JP5277577B2 - Image forming apparatus and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing color shift detection error compared with the conventional art even when the skewing of a belt happens rapidly during image forming. <P>SOLUTION: A belt position sensor starts detection of the position of an intermediate transfer belt (S101), forms a pattern in each photosensitive drum (S102), primarily transfers it to the intermediate transfer belt (S103), and performs sampling with a color shift detection sensor (S104). A difference amount &Delta;D indicating the difference between the positional relation of the sampled data and the positional relation when it is assumed that there is no color shift of the predetermined pattern of each color is detected (S105), and the register shift amount &Delta;R of each color is calculated (S106). The calculation result is compared with a reference value (S107). When the shift is determined, writing timing of a laser exposure machine of each image forming unit is corrected, and the position of parts of an optical system are corrected, thereby correcting the register shift (S108). <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus and program using an electrophotographic system such as a copying machine, a printer, a facsimile machine, and a multifunction machine of these.

2. Description of the Related Art Conventionally, among image forming apparatuses such as copying machines and printers, there is a color image forming apparatus that forms a multicolor image using an endless intermediate transfer belt, a photoreceptor belt, or a paper transport belt. Conventionally, there has been proposed a technique for dealing with a case where the belt is skewed due to disturbances such as temperature, humidity, paper size, paper type, image size, and image density (see, for example, Patent Document 1). ).
This patent document 1 describes an image forming apparatus that forms an image by an image forming unit using an endless belt member that is stretched and conveyed by a plurality of rolls, in which the endless belt member is transported in the endless belt member. And an endless belt detected by the skew detecting means when the skew detecting means detects the skew of the endless belt member. An image correction unit that corrects image distortion by an image forming unit based on a skew amount of a member is disclosed.

JP 2006-276427 A

Here, for example, when the skew of the belt suddenly occurs during a so-called regicon operation performed immediately after the power is turned on, an accurate color misregistration detection value may not be obtained. An error will occur.
An object of the present invention is to provide an image forming apparatus and a program capable of reducing a color misregistration detection error as compared with the conventional case even when the skew of the belt suddenly occurs during image formation. is there.

An image forming apparatus to which the present invention is applied includes an image forming unit that transfers a plurality of images formed for each color to a transfer target, and an oblique of the transfer target that is generated during the formation of the plurality of images by the image forming unit. Detection means for detecting a line state and stable position information about the transfer target during formation of the plurality of images are obtained and stored by a belt stable position measurement operation performed separately from a printing operation when power is turned on and stored in advance. a storage unit for updating recorded during the belt stable position measurement operation performed in response to the number of printing operation exceeds the value defined is carried out, obtaining means for obtaining a color shift value by reading a front Symbol plurality of images, Correction means for correcting the color misregistration value obtained by the acquisition means using the detection result of the detection means and the stable position information stored in the storage unit.

Here, before Symbol detection means may be characterized by comprising at least two sensors for detecting the position of the end of the transfer object.

A program to which the present invention is applied includes an image forming apparatus that transfers a toner image formed by developing an electrostatic latent image written by an exposure device on a photosensitive member to a belt member or a recording material held by the belt member. In the computer device, a detection function for detecting a skew state of the belt member generated during formation of a plurality of images formed for each color, and stable position information about the recording material during formation of the plurality of images, Obtained and stored by the belt stable position measurement operation performed separately from the printing operation when the power is turned on, and obtained and updated by the belt stable position measurement operation performed when the number of printing operations exceeding a predetermined value is performed. a storage function of an acquisition function of acquiring a color shift value by reading a front Symbol plurality of images, the color shift value by the acquisition function, Oyo detection result of the detection function A correction function of correcting using the stable position information said storage function stores, is used for realizing the.

According to the first aspect, it is possible to correct the error of the color misregistration value accompanying the skew of the transfer target during image formation .
According to claim 2 , it is possible to further improve the accuracy of the detection result of the detection means.
According to the third aspect , it is possible to correct the error of the color misregistration value accompanying the skew of the belt member during image formation .

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram showing an image forming apparatus 1 according to the present embodiment. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem type image forming apparatus, and a plurality of image forming units 10 (10Y, 10M, 10C, 10K) on which toner images of respective color components are formed by, for example, electrophotography. ). In addition, the image forming apparatus 1 sequentially transfers (primary transfer) each color component toner image formed by each image forming unit 10 and holds it as an intermediate transfer body (transfer object, toner image holding body). ) 15 and a secondary transfer device 20 that collectively transfers (secondary transfer) the superimposed image transferred onto the intermediate transfer belt 15 onto a sheet P as a transfer material. In addition, the image forming apparatus 1 includes a fixing device 30 that fixes the second-transferred image on the paper P, and a control unit (detection unit, acquisition unit, correction unit) 40 that controls the operation of each unit (each unit). And a storage unit 41 in which various types of information are stored. In addition, the control part 40 can be comprised by CPU, for example, and the memory | storage part 41 can be comprised by memory, for example.

  In the present embodiment, each image forming unit 10 includes a charger 12 for charging the photosensitive drums 11 around the photosensitive drums 11 rotating in the direction of arrow A, and a static on the photosensitive drums 11. A laser exposure device 13 in which an electrostatic latent image is written (exposure beam is indicated by a symbol Bm in the figure), and development for accommodating each color component toner and making the electrostatic latent image on the photosensitive drum 11 visible with toner. Electronic devices such as a device 14, a primary transfer roll 16 for transferring each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15, and a drum cleaner 17 for removing residual toner on the photosensitive drum 11. Photographic devices are arranged sequentially. These image forming units 10 are arranged substantially linearly in the order of yellow (Y color), magenta (M color), cyan (C color), and black (K color) from the upstream side of the intermediate transfer belt 15. .

The intermediate transfer belt 15 is made of a resin such as polyimide or polyamide containing a suitable amount of a conductive agent such as carbon black, and is formed so that its volume resistivity is 10 ⁶ to 10 ¹⁴ Ω · cm. The intermediate transfer belt 15 is a film-like endless belt having a thickness of, for example, about 0.08 mm. The intermediate transfer belt 15 is configured to be circulated and driven (rotated) at a predetermined speed in the direction of arrow B shown in the figure by various rolls. As these various rolls, a drive roll 31 that is driven by a motor (not shown) to rotate the intermediate transfer belt 15 and an idler roll 32 for maintaining the flatness of the intermediate transfer belt 15 with respect to a color shift detection sensor 42 described later. There is. Further, as these various rolls, a tension roll (not shown) that is disposed adjacent to the idler roll 32 and applies a constant tension to the intermediate transfer belt 15 and a skew (meandering) in the width direction of the intermediate transfer belt 15. ), And a backup roll 22 provided at a secondary transfer portion described later.

  A method for correcting the skew of the intermediate transfer belt 15 by the steering roll 33 will be briefly described. A position change in the width direction of the intermediate transfer belt 15 is detected by a belt position sensor 44 described later, and a steering motor (not shown) is driven based on the detection result. An eccentric cam (not shown) is connected to the steering motor. A steering roll 33 is connected to the eccentric cam, and the inclination of the steering roll 33 changes according to the eccentric amount of the eccentric cam. For this reason, when the steering motor is driven, the eccentric cam rotates, and the steering roll 33 is tilted accordingly. The skew of the intermediate transfer belt 15 is corrected by appropriately controlling the inclination of the steering roll 33.

  In the intermediate transfer module 18 provided to face each photoconductor drum 11, each primary transfer roll 16 provided inside the intermediate transfer belt 15 extending substantially linearly has a voltage having a polarity opposite to the charging polarity of the toner. It is to be applied. As a result, the toner images on the respective photosensitive drums 11 are sequentially electrostatically attracted to the intermediate transfer belt 15, and a superimposed toner image is formed on the intermediate transfer belt 15.

The secondary transfer device 20 includes a secondary transfer roll 21 disposed on the toner image holding surface side of the intermediate transfer belt 15 and a backup roll 22 as an opposite roll. That is, the secondary transfer roll 21 is disposed in pressure contact with the backup roll 22 with the intermediate transfer belt 15 interposed therebetween. By the secondary transfer device 20 configured as described above, the visible image that has been multiplex-transferred onto the intermediate transfer belt 15 is transferred to a sheet P conveyed from a sheet tray 50 described later.
A belt cleaner 34 that cleans the surface of the intermediate transfer belt 15 by removing residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer is provided on the downstream side of the backup roll 22.

  Here, on the downstream side of the black image forming unit 10K, a color misregistration detection sensor as a CCD that detects the misregistration of each color resist pattern for register operation and detects the density of each color toner image for image quality adjustment. (Acquisition means) 42 is provided. More specifically, the color misregistration detection sensor 42 is a color misregistration detection pattern (ladder toner patch, chevron patch) formed on the intermediate transfer belt 15 on a detector composed of a PD (Photo Diode) sensor or the like. The reflection type sensor outputs a pulse when the center of gravity line of the patch coincides with the center line of the detector. This detector is composed of two Bi-Cells (two-divided diodes) arranged at an angle of 90 degrees. The color misregistration detection sensor 42 detects the relative color misregistration of the color misregistration detection pattern by the patches formed by the image forming units 10Y, 10M, 10C, and 10K. And three are arranged along the main scanning direction (perpendicular to the sheet) (see FIG. 8). For example, two infrared LEDs (wavelength 880 nm) are used for the light emitting unit of the color misregistration detection sensor 42, and the light emission amount of the two LEDs can be adjusted (for example, in two stages) in order to ensure stable pulse output. It is configured.

  Further, a belt position sensor (edge sensor, detection means) 44 is disposed downstream of the black image forming unit 10K. A belt position sensor (detecting means) 43 is disposed upstream of the yellow image forming unit 10Y.

  In addition, a belt home sensor 45 that generates a mark detection signal (reference signal, belt home signal) serving as a reference for taking an image forming timing in each image forming unit 10 is disposed upstream of the yellow image forming unit 10Y. Has been. When the belt home sensor 45 recognizes a belt home mark (not shown) provided on the back side of the intermediate transfer belt 15, the belt home sensor 45 outputs a mark detection signal to the control unit 40. In addition, each image forming unit 10 starts image formation in response to an instruction from the control unit 40 based on recognition of the mark detection signal.

  Furthermore, in the present embodiment, the paper transport system includes a paper tray 50 that stores the paper P, and a pickup roll 51 that picks up and transports the paper P accumulated in the paper tray 50 at a predetermined timing. Yes. Further, as a paper transport system, a transport roll 52 that transports the paper P fed by the pickup roll 51, and the paper P transported by the transport roll 52 are temporarily stopped and the paper P is secondarily transferred at a predetermined timing. And a registration roll 53 to be conveyed to the section.

  Next, a basic image forming process of the image forming apparatus 1 according to the present embodiment will be described. Image data output from an image reading device (not shown) or a computer device (not shown) is input to the image forming apparatus 1. In the image forming apparatus 1, after predetermined image processing is performed by an image processing apparatus (not shown), an image forming operation is performed by the image forming units 10Y, 10M, 10C, and 10K. In an image processing apparatus (not shown), input reflectance data is subjected to image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, and movement editing. The image data subjected to the image processing is converted into color material gradation data of four colors of yellow (Y), magenta (M), cyan (C), and black (K), and image forming units 10Y, 10M, and 10C. , 10K is output to the laser exposure unit 13.

  In the laser exposure device 13, the photosensitive drum 11 of each of the image forming units 10Y, 10M, 10C, and 10K is irradiated with, for example, an exposure beam Bm emitted from a semiconductor laser in accordance with the input color material gradation data. ing. In the photosensitive drums 11 of the image forming units 10Y, 10M, 10C, and 10K, after the surface is charged by the charger 12, the surface is scanned and exposed by the laser exposure device 13 at a predetermined timing and a predetermined writing start position. An electrostatic latent image is formed. The formed electrostatic latent image is developed as a toner image of each color of yellow, magenta, cyan, and black in each of the image forming units 10Y, 10M, 10C, and 10K. More specifically, the writing start position of scanning exposure in the circumferential direction (sub-scanning direction) of the photosensitive drum 11 is determined based on the mark detection signal output from the belt home sensor 45. The timing of scanning exposure in the axial direction (main scanning direction) of the photosensitive drum 11 is determined based on information obtained by predicting the behavior of the intermediate transfer belt 15 described later.

  The toner images formed on the respective photosensitive drums 11 of the image forming units 10Y, 10M, 10C, and 10K are moved in the middle of the traveling at the primary transfer portion where the respective photosensitive drums 11 and the intermediate transfer belt 15 are in contact with each other. Transferred onto the transfer belt 15.

Here, the primary transfer portion will be further described. A primary transfer power source 19 controlled by the control unit 40 is connected to the primary transfer roll 16, while the photosensitive drum 11 is grounded. The primary transfer power source 19 supplies positive primary transfer bias (primary transfer current) to the primary transfer roll 16 by performing constant current control. A primary transfer current flows from the primary transfer power source 19 through the primary transfer roll 16, the intermediate transfer belt 15, and the photosensitive drum 11, whereby a transfer electric field is formed between the photosensitive drum 11 and the intermediate transfer belt 15. . Then, the toner image on the photosensitive drum 11 is transferred to an intermediate transfer belt 15 as a transfer target.
In this way, in the primary transfer portion, the primary transfer roll 16 applies a voltage having a polarity opposite to the charged polarity of the toner to the base material of the intermediate transfer belt 15, and the unfixed toner images are sequentially applied to the surface of the intermediate transfer belt 15. The primary transfer is performed by superimposing. The primary transfer unfixed toner image is conveyed to the secondary transfer device 20 as the intermediate transfer belt 15 rotates in the arrow B direction.

  On the other hand, in the paper transport system, the pickup roll 51 rotates in accordance with the image formation timing, and the paper P is supplied from the paper tray 50. The paper P supplied by the pickup roll 51 is transported by the transport roll 52 and reaches the secondary transfer device 20. At that time, the position of the sheet P and the position of the toner image are aligned on the sheet P by rotating the registration roll 53 in accordance with the movement timing of the intermediate transfer belt 15 on which the toner image is held.

  In the secondary transfer device 20, the secondary transfer roll 21 is pressed against the backup roll 22 in accordance with the timing of the secondary transfer onto the paper P. At this time, the sheet P conveyed at the same timing is sandwiched between the intermediate transfer belt 15 and the secondary transfer roll 21. At this time, when a secondary transfer voltage (normal transfer bias) having the same polarity as the toner charging polarity is applied to the power supply roll 23, a transfer electric field is formed on the secondary transfer roll 21 as a counter electrode, and the secondary transfer. The unfixed toner image held on the intermediate transfer belt 15 is electrostatically transferred onto the paper P at the secondary transfer position pressed by the roll 21 and the backup roll 22.

  Thereafter, the sheet P on which the toner image has been electrostatically transferred is peeled off from the intermediate transfer belt 15 and conveyed to a fixing device 30 provided downstream of the secondary transfer roll 21 in the sheet conveying direction. The unfixed toner image on the paper P is fixed on the paper P by being subjected to a fixing process with heat and pressure by the fixing device 30. The paper P on which the fixed image is formed is discharged outside the image forming apparatus 1 by a discharge roll (not shown). On the other hand, after the transfer to the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit as the intermediate transfer belt 15 rotates, and is removed from the intermediate transfer belt 15 by the belt cleaner 34. Removed.

FIG. 2 is a plan view of the intermediate transfer belt 15.
As shown in FIG. 2, a belt position sensor 43 is positioned adjacent to the drive roll 31 wound around the intermediate transfer belt 15, and a belt position sensor 44 is positioned adjacent to the idler roll 32. . These belt position sensors 43 and 44 are for detecting the position of the side edge of the intermediate transfer belt 15 (the position of the edge 15a), and the same configuration can be used. The detection results of the belt position sensors 43 and 44 are output to the control unit 40 as a width direction belt position detection signal.
Between the belt position sensor 43 and the belt position sensor 44 in the direction of arrow B of the intermediate transfer belt 15, the Y color primary transfer position (the most upstream transfer position), the M color primary transfer position, the C color primary transfer position, The K color primary transfer position (the most downstream transfer position) is arranged in order. Thus, the separation distance between the belt position sensors 43 and 44 is larger than the separation distance between the Y-color primary transfer position, which is the most upstream transfer position, and the K-color primary transfer position, which is the most downstream transfer position. In other words, the belt position sensor 43 is disposed upstream of the Y color primary transfer position, and the belt position sensor 44 is disposed downstream of the K color primary transfer position.

FIG. 3 is a time chart showing the on / off timing of the primary transfer power source 19 in each of the image forming units 10Y, 10M, 10C, and 10K.
In the time chart shown in FIG. 3, when the belt home sensor 45 receives a mark detection signal, the control unit 40 switches on the primary transfer power source 19 in each of the image forming units 10Y, 10M, 10C, and 10K. That is, the control unit 40 first turns on the primary transfer power source 19 of the image forming unit 10Y at time t01, turns on the primary transfer power source 19 of the image forming unit 10M at time t02, and turns on the image forming unit 10C at time t03. The primary transfer power source 19 is turned on, and the primary transfer power source 19 is turned on at time t04. When the predetermined time elapses and time t11 is reached, the control unit 40 switches off the primary transfer power source 19 of the image forming unit 10Y. Thereafter, the primary transfer power source 19 of the image forming unit 10M is turned off at time t12, the primary transfer power source 19 of the image forming unit 10C is turned off at time t13, and the primary transfer power source 19 of the image forming unit 10K is turned off at time t14. Turn off. Thus, the primary transfer power supply 19 is not switched on and off simultaneously in each of the image forming units 10Y, 10M, 10C, and 10K.
The control unit 40 starts charging by the charger 12 in each of the image forming units 10Y, 10M, 10C, and 10K after receiving the mark detection signal and before turning on the primary transfer power source 19. Writing is started by the laser exposure unit 13 and development is started by the developing device 14.

FIG. 4 is a schematic configuration diagram showing a contact type sensor 431 which is an example of the belt position sensor 43. Since the belt position sensor 44 has the same structure as the belt position sensor 43 as described above, the illustration and description of the belt position sensor 44 are omitted.
A contact sensor 431 shown in FIG. 4 is a detector that detects the position of the edge 15a with respect to the width direction (vertical direction in FIG. 1) X of the intermediate transfer belt 15 by contacting the edge 15a of the intermediate transfer belt 15. is there.
The contact-type sensor 431 includes a plate-like contact 431a located in the vicinity of the edge 15a of the intermediate transfer belt 15, a support shaft 431b that rotatably supports an intermediate portion of the contact 431a, and the contact 431a formed by the edge 15a. A spring 431c that applies a biasing force to the contact 431a so as to be in pressure contact with the contact 431a, and a displacement sensor 431d that detects a displacement of the contact 431a as the contact 431a rotates around the support shaft 431b. . More specifically, on the edge 15a side of the intermediate transfer belt 15, one end side (upper side in the figure) of the contact 431a is held in a pressure contact state by the tensile force of the spring 431c. In this case, the pressing force of the contact 431a by the spring 431c is set to an appropriate magnitude (for example, 0.1 N) that does not deform the intermediate transfer belt 15. The contact 431a is rotatably supported at its intermediate portion by a support shaft 431b, and the displacement sensor 431d is opposed to the other end side (the lower side of the figure) of the contact 431a with the support shaft 431b as a boundary. It is arranged.
In this contact-type sensor 431, the movement of the intermediate transfer belt 15 in the width direction (in / out direction of the apparatus, main scanning direction) X is replaced with the movement (swinging movement) of the contact 431a in pressure contact with the edge 15a. It is done. At this time, since the output level of the displacement sensor 431d varies in accordance with the movement (displacement) of the contact 431a, the position variation of the edge 15a of the intermediate transfer belt 15 is detected based on the output of the displacement sensor 431d.

FIG. 5 is a schematic configuration diagram showing a non-contact type sensor 432 that is another example of the belt position sensor 43.
The non-contact sensor 432 illustrated in FIG. 5 includes a light emitting unit 432a and a light receiving unit 432b that are close to the edge 15a of the intermediate transfer belt 15. The light emitting unit 432a emits predetermined light, and the light receiving unit 432b detects the light from the light emitting unit 432a and outputs the detection result as a signal to the control unit 40. The light emitting portion 432a is disposed on one surface side (upper surface side in the figure) of the intermediate transfer belt 15, and the light receiving portion 432b is disposed on the other surface side (lower surface side in the drawing). . Further, the light emitting part 432a and the light receiving part 432b are arranged so that the edge 15a of the intermediate transfer belt 15 is located in a detection region by the light emitting part 432a and the light receiving part 432b. More specifically, a part of the light emitted from the light emitting unit 432a is blocked by the intermediate transfer belt 15, and the remaining light is received by the light receiving unit 432b. When the intermediate transfer belt 15 moves in the width direction X, the amount of light passing through the edge 15a of the intermediate transfer belt 15 changes. Therefore, by using the non-contact sensor 432, the position in the width direction X of the edge 15a of the intermediate transfer belt 15 is continuously detected.

FIG. 6 is a block diagram for explaining the configuration of the control unit 40.
As illustrated in FIG. 6, the control unit 40 includes a reception unit 401, a determination unit 402, a calculation unit 403, and a transmission unit 404. The accepting unit 401 accepts signals from each device (each unit) of the image forming apparatus 1. For example, the reception unit 401 receives a pulse output from the color misregistration detection sensor 42 (see FIG. 1), receives a width direction belt position detection signal from the belt position sensors 43 and 44 (see FIG. 1), or belt home. A mark detection signal from the sensor 45 (see FIG. 1) is received.
The receiving unit 401 receives a measurement result from a current detection unit (not shown) that measures the combined resistance at the primary transfer position as a signal. The combined resistance refers to the total resistance between the photosensitive drum 11, the intermediate transfer belt 15, and the primary transfer roll 16.
The accepting unit 401 accepts, as a signal, pixel information when the laser exposure device 13 irradiates the exposure drum Bm onto the photosensitive drum 11 to create an electrostatic latent image. More specifically, since the density of the image is controlled by the number of irradiated pixels, the image density as the pixel information can be acquired by counting the number of pixels per unit area.
In addition, the reception unit 401 receives measurement results of the internal temperature and internal humidity of the image forming apparatus 1 by an ambient environment sensor (not shown) as signals.

  The determination unit 402 reads out information stored in the storage unit 41 as necessary, and requests the calculation unit 403 to perform a predetermined calculation on the signal received by the reception unit 401. The determination unit 402 performs a predetermined determination based on the information read from the storage unit 41, the information received by the reception unit 401, and / or the calculation result calculated by the calculation unit 403, and each device ( An instruction for the control of each unit is performed via the transmission unit 404. For example, the determination unit 402 instructs the laser exposure unit 13 to start scanning exposure and also instructs the writing start position of the exposure beam Bm in the sub-scanning direction. The determination unit 402 instructs the primary transfer power supply 19 to turn on and off, and also instructs the primary transfer power supply 19 to apply a transfer bias so that an appropriate transfer bias corresponding to the process speed is applied, for example.

FIG. 7 is a flowchart showing the procedure of the regicon operation. FIG. 8 is a perspective view showing an image position recognition pattern (image position recognition pattern, register pattern, and color misregistration detection pattern) PTN used for the register control operation. T in FIG. 8 indicates the time when the pattern PTN is primarily transferred. The timing for performing the regicon operation is performed immediately after the power is turned on or before the image forming process, and the same regicon operation is performed at the time of factory shipment.
In the flowchart shown in FIG. 7, first, the belt position sensors 43 and 44 start detecting the position of the edge 15 a (see FIG. 2) of the intermediate transfer belt 15 and transmit the detection result to the receiving unit 401 of the control unit 40. (Step 101). Then, a predetermined image position recognition pattern PTN shown in FIG. 8 is formed on the photosensitive drum 11 by the laser exposure device 13 of each of the image forming units 10Y, 10M, 10C, and 10K (step 102). Thereafter, the control unit 40 sequentially primary-transfers each color pattern PTN formed on each photosensitive drum 11 onto the intermediate transfer belt 15 (step 103). Then, the image position recognition pattern PTN of each color shown in FIG. 8 is sampled by the color misregistration detection sensor 42 arranged on the downstream side of the final image forming unit 10K (step 104). The sampled data is output to the reception unit 401 of the control unit 40. In FIG. 8, the area indicated by the one-dot chain line is Y color, the area indicated by the two-dot chain line is M color, the area indicated by the solid line is C color, and the area indicated by the broken line is K color.

  A difference amount (a color acquired by the acquisition unit) indicating how much difference there is between the positional relationship of the sampled data and the positional relationship when it is assumed that there is no color shift of the predetermined pattern PTN of each color. The determination unit 402 of the control unit 40 detects (deviation values) ΔDy, ΔDm, ΔDc, ΔDk (step 105). Then, the calculation unit 403 of the control unit 40 calculates the registration shift amounts (color shift values corrected by the correction means) ΔRy, ΔRm, ΔRc, and ΔRk of each color as the X margin from the detected data (step 106). Details of step 106 will be described later.

Then, the calculation unit 403 of the control unit 40 compares the calculation result with the reference value (step 107), and when it is determined that there is a deviation, the transmission unit 404 of the control unit 40 outputs a control signal to each image. The registration deviation is corrected by correcting the writing timing of the laser exposure unit 13 of the forming units 10Y, 10M, 10C, and 10K or correcting the position of the components of the optical system (step 108).
Such a registration control operation corrects the detected registration error and provides a high-quality image with little registration error.

Here, FIG. 9 is a graph showing an example of fluctuations in the position of the belt position sensor 43 in the main scanning direction, where the vertical axis represents the belt position (μm) and the horizontal axis represents time (t). FIG. 10 is a graph showing an example of fluctuations in the position of the belt position sensor 44 in the main scanning direction. The vertical axis represents the belt position (μm) and the horizontal axis represents time (t).
As shown in FIGS. 9 and 10, during image formation (in step 102 and step 103), electrostatic attraction between the photosensitive drum 11 and the intermediate transfer belt 15 is generated, and the intermediate transfer belt 15 is inclined. The line gets bigger. On the other hand, when the image formation is completed and the image is being detected (in step 104), the electrostatic adsorption force between the photosensitive drum 11 and the intermediate transfer belt 15 is decreased, and the intermediate transfer belt 15 is skewed. Is getting smaller. In this way, the belt position moves during the image formation of the pattern PTN, and returns to the original position as the image formation ends.
More specifically, since an electrostatic attraction force is generated between the photosensitive drum 11 and the intermediate transfer belt 15, if the alignment between the photosensitive drum 11 and the intermediate transfer belt 15 is not complete, the intermediate transfer belt 15 The intermediate transfer belt 15 is skewed by receiving a force in a direction crossing the traveling direction. When the electrostatic attraction force between the photosensitive drum 11 and the intermediate transfer belt 15 varies, the skew state varies. The skew of the intermediate transfer belt 15 is detected by belt position sensors 43 and 44. In other words, the reason why the amplitude of the belt position sensor 44 (the amount of skew movement) is smaller than the amplitude of the belt position sensor 43 is that the skew of the intermediate transfer belt 15 is corrected by the steering roll 33.

FIG. 11 is a flowchart for explaining the calculation in step 106 of FIG. 7, and FIG. 12 is a diagram for explaining the calculation in step 106 of FIG.
In the flowchart shown in FIG. 11, the reception unit 401 acquires the detection information of the belt position sensors 43 and 44 (step 201). Based on the information, the determination unit 402 determines whether or not the intermediate transfer belt 15 is in a stable position (step 202). When the determination unit 402 determines that the intermediate transfer belt 15 is in the stable position, the process proceeds to step 205.

  Here, several methods are conceivable as a method for calculating the stable position. For example, it is conceivable to use a preset value as it is. This value is stored in advance in the storage unit 41 and is read out as necessary.

  Further, as a method for calculating the stable position for determining the stable position, it is conceivable to measure and use the belt stable position in a printing operation of a predetermined number or more performed in the past. That is, the belt stable position is measured and updated every time a predetermined number or more of printing operations are performed. When there is a change in the position in the main scanning direction as shown in FIGS. 9 and 10, for example, the stable position may be set to a value within the range of 80 to 100 μm.

  In addition, as a method for calculating the stable position for determining the stable position, a belt stable position measuring operation during image formation is provided before the color misregistration detection cycle, and the belt is rotated for a certain time or longer while performing image formation. It is conceivable to measure the stable position and use the value as the stable position. This color is stored in the storage unit 41 and read out as necessary.

  It is also conceivable to implement a combination of the above three methods. For example, the belt stable position measuring operation is performed immediately after the power is turned on. After that, when a predetermined number of printing operations or more are performed, the belt stable position in the printing operation is measured, and the stable position is updated.

  Here, FIG. 13 is a diagram illustrating an example of a method for calculating the stable position of the intermediate transfer belt 15. As shown in FIG. 13, in the state where the intermediate transfer belt 15 is at the stable position, the measurement result by the belt position sensor 43 is the measurement value W43 (stb), and the measurement result by the belt position sensor 44 is the measurement value. It is assumed that W44 (stb). The distance from the belt position sensor 43 to the Y color primary transfer position is Ly, and the distance from the Y color primary transfer position to the belt position sensor 44 is My. The distances Ly and My are stored in advance in the storage unit 41, and the determination unit 402 can read the distances Ly and My from the storage unit 41 as necessary.

  Then, the determination unit 402 reads out the distances Ly and My from the storage unit 41 and also reads out an arithmetic expression for obtaining the belt stable position Sy (stb) from the storage unit 41. The determination unit 402 sends the measured values W43 (stb) and W44 (stb) together with the read calculation formula and distances Ly and My to the calculation unit 403 to calculate the belt stable position Sy (stb) as belt stable position information. Instruct. Receiving the instruction, the calculation unit 403 substitutes the measured values W43 (stb), W44 (stb) and the distances Ly, My for the calculation formula, so that the belt stable position Sy (Y-color primary transfer position in the stable state) is obtained. Stb) is calculated. Specifically, the calculation unit 403 can obtain the belt stable position Sy (stb) using one of the following calculation formulas.

  The determination unit 402 acquires the belt stable position Sy (stb) at the Y color primary transfer position in the stable state from the calculation unit 403 and stores it in the storage unit 41. Similarly, the determination unit 402 includes a belt stable position (Sm (stb)) at the M color primary transfer position, a belt stable position (Sc (stb)) at the C color primary transfer position, and a belt at the K color primary transfer position. The stable position (Sk (stb)) is obtained by calculation, and the result is stored in the storage unit 41.

Returning to FIG. 11, the description will be continued. When the determination unit 402 determines that the intermediate transfer belt 15 is not in the stable position in step 202, the measured value W 43 (t) at the time t output from the belt position sensor 43 and the measurement at the time t output from the belt position sensor 44. The accepting unit 401 accepts the value W44 (t) and passes these to the determining unit 402. Thereby, the determination unit 402 acquires the measured values W43 (t) and W44 (t) at time t (step 203), and calculates the belt position S (t) at time t (step 204). Further, the determination unit 402 has errors (error due to deviation in the belt main scanning direction) ΔG (t), that is, error ΔGy (t), ΔDy, ΔDm, ΔDc, ΔDk when the intermediate transfer belt 15 is skewed. ΔGm (t), ΔGc (t), ΔGk (t) are determined (step 205), and the determination result is stored in the storage unit 41 (step 206). If the intermediate transfer belt 15 is in the stable position, it can be considered that there are no errors in the difference amounts ΔDy, ΔDm, ΔDc, ΔDk. On the other hand, if the intermediate transfer belt 15 is not in the stable position, the difference amounts ΔDy, ΔDm. , ΔDc, ΔDk, it is necessary to consider their errors ΔGy (t), ΔGm (t), ΔGc (t), ΔGk (t). The errors ΔGy (t), ΔGm (t), ΔGc (t), and ΔGk (t) can be regarded as deviation amounts from the stable position.
Thereafter, the determination unit 402 calculates registration misregistration amounts ΔRy, ΔRm, ΔRc, and ΔRk for each color (step 207), stores the calculation results in the storage unit 41 (step 208), and ends a series of processing.

  Here, step 204 in FIG. 11 will be described more specifically. That is, the calculation of the belt position Sy (t1) at the time t1 at the Y primary transfer position will be described with reference to FIG. In the skew state of the intermediate transfer belt 15 at time t = t1 shown in FIG. 12, the measurement result by the belt position sensor 43 is the measurement value W43 (t1), and the measurement result by the belt position sensor 44 is the measurement value. It is assumed that W44 (t1).

  Then, the determination unit 402 reads out the distances Ly and My from the storage unit 41 and also reads out an arithmetic expression for obtaining the belt position Sy (t) from the storage unit 41. The determination unit 402 sends the measured values W43 (t1) and W44 (t1) together with the read calculation formula and the distances Ly and My to the calculation unit 403 to instruct calculation of the belt position Sy (t1). Receiving the instruction, the calculation unit 403 substitutes the measured values W43 (t1) and W44 (t1) and the distances Ly and My into the calculation formula, so that the belt position Sy (Y color primary transfer position at time t = t1). Calculate t1). Specifically, the calculation unit 403 can obtain the belt position Sy (t1) by any one of the following calculation expressions.

Such calculation in step 204 is continuously performed for the times t = t1, t2, t3... Shown in FIG. The intervals between times t1, t2, t3,... Are appropriately determined according to the changing speed of the belt skew.
In addition to the belt position Sy (t) at the Y color primary transfer position, such calculation is also performed for the M color primary transfer position, the C color primary transfer position, and the K color primary transfer position. In this embodiment, the two belt position sensors 43 and 44 are provided, but the present invention is not limited to this. By providing a larger number than this, it becomes possible to calculate the belt position more accurately.

  Here, step 205 in FIG. 11 will be described more specifically. When the determination unit 402 obtains the belt position Sy (t1) at the time t1 at the Y color primary transfer position from the calculation unit 403, the determination unit 402 determines the error ΔGy (t1).

This error ΔGy (t1) is a deviation amount in the main scanning direction of the intermediate transfer belt 15, and is a value obtained by subtracting the belt stable position Sy (stb) from the belt position Sy (t1). Specifically, when the intermediate transfer belt 15 is not in the stable position, the value obtained by the following calculation formula is determined as the error ΔGy (t1).
ΔGy (t1) = Sy (t1) −Sy (stb)

Further, when the intermediate transfer belt 15 is in the stable position, the determined error ΔGy (t1) can be obtained by the following arithmetic expression.
ΔGy (t1) = 0

  Such determination in step 205 is continuously performed for the times t = t1, t2, t3... Shown in FIG. In addition to the error ΔGy (t) at the Y color primary transfer position, such a determination is also made for the M color primary transfer position, the C color primary transfer position, and the K color primary transfer position.

  Here, step 207 in FIG. 11 will be described more specifically. That is, the determination unit 402 uses the error ΔG (t) stored in the storage unit 41 and the difference amounts ΔDy, ΔDm, ΔDc, ΔDk detected in step 105 in FIG. , ΔRm, ΔRc, ΔRk.

More specifically, errors ΔGy (t1), ΔGm (t1), ΔGc (t1), and ΔGk (t1) are used in a period T12 from time t1 to time t2 shown in FIG. Accordingly, the registration misregistration amounts ΔRy, ΔRm, ΔRc, and ΔRk of each color in the period T12 are calculated by the following equations.
ΔRy = ΔDy−ΔGy (t1)
ΔRm = ΔDm−ΔGm (t1)
ΔRc = ΔDc−ΔGc (t1)
ΔRk = ΔDk−ΔGk (t1)
In the period T23 from time t2 to time t3 shown in FIG. 8, the same calculation is performed using the errors ΔGy (t2), ΔGm (t2), ΔGc (t2), ΔGk (t2).

1 is a schematic configuration diagram illustrating an image forming apparatus according to an exemplary embodiment. 2 is a plan view of an intermediate transfer belt. FIG. 6 is a time chart showing the on / off timing of the primary transfer power supply in each of the image forming units. It is a schematic block diagram which shows the contact type sensor which is an example of a belt position sensor. It is a schematic block diagram which shows the non-contact type sensor which is another example of a belt position sensor. It is a block diagram for demonstrating the structure of a control part. It is a flowchart which shows the procedure of a regicon operation. It is a perspective view which shows the pattern for image position recognition used for registration control operation | movement. It is a graph which shows an example of the fluctuation | variation of the main scanning direction position of a belt position sensor, a vertical axis | shaft is a belt position (micrometer) and a horizontal axis is time (t). It is a graph which shows an example of the fluctuation | variation of the main scanning direction position of a belt position sensor, a vertical axis | shaft is a belt position (micrometer) and a horizontal axis is time (t). It is a flowchart explaining the calculation in step 106 of FIG. It is a figure for demonstrating the calculation in step 106 of FIG. FIG. 6 is a diagram illustrating an example of a method for calculating a stable position of an intermediate transfer belt.

Explanation of symbols

DESCRIPTION OF SYMBOLS 15 ... Intermediate transfer belt, 15a ... Edge, 40 ... Control part, 41 ... Memory | storage part, 42 ... Color misregistration detection sensor, 43, 44 ... Belt position sensor, Ly, My ... Distance, PTN ... Pattern, S (t), Sy (t), Sy (t1) ... belt position, Sy (stb), Sm (stb), Sc (stb), Sk (stb) ... belt stable position, T12, T23 ... period, t1, t2, t3 ... time , W43 (stb), W44 (stb), W43 (t), W44 (t), W43 (t1), W44 (t1) ... measured values, ΔD, ΔDy, ΔDm, ΔDc, ΔDk ... difference amounts, ΔR, ΔRy , ΔRm, ΔRc, ΔRk... Registration displacement amount, ΔG (t), ΔGy (t), ΔGm (t), ΔGc (t), ΔGk (t), ΔGy (t1), ΔGm (t1), ΔGc (t1) , ΔGk (t1) ... error

Claims (3)

An image forming unit that transfers a plurality of images formed for each color to a transfer target;
Detecting means for detecting a skew state of the transfer target generated during the formation of the plurality of images in the image forming unit;
The stable position information about the transfer target during formation of the plurality of images is obtained and stored by a belt stable position measuring operation that is performed separately from the printing operation when the power is turned on, and the printing operation exceeds the predetermined value. A storage unit that is obtained and updated by the belt stable position measuring operation performed when
Obtaining means for obtaining a color shift value by reading a front Symbol plurality of images,
Correction means for correcting the color misregistration value obtained by the acquisition means using the detection result of the detection means and the stable position information stored in the storage unit;
An image forming apparatus including:   The image forming apparatus according to claim 1, wherein the detection unit includes at least two sensors that detect a position of an end of the transfer target. A computer apparatus provided in an image forming apparatus that transfers a toner image formed by developing an electrostatic latent image written by an exposure device on a photoreceptor to a belt member or a recording material held by the belt member.
A detection function for detecting a skew state of the belt member generated during formation of a plurality of images formed for each color;
The stable position information about the recording material during the formation of the plurality of images is obtained and stored by a belt stable position measuring operation performed separately from the printing operation when the power is turned on, and the printing operation exceeds the predetermined value. A storage function that is obtained and updated by the belt stable position measurement operation that is performed when
An acquisition function of acquiring a color shift value by reading a front Symbol plurality of images,
A correction function for correcting the color misregistration value by the acquisition function using the detection result of the detection function and the stable position information stored in the storage function;
A program that realizes

Images