JP4798878B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to drive color shift control of an image forming apparatus having a plurality of image forming units, such as a color printer and a color copying machine.
[0002]
[Prior art]
An electrophotographic color image forming apparatus has a plurality of image forming units for speeding up, and sequentially prints different colors (black Bk, cyan C, magenta M, yellow on a recording material held on a conveying belt. Various methods for transferring the image Y) have been proposed.
[0003]
By the way, as a problem of the apparatus having a plurality of image forming units, due to mechanical accuracy and the like, the movement unevenness of the plurality of photosensitive drums and the conveyor belt, and the outer peripheral surface of the photosensitive drum at the transfer position of each image forming unit For example, the relationship between the amount of movement and the amount of movement of the conveying belt is different for each color and does not match when the images are superimposed, resulting in color misregistration (positional misregistration).
[0004]
Color misregistration includes a main scanning direction and a sub-scanning (conveying) direction perpendicular to the main scanning direction. In addition, there is a steady error with a constant amount of deviation in the paper and an unsteady error in which the amount of deviation fluctuates periodically. The
[0005]
Examples of color misregistration in the main scanning direction include a left end writing position error and a main scanning width error. On the other hand, the color misregistration in the sub-scanning direction includes a leading edge writing position error. Examples of unsteady color misregistration in the sub-scanning direction include those caused by uneven conveyance.
[0006]
Further, the steady color misregistration is detected by the color misregistration detection means. That is, a color misregistration detection pattern is formed for each color on the transport belt, and this is detected by a pair of optical sensors provided on both sides of the downstream portion in the transport belt rotation direction. Some adjustments are performed in accordance with the detected amount of deviation.
[0007]
As for non-stationary color misregistration, particularly those caused by uneven conveyance, there are some which monitor the rotational state of the photosensitive drum and the conveyance belt and control the drive source such as a motor so that the rotation is constant. For example, an encoder is provided on the rotation shaft of the photosensitive drum, the rotation state of the photosensitive drum is detected, the error is calculated, and the rotation of the motor is controlled by the rotation phase control means so as to cancel the error.
[0008]
FIG. 10 is an explanatory diagram of non-stationary color misregistration in the sub-scanning direction caused by uneven rotation of the photosensitive drum. A case where color misregistration occurs in black Bk and yellow Y is shown. Although the total amount of movement is the same for black Bk and yellow Y, the phase and amplitude of rotation unevenness differ between black Bk and yellow Y, and color misregistration (approaching and leaving) occurs periodically.
[0009]
FIG. 11 is an explanatory diagram of the rotation state detection means, the drive source, and the drive transmission means. One color is shown, and there are four similar colors. In the figure, 1 is a photosensitive drum, 13 is a rotating shaft that rotates with the photosensitive drum 1, 11 is a stepping motor, 12 is a reduction gear that transmits the rotation of the motor 11 to the rotating shaft 13, and 18 is rotated with the rotating shaft 13. A code wheel provided with slits at equal intervals on a concentric circle, 19 outputs a pulse signal according to the passage of the slit of the code wheel 18, an encoder composed of a light emitting part and a light receiving part, and 21 outputs a pulse output of the encoder 19. It is a control unit that performs arithmetic processing and controls the rotation of the motor 11. A pulse is output from the encoder 19 as the code wheel 18 attached to the rotating shaft 13 rotates.
[0010]
FIG. 12 is an explanatory view of rotation unevenness of the photosensitive drum when drive control is not performed. The transition of the pulse output cycle of the encoder 19 and the transition of the position error obtained by integrating the output pulse cycle of the encoder 19 are shown. Due to uneven rotation of the motor 11 and dimensional error (meshing error) of the reduction gear 12, the rotation of the photosensitive drum 1 is not constant, the output pulse cycle of the encoder 19 fluctuates, and position errors occur periodically. Is appearing.
[0011]
The phase and amplitude of the position error are different for each color, resulting in a periodic color shift. Since the rotation cycle of the reduction gear 12 and the motor 11 is configured to be 1 / integer of one rotation of the photosensitive drum 1, the rotation unevenness is repeated in the rotation cycle of the photosensitive drum 1.
[0012]
FIG. 13 is a detailed explanatory view of the drive control unit 21, and FIG. 14 is an explanatory view showing rotation unevenness of the photosensitive drum after the drive control. Each one represents one color, and there are four similar ones. The code wheel 18 has, for example, 1000 slits, and 1000 pulses are output from the encoder 19 by one rotation of the photosensitive drum 1. The detection unit counts the pulse period of the encoder 19, obtains an error from the encoder reference value, and temporarily holds it in the encoder error memory (FIFO). From the encoder error data held in the encoder error memory, a high-frequency component having no periodicity due to the tooth pitch of the reduction gear 12 or the like is removed by a low-pass filter (LPF). This low-pass filter is formed of, for example, a symmetric FIR (Finite Impulse Response) filter of order 100. The encoder error memory holds encoder error data corresponding to the order of the FIR filter and performs a first in first out (FIFO) operation. When the latest encoder error data is detected, the low-pass filter process is performed on the encoder error data of the 1/2 FIR order. In addition, there may be a simple average, an IIR (Infinite Impulse Response) filter, or the like.
[0013]
Then, a value obtained by multiplying the encoder error data subjected to the low-pass filter processing by the integration constant Gi is added to the motor correction value (drive value) at the time of detecting the encoder error data subjected to the low-pass filter processing to obtain a new motor correction value. The motor correction value memory holds one motor revolution value of the photosensitive drum 1, that is, 1000 motor correction values, and performs a FIFO operation. The motor reference value is added to the new motor correction value calculated from the motor correction value (drive value) and the encoder error at the same rotational position one revolution before the photosensitive drum 1 held in the motor correction value memory. Then, the motor 11 is driven with the latest motor cycle.
[0014]
That is, the motor 11 is driven so as to cancel the encoder error at the same rotational position one revolution before the photosensitive drum 1. For example, the motor 11 is a hybrid two-phase stepping motor with 200 steps per revolution, and the drive rate of the motor reference value is 2000 pps. Driven with a variable step period corrected around the motor reference value, rotation irregularities and position errors of the photosensitive drum 1 are suppressed, and color misregistration is reduced.
[0015]
[Problems to be solved by the invention]
However, the above conventional example has the following problems.
[0016]
The life of the photosensitive drum is shorter than the life of the apparatus main body, and is configured to be removable from the apparatus main body and replaceable. The photosensitive drum is integrally formed with the cartridge together with the charging mechanism and the developing mechanism so that the user can easily handle it. In the image forming apparatus having such a configuration, the rotation shaft of the main body that rotates together with the photosensitive drum does not completely coincide with the angular velocity of the photosensitive drum in the cartridge.
[0017]
Therefore, although the motor is driven and controlled so as to cancel the angular velocity error of the encoder attached to the rotating shaft of the main body that rotates together with the photosensitive drum, the color misregistration due to the uneven driving of the photosensitive drum is sufficient. It was not possible to reduce it.
[0018]
FIG. 15 is an explanatory diagram of the drive transmission means according to the above-described problem. Portions that overlap the description of FIG. 11 described above are denoted by the same reference numerals, and description thereof is omitted.
[0019]
In FIG. 15, the photosensitive drum 1 is held in a cartridge (not shown) that is detachable from the apparatus main body. 16 is one flange of the photosensitive drum 1, 15 is the other flange having a coupling on the cartridge side for driving transmission to the photosensitive drum 1, and 17 is press-fitted into flanges 15 and 16 that rotate together with the photosensitive drum 1. A photosensitive drum rotating shaft on the cartridge side, 13 is a photosensitive drum rotating shaft on the main body provided coaxially with the photosensitive drum rotating shaft 17 on the cartridge side, and 14 is a cup on the main body side for driving transmission to the photosensitive drum 1. It is a ring.
[0020]
The driving of the photosensitive drum rotating shaft 13 on the apparatus main body side is transmitted from the coupling 14 on the apparatus main body side to the photosensitive drum 1 through the coupling and flange 15 on the cartridge side. The photosensitive drum rotating shaft 17 on the cartridge side mainly holds the position of the photosensitive drum 1, and the drive is transmitted through the flanges 15 and 16. The photosensitive drum rotation shaft 13 on the main body side and the photosensitive drum rotation shaft 17 on the cartridge side do not completely coincide on the same line due to component tolerances or deformation of the apparatus main body and cartridge, and the rotation of the photosensitive drum on the main body side. The angular velocity of the shaft 13 and the angular velocity of the photosensitive drum 1 do not completely match.
[0021]
FIG. 16 and FIG. 17 are explanatory diagrams of color misregistration caused by uneven driving of the photosensitive drum related to the above-described problem. FIG. 16 shows a state when the rotation control of the photosensitive drum is suppressed by controlling the driving by the motor.
[0022]
As described with reference to FIG. 14, the motor is driven and controlled so as to cancel the angular velocity error of the encoder 19 attached to the photosensitive drum rotating shaft on the apparatus main body side that rotates together with the photosensitive drum. Almost no position error occurs.
[0023]
However, when the device main body and the cartridge are driven and connected by coupling, as described above, the angular velocity of the photosensitive drum rotating shaft on the main body side and the photosensitive drum does not completely coincide with each other, so that a positional error of the cartridge drum shaft occurs. To do.
[0024]
FIG. 17 shows a case where a drum position error Δa occurs in black Bk. FIG. 18 is a diagram for explaining the relationship between the exposure of the photosensitive drum 1 and the transfer position. The drum position error is a position error of the image formed on the peripheral surface of the photosensitive drum 1, and the position error after being transferred onto the sheet is a difference in position error between the exposure position and the transfer position.
[0025]
The interval between exposure and transfer is approximately 180 degrees in the rotation direction of the photosensitive drum 1, and the position error that varies with the photosensitive drum cycle is opposite in phase between exposure and transfer, and the amplitude is doubled after transfer. As shown in FIG. 17, the position error between exposure and transfer of black Bk is 2Δa. Similarly, a cyan C exposure / transfer position error 2Δb occurs. The phase relationship of the position error caused by the non-uniform driving of the photosensitive drum between the colors is arbitrary, and when the peak of the position error between the two colors is in the opposite phase, the color shift is maximized. That is, the color misregistration caused by uneven driving of the photosensitive drum between black Bk and cyan C is 2Δa + 2Δb. The color misregistration is four times as much as the drum position error amount.
[0026]
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of reducing color misregistration caused by driving unevenness of an image carrier with high accuracy. Is.
[0027]
[Means for Solving the Problems]
A typical configuration according to the present invention for achieving the above object includes a plurality of image carriers that can be mounted on the apparatus main body, and a color image formed by superimposing a plurality of color images formed by the plurality of image carriers. The reference color image carrier having a first phase difference which is the difference between the phase of the reference color image carrier and the phase of the detected color image carrier relative to the reference color And a plurality of sets of first patterns for color misregistration detection on the image carrier of the detected color over one period or more of the image carrier in the sub-scanning direction of the image carrier of the reference color and the image carrier of the detected color The difference between the phase of the reference color image carrier and the phase of the detected color image carrier relative to the reference color is changed from the first phase difference to the second phase difference, and the reference color image carrier and the detected color. A second pattern for color misregistration detection is applied to the image carrier of the reference color and the front of the image carrier of the reference color. A plurality of sets are formed in the sub-scanning direction of the image carrier of the detected color over one period of the image carrier, and the first pattern and the second pattern are transferred to the transfer belt, and the first image transferred to the transfer belt is transferred to the transfer belt. Color misregistration detecting means for detecting a plurality of sets of the first patterns corresponding to one phase difference and a plurality of sets of the second patterns corresponding to the second phase difference, and detected by the color misregistration detecting means. Based on the color misregistration detection results of the plurality of sets of the first patterns and the color misregistration detection results of the plurality of sets of the second patterns, Of the first phase difference and the second phase difference, Difference between image carrier position error during exposure transfer of the reference color and image carrier position error between exposure transfer of the detected color The phase difference that minimizes Difference between the phase of the reference color image carrier during image formation and the phase of the detected color image carrier relative to the reference color As Setting means to set and , It is characterized by having.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Next, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.
[0029]
[First Embodiment]
(Overall configuration of the device)
FIG. 1 is an overall schematic explanatory view of an image forming apparatus according to an embodiment of the present invention. The embodiment of the present invention shows a color image forming apparatus having image forming means for four colors, that is, yellow Y, magenta M, cyan C, and black Bk. In the figure, 1 forms an electrostatic latent image. Photoconductor drums 1a, 1b, 1c, and 1d as image carriers to be performed (a, b, c, and d are for black Bk, cyan C, magenta M, and yellow Y, respectively), 2a, 2b, 2c, and 2d are A laser scanner that performs exposure in accordance with an image signal to form an electrostatic latent image on the photosensitive drum 1, 3 is an endless conveyance belt that also serves as a transfer belt, and sequentially conveys paper to an image forming unit of each color, 4 Is connected to a driving means including a motor and a gear as a driving source (not shown), a driving roller for driving the conveying belt 3, and 5 rotates according to the movement of the conveying belt 3 and applies a constant tension to the conveying belt 3. Follow The rollers 6a and 6b are a pair of color misregistration detection sensors provided on both sides of the conveyor belt 3 for detecting a color misregistration detection pattern formed on the conveyor belt 3. It constitutes.
[0030]
When data to be printed is sent from an unillustrated host computer to the image forming apparatus and printing is enabled when image processing according to the printer engine system is completed, paper is supplied from a paper cassette (not shown), and the conveyor belt 3 Then, the paper is sequentially conveyed to the image forming units of the respective colors by the conveyance belt 3.
[0031]
The image signals of the respective colors are sent to the laser scanners 2a, 2b, 2c, and 2d in synchronism with the conveyance of the paper by the conveyor belt 3, and electrostatic latent images are formed on the photosensitive drums 1a, 1b, 1c, and 1d. Then, the toner is developed by a developing device (not shown) and transferred onto a sheet by a transfer unit (not shown). In FIG. 1, images are sequentially formed in the order of yellow Y, magenta M, cyan C, and black Bk. Thereafter, the sheet is separated from the conveying belt, and the toner image is fixed on the sheet by heat with a fixing device (not shown) and discharged to the outside.
[0032]
(Color misregistration correction configuration)
The image forming apparatus is configured to minimize color misregistration of a color image formed by a plurality of photosensitive drums. For this purpose, phase correction means for correcting the rotational phase of the photosensitive drum is provided at the phase where the color shift amount calculated by the color shift detection means is minimized.
[0033]
Next, the color misregistration correction configuration of this embodiment will be described. FIG. 2 is an explanatory diagram of the rotation state detection means, the drive source, and the drive transmission means. Note that the same parts as those in FIG. 15 described above are denoted by the same reference numerals, and description thereof is omitted.
[0034]
In FIG. 2, 18 is a code wheel that rotates together with a rotating shaft 13, is provided with a concentric equidistant slit and another slit provided on the inner periphery, and 20 is a code wheel 18 according to the passage of one slit. This is a photosensor composed of a light emitting portion and a light receiving portion that outputs a pulse signal once for each rotation of the photosensitive drum 1.
[0035]
FIG. 3 is an explanatory diagram of the code wheel 18. Reference numeral 18a denotes slits provided at equal intervals on a concentric circle, and has, for example, 1000 slits at 150 LPI (Line Per Inch). Reference numeral 18b denotes another slit provided at one location.
[0036]
When forming an image, the motor 11 is driven so as to cancel the error of the encoder 19, color misregistration is detected by the color misregistration detecting means, and rotation unevenness and position error of the photosensitive drum 1 are suppressed by the rotation phase varying means. The point of reducing the color shift is the same as in the conventional example.
[0037]
FIG. 4 is a flowchart of rotational phase correction of the photosensitive drums of each color, and FIG. 6 is an explanatory diagram showing the rotational phase correction timing of the photosensitive drums of each color.
[0038]
The operation procedure for detecting the color shift of the detected color with respect to the reference color while changing the photoconductive drum phase of the detected color with respect to the reference color and obtaining the photosensitive drum phase with the minimum color shift is based on the flowchart of FIG. I will explain.
[0039]
First, a “phase difference between reference color and detected color P ← P0 setting” processing is executed. For example, P0 = 0 degree is set (step S1).
[0040]
Next, a “drum motor start” process is executed (step S2). Thus, when driving of the motor 11 for rotating the photosensitive drum is started, a pulse is output from the photosensor 20 every rotation of the photosensitive drum. 5A and 5B are diagrams for explaining the pulse output for each rotation of the photosensitive drum. FIG. 5A shows a case where all the colors are in phase, and FIG. 5B shows a case where yellow Y is -180 degrees with respect to black Bk, magenta. It is explanatory drawing which shows the case where M is -270 degree | times and cyan C is -90 degree | times.
[0041]
When the photosensitive drum is driven and rotated, the process proceeds to step S3 to perform the process of “phase adjustment subroutine”.
[0042]
In this subroutine, first, a process of “variing the drum motor speed of the detected color and adjusting the phase difference between the reference color and the detected color to P” is performed (step S31). In this process, the timing of pulse output for each rotation of the photosensitive drum for each color is detected, and the speed of the motor 11 is varied so that the pulse timing of the reference color and the detected color becomes the set value P.
[0043]
The motor speed can be varied by either deceleration or acceleration. However, considering that the motor output is not increased more than necessary, it is desirable to adjust the detected color by decelerating while keeping the reference color at a constant speed. Further, since the motor speed is not constant during the phase adjustment of the detected color, the drive control of the motor 11 that cancels the error of the encoder 19 is not performed.
[0044]
Next, after the phase adjustment is completed, “drum phase color misregistration detection pattern formation” processing is performed (step S32). In this process, the drive control of the motor 11 that cancels the error of the encoder 19 is resumed. Since the drive control is performed before one revolution of the photosensitive drum, image formation of the color correction detection pattern for phase correction is started after at least one drive control of the photosensitive drum is performed.
[0045]
In FIG. 6, the reference color is black Bk, and phase correction color misregistration detection patterns are formed on the conveyor belt 3 in the order of combination of cyan C and black Bk, magenta M and black Bk, yellow Y and black Bk.
[0046]
FIG. 7 is an explanatory diagram of a color correction detection pattern for phase correction. In the figure, 9a and 9b indicate reference colors, and 10a and 10b indicate detected colors. Corresponding to the pair of color misregistration detection sensors 6a and 6b provided on both sides of the conveyor belt 3, the same pattern is formed on the left and right. In order to detect the average value of the color misregistration that fluctuates with the photosensitive drum period, a plurality of sets of color misregistration detection patterns 9a, 9b, 10a, and 10b are formed over one period or more of the photosensitive drum in the sub-scanning direction.
[0047]
In the “color misregistration detection” process (step S33 in FIG. 4), the color misregistration detection sensors 6a and 6b output pulses according to the passage timing of each pattern, and a CPU (not shown) detects the interval between the detected pulses. The amount of color misregistration is calculated from the difference between the timing and the reference value and stored in a memory (not shown).
[0048]
Next, the process proceeds to step S4 shown in the flowchart of FIG. 4 to perform the “P ← P−ΔP setting” process. In this process, the phase difference P between the reference color and the detected color is set to P−ΔP. For example, ΔP is set to −45 degrees, and the same operation is repeated eight times (P = 0, −45, −90, −135, −180, −225, −270 until the condition of P ≦ −360 degrees is satisfied. , -315 degrees) (step S5).
[0049]
After repeating 8 times, the amount of color misregistration for each phase is compared for each color, and the process of “setting the phase difference Ps with minimum color misregistration” is performed (step S6). In this process, the phase difference Ps with the smallest color misregistration is held, and the driving of the motor 11 is stopped in the “drum motor stop” process (step S7).
[0050]
The above phase correction sequence is carried out following the correction sequence related to steady color misregistration in the conventional example.
[0051]
In a normal printing operation, an image is formed after adjusting the pulse phase for each rotation of the photosensitive drum output from the photosensor 20 to Ps.
[0052]
FIG. 8 is an explanatory diagram of the color shift after the phase correction as described above. The photoconductor drum position error between black Bk exposure and transfer is 2Δa, the photoconductor drum position error between cyan C exposure and transfer is 2Δb, and the color misregistration between cyan C and black Bk due to uneven driving of the photoconductor drum is 2Δa. −2Δb.
[0053]
The time axis in FIG. 8 is not absolute time, and the timing at which black Bk and cyan C are at the same position on the image is shown at the same position on the time axis. In FIG. 8, the phase adjustment in the phase correction sequence is equivalent to moving cyan C to the right on the time axis with respect to black Bk every 1/8 step (45 degrees) of one drum cycle. At each step, the color misregistration 2Δa−2Δb of cyan C and black Bk due to uneven driving of the photosensitive drum varies, and the color misregistration detection amount also varies accordingly. The phase difference Ps with the smallest color misregistration corresponds to the case where the phases of the photoconductor drum position errors of the reference color and the detected color coincide as shown in FIG.
[0054]
By performing the phase correction sequence as described above, the phase of the photosensitive drum drive unevenness caused by the coupling error between the cartridge for each color and the main body can be adjusted between each color, and color misregistration can be reduced with high accuracy. It becomes.
[0055]
[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the apparatus of the first embodiment described above, the error value between the photosensitive drum rotating shaft 13 on the apparatus main body side and the angular velocity of the photosensitive drum 1 in the cartridge is the difference between the coupling 14 on the apparatus main body side and the flange 15 on the cartridge side. Depends on the fit. This fitting condition is influenced by the deformation amount of the apparatus main body and the fitting position of the coupling. For this reason, it is preferable to perform phase correction when the installation state of the apparatus main body is changed or when the cartridge is detached.
[0056]
The steady color shift is affected by fluctuations in the environment, particularly temperature, in addition to the case where phase correction is necessary. The phase correction sequence does not always need to be performed together with the steady phase correction sequence, and may be performed only when the power is turned on and when the cartridge is detached.
[0057]
Therefore, in this embodiment, since the cover is opened when the cartridge is attached / detached, the phase correction sequence is performed after the cover is closed regarding the attachment / detachment of the cartridge. Further, when it has a function of electrically and mechanically detecting the cartridge detachment, the cartridge detachment itself is detected and the phase correction sequence is performed. If the cartridge has storage means such as a memory, the cartridge memory is accessed while the cover is open, and if the access is not performed normally, it is determined that the cartridge has been removed.
[0058]
As described above, when the fitting state between the apparatus main body and the cartridge is changed, by performing the phase correction sequence, the color misregistration can be more reliably reduced. The downtime of the printing operation can be reduced by limiting the time when the cartridge is detached.
[0059]
[Third Embodiment]
Next, a third embodiment will be described. When the photosensitive drum drive motor is a motor whose rotation angle is guaranteed by the number of drive pulses, such as a stepping motor, one pulse signal for each rotation for detecting the rotation phase of the photosensitive drum is not necessary. .
[0060]
FIG. 9 is a flowchart for explaining the rotational phase correction procedure of the photosensitive drums of the respective colors according to the third embodiment. Here, a different part from the procedure of the flowchart of FIG. 4 shown by 1st Embodiment mentioned above is demonstrated.
[0061]
In this embodiment, the “phase difference P ← P0 setting” process of step S1 in FIG. 4 is not performed, the drum motor is started at an arbitrary phase, and a phase correction color misregistration detection sequence is performed.
[0062]
Next, the phase of the detected color is set to −ΔP for an arbitrary phase. In the case of a stepping motor, the amount of change in the rotational phase of the detected color with respect to the reference color is guaranteed by the deceleration including the slow-down and the number of steps. The same operation is repeated 8 times.
[0063]
Then, after the “set phase difference Ps with minimum color misregistration” process, the process proceeds from step S6 to step SA and “varies the drum motor speed of the detected color and adjusts the phase difference between the reference color and the detected color to Ps” process. Is executed, the “drum motor stop” process of step S7 is executed. Here, the phase difference Ps means a difference of −ΔP steps from an arbitrary phase when the drum motor is started.
[0064]
Until the next phase correction sequence, the photosensitive drum phase does not fluctuate. Therefore, in the normal printing operation, the phase of the photosensitive drum is not adjusted, and image formation is started immediately.
[0065]
By configuring as described above, a mechanism for detecting the phase of the photosensitive drum of each color becomes unnecessary, so that color misregistration can be accurately reduced with an inexpensive configuration and an increase in first print time due to phase adjustment is avoided. I can do it.
[0066]
[Other Embodiments]
In the embodiment described above, the conveyance belt conveys an endless belt recording material that records a color misregistration detection pattern. However, even in an image forming apparatus using an intermediate transfer member, a similar phase correction sequence is executed. A high quality image can be obtained. That is, the toner images formed on the photosensitive drums of the respective colors are sequentially primary transferred onto an endless intermediate transfer belt as an intermediate transfer member to form a color image, and the color images are collectively transferred to a recording material conveyed by a conveying unit. Then secondary transfer. Even in such an image forming apparatus, a high-quality image can be obtained by recording a color misregistration detection pattern on the intermediate transfer belt and executing a phase correction sequence in the same manner as in the above-described embodiment. .
[0067]
In addition, the coupling mechanism in the above-described embodiment may be another mechanism in which the apparatus main body shaft and the photosensitive drum shaft in the cartridge are coupled.
[0068]
Further, the motor of the drive source is not limited to the stepping motor, and the above-described phase correction sequence can be executed by another motor such as a DC brushless motor.
[0069]
Further, the optical encoder may be a reflective type. Further, instead of the code wheel and the optical encoder, a magnetic rotary encoder using an MR element or the like may be used.
[0070]
The phase correction color misalignment detection pattern may be another pattern. In order to shorten the pattern length, the left and right colors may be combined differently, or may be formed only on one side instead of the left and right sides.
[0071]
Further, the phase detection means of the photosensitive drum can be performed by other means such as a photo interrupter.
[0072]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce the color misregistration caused by driving unevenness of the image carrier with high accuracy.
[0073]
Further, if the phase correction sequence is limited to when the power is turned on and when the cartridge is detached, the number of phase corrections can be reduced and the downtime of the printing operation can be reduced.
[0074]
Furthermore, if the image carrier is driven by a motor whose rotation angle is guaranteed by the number of drive pulses, a mechanism for detecting the phase of the photosensitive drum of each color is not required, and color misregistration is reduced with high accuracy at a low cost. In addition, the increase in the first print time due to the phase adjustment can be avoided.
[Brief description of the drawings]
FIG. 1 is an overall schematic explanatory diagram of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of a rotation state detection unit, a drive source, and a drive transmission unit.
FIG. 3 is an explanatory diagram of a code wheel.
FIG. 4 is a flowchart of rotational phase correction of the photosensitive drums of respective colors.
FIGS. 5A and 5B are diagrams for explaining a pulse output for each rotation of the photosensitive drum. FIG. 5A shows a case where all colors have the same phase, and FIG. 5B shows a yellow Y of −180 degrees with respect to black Bk. It is explanatory drawing which shows the case where magenta M is -270 degree | times and cyan C is -90 degree | times.
FIG. 6 is an explanatory diagram showing rotation phase correction timings of the photosensitive drums of the respective colors.
FIG. 7 is an explanatory diagram of a color correction detection pattern for phase correction.
FIG. 8 is an explanatory diagram of color misregistration after phase correction.
FIG. 9 is a flowchart illustrating a rotational phase correction procedure for each color photosensitive drum according to the third embodiment.
FIG. 10 is an explanatory diagram of unsteady color misregistration in the sub-scanning direction caused by uneven rotation of the photosensitive drum.
FIG. 11 is an explanatory diagram of a rotation state detection unit, a drive source, and a drive transmission unit.
FIG. 12 is an explanatory diagram of rotation unevenness of the photosensitive drum when drive control is not performed.
FIG. 13 is a detailed explanatory diagram of a drive control unit.
FIG. 14 is an explanatory diagram showing uneven rotation of the photosensitive drum after drive control.
FIG. 15 is an explanatory diagram of a rotation state detection unit, a drive source, and a drive transmission unit.
FIG. 16 is an explanatory diagram of rotation unevenness of the photosensitive drum after drive control.
FIG. 17 is an explanatory diagram of color misregistration caused by uneven driving of the photosensitive drum.
FIG. 18 is an explanatory diagram showing a relationship between exposure of a photosensitive drum and a transfer position.
[Explanation of symbols]
1a, 1b, 1c, 1d ... photosensitive drum
2a, 2b, 2c, 2d ... Laser scanner
3 ... Conveyor belt
4 ... Driving roller
5 ... Follower roller
6a, 6b ... Color shift detection sensor
11… Stepping motor
12… Reduction gear
13… Rotation axis
14… Coupling
15… Flange
16… Flange
17… Photoreceptor drum rotation shaft
18… Cord wheel
18a ... slit
18b ... slit
19… Encoder
20… Photo sensor
21… Control unit

Claims (1)

An image forming apparatus having a plurality of image carriers that can be attached to the apparatus body, and forming a color image by superimposing images of a plurality of colors formed by the plurality of image carriers,
A color is applied to the reference color image carrier and the detected color image carrier having a first phase difference which is a difference between the phase of the reference color image carrier and the phase of the detected color image carrier relative to the reference color. A plurality of sets of first patterns for detecting deviation are formed over one period of the image carrier in the sub-scanning direction of the reference color image carrier and the detected color image carrier, and the phase of the reference color image carrier is formed. The phase difference of the detected color image carrier with respect to the reference color is changed from the first phase difference to the second phase difference, and the reference color image carrier and the detected color image carrier are used for color shift detection. A plurality of second patterns are formed in the sub-scanning direction of the reference color image carrier and the detection color image carrier over one period of the image carrier, and the first pattern and the second pattern are transferred to the transfer belt. Control means to
Color misregistration detection means for detecting a plurality of sets of the first patterns corresponding to the first phase difference transferred to the transfer belt and a plurality of sets of the second patterns corresponding to the second phase difference;
The first phase difference and the second phase difference based on the color misregistration detection results of the plurality of sets of the first patterns and the color misregistration detection results of the plurality of sets of the second patterns detected by the color misregistration detection means. Among them, the phase difference that minimizes the difference between the image carrier position error between the exposure transfer of the reference color and the image carrier position error between the exposure transfer of the detected color is the image carrier of the reference color at the time of image formation. an image forming apparatus, comprising setting means for setting a difference in phase of the image carrier detection colored body phase and with respect to the reference color, the.

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