JP3788216B2 - Image forming apparatus and image forming method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and an image forming method for forming a color image by superimposing a plurality of color toner images. In particular, the present invention relates to a toner image formed on a photoconductor as an intermediate transfer belt and an intermediate transfer drum. A transfer process of transferring onto a transfer medium such as a transfer sheet is performed for each toner color to form a color image on the transfer medium.
[0002]
[Prior art]
In this type of image forming apparatus, each time a reference signal is output, a toner image is formed on the photoreceptor, and then the toner image is primarily transferred onto a transfer medium that rotates at a constant conveyance speed in synchronization with the photoreceptor. Thus, the toner images of a plurality of colors are accurately superimposed by controlling the registration in this way. Accordingly, it is necessary to rotate and convey the transfer medium at a constant speed in synchronization with the photosensitive member from when the reference signal is output until the primary transfer is completed.
[0003]
However, the secondary transfer roller temporarily contacts the transfer medium for secondary transfer, or the cleaning blade is used to clean and remove residual toner remaining on the transfer medium after the secondary transfer. Temporarily abut. For this reason, the contact causes a load variation on the transfer medium, which causes the toner images to deviate from each other between toner colors, that is, causes a registration shift, resulting in a decrease in image quality.
[0004]
In view of this, a technique has been conventionally proposed in which the amount of deviation of the toner image for each color is suppressed by increasing or decreasing the rotational speed of the transfer medium in response to this registration deviation. For example, in Japanese Patent Laid-Open No. 11-231599, a dummy cycle is executed prior to actually forming a color image, a registration shift amount between toner colors is obtained, and a correction value for minimizing the registration shift is also obtained. (Corresponding to “registration control amount establishment processing” of the present invention). In actual color image formation, the rotational speed of the transfer medium is increased or decreased by a correction value to adjust the position of the toner image on the transfer medium, thereby suppressing registration deviation.
[0005]
[Problems to be solved by the invention]
By the way, the tolerance of registration error varies greatly depending on factors such as the user industry and the image type. For example, the tolerance of registration deviation is generally large for a photographic image such as a natural image or a human image, but an image that causes severe line deviation or an image that frequently uses color characters, such as a CAD drawing. On the other hand, even a slight misregistration is often not allowed, and it can be said that the tolerance of the misregistration is generally small.
[0006]
Therefore, when the image forming apparatus is configured to obtain the correction value with accuracy matching the photographic image, that is, medium / low accuracy, an image satisfying the user's request can be obtained for the photographic image, but it is acceptable in a CAD drawing or the like. A line shift exceeding the range may occur, and an image having a quality that satisfies the user's request may not be obtained.
[0007]
On the other hand, when the image forming apparatus is configured so as to obtain a correction value with accuracy that matches a CAD drawing, that is, with high accuracy, a high-quality image can be obtained in a photographic image and a CAD drawing, but the accuracy of the correction value In order to increase the number of dummy cycles, it is necessary to increase the number of dummy cycles, which causes a problem that it takes a long time to start creating a color image. In particular, users who exclusively form photographic images have to wait for the start of color image creation because an unnecessary dummy cycle is executed even though a medium- and low-precision correction value can form an image of a desired quality. There is a problem of being. Therefore, in a conventional image forming apparatus configured to execute a predetermined uniform registration control amount establishment process and obtain a correction value, and to always correct the registration deviation based on the correction value, It was not possible to respond flexibly to user requests.
[0008]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus and an image forming method capable of appropriately suppressing registration displacement while flexibly responding to user requests.
[0009]
[Means for Solving the Problems]
In the present invention, a transfer process for transferring a toner image formed on a photoreceptor to a rotationally driven transfer medium is repeated for a plurality of different toner colors, and a toner image of each toner color is superimposed to form a color image. In order to achieve the above object, the image forming apparatus and the image forming method are configured as follows.
[0010]
The image forming apparatus includes a contact unit that temporarily contacts the transfer medium when the transfer process is repeated, and a reference signal detection unit that outputs a reference signal related to the rotation operation of the transfer medium. Based on the reference signal, (1) a period when the abutting means that is separated from the transfer medium abuts on the transfer medium, and (2) the abutting means continues to abut on the transfer medium. And (3) a period when the abutting means that has been in contact with the transfer medium is separated from the transfer medium, and (4) a period when the abutment means continues to be separated from the transfer medium. And a relative registration shift of the toner image on the transfer medium caused by the contact between the contact means and the transfer medium is corrected based on the difference between the periods. The amount of resist control required to And a control means for correcting the transfer start position of the toner image for each toner color in accordance with the registration control amount at the time of forming a color image. The amount can be changed and set.
[0011]
Further, in this image forming method, a reference signal detection step for detecting a reference signal related to the rotation operation of the transfer medium, and (1) the contact means that is separated from the transfer medium based on the reference signal A period when abutting on the transfer medium, (2) a period when the abutting means continues to abut on the transfer medium, and (3) the abutting means abutting on the transfer medium is the transfer medium And (4) the period when the abutting means continues to be separated from the transfer medium, respectively, are measured by a predetermined number of times, and from the difference between these periods, the abutting means A registration control amount establishment step for executing a registration control amount establishment process for obtaining a registration control amount necessary for correcting a relative registration deviation of a toner image on the transfer medium caused by separating and contacting the transfer medium; The Regis A correction step of correcting transfer start positions of toner images for each toner color based on the control amount, is configured and a changing step of changing the setting registration control amount as needed.
[0012]
In the invention configured as described above, the registration control amount is obtained by the registration control amount establishment process. This registration control amount can be changed and set as necessary. Therefore, by appropriately changing the registration control amount according to the user request, it is possible to suppress the registration shift while responding to the user request.
[0013]
Here, in order to change and set the registration control amount, for example, the registration control amount obtained by the registration control amount establishment process is directly rewritten, or the number of periodic measurements performed in the registration control amount establishment process is changed, and the number of times The registration control amount obtained from the registration control amount establishment process may be changed by the change.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
A. About device configuration
FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This image forming apparatus is an apparatus that forms a full color image by superposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K), and is supplied from an external device such as a host computer. When an image signal (image formation command) is given to the main controller 11 of the control unit 1, the CPU 111 of the main controller 11 converts it into job data in a format suitable for an operation instruction of the engine unit E. The engine controller 12 controls each part of the engine unit E in accordance with job data from the main controller 11 to form an image corresponding to the image signal on a sheet S such as transfer paper, copy paper, or OHP sheet.
[0015]
In the engine unit E, a toner image can be formed on the photosensitive member 21 of the process unit 2. That is, the process unit 2 includes a photoconductor 21 that can rotate in the direction of the arrow in FIG. 1, and further, around the photoconductor 21 along the rotation direction, a charging roller 22 as a charging unit, and a developing unit as a developing unit. Developing units 23Y, 23C, 23M, and 23K, and a photoreceptor cleaner blade 24 are respectively disposed.
[0016]
In this apparatus, the charging roller 22 contacts the outer peripheral surface of the photoconductor 21 to uniformly charge the outer peripheral surface, and then the laser light L is emitted from the exposure unit 3 toward the outer peripheral surface of the photoconductor 21. As shown in the figure, the exposure unit 3 includes a light emitting element 31 such as a semiconductor laser that is modulated and driven in accordance with an image signal. The laser light L from the light emitting element 31 is rotationally driven by a high speed motor 32. Is incident on the polygon mirror 33. The laser beam L reflected by the polygon mirror 33 scans the photoconductor 21 via the lens 34 and the mirror 35 in the main scanning direction (direction perpendicular to the paper surface of the figure) and corresponds to the image signal. An electrostatic latent image is formed. Reference numeral 36 denotes a horizontal synchronization reading sensor for obtaining a synchronization signal in the main scanning direction, that is, a horizontal synchronization signal HSYNC.
[0017]
The electrostatic latent image thus formed is developed with toner by the developing unit 23. That is, in this embodiment, as the developing unit 23, a yellow developing unit 23Y, a cyan developing unit 23C, a magenta developing unit 23M, and a black developing unit 23K are arranged along the photoconductor 21 in this order. Has been. These developing units 23Y, 23C, 23M, and 23K are configured so as to be able to come into contact with and separate from the photosensitive member 21, and in response to a command from the engine controller 12, the four developing units 23Y, 23M, 23C, One of the developing units 23B selectively comes into contact with the photoconductor 21, and a high voltage is applied to apply toner of the selected color to the surface of the photoconductor 21 to thereby cause electrostatic latent image on the photoconductor 21. Reveal the image.
[0018]
The toner image developed by the developing unit 23 is primarily transferred onto the intermediate transfer belt 41 of the transfer unit 4 in the primary transfer region R1 positioned between the black developing device 23K and the photoreceptor cleaner blade 24. Further, a photoreceptor cleaner blade 24 is disposed at a position advanced in the circumferential direction (arrow direction in FIG. 1) from the primary transfer region R1, and remains adhered to the outer peripheral surface of the photoreceptor 21 after the primary transfer. Scrape off the toner.
[0019]
Next, the configuration of the transfer unit 4 will be described. In this embodiment, the transfer unit 4 includes rollers 42 to 47, an intermediate transfer belt 41 stretched over the rollers 42 to 47, and an intermediate toner image transferred to the intermediate transfer belt 41 on the sheet S. A secondary transfer roller 48 for next transfer and a photoconductor / belt drive unit 41a (FIG. 2) for rotating and driving the photoconductor 21 and the intermediate transfer belt 41 synchronously are provided. When a color image is transferred onto the sheet S, the color toner images formed on the photosensitive member 21 are superimposed on the intermediate transfer belt 41 to form a color image, and the paper supply / discharge unit 6 supplies the color image. The sheet S is taken out from the cassette 61, the manual feed tray 62, or an additional cassette (not shown) by the paper portion 63 and conveyed to the secondary transfer region R2. Further, a full color image is obtained by secondary transfer of the color image onto the sheet S.
[0020]
Note that toner remaining on the outer peripheral surface of the intermediate transfer belt 41 after the secondary transfer is removed by a cleaner blade 491 provided in the belt cleaner 49. In other words, the belt cleaner 49 is disposed so as to face the roller 46 with the intermediate transfer belt 41 interposed therebetween, and the cleaner blade 491 comes into contact with the intermediate transfer belt 41 at the timing described later and remains on the outer peripheral surface thereof. Scrape off the toner.
[0021]
A sensor 40 for detecting the reference position of the intermediate transfer belt 41 is disposed in the vicinity of the roller 43, and obtains a synchronization signal in the sub-scanning direction substantially perpendicular to the main scanning direction, that is, a vertical synchronization signal VSYNC. Functions as a vertical synchronization reading sensor.
[0022]
The sheet S on which the toner image has been transferred by the transfer unit 4 as described above is downstream of the secondary transfer region R2 along a predetermined paper feed path (two-dot chain line) by the paper feed unit 63 of the paper feed / discharge unit 6. The toner image on the sheet S is fixed to the sheet S by being conveyed to the fixing unit 5 disposed on the side. Then, the sheet S is further conveyed along the paper feed path to the paper discharge unit 64 and then discharged to the standard paper discharge tray.
[0023]
Next, the electrical configuration of the image forming apparatus configured as described above will be described. The engine controller 12 includes a CPU 121, and as an input signal from the engine unit E, the horizontal synchronization signal HSYNC from the horizontal synchronization read sensor 36, the vertical synchronization signal VSYNC from the vertical synchronization read sensor 40, and the fixing unit 5. A temperature signal indicating a fixing temperature is received from a temperature sensor 51 provided in the printer. Further, based on these input signals and various information, the CPU 121 sends a photoconductor / belt drive unit 41a for rotationally driving the photoconductor 21 and the intermediate transfer belt 41 in synchronization with each other, and a drive command signal for driving control. To the belt drive control circuit 122, and the photoreceptor / belt drive control circuit 122 controls the photoreceptor / belt drive unit 41 a using a DC motor as a drive source to control the rotation speed of the photoreceptor 21 and the conveyance of the intermediate transfer belt 41. Acceleration / deceleration control of speed V is performed. Further, the CPU 121 executes registration control amount establishment / storage processing, transfer start position correction processing based on the registration control amount, registration control amount change setting processing, and the like, which will be described later.
[0024]
In addition to the photoconductor / belt drive control circuit 122, the engine controller 12 further includes a transfer roller separation / contact control circuit 123 and a belt cleaner separation / contact control circuit 124 as dedicated control circuits for controlling the transfer unit 4. I have. The transfer roller separation / contact control circuit 123 controls the secondary transfer roller drive unit 48a based on a command signal from the CPU 121 to bring the secondary transfer roller 48 into contact with the intermediate transfer belt 41 at an appropriate timing. . On the other hand, the belt cleaner separation / contact control circuit 124 gives a CB signal to the belt cleaner drive unit 49a based on a command signal from the CPU 121 to control the belt cleaner drive unit 49a, and intermediately moves the cleaner blade 491 at an appropriate timing. Separated and brought into contact with the transfer belt 41.
[0025]
Reference numeral 113 in the figure denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112, and reference numeral 125 denotes registration control as will be described later. Memory for storing period data acquired during the amount establishment process, registration control amount obtained by the CPU 121 based on the data, job repetition number, control data for controlling the engine unit E, calculation results in the CPU 121, and the like It is.
[0026]
B. Basic operation
FIG. 3 is a flowchart showing the basic operation of the image forming apparatus configured as described above. In such an image forming apparatus, when the primary transfer process is repeated, if the abutting means such as the secondary transfer roller 48 or the cleaner blade 491 comes into contact with the intermediate transfer belt 41, the subsequent “B-1. As described in detail in the section “Regarding misalignment”, various misregistrations occur. However, by correcting the transfer start position by the resist control amount, the misregistration is suppressed and the image quality is improved.
[0027]
In this image forming apparatus, when the apparatus power is turned on, prior to actual image forming processing, registration control amount establishment processing (step S1) is executed to automatically establish three types of registration control amounts. Is stored in the memory 125 as a storage unit as an initial registration control amount. In this embodiment, the following resist control amounts Ra, Rb, Rc as three types of initial resist control amounts, that is,
Ra: A resist control amount for correcting a registration shift generated when the cleaner blade 491 comes into contact during the primary transfer process and the primary transfer process is completed in the contact state.
Rb: A resist control amount for correcting a registration shift that occurs when the cleaner blade 491 comes into contact before the start of the primary transfer, the primary transfer process is continued in the contact state, and the cleaner blade 491 is separated during the process. ,
Rc: a resist control amount for correcting a registration shift that occurs when the cleaner blade 491 that has been in contact before the start of the primary transfer is separated and then the primary transfer process is performed in the separated state.
Is enacted. Details of these three types of registration control amount automatic establishment operations (step S1) will be described in detail later in “B-2. Initial registration control amount establishment processing”.
[0028]
When the establishment of the three types of initial registration control amounts Ra, Rb, and Rc (step S1) is completed in this way, an image signal from an external device such as a host computer, that is, a print request is waited (step S2). When there is a print request, it is determined whether the print mode is monochrome print or color print (step S3). If it is determined that the print mode is monochrome print, normal image forming processing is performed without performing registration control. Execute and return to step S2. On the other hand, if it is determined in step S3 that color printing is being performed, a sequence flag corresponding to the print sequence state is selectively set from the three sequence flags F0, F1, and F2 (step S4).
[0029]
Then, after the registration control amount corresponding to the sequence flag is set (step S5), in the primary transfer of each toner image, the photosensitive member 21 is subjected to acceleration / deceleration control during a predetermined acceleration / deceleration period to form a latent image. The position is shifted by the registration control amount in the sub-scanning direction with respect to the reference latent image forming position. As a result, the transfer position of the toner image on the intermediate transfer belt 41 to which the primary transfer is performed is also moved by the registration control amount in the sub-scanning direction. In this way, the registration start is suppressed by correcting the transfer start position. Details of this will be described later in the section “B-3. Correction of transfer start position”.
[0030]
In this way, when the formation of the color image is completed while suppressing the registration shift based on the registration control amount, it is determined whether or not the printing is finished in step S6. If the printing is judged to be finished, the process proceeds to step S2. Return and wait for the next print request. On the other hand, if it is determined that printing has not ended, the process returns to step S3 and the same processing as described above is repeated.
[0031]
B-1. About Registrar
Here, with reference to FIG. 4 to FIG. 9, detailed description will be given of the occurrence of registration misalignment when the image forming apparatus of FIG. 1 is operated in the operation sequence shown in FIG. 4 without any correction of the transfer start position. To do.
[0032]
FIG. 4 is a timing chart showing an example of an operation sequence in the image forming apparatus of FIG. As shown in the figure, after the apparatus power is turned on or when the sleep mode of the image forming apparatus is released, the intermediate transfer belt 41 is rotated and conveyed, and the vertical synchronization signal VSYNC is intermittently transmitted from the vertical synchronization reading sensor 40. Is output. Each time the vertical synchronization signal VSYNC is output at timings VT1 to VT7,..., A yellow electrostatic latent image, a cyan electrostatic latent image, a magenta electrostatic latent image, and a black electrostatic latent image are displayed at a predetermined time. It is repeatedly formed in order on the photoconductor 21. After the electrostatic latent image is formed, one of the developing units 23Y, 23M, 23C, and 23K selectively comes into contact with the photosensitive member 21 to reveal the electrostatic latent image on the photosensitive member 21, The toner image is primarily transferred onto the intermediate transfer belt 41. Accordingly, the toner images of the respective colors are all formed at a predetermined position on the photoconductor 21, that is, at the reference latent image forming position, and the intermediate transfer belt 41 that rotates in synchronization with the photoconductor 21 is also primary at the same position. Transferred (primary transfer process for each toner color).
[0033]
When the primary transfer process is repeated for four colors, four color toner images are superimposed on the intermediate transfer belt 41 to form a color image. When a color image is obtained in this way, the secondary transfer roller 48 contacts the intermediate transfer belt 41 with the sheet S interposed therebetween, and the color image is secondarily transferred to the sheet S, and the cleaner blade 491 receives the intermediate transfer according to the CB signal. The toner remaining on the belt surface in contact with the belt 41 is removed. The sheet S on which the color image is formed by repeating such an operation is sequentially discharged to the standard discharge tray.
[0034]
This is an outline of the operation of the image forming apparatus according to the operation sequence of FIG. 4. When the relationship between such operation and the amount of registration deviation in the sub-scanning direction is examined, the results differ between the first sheet and the second and subsequent sheets. was gotten. Such a difference is caused by a difference in operation sequence. Hereinafter, an operation sequence for forming an image on the first sheet (hereinafter referred to as “first print sequence”) and an image formation on the second and subsequent sheets are performed. The operation sequence will be described separately (hereinafter referred to as “second print sequence”). In addition, in this type of apparatus, there is a third print sequence that accompanies the idling process, and this will also be described.
[0035]
B-1-1. First printing sequence
First, when the apparatus power is turned on (or the sleep mode of the image forming apparatus is canceled), the intermediate transfer belt 41 is rotated and conveyed, and the vertical synchronization signal VSYNC is sequentially transmitted from the vertical synchronization reading sensor 40 at timings VT1 to VT3. The yellow toner image Y1 is primarily transferred onto the intermediate transfer belt 41 as described above corresponding to the first timing VT1, and the cyan toner image C1 is converted to the yellow toner image Y1 corresponding to the timing VT2. The magenta toner image M1 is primarily transferred onto the intermediate transfer belt 41 so as to overlap the yellow toner image Y1 and the cyan toner image C1 corresponding to the timing VT3. During this time, the cleaning process and the secondary transfer process of the intermediate transfer belt 41 are not performed, and the contact means (the secondary transfer roller 48 and the cleaner blade 491) are separated from the intermediate transfer belt 41. Therefore, these three toner images Y1, C1, and M1 are all superimposed at the same position on the intermediate transfer belt 41, and are accurately registered in the sub-scanning direction. That is, as shown in FIG. 5, the transfer start positions of these three toner images Y1, C1, and M1 all coincide with the reference transfer start position, and the transfer rear end position also coincides with the reference transfer rear end position. ing. In the figure, the alternate long and short dash line indicates the primary transfer position to which each toner image is transferred, and in the actual primary transfer process, the respective toner images are sequentially overlapped at the one-dot chain line portion. For convenience of explanation, the respective toner images are shown separated in the vertical direction (the same applies to FIG. 12 described later).
[0036]
Next, when the vertical synchronization signal VSYNC is output at timing VT4, as shown in FIG. 6, a VIDEO signal is given to the exposure unit 3 after a predetermined time T10, and the electrostatic latent image corresponding to the black toner image K1 is displayed. The toner is developed by the black developing device 23K while being formed at a predetermined reference latent image forming position in the same manner as the toner color of. Then, the primary transfer process is started when a certain time T20 has elapsed from the output of the vertical synchronization signal VSYNC (timing VT4). At this time, as in the case of the yellow toner image Y1, the cyan toner image C1, and the magenta toner image M1, the cleaner blade 491 is separated from the intermediate transfer belt 41. As a result, as shown in FIG. Similarly to the other toner images Y1, C1, and M1, the transfer start position of the image K1 also coincides with the reference transfer start position. During the separation, the conveying speed V of the intermediate transfer belt 41 is constant, and the black toner image K1 is superimposed while being accurately registered with the other toner images Y1, C1, and M1 that have already been primarily transferred. Go.
[0037]
However, the CB signal for controlling the operation of the cleaner blade 491 rises from the L level to the H level at a certain point in time during the first half of the primary transfer of the black toner image K1, that is, at timing t1, and the cleaner blade 491 moves to the intermediate transfer belt 41. The black toner image K1 is in contact with the other toner images Y1, C1, and M1 in the sub-scanning direction. That is, at timing t1, the cleaner blade 491 contacts the intermediate transfer belt 41 and acts as a transport load for the intermediate transfer belt 41, and the intermediate transfer belt 41 instantaneously extends in the sub-scanning direction A27. As a result, a resist misalignment occurs in the (−) direction by a resist misalignment amount A27.
[0038]
Further, after the timing t1, the cleaner blade 491 is maintained in contact with the intermediate transfer belt 41 until the CB signal rises again from the L level to the H level, and the intermediate transfer belt 41 is cleaned. The primary transfer process of the black toner image K1 is continued in the contact state until the timing t2. As a result, the registration deviation is further increased, and the registration deviation amount in the sub-scanning direction of the final black toner image K1 is
A32 = A27 + A6
Thus, as shown in FIG. 5, the transfer rear end position of the black toner image K1 is shifted from the reference transfer rear end position by the amount of deviation A32 in the (−) direction. However, symbol A6 corresponds to belt elongation caused by the cleaner blade 491 being kept in contact with the intermediate transfer belt 41 from timing t1 to timing t2 (that is, time A7). In FIG. 6 (and a diagram showing a registration error state described later), a thick solid line indicates a registration error for a toner image of a corresponding toner color, while a thick broken line indicates an assist for helping understanding of the registration error occurrence state. Is a line.
[0039]
Thus, as shown in FIG. 5, for the first color image, only the black toner image K1 is shifted from the other toner images Y1, C1, and M1 in the latter half, and particularly in the last part of the color image. It will shift by the amount of deviation A32. More specifically, as shown in FIG. 6, with respect to the first black toner image, the registration deviation in the sub-scanning direction during the primary transfer is (+) and (+) in the sub-scanning direction centering on the shake width center AC1. This occurs in the range of the amount of deviation (A32 / 2) in the-) direction, leading to a decrease in image quality. The secondary transfer roller 48 also comes into contact with the intermediate transfer belt 41 before the cleaner blade 491 comes into contact, and the same registration shift occurs. However, the corresponding registration shift amount is smaller than that of the cleaner blade 491. In order to facilitate understanding of the basic principle of the invention, here, the description will be made ignoring the registration shift caused by the separation and contact of the secondary transfer roller 48 with respect to the intermediate transfer belt 41.
[0040]
B-1-2. Second printing sequence
Such a registration error does not occur only in the first sheet but also appears in the second color image. That is, in order to form the second yellow toner image Y2, as shown in FIG. 7, in order to form the yellow toner image Y2 after a predetermined time T10 has elapsed since the vertical synchronization signal VSYNC was output at the timing VT5. The VIDEO signal is supplied to the exposure unit 3. Then, while developing an electrostatic latent image corresponding to the yellow toner image Y2 on the photosensitive member 21, the toner is developed by the yellow developing unit 23Y. Further, the primary transfer process is started when a predetermined time T20 has elapsed from the output of the vertical synchronization signal VSYNC (timing VT5), that is, at timing t3.
[0041]
However, after a while from the output timing VT5 of the vertical synchronization signal VSYNC, the cleaner blade 491 comes into contact with the intermediate transfer belt 41 as described above, and an instantaneous extension A27 occurs in the sub-scanning direction of the intermediate transfer belt 41. Moreover, since the contact state continues until the CB signal rises to the H level next time as will be described later, the extension in the sub-scanning direction increases with time. At the primary transfer start timing t3, the registration deviation amount A30 in the sub-scanning direction is
A30 = A27 + A9
It becomes. However, reference symbol A9 corresponds to belt elongation caused by the cleaner blade 491 being kept in contact with the intermediate transfer belt 41 from timing t1 to timing t3 (that is, time A10).
[0042]
When the intermediate transfer belt 41 passes the belt cleaner 49 for about one turn, the entire belt is cleaned and the cleaning process is completed. Therefore, the CB signal rises from the L level to the H level again at the timing t4, and the cleaner blade 491 is returned. Is separated from the intermediate transfer belt 41. During the period from the start of primary transfer (timing t3) to the separation of the cleaner blade 491 (timing t4), the cleaner blade 491 continues to contact the intermediate transfer belt 41, and during this time, the intermediate transfer belt 41 is at A12 (= t4−t3). The registration shift is further increased by extending by the extension amount A11 in the sub-scanning direction, and the registration shift amount immediately before the timing t4 becomes the shift amount A35 in the (-) direction.
[0043]
On the other hand, at this timing t 4, the cleaner blade 491 is separated from the intermediate transfer belt 41. Therefore, contrary to the contact, the load applied to the intermediate transfer belt 41 is released, so that the intermediate transfer belt 41 contracts by the contraction amount A26 and the registration shift amount in the sub-scanning direction decreases by A26.
[0044]
As described above, for the second color image, the transfer start position of the yellow toner image Y2 is greatly shifted from the reference transfer start position. In addition, as the primary transfer progresses, the amount of deviation increases, and if the cleaner blade 491 is separated at the timing t4 during the primary transfer, the amount of registration deviation is reduced. That is, as shown in FIG. 7, with respect to the second yellow toner image Y2, the registration shift in the sub-scanning direction during the primary transfer is (+) and (− ) Occurs in the range of the amount of deviation (A26 / 2) in each of the directions), causing a reduction in image quality.
[0045]
Further, the cyan toner image C2 that is primarily transferred following the yellow toner image Y2 is also affected by the separation and contact of the cleaner blade 491, so that the transfer start position deviates from the reference transfer start position. This phenomenon will be described with reference to FIG.
[0046]
In order to form the second cyan toner image C2, a VIDEO signal for forming the cyan toner image C2 is given to the exposure unit 3 after a predetermined time T10 has elapsed since the vertical synchronization signal VSYNC was output at the timing VT6. It is done. The toner is developed by the cyan developer 23C while an electrostatic latent image corresponding to the cyan toner image C2 is formed on the photosensitive member 21. Further, the primary transfer process is started when a predetermined time T20 has elapsed from the output of the vertical synchronization signal VSYNC (timing VT6), that is, at timing t5.
[0047]
Here, at the output timing VT6 of the vertical synchronization signal VSYNC, the cleaner blade 491 is in contact with the intermediate transfer belt 41 as described above, and until timing t4 (the CB signal rises again from the L level to the H level), that is, This contact state is maintained only for time A14. Therefore, the intermediate transfer belt 41 extends by A13 between timing VT6 and timing t4. On the other hand, when the cleaner blade 491 is separated from the intermediate transfer belt 41 at the timing t4, the load applied to the intermediate transfer belt 41 is released and the intermediate transfer belt 41 is released, as described above, contrary to the contact at this time. Shrinks by A26. Thereafter, the CB signal is kept in the separated state until the CB signal rises again from the L level to the H level. As a result, at the primary transfer start time (timing t5) of the cyan toner image C2, the registration deviation amount A34 in the sub-scanning direction is
A34 = A26-A13
It becomes.
[0048]
As described above, for the second cyan toner image C2, the registration deviation in the sub-scanning direction during the primary transfer has an amplitude amount of 0 centering on the fluctuation center AC3, and the registration deviation during the primary transfer process. Although the amount does not change, the fluctuation center AC3 itself is shifted in parallel in the sub-scanning direction (+) by the amount of deviation A34, which causes a reduction in image quality.
[0049]
When the primary transfer of the cyan toner image C2 is completed as described above, the toner image formation and the primary transfer process of the magenta toner image M2 are performed next. During this process, the cleaner blade 491 is removed from the intermediate transfer belt 41. Since the separated state remains, no registration deviation occurs in the sub-scanning direction as in the first sheet, and the deviation amount becomes zero. Therefore, with respect to the magenta toner image M2, the registration deviation in the sub-scanning direction during the primary transfer is centered on the fluctuation width center (the one-dot chain line AC0 in FIGS. 6 and 7) and the amplitude thereof. The amount is also zero. Therefore, in the image forming apparatus that forms an image in the operation sequence shown in FIG. 4, the magenta toner image is used as the reference toner image, and the transfer start position and the transfer rear end position are set to “reference transfer start position” and “reference transfer position”, respectively. It can be referred to as “transfer rear end position”.
[0050]
When the primary transfer of the magenta toner image M2 is completed, image formation and primary transfer processing of the second black toner image are performed. In this case, the cleaner blade 491 is moved during the primary transfer in the same manner as the first sheet. The intermediate transfer belt 41 is brought into contact with the intermediate transfer belt 41 to extend by A32, and registration shift occurs in the (−) direction in the sub-scanning direction. Note that the profile (hereinafter simply referred to as “profile”) showing the change in the amount of registration deviation with respect to the operation sequence is the same as that in FIG. 6, and the registration deviation in the sub-scanning direction during the primary transfer is the fluctuation width center AC1. Centering on the center, and in the (+) and (−) directions in the sub-scanning direction within the range of the amount of deviation (A32 / 2), respectively, leading to a decrease in image quality.
[0051]
Further, when the fourth and subsequent color images are successively formed following the third color image, the same registration shift as that of the second image described above occurs.
[0052]
B-1-3. Third printing sequence
Further, in this type of image forming apparatus, the intermediate transfer belt 41 may be idled. For example, if the interval between image signals from an external device such as a host computer exceeds a certain value, the intermediate transfer belt 41 is idled. If it is necessary to idle twice or more, the device is temporarily stopped. At this time, the cleaner blade 491 is in contact with the intermediate transfer belt 41. When a new image formation is started, the intermediate transfer belt 41 is rotationally driven to start the image formation. When the first yellow toner image is primarily transferred, the second and subsequent sheets shown in FIG. The same registration deviation as in the case of a cyan toner image occurs.
[0053]
That is, as shown in FIG. 9, when image formation is resumed and the intermediate transfer belt 41 is rotationally driven, a vertical synchronization signal VSYNC is output from the vertical synchronization reading sensor 40 at timing VT01, and from the timing VT01 for a certain period of time. After A14, after the cleaner blade 491 is separated from the intermediate transfer belt 41, the primary transfer of the yellow toner image is started. Therefore, for the same reason as in the case of the cyan toner image C2 in “B-1-2. Second printing sequence”, the transfer start position is shifted in the (+) direction by the shift amount A34. That is, the registration deviation in the sub-scanning direction during the primary transfer has an amplitude amount of 0 centering on the fluctuation width center AC4, and the registration deviation amount does not change during the primary transfer process, but the fluctuation width center AC4 itself is the secondary deviation. The amount of shift A34 is shifted in parallel in the scanning direction (+), which causes a reduction in image quality.
[0054]
Then, the subsequent primary transfer of the cyan and magenta toner images is executed in a state where the cleaner blade 491 is always separated from the intermediate transfer belt 41, so that no registration misalignment occurs, but for the last black toner image, the first and first toner images are transferred. As in the case of the two-printing sequence, during the primary transfer, the cleaner blade 491 and the secondary transfer roller 48 come into contact with the intermediate transfer belt 41, and a registration shift of a shift amount A32 occurs in the (−) direction.
[0055]
As described above, when the contact means such as the cleaner blade 491 separates from the intermediate transfer belt 41 while the primary transfer process is repeated, a predetermined registration shift amount is generated according to the separation contact timing. This profile itself is unique depending on the device configuration and operating conditions. The profile itself does not change unless the device configuration or operation sequence is changed, but the transfer start position is moved in the sub-scanning direction according to the amount of registration displacement. By doing so, the registration deviation with respect to the reference toner image can be zero or suppressed. For example, for the cyan toner image C2, as shown in FIG. 8, the transfer start position of the cyan toner image C2 is a shift amount A34 in the (+) direction with respect to the reference transfer start position. Therefore, the amount of registration deviation can be reduced to zero by controlling the transfer start position of the cyan toner image C2 to shift in the (−) direction by the amount of registration deviation A34.
[0056]
Therefore, in this embodiment, as described above, prior to the actual image forming process, the same analysis as described above is performed in advance from the apparatus configuration and the operation sequence to derive the registration deviation amount, and the registration deviation amount is reduced to zero. Alternatively, a registration control amount (for example, equivalent to A34 in the case of cyan) described above is obtained, and in the actual image forming process, the transfer start position is corrected in the sub-scanning direction based on the registration control amount. Therefore, the deviation centers AC1 to AC4 of toner colors (Y, C, K) other than the reference toner color (magenta) are made to coincide with the fluctuation center AC0 of the reference toner color, thereby suppressing registration deviation and high quality. An image is formed.
[0057]
B-2. Establishing initial registration control amount
FIG. 10 is a flowchart showing processing for automatically establishing an initial registration control amount (registration control amount establishment processing). First, the following initial setting conditions are set in advance based on the apparatus configuration and operation sequence of the image forming apparatus according to the embodiment, and stored in the memory 125. As shown in FIG. 11, with reference to the VSYNC signal, (1) a period T1 in which the cleaner blade 491 and the secondary transfer roller 48 contact the intermediate transfer belt 41, and (2) a cleaner blade 491 and the secondary transfer roller 48. Is continuously in contact with the intermediate transfer belt 41, (3) the period T3 in which the cleaner blade 491 and the secondary transfer roller 48 are separated from the intermediate transfer belt 41, and (4) the cleaner blade 491 and the secondary transfer roller 48 are The registration control amount establishment job (step S11) in which the period T4 that continues to be separated from the intermediate transfer belt 41 is one job is repeated a predetermined number of times, for example, 20 times (step S12).
[0058]
The initial condition is
A2: Process speed (peripheral speed of the intermediate transfer belt 41),
A7: Time from the contact of the cleaner blade 491 to the end of the primary transfer of the black toner image (see FIG. 6),
A8: Time required for the intermediate transfer belt 41 to make a round
A10: Time from contact of cleaner blade to start of primary transfer of yellow toner image (see FIG. 7)
A12: Time from the transfer start position of the yellow toner image to the separation of the cleaner blade (see FIG. 7),
A14: Time from VSYNC signal to cleaner blade separation (see Fig. 8),
A17: Time interval from VSYNC signal to cleaner blade contact in period T1 (see FIG. 11),
A18: Time interval from VSYNC signal to cleaner blade separation in period T3 (see FIG. 11),
It has become.
[0059]
In this embodiment, the cycle data (cycles T1 to T4) obtained every moment is stored in the memory 125 while the registration control amount establishment job (step S11) is repeatedly executed. In the meantime, the charging bias and the primary transfer bias are always set to the ON state. Although not shown in FIG. 1, a static elimination lamp is provided between the primary transfer region R1 and the photoreceptor cleaner blade 24. This static elimination lamp is also always set to an ON state. . Further, while the secondary transfer roller 48 is in contact with the intermediate transfer belt 41, a secondary transfer bias is applied to obtain the initial registration control amount in a state close to actual printing.
[0060]
Thus, when 20 actually measured values are obtained for each of the periods T1 to T4, the period data is read from the memory 125, and the average values T1 (av) to T4 (av) are respectively calculated (step S13). . Further, initial registration control amounts Ra, Rb, and Rc are obtained by calculation based on the following equations, respectively (step S14). The reason will be described separately.
[0061]
<Regarding the initial resist control amount Ra>
As shown in FIG. 6, during the primary transfer of the black toner image K1 to the intermediate transfer belt 41, the contact of the cleaner blade 491 is started, and the primary transfer of, for example, the A3 size black toner image K1 is completed. Since the contact of the cleaner blade 491 is continued even at the time point, a registration deviation amount A32 in the sub-scanning direction is generated. The resist misregistration amount A32 is the sum of the two elongations A6 and A27. That means
A32 = A6 + A27
It becomes.
[0062]
Here, the contact elongation A6 is a contact elongation generated when the intermediate transfer belt 41 is rotated and conveyed in a state in which the cleaner blade 491 is in contact. It is the instantaneous elongation (elasticity + sliding) when abutting.
[0063]
First, consider the elongation A6. When the cleaner blade 491 is in contact, a period difference A1 occurs. The period difference A1 is expressed by the following equation:
A1 = (T2 (av) −T4 (av)) × A2 × 1000
Can be obtained. During the primary transfer of the black toner image K1, the cleaner blade 491 is in contact only for a predetermined time A7.
A6 = A1 × A7 / A8
It becomes.
[0064]
On the other hand, the instantaneous elongation A27 can be obtained by comparing the periods T1 and T4. That is, the instantaneous elongation A27 is given by
A27 = (T1 (av) −T4 (av)) × A2 × 1000−A15
Can be obtained. However, as shown in FIG. 11, the elongation A15 is an elongation due to the cleaner blade 491 being in contact for a predetermined time A17 during the period T1, and this elongation A15 is:
A15 = A1 × (A8-A17) / A8
Can be obtained.
[0065]
Therefore, the resist misregistration amount A32 is
A32 = A6 + A27
The registration shift of the black toner image K1 can be minimized by shifting the transfer start position in the sub-scanning direction in advance by half of this value. Therefore, in this embodiment, the initial registration control amount Ra is set to
Ra = A32 / 2
Is set.
[0066]
<Regarding the initial resist control amount Rb>
As shown in FIG. 7, when the yellow toner image Y2 is primarily transferred to the intermediate transfer belt 41 following the primary transfer of the black toner image K1, a time period A10 from the contact of the cleaner blade to the start of the primary transfer of the yellow toner image. A30 (= A27 + A9) is generated in the sub-scanning direction. Further, since the cleaner blade 491 is in contact with the intermediate transfer belt 41 even after the primary transfer is started, elongation A11 occurs, but the cleaner blade 491 is separated from the intermediate transfer belt 41 immediately before the completion of the primary transfer. Shrinkage A26 occurs. Therefore, as shown in the figure, when the shrinkage A26 is larger than the elongation A11, the initial resist control amount Rb is set to
Rb = A35-A26 / 2
However, A35 = A30 + A11
In the opposite case (A26 <A11), the initial registration control amount Rb is set to
Rb = A35-A11 / 2
By setting to, the registration error of the yellow toner image can be minimized.
[0067]
Here, the elongation A30 at the start of the primary transfer is as described above.
A30 = A27 + A9
However, the elongation A9 is an elongation generated by the intermediate transfer belt 41 being rotated and conveyed for a time A10 in a state where the cleaner blade 491 is in contact with the following equation.
A9 = A1 × A10 / A8
Can be obtained.
[0068]
Further, the elongation A11 is an elongation generated because the cleaner blade 491 is in contact with the intermediate transfer belt 41 even after the primary transfer is started.
A11 = A1 × A12 / A8
Can be obtained.
[0069]
Further, the shrinkage A26 is caused by the cleaner blade 491 being separated from the intermediate transfer belt 41, and can be obtained by comparing the periods T3 and T4. That is, the following formula
A26 = A25− (T3 (av) −T4 (av)) × A2 × 1000
Can be determined based on In addition, A25 in the equation is an elongation in the cycle T3 as shown in FIG.
A25 = A1 × A18 / A8
Can be obtained.
[0070]
<Regarding the initial resist control amount Rc>
As shown in FIG. 8, when the cyan toner image is primarily transferred to the intermediate transfer belt 41 following the primary transfer of the yellow toner image, the cleaner blade 491 is moved when the VSYNC signal VT6 serving as a reference for the primary transfer is output. The intermediate transfer belt 41 is in contact with the intermediate transfer belt 41, and after that, until the primary transfer of the cyan toner image is started, the intermediate transfer belt 41 is rotated and conveyed in the contact state for a time A14. appear. In other words, the elongation A13 is
A13 = A1 × A14 / A8
It becomes.
[0071]
Further, when the cleaner blade 491 is separated from the intermediate transfer belt 41, the shrinkage A26 occurs as described in the above section <Regarding the initial registration control amount Rb>. Therefore, a registration deviation amount A34 (= A13-A26) occurs at the time of the primary transfer start of the cyan toner image, but no deviation in the sub-scanning direction occurs during the primary transfer. Therefore, in this embodiment, by shifting in advance in the sub-scanning direction by this value (registration deviation amount A34), the registration deviation of the cyan toner image can be suppressed to zero.
Rc = A34
Is set.
[0072]
As described above, in the initial registration control amount establishment process (registration control amount establishment process), the secondary transfer bias is applied while the secondary transfer roller 48 is in contact with the intermediate transfer belt 41. This is not an essential requirement for establishing the initial resist control amount, and a secondary transfer bias may not be given, or a bias having a polarity opposite to that of the secondary transfer bias may be given. Effects can be obtained. That is, when the secondary transfer bias is not applied, the initial registration control amount establishment process can be simplified. Further, when the secondary transfer bias is applied, the load applied to the intermediate transfer belt 41 and the photoreceptor / belt drive unit 41a by the secondary transfer roller 48 approaches the actual printing state, and the initial registration control amount is accurately set. Can be sought. Further, when a reverse polarity bias is applied, the toner adhering to the secondary transfer roller 48 is returned to the intermediate transfer belt 41 side, and the secondary transfer roller 48 is cleaned to remove the backside contamination of the sheet by the secondary transfer roller 48. In this way, good printing results can be obtained.
[0073]
In the initial registration control amount establishment process described above, the primary registration control amount is obtained in a state close to actual printing by applying the primary transfer bias to the intermediate transfer belt 41, so that the initial registration control amount can be obtained accurately. it can.
[0074]
Further, in the above-described initial registration control amount establishment process, the registration control amount establishment job (step S11) is repeated 20 times from the start of driving (step S12), and 20 actually measured values of the periods T1 to T4 are measured. The initial resist control amount is obtained based on the actually measured value. However, the rotational transfer of the intermediate transfer belt 41 may not be stable immediately after the start of driving. If the initial registration control amount is obtained based on the periods T1 to T4 measured in such a state, the initial registration control amount is obtained. There is a risk that the accuracy of the lowering. In order to solve such problems, the intermediate transfer belt 41 is rotated and conveyed a predetermined number of times from the start of driving, and after its operation is stabilized, the periods T1 to T4 are measured, and the measured values are obtained. The initial registration control amount may be obtained based on this, and by doing so, the initial registration control amount can be obtained with high accuracy.
[0075]
B-3. Correction of transfer start position
Actually, when a color image is sequentially printed from the first sheet, the transfer start position is corrected as described below, and registration shift is suppressed. When printing the first color image, the sequence flag F0 corresponding to the first print sequence is set in step S4 of FIG. 3, so that the yellow toner image Y1 and cyan toner image C1 are set in step S5 of FIG. Then, “0” is set as the registration control amount of the magenta toner image M1, while the initial registration control amount Ra is set as the registration control amount of the black toner image K1. Accordingly, the yellow toner image Y1, the cyan toner image C1, and the magenta toner image M1 are all formed at a predetermined position on the photoconductor 21, that is, the reference latent image forming position, as in the conventional example. The intermediate transfer belt 41 that rotates synchronously is also primarily transferred at the same position. As a result, as shown in FIG. 12, the transfer start positions of these three toner images Y1, C1, and M1 are all coincident with the reference transfer start position, and the transfer rear end positions are all equal to the reference transfer rear end position. I'm doing it.
[0076]
On the other hand, since the initial registration control amount Ra is set as the registration control amount for the black toner image K1, as shown in FIG. 13, the acceleration / deceleration possible period is based on the vertical synchronization signal VSYNC output at the timing VT4. At timing t11 of T11, the photosensitive member 21 is controlled to accelerate / decelerate, and the latent image forming position of the black toner image is controlled by a control amount Ra (= A32 / 2) on the (+) side in the sub-scanning direction with respect to the reference latent image forming position. Shift shift. Here, the “acceleration / deceleration possible period” refers to a period during which the VIDEO signal is at the H level and the exposure process is stopped. In the acceleration / deceleration possible period T11, the primary transfer process of the previous toner image (magenta toner image M1) is continued. In this embodiment, the intermediate transfer belt 41 is synchronized with the photosensitive member 21. Since the drive is controlled, the toner image that is primarily transferred in parallel with the acceleration / deceleration control of the photosensitive member 21 and the intermediate transfer belt 41 is not disturbed.
[0077]
The latent image formed on the photoconductor 21 as described above is visualized by the developing unit 23K, and the black toner image K1 is primarily transferred onto the intermediate transfer belt 41. As a result, as shown in FIG. 12, the transfer start position of the black toner image K1 is shifted by the registration control amount Ra in the (+) direction with respect to the reference transfer start position.
[0078]
As shown in FIG. 13, the CB signal for controlling the operation of the cleaner blade 491 rises from the L level to the H level at the timing t1 when the primary transfer process proceeds and the latter half of the process proceeds. Comes into contact with the intermediate transfer belt 41, and the black toner image K1 shifts in the sub-scanning direction with respect to the other toner images Y1, C1, and M1. Further, the contact state is continued until timing t2, and as a result, the registration deviation is further increased. However, the registration deviation amount of the final black toner image K1 in the sub-scanning direction is a deviation amount (A32 / 2). That is, by moving the transfer start position of the black toner image K1 by the registration control amount Ra in the (+) direction with respect to the reference transfer start position, the fluctuation width center AC1 for the black color is set for the magenta color that is the reference toner color. In this way, the center of the deviation width of the registration shift in the sub-scanning direction for each toner color during the primary transfer process coincides with each other.
[0079]
As a result, in this embodiment, as shown in FIG. 12, the black toner image K1 is shifted by (A32 / 2) in the (+) direction on the transfer start side with respect to the other toner images Y1, C1, and M1. It is shifted by (A32 / 2) in the (-) direction on the rear end side of the transfer, and the maximum shift amount is half that when the resist control is not performed (FIGS. 5 and 6).
[0080]
Next, in the case of forming the second color image following the first color image formation (second print sequence), after the flag F1 is set as the sequence flag in step S4 in FIG. In this way, high-quality image formation can be achieved while suppressing registration shift.
[0081]
That is, in step S5, the registration control amount corresponding to the sequence flag F1 is set. That is, the initial registration control amount Rb is set as the registration control amount of the yellow toner image Y2, the initial registration control amount Rc is set as the registration control amount of the cyan toner image C2, and “0” is set as the registration control amount of the magenta toner image M2. Is set, and an initial registration control amount Ra is set as the registration control amount of the black toner image K2. Then, registration control is executed for each toner image.
[0082]
First, since the initial registration control amount Rb is set as the registration control amount for the yellow toner image Y2, as shown in FIG. 14, the acceleration / deceleration possible period is based on the vertical synchronization signal VSYNC output at the timing VT5. At timing t11 of T11, the photosensitive member 21 is controlled to accelerate and decelerate, and the latent image forming position of the yellow toner image is shifted by a control amount Rb to the (+) side in the sub-scanning direction with respect to the reference latent image forming position. Then, this latent image is made visible by the developing unit 23Y.
[0083]
At time t1, the CB signal rises from the L level to the H level, and the cleaner blade 491 that has been separated comes into contact with the intermediate transfer belt 41. Thereafter, while the amount of registration deviation changes with the profile indicated by the thick solid line in the figure, the transfer process of the yellow toner image Y2 is performed and the transfer rear end side shifts by (A26 / 2) in the (+) direction. The maximum deviation amount with respect to the toner image (magenta toner image M2) is greatly reduced as compared with the case where the resist control is not performed (FIG. 7).
[0084]
As described above, in this embodiment, the second yellow toner image Y2 is obtained by shifting the latent image forming position on the photosensitive member 21 in the sub-scanning direction with respect to the reference latent image forming position by the registration control amount Rb. The transfer start position is adjusted. Thus, the shake width center AC2 for the yellow color is matched with the shake width center AC0 for the magenta color that is the reference toner color. Therefore, the amount of deviation with respect to the reference toner image (magenta toner image M2) can be suppressed within the range of the shake width (A26 / 2).
[0085]
Subsequent to the yellow toner image Y2, primary transfer processing of the cyan toner image C2 is performed, and an initial registration control amount Rc is set as the registration control amount of the cyan toner image C2. Therefore, as shown in FIG. 15, the rotational speed of the photosensitive member 21 and the conveyance speed V of the intermediate transfer belt 41 are temporarily set at the timing t11 of the acceleration / deceleration possible period T11 with reference to the vertical synchronization signal VSYNC output at the timing VT6. Therefore, the rotation amount of the photosensitive member 21 and the conveyance amount of the intermediate transfer belt 41 are reduced by the registration control amount Rc as compared with the case of rotating and conveying at a constant speed (in the case of a reference toner image, that is, a magenta toner image). . As a result, the latent image forming position on the photosensitive member 21 is shifted by the registration control amount Rc in the sub scanning direction with respect to the reference latent image forming position.
[0086]
Then, the latent image formed on the photoconductor 21 as described above is visualized by the developing unit 23C, and the cyan toner image C2 is primarily transferred onto the intermediate transfer belt 41. Accordingly, the registration deviation amount (A26) due to the separation and contact of the cleaner blade 491 and the shift amount Rc of the toner image C2 on the photosensitive member 21 coincide with each other, and the transfer start position of the cyan toner image C2 is the reference transfer start position. Match.
[0087]
In addition, the CB signal rises from the L level to the H level at a timing t4 before the primary transfer processing of the cyan toner image C2 to the intermediate transfer belt 41 is started, and the cleaner blade 491 that is in contact with the intermediate transfer belt 41 is separated. Therefore, there is no registration shift during the primary transfer process. For this reason, the transfer rear end position of the cyan toner image C2 coincides with the transfer rear end position.
[0088]
As described above, in this embodiment, the photosensitive member 21 and the intermediate transfer belt 41 are subjected to acceleration / deceleration control based on the registration control amount Rc, so that the shake center AC3 for cyan is the shake for the magenta color that is the reference toner color. It is made to coincide with the width center AC0. For this reason, the amount of deviation with respect to the reference toner image (magenta toner image M2) can be suppressed to zero.
[0089]
The primary transfer process of the magenta toner image M2 is executed following the cyan toner image C2. In this transfer process, the cleaner blade 491 and the secondary transfer roller 48 are not separated and contacted at all, and the magenta toner image M2 is transferred. The start position and the transfer rear end position coincide with the reference transfer start position and the transfer rear end position, respectively.
[0090]
When the three-color toner images Y2, C2, and M2 are completed in this manner, the final transfer process for the final toner color, that is, the black toner image K2, is executed. In this primary transfer process, as in the case of the first black toner image K1, the latent image formation position on the photoconductor 21 is shifted in the sub-scanning direction by the registration control amount Rb, so that the black color is changed. The shake width center AC1 is made to coincide with the shake width center AC0 for the magenta color that is the reference toner color.
[0091]
Therefore, it is shifted by (A32 / 2) in the (+) direction on the transfer start side with respect to the reference toner image, and is shifted by (A32 / 2) in the (−) direction on the transfer rear end side. This is half that when the resist control is not performed (FIGS. 5 and 6).
[0092]
As described above, the second sheet also corresponds to each toner color so that the center of the width of the registration shift in the sub-scanning direction for each toner color during the transfer process coincides with each other. The toner image transfer start position is corrected by performing acceleration / deceleration control in synchronism with the rotation speed of the photosensitive member 21 and the conveyance speed of the intermediate transfer belt 41 based on the registration control amount. As a result, the cyan toner image C2 can be completely registered with the magenta toner image M2 that is the reference toner image, and the yellow toner image Y2 and the black toner image K2 cannot be completely registered with the reference toner image. However, the amount of resist misregistration can be minimized, and high-quality image formation is possible.
[0093]
When the sequence flag F2 is set, the initial registration control amount Rc is set as the registration control amount for the yellow toner image Yn, and “0” is set as the registration control amount for the cyan toner image Cn and the magenta toner image Mn. In addition, the initial registration control amount Ra is set as the registration control amount of the black toner image Kn. Then, registration control is executed for each toner image.
[0094]
First, since the initial registration control amount Rc is set as the registration control amount for the yellow toner image Yn, as shown in FIG. 16, the acceleration / deceleration possible period is based on the vertical synchronization signal VSYNC output at the timing VT01. At the timing t11 of T11, when the rotational speed of the photosensitive member 21 and the transport speed V of the intermediate transfer belt 41 are temporarily reduced to rotate and transport at a constant speed (in the case of a reference toner image, that is, a magenta toner image). In comparison, the rotation amount of the photosensitive member 21 and the conveyance amount of the intermediate transfer belt 41 are reduced by the registration control amount Rc. As a result, the latent image forming position on the photosensitive member 21 is shifted by the registration control amount Rc in the sub scanning direction with respect to the reference latent image forming position.
[0095]
Then, the latent image formed on the photoreceptor 21 as described above is manifested by the developing unit 23Y, and the yellow toner image Yn is primarily transferred onto the intermediate transfer belt 41. Therefore, the registration deviation amount (A26) due to the separation and contact of the cleaner blade 491 and the shift amount Rc of the toner image Yn on the photosensitive member 21 coincide with each other, and the transfer start position of the yellow toner image Yn is the reference transfer start position. Match.
[0096]
The CB signal rises from the L level to the H level at the timing t4 before the primary transfer process of the yellow toner image Yn to the intermediate transfer belt 41 is started, and the cleaner blade 491 that has been in contact with the intermediate transfer belt 41 is separated. Therefore, there is no registration shift during the primary transfer process. Therefore, the transfer rear end position of the yellow toner image Yn coincides with the transfer rear end position.
[0097]
As described above, in this embodiment, the photosensitive member 21 and the intermediate transfer belt 41 are subjected to acceleration / deceleration control based on the registration control amount Rc, so that the shake center AC4 for yellow is the shake for the magenta color that is the reference toner color. It is made to coincide with the width center AC0. For this reason, the deviation amount with respect to the reference toner image (magenta toner image Mn) can be suppressed to zero.
[0098]
Subsequent to the yellow toner image Yn, the primary transfer process of the cyan toner image Cn and the magenta toner image Mn is sequentially performed. In these transfer processes, there is no separation contact between the cleaner blade 491 and the secondary transfer roller 48. The center of shake width for both toner colors coincides with each other, and the transfer start position and the transfer rear end position of both toner images Cn and Mn match the reference transfer start position and the transfer rear end position, respectively.
[0099]
When the three color toner images Yn, Cn, and Mn are completed in this manner, the final transfer process of the final toner color, that is, the black toner image Kn is performed. In this primary transfer process, as in the case of the first and second printing sequences, the photosensitive member 21 and the intermediate transfer belt 41 are subjected to acceleration / deceleration control based on the registration control amount Rc, so that the fluctuation width center AC1 for the black color is obtained. It is made to coincide with the shake width center AC0 for the magenta color which is the reference toner color. Therefore, it is shifted by (A32 / 2) in the (+) direction on the transfer start side with respect to the reference toner image, and is shifted by (A32 / 2) in the (−) direction on the transfer rear end side. This is half that when the resist control is not performed (FIGS. 5 and 6).
[0100]
As described above, for the color printing after the idling process, for each toner color, the registration deviation center in the sub-scanning direction for each toner color during the transfer process coincides with each other. In addition, the toner image transfer start position is corrected by controlling the acceleration and deceleration of the photosensitive member 21 and the intermediate transfer belt 41 based on the registration control amount Rc. As a result, the yellow toner image Yn, the cyan toner image Cn, and the magenta toner image (reference toner image) Mn can be completely registered, and the black toner image Kn cannot be completely registered with the reference toner image. However, the amount of resist misregistration can be minimized, and high-quality image formation is possible.
[0101]
C. Registration control amount change setting process
By the way, as described above, the tolerance of the registration error varies greatly depending on factors such as the user type of business and the image type, and there is a case where it is desired to adjust the registration error based on the contents printed out depending on the user request. Therefore, in this embodiment, the registration control amounts Ra, Rb, and Rc can be individually changed and set, and when it is desired to obtain a higher quality image by further suppressing registration deviation, a registration control amount change setting program ( (Hereinafter referred to as “control amount change setting program”). Of course, if a sufficiently high quality image output has already been obtained with the registration control amount automatically obtained, it is not necessary to change the registration control amount, and without performing the registration control amount change setting process, What is necessary is just to continue printing as it is. Hereinafter, the registration control amount change setting process will be described in detail with reference to FIGS.
[0102]
FIG. 17 is a flowchart showing the registration control amount change setting operation in the image forming apparatus according to the present invention. FIG. 18 is a schematic diagram showing a connection relationship between the image forming apparatus of FIG. 1 and an external apparatus. The image forming apparatus in FIG. 1 is electrically connected to the external apparatus 100 such as a host computer as described above, and a control amount change setting program is executed by an arithmetic processing unit (not shown) of the apparatus main body 101 of the external apparatus 100. The registration control amounts Ra, Rb, and Rc stored in the memory 125 of the image forming apparatus are changed and set according to the flowchart shown in FIG. 17 by being executed as necessary.
[0103]
When the control amount change setting program is executed on the external device 100 side, for example, a registration control amount change setting screen shown in FIG. 19 is displayed on the display 102 of the external device 100. Then, in accordance with steps S31 to S36, the changed values for all or part of the registration control amounts Ra, Rb, and Rc are input by the keyboard 103 and the mouse (not shown) of the external apparatus 100. For example, when a line deviation exceeding an allowable range is generated in a CAD drawing or the like, it is possible to estimate how much toner color is shifted by examining the printed image. Can be determined.
[0104]
When the input of the change value is completed and the setting button on the screen is selected in step S37, registration control amounts Ra, Rb, and Rc displayed on the screen from the external apparatus 100 are given to the image forming apparatus. It is done. In response to this, the image forming apparatus side rewrites the contents stored in the memory 125 with these values (step S38). On the other hand, when the cancel button on the screen is selected in step S37, rewriting of the registration control amount is stopped and the contents stored in the memory 125 are maintained as they are.
[0105]
As described above, according to the image forming apparatus of this embodiment, all or part of the registration control amounts Ra, Rb, Rc stored in the memory 125 of the image forming apparatus can be rewritten. If necessary, a control amount change setting program is executed on the external device 100 side to rewrite the resist control amounts Ra, Rb, and Rc, and to correct the registration shift with higher accuracy.
[0106]
In this embodiment, the registration control amount is changed and set by directly inputting the changed values of the registration control amounts Ra, Rb, and Rc. However, as shown in FIG. The registration control amounts Ra, Rb, and Rc may be changed and set by changing them. For example, at the factory shipment stage of the image forming apparatus, the number of repetitions is set to “20 times” so that the registration control amount can be obtained with medium / low accuracy corresponding to a photographic image or the like. If the tolerance is low, starting the number change setting program and setting a high number of job repetitions increases the accuracy of the registration control amount required by the registration control amount establishment process, and further suppresses registration deviation. it can.
[0107]
In the above-described embodiment, a program such as a control amount change setting program or a number change setting program is executed in the external apparatus 100, and changed data (registration control amount and repetition number) is transferred from the external apparatus 100 to the image forming apparatus side. However, the image forming apparatus is provided with an input means for inputting the registration control amount, the number of repetitions, and the like, and the control amount change setting program is executed in the control unit 1 to change and set the registration control amount. May be. In this case, even if the image forming apparatus is not electrically connected to an external apparatus, the registration control amount can be changed and set independently.
[0108]
Further, the input of change values of the resist control amounts Ra, Rb, and Rc and the change value of the number of measurements may be directly performed by the user or may be performed by a service engineer.
[0109]
D. Other
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the latent image on the photoconductor 21 is controlled by performing variable speed control in synchronization with the photoconductor 21 and the intermediate transfer belt 41 in order to adjust the transfer start position according to the registration control amount. The formation position is shifted in the sub-scanning direction according to the registration control amount. However, as a method for shifting the latent image formation position on the photosensitive member 21, exposure timing is used in addition to the photosensitive member / belt driving control. It is also possible to control. Further, the photoconductor / belt drive control and the exposure timing control may be combined.
[0110]
In addition, when the photosensitive member driving unit and the belt driving unit are provided separately, the photosensitive member 21 is rotationally driven at a constant speed, while the region of the intermediate transfer belt 41 where the toner image is not formed becomes the primary transfer region R1. During the position period (period in which primary transfer is not performed), only the intermediate transfer belt 41 may be controlled at a variable speed based on the registration control amount to adjust the transfer start position.
[0111]
In the above embodiment, a DC motor is employed as a drive source for rotationally driving the intermediate transfer belt 41, and registration control is performed by accelerating / decelerating the DC motor based on the registration control amount. Registration control may be performed by using a pulse motor such as a stepping motor and performing pulse drive control based on the registration control amount.
[0112]
The image forming apparatus according to the above embodiment is a printer that prints an image given from an external device such as a host computer via an interface 112 on a sheet such as copy paper, transfer paper, paper, and an OHP transparent sheet. However, the present invention can be applied to electrophotographic color image forming apparatuses such as copying machines and facsimile machines, that is, image forming apparatuses in general that form a color image by superposing a plurality of color toners.
[0113]
Further, in the above embodiment, a color image is formed on the intermediate transfer belt 41 by performing a transfer process for transferring the toner image formed on the photosensitive member 21 onto the intermediate transfer belt 41 for each toner color. However, the toner image is transferred to a transfer medium other than the intermediate transfer belt (transfer drum, transfer belt, transfer sheet, intermediate transfer drum, intermediate transfer sheet, reflective recording sheet, or transmissive storage sheet) to form a color image. The present invention can also be applied to an image forming apparatus.
[0114]
【The invention's effect】
As described above, according to the present invention, the registration control amount can be changed and set as necessary. Therefore, the registration control amount can be appropriately changed according to the user request, and the user request can be handled. However, resist misalignment can be suppressed.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention.
2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG.
FIG. 3 is a flowchart showing a basic operation of the image forming apparatus of FIG. 1;
4 is a timing chart showing an example of an operation sequence in the image forming apparatus of FIG. 1. FIG.
FIG. 5 is a diagram schematically showing the registration status of each toner image when the primary transfer process is performed at the operation timing of FIG. 4 without performing registration control.
FIG. 6 is a diagram illustrating a registration shift state when a black toner image is transferred without performing registration control.
FIG. 7 is a diagram illustrating a registration shift state when a yellow toner image is transferred without performing registration control.
FIG. 8 is a diagram illustrating a registration shift state when a cyan toner image is transferred without performing registration control.
FIG. 9 is a diagram illustrating a registration shift state when a yellow toner image is transferred without performing registration control.
FIG. 10 is a flowchart showing processing contents for automatically establishing an initial registration control amount.
FIG. 11 is a timing chart showing the contents of a registration control amount establishment job.
12 is a diagram schematically illustrating a registration state of each toner image when primary transfer processing is performed at the operation timing of FIG. 4 while performing registration control.
13 is a diagram showing registration control contents when a black toner image is transferred in the image forming apparatus shown in FIG. 1. FIG.
14 is a diagram showing registration control contents when a yellow toner image is transferred in the image forming apparatus shown in FIG. 1. FIG.
15 is a diagram showing registration control contents when a cyan toner image is transferred in the image forming apparatus shown in FIG. 1. FIG.
16 is a diagram showing registration control contents when a yellow toner image is transferred in the image forming apparatus shown in FIG. 1. FIG.
FIG. 17 is a flowchart showing a registration control amount change setting operation in the image forming apparatus according to the present invention;
18 is a schematic diagram showing a connection relationship between the image forming apparatus of FIG. 1 and an external device.
19 is a schematic diagram showing an example of a screen displayed on the display of the external device shown in FIG.
20 is a schematic diagram showing another example of a screen displayed on the display of the external device shown in FIG. 18. FIG.
[Explanation of symbols]
1 ... Control unit (control means)
11 ... Main controller
12 ... Engine controller (control means)
21 ... Photoconductor
41. Intermediate transfer belt (transfer medium)
48. Secondary transfer roller (contact means)
121 ... CPU (control means)
125 ... Memory (storage unit)
491 ... Cleaner blade (contact means)
C1, C2, Cn ... cyan toner image
K1 ... Black toner image
M1, M2 ... Magenta toner image
Ra, Rb, Rc (initial) resist control amount
T1 ~ T4 ... cycle
Y1, Y2, Yn ... Yellow toner image

Claims (3)

An image forming apparatus that repeats a transfer process for transferring a toner image formed on a photosensitive member to a transfer medium that is rotationally driven for a plurality of different toner colors, and superimposes the toner images of the respective toner colors to form a color image. In
A contact means for temporarily contacting the transfer medium when the transfer process is repeated;
Reference signal detection means for outputting a reference signal in relation to the rotation operation of the transfer medium;
Based on the reference signal
(1) a period when the contact means that has been separated from the transfer medium contacts the transfer medium;
(2) a period when the contact means continues to contact the transfer medium;
(3) a period when the contact means that has been in contact with the transfer medium is separated from the transfer medium;
(4) The period when the abutting means continues to be separated from the transfer medium is measured by a predetermined number of times, and the abutting means is separated from and abutted on the transfer medium based on the difference between these periods. And a registration control amount establishment process for obtaining a registration control amount required for correcting a relative registration shift of the toner image on the transfer medium caused by the Control means for correcting the transfer start position of the toner image for each toner color,
An image forming apparatus, wherein the registration control amount can be changed and set as necessary.   The image forming apparatus according to claim 1, wherein the number of times of measurement is configured to be changeable, and the registration control amount is changed and set by changing the number of times of measurement. An image forming method for forming a color image by repeating a transfer process for transferring a toner image formed on a photosensitive member to a rotationally driven transfer medium for a plurality of different toner colors and superimposing the toner images of the respective toner colors In
A reference signal detection step of detecting a reference signal related to the rotation operation of the transfer medium;
Based on the reference signal
(1) a period when the contact means that has been separated from the transfer medium contacts the transfer medium;
(2) a period when the contact means continues to contact the transfer medium;
(3) a period when the contact means that has been in contact with the transfer medium is separated from the transfer medium;
(4) The period when the abutting means continues to be separated from the transfer medium is measured by a predetermined number of times, and the abutting means is separated from and abutted on the transfer medium based on the difference between these periods. A registration control amount establishment process for executing registration control amount establishment processing for obtaining a registration control amount necessary for correcting a relative registration deviation of the toner image on the transfer medium caused by
A correction step of correcting the transfer start position of the toner image for each toner color based on the registration control amount;
An image forming method comprising: a changing step for changing and setting a resist control amount as needed.

Images