JP2006182460A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of controlling an image forming position on a paper with high precision even when mounting error occurs due to mounting and dismounting of a paper conveyance part. <P>SOLUTION: When forming image usually, position information of a conveyance module when forming image is computed, and each of position information computed based on the result of detection by each position detection sensor when forming image is compared with corresponding reference position information to compute amount of difference. Initial compensation amount stored in a nonvolatile memory is read, and the initial compensation amount is corrected in accordance with the computed amount of difference to end routine. Consequently, as for a series of jobs, a compensation means for compensating image registration based on the corrected compensation amount is controlled. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus that forms and outputs an image on a sheet, such as a copying machine or a printer.

  An image forming apparatus that forms an image on a sheet by using an electrophotographic method, such as a copying machine or a printer, includes a toner image forming unit that forms a toner image on an intermediate transfer belt, and conveyance of printing paper. And a paper transport unit that accurately enters the paper into the toner image forming unit. A toner image formed on the intermediate transfer belt is transferred onto a sheet at a position called a secondary transfer position.

  The toner image forming unit is fixed to the frame of the main body of the image forming apparatus, and is normally configured so that the operator cannot remove it. On the other hand, the paper transport unit is configured to be detachable from the toner image forming unit, that is, the apparatus main body so that the operator can easily remove the paper even when the transported paper is jammed or the like. Has been.

  On the other hand, in the image forming apparatus configured as described above, when transferring the toner image formed on the intermediate transfer belt onto the sheet, a method for controlling the alignment of the image with high accuracy, that is, image registration (so-called image registration). ) Adjustment methods have been proposed. The image registration elements include a lead registration in the same direction as the conveyance direction of the intermediate transfer belt, a side registration in a direction perpendicular thereto, and a side skew in an oblique direction. Various control methods have been proposed for reducing the variation of each and achieving a highly accurate image registration (Patent Documents 1 to 3).

  According to the various controls described in Patent Documents 1 to 3, the variation of the output image register in the image forming apparatus for each sheet can be suppressed with high accuracy. These controls are performed on the premise that “the mechanical error is stable”, that is, “the positional relationship between the toner image forming unit and the sheet conveying unit is constant”.

Of course, the individual parts constituting the image forming apparatus have variations within the tolerances of the parts. An assembly error also occurs when an image forming apparatus is assembled using these components. Mechanical errors such as errors due to variations in these parts and assembly errors do not vary under normal conditions. Therefore, at the time of product shipment or delivery, initial adjustment is performed on each element of the image register so that each element becomes a target value, and if this assembled state is maintained, a desired image register is always set. Obtainable.
JP 2000-238931 A JP-A-11-189355 JP 2003-81490 A

  However, when a jam occurs in the vicinity of the secondary transfer unit in the image forming apparatus configured as described above, the operator pulls out the paper transport unit from the apparatus main body and forms the toner image on the paper transport unit in order to remove the paper. It must be separated from the part.

  The paper transport unit pulled out from the apparatus main body is stored in the original position of the apparatus main body after the operator removes the paper. The reproducibility of the position of the paper transport unit relative to the main body of the device is a mechanical structure with a certain degree of accuracy, such as an abutment method, but it is designed with consideration given to the ease (operability) of the operator when inserting and removing Therefore, it is difficult to eliminate the error of position reproducibility.

  Accordingly, the positional relationship between the toner image forming unit and the sheet conveying unit changes due to the attachment / detachment of the sheet conveying unit, and an error in image registration occurs when the image is formed again after the sheet is removed. It was. Because of the various controls described above, the image registration is more accurate, so these errors cannot be ignored.

  On the other hand, if the image registration is readjusted every time the paper transport unit is attached / detached, there is a problem that the working efficiency is remarkably lowered.

  The present invention has been made to solve the above problems, and an object of the present invention is to control the image forming position on the paper with high accuracy even when an attachment error occurs due to the attachment / detachment of the paper transport unit. It is an object of the present invention to provide an image forming apparatus capable of doing so.

  In order to achieve the above object, an image forming apparatus of the present invention is fixedly arranged in the apparatus main body, an image recording means for recording an image on a sheet at a predetermined image recording position, and the image recording means is fixedly arranged. A sheet conveying unit configured to be detachable from the apparatus main body and configured to detach the sheet to the image recording position; and an image recording condition by the image recording unit in order to adjust an image forming position on the sheet; Based on the correction means for correcting at least one of the paper conveyance conditions by the paper conveyance means, the detection means for detecting the distance between the paper conveyance means and the apparatus main body, and the distance detected by the detection means Calculating means for calculating the amount of deviation from the reference position of the paper conveying means at the time, and the correction so that the image forming position on the paper is adjusted according to the amount of deviation calculated by the calculating means. It is characterized by comprising a control means for controlling the means.

  In the image forming apparatus of the present invention, the image recording means is fixedly arranged in the apparatus main body, whereas the paper conveying means for conveying the paper to the image recording position is configured to be detachable from the apparatus main body. ing. For this reason, there is a possibility that the sheet conveying means is displaced from the reference position during image recording due to the attachment / detachment of the sheet conveying means. The amount of deviation from the reference position of the sheet conveying means during image recording is calculated based on the detected distance by detecting the distance between the sheet conveying means and the apparatus main body by the detecting means. The image forming apparatus of the present invention is provided with a correcting means for correcting at least one of the image recording condition and the paper transport condition in order to adjust the image forming position on the paper, and the control means is an arithmetic means. The correction unit is controlled so that the image forming position on the paper is adjusted according to the calculated deviation amount.

  As a result, even when the paper transport unit is deviated from the reference position during image recording due to the attachment / detachment of the paper transport unit, the image forming position on the paper can be controlled with high accuracy.

  As described above, according to the present invention, there is an effect that the image forming position on the paper can be controlled with high accuracy even when an attachment error occurs due to the attachment / detachment of the paper transport unit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Overall configuration of image forming apparatus)
FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus to which the present invention is applied.

  As shown in FIG. 1, the image forming apparatus 1 includes an image reading unit 2, an image forming unit 3, and a sheet conveying device 4.

  The image reading unit 2 reads an image of a document set on a transparent document table (platen glass). The image reading unit 2 includes, for example, an optical scanning system including a lamp, a mirror, a carriage, and the like, a lens system that forms an optical image read and scanned by the optical scanning system, and an optical image formed by the lens system. And an image reading sensor (for example, a three-line CCD sensor) that receives the light and converts it into an electrical signal.

  The image forming unit 3 forms an image by a general electrophotographic method, and corresponds to each color of K (black), Y (yellow), M (magenta), and C (cyan). And a development unit 10K, 10Y, 10M, and 10C including a primary transfer roller, an intermediate transfer belt 15, a secondary transfer roller 20, a vacuum transport unit 45, and a fixing device 46, and a quadruple tandem configuration. It is said that.

  The toner images formed on the photosensitive drums of the developing units 10K, 10Y, 10M, and 10C are transferred (primary transfer) to the intermediate transfer belt 15. The intermediate transfer belt 15 is looped around a plurality of support rollers. The secondary transfer roller 20 is disposed so as to face the intermediate transfer belt 15. The secondary transfer roller 20 transfers the toner image formed on the intermediate transfer belt 15 to the paper as described above (secondary transfer), and the transfer position (secondary transfer position) of the toner image is the image formation. This is the image output position in the unit 3.

  The vacuum conveyance unit 45 conveys the sheet on which the toner image is transferred by the secondary transfer roller 20 to the fixing unit 46. The fixing device 46 fixes the toner image on the paper by heating and pressing.

  On the other hand, the paper transport device 4 uses the paper in the tray selected by the user operation or the automatic selection function from among the papers stored in the first tray 50, the second tray 51, and the third tray 52. Each sheet of the selected tray is conveyed by a predetermined route. In the vicinity of each of the trays 50, 51, 52, corresponding delivery rollers 53, 54, 55 are disposed.

  Each of the feed rollers 53, 54, and 55 feeds the paper to the downstream side in the paper transport direction by pinching (niping) the called paper separately from the corresponding tray 50, 51, 52 one by one. is there. In the vicinity of the image reading unit 2, an operation panel 56 operated by a user and a control unit 40 for controlling each unit of the image forming apparatus are provided.

  Here, a series of paper transport paths R1 to R5 from the paper delivery position by the delivery rollers 53, 54, 55 to the discharge tray 57 via the image output position in the image forming unit 3 are respectively provided for the paper. Rollers for conveyance are provided as appropriate. The paper stored in the first tray 50 is sent out by the feed roller 53 and then sent to the merging / conveying section 58 via the first paper transport path R1. The paper stored in the second tray 51 is sent out by the feed roller 54 and then sent to the merging / conveying section 58 via the first paper transport path R1. On the other hand, the paper stored in the third tray 52 is sent directly to the merging and conveying unit 58 by the delivery roller 55.

  Further, the sheet sent to the merging / conveying unit 58 is sent to the image output position of the image forming unit 3 after the orientation of the sheet is adjusted via the second sheet conveying path R2. Further, the paper that has passed through the image output position is sent to the fixing device 46 by the vacuum transport unit 45 and then discharged to the discharge tray 57 via the third paper transport path R3. On the other hand, the sheet on which images are formed on both sides (the first side and the second side) passes through the fixing unit 46 and is sent to the double-side reversing unit 59 via the fourth sheet conveyance path R4. Then, after being turned upside down, the paper is again fed into the merging and conveying unit 58 via the fifth sheet conveying path R5.

  In such paper transport paths R1 to R5, a paper alignment section 60 and a registration roller 61 are disposed in the second paper transport path R2. The sheet aligning unit 60 is a part that performs skew correction of the sheet conveyed along the second sheet conveyance path R2. The sheet aligning unit 60 includes, for example, an aligning mechanism that reduces the side skew of the conveyed sheet and a side shift mechanism that performs side registration control of the conveyed sheet.

  The registration roller 61 is composed of a pair of rollers held in pressure contact with each other, and feeds the paper to the image output position by the rotation of the rollers while sandwiching the paper between the pair of rollers.

  When the sheet is fed by the registration roller 61, the timing of arrival of the sheet with respect to the image output position is adjusted by a timing adjusting unit (not shown). The timing adjusting unit varies the sheet conveyance speed by the registration roller 61 based on the timing at which a registration sensor (not shown) provided in front of the registration roller 61 (upstream side) detects the passage of the sheet. The servo registration mechanism adjusts the arrival timing of the paper at the image output position in accordance with the arrival timing of the toner image at the output position.

  In other words, the sheet aligning unit 60 and the timing adjusting unit correspond to the correcting unit of the present invention, and are controlled by the control unit 40 to operate to correct the sheet skew, the drawing timing, and the sheet transport timing.

  In addition, curl correction units 62 and 63 are provided in the paper transport paths R3 and R5, respectively. Each of the curl correcting units 62 and 63 is for correcting the curling of the paper that occurs when the fixing device 46 fixes the toner image.

  A sheet aligning unit 60, a registration roller 61, a secondary transfer roller 20, a vacuum conveying unit 45, and a fixing unit 46 disposed along the second sheet conveying path R2 are disposed on the same housing 30. A transport module 31 is configured. The transport module 31 is configured to be detachable from the frame of the image forming unit 3 so that paper remaining due to jam or the like can be removed. The transport module 31 is configured to be pulled out to the front side of the drawing, for example.

(Location sensor placement)
FIG. 2 is a schematic view showing a mounted state of the transport module. As shown in FIG. 2, the transport module 31 is housed in the frame 32 of the image forming unit 3 when mounted. Further, the transport module 31 is configured to be movable in the direction of arrow A perpendicular to the paper transport direction, and is pulled out from the frame 32 of the image forming unit 3 when the paper is removed. Note that the registration roller 61 is supported by the casing 33 and is disposed upstream of the secondary transfer position 34.

  A plurality of reflecting plates 35 are attached to the surface of the housing 30 of the transport module 31. As the reflecting plate 35, a white plate having a high reflectance can be used. A reflective position detection sensor (PSD) that detects the distance to the reflecting plate 35 by irradiating the reflecting plate 35 with light and receiving the reflected light at a position facing each of the plurality of reflecting plates 35 on the frame 32 side. Position sensitive devices) 36 are respectively arranged.

  The mounting position of the transport module 31 is detected by the PSD 36. In the case of using the PSD 36, it is only necessary to provide the reflector 35 on the transport module 31 side, and it is not necessary to provide an electrical member.

  As shown in FIG. 2, the reflection plate 35 can be attached to the corner of the housing 30. Detection accuracy is improved by detecting the mounting position of the transfer module 31 at the corner of the housing 30. In this example, reflection plates 35 are attached to two sides on the side surface of the housing 30 along the paper conveyance direction. Further, a reflective plate 35 is attached to one side on the right back side on the side surface orthogonal to the paper transport direction.

(Control system configuration)
FIG. 3 is a block diagram showing the configuration of the control system of the image forming apparatus 1 described above. As illustrated in FIG. 3, the control unit 40 includes a CPU, a ROM, a RAM, and a nonvolatile memory 41. A position detection sensor 36 is connected to the control unit 40, and a detection result of the position detection sensor 36 is input to the control unit 40. Although not shown, various correction means for correcting the image registration are connected to the control unit 40, and these correction means are controlled by the control unit 40.

(Operation of image forming apparatus)
Next, the operation of the image forming apparatus 1 configured as described above will be described with reference to FIG.

  First, when an image of a document is read by the image reading unit 2, a toner image is formed by the image forming unit 3 based on an image signal obtained thereby. In the image forming unit 3, the toner images of each color formed by the four developing units 10 K, 10 Y, 10 M, and 10 C are sequentially transferred onto the intermediate transfer belt 15. As a result, a multicolor (full color) toner image in which four color toners are superimposed is formed on the intermediate transfer belt 15. The toner image formed on the intermediate transfer belt 15 in this way is carried on the intermediate transfer belt 15 and sent to the image output position (secondary transfer position).

  On the other hand, the tray paper selected by the user using the operation panel 56 or the tray paper selected by the automatic selection function is fed by the registration roller 61 in accordance with the timing at which the toner image reaches the image output position. Thereby, at the image output position of the image forming unit 3, the toner image carried on the intermediate transfer belt 15 is collectively transferred (secondary transfer) onto the paper by the secondary transfer roller 20. Thereafter, the sheet is sent to the fixing unit 46 by the vacuum conveyance unit 45, where the toner image is fixed, and then discharged to the discharge tray 57 via the third sheet conveyance path R3.

  Further, the sheet on which the image is formed on both sides is sent to the double-side reversing unit 59 via the fourth sheet conveyance path R4, and is turned upside down and sent to the fifth sheet conveyance path R5. Thereafter, the sheet is conveyed along the fifth sheet conveyance path R5, and then the timing is adjusted by the rotation of the delivery roller 69, and the sheet is fed again to the merging and conveying unit 58. Thereafter, as described above, the toner image is transferred and fixed on the sheet, and then the sheet is discharged to the discharge tray 57 via the third sheet conveyance path R3.

(Initial adjustment of image registration)
Next, initial adjustment of the image registration performed when the image forming apparatus is assembled will be described.

  During this initial adjustment, a dedicated chart is output by the image forming apparatus, and the state of the obtained output image is measured by visual observation, an external scanner, a sensor disposed in the machine, etc. A deviation amount from the target value (hereinafter referred to as “initial registration deviation amount”) is obtained. This “initial registration deviation amount” is a registration deviation amount based on a mechanical error during assembly. Image registration adjustment elements include not only lead registration, side registration, and side skew, but also image squareness, parallelism, and magnification.

  In accordance with the obtained “initial registration deviation amount”, a correction amount is calculated for each correction unit of the image forming apparatus, and the calculated correction amount is set as an “initial correction amount” in the nonvolatile memory 41 of the control unit 40. Store in advance. Normally, correction means are provided for each adjustment element of the image registration such as the lead registration, the side registration, and the side skew. Therefore, the correction amount is calculated for each adjustment element of the image registration, and the calculated correction amount is stored. Until the initial correction amount is updated, each correction unit is controlled based on the initial correction amount.

(Initial correction amount correction processing)
Next, a control routine for performing the correction process of the initial correction amount according to the positional deviation of the transport module 31 will be described. This control routine is executed by the control unit 40.

  First, the processing at the time of initial adjustment of the image registration will be described with reference to FIG.

  When the image registration is initially adjusted, it is determined in step 100 whether or not the initial correction amount is set in the nonvolatile memory 41. If it is determined that the initial correction amount has been set, the detection result of the position detection sensor 36 is read in step 102. In the next step 104, position information of the transport module 31 at the time of initial adjustment is calculated based on the read detection result. The mounting position of the transport module 31 at the time of initial adjustment is the “reference position” of the transport module 31. The position information of the conveyance module 31 can be obtained for each adjustment element of the image registration, for example.

  For example, as shown in FIG. 5, when the position detection sensors 36A, 36B, and 36C are provided, the detection result of each position detection sensor, that is, the housing 30 and the frame 32 at each position detection sensor mounting position. The distance between the position detection sensor 36A and the secondary transfer position 34 is p, and the distance from the position detection sensor 36B to the secondary transfer position 34 is q. The position information 31 can be calculated according to the following formulas (1) to (3) for each adjustment element of the image registration.

Lead register position information LR = PC (1)
Side register position information SR = (p × PB + q × PA) ÷ (p + q) (2)
Side skew information SS = PA-PB (3)

  In the next step 106, the position information LRadj, SRadj, SSadj calculated based on the detection result of each position detection sensor at the time of initial adjustment is stored in the nonvolatile memory 41 as “reference position information”, and the routine is ended. To do.

  In the above control routine, the detection result of the position detection sensor 36 is read when the initial correction amount is set, but the detection result of the position detection sensor 36 is output when a dedicated chart for image registration adjustment is output. May be read. Further, when the image registration is adjusted after the initial adjustment, the same processing may be performed to update the already stored reference position information to the latest information at that time.

  Next, processing during image formation will be described with reference to FIG.

  At the time of normal image formation, it is determined in step 200 whether or not the job has been started. Here, the job refers to processing from when the image forming apparatus is activated and printing is started until printing is completed. If it is determined that the job has started, the detection result of the position detection sensor 36 is read in step 202. In the next step 204, position information of the transport module 31 at the time of image formation is calculated based on the read detection result.

  In the next step 206, each of the position information LRprint, SRprint, and SSprint calculated based on the detection result of each position detection sensor at the time of image formation is compared with the corresponding reference position information, and the difference amount is calculated.

  If the transport module 31 has not been attached / detached at the time when the image registration is adjusted, the position information LRprint, SRprint, SSprint acquired this time and the reference position information LRadj, SRadj, SSadj stored in the memory 41 in advance are almost It becomes the same value. However, if an error occurs in the mounting position due to the attachment / detachment of the transfer module 31, a difference amount is generated.

  In the next step 208, the initial correction amount stored in the nonvolatile memory 41 is read, and in step 210, the initial correction amount is corrected according to the difference amount calculated in step 206. For example, the relationship between the “difference amount with respect to the reference position information” and the “correction amount for correcting the initial correction amount” is stored in advance, the initial correction amount is corrected based on these relationships, and the routine is terminated. To do. As a result, for a series of jobs, the correction means for correcting the image registration based on the corrected correction amount is controlled.

  As described above, the image forming apparatus according to the present embodiment acquires the position information of the transport module at the start of the job, calculates the amount of deviation from the reference position (the amount of difference in position information), and stores the image registration. Since the correction amount of the correction means to be corrected is corrected according to the calculated deviation amount, if the mounting error occurs due to the removal or mounting of the transport module, or the position of the transport module is very small due to temperature changes in the device. When this occurs, the image registration can be controlled with high accuracy. Further, it is not necessary to redo image registration adjustment using a dedicated chart many times, and the operator's work efficiency can be improved.

(Modification)
In the above embodiment, the reflection plate 35 is attached to the side surface of the casing 30 of the transport module 31 as shown in FIG. 2, but the casing 33 that supports the registration roller 61 as shown in FIG. It can also be attached to the side. In this example, reflection plates 35 are attached to the left and right locations on the side surface of the housing 33 along the paper conveyance direction. Further, a reflective plate 35 is attached to one side of the back side on the side surface that is orthogonal to the paper transport direction and faces the secondary transfer position. Thus, by detecting the mounting position of the transport module 31 in the vicinity of the secondary transfer position, the disturbance error is reduced and the detection accuracy is improved.

  In addition, a two-dimensional CCD can be used as the position detection means instead of PSD (reflection type position detection sensor). In this case, as shown in FIG. 8, a plurality of light emitting elements 37 are attached to the upper surface of the housing 30 of the transport module 31. In this example, light emitting elements 37 are attached to both left and right end portions of the upper surface of the housing 30. Two-dimensional CCDs 38 that receive the light beams emitted from the light emitting elements 37 are arranged at positions facing the light emitting elements 37 on the frame 32 side.

  The mounting position of the transport module 31 is detected by two-dimensionally detecting the position of the light beam by the light emitting element 37 and the two-dimensional CCD 38. When the two-dimensional CCD 38 is used, it is necessary to provide wiring on the transport module 31 side. As shown in FIG. 9, the paper transport direction is the x direction, and the direction orthogonal thereto is the y direction. By detecting 39 two-dimensionally, the position of the transport module 31 can be detected with high accuracy.

  In the above-described embodiment, the initial correction amount correction process is performed for each job at the start of the job. However, immediately after the image forming apparatus is turned on or when the attachment / detachment of the transport module is detected. Thus, it is also possible to perform an initial correction amount correction process.

  In the above embodiment, a plurality of position detection sensors are provided so that all position information corresponding to the image registration elements such as the lead registration, side registration, and side skew can be detected according to the image registration element. If a plurality of position detection sensors cannot be arranged due to space, it may be controlled to detect position information corresponding to a predetermined image registration element and correct the predetermined image registration element.

  In the above embodiment, a full-color image forming apparatus using an electrophotographic system and an intermediate transfer belt system is premised. However, any other image forming apparatus can be used as long as the paper transport unit is configured to be detachable. The present invention can also be applied to an apparatus that forms an image by a method. For example, an image forming apparatus using a paper conveyance belt system, a single color image forming apparatus, an image forming apparatus for forming a toner image by forming a latent image on a drum with an LED bar, an ink jet system for directly ejecting ink on a paper The present invention can also be applied to other image forming apparatuses.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus to which the present invention is applied. It is the schematic which shows an example of the mounting state of a conveyance module. 2 is a block diagram illustrating a configuration of a control system of the image forming apparatus. FIG. It is a flowchart which shows the processing routine at the time of the initial adjustment of an image registration. It is a figure explaining the calculation method of the positional information on a conveyance module. It is a flowchart which shows the processing routine at the time of image formation. It is the schematic which shows the other example of the mounting state of a conveyance module. It is the schematic which shows the other example of the mounting state of a conveyance module. It is a figure explaining the detection method which detects the position of a light beam two-dimensionally.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image reading part 3 Image forming part 4 Paper conveyance apparatus 10 Developing unit 15 Intermediate transfer belt 20 Secondary transfer roller 30 Case 31 Transport module 32 Frame 33 Case 34 Secondary transfer position 35 Reflecting plate 36 Position detection Sensor 38 2D CCD
37 Light Emitting Element 40 Control Unit 41 Memory 41 Non-Volatile Memory 45 Vacuum Conveying Unit 46 Fixing Device 50, 51, 52 Tray 53, 54, 55 Roller 56 Operation Panel 57 Discharge Tray 58 Joining Conveying Unit 59 Double Side Reversing Unit 60 61 Registration roller 62, 63 Curl correction unit 69 Roller R1, R2, R3, R4, R5 Paper transport path

Claims (10)

An image recording means which is fixedly arranged in the apparatus main body and records an image on a sheet at a predetermined image recording position;
A sheet conveying means configured to be detachable from the apparatus main body in which the image recording means is fixedly arranged, and conveys a sheet to the image recording position;
Correction means for correcting at least one of an image recording condition by the image recording means and a paper transport condition by the paper transport means in order to adjust an image forming position on the paper;
Detecting means for detecting a distance between the sheet conveying means and the apparatus main body;
An arithmetic unit that calculates an amount of deviation from a reference position of the paper conveying unit during image recording based on the distance detected by the detecting unit;
Control means for controlling the correction means so that the image forming position on the paper is adjusted according to the amount of deviation calculated by the calculation means;
An image forming apparatus. Storage means for storing a correction amount by the correction means at the reference position;
The control unit corrects the correction amount so that the image forming position on the sheet is adjusted according to the shift amount calculated by the calculation unit, and controls the correction unit based on the corrected correction amount. The image forming apparatus according to claim 1.   3. The image forming apparatus according to claim 1, wherein the reference position is a position of the sheet conveying unit at the time of image adjustment in which an image forming position on a sheet is first adjusted.   4. The image forming apparatus according to claim 1, wherein the detection unit detects a distance between the sheet conveying unit and the apparatus main body during the image adjustment and the image recording. 5.   The calculation means obtains a first adjustment value of an image adjustment element for adjusting an image forming position on the paper from the distance detected at the time of the image adjustment, and at the same time on the paper from the distance detected at the time of the image recording. The image forming apparatus according to claim 4, wherein a second adjustment value of an image adjustment element for adjusting an image forming position is obtained, and a difference amount between the first adjustment value and the second adjustment value is calculated.   The said detection means is provided with any one of Claims 1 thru | or 5 provided with the reflecting plate and the position detection sensor which irradiates light to this reflecting plate, light-receives reflected light, and detects the distance to the said reflecting plate. The image forming apparatus described.   The image forming apparatus according to claim 6, wherein the reflection plate is provided on the sheet conveying unit side, and the position detection sensor is provided on the apparatus main body side.   The image forming apparatus according to claim 1, further comprising a plurality of the detection units.   The image forming apparatus according to claim 1, wherein the detection unit is disposed in the vicinity of the image recording position.   The image forming apparatus according to claim 1, wherein the image recording unit records an image by transferring a toner image formed on an intermediate transfer member onto a sheet.

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