JP2007316608A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of avoiding deterioration of accuracy in a positional displacement correction and phase adjustment caused by forming an image for detecting positional displacement and an image for detecting speed variation in such a state that a linear velocity difference is provided to photoreceptors 3Y, 3C, 3M and 3K. <P>SOLUTION: The image for detecting positional displacement and the image for detecting speed variation are formed in such a state that the photoreceptors 3Y, 3C, 3M and 3K are driven at the same linear velocity as one another by a positional displacement correction control where toner images formed on the photoreceptors 3Y, 3C, 3M and 3K are transferred to an intermediate transfer belt 41 so as to form the image for detecting positional displacement, and the positional displacement of each toner image is restrained by setting the drive speed of the photoreceptors 3Y, 3C, 3M and 3K respectively individually on the basis of a result obtained by detecting the image for detecting positional displacement by an optical sensor unit 136, and a variation pattern detection control where the image for detecting speed variation comprising a plurality of toner images is formed on the photoreceptors 3Y, 3C, 3M and 3K and transferred to the intermediate transfer belt 41, and a speed variation pattern per rotation of the photoreceptor is detected on the basis of a result obtained by detecting the image for detecting speed variation by the optical sensor unit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, or the like that obtains a superimposed image by superimposing and transferring a visible image formed on each of a plurality of latent image carriers.

  Conventionally, as this type of image forming apparatus, the one described in Patent Document 1 is known. The image forming apparatus includes a plurality of photosensitive members that are latent image carriers and a belt member that is an endless moving member that can be moved endlessly so as to sequentially pass through transfer positions facing the respective photosensitive members. Then, toner images having different colors formed on the surface of each photoconductor are formed by an electrophotographic process. These toner images are transferred while being superimposed on the surface of the recording paper sequentially passing through the transfer positions while being held on the surface of the belt member. By this superposition transfer, a multicolor toner image is formed on the surface of the recording paper.

  In such a configuration, the position of the toner image formed on each photoconductor is relatively shifted due to fluctuations in the optical path due to temperature changes of the optical system that optically scans each photoconductor, or rattling of each photoconductor that can be attached and detached. It may end up. When such a shift occurs, a registration shift of each color toner image with respect to the recording paper occurs, and the image quality deteriorates.

  In view of this, in the image forming apparatus described in Patent Document 1, a linear velocity difference obtained by positional deviation correction control is provided between the photoconductors so as to suppress misalignment of the color toner images. In this misalignment correction control, first, a predetermined reference toner image is formed on each photoconductor at a predetermined timing, and then transferred to the surface of the belt member to obtain an image for detecting misalignment. If the toner image forming positions of the respective photoconductors are not relatively shifted, these reference toner images are transferred to the belt member at a predetermined pitch in the moving direction. For this reason, based on the timing at which these reference toner images are detected by the photosensor, the relative positional shift amounts of the respective reference toner images can be calculated. Then, based on the calculation result, for each photoconductor, an individual driving speed capable of canceling the positional deviation of each toner image is obtained. In a print job, each photoconductor is driven at the drive speed thus obtained, and a linear speed difference is provided between the photoconductors, so that the toner image on each photoconductor is not displaced on the recording paper. It becomes possible to superimpose.

  In this positional deviation correction control, the positional deviation of the toner image in the sub-scanning direction (photosensitive member surface moving direction) is roughly corrected by correcting the optical writing start timing for each photosensitive member, and the driving speed of each photosensitive member is adjusted. Appropriate correction amount is calculated to correct subtle misalignment. Specifically, in the method of performing main scanning while deflecting light (writing light) for writing a latent image to each photoconductor by a common single polygon mirror, the optical writing start timing for each photoconductor Can be adjusted only in time units corresponding to writing of one line (one scanning line). As a result, even when the optical writing start timing is adjusted, a positional deviation of 1/2 dot or less in the sub-scanning direction (photosensitive member surface moving direction) may remain. For example, when a positional deviation of 3/4 dots occurs between the two photoconductors in the sub-scanning direction, the optical writing start timing for one of the photoconductors is set as the writing time for one line. Suppose you just shifted back and forth. Then, the amount of positional deviation in the sub-scanning direction can be reduced to an amount corresponding to ¼ dot. However, if the optical writing start timing is further shifted back and forth by the writing time for one line, the positional deviation amount in the sub-scanning direction is set to an amount corresponding to 5/4 dots which is larger than the initial amount. For this reason, the optical writing timing is shifted back and forth by the writing time for one line, but in this case, a positional deviation of 1/4 dot remains. Therefore, the remaining 1/4 dot position shift is reduced by the difference in the linear velocity of the photosensitive member.

  On the other hand, as the positional deviation of the toner image, in addition to the above-described fluctuations in the optical path of the optical system and backlash of the photoconductor, a photoconductor gear that transmits driving force to the photoconductor while rotating on the same axis as the photoconductor And the like due to the eccentricity of the drive transmission rotating member such as the coupling. If the drive transmission member that rotates on the same axis as the photoconductor is decentered, the area on the photoconductor surface that moves from the optical writing position to the transfer position at a faster speed than any other surface area. And a portion moving at a slower speed than any other surface portion is generated at a position shifted from each other by 180 [°]. The dots formed on the former surface portion reach the transfer position at an earlier timing than originally intended, and the dots formed on the latter surface portion arrive at the transfer position at an earlier timing than originally intended. If the latter dot is superimposed on the former dot from another photoconductor, or if the former dot is superimposed on the latter dot from another photoconductor, the misalignment due to the misalignment of the two will occur. It will occur.

  As in the image forming apparatus described in Patent Document 2, if the fluctuation pattern detection control for detecting the speed fluctuation pattern on the surface of each photoconductor and the phase adjustment control for adjusting the phase of the speed fluctuation pattern are performed. This kind of overlay displacement can be suppressed. In the fluctuation pattern detection control, first, a speed fluctuation detection image composed of a plurality of toner images arranged at a predetermined pitch in the surface movement direction is formed on the surface of the photoreceptor. Then, after this speed fluctuation detection image is transferred to the belt member, each toner image in the speed fluctuation detection image is detected by a photo sensor, and a speed fluctuation pattern per one rotation of the photosensitive member is determined based on the detection interval. To detect. On the other hand, a mark provided on the photoconductor gear or the like is detected by another photosensor to detect the timing at which the photoconductor reaches a predetermined rotation angle. As a result, the time difference between the time when the photoconductor reaches a predetermined rotation angle and the time when the surface speed of the photoconductor becomes maximum or minimum is obtained for each photoconductor. When speed pattern detection control is performed in this way, phase adjustment control is performed every time a print job is generated, and the phase difference of the speed variation pattern of each photoconductor is adjusted. Specifically, the timing at which each photoconductor has reached a predetermined rotation angle is grasped by, for example, detecting a mark attached to a predetermined portion of the photoconductor gear with a photo sensor. Then, based on the timing and the time difference obtained in advance by the variation pattern detection control, by temporarily changing the drive amounts of a plurality of drive motors that individually drive each photoconductor, each photoconductor Adjust the phase difference of the speed fluctuation pattern. Alternatively, at the end of the print job, each drive motor is stopped with the phase difference of the speed variation pattern of each photoconductor adjusted, and then the next print job is started with the phase difference adjusted. By adjusting in this way, at each transfer position, the dots that arrive at the transfer position at an earlier timing than the original or the dots that arrive at the transfer position at an earlier timing than the original are synchronized so that the respective colors are superimposed. Misalignment can be suppressed.

  In the case where the arrangement pitch of the plurality of photoconductors is an integral multiple of the circumference of the photoconductor, while the toner image transferred from the photoconductor to a recording sheet or the like moves to the adjacent transfer position, Each photoconductor rotates an integer number of times. For this reason, by adjusting the phase difference of the speed variation pattern of each photoconductor to zero, it is possible to synchronize dots having an appropriate relationship at each transfer position. On the other hand, in the configuration in which the arrangement pitch of the plurality of photoconductors is not an integral multiple of the circumferential length of the photoconductor, each phase difference of speed fluctuation is provided between the photoconductors for each predetermined time, so that each transfer It is possible to synchronize dots having an appropriate relationship in position.

Japanese Patent Laid-Open No. 10-20607 JP-A-9-146329

  However, even when the above-described positional deviation correction control and phase adjustment control are performed, the positional deviation of the toner image may not be sufficiently suppressed. Therefore, the present inventors have conducted various experiments and investigated the cause, and have found the following. That is, if a linear velocity difference is provided between the photosensitive members, a linear velocity difference is also provided between the belt member and the photosensitive member. If the above-described positional deviation detection image or fluctuation pattern detection image is formed in such a state, a subtle density unevenness occurs in each toner image inside the image. For example, a toner image transferred to a belt member from a photosensitive member moving at a higher linear velocity than the belt member has a higher density on the upstream side in the belt moving direction than on the downstream side. Conversely, the toner image transferred to the belt member from the photosensitive member moving at a slower linear speed than the belt member has a density on the downstream side in the belt moving direction that is higher than the density on the upstream side. When positional deviation correction control is performed in a state where a linear velocity difference is provided for each photoconductor, the position of each toner image in the belt moving direction (sub-scanning direction) may not be accurately detected due to such density unevenness. As a result, it was found that proper positional deviation correction and phase adjustment were not performed.

  The present invention has been made in view of the above background, and an object thereof is to provide the following image forming apparatus. That is, it is possible to avoid deterioration in accuracy of position shift correction and phase adjustment by forming a position shift detection image and a speed fluctuation detection image with a plurality of latent image carriers provided with linear velocity differences. Forming device.

In order to achieve the above object, a first aspect of the present invention provides a plurality of latent image carriers that carry a latent image on a surface that moves endlessly, and a plurality of drive sources that individually drive each latent image carrier. A latent image writing means for writing a latent image on each latent image carrier based on image information, and a plurality of latent images written on each latent image carrier to individually develop a visible image. A visible image forming unit having a developing unit, an endless moving body that moves the surface endlessly so as to sequentially pass through positions facing each latent image carrier, and a surface formed on each latent image carrier. A transfer means for transferring a visible image to a recording medium held on the surface of the endless moving body, or transferring the visible image to the recording body after being transferred to the surface of the endless moving body; Image detection means for detecting the image and a predetermined visible image on each latent image carrier Based on the detection result by the image detection means of the position shift detection image obtained by transferring to the surface of the endless moving body, the relative position shift amount of the visible image on each latent image carrier is calculated. And an image forming apparatus including a control unit that performs positional deviation correction control that individually calculates a driving speed for each of the driving sources based on the calculation result, and each driving source is driven at the same speed And the control means is configured to form and detect the image for detecting misalignment.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, when an error occurs during the execution of the positional deviation correction control, the drive source is driven in the subsequent image forming operation. The control means is configured to individually set the speed to the speed obtained by the previous positional deviation correction control.
According to a third aspect of the present invention, in the image forming apparatus of the first aspect, when the positional deviation correction control ends abnormally, the drive speed of each drive source is set to the previous time in the subsequent image forming operation. The control means is configured to individually set the speed determined by the positional deviation correction control.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, after the positional deviation correction control is normally completed, the respective driving sources are transferred to the recording body without being stopped. When the image forming operation is performed, the control means is configured to set the driving speed of each driving source to the speed obtained by the positional deviation correction control prior to the image forming operation. It is characterized by.
Further, the invention of claim 5 is based on a plurality of latent image carriers that carry a latent image on a rotating surface, a plurality of drive sources for individually driving each latent image carrier, and image information. A visible image writing unit that writes a latent image on each latent image carrier and a plurality of developing units that individually develop the latent image written on each latent image carrier to obtain a visible image. An endless moving body that moves the surface endlessly so as to sequentially pass through the opposing positions of the image forming means and each latent image carrier, and a visible image formed on the surface of each latent image carrier. Transfer means for transferring to the recording body held on the surface of the moving body or transferring to the surface of the endless moving body and then transferring to the recording body, and image detecting means for detecting a visible image on the endless moving body And each of the plurality of latent image carriers has a predetermined rotation angle. A rotation angle detecting means for detecting a predetermined angle and a control means for performing a predetermined control, the control means obtaining a predetermined visible image from each latent image carrier onto the surface of the endless moving body. Based on the detection result of the image for detecting the positional deviation by the image detecting means, the relative positional deviation amount of the visible image on each latent image carrier is calculated, and the respective driving based on the calculation result. After the positional deviation correction control for individually calculating the driving speed of the source and the image for detecting the speed fluctuation composed of a plurality of predetermined visible images formed on the latent image carrier and transferred to the endless moving body A fluctuation pattern detection control for detecting a speed fluctuation pattern per one rotation of the latent image carrier based on a detection result of the image for speed fluctuation detection by the image detection means and a detection result by the rotation angle detection means; Each dive In the image forming apparatus for performing phase adjustment control for adjusting the phase of the speed fluctuation pattern of each latent image carrier based on the result of the speed fluctuation pattern for the carrier, each drive source is The control means is configured to form and detect the speed variation detection image while being driven at the same speed.
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the control means is configured to form and detect the misalignment detection image in a state where the respective driving sources are driven at the same speed. It is characterized by comprising.
According to a seventh aspect of the present invention, in the image forming apparatus of the sixth aspect, after the image based on the image information is formed on the recording body, the phase of the speed variation pattern in each of the plurality of latent image carriers is determined. In the adjusted state, by stopping the driving of the plurality of driving sources, the control for previously adjusting the phase of the speed fluctuation pattern of the plurality of latent image carriers when the driving sources are next driven The control means is configured to be implemented as adjustment control.
According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, in the variation pattern detection control, the speed variation with respect to a reference latent image carrier that is one of the plurality of latent image carriers. The reference latent image carrier so as to transfer the detection image and the speed fluctuation detection image for the other latent image carrier in a direction perpendicular to the surface movement direction with respect to the surface of the endless moving body. The formation of the speed fluctuation detection image on the body is started based on the detection result of the rotation angle detection means on the reference latent image carrier, while the speed fluctuation detection image on the other latent image carrier Of the drive source corresponding to the other latent image carrier in the phase adjustment control based on the phase shift of the speed fluctuation pattern of the speed fluctuation detection image. Drive stop To determine the timing, it is characterized in that constitute the control means.
According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, prior to performing the variation pattern detection control, the plurality of drive sources are driven, and the drive sources are stopped. Instead of the timing, the control means is configured to stop at a predetermined reference timing and re-drive each of the driving sources, and then perform the variation pattern detection control. Is.
According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, when the fluctuation pattern detection control is performed, the driving of each driving source is started with the respective driving sources set to the same driving speed. As described above, the control means is configured.
The invention according to claim 11 is the image forming apparatus according to claim 10, wherein after performing the fluctuation pattern detection control, an image forming operation is performed for transferring to the recording body without stopping each drive source. In this case, the control means is configured to perform the image forming operation after the phase adjustment control is performed and the driving speed of each driving source is set to the speed determined by the positional deviation correction control. It is characterized by that.
According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, the positional deviation correction control or the fluctuation pattern detection control is normally performed while the drive sources are driven at the same drive speed. The control means is configured to turn on the setting for driving each drive source at the drive speed obtained by the positional deviation correction control after each drive source is stopped after It is characterized by.

  In these inventions, the position shift detection image or the speed fluctuation detection image is formed in a state where the drive sources are driven at the same speed, that is, in a state where a plurality of latent image carriers are driven at a constant speed. Further, it is possible to avoid deterioration in accuracy of position shift correction and phase adjustment due to formation of a position shift detection image and a speed variation detection image in a state where a linear velocity difference is provided in a plurality of latent image carriers.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described.
First, the basic configuration of the printer according to this embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a printer according to the present embodiment. The printer shown in the figure includes four process units 1Y, 1C, 1M, and 1K for yellow, magenta, cyan, and black (hereinafter referred to as Y, C, M, and K) as process units as toner image forming means. ing. These use Y, C, M, and K toners of different colors as image forming substances for forming an image, but the other configurations are the same. Taking a process unit 1Y for generating a Y toner image as an example, this has a photoconductor unit 2Y and a developing unit 7Y as shown in FIG. As shown in FIG. 3, the photosensitive unit 2Y and the developing unit 7Y are integrally attached to and detached from the printer body as a process unit 1Y. However, in a state where it is detached from the printer main body, the developing unit 7Y can be attached to and detached from a photosensitive unit (not shown) as shown in FIG.

  In FIG. 2 described above, the photoconductor unit 2Y includes a drum-shaped photoconductor 3Y serving as a latent image carrier, a drum cleaning device 4Y, a static eliminator (not shown), a charging device 5Y, and the like.

  The charging device 5Y uniformly charges the surface of the photoreceptor 3Y that is driven to rotate in the clockwise direction in the drawing by a driving unit (not shown). In the figure, the charging roller 6Y that is driven to rotate counterclockwise in the drawing while a charging bias is applied by a power source (not shown) is brought close to the photosensitive member 3Y, thereby charging the photosensitive member 3Y uniformly. Device 5Y is shown. Instead of the charging roller 6Y, a roller that contacts a charging brush may be used. Further, a charger that uniformly charges the photoreceptor 3Y by a charger method, such as a scorotron charger, may be used. The surface of the photoreceptor 3Y uniformly charged by the charging device 5Y is exposed and scanned by a laser beam emitted from an optical writing unit to be described later, and carries a Y electrostatic latent image.

  The developing unit 7Y as developing means has a first agent accommodating portion 9Y in which a first conveying screw 8Y is disposed. Further, it also has a second agent storage portion 14Y in which a toner concentration sensor (hereinafter referred to as a toner concentration sensor) 10Y composed of a magnetic permeability sensor, a second conveying screw 11Y, a developing roll 12Y, a doctor blade 13Y, and the like are disposed. . In these two agent storage portions, a Y developer (not shown) composed of a magnetic carrier and a negatively chargeable Y toner is included. The first transport screw 8Y is driven to rotate by a driving unit (not shown), thereby transporting the Y developer in the first agent storage unit 9Y from the near side to the far side in the direction perpendicular to the drawing sheet. And it penetrates into the 2nd agent accommodating part 14Y through the communication port which is not shown in the partition wall between the 1st agent accommodating part 9Y and the 2nd agent accommodating part 14Y.

  The second transport screw 11Y in the second agent storage portion 14Y is driven to rotate by a driving means (not shown), thereby transporting the Y developer from the back side to the front side in the drawing. The toner concentration of the Y developer being conveyed is detected by the toner concentration sensor 10Y fixed to the bottom of the first agent storage portion 14Y. In this manner, the developing roll 11Y is arranged in a posture parallel to the second transport screw 11Y above the second transport screw 11Y that transports the Y developer. The developing roller 11Y includes a magnet roller 16Y in a developing sleeve 15Y made of a non-magnetic pipe that is driven to rotate counterclockwise in the drawing. A part of the Y developer conveyed by the second conveying screw 11Y is pumped up to the surface of the developing sleeve 15Y by the magnetic force generated by the magnet roller 16Y. Then, after the layer thickness is regulated by the doctor blade 13Y disposed so as to maintain a predetermined gap from the developing sleeve 15Y as a developing member, the layer thickness is regulated and conveyed to the developing area facing the photosensitive member 3Y. Y toner is adhered to the Y electrostatic latent image. This adhesion forms a Y toner image on the photoreceptor 3Y. The Y developer that has consumed the Y toner by the development is returned to the second conveying screw 11Y as the developing sleeve 15Y of the developing roll 12Y rotates. And if it conveys to the near end in a figure, it will return in the 1st agent accommodating part 9Y via the communication port which is not shown in figure.

  The result of detecting the magnetic permeability of the Y developer by the toner concentration sensor 10Y is sent as a voltage signal to a control unit (not shown). Since the magnetic permeability of the Y developer shows a correlation with the Y toner density of the Y developer, the toner density sensor 10Y outputs a voltage having a value corresponding to the Y toner density. The control unit includes a RAM, in which a V Vref for Y which is a target value of the output voltage from the toner density sensor 10Y and a toner density sensor for C, M, and K mounted in another developing unit. The data of C Vtref, M Vtref, and K Vtref, which are target values of the output voltage, are stored. For the Y developing unit 7Y, the value of the output voltage from the toner density sensor 10Y is compared with the Y Vtref, and the Y toner supply device (not shown) is driven for a time corresponding to the comparison result. By this driving, an appropriate amount of Y toner is supplied to the Y developer whose Y toner density has been reduced due to the consumption of Y toner accompanying development in the first agent storage portion 9Y. For this reason, the Y toner concentration of the Y developer in the second agent container 14Y is maintained within a predetermined range. Similar toner supply control is performed for the developers in the process units (1C, M, K) for other colors.

  The Y toner image formed on the photoreceptor 3Y is intermediately transferred to an intermediate transfer belt described later. The drum cleaning device 4Y of the photoreceptor unit 2Y removes the toner remaining on the surface of the photoreceptor 3Y after the intermediate transfer process. As a result, the surface of the photoreceptor 3Y that has been subjected to the cleaning process is neutralized by a neutralizing device (not shown). By this charge removal, the surface of the photoreceptor 3Y is initialized and prepared for the next image formation. In FIG. 1 described above, in the process units 1C, M, and K for other colors, C, M, and K toner images are similarly formed on the photoreceptors 3C, M, and K, and the intermediate transfer belt is formed. Intermediate transfer.

  An optical writing unit 20 is arranged below the process units 1Y, 1C, 1M, and 1K in the drawing. The optical writing unit 20 serving as a latent image forming unit irradiates the photoreceptors 3Y, C, M, and K of the process units 1Y, C, M, and K with the laser light L emitted based on the image information. Thereby, electrostatic latent images for Y, C, M, and K are formed on the photoreceptors 3Y, 3C, 3M, and 3K. The optical writing unit 20 deflects the laser light L emitted from the light source by the polygon mirror 21 that is rotationally driven by a motor, and passes through the photosensitive members 3Y, 3C, 3M, and 3K via a plurality of optical lenses and mirrors. Is irradiated. In place of such a configuration, an optical scanning device using an LDE array may be employed.

  A first paper feed cassette 31 and a second paper feed cassette 32 are disposed below the optical writing unit 20 so as to overlap in the vertical direction. In each of these paper feed cassettes, a plurality of recording papers P as recording members are accommodated in a stack of recording papers. The uppermost recording paper P includes a first paper feed roller 31a, The second paper feed rollers 32a are in contact with each other. When the first paper feed roller 31a is driven to rotate counterclockwise in the figure by a driving means (not shown), the uppermost recording paper P in the first paper feed cassette 31 is vertically oriented on the right side of the cassette in the figure. The paper is discharged toward the paper feed path 33 arranged so as to extend. Further, when the second paper feed roller 32 a is driven to rotate counterclockwise in the figure by a driving means (not shown), the uppermost recording paper P in the second paper feed cassette 32 is directed toward the paper feed path 33. Discharged. A plurality of transport roller pairs 34 are arranged in the paper feed path 33, and the recording paper P fed into the paper feed path 33 is sandwiched between the rollers of the transport roller pair 34 while being fed between the paper feed paths 33. 33 is conveyed from the lower side to the upper side in the figure.

  A registration roller pair 35 is disposed at the end of the paper feed path 33. The registration roller pair 35 temporarily stops the rotation of both rollers as soon as the recording paper P fed from the conveyance roller pair 34 is sandwiched between the rollers. Then, the recording paper P is sent out toward a later-described secondary transfer nip at an appropriate timing.

  Above each of the process units 1Y, 1C, 1M, and 1K, a transfer unit 40 that is endlessly moved counterclockwise in the drawing while an intermediate transfer belt 41 that is an endless moving body is stretched is disposed. The transfer unit 40 serving as transfer means includes an intermediate transfer belt 41, a belt cleaning unit 42, a first bracket 43, a second bracket 44, and the like. Further, four primary transfer rollers 45Y, 45C, 45M, 45K, a secondary transfer backup roller 46, a drive roller 47, an auxiliary roller 48, a tension roller 49, and the like are also provided. The intermediate transfer belt 41 is endlessly moved counterclockwise in the figure by the rotational driving of the driving roller 47 while being stretched by these eight rollers. The four primary transfer rollers 45Y, 45C, 45M, 45K each sandwich the intermediate transfer belt 41 moved endlessly in this manner from the photoreceptors 3Y, 3C, 3M, and 3K to form primary transfer nips. ing. Then, a transfer bias having a polarity opposite to that of the toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 41. The intermediate transfer belt 41 sequentially passes through the primary transfer nips for Y, C, M, and K along with its endless movement, and on the photoreceptor 3Y, C, M, and K on the front surface. The Y, C, M, and K toner images are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 41.

  The secondary transfer backup roller 46 sandwiches the intermediate transfer belt 41 with the secondary transfer roller 50 disposed outside the loop of the intermediate transfer belt 41 to form a secondary transfer nip. The registration roller pair 35 described above feeds the recording paper P sandwiched between the rollers toward the secondary transfer nip at a timing at which the recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 41. The four-color toner image on the intermediate transfer belt 41 is affected by the secondary transfer electric field formed between the secondary transfer roller 50 to which the secondary transfer bias is applied and the secondary transfer backup roller 46, and the influence of the nip pressure. The secondary transfer is batch-transferred onto the recording paper P in the secondary transfer nip. Then, combined with the white color of the recording paper P, a full color toner image is obtained.

  Untransferred toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 41 after passing through the secondary transfer nip. This is cleaned by the belt cleaning unit 42. In the belt cleaning unit 42, the cleaning blade 42a is brought into contact with the front surface of the intermediate transfer belt 41, whereby the transfer residual toner on the belt is scraped off and removed.

  The first bracket 43 of the transfer unit 40 swings at a predetermined rotation angle about the rotation axis of the auxiliary roller 48 as the solenoid (not shown) is turned on / off. When forming a monochrome image, the printer of the present image forming system rotates the first bracket 43 a little counterclockwise in the drawing by driving the solenoid described above. This rotation causes the Y, C, M primary transfer rollers 45Y, C, M to revolve counterclockwise in the drawing around the rotation axis of the auxiliary roller 48, thereby causing the intermediate transfer belt 41 to move in the Y, C direction. , M is separated from the photoconductors 3Y, 3C, 3M. Of the four process units 1Y, 1C, 1M, and 1K, only the K process unit 1K is driven to form a monochrome image. As a result, it is possible to avoid exhaustion of the process units due to wastefully driving the process units for Y, C, and M during monochrome image formation.

  A fixing unit 60 is disposed above the secondary transfer nip in the drawing. The fixing unit 60 includes a pressure heating roller 61 that includes a heat source such as a halogen lamp, and a fixing belt unit 62. The fixing belt unit 62 includes a fixing belt 64 as a fixing member, a heating roller 63 containing a heat source such as a halogen lamp, a tension roller 65, a driving roller 66, a temperature sensor (not shown), and the like. Then, the endless fixing belt 64 is endlessly moved in the counterclockwise direction in the drawing while being stretched by the heating roller 63, the tension roller 65, and the driving roller 66. In the process of endless movement, the fixing belt 64 is heated from the back side by the heating roller 63. A pressure heating roller 61 that is rotationally driven in the clockwise direction in the drawing is in contact with the surface of the fixing belt 64 that is heated in this manner from the front side. Thereby, a fixing nip where the pressure heating roller 61 and the fixing belt 64 abut is formed.

  Outside the loop of the fixing belt 64, a temperature sensor (not shown) is disposed so as to face the front surface of the fixing belt 64 with a predetermined gap, and the fixing belt 64 just before entering the fixing nip. Detect surface temperature. This detection result is sent to a fixing power supply circuit (not shown). The fixing power supply circuit performs on / off control of power supply to the heat generation source included in the heating roller 63 and the heat generation source included in the pressure heating roller 61 based on the detection result of the temperature sensor. As a result, the surface temperature of the fixing belt 64 is maintained at about 140 [°].

  In FIG. 1 described above, the recording paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 41 and then sent into the fixing unit 60. Then, in the process of being conveyed from the lower side to the upper side in the figure while being sandwiched between the fixing nips in the fixing unit 60, the full-color toner image is fixed by being heated or pressed by the fixing belt 64.

  The recording paper P subjected to the fixing process in this manner is discharged outside the apparatus after passing between the rollers of the paper discharge roller pair 67. A stack unit 68 is formed on the upper surface of the housing of the printer main body, and the recording paper P discharged to the outside by the discharge roller pair 67 is sequentially stacked on the stack unit 68.

  Above the transfer unit 40, four toner cartridges 100 Y, C, M, and K that store Y, C, M, and K toners are disposed. The Y, C, M, and K toners in the toner cartridges 100Y, 100C, M, and K are appropriately supplied to the developing units 7Y, C, M, and K of the process units 1Y, C, M, and K. These toner cartridges 100Y, 100C, 100M, and 100K are detachable from the printer main body independently of the process units 1Y, 1C, 1M, and 1K.

  FIG. 5 is a perspective view showing a main body side drive transmission unit which is a drive transmission system fixed in the printer housing. FIG. 6 is a plan view showing the main body side drive transmission portion from above. A support plate is erected in the printer housing, and four process drive motors 120Y, 120C, 120M, 120K, and 120K are fixed thereto. Driving gears 121Y, 121C, 121M, and 121K are fixed to the rotation shafts of process drive motors 120Y, 120C, 120M, and 120K that are drive sources. Below the rotation shafts of the process drive motors 120Y, 120C, 120M, 120K, development gears 122Y, 122C, 122M, 122K, which are slidably rotatable while engaging with a fixed shaft (not shown) projecting from the support plate. Is arranged. The developing gears 122Y, 122C, 122C, 122M, 122C, 122C, 122C, 122C, 122C, 122C, 122C, and 122-C have first gear portions 123Y, 123M, 123K that rotate on the same rotational axis. The second gear portions 124Y, 124C, 124M, and 124K are positioned closer to the front end side of the rotation shafts of the process drive motors 120Y, 120C, 120M, and 120K than the first gear portions 123Y, 123C, 123M, and 130K. The developing gears 122Y, 122M, 122C, 122K, and 122K are engaged with the first gear portions 123Y, 123M, 123C, and 123K in mesh with the driving gears 121Y, 121C, 121M, 121K of the process drive motors 120Y, 120C, 120M, 120K By the rotation of the drive motors 120Y, 120C, 120M, and 120K, sliding rotation is performed on the fixed shaft.

  The process drive motors 120Y, 120C, 120M, 120K, and 120K, which are drive sources, are DC servo motors that are a type of DC brushless motor. The reduction ratio between the driving gears 121Y, 121C, 121M, and 121K and the photoconductor gears 133Y, 133C, 133M, and 133K is, for example, 1:20. The reason why the number of speed reduction stages from the driving gear to the photoconductor gear is set to one is to reduce the number of parts and reduce the cost, and to reduce the cause of meshing error and transmission error due to eccentricity by using two gears. It is from the aim to do. By reducing the speed by one step, the photosensitive member gear has a larger diameter than the photosensitive member at a relatively large reduction ratio of 1:20. By using such a large-diameter photoconductor gear, the pitch error on the photoconductor surface corresponding to the one-tooth engagement of the gear is reduced, and the influence of uneven print density (banding) in the sub-scanning direction is reduced. There is also an aim. The reduction ratio is determined based on the speed region where high efficiency and high rotation accuracy can be obtained from the relationship between the target speed of the photoreceptor and the motor characteristics.

  On the left side of the developing gears 122Y, 122C, 122M, and 122K, first relay gears 125Y, 125C, 125M, and 125K that slide and rotate while engaging with a fixed shaft (not shown) are disposed. These mesh with the second gear portions 124Y, C, M, and K of the developing gears 122Y, 122C, 122K, and receive rotational driving force from the developing gears 122Y, 122C, 122M, and 122K, on the fixed shaft. Slide and rotate. The first relay gears 125Y, C, M, and K are engaged with the second gear portions 124Y, C, M, and K on the upstream side in the drive transmission direction, and the clutch input gears 126Y, C on the downstream side in the drive transmission direction. , M, K are engaged. These clutch input gears 126Y, C, M, and K are supported by the developing clutches 127Y, 127C, 127M, and 127K. The development clutches 127Y, 127C, 127M, 127K, and the like are connected to the clutch shaft with the rotational driving force of the clutch input gears 126Y, 126C, 126M, 126K, as the power supply is turned on / off by a control unit (not shown). The input gear 126Y, C, M, K is idled. Clutch output gears 128Y, 128C, 128M, and 128K are fixed to the front ends of the clutch shafts of the developing clutches 127Y, 127C, 127M, and 127K. When power is supplied to the developing clutches 127Y, 127C, 127C, 127M, 127K, the rotational driving force of the clutch input gears 126Y, 126C, 126M is connected to the clutch shaft, and the clutch output gears 128Y, 128C, 128M, 128K Rotate. On the other hand, when the power supply to the development clutches 127Y, 127C, 127M, 127K is cut off, the clutch input gears 126Y, 126C, 126M, 126K, 126Y, 126C, 126M, 126K, 126Y, 126C, 126M Rotates idly on the clutch shaft, the rotation of the clutch output gears 128Y, 128C, 128M, 128K stops.

  On the left side of the clutch output gears 128Y, C, M, and K, second relay gears 129Y, 129Y, C, M, and K that are slidably rotated while being engaged with a fixed shaft (not shown) are disposed. It rotates while meshing with the clutch output gear 128Y, C, M, K.

  On the printer body side, the following drive transmission system is configured to correspond to each of the four process units. That is, the process drive motor 120 → the driving gear 121 → the first gear portion 123 of the developing gear 122 → the second gear portion 124 → the first relay gear 125 → the clutch input gear 126 → the clutch output gear 128 → the second relay gear 129. It is a drive transmission system.

  FIG. 7 is a partial perspective view showing one end of the Y process unit 1Y. The developing sleeve 15Y in the casing of the developing unit 7Y has a shaft member penetrating the side surface of the casing and protruding outside. The sleeve upstream gear 131Y is fixed to the protruding shaft member portion. A fixed shaft 132Y projects from the side of the casing, and the third relay gear 130Y engages with the sleeve upstream gear 131Y while being slidably rotated.

  In a state where the Y process unit 1Y is set in the printer main body, the second relay gear 129Y previously shown in FIGS. 5 and 6 is engaged with the third relay gear 130Y in addition to the sleeve upstream gear 131Y. Then, the rotational driving force of the second relay gear 129Y is sequentially transmitted to the third relay gear 130Y and the sleeve upstream gear 131Y, and the developing sleeve 13Y is rotationally driven.

  Although only the process unit 1Y for Y has been described with reference to the drawings, the rotational driving force is similarly transmitted to the developing sleeve also in the process units for other colors.

  Further, in FIG. 7, only one end portion of the Y process unit 1Y is shown, but the shaft member on the other end side of the developing sleep 15Y penetrates the side surface on the other end side of the casing and protrudes to the outside. A sleeve downstream gear (not shown) is fixed to the protruding portion. Further, the first conveying screw 7Y and the second conveying screw 10Y previously shown in FIG. 2 also have their shaft members penetrating through the side surface on the other end side of the casing, and the protruding portion includes a first screw gear (not shown), The second screw gear is fixed. When the developing sleeve 15Y is rotated by drive transmission by the sleeve upstream gear 131Y, the sleeve downstream gear is rotated on the other end side. Then, the second conveying screw 11Y receiving the driving force by the second screw gear meshed with the sleeve downstream gear rotates and the first conveying screw 8Y receiving the driving force by the first screw gear meshed with the second screw gear. Rotates. The process units for other colors have the same configuration.

  Thus, the driving gear 121, the developing gear 122, the first relay gear 125, the clutch input gear 126, the clutch output gear 128, the second relay gear 129, the third relay gear 130, the sleeve upstream gear 131, the sleeve downstream gear, Four sets of developing gear groups including two screw gears and a first screw gear are configured corresponding to each process unit.

  FIG. 8 is a perspective view showing the Y photoconductor gear 133Y and its peripheral configuration. In the figure, the driving gear 121Y is engaged with the first gear portion 123Y of the developing gear 122Y and the photosensitive member gear 133Y as a latent image gear. The photoconductor gear 133Y as a drive transmission rotating member is forcibly turned by the main body side drive transmission unit. The diameter of the photoconductor gear 133Y is larger than the diameter of the photoconductor. When the process drive motor 120Y rotates, the rotational driving force is transmitted from the driving gear to the photosensitive member gear 121Y at a one-step reduction, and the photosensitive member is driven to rotate. The process units for other colors have the same configuration. As described above, in the printer of the image forming system, the latent image gear group including the driving gear 121 and the photoconductor gear 133 is configured in four sets corresponding to each process unit.

  The rotating shaft of the photosensitive member of the process unit and the photosensitive member gear 133 supported on the printer main body side are connected by a coupling fixed to the end of the rotating shaft of the photosensitive member. In each color, the developing gear may be driven by a developing motor different from the photoconductor gear.

  Next, a characteristic configuration of the printer will be described. FIG. 9 is a side view showing the four photoconductors 1Y, 1C, 1M, 1K, the transfer unit 40, and the optical writing unit 20. Markings 134Y, C, M, and K are attached to predetermined positions on the photoconductor gears 133Y, 133C, M, and K that transmit the rotational driving force to the photoconductors 1Y, 1C, 1M, and 1K. These markings 134Y, C, M, and K are detected at predetermined timings by the position sensors 135Y, 135C, M, and K, which are photosensors, every time the photoreceptor gears 133Y, 133Y, 133K, and K are rotated once. . Thus, the timing at which the photoreceptors 1Y, 1C, 1M, and 1K reach a predetermined rotation angle is detected every time they rotate one time.

  Above the transfer unit 40, an optical sensor unit 136 made up of two reflection type photosensors (not shown) arranged in the width direction of the intermediate transfer belt 41 at a predetermined interval is disposed between the upper stretched surface of the intermediate transfer belt 41 and a predetermined gap. It arrange | positions so that it may oppose through.

  FIG. 10 is a perspective view showing a part of the intermediate transfer belt 41 together with the optical sensor unit 136. A control unit (not shown) of the printer performs a positional deviation correction control as a timing adjustment control immediately after a power switch (not shown) is turned on or every time a predetermined time elapses. In this misalignment correction control, misalignment detection images PV made up of a plurality of toner images are formed at one end and the other end in the width direction of the intermediate transfer belt 41, respectively. On the other hand, an optical sensor unit 136 including a first optical sensor 137 and a second optical sensor 138 is disposed above the intermediate transfer belt 41. The first optical sensor 137 passes the light emitted from the light emitting means through the condenser lens, reflects the light on the surface of the intermediate transfer belt 41, and receives the reflected light by the light receiving means. And the voltage according to the amount of received light is output. When the toner image in the position shift detection image PV formed at one end of the intermediate transfer belt 41 passes directly under the first optical sensor 137, the amount of light received by the light receiving means of the first optical sensor 137 is large. Change. Accordingly, the first optical sensor 137 detects the toner image and greatly changes the output voltage value from the light receiving means. Similarly, the second optical sensor 138 detects each toner image in the positional deviation detection image PV formed on the other end of the intermediate transfer belt 41. As described above, the first optical sensor 137 and the second optical sensor 138 function as image detection means for detecting each toner image in the position shift detection image PV. As the light emitting means, an LED or the like having an amount of light that can generate reflected light necessary for detecting a toner image is used. As the light receiving means, a CCD in which a large number of light receiving elements are arranged in a straight line is used.

  By detecting each toner image in the position shift detection image PV formed at both ends in the width direction of the intermediate transfer belt 41, the position of each toner image in the main scanning direction (scanning direction by laser light), sub-scanning The position in the direction (belt moving direction), the magnification error in the main scanning direction, and the skew from the main scanning direction can be adjusted.

  As shown in FIG. 11, the positional deviation detection image PV is a belt movement in the sub-scanning direction in a posture in which the toner images of the respective colors Y, C, M, and K are inclined by about 45 ° from the main scanning direction. A group of line patterns called chevron patches arranged in a direction at a predetermined pitch is formed. Then, for the Y, C, M toner images in the position shift detection image PV, the detection time difference from the K toner image is read. In this figure, the vertical direction of the paper surface corresponds to the main scanning direction, and after the Y, C, M, and K toner images are arranged in order from the left, the postures are different from those by 90 [°]. , Y toner images are further arranged. Based on the difference between the actual measurement value and the theoretical value for the detection time differences tyk, tck, and tmk with respect to K as the reference color, it is possible to determine the amount of deviation in the sub-scanning direction of each color toner image. Each color toner is adjusted by adjusting the optical writing start timing with respect to the photosensitive member on the basis of the deviation amount every other polygon mirror surface of the optical writing unit (20), that is, one scanning line pitch as one unit. Suppress misalignment of images in the sub-scanning direction. Further, based on the difference between the actual measurement value and the theoretical value for the detection time differences tk, tm, tc, and ty of two toner images of the same color with different attitudes of 90 [°], the amount of deviation in the main scanning direction of each color toner image is determined. Can be sought. The inclination (skew) of each color toner image from the main scanning direction can be obtained based on the difference in the amount of deviation in the sub-scanning direction between the both ends of the belt. Then, based on the result, by driving a lens inclination adjusting mechanism (not shown) that adjusts the inclination of a toroidal lens (not shown) in the optical writing unit (20), the inclination deviation of each color toner image from the main scanning direction is corrected. Reduce.

  As in this printer, four laser beams for four photoconductors (1Y, C, M, K) are deflected by a common polygon mirror to perform optical scanning in the main scanning direction for each photoconductor. In this case, the optical writing start timing for each photoconductor is adjusted in units of time corresponding to writing for one line (one scanning line) by positional deviation correction control. For example, when an overlay shift exceeding 1/2 dot occurs in the sub-scanning direction (photoconductor surface movement direction) between two photoconductors, the optical writing start timing for one of the photoconductors is The writing time is shifted back and forth by an integral multiple of the writing time for one line. More specifically, for example, in the case of 3/4 dot overlay deviation, it is 1 time of writing time for one line, and in the case of 7/4 dot overlay deviation, it is twice of writing time for 1 line. Therefore, the optical writing start timing is shifted back and forth with respect to the previous timing. Thereby, the amount of misalignment in the sub-scanning direction is suppressed to ½ dot or less.

  However, when the overlay shift amount in the sub-scanning direction is 1/2 dot, the overlay shift amount remains 1 even if the optical writing start timing is shifted back and forth by the writing time for one line. / 2 dots remain. In addition, when the overlay deviation amount is smaller, if the optical writing start timing is shifted back and forth in units of writing time for one line, the overlay deviation amount is increased. For this reason, even if the optical writing start timing is adjusted, an overlay deviation amount of 1/2 dot or less remains.

  In order to meet the demand for higher image quality in recent years, it is necessary to suppress misalignment of less than 1/2 dot. Therefore, in this printer, when the misalignment of less than ½ dot still remains after adjusting the optical writing start timing, a drive speed correction value corresponding to the misalignment amount is calculated, Store in the drive control unit 150. Then, in a print job performed based on image information sent from an external personal computer or the like, each photoconductor (process drive motor 120Y, C, M, K) is driven at a drive speed based on the drive speed correction value. To do. Thereby, in the print job, a linear velocity difference corresponding to the amount of deviation of less than 1/2 dot is provided between the photoconductors as necessary. Then, the remaining misalignment of less than 1/2 dot is further reduced.

  FIG. 12 is a flowchart showing the contents of the positional deviation correction control performed by the control means of the printer. In the positional deviation correction control, first, after the driving of each process drive motor (120Y, C, M, K) is started (step a: step is hereinafter referred to as S), the above-described optical sensor unit 136 is turned on. (Sb). Next, after the above-described misregistration detection image is formed on the intermediate transfer belt 41 (Sc), it is detected by the optical sensor unit 136 (Sd). Then, after the optical sensor unit 136 is turned off (Se), the skew correction amount, the main scanning position correction amount, the sub-scanning position correction amount, and the main scanning magnification error for each color based on the detection result of the position shift detection image. A correction amount and a main scanning deviation correction amount are obtained (Sf, Sg). Also, the speed of each process drive motor (120Y, C, M, K) for reducing the positional deviation in the sub-scanning direction of less than 1/2 dot is calculated (linear speed difference). After that, after performing main scanning position correction, sub-scanning position correction, main scanning magnification error correction, main scanning deviation correction, and skew correction based on various correction amounts (Sj), driving of each process drive motor is stopped. (Sk).

  The control means (not shown) of the printer also performs fluctuation pattern detection control for detecting a speed fluctuation pattern per rotation for each photoconductor at a predetermined timing. In this variation pattern detection control, a speed variation detection image is formed on the surface of the intermediate transfer belt 41 for each of the colors Y, C, M, and K. As an example of the speed fluctuation detection image, as shown in FIG. 13, a plurality of K toner images tk01, tk02, tk03, tk04, tk05, tk06,... Those arranged in a predetermined pitch along the belt moving direction are formed. Although theoretically arranged at a predetermined pitch, the actual arrangement pitch of these K toner images has an error corresponding to the speed fluctuation due to the speed fluctuation of the K photoconductor. This error is read as a time pitch error by the first optical sensor (137) or the second optical sensor (138).

  In this printer, the Y, C, M speed fluctuation detection image is always formed as one set with the K speed fluctuation detection image. Specifically, for the speed variation detection image for Y, it is formed at one end of the intermediate transfer belt, while the image for speed variation detection for K is formed at the other end of the intermediate transfer belt, These are simultaneously detected by the first optical sensor and the second optical sensor. Similarly, the C and M speed fluctuation detection images are detected simultaneously with the K speed fluctuation detection image. Therefore, in the fluctuation pattern detection control of this printer, two speed fluctuation detection images Y and K are formed and detected by the optical sensor unit, and two speed fluctuation detection images C and K are detected. Are formed and detected by the optical sensor unit, and two speed variation detection images M and K are formed and detected by the optical sensor unit. The reason for detecting the speed variation pattern in this way will be described later.

  In FIG. 1 described above, the positional deviation detection image and the speed fluctuation detection image formed on the intermediate transfer belt 41 are being conveyed to a position facing the optical sensor unit 136 along with the endless movement of the belt. Thus, it passes through the position facing the secondary transfer roller 50. At this time, if the secondary transfer roller 50 is in contact with the intermediate transfer belt 41 to form a secondary transfer nip, the positional deviation detection image and the speed fluctuation detection image on the belt come into contact with the secondary transfer roller 50. Then, it will transfer to the roller surface. Therefore, when performing positional deviation correction control and fluctuation pattern detection control, the printer drives a roller contact / separation mechanism (not shown) to separate the secondary transfer roller 50 from the intermediate transfer belt 50 prior to that. . This avoids the transfer of the position deviation detection image and the speed fluctuation detection image to the secondary transfer roller 50.

  FIG. 14 is a block diagram showing a circuit configuration in the control means of the printer. When the positional deviation correction control and the fluctuation pattern detection control are started, first, after the output signal from the optical sensor unit 136 is amplified by the amplifier circuit 139, only the signal component for line detection is selected by the filter circuit 140, and A The analog data is converted into digital data by the / D conversion converter 141. Sampling of data is controlled by the sampling controller 142, and the sampled data is stored in a FIFO (First-In First-Out) type memory circuit 143. When the detection of the position shift detection image (PV) or the speed fluctuation detection image is completed, the data stored in the memory circuit is loaded to the CPU 146 and the RAM 147 via the I / O port 144 by the data bus 145. Then, the CPU 146 performs arithmetic processing for calculating various deviation amounts. The various misregistration amounts include a positional misalignment amount, a skew misalignment amount, a phase misalignment amount of a speed variation pattern of each photoconductor, and the like. In addition, the main scanning and sub-scanning magnification amounts of each color toner image are also calculated.

  The CPU 146 provides data for performing skew correction, position correction in the main scanning direction, position correction in the sub-scanning direction, magnification correction, and the like for each color toner image based on the obtained deviation amount, and the drive control unit 150 and the writing control unit. 151 is stored. The drive control unit 150 is a circuit that controls four process drive motors that drive each photoconductor. The write control unit 151 is a circuit that controls the optical writing unit.

  The writing control unit 151 adjusts the writing start position in the main scanning direction and the sub-scanning direction for each photoconductor based on data sent from the CPU 146, and can set a very fine output frequency, for example, a VCO. A clock generator using a (voltage controlled oscillator) is provided for each color. In this printer, the output is used as an image clock.

  Based on the data sent from the CPU 146, the drive control unit 150 sets the drive control data for each process drive motor so that the phase of the speed fluctuation per rotation of each photoconductor can be adjusted appropriately. To construct.

  In this printer, the light emission amount control unit 152 controls the light emission amount of the light emitting means so that the toner image in the detection image can be reliably captured even if the light emitting means of the optical sensor unit 136 deteriorates. is doing. Thereby, the amount of light received from the light emitting means of the optical sensor unit 136 is always kept constant.

  The ROM 148 connected to the data bus 145 stores an algorithm for calculating various misalignment amounts, a control program for performing a print job, a program for performing misalignment correction control and fluctuation pattern detection control, and the like. ing. A program for performing phase adjustment control, which will be described later, is also stored. Note that the CPU 146 designates a ROM address, a RAM address, and various input / output devices via the address bus 149.

  As described above, the speed variation detection image is composed of a plurality of toner images of the same color formed so as to be arranged at a predetermined pitch along the sub-scanning direction. In FIG. 13 described above, the interval Ps between individual toner images in the speed variation detection image needs to be set as short as possible. Limits are determined. The length Pa in the sub-scanning direction (belt movement direction) of the speed variation detection image is set to an integral multiple of the circumferential length of the photoreceptor. In this setting, it is necessary to consider other periodic fluctuations that occur when an image for speed fluctuation detection is formed or detected on the intermediate transfer belt. Other periodic fluctuations include fluctuations in the linear speed per rotation of the driving roller of the intermediate transfer belt, pitch errors and eccentric components of gears that drive and transmit them, and meandering distribution of the intermediate transfer belt 10 and a thickness deviation distribution in the circumferential direction. Various frequency components are raised. The detected value of the speed fluctuation pattern includes all of these periodic fluctuation components in a superimposed manner, and it is necessary to detect only the speed fluctuation component per one rotation of the photoreceptor.

  For example, in addition to the speed fluctuation component per rotation of the photosensitive member, the speed fluctuation component per rotation of the driving roller of the intermediate transfer belt is often included in the time pitch error for each toner image in the speed fluctuation detection image. Suppose that In this case, it is necessary to set the length Pa of the speed fluctuation detection image in consideration of the speed fluctuation component of the driving roller. If the diameter of the photoreceptor is 40 [mm] and the diameter of the drive roller is 30 [mm], the period of the photoreceptor and the period of the drive roller converted to the moving distance of the intermediate transfer belt are 125.7 [mm]. 94.2 [mm]. The common multiple of both periods may be set to the length Pa of the speed variation detection image. For example, it is 377 [mm]. Then, the interval Ps between the toner images may be set according to the length Pa. With such a setting, the maximum amplitude and phase value of the speed fluctuation pattern per rotation of the photosensitive member can be detected with high accuracy without being affected by the periodic variation component of the drive roller. This utilizes the fact that in the calculation of the maximum amplitude and the phase value, the operation term including the period fluctuation component of the driving roller is exactly “0” in theory. Similarly, in the case where many cyclic fluctuation components due to the thickness deviation distribution in the circumferential direction of the intermediate transfer belt are included, the length Pa is set to a value closest to the circumference of the belt by an integral multiple of the circumference of the photoreceptor. Thus, it becomes possible to reduce the influence of the periodic fluctuation component of the intermediate transfer belt. In addition, if the difference in frequency with the periodic fluctuation component of the photosensitive member is 10 times or more, such as the periodic fluctuation component of the roller drive motor that drives the drive roller, it can be removed by a low-pass filter. It is.

  Each pulse width of the data stored in the memory circuit 143 differs depending on the amount of light received by the light receiving means of the optical sensor unit 136. Since the amount of light received by the light receiving means varies depending on the density of the toner image, each pulse width of the data stored in the memory circuit 143 varies depending on the density of the corresponding toner image. In the misalignment correction control and the fluctuation pattern detection control, each toner image in the detection image must be detected with high accuracy. Therefore, even if each pulse width is different, each corresponds to an individual toner image. It is necessary to make the CPU 146 recognize that there is. Therefore, in this printer, the CPU 146 does not identify a pulse having a width exceeding a preset threshold value, but identifies a pulse peak. As a result, it is possible to make it less susceptible to the density change due to the collapse of the toner image accompanying the speed fluctuation of the photoreceptor.

The reason will be described in detail with reference to FIG. 15 and FIG. FIG. 15 is an enlarged schematic view showing a primary transfer nip due to contact between the photosensitive member 3 and the intermediate transfer belt 41. FIG. 16A is a graph showing output pulses from the optical sensor unit that detects the detection image transferred when there is no speed difference between the photosensitive member 3 and the intermediate transfer belt 41. FIG. 16B shows an optical for detecting a detection image transferred when the surface speed V ₀ of the photosensitive member 3 in the primary transfer nip is higher than the surface speed V _b of the intermediate transfer belt 41. It is a graph which shows the output pulse from a sensor unit. FIG. 16C shows an optical for detecting a detection image transferred when the surface speed V ₀ of the photoreceptor 3 at the primary transfer nip is slower than the surface speed V _b of the intermediate transfer belt 41. It is a graph which shows the output pulse from a sensor unit.

In the primary transfer nip, the photosensitive member 3 and the intermediate transfer belt 41 are moved at independent speeds while being in contact with each other. When the surface speed V ₀ of the photoreceptor 3 and the surface speed V _b of the intermediate transfer belt 41 are equal, as shown in FIG. 16A, pulse waves corresponding to the toner images output from the optical sensor unit. Are each rectangular. At this time, the detection interval of each pulse width is approximately PaN even if there is some error. On the other hand, when the surface speed V ₀ of the photoreceptor 3 is faster than the surface speed V _b of the intermediate transfer belt 41, the detection interval of each pulse width is longer than PaN as shown in FIG. Short PaH. Then, the shape of each pulse width is a shape of a right skirt length that gradually rises and then gradually drops. The reason for this waveform is that the toner image collapses to the upstream side in the belt moving direction due to the speed difference between the photosensitive member 3 and the intermediate transfer belt 41, thereby causing density unevenness. Further, when the surface velocity V ₀ which photoreceptor 3 is slower than the surface speed V _b of the intermediate transfer belt 41, as shown in FIG. 16 (c), the detection intervals of the pulse width is longer than PaN PaL It becomes. The shape of each pulse width is a waveform with a left skirt length that gradually rises and then drops rapidly. The reason for this waveform is that the toner image collapses to the downstream side in the belt moving direction due to the speed difference between the photosensitive member 3 and the intermediate transfer belt 41, thereby causing density unevenness.

  When the pulse exceeding the threshold is recognized as corresponding to the toner image, the peak of the pulse does not exceed the threshold due to the influence of the collapse of the toner image in the modes of FIGS. 16B and 16C. There is a risk that the toner image cannot be detected. In addition, there is a possibility that the highest density portion of the toner image cannot be detected. Therefore, in this printer, the peak value of the pulse is handled as the toner image detection timing. Specifically, based on the data previously stored in the memory circuit 143 shown in FIG. 14, the CPU 146 recognizes the peak of each pulse and stores the timing (data number) data in the RAM 147. Thereby, the time pitch error can be detected more accurately.

  The time pitch error reflected in the data stored in the RAM 147 corresponds to the speed fluctuation per rotation of the photosensitive member. For each rotation of the photoconductor, the maximum speed and the minimum speed are generated at the upper limit and lower limit of the sine curve generated by the photoconductor, the photoconductor gear, and the coupling connecting the two having the largest amount of eccentricity. It is time to greet. Therefore, the pattern and amplitude of the sine curve are analyzed as a speed variation pattern in association with the timing when the marking is detected by the position sensor. As one of the analysis methods at this time, there is a method of analyzing the amplitude and phase of the fluctuation component from the zero cross of the fluctuation value or the peak value by setting the average value of all data to zero. However, since the detection data is greatly affected by noise, the error becomes large and is not practical. Therefore, this printer employs a method of analyzing the amplitude and phase of the speed variation pattern by orthogonal detection processing.

  The quadrature detection processing is a known signal analysis technique used in a demodulation circuit in the communication field. An example of the circuit configuration for doing this is shown in FIG. The stored data in the RAM based on the output waveform from the optical sensor unit is a monotonically increasing data group in which several speed fluctuation components are superimposed in addition to the speed fluctuation components of the photosensitive member. It is converted to fluctuation data from which is removed. The increasing tendency (gradient) can be obtained from the data group by the least square method, and is treated as a magnification correction numerical value. The converted fluctuation data is processed as follows. That is, the oscillator 160 oscillates a frequency component to be detected, here, a frequency signal adjusted to the frequency of the rotation period ωo of the photosensitive member, with a phase based on the reference timing used when the detection image is formed. This frequency signal is directly output to the first multiplier 161 or is output to the second multiplier 163 via the 90 ° phase shifter 162. The rotation period ωo of the photoconductor can be accurately obtained by measuring the detection signal interval of the marking on the photoconductor gear. The first multiplier 161 multiplies the fluctuation data stored in the RAM and the frequency signal from the oscillator 160. The second multiplier 163 multiplies the fluctuation data stored in the RAM by the frequency signal from the 90 ° phase shifter 162. By these multiplications, the fluctuation data is separated into a signal having the same phase component (I component) as that of the photosensitive member and a signal having a quadrature component (Q component). The output from the first multiplier 161 is the I component, and the output from the second multiplier 163 is the Q component. The first LPF 164 passes only the low frequency band signal in the I component. This printer employs a low-pass filter that smoothes the data corresponding to the length Pa of the speed variation detection image so as to transmit only data corresponding to an integral multiple of the oscillation period ωo. The same applies to the second LPF 165. By smoothing the data corresponding to the length Pa, the rotation period component such as the driving roller is canceled by the smoothing process and becomes “0”. Then, the amplitude calculator 166 calculates the amplitude a (t) corresponding to the two inputs (I component and Q component). In addition, the phase calculator 167 calculates a phase b (t) corresponding to two inputs (I component and Q component). The amplitude a (t) and the phase b (t) correspond to the period fluctuation amplitude and the phase angle from any reference timing. If it is desired to detect the amplitude and phase of the rotational period component of the driving gear, the same processing may be performed in which the oscillation period ωo is set to the higher-order component motor rotational period.

  By performing such quadrature detection processing, it is possible to calculate the amplitude and phase with a small amount of fluctuation data, which was difficult to calculate by the zero crossing and peak detection of fluctuation. In particular, by setting the interval Ps between the toner images so that the number of toner images in the detection image is 4NP (NP is a natural number) with respect to one rotation of the photosensitive member, the amplitude and phase can be reduced even with a small number of toner images. Can be calculated with high accuracy. This is because the positional relationship of the 4NP toner images is the positional relationship having the largest difference with respect to the fluctuation component, so that the sensitivity is the highest. For example, in the case of four toner images, each corresponds to a fluctuation zero cross and a peak position, so that the detection sensitivity becomes high. Even if the four patterns are out of phase, the positional relationship is still high in detection sensitivity.

  Based on the speed variation pattern thus analyzed, the CPU 146 calculates drive control correction data for each photoconductor, and transmits the drive control correction data to the drive control unit 150. This drive control correction data is data for adjusting the phase of each speed fluctuation pattern by adjusting the rotation phase of each photoconductor so as to cancel the rotation cycle fluctuation of each photoconductor.

  The above-mentioned drive control correction data calculated according to the speed fluctuation pattern by the fluctuation pattern detection control for detecting the speed fluctuation pattern of each photoconductor is used in the phase adjustment control for adjusting the phase of the speed fluctuation pattern of each photoconductor. Is done. By this phase adjustment control, the leading edge of each color toner image is synchronized on the surface of the intermediate transfer belt. In this printer, since the arrangement pitch of each photoconductor is one time the circumference of the photoconductor, the phase of the speed variation pattern of each photoconductor is synchronized. That is, the drive amount of each process drive motor is temporarily changed so that the time point at which the surface speed of each photoconductor becomes the maximum speed and the time point at which the surface speed becomes the minimum speed are completely matched. Thereby, the leading ends of the toner images of the respective colors can be synchronized on the surface of the intermediate transfer belt.

  In this printer, such phase adjustment control is performed at the end of each job. The phase adjustment control may be performed at the start of each print job, but in this case, since the phase adjustment control is performed from the start of the job operation until the first print is performed, the first print time Makes it longer. Therefore, phase adjustment control is performed at the end of the job. In this way, it is possible to start driving each photosensitive member with the ideal phase relationship of the speed variation pattern in the next print job without increasing the first print time.

  By the way, in general, in an image forming apparatus, the position and size of each process unit may slightly change due to a change in internal temperature or an external force. These changes are inevitable. For example, when operations such as paper jam recovery, parts replacement by maintenance, parts removal / attachment, and movement of the image forming apparatus are performed, an external force is applied to the process unit. When such an external force or a change in the internal temperature occurs, the overlay accuracy of the color toner images formed by the process units of the respective colors deteriorates. Therefore, in this printer, the positional deviation correction control is performed immediately after the power switch is turned on or every time a predetermined time elapses to suppress the registration deviation of the color toner images.

  However, if a linear velocity difference is provided for each photoconductor, the phase relationship of the speed fluctuation pattern of each photoconductor is shifted from the ideal relationship every time the photoconductor is rotated once. There is no problem if only a single sheet is printed, but in the case of a continuous printing operation in which printing is continuously performed on a plurality of recording sheets, the amount of phase shift increases as the number of printed sheets increases. As a result, the misalignment becomes considerably large. Therefore, in this printer, the image quality priority mode that prioritizes image quality over the print speed and the opposite speed priority mode can be selected by an input operation to an operation display unit (not shown) or a print driver of a personal computer. When the image quality priority mode is selected and continuous printing is performed, the continuous print job is temporarily suspended and phase adjustment control is performed every time a predetermined number of continuous prints are performed. To do.

  In this way, the misalignment of less than 1/2 dot is reduced. However, when performing the misalignment correction control and the fluctuation pattern detection control, the same speed is maintained without providing a linear velocity difference between the photoconductors. Drive at speed. Thereby, it is possible to avoid the deterioration of the positional deviation correction accuracy and the phase adjustment system due to the formation of the positional deviation detection image and the speed fluctuation detection image in a state where the linear velocity difference is provided on each photoconductor.

  The speed fluctuation pattern per one rotation of the photosensitive member is not easily affected by a change in internal temperature or an external force. For this reason, unlike the positional deviation correction control, the variation pattern detection control does not need to be performed so frequently. However, when the process unit is detached, the speed fluctuation pattern of the photoconductor of the process unit may change greatly. Therefore, in this printer, the variation pattern detection control is performed only when any of the four process units is detached. The positional deviation correction control is performed at a predetermined timing even when the process unit is not attached or detached. In addition, the removal of the process unit is detected by a removal detection unit (not shown).

  Examples of the desorption detection means include a detection type based on the fact that one of the output signals from the four unit detection sensors that individually detect each process unit is turned on after being turned off. can do.

  The fluctuation pattern detection control is always executed in combination with the positional deviation correction control. Specifically, when the removal / attachment of the process unit is detected, after performing the positional deviation correction control, the fluctuation pattern detection control and the phase adjustment control are performed, and then the positional deviation correction control is performed again. In the middle of such a series of control flows (hereinafter referred to as a routine after detection of process unit attachment / detachment), a print job is not entered.

  In this printer, the positional deviation correction control is performed twice in the routine after the process unit removal / removal detection. Specifically, the variation pattern detection control is performed after the first positional deviation correction control, and the second positional deviation correction control is further performed. In the first positional deviation correction control, in order to avoid the deterioration of the fluctuation pattern detection accuracy due to the fluctuation pattern detection control in a state where a large positional deviation accompanying the attachment / detachment of the process unit has occurred, the positional deviation is controlled to some extent. We carry out for the purpose of reducing. Accurate misalignment correction is performed a second time.

  When the first positional deviation correction control is completed, the driving of each photoconductor is stopped before the variation pattern detection control is performed. At this time, the driving of each photoconductor is not stopped based on the phase adjustment control in accordance with the phase of the speed variation pattern before removal, but each photoconductor is stopped at a predetermined reference rotation phase. Specifically, each process drive motor is stopped at a reference timing that is a predetermined time after the detection of the marking of the photoconductor gear. Accordingly, each photoconductor is stopped in a state where the markings of the respective photoconductor gears are positioned at the same rotation angle. By stopping the respective photoconductors in this way, the respective photoconductors are rotated from the same posture when the variation pattern detection control is performed.

  In the fluctuation pattern detection control, Y, C, and M speed fluctuation detection images are formed together with the K speed fluctuation detection images, respectively, and both are detected simultaneously. This is based on the speed fluctuation pattern of the K photoconductor as the reference latent image carrier, and the phase of the speed fluctuation pattern on the other photoconductor is accurately set to the phase of the speed fluctuation pattern on the K photoconductor. This is to match. Furthermore, it is also for more reliably removing the influence of the speed fluctuation component of the intermediate transfer belt. More specifically, the speed fluctuation pattern reflects the speed fluctuation of the intermediate transfer belt at the position facing the optical sensor unit in addition to the speed fluctuation of the photosensitive member. For this reason, even if the toner images in the speed detection image are arranged at exactly equal intervals on the intermediate transfer belt, if the speed of the intermediate transfer belt at the position facing the optical sensor unit changes, A time pitch error occurs for each toner image. In order to remove the time pitch error, it is necessary to simultaneously detect the reference speed variation detection image for K and the velocity variation detection image of another color.

  Therefore, in this printer, the Y, C, and M speed fluctuation detection images are each paired with the K speed fluctuation detection image, one at one end in the width direction of the intermediate transfer belt, and the other as the other. Formed at the other end. At this time, the formation of the K speed fluctuation detection image is started based on the timing when the K marking (134K) is detected (optical writing is started). The Y, C, and M speed variation detection images are also formed based on the timing at which the K marking is detected, not the corresponding markings (134Y, C, and M). Thus, the leading end of the Y, C, M speed fluctuation detection image and the leading edge of the K speed fluctuation detection image are positioned on a straight line in the belt width direction.

  In this way, a phase shift between the speed fluctuation pattern detected based on the Y, C, M speed fluctuation detection image and the speed fluctuation pattern detected based on the K speed fluctuation detection image is detected. To detect. Then, if the rotational positions of the K marking and the Y, C, and M markings are shifted by an amount corresponding to the phase shift, the phases of both speed fluctuation patterns can be aligned. This is because the rotational phase of each marking is synchronized prior to the fluctuation pattern detection control, so that the phase deviation amount of the speed fluctuation pattern corresponds to the desired phase deviation amount of the marking.

  In such a fluctuation pattern detection control, a phase shift between the speed fluctuation pattern for Y, C, M and the speed fluctuation pattern for K is detected without referring to the detection timing of the marking for Y, C, M. can do. However, if the amount of misalignment of each color is larger than that before the desorption due to the process unit desorption, the detection result of the phase shift is shifted by that amount. Therefore, prior to the variation pattern detection control, positional deviation correction control is performed to reduce the amount of overlay deviation between colors in advance.

  FIG. 18 is a flowchart showing a control flow of a routine after the process unit removal detection. When the attachment / detachment of any one of the process units is detected, first, positional deviation correction control is performed (S1), and then whether or not an error has occurred is determined (S2). If an error occurs (Y in S2), after the drive control correction data for adjusting the phase of the speed variation pattern is returned to the value before removal (S3), the phase adjustment control is performed. (S4). By this phase adjustment control, after each photoconductor is stopped in a posture that synchronizes the phase of the speed variation pattern based on the drive control correction data before removal, an error display is made on an operation display unit (not shown) (S5). ). Then, after the linear speed difference setting of each process drive motor is turned on (S6), a series of control flow is completed. When the linear velocity difference setting is turned ON, a linear velocity difference is provided to each photoconductor so as to suppress an overlay shift of less than ½ dot in subsequent print jobs.

  If it is determined in step S2 that no error has occurred, the driving of each process drive motor is stopped at a predetermined reference timing (S7). Thereby, each photoconductor gear stops in a posture in which the marking is positioned at the same rotational position. Thereafter, after the linear velocity difference setting of each process drive motor is turned off (S8), the process drive motor is re-driven, and then variation pattern detection control is performed (S9, S10). Prior to the fluctuation pattern detection control, the linear velocity difference setting of each process drive motor is turned OFF, so that each photosensitive member is driven at a constant speed in the fluctuation pattern detection control and the second positional deviation correction control. As a result, it is possible to avoid the deterioration of the detection accuracy of each speed fluctuation pattern and the deterioration of the positional deviation correction accuracy due to the provision of the linear velocity difference of the photosensitive member by the fluctuation pattern detection control. When the variation pattern detection control is completed, it is determined whether or not there is a reading error (S11). If it is determined that a reading error has occurred (Y in S11), the above-described steps S2 to S6 are executed, and then a series of control flows is completed.

  If it is determined in step S11 that no reading error has occurred, phase adjustment control is performed (S12). Thus, based on the new drive control correction data, each photoconductor is stopped in a posture that synchronizes the phase of the speed variation pattern. Then, after each process drive motor is re-driven (S13), the positional deviation correction control is performed again (S14). By the second positional deviation correction control, the optical writing start timing of each color that has become inappropriate due to the change in the speed fluctuation pattern of any one of the photosensitive members due to the attachment / detachment of the process unit is corrected. Then, after it is determined whether or not there is an error (S15), if an error occurs (Y in S15), a series of control flow is completed through the above-described steps S4 to S6.

  If it is determined in step S15 that no error has occurred, the drive of each process drive motor is stopped by phase adjustment control (S16), and then the linear speed difference setting of each process drive motor is turned ON. A series of control flow ends.

  Here, when the linear velocity difference setting of each process drive motor is turned off in S8, the redrive of each process drive motor prior to the execution of the fluctuation pattern detection control (S10) makes each motor drive speed constant. Done on condition. Thereby, it is possible to avoid deterioration in detection accuracy of the speed fluctuation pattern due to the difference in linear velocity between the Y, C, and M photoconductors at the initial stage of re-driving and the K photoconductor. Specifically, as a method of making each process drive motor have a constant speed, a method of returning to a constant speed after driving with a linear speed difference, and a start of driving each process drive motor in a state of constant speed from the beginning. There is a method. However, if the former method is adopted, the rotation angles are shifted from each other due to the difference in linear velocity even though the respective photoconductors are stopped with the markings of the respective photoconductor gears positioned at the same rotation angle. After that, a speed fluctuation detection image is formed. As in this printer, the Y, C, M speed fluctuation detection image is combined with the K speed fluctuation detection image to form a set based on the detection timing of the K marking (134K). If there is such a deviation, a relative positional deviation occurs between the Y, C, M speed fluctuation detection image and the K speed fluctuation detection image.

  This will be described in more detail. For example, when a certain photosensitive member (Y, C, or M) starts to be driven at the same speed as the photosensitive member for K, as shown by the solid line in the graph of FIG. Let us show the velocity characteristics. That is, after starting driving at time t0, the speed stabilizes at a predetermined speed V1 at time t1. On the other hand, it is assumed that the driving of the photoconductor (Y, C, or M) is started at a speed higher than that of the K photoconductor. Then, as shown by the dotted line in the figure, the driving speed of the photoconductor is stabilized at a speed V2 that is faster than the speed V1 at a time t2 slightly delayed from the time t1. After that, when the driving speed of the photoconductor is decreased at time t3 and stabilized at speed V1 at time t4, the photoconductor is driven at a speed different from that of the K photoconductor from time t1 to time t4. It will be. During this time, the rotational amplitude (corresponding to the rotational phase) of the photoconductor for K shown by the solid line in FIG. 29 is shifted as shown by the dotted line.

  The rotational amplitude referred to here is “0” when the predetermined reference position on the surface of the photoreceptor moves at a constant speed, and the amount of positional deviation from “0” due to the actual speed fluctuation of the reference position. It is shown. As described above, the speed fluctuation of the photosensitive member has a characteristic of drawing a sine curve for one cycle per one rotation, so that the illustrated rotational amplitude also has a characteristic of drawing a sine curve for one cycle per one rotation of the photosensitive member. In FIG. 28, for the sake of convenience, subtle speed fluctuations caused by the eccentricity of the photoreceptor and gears are not reflected in the graph.

  When the deviation shown in FIG. 29 occurs, it becomes impossible to accurately detect the Y, C, and M speed fluctuation patterns. Therefore, the linear speed difference setting of each process drive motor is turned OFF in S8, and the drive of each process drive motor is started under the condition of constant speed. Thereby, it is possible to avoid deterioration in detection accuracy of the speed variation pattern due to the difference in linear velocity between the Y, C, and M photoconductors at the initial stage of re-driving and the healthy body for K.

  As described above, in this printer, the positional deviation correction control is performed at a predetermined timing even when the attachment / detachment of the process unit is not detected. When the positional deviation correction control is performed alone, it is not always necessary to drive each process drive motor at a constant speed. However, it is necessary to drive each process drive motor at a constant speed when forming or detecting a position shift detection image.

Next, modifications of the printer according to the embodiment will be described. Unless otherwise specified below, the configuration of the printer according to each modification is the same as the print according to the embodiment.
[First Modification]
FIG. 19 is a perspective view showing a process unit 1Y for Y in the printer according to the first embodiment. On the side surface of the photoreceptor unit 2Y in the process unit 1Y, a unit identification electronic circuit board 200Y on which an IC chip (not shown) is mounted is provided. The IC chip of the unit identification electronic circuit board 200Y stores a unit ID number to which a different value is assigned for each individual product of the photoreceptor unit 2Y. When the process unit 1Y is mounted on the printer main body, the unit identification electronic circuit board 200Y and the control means on the printer main body side are connected via the abutting contact, and communication between both becomes possible. In this state, the control means can read the unit ID number stored in the IC chip of the unit identification electronic circuit board 200Y.

  The unit identification electronic circuit board 200Y continues to transmit a predetermined unit mounting signal to the control means in the state described above. The control means detects the attachment / detachment of the Y process unit 1Y based on the fact that it receives the unit attachment signal again after it no longer receives it. That is, in the printer according to the first modified example, the attachment / detachment detection means for detecting attachment / detachment of the process unit 1Y is configured by the unit identification electronic circuit board 200Y, the control means, the abutting contact described above, and the like.

  When the control unit detects the mounting of the process unit 1Y, it reads the unit ID number stored in the IC chip and updates the data of the mounting unit ID number stored in the RAM to the read result data. To do. However, prior to this update, it is determined whether or not the unit ID number that has just been read is the same as the unit ID number that is stored in the RAM. If they are not identical, it is determined that the process unit 1Y has been replaced. That is, in the printer according to the first modified example, whether the process unit 1Y is attached to or detached from the printer main body as the attachment / detachment detection means including the control means or the like is an operation in which the process unit 1Y is temporarily removed and then reattached. What can determine whether it is replacement | exchange operation of the process unit 1Y is used.

  Although the Y process unit 1Y has been described, the process units (1C, M, K) for other colors have the same configuration, and whether the control means has been replaced for all the process units. Or it can be judged whether it is reattachment after temporary removal.

  Here, when the process unit is replaced, whether the replaced unit is a new unit, whether it has been used to some extent by another printer, or whether it has been used to some extent by this printer in the past. Regardless, there is a possibility that the image forming conditions such as the developing bias have become inappropriate. If the position deviation correction control and the fluctuation pattern detection control are performed with the image forming conditions before the replacement in spite of being inappropriate, the position deviation detection image and the speed fluctuation detection image are appropriately displayed. Since it cannot be formed with the density, there is a risk of causing an error in detecting these images or misadjustment.

  Therefore, in this printer, when the attachment / detachment of any of the process units is detected and it is determined that the attachment / detachment is due to the replacement of the unit, the image formation condition adjustment control is performed to make an image suitable for the new unit. After satisfying the conditions, positional deviation correction control and fluctuation pattern detection control are performed. However, if it is determined that the unit is to be remounted after the unit is temporarily removed, the positional deviation correction control and the variation pattern detection control are performed without performing the image forming condition adjustment control. This is because the appropriate value of the image forming condition does not change so much in the case of remounting.

  FIG. 20 is a flowchart showing a control flow of a routine after the process unit detachment detection which is executed by the control means of the printer when any one of the process units is replaced. What is different from the flowchart shown in FIG. 18 is that image formation condition adjustment control is performed before position shift correction control and phase adjustment control are performed (S0). With such a flow, the detection error of the image (PV or speed fluctuation detection image) caused by performing positional deviation correction control or phase adjustment control while the image forming condition of the process unit after replacement is inappropriate, The occurrence of misadjustment can be avoided.

  In the image formation condition adjustment control, a gradation pattern image is formed on the surface of each of the photoreceptors 3Y, 3C, 3M, and 3K for the four process units 1Y, 1C, 1M, and 1K, and this is transferred onto the intermediate transfer belt 41. To do. The gradation pattern images of Y, M, C, and K are each composed of a plurality of reference patches (reference toner images) having different toner adhesion amounts per unit area. Specifically, an M gradation pattern image composed of a plurality of M reference patches, a C gradation pattern image composed of a plurality of C reference patches, and a Y gradation pattern image composed of a plurality of Y reference patches are placed on the intermediate transfer belt 41. It forms. These gradation pattern images are formed so as to be aligned with each other in the belt moving direction.

  In the image forming condition adjustment control, various image forming conditions such as a developing bias are adjusted based on the result of detecting these gradation pattern images by the optical sensor unit 136 described above. The processing performed in the image forming condition adjustment control is roughly classified into three types, that is, Vsg adjustment processing, potential set value adjustment processing, and intermediate light control writing γ correction processing. In the Vsg adjustment processing, the output voltage value from the optical sensor unit 136 that has detected the background portion (surface without toner adhesion) of the intermediate transfer belt 41 that is the detection target surface is a predetermined value (for example, 4.0 ± 0. 0). 2V), the light emission amount from the light emitting element of the optical sensor unit 136 is adjusted. In the potential set value adjustment processing, each reference patch in the gradation pattern image (for example, 10 gradation patterns for each color) formed on the intermediate transfer belt 41 is detected by the optical sensor unit, and the output corresponding to each reference patch. An appropriate development γ is calculated based on the voltage value. Then, based on the calculation result, the photosensitive member uniform charging potential, the developing bias, and the optical writing intensity capable of obtaining the target image density are specified and set as the set values. Further, in the halftone light writing γ correction processing, the optical writing corresponding to each gradation is based on the deviation amount between the output voltage value from the optical sensor unit 136 corresponding to each reference patch and the target gradation characteristic. By correcting the writing γ, which is the setting value of the strength, the target gradation characteristics can be obtained. The development γ is the slope of a graph showing the relationship between the development potential and the toner adhesion amount per unit area. The development potential is a potential difference between the electrostatic latent image on the surface of the photoreceptor and the surface of the developing sleeve to which a developing bias is applied.

[Second Modification]
FIGS. 21 to 25 are flowcharts showing the control flow of a routine after detection of removal of a process unit executed by the control means of the printer according to the second modification when any one of the process units is replaced. . In this control flow, speed variation pattern detection control for Y, M, and C is performed individually. Each time the positional deviation correction control or the Y, C, M speed variation pattern detection control is performed, the process drive motors (120Y, C, M, K) are repeatedly stopped and restarted. In addition, each process drive motor is started to be driven in a state in which the setting of the linear velocity difference is always turned off, that is, a condition in which all process drive motors are driven at a constant speed. In this printer, as with the printer according to the embodiment, the Y, C, and M speed fluctuation patterns are each detected to be shifted from the K speed fluctuation pattern.

  When attachment / detachment of any of the process units is detected, first, as shown in FIG. 21, the value of the drive stop delay time T1 is reset to “0” (S1). The drive stop delay time T1 is a drive stop delay time from the reference timing in each process drive motor when the phase adjustment control is performed. By resetting to “0”, each process drive motor is stopped at the reference timing described above.

  When the drive stop delay time T1 is reset to “0”, next, after position shift correction control is performed (S2), it is determined whether or not an error has occurred (S3). If there is an error (Y in S3), the driving of each process drive motor is stopped and an error message is displayed on the operation display unit (S4). Thereafter, after the drive stop delay time T1 is returned to the previous value (S5), a series of control flow ends. On the other hand, if there is no error (N in S3), each process drive motor is stopped at the reference timing (S6), and then the flow after S7 described later is executed.

  When each process drive motor is stopped at the reference timing in S6, next, as shown in FIG. 22, after the linear speed difference setting of each process drive motor is turned off (S7), each process drive motor is driven. Is started (S8). In this way, when the drive of each process drive motor is started with the linear speed difference setting turned OFF, the phase shift of the speed variation pattern of each process drive motor is the reference when the motor drive is stopped at the reference timing. This is the amount of phase shift. On the other hand, if the linear speed difference setting is turned OFF after starting the drive of each process drive motor with the linear speed difference provided, the speed of each process drive motor is between the start of driving and the linear speed difference setting OFF. The phase shift of the fluctuation pattern further deviates from the reference phase shift amount, which makes it difficult to accurately correct the position shift and detect the speed fluctuation pattern.

  When the process drive motors are driven in the above-described step S8 with no linear speed difference, formation and reading of KY speed fluctuation detection images are performed by Y fluctuation pattern detection control (S9, S10). . Then, it is determined whether or not there is a reading error (S11). If there is an error (Y in S11), the driving of each process drive motor is stopped and an error message is displayed on the operation display unit (S12). Thereafter, the drive stop delay time T1 is returned to the previous value (S13), and the linear speed difference setting is turned on, and then a series of control flow ends. On the other hand, if there is no error (N in S11), each process drive motor is stopped at the reference timing (S15) and the linear velocity difference setting is turned on (S16), and thereafter S17 and later described later. The flow of is executed.

  As shown in FIG. 23, the flow from S17 to S26 is the same as the flow shown in FIG. 22 except that C variation pattern detection control is performed instead of Y variation pattern detection control (S19, S20). is there. Further, as shown in FIG. 24, the flow from S27 to S34 is from S7 to S14 in FIG. 22 except that M fluctuation pattern detection control is performed instead of Y fluctuation pattern detection control (S29, S30). It is the same as the flow. If it is determined that there is no reading error after the M variation pattern detection control (N in S31), the drive stop delay time T1 for Y, C, M is set to the value calculated by the Y, C, M variation pattern detection control. After the setting (S35), each process drive motor is stopped in a state where the phase of the speed variation pattern is adjusted by performing the phase adjustment control (S36). Then, after the linear velocity difference setting is turned on (S37), the flow after S38 described later is executed.

  In the flow after S38, as shown in FIG. 25, first, after the linear velocity difference setting is turned off (S38), each process drive motor is driven (S39). Next, after the positional deviation correction control is performed (S40), it is determined whether or not an error has occurred (S41). If there is an error (Y in S41), an error is displayed and the driving of each process drive motor is stopped, and then the linear speed difference setting is turned on, and then a series of control flows is completed. On the other hand, if there is no error (N in S41), the drive of each process drive motor is stopped in a state where the phase of the variation pattern is adjusted by the phase adjustment control (S45), and then the linear velocity difference setting is performed. A series of control flow is completed after turning ON.

  In the printer according to the second modified example having such a configuration, when the driving of each process drive motor is started in order to perform the positional deviation correction control and the fluctuation pattern detection control, All process drive motors are driven under the condition of driving at a constant speed. As a result, it is possible to avoid deterioration in correction accuracy and detection accuracy due to turning off the linear velocity difference setting after starting the driving of each process drive motor with the linear velocity difference provided.

[Third Modification]
FIG. 26 is a perspective view showing a printer according to the third modification. This printer has a front door 205 that can be opened and closed with respect to the main body casing in accordance with the rotation on the front surface of the main body casing. The maintenance opening 206 provided on the front surface can be exposed. When this opening 206 is exposed, as shown in the figure, the internal transfer unit 40 and the process units 1Y, C, M, and K of each color are exposed to the outside. In this state, the transfer unit 40 and the process units 1Y, 1C, 1M, and 1K are slid in the front-rear direction of the printer, so that they can be pulled out of the housing or mounted in the housing. .

  The opening / closing operation of the front door 205 is detected by an opening / closing detection switch 207 provided near the lower corner of the opening 206. This open / close detection switch 207 is indispensable for safety considerations such as forcibly stopping the operation when the front door 205 is opened during the printing operation.

  In this printer, instead of the method of directly detecting the attachment / detachment of the process units 1Y, 1C, 1M, and 1K of each color directly to the housing, it is indirectly based on the detection result by the open / close detection switch 207 serving as the open / close operation detecting means. To detect automatically. Specifically, after the opening operation of the front door 205 is detected by the open / close detection switch 207, when the closing operation is detected, the control means indicates that any process unit has been attached or detached based on the closing operation. I reckon.

  In such a configuration, the attachment / detachment of the process units of each color is indirectly detected based on the detection result by the open / close detection switch 207 without providing a dedicated sensor for individually detecting the attachment / detachment of each color process unit. By doing so, cost reduction can be achieved.

  Up to this point, a description has been given of a printer in which each color toner image on each photoconductor is primarily transferred to the intermediate transfer belt 41 and then secondarily transferred onto a recording sheet as a recording body. Instead of such a method, a method may be employed in which each color toner image on each photoconductor is directly superimposed and transferred onto a recording paper held on a paper conveyance belt as an endless moving body. In this case, in the positional deviation correction control and the fluctuation pattern detection control, each toner image may be transferred to the paper transport belt and detected by the optical sensor unit. For example, as shown in FIG. 27, the toner images on the photoconductors 3Y, 3C, 3M, and 3K are directly superimposed on the recording paper P that is conveyed while being held on the surface of the paper conveying belt 201 that is an endless moving body. This is an image forming apparatus of a transfer type. Even in such a system, the positional deviation correction control and the fluctuation pattern detection control can be performed by transferring the positional deviation detection image and the speed fluctuation detection image from the photoconductors 3Y, 3C, 3M, and K to the paper conveyance belt 201. Can do.

[Fourth Modification]
The control means of the printer according to the fourth modified example does not detect the attachment / detachment of each process unit, and continuously during the continuous printing in which continuous printing is performed on a plurality of recording papers P. When the number of times of printing exceeds a predetermined number of times, the continuous printing operation is temporarily interrupted and the positional deviation correction control is performed independently. After the positional deviation correction control is completed, the continuous printing operation is resumed without stopping each process drive motor. However, the phase of the speed variation pattern of each photoconductor needs to be adjusted prior to the continuous printing operation. Also, the linear velocity difference setting of each photoconductor needs to be turned on. Therefore, first, phase adjustment control is performed for continuous operation different from that performed in the routine after the process unit detachment detection. Specifically, the driving speed of each photoconductor is slightly changed while grasping the rotation angle of each photoconductor based on the detection timing of the markings (134Y, C, M, K) attached to the photoconductor gear. Thus, the phase of the speed variation pattern of each photoconductor is adjusted. When the phase adjustment control for continuous operation is performed in this way, the linear speed difference setting is turned ON so that the driving speed of each photoconductor is the value obtained by the positional deviation correction control. Then, after each photoconductor is stably driven with the difference in linear velocity, the interrupted continuous printing operation is resumed.

[Fifth Modification]
In the case where the control unit of the printer according to the fifth modification performs the printing operation based on the image forming instruction immediately after the routine after the process unit attachment / detachment detection, the process driving motors are not stopped after the execution of the routine. Execute the print operation. However, it is necessary to adjust the phase of the speed variation pattern of each photoconductor prior to the printing operation. Also, the linear velocity difference setting of each photoconductor needs to be turned on. Therefore, the phase adjustment control immediately before the printing operation is performed without stopping the driving of each photoconductor. While grasping the rotation angle of each photoconductor based on the detection timing of the markings (134Y, C, M, K) attached to the photoconductor gear, the driving speed of each photoconductor is slightly changed to change each photoconductor. The phase of the speed fluctuation pattern is adjusted. When the phase adjustment control is performed in this way, the linear velocity difference setting is turned ON so that the driving speed of each photoconductor is set to the value obtained by the positional deviation correction control. Then, after each photoconductor is stably driven with the linear velocity difference, the printing operation is performed.

[Sixth embodiment]
The control means of the printer according to the sixth embodiment executes a routine after the process unit detachment detection which is almost the same as that shown in FIG. 20, but the control flow is different from that shown in FIG. That is, when an error occurs during the execution of the positional deviation correction control (S1 or S14) or the positional deviation correction control ends abnormally (Y in S2 or S15), the subsequent image forming operation is performed. Each process drive motor is driven at the drive speed obtained by the previous positional deviation correction control. In such a configuration, even when an error occurs during the positional deviation correction control or the positional deviation correction control ends abnormally, the positional deviation correction can be executed in the subsequent image forming operation.

  Up to this point, a description has been given of a printer in which each color toner image on each photoconductor is primarily transferred to the intermediate transfer belt 41 and then secondarily transferred onto a recording sheet as a recording body. Instead of such a method, a method may be employed in which each color toner image on each photoconductor is directly superimposed and transferred onto a recording paper held on a paper conveyance belt as an endless moving body. In this case, in the positional deviation correction control and the fluctuation pattern detection control, each toner image may be transferred to the paper transport belt and detected by the optical sensor unit. For example, as shown in FIG. 27, the toner images on the photoconductors 3Y, 3C, 3M, and 3K are directly superimposed on the recording paper P that is conveyed while being held on the surface of the paper conveying belt 201 that is an endless moving body. This is an image forming apparatus of a transfer type. Even in such a system, the positional deviation correction control and the fluctuation pattern detection control can be performed by transferring the positional deviation detection image and the speed fluctuation detection image from the photoconductors 3Y, 3C, 3M, and K to the paper conveyance belt 201. Can do.

  As described above, in the printer according to the sixth modified example, when an error occurs during the execution of the positional deviation correction control, the process drive motor serving as each drive source is set to the previous position in the subsequent image forming operation. Since the speed obtained in the deviation correction control is individually set, even when an error occurs during the position deviation correction control, the position deviation correction can be executed in the subsequent image forming operation.

  In the printer according to the sixth modification, when the positional deviation correction control ends abnormally, the process drive motors serving as the respective driving sources are used in the previous positional deviation correction control in the subsequent image forming operation. Since the obtained speed is individually set, even when the positional deviation correction control ends abnormally, the positional deviation correction can be executed in the subsequent image forming operation.

  In the printer according to the fifth modified example, after the positional deviation correction control is normally completed, continuous printing, which is an image forming operation for transferring to the recording medium P without stopping each process drive motor, is performed. In this case, the control means is configured so that the driving speed of each process driving motor is set to the speed obtained by the positional deviation correction control prior to the continuous printing (linear speed difference setting is ON). Therefore, during continuous printing, it is possible to suppress a slight positional shift of each color toner image due to a difference in linear velocity.

  In the printers of the embodiments and the modified examples, after an image based on image information is formed on the recording paper P, the phase of the speed variation pattern on each of the photoreceptors as a plurality of latent image carriers is adjusted. The control of preliminarily adjusting the phase of the speed variation pattern of each photoconductor when the process drive motor is driven next by stopping the driving of each process drive motor is performed as phase adjustment control. It constitutes a control means. In this configuration, as described above, it is possible to avoid an increase in the first print time due to the phase adjustment control at the start of the print job.

  Further, in the printer according to the embodiment and each modification, in the fluctuation pattern detection control, the speed fluctuation detection image for the K photoconductor as the reference latent image carrier and the Y, C, and M photoconductors are used. Speed fluctuation detection for the K photoconductor so that the image for speed fluctuation detection is transferred side by side in the belt width direction, which is a direction orthogonal to the surface movement direction, on the surface of the intermediate transfer belt 41 which is an endless moving body. The formation of the image for the start is started based on the detection timing of the marking 134K by the position sensor 135K for the photoconductor for K, while the formation of the image for detecting the speed fluctuation on the photoconductor for Y, C, M is also the K Y in phase adjustment control based on the phase shift of the speed fluctuation pattern of the speed fluctuation detection image C, so as to determine a driving stop timing of the process drive motor corresponding to the photosensitive material for M, constitute a control means. In this configuration, as described above, the speed variation pattern for Y, C, and M and the speed for K are referred without referring to the detection timing of the markings for Y, C, and M (134Y, C, and M). A phase shift from the fluctuation pattern can be detected. Furthermore, it is possible to accurately detect the speed fluctuation pattern of each photoconductor by removing the time pitch error caused by the speed of the intermediate transfer belt 41 at the position facing the optical sensor unit.

  In addition, in the printers of the embodiments and modifications, each process drive motor is driven prior to the execution of the fluctuation pattern detection control, and the drive stop timing obtained by the previous fluctuation pattern detection control is driven. Instead, the control means is configured to perform the fluctuation pattern detection control after stopping at a predetermined reference timing and re-driving each process drive motor. In such a configuration, each photoconductor is rotated from a predetermined rotational position and fluctuation pattern detection control is performed, so that the speed fluctuation pattern of each photoconductor is detected while clearly grasping the rotational phase relationship between the photoconductors. To do. Thereby, the phase shift of the speed variation pattern can be easily obtained.

  Further, in the printer according to the embodiment and each modification, in performing the variation pattern detection control, in order to start driving of each process drive motor in a state where the respective process drive motors are set to the same drive speed, It constitutes a control means. In this configuration, as described with reference to the graph of FIG. 28, as already described, the Y, C, M photoconductor in the initial stage of re-driving, the healthy body for K, and the speed fluctuation pattern due to the difference in linear velocity. Deterioration of detection accuracy can be avoided.

  In the printer according to the fifth modification, after the process unit detachment detection routine including the fluctuation pattern detection control is performed, the image forming operation for transferring the process drive motor to the recording paper P without stopping the process drive motor. When performing the above, perform special phase adjustment control that does not stop each process drive motor, and further set the drive speed of each process drive motor to the speed obtained by the positional deviation correction control, and then perform the image forming operation. The control means is configured to do so. In this configuration, the waiting time of the user due to temporarily stopping each process drive motor between the routine after the process unit detachment detection and the image forming operation is avoided, and the linear velocity difference between each photoconductor is avoided in the image forming operation. Therefore, the positional deviation can be suppressed satisfactorily.

  Further, in the printers according to the embodiments and the modifications, each process drive motor is stopped after the positional deviation correction control and the variation pattern detection control are normally finished while driving each process drive motor at the same drive speed. After that, the control means is configured to turn ON the setting to drive each process drive motor at the driving speed obtained by the positional deviation correction control (linear speed difference setting ON). It is possible to avoid the deterioration of positional deviation caused by forgetting to turn on the linear velocity difference setting at the start of driving of the process drive motor.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 3 is an enlarged configuration diagram illustrating a process unit for Y of the printer. The perspective view which shows the process unit. The perspective view which shows the image development unit of the process unit. The perspective view which shows the main body side drive transmission part which is a drive transmission system fixed in the housing of the printer. The top view which shows the same main body side drive transmission part from upper direction. The fragmentary perspective view which shows the one end part of the process unit for Y. FIG. 2 is a perspective view showing a Y photoconductor gear and its peripheral configuration in the printer. FIG. 3 is a side view showing each photoconductor, a transfer unit, and an optical writing unit in the printer. FIG. 3 is a perspective view showing a part of an intermediate transfer belt in the printer together with an optical sensor unit. The expansion schematic diagram which shows the image for position shift detection. 5 is a flowchart showing the processing content of positional deviation correction control performed by the control unit of the printer. The expansion schematic diagram which shows the image for speed fluctuation detection for K. FIG. 2 is a block diagram showing a circuit configuration in control means of the printer. FIG. 3 is an enlarged schematic diagram illustrating a primary transfer nip due to contact between a photoconductor and an intermediate transfer belt. (A), (b), (c) is a graph which respectively shows the output pulse from an optical sensor unit. The block diagram which shows an example of the circuit structure for performing a quadrature detection process. 6 is a flowchart showing a series of control flows that are performed after a process unit is detected and before a print job is performed. FIG. 3 is a perspective view showing a process unit 1Y for Y in the printer according to the first embodiment. 9 is a flowchart showing a control flow of a routine after detection of attachment / detachment of a process unit, which is performed by a control unit of a printer according to a first modification when any one of the process units is replaced. The flowchart which shows the 1st step of the control flow of the routine after the process unit removal | desorption detection implemented by the control means of the printer which concerns on a 2nd modification. The flowchart which shows the 2nd step of the control flow of the routine after the process unit removal | desorption detection implemented by the control means. The flowchart which shows the 3rd step of the control flow of the routine after the process unit removal | desorption detection implemented by the control means. The flowchart which shows the 4th step of the control flow of the routine after the process unit removal | desorption detection implemented by the control means. The flowchart which shows the 5th step of the control flow of the routine after the process unit removal | desorption detection implemented by the control means. The perspective view which shows the printer which concerns on a 3rd modification. FIG. 2 is a schematic configuration diagram illustrating an example of a printer that transfers a toner image on each photosensitive member directly on a recording sheet. The graph which shows the rotational speed characteristic of the process drive motor of the drive start initial stage. 6 is a graph for explaining a shift in the rotational phase of a photoconductor.

Explanation of symbols

1Y, C, M, K: Process unit (part of visible image forming means)
3Y, C, M, K: photoconductor (image carrier)
3K: Photoconductor for K (reference image carrier)
40: Transfer unit (transfer means)
41: Intermediate transfer belt (endless moving body)
20: Optical writing unit (part of visible image forming means, latent image writing means)
120Y, C, M, K: Process drive motor (drive source)
135Y, C, M, K: Position sensor (rotation angle detection means)
136: Optical sensor unit (image detection means)
P: Recording paper (recording medium)
PV: Image for detecting displacement

Claims (12)

A plurality of latent image carriers that carry a latent image on a surface that moves endlessly, a plurality of drive sources that individually drive each latent image carrier, and a latent image that is latent in each latent image carrier based on image information. A visible image forming means having a latent image writing means for writing an image, and a plurality of developing means for individually developing the latent image written on each latent image carrier to obtain a visible image;
An endless moving body that moves the surface endlessly so as to sequentially pass a position facing each latent image carrier;
The visible image formed on the surface of each latent image carrier is transferred to the recording medium held on the surface of the endless moving body, or transferred to the recording body after being transferred to the surface of the endless moving body. Transcription means;
Image detection means for detecting a visible image on the endless moving body;
Based on the detection result by the image detection means of the position shift detection image obtained by transferring a predetermined visible image from the latent image carrier to the surface of the endless moving body, the image on the latent image carrier is displayed. In an image forming apparatus, comprising: a control unit that performs a positional shift correction control that calculates a relative positional shift amount of a visible image and individually calculates a driving speed for each of the drive sources based on the calculation result. ,
An image forming apparatus, wherein the control means is configured to form and detect the image for detecting misalignment in a state where the respective driving sources are driven at the same speed. The image forming apparatus according to claim 1.
If an error occurs during the above-mentioned positional deviation correction control, the drive speed of each drive source is individually set to the speed obtained by the previous positional deviation correction control in the subsequent image forming operation. An image forming apparatus characterized in that the control means is configured to set. The image forming apparatus according to claim 1.
When the above positional deviation correction control ends abnormally, the drive speed of each drive source is individually set to the speed obtained by the previous positional deviation correction control in the subsequent image forming operation. An image forming apparatus comprising the control means. The image forming apparatus according to any one of claims 1 to 3,
After performing the positional deviation correction control normally, when performing an image forming operation for transferring to the recording body without stopping the respective driving sources, prior to the image forming operation, An image forming apparatus characterized in that the control means is configured to set the driving speed to the speed determined by the positional deviation correction control. A plurality of latent image carriers that carry a latent image on a rotating surface, a plurality of drive sources for individually driving each latent image carrier, and a latent image on each latent image carrier based on image information A visible image forming means, and a plurality of developing means for individually developing the latent image written on each latent image carrier to obtain a visible image;
An endless moving body that moves the surface endlessly so as to sequentially pass a position facing each latent image carrier;
The visible image formed on the surface of each latent image carrier is transferred to the recording medium held on the surface of the endless moving body, or transferred to the recording body after being transferred to the surface of the endless moving body. Transcription means;
Image detection means for detecting a visible image on the endless moving body;
For each of the plurality of latent image carriers, rotation angle detection means for detecting that a predetermined rotation angle has been reached,
Control means for performing predetermined control,
The control means
Based on the detection result by the image detection means of the position shift detection image obtained by transferring a predetermined visible image from the latent image carrier to the surface of the endless moving body, the image on the latent image carrier is displayed. A positional shift correction control for calculating a relative positional shift amount of the visible image, and individually calculating a driving speed for each of the driving sources based on the calculation result;
A speed fluctuation detection image consisting of a plurality of predetermined visible images is formed on the latent image carrier and transferred to the endless moving body, and then the detection result of the speed fluctuation detection image by the image detection means, And a fluctuation pattern detection control for detecting a speed fluctuation pattern per rotation of the latent image carrier based on a detection result by the rotation angle detection means;
In the image forming apparatus for performing phase adjustment control for adjusting the phase of the speed fluctuation pattern of each latent image carrier based on the result of the speed fluctuation pattern for each latent image carrier.
An image forming apparatus, wherein the control means is configured to form and detect the speed fluctuation detection image in a state where the respective driving sources are driven at the same speed. The image forming apparatus according to claim 5.
An image forming apparatus, wherein the control means is configured to form and detect the image for detecting misalignment in a state where the respective driving sources are driven at the same speed. The image forming apparatus according to claim 6.
After the image based on the image information is formed on the recording body, the driving of the plurality of driving sources is stopped while the phase of the speed variation pattern in each of the plurality of latent image carriers is adjusted. The control means is configured such that control for adjusting in advance the phases of the speed fluctuation patterns of a plurality of latent image carriers when the drive sources are driven next is performed as the phase adjustment control. Image forming apparatus. The image forming apparatus according to claim 7.
In the fluctuation pattern detection control, the speed fluctuation detection image for the reference latent image carrier that is one of the plurality of latent image carriers and the speed fluctuation detection for the other latent image carrier. The reference latent image carrier is formed with the speed variation detection image formed on the reference latent image carrier so that the image is aligned and transferred to the surface of the endless movable body in a direction orthogonal to the surface movement direction. On the basis of the detection result by the rotation angle detection means for, on the other hand, the formation of the speed fluctuation detection image on the other latent image carrier is started based on the detection result,
The control means is configured to determine the drive stop timing of the drive source corresponding to the other latent image carrier in the phase adjustment control based on the phase shift of the speed change pattern of the speed change detection images. An image forming apparatus comprising: The image forming apparatus according to claim 8.
Prior to performing the variation pattern detection control, each of the plurality of drive sources is driven, the drive of these drive sources is stopped at a predetermined reference timing instead of the drive stop timing, and An image forming apparatus, wherein the control means is configured to perform the variation pattern detection control after each drive source is re-driven. The image forming apparatus according to claim 9.
In performing the variation pattern detection control, the image forming apparatus is characterized in that the control means is configured to start driving the respective drive sources with the respective drive sources set at the same drive speed. . The image forming apparatus according to claim 10.
After performing the variation pattern detection control, when performing an image forming operation for transferring to the recording body without stopping each drive source, the phase adjustment control is performed, and each drive source is further controlled. An image forming apparatus, wherein the control means is configured to perform the image forming operation after the driving speed is set to the speed obtained by the positional deviation correction control. The image forming apparatus according to claim 1,
After the position deviation correction control or fluctuation pattern detection control while driving each of the drive sources at the same driving speed is terminated normally and the respective drive sources are stopped, the respective drive sources are moved to the position deviation. An image forming apparatus characterized in that the control means is configured to turn on a setting for driving at a driving speed determined in correction control.

Images