposed relative to the photoreceptors 104A to 104D, photoreceptors 104A to 104D, and transfer roller 105A. Guide plates 109A to 109D for feeding paper to a nip portion that is in contact with .about.105D.

  Write positions LA to LD are formed above the respective photoreceptors 104A to 104D. After the paper P is detected by the timing sensor 113, an image is transferred to the writing positions LA to LD of the photoconductors 104A to 104D at the writing timing of the print heads (PH) corresponding to the photoconductors 104A to 104D after a predetermined time. Writing starts.

  Here, the timing at which writing is started at the writing position LA of the photosensitive member 104A is when the leading edge of the sheet reaches the position "A". The timing at which writing is started at the writing position LB of the photoconductor 104B is when the leading edge of the sheet comes to the position “B”. The timing at which writing is started at the writing position LC of the photosensitive member 104C is when the leading edge of the sheet comes to the "C" position. The timing at which writing is started at the writing position LD of the photosensitive member 104D is when the leading edge of the sheet comes to the "D" position.

  These timings are all determined based on the detection result of the timing sensor 113. That is, it is assumed that the conveyance speed of the paper P is constant, and writing is started at a timing when a predetermined time has elapsed after the timing sensor 113 detects the leading edge of the paper.

  Each photoconductor rotates at a predetermined speed in the direction of the arrow so that when the image at the writing position reaches the nip portion, the image forming position of the paper P is adjusted to reach the nip portion.

  FIG. 7 is a flowchart showing processing executed in the image forming apparatus of the first conventional example.

  The process of FIG. 7 is executed for each of the image forming units 108A to 108D. Here, processing for the image forming unit 108A will be described.

  Referring to the figure, the image forming apparatus waits until it detects that the leading edge of paper P conveyed from the paper supply unit has reached the position of timing sensor 113 (S301). When the sheet is detected by the timing sensor 113 (YES in S301), the image writing start timing in the image forming unit 108A is calculated (S302).

  When the timing set for the image forming unit 108A is reached, the writing of the image to the photosensitive member 104A is started (S303). The image is developed by a toner developing device (not shown). The toner image written on the photoconductor 104A is transferred to a sheet at the nip (S304).

  Similar processing is performed in each of the image forming units 108B to 108D.

  In this manner, the image forming timing for the downstream photoreceptor is determined based on the timing at which the sheet enters the image forming unit.

  FIG. 8 is a diagram for explaining the configuration around the image forming unit in the image forming apparatus of the second conventional example.

  Unlike the intermediate transfer belt method and the direct transfer method, the beltless tandem method conveys the sheet between the photosensitive member and the transfer roller. For this reason, there is a high possibility that the behavior of the paper becomes unstable. As a result, the timing and angle at which the sheet enters the nip portion changes, and there is a possibility that image misregistration or color misregistration occurs in the sub-scanning direction.

  The second conventional example is for alleviating such a problem, and is provided with leading edge detection sensors 214A to 214D for detecting the leading edge of the sheet upstream of each nip portion. The leading edge detection sensors 214 </ b> A to 214 </ b> D detect the timing when the sheet enters the nip portion.

  By disposing the leading edge detection sensor upstream of each photoconductor in this way, the time from paper detection by the timing sensor 113 to paper detection by each leading edge detection sensor is measured. By adjusting the writing timing of the print head after a certain time, the image writing position on the paper is adjusted.

  That is, by adjusting the positions of “A” to “D” in FIG. 6 forward and backward, writing is started earlier when the paper is transported earlier than scheduled, and writing timing is delayed when it is late.

  Further, after the pair of the most upstream photoconductor 104A and transfer roller 105A, the sheet moving time from the timing sensor 113 to each leading edge detection sensor may be measured, or from the upstream leading edge detection sensor to the next leading edge detection sensor. You may measure the movement time of the paper until.

  FIG. 9 is a flowchart showing processing executed in the image forming apparatus of the second conventional example.

  The process of FIG. 9 is executed for each of the image forming units 108A to 108D. Here, processing for the image forming unit 108A will be described.

  Referring to the drawing, the image forming apparatus waits until it detects that the leading edge of paper P conveyed from the paper feeding unit has reached the position of timing sensor 113 (S401). When the sheet is detected by the timing sensor 113 (YES in S401), it is next detected that the leading edge of the sheet has passed the position of the leading edge detection sensor 214A (S402).

  When the leading edge detection sensor 214A detects a sheet, it is determined whether the time from the detection of the timing sensor 213 to the detection of the leading edge detection sensor 214A (sensor ON timing) is appropriate (S403).

  If not appropriate (NO in S402), the amount of deviation between the paper and the image is calculated (S404). Based on the calculated shift amount, the timing for starting image writing in the image forming unit 108A is calculated (S405). If appropriate (YES in S402), image writing is performed at a normal timing on the assumption that no deviation occurs.

  When the predetermined timing set for the image forming unit 108A is reached (YES in S406), writing of an image on the photosensitive member 104A is started (S407). The image written on the photoconductor 104A is transferred to the paper at the nip (S408).

  Similar processing is performed in each of the image forming units 108B to 108D.

  In this manner, the sheet conveyance speed is calculated based on the timings detected by the timing sensor 113 and the leading edge detection sensors 214A to 214D. By correcting the image formation timing on the photoconductor according to the conveyance speed, it is possible to obtain an image with no positional deviation with respect to the paper.

  Patent Document 1 below discloses an image forming apparatus that detects the timing at which a sheet enters a photoreceptor based on a load variation of the photoreceptor driving member. Based on this entry timing, the image formation timing for the downstream photoreceptor is determined.

Patent Document 2 below discloses an image forming apparatus that detects the timing at which a sheet enters a plurality of transfer rollers based on fluctuations in transfer current. Based on the detection result, the sheet conveyance speed is calculated, and the image formation timing is corrected.
JP 2001-209224 A JP-A-2005-221622

  The conventional resist control method described above has the following problems.

  In the technique of the first conventional example, the image formation timing is determined based only on the output of the most upstream timing sensor, so that the positional deviation of the image in the sub-scanning direction may increase. In particular, in the beltless tandem system, deviation tends to occur.

  In the technology of the second conventional example, as a constraint condition, it is necessary that the leading edge detection sensor is positioned upstream from the leading edge position of the paper at the print head writing timing. That is, in FIG. 8, the position of the tip detection sensor 214A must be upstream of the position “A” (the same applies to other tip detection sensors). As a result, it is necessary to separate the positions of the photosensitive member and the tip detection sensor to some extent, which is an obstacle to downsizing the apparatus.

  Further, in order to employ the technique of Patent Document 1, the distance between the photoconductors is the distance from the image writing position on the photoconductor (the exposure position of the photoconductor) to the transfer point (nip portion) ( That is, it is necessary that the distance at which the image at the image writing position moves to the transfer point is longer. This is a limitation in downsizing the apparatus.

  According to the technique of Patent Document 2, the timing of image formation for subsequent printing or the next job can be corrected by calculating the conveyance speed. That is, it is possible to prevent image positional deviation and color misregistration by feeding back the calculated speed to subsequent prints. However, the correction can be made from the next print, and there is a problem that correction for the print cannot be performed during execution of one print.

  The present invention has been made to solve such a problem, and is capable of appropriately aligning an image formed on a sheet, an image forming apparatus control method, and an image forming apparatus. The purpose is to provide a control program.

  In order to achieve the above object, according to one aspect of the present invention, an image forming apparatus includes an image carrier that carries an image to be transferred to a paper, a transfer unit that is provided to face the image carrier, and a paper conveyance path. A detection unit for detecting the conveyance state of the sheet upstream of the nip portion of the image carrier and the transfer unit, and a writing unit for writing an image on the image carrier, before the detection by the detection unit And a correction unit that corrects the position of the image carrier based on the detection result of the detection unit.

  Preferably, the detection unit detects that the leading edge of the paper has arrived.

  Preferably, the image carrier is a photoconductor, and the transfer portion is a transfer belt.

  Preferably, the correction unit moves the image carrier about the writing position on the image carrier on which an image is written by the writing unit as the center of rotation.

  Preferably, the exposure incident angle from the writing unit to the image carrier is oblique incidence in the moving range of the image carrier moved by the correction unit.

  Preferably, the image carrier stops at a predetermined position based on the detection result of the detection unit.

  Preferably, the correction unit ends the movement of the image carrier before the sheet reaches the nip portion, and stops the image carrier while the transfer is performed in the nip portion.

  Preferably, after the position of the image carrier is corrected by the correction unit, the image carrier moves to a predetermined position until the detection unit detects the conveyance state of the next sheet.

  Preferably, a plurality of image carriers corresponding to each of a plurality of colors are provided, a plurality of transfer units corresponding to each of the plurality of image carriers are provided, and a detection unit includes a plurality of image carriers and A plurality of correction units are provided upstream of each nip portion of the plurality of transfer units, and the correction unit corrects the position of the nip portion based on the detection results of at least two detection units arranged upstream of the nip unit to be corrected. .

  According to another aspect of the present invention, an image carrier that carries an image to be transferred to a sheet, a transfer unit that is provided to face the image carrier, and a nip portion between the image carrier and the transfer unit in the sheet conveyance path. The control method of the image forming apparatus provided with the detection unit for detecting the conveyance state of the upstream sheet is a writing step for writing an image on the image carrier, and the image is detected before the detection by the detection unit. And a correction step of correcting the position of the image carrier based on the detection result of the detection unit.

  According to still another aspect of the present invention, an image carrier that carries an image to be transferred to a sheet, a transfer unit that is provided to face the image carrier, and a nip portion between the image carrier and the transfer unit in the sheet conveyance path. Is a writing step for writing an image on the image carrier before the detection by the detection unit. A computer executes a writing step for starting writing of an image and a correction step for correcting the position of the image carrier based on the detection result of the detection unit.

  According to these inventions, image writing is started before detection by the detection unit that detects the conveyance state of the sheet upstream of the nip portion of the image carrier and the transfer unit. The position of the image carrier is corrected based on the detection result of the detection unit. Accordingly, it is possible to provide an image forming apparatus, an image forming apparatus control method, and an image forming apparatus control program capable of appropriately aligning an image formed on a sheet.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described.

  The image forming apparatus is a tandem color printer that prints all colors of YMCK (yellow, magenta, cyan, black) in one cycle. In a tandem color printer, photoconductors of a plurality of colors are arranged in series. A color image is formed by sequentially transferring the toner images of the respective colors from the photoreceptor to the paper while the paper is being passed and conveyed.

  FIG. 1 is a diagram showing a hardware configuration of an image forming apparatus according to one embodiment of the present invention.

  Referring to the drawing, an image forming apparatus 1 includes a paper feed cassette 2, a paper feed unit 3, a Y color photoconductor 4A, an M color photoconductor 4B, a C color photoconductor 4C, and a K color photoconductor 4D. , Y color transfer unit 412A, M color transfer unit 412B, C color transfer unit 412C, K color transfer unit 412D, fixing unit 6, and paper discharge unit 7.

  The paper feed cassette 2 contains paper for forming an image. The presence or absence of paper is detected by a sensor. When the paper is not set or when the paper runs out during printing, the sensor detects the situation and notifies the user with a display panel or the like. In front of the paper feed cassette 2 (on the right side in the figure), a paper feed unit (conveyance roller) 3 for sending out the paper in the paper feed cassette 2 to the image forming unit (image writing unit) is provided. The image forming apparatus 1 includes a controller (image data processing unit) 51 including a CPU that controls the apparatus.

  The image forming apparatus 1 is used by being connected to a computer directly or via a network. Image data to be printed on paper is transferred from the computer to the controller 51 in the image forming apparatus. The image forming unit forms a latent image on the Y color photoconductor 4A based on the transferred image data. The developing unit forms an image on the Y-color photoconductor 4A with a developer according to the latent image. The image formed by the developer formed on the Y color photoreceptor 4A is transferred to the paper by the Y color transfer unit 412A. This sheet is the sheet in the sheet feeding cassette 2 sent out from the sheet feeding unit 3. The sheet is controlled by the sheet feeding unit 3 so that the position of the image with respect to the sheet is appropriate, and is conveyed to the Y color transfer unit 412A. Similarly, transfer processing by the M color photoconductor 4B and the M color transfer unit 412B, transfer processing by the C color photoconductor 4C and the C color transfer unit 412C, and transfer by the K color photoconductor 4D and the K color transfer unit 412D. Processing is performed for each color continuously. The sheet on which the developer has been transferred in each of the color transfer units 412A to 412D is sent to the fixing unit 6 where heat and pressure are applied. The developer on the paper passes through the fixing unit 6 and develops color as soon as it is fixed on the paper. Thereafter, the paper is discharged to the paper discharge unit 7. Thereby, the image formation is completed.

  The positions where the photoconductors 4A to 4D and the transfer units 412A to 412D are installed constitute the image forming unit 8.

  FIG. 2 is a side view showing the configuration of the image forming unit 8.

  The image forming unit 8 forms yellow (Y), magenta (M), cyan (C), and black (BK) toner images. In the image forming unit 8, image forming units 8A to 8D corresponding to the respective colors are provided. Image forming units 8A to 8D are arranged in the order of Y → M → C → BK from the upstream side of the sheet conveyance direction (left side in the drawing).

  The image forming unit 8A has the photosensitive member 4A, a charger for uniformly charging the photosensitive member 4A, an image writing unit for writing an image on the charged photosensitive member 4A, and the photosensitive member 4A. A developing device for developing the electrostatic latent image with Y-color toner, a transfer belt (transfer portion) 412A disposed relative to the photoreceptor 4A, and a cleaner for removing the toner remaining on the photoreceptor 4A , A guide plate 9A for feeding the paper P to the nip portion, which is a transfer point, and a leading edge detection sensor 14A.

  When the leading edge of the paper P reaches the position “A”, image writing (exposure) is started at the writing position LA of the photoreceptor 4A. The leading edge detection sensor 14A is disposed downstream of the leading edge position “A” of the sheet when image exposure is started on the photoreceptor 4A in the sheet conveyance direction.

  Since the conveyance speed of the paper and the moving speed of the surface of the photoconductor when the photoconductor rotates are usually equal, the distance between the position “A” and the nip portion of the photoconductor 4A downstream thereof is the writing speed. It is equal to the distance until the image at the position LA moves to the nip portion.

  Further, the distance from the tip detection sensor 14A to the nip portion of the photoreceptor 4A downstream thereof is set shorter than the distance until the image at the image writing position LA of the photoreceptor 4A moves to the nip portion. Yes. This is intended to make the apparatus compact.

  The configuration of the image forming units 8B to 8D and the positional relationship between the leading edge detection sensors 14B to 14D and the leading edge positions “B” to “D” of the paper at the start of image writing of the photoconductors 4B to 4D are the same.

  That is, in order to shorten the distance between the photosensitive member / transfer belt pair, the installation position of the leading edge detection sensor is a position between the leading edge position of the sheet and the nip portion at the print head writing timing.

  When it is assumed that a predetermined time has elapsed after the timing sensor 13 detects the leading edge of the paper P, the image writing position LA on the photoconductor 4A is assumed when the leading edge of the paper has come to the position “A”. The print head starts writing the image.

  Thereafter, when the leading edge of the sheet P reaches the leading edge detection sensor 14A, the theoretical value and the measured value of the time required to transport the sheet from the position of the timing sensor 13 to the position of the leading edge detection sensor 14A are compared. . When it is determined that there is a deviation between them, the position of the photosensitive member 4A is moved in the left-right direction in FIG.

  When such control is performed, a method of measuring the sheet conveyance time from the position of the timing sensor 13 to the positions of the leading edge detection sensors 14B to 14D after the pair of the most upstream photoconductor 4A and transfer belt 412A. And a method of measuring the sheet conveyance time from the position of the upstream leading edge detection sensor to the position of the next leading edge detection sensor may be used.

  The transfer belt always contacts the photoconductor even when the photoconductor moves to form a nip portion.

  After the transfer to the paper P is completed, each photoconductor returns to the original position before the next paper reaches the position of the timing sensor 13. Thereafter, the same sequence as described above is repeated for the next sheet.

  FIG. 3 is a block diagram illustrating a hardware configuration of the image forming apparatus.

  Referring to the figure, detection information from timing sensor 13 and tip detection sensors 14A to 14D is input to CPU 31 provided in the image forming apparatus. The transport roller 3 is driven by a transport roller drive motor 34. Each of the photoreceptors 4 </ b> A to 4 </ b> D is driven by a photoreceptor drive motor 37.

  The image writing units 16A to 16D are configured by a scanning system such as a laser diode (or LED) or a polygon mirror, and the drive timing is controlled by the CPU 31. The image writing units 16A to 16D include a print head 20 and folding mirrors 19A to 19D.

  The CPU 31 includes an input / output I / F 41 for communicating with an external device (external PC (personal computer)), and a toner developing unit for developing latent images written by the image writing units 16A to 16D. 43A to 43D and the fixing device 6 are connected.

  The CPU 31 controls the transport roller drive motor 34 according to the detection signal of the timing sensor 13 to transport the paper by the transport roller 3. At the same time, the CPU 31 controls the photoconductor drive motor 37 to rotate the photoconductors 4A to 4D. Further, the image writing units 16A to 16D are controlled to form latent images on the photoreceptors 4A to 4D.

  When the CPU 31 obtains the detection signals of the tip detection sensors 14A to 14D, it checks whether or not the output timing is a prescribed timing. If it is the specified timing, the state is continued.

  If it is not the prescribed timing, the CPU 31 drives the photosensitive member moving motors 35A to 35D in order to align the position of the image with the paper. The photosensitive member moving motors 35A to 35D move the nip portions by moving the photosensitive members 4A to 4D, respectively. As a result, the position of the nip portion is corrected.

  It should be noted that the present invention can be carried out even when the number of photoconductors is one, and in that case, one tip detection sensor, one image writing unit, and one developing device may be provided.

  Note that the conveyance roller drive motor 34 does not have to be an independent motor, and the photoconductor drive motor may also be used.

  As the photosensitive member driving motor, one motor may be used for four photosensitive members, or four motors corresponding to the respective photosensitive members may be used.

  FIG. 4 is a diagram for explaining a method of adjusting the position of the nip portion of the image unit 8A.

  The image writing unit 16A includes a print head (PH) 20 including a laser diode (or LED) as an exposure unit, and a folding mirror 19A for causing light from the exposure unit to enter the photoconductor 4A.

  The photoconductor moving motor 35A that is a correction unit moves the photoconductor 4A and corrects the nip position that is a transfer point.

  That is, the image writing position on the paper P is adjusted by moving the photosensitive member 4A in the sub-scanning direction as shown in the figure. By such movement, the sheet can be quickly and slowly rushed into the nip portion. As a result, the image writing position on the paper can be adjusted.

  The amount of movement of the photosensitive member is calculated according to the detection output of the timing sensor 13 and the detection output of the tip detection sensor 14A.

  The folding mirror 19A is disposed on the optical path of the print head 20, and determines the image writing position LA on the photosensitive member. It is desirable to avoid regular reflection of light from the photoreceptor 4A to the print head 20. Therefore, control is performed so that the rotation axis at the center of the photoconductor 4A is not positioned in the traveling direction of light from the print head 20 within the range in which the photoconductor 4A moves. That is, the straight line connecting the reflection position at the folding mirror 19A and the writing position LA does not pass through the rotation axis at the center of the photosensitive member 4A (the tangent at the writing position LA of the circle indicating the photosensitive member 4A in FIG. 4 is The photosensitive member 4A is moved so as not to be orthogonal to the straight line connecting the reflection position at the folding mirror 19A and the writing position LA. Thereby, the incidence of light on the photosensitive member 4A is always oblique incidence (the incident direction of light on the photosensitive member 4A is not perpendicular to the contact surface at the writing position LA of the photosensitive member 4A).

  The normal position of the photoconductor 4A is a position indicated by “4A” in FIG. 4. However, when the paper is transported earlier than expected and the paper is to be entered into the nip portion later, the photoconductor 4A is positioned at the position 4A. Move in the direction indicated by '. On the contrary, when the sheet is transported later than expected and the sheet is desired to enter the nip portion earlier, the photoconductor 4A moves in the direction indicated by the position 4A ″.

  The photosensitive member 4A moves around the image writing position LA of the photosensitive member 4A as the rotation center. Thereby, the positional relationship between the folding mirror 19A and the writing position LA does not change, and the exposure length from the print head 20 to the photosensitive member can be kept constant. Thereby, a stable output image can be supplied.

  The movement of the photoconductor 4A is performed based on an arbitrary movement amount calculated by the CPU from the output result of the sensor. The movement is completed until the leading edge of the sheet reaches the nip portion, and the photosensitive member 4A stops moving while the image is transferred onto the sheet.

  Further, when the amount of sheet misalignment is detected, the nip portion may be moved by calculating the amount of movement of the nip portion, or the photosensitive member is moved by calculating the amount of movement of the photosensitive member 4A ( As a result, the nip portion may move).

  Since image writing units 8B to 8D have the same configuration, description thereof will not be repeated.

  As described above, when the sheet is conveyed to the transfer region (nip portion) of the image forming unit, the time t actually taken until the sheet passes through the leading edge detection sensors 14A to 14D from the timing sensor 13 is assumed in advance. When the required time t1 is the same (t = t1) (or when there is only a deviation from the error), the CPU 31 does not move the photoconductor.

  When the time t actually taken until the paper passes the leading edge detection sensors 14A to 14D from the timing sensor 13 exceeds a previously assumed required time t1 (t> t1), the CPU 31 removes the photoconductor from the paper. Move upstream in the transport direction.

  When the time t actually required for the sheet to pass from the timing sensor 13 to the leading edge detection sensors 14A to 14D is less than the predetermined required time t1 (t <t1), the CPU 31 conveys the photosensitive member to the sheet. Move to the downstream side.

  Also, by moving the nip around the image writing position as the rotation center, the distance relationship between the folding mirror and the image writing position does not change, and the exposure length can be kept constant, providing a stable image. can do.

  Although the photosensitive member is moved along the arc with the writing position (exposure position) as the rotation center, the nip position can be moved in accordance with the speed of the sheet to be conveyed, and the writing tip can be aligned. In this case, the movement trajectory is not limited to an arc.

  In the above-described embodiment, the combination of the timing sensor 13 and the leading edge detection sensors 14A to 14D detects the paper speed. However, the combination of one leading edge detection sensor and another leading edge detection sensor detects the paper speed. It is good as well.

  FIG. 5 is a flowchart showing a process in which the CPU 31 adjusts the positions of the photoconductors 4A to 4D based on the detection result of the CPU 31.

  This is because the CPU 31 of the image forming apparatus 1 controls the operation of the photoreceptors 4A to 4D based on the detection results of the timing sensor 13 and the tip detection sensors 14A to 14D of the image forming unit 8.

  In the following, the control on the photoconductor 4A will be described, but the control on the photoconductors 4B to 4D is also performed by the processing of the same flowchart.

  First, the CPU 31 uses the timing sensor 13 to check whether the leading edge of the paper has reached that position (S101). When the timing sensor 13 is turned on (YES in S101), the CPU 31 calculates the timing for starting image writing in the image writing unit 16A (S102).

  The CPU 31 uses the transport roller 3 to transport the paper P at an appropriate timing so that the paper P can reach the nip portion between the photoconductor 4A and the transfer belt 412A in accordance with the image writing timing. The CPU 31 checks whether or not the image writing timing has arrived (S103). If the image writing timing has arrived (YES in S103), the CPU 31 starts writing an image on the photoconductor 4A (S104).

  As a result, a first color latent image based on the image data transferred from the computer is formed on the photoreceptor 4A. The latent image formed on the photoconductor 4A becomes a toner image by the developing device until it reaches the nip portion.

  The CPU 31 uses the leading edge detection sensor 14A to check whether the leading edge of the sheet has reached that position (S105). When the tip detection sensor 14A is turned on (YES in S105), the CPU 31 checks whether or not the timing when the tip detection sensor 14A is turned on is within a specified range (S106). In steps S105 and S106, it is checked whether the paper arrival timing set based on the detection result of the timing sensor 13 is different from the actual paper arrival timing.

  If the detection timing of the leading edge detection sensor 14A is within the specified range (YES in S106), the CPU 31 directly conveys the sheet to the nip portion and transfers the toner image to the sheet (S110). Thereafter, the sheet is conveyed by the CPU 31 toward the nip portion between the photoreceptor 4B and the transfer belt 412B. In the meantime, the writing timing of the image writing unit 16B, the detection timing of the tip detection sensor 14B, and the like are checked by the processing in the same flowchart as FIG. Since this overlaps with the content already described, the description will not be repeated. In this case, the positional relationship between the image of the first color and the paper is a predetermined relationship. For this reason, when considering the positional relationship of the second color image, it is not necessary to consider the position of the first color image.

  If the detection timing of the leading edge detection sensor 14A is not within the specified range (NO in S106), the CPU 31 calculates the amount of deviation between the sheet and the image (S107), and calculates the movement amount of the photosensitive member (S107). S108).

  In the correction of the deviation amount, a method of moving the photoconductor 4A and moving the nip portion is executed (S109). Prior to transfer, the photoconductor stops at the movement end position. The CPU 31 conveys the paper to the nip portion and transfers the toner image onto the paper (S110). If the photosensitive member 4A is moved in step S109 after the transfer process is performed (NO in S111), a process of returning the photosensitive member 4A to a predetermined position (initial position) is performed (S112).

  Accordingly, a first color toner image in which the positional relationship between the paper and the image is corrected can be obtained. Thereafter, the sheet is conveyed toward the nip portion between the photoreceptor 4B and the transfer belt 412B. In the meantime, the writing timing of the image writing unit 16B, the detection timing of the tip detection sensor 14B, and the like are checked. That is, almost the same control as described above is repeated. However, there is a case where correction is required in consideration of the positional relationship between the second color image and the paper or the positional relationship between the second color image and the first color image.

  The writing timing of the image writing unit 16B is determined based on the detection result of the timing sensor 13. However, if possible from the viewpoint of calculation time and the arrangement of the tip detection sensor 14A, the writing timing of the tip detection sensor 14A is determined. You may determine based on a detection result.

  The determination based on the detection result of the sensor closer to the image writing unit 16B is preferable because the amount of deviation is small. In some cases, the writing timing of the image writing unit 16B may be determined based on the detection result of the timing sensor 13, and the timing may be finely adjusted based on the detection result of the tip detection sensor 14A.

  The same applies to the processing for the image writing units 16C and 16D. That is, the image writing timing may be determined using the detection result of the upstream sensor.

  Even when it is determined that the positional relationship between the image of the first color and the paper is a predetermined relationship and correction is not performed, there may be a slight difference from the ideal image position. In this case, the positional relationship between the second color image and the paper, or the positional relationship between the second color image and the first color image is taken into consideration, as in the case of correcting and controlling the shift amount of the first color. It is possible to obtain a better image by performing the correction control.

  Note that in an image forming apparatus that performs monochromatic printing, image formation is completed if the first color toner image is obtained by the processing of FIG.

  [Effects of the embodiment]

  According to the configuration in the above embodiment, the positional relationship between the sheet and the image is detected based on the detection result of the leading end of the sheet. The position of the photoconductor can be adjusted before the leading edge of the paper reaches the nip portion between the photoconductor and the transfer roller. By moving the photoconductor, it is possible to correct (or reduce) the shift of the image transfer onto the paper even when the image has already been written on the photoconductor. Further, when an image is formed with a plurality of colors, color misregistration can be corrected.

  In addition, since the nip portion can be moved, the writing position on the paper can be adjusted even if writing on the photoconductor is started before the paper is detected by the leading edge detection sensor (an image is written on the photoconductor). Even after it has been released, it can be corrected). As a result, the distance between the photoconductors can be shortened to achieve downsizing of the apparatus. In addition, since correction can be performed when detection is performed by the sensor during printing, correction can be performed for all prints including the print.

  [Others]

  The photosensitive member can be moved by a driving mechanism such as a motor or an actuator.

  Further, by providing the transfer belt with a function of transporting the sheet by the driving mechanism, it is possible to stabilize the transport of the sheet and to reduce the image shift. One of the transfer belt and the photosensitive member may operate, and the other may be driven. The sheet is conveyed by being sandwiched between the transfer belt and the photoconductor.

  In addition, the image alignment may be performed based on the position of the sheet, or may be performed based on the position of the image formed on the sheet upstream.

  In the embodiment, the timing sensor 13 that detects the arrival of the front end of the paper and the front end detection sensors 14A to 14D are used to detect the paper speed. A sensor to detect may be used. In other words, the arrival timing of the sheet at the nip portion is determined based on the sheet conveyance speed, thereby correcting the positions of the photosensitive member and the transfer roller.

  In addition, the device for returning the photosensitive member to the original position (predetermined position) after completion of the transfer process when the position of the photosensitive member is corrected has been described. The position correction for the next transfer process may be performed without returning it to the position (1).

  The image forming apparatus may be any one of a monochrome / color copying machine, a printer, a facsimile machine, and a complex machine (MFP) thereof.

  Further, the processing in the above-described embodiment may be performed by software or by using a hardware circuit.

  In addition, a program for executing the processing in the above-described embodiment can be provided, and the program is recorded on a sheet such as a CD-ROM, a flexible disk, a hard disk, a ROM, a RAM, or a memory card and provided to the user. You may decide. The program may be downloaded to the apparatus via a communication line such as the Internet.

  In addition, it should be thought that the said embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a diagram illustrating a hardware configuration of an image forming apparatus according to one embodiment of the present invention. 3 is a side view showing a configuration of an image forming unit 8. FIG. 2 is a block diagram illustrating a hardware configuration of the image forming apparatus. FIG. It is a figure for demonstrating the method of position adjustment of the photoreceptor of the image unit 8A. It is a flowchart which shows the process which CPU31 adjusts the position of photoreceptor 4A-4D based on the detection result of CPU31. FIG. 6 is a diagram illustrating a configuration around an image forming unit in an image forming apparatus according to a first conventional example. It is a flowchart which shows the process performed in the image forming apparatus of a 1st prior art example. It is a figure explaining the structure of the image formation part periphery in the image forming apparatus of the 2nd prior art example. It is a flowchart which shows the process performed in the image forming apparatus of the 2nd prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Paper feed cassette 3 Paper feed part 4A Y color photoreceptor 4B M color photoreceptor 4C C color photoreceptor 4D K color photoreceptor 412A Y color transfer belt (transfer part)
412B M color transfer belt (transfer section)
412C C color transfer belt (transfer section)
412D K-color transfer belt (transfer section)
REFERENCE SIGNS LIST 6 fixing unit 7 paper discharge unit 8 image forming unit 13 timing sensor 14A to 14D tip detection sensor 16A to 16D image writing unit 19A to 19D folding mirror 20 print head 35A to 35D photoconductor moving motor LA to LD writing position P paper (Transfer material)

Claims (11)

An image carrier for carrying an image to be transferred to paper;
A transfer portion provided to face the image carrier;
A detection unit that detects a conveyance state of the sheet upstream of a nip portion of the image carrier and the transfer unit in a sheet conveyance path;
A writing unit for writing an image on the image carrier, the writing unit starting writing of an image before detection by the detection unit;
An image forming apparatus comprising: a correction unit that corrects a position of the image carrier based on a detection result of the detection unit.   The image forming apparatus according to claim 1, wherein the detection unit detects that the leading edge of the sheet has arrived. The image carrier is a photoreceptor;
The image forming apparatus according to claim 1, wherein the transfer unit is a transfer belt.   4. The image according to claim 1, wherein the correction unit moves the image carrier around a writing position on the image carrier on which an image is written by the writing unit as a rotation center. 5. Forming equipment.   5. The image forming apparatus according to claim 1, wherein an exposure incident angle from the writing unit to the image carrier is oblique incidence in a moving range of the image carrier moved by the correction unit. 6. .   The image forming apparatus according to claim 1, wherein the image carrier is stopped at a predetermined position based on a detection result of the detection unit.   The correction unit finishes the movement of the image carrier before the sheet reaches the nip portion, and stops the image carrier while the transfer is performed in the nip portion. The image forming apparatus according to any one of the above.   8. The image carrier according to claim 1, wherein the position of the image carrier is corrected by the correction unit, and then the image carrier is moved to a predetermined position until the detection unit detects a conveyance state of the next sheet. Image forming apparatus. The image carrier is provided with a plurality corresponding to each of a plurality of colors,
A plurality of transfer portions corresponding to each of the plurality of image carriers are provided,
A plurality of the detection units are provided upstream of the nip portions of the plurality of image carriers and the plurality of transfer units,
9. The image formation according to claim 1, wherein the correction unit corrects the position of the nip portion based on detection results of at least two detection units arranged upstream of the nip portion to be corrected. apparatus. An image carrier for carrying an image to be transferred to paper;
A transfer portion provided to face the image carrier;
A control method for an image forming apparatus, comprising: a detection unit that detects a conveyance state of the sheet upstream of the image carrier and a nip portion of the transfer unit in a sheet conveyance path;
A writing step of writing an image on the image carrier, the writing step starting writing of the image before detection by the detection unit;
And a correction step of correcting the position of the image carrier based on a detection result of the detection unit. An image carrier for carrying an image to be transferred to paper;
A transfer portion provided to face the image carrier;
A control program for an image forming apparatus, comprising: a detection unit that detects a conveyance state of the sheet upstream of the image carrier and a nip portion of the transfer unit in a sheet conveyance path;
A writing step of writing an image on the image carrier, the writing step starting writing of the image before detection by the detection unit;
A control program for an image forming apparatus, which causes a computer to execute a correction step of correcting the position of the image carrier based on a detection result of the detection unit.

Images