JP2005275254A - Color image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming device which can shorten the control time necessary for correction of misalignment. <P>SOLUTION: A pattern for detecting both a steady misalignment in the carrying direction and a periodically fluctuating misalignment is formed on a carrying means, the pattern is detected (44), a steady misalignment and a periodically fluctuating misalignment is calculated based on the detection result, and the misalignment is corrected based on the calculated misalignment. The same pattern as the pattern to detect the steady misalignment and the pattern to detect the periodically fluctuating misalignment is used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a color image forming apparatus such as a color copying machine or a color printer, and more particularly to correction of color misregistration (also referred to as misregistration).

  2. Description of the Related Art Conventionally, there is a color image forming apparatus called a so-called in-line system in which photosensitive drums that form a plurality of image carriers are arranged in a line. This is because four photosensitive drums arranged along the transfer material conveyance path are used to convey yellow (yellow), while carrying and conveying a transfer material (also referred to as a sheet) by an electrostatic transfer belt stretched by a plurality of rollers. A toner image composed of magenta, cyan, and black is sequentially transferred onto a transfer material, and a color image is formed by superimposing each color.

  This configuration has attracted attention in recent years because it can perform printing at high speed. However, since each color is formed by four photosensitive drums, a configuration in which colors are superimposed on one photosensitive drum via four conveyance paths for each color (hereinafter simply referred to as “four-pass method”). Compared with the color image forming apparatus (2), a higher accuracy is required for the rotational driving of the photosensitive drum.

  In other words, a gear train is generally used for driving the photosensitive drum, and low-frequency rotation unevenness such as one rotation component of the gear always occurs. However, in the case of the 4-pass system, the reduction ratio of the drive gear train is an integer. By combining them, it is possible to avoid the accumulated pitch error of the gears and to adjust the image forming positions of the respective colors.

  However, in the case of the in-line method, since the plurality of photosensitive drums are independent, the drive gear train is also independent, which makes it difficult to avoid the problem as in the 4-pass method described above, and the image forming positions of the respective colors are shifted. It is easy for image quality deterioration called color shift to occur.

Conventionally, as measures against color misregistration, measures such as detecting the angular velocity of the photosensitive drum or reading an image transferred onto a transfer material to detect the velocity unevenness and controlling the rotation of the motor to cancel the velocity unevenness As described in the following Patent Document 1 and Patent Document 2, measures are taken to reduce relative color misregistration by matching the rotational phase of each photosensitive drum to a desired state.
JP-A-9-146329 JP-A-10-333398

  However, in the above-described conventional example, the driving of the image carrier that forms the photosensitive drum is a reduction system via a plurality of gears. It becomes a complicated speed waveform including a component of one rotation cycle. For this reason, high-precision speed unevenness detection means and motor control are required, and even if the phase of the photosensitive drum is adjusted, the influence of the intermediate gear remains, and in order to accurately detect the drive unevenness of one rotation period of the image carrier. Therefore, it is necessary to shift the rotational phase of the detected color with respect to the reference color, and to detect the relative positional shift of the detected color with respect to the reference color by the positional shift detection pattern for each rotational phase, which takes time.

  In addition, in order to eliminate all the positional deviations, in addition to the above-described control for detecting the positional deviation that fluctuates periodically, the control for detecting the stationary positional deviation must be executed, which takes a considerable time. .

  The present invention has been made under such circumstances, and it is an object of the present invention to provide a color image forming apparatus capable of shortening the control time required for misalignment correction.

  In order to solve the above problems, in the present invention, the image forming apparatus is configured as described in the following (1) to (3).

(1) a plurality of image forming units having an optical unit and an image carrier;
A plurality of transfer means for transferring an image on a conveying means for forming an endless belt that sequentially passes through the plurality of image forming sections, or on a recording material placed and conveyed on the conveying means;
A pattern forming unit for forming a dual-purpose pattern for detecting a stationary position shift in the transport direction and a position shift that varies periodically on the transport unit;
Pattern detecting means for detecting a pattern formed by the pattern forming means;
A calculation means for calculating a steady position shift in the transport direction and a position shift that varies periodically based on the detection result of the pattern detection means;
A positional deviation correction means for correcting the positional deviation based on the positional deviation calculated by the computing means;
A color image forming apparatus.

(2) In the color image forming apparatus according to (1),
Comprising an exchange detection means for detecting the exchange of the image carrier,
When the replacement detection unit detects the replacement of the image carrier, the correction unit newly calculates a positional shift using the pattern forming unit, the pattern detection unit, and the calculation unit, and based on the calculated positional shift. A color image forming apparatus that performs correction of misregistration.

(3) In the color image forming apparatus according to (2),
The color image forming apparatus, wherein when the replacement detection unit does not detect the replacement of the image carrier, the correction unit corrects the positional shift based on the positional shift already calculated by the calculation unit.

  According to the present invention, it is possible to shorten the control time required for correcting the misregistration by combining the control for adjusting the rotational phase of each photosensitive drum to a desired state and the control for suppressing the steady color misregistration. A color image forming apparatus can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  FIG. 1 is a longitudinal sectional view showing a main part configuration of a “color image forming apparatus” according to a first embodiment, and FIG. 2A is a perspective view showing a main part configuration of a drive unit / drive transmission unit of a photosensitive drum. 2B is a cross-sectional view showing the configuration of the main part of the drive unit / drive transmission unit of the photosensitive drum, FIG. 3 is a diagram showing the configuration of the main part of the drive unit of the photosensitive drum and the control system, and FIG. FIG. 5 is a diagram showing a state of color misregistration of each color before control, FIG. 5 is a diagram showing a pattern for detecting color misregistration, and FIG. 6 is a state in which the color misregistration of each color after phase control of the photosensitive drum is eliminated. FIGS. 7A and 7B are diagrams showing a misregistration detection pattern and an arrangement example thereof.

  In FIG. 1, a color image forming apparatus 100 includes four electrophotographic photosensitive drums 1a, 1b for yellow, magenta, cyan, and black, which are image carriers linearly arranged in a vertical direction in FIG. 1c and 1d (hereinafter simply referred to as “photosensitive drums 1”), which is a transfer material carrying member that is opposed to the respective photosensitive drums 1 and adsorbs and conveys the transfer material S by electrostatic adsorption. A material conveying belt (endless belt) 11 is disposed.

  Each of the photosensitive drums 1 is fixed to a drum shaft that is a rotation shaft of the photosensitive drum 1, and is engaged with a coupling 36 that is a first engaging member, which will be described in detail later, and the coupling 36. A rotational driving force is transmitted from a driving motor (not shown) serving as a driving source to the gear 18 on the coupling 33 side serving as a second engaging member to be coupled to be rotated counterclockwise in FIG. a) and (b)).

  Around each photosensitive drum 1, primary chargers 5 a, 5 b, 5 c, 5 d (hereinafter simply referred to as “charging means” for uniformly charging the surface of the photosensitive drum 1 in order from the upstream side in the rotation direction). An exposure unit 3a for forming an electrostatic latent image by irradiating the surface of the photosensitive drum 1 uniformly charged by the primary charger 5 with a laser beam based on image information. 3b, 3c, 3d (hereinafter simply referred to as "exposure means 3") are arranged.

  Further, developing means 4a, 4b, 4c, 4d (hereinafter simply referred to as "developing means 4") that make each color toner adhere to the surface of the photosensitive drum 1 on which the electrostatic latent image is formed to visualize the toner image. Cleaning means 6a, 6b, 6c, 6d (hereinafter simply referred to as “cleaning means 6”) for removing toner remaining on the surface of the photosensitive drum 1 after transfer are disposed.

  The photosensitive drum 1, the primary charger 5, the developing unit 4, and the cleaning unit 6 are unitized as process cartridges 7 a, 7 b, 7 c, and 7 d (hereinafter simply referred to as “process cartridge 7”). It is comprised so that attachment or detachment is possible. Further, it has means for detecting the replacement of the process cartridge (not shown), and detects the loading state during the initialization operation.

  In addition, a transfer material conveying belt (endless belt) 11 is sandwiched between the transfer material conveying belts 11 on the surface of the photosensitive drum 1 at positions facing the respective photosensitive drums 1. Transfer rollers 12a, 12b, 12c and 12d (hereinafter simply referred to as “transfer roller 12”) serving as transfer means for transferring the toner image are disposed.

  The drive unit is positioned in front of the left side of the machine, and applies a rotational driving force to the four color process cartridges 7 arranged in the substantially vertical direction. Each process cartridge 7 includes a photosensitive drum 1, a developing unit 4, a cleaning unit 6 and the like, and supplies all of these driving forces.

  Since the cartridge 7 can be detached and attached independently for each color, the drive transmission unit is also arranged in a substantially vertical direction independently for each color and directly transmits to the photosensitive drum 1 that requires rotational accuracy. The driving, for example, the driving of the developing unit 4 and the cleaning unit 6 may be transmitted in another series. The driving force supplied to the cartridge 7 is distributed to each element by a driving system in the cartridge 7.

  As shown in FIGS. 2A and 2B, the driving means includes a gear 18 for driving the process cartridge 7, a shaft portion 32a that rotates integrally with the gear 18, and a shaft portion 32a. And a coupling hole 33 for transmitting rotational driving force to the process cartridge 7 and a drum shaft 22 fixed concentrically with the photosensitive drum 1, and a positioning hole 34 for determining the position. Are integrally formed. This integral component can be a resin molded product.

  As shown in FIG. 2, the shaft portion 32a is supported by the cylinder bearing portion 35 installed on the main body side so that only the shaft portion 32a in the vicinity of the gear root is freely rotated and linearly moved. The periphery of 33 is supported to such an extent that the positioning hole 34 is determined by fitting to the drum shaft 22 described later, and does not interfere with the shaft position and does not hinder the coupling. Clearance is provided.

  Although the gear shaft is inclined due to the positional accuracy of the cylinder bearing portion 35 and the drum shaft 22, the distance from the shaft portion 32 a near the gear root to the positioning hole 34 is made sufficiently long so that there is no actual harm.

  The gear 18 and the integral part are movable in the axial direction, and are pressed toward the photosensitive drum 1 by a plate spring 37.

  A drum shaft 22 that rotates integrally with the photosensitive drum 1 is fixed to the photosensitive drum 1, and the drum shaft 22 is accurately positioned on the machine body via a bearing 38.

  A non-driving side (driven side) coupling 36 is fixed to the end of the drum shaft 22, and meshes with the driving side (main driving side) coupling 33 to transmit the rotational driving force.

  As shown in FIGS. 2A and 2B, the driving side coupling and the non-driving side coupling are triangular spiral couplings that are configured to always engage with each other when driven in a predetermined direction. ing.

  In FIG. 3, the motors 41y, 41m, 41c and 41k (hereinafter referred to as motor 41) provided exclusively for the respective photosensitive drums 1y, 1m, 1c and 1k (hereinafter referred to as photosensitive drum 1) are engaged with the photosensitive drum 1. The photosensitive drum 1 is driven through the gear 18.

  The tooth 31 of the gear 18 is provided with a target for detecting the phase, and a phase signal is detected once per rotation by an optical or magnetic phase detector (42y, 42m, 42c, 42k) 42. can do.

  In the configuration of this embodiment, the main component of the angular velocity unevenness is only one rotation cycle of the photosensitive drum 1, so that a pattern formed on the photosensitive drum 1 at equal time intervals is transferred to the transfer material conveying belt 11. When the image detection sensor 44 reads and obtains the accumulated fluctuation component of the pattern interval, a sine waveform as shown in FIG. 4 is obtained.

  In FIG. 4, the horizontal axis represents the distance from the front end of the image, and the vertical axis represents the amount of displacement. In order to obtain the phase relationship of the four colors, processing is performed by creating and detecting one color at a time while managing the image formation start timing of each color, obtaining a sine waveform, correcting the comparison by the start timing interval, and comparing them. Just do it.

  As shown in FIG. 4, when Bk is used as a reference, the color shift (position shift) relative to the Bk color can be reduced by shifting the Y color by the distance y to the image leading end side. Similarly, the M color may be shifted by the distance m, and the C color may be shifted by the distance c. However, since this rotation phase detection requires a predetermined time, if it is frequently performed, a loss of image formation time occurs.

  Therefore, a phase detection device 42 that detects the phase of the gear 18 that rotates the photosensitive drum 1 is used, and in a normal state (the cartridge is not replaced), the positional deviation and phase detection when the process cartridge is replaced or loaded are detected. Based on the phase information detected by the device 42, the control of the misalignment correction is performed.

  When the phase waveform detected by the phase detector 42 is in a state as shown in FIG. 4, if the phase of the Y-color gear 18y is controlled so as to be turned earlier by the time y 'corresponding to the distance y in FIG. The relative color shift between the Bk color and the Y color decreases. Similarly, the M-color gear 18m may be phase-controlled so that the distance m is earlier by a time m ', and the C-color gear 18c is rotated by a distance c by a time c' earlier. This phase control can be performed by adjusting the speed of each motor 41.

  When such phase control is performed and the above-described phase relationship is obtained, the result is as shown in FIG. 6, and the relative color shift can be reduced to about ½ or less.

  In order to detect a steady color misregistration amount between colors, a toner pattern (hereinafter referred to as a toner pattern) for measuring the color misregistration amount is formed on the surface of the conveyance belt. The toner pattern has separate patterns with respect to the transfer direction and the scanning direction of the transfer paper, and examples include a toner pattern 501 for detecting a color shift in the transfer direction and a toner pattern 502 for detecting a color shift in the scan direction. (FIG. 5). The toner pattern 501 for detecting color misregistration in the transport direction is the same pattern as the pattern used when performing phase control (FIG. 7).

  Hereinafter, the operation of this embodiment will be described.

  By detecting the replacement of the process cartridge, it is detected that the process cartridge CRG has been replaced or newly loaded, and rotational phase detection is executed. A misregistration detection pattern as shown in FIG. 7 is formed on the transfer material conveyance belt 11 and is read by the image detection sensors 44 provided on both sides of the transfer material conveyance belt 11 to detect the misregistration amount of each color.

  FIG. 7 shows a pattern for detecting a positional deviation amount in the paper transport direction. In this example, a reference color a (hereinafter Bk: black) is detected on one side, and a detection color b (hereinafter Y: yellow, M: magenta, C: cyan). a1 to a19 and b1 to b19 indicate the detection timing of each pattern. The arrows indicate the conveyance direction of the transfer material conveyance belt 11.

  In the misregistration detection pattern, the reference color and the detection color are arranged at the same position with respect to the transport direction, and therefore, it is difficult to be affected by the speed unevenness caused by the transfer material transport belt 11.

  Measure the color relative to the reference color by fixing the rotation phase of the reference color, detecting the rotation phase of the detected color with respect to the reference color by shifting it by a certain predetermined angle, and repeating the above detection. A waveform as shown in FIG. 6 is obtained with respect to the relationship between the rotation phase and the amplitude of the color, and the optimum phase of each color can be easily determined. Based on the determination of the optimum phase, the color shift can be reduced by feeding back to the rotation phase control of the motor 41 (the rotation phase is detected by the phase detection device 42).

  Here, in this embodiment, the above-described rotational phase detection is performed, and at the same time, a steady color shift amount of each color is detected. In the rotation phase detection described above, the rotation phase of the reference color is fixed, and the rotation phase of the measurement color with respect to the reference color is shifted at certain predetermined angles. Then, the steady color misregistration amount for each angle is temporarily stored in the main body. Thereafter, as a method for determining a steady color misregistration amount, correction is performed using only the color misregistration amount data of the rotational phase actually used. As another correction method, there is also a method of averaging color misregistration amount data for each predetermined angle.

  As described above, according to the present embodiment, it is necessary for the positional deviation correction by combining the control for adjusting the rotational phase of each photosensitive drum to a desired state and the control for suppressing the steady color deviation. Control time can be shortened.

  FIG. 8 is a longitudinal sectional view showing a configuration of an “image forming apparatus” according to the second embodiment. Note that the description of the same components as those in the first embodiment is omitted.

  In this embodiment, as shown in FIG. 8, the toner image formed on the surface of the photoconductive drum 56 facing the photoconductive drum 56 which is a plurality of image carriers arranged side by side in the horizontal direction is primarily transferred. An intermediate transfer belt 54 serving as an intermediate transfer member is stretched between a driving roller and a driven roller, and a secondary transfer unit 55 is disposed at a position facing the driven roller with the intermediate transfer belt 54 interposed therebetween.

  In the same manner as in the first embodiment, the toner images formed on the respective photosensitive drums 55 are transferred to the intermediate transfer belt 54 by the action of transfer means 57a, 57b, 57c, 57d (hereinafter simply referred to as “transfer means 57”). The primary transfer.

  On the other hand, the transfer material S fed from the paper feed cassette 50 by the pickup roller 51 is separated and fed one by one by a separation means (not shown), and then sent to the registration roller pair 53 by the conveying roller pair 52. The toner image that is conveyed between the intermediate transfer belt 54 and the secondary transfer unit 55 at a predetermined timing by the pair 53 and is primarily transferred to the intermediate transfer belt 54 by the action of the secondary transfer unit 55 is transferred to the transfer material S. Secondary transferred.

  The transfer material S onto which the toner image has been transferred is fixed by the fixing unit 21 and then conveyed by the discharge roller pair 57 and discharged onto a discharge tray 24 provided on the upper portion of the apparatus main body 200.

  Also in the second embodiment, a pattern for detecting a stationary positional shift and a cyclically shifted positional shift is formed on the intermediate transfer belt, and the positional shift is detected and corrected in the same manner as in the first embodiment. As a result, the same effect as in the first embodiment can be obtained.

FIG. 3 is a longitudinal sectional view showing the main configuration of a color image forming apparatus that is Embodiment 1. FIG. 5 is a diagram illustrating a configuration of a main part of a drive unit / drive transmission unit of a photosensitive drum in Embodiment 1. FIG. 3 is a diagram illustrating a configuration of a main part of a driving unit and a control system of a photosensitive drum in Embodiment 1. The figure which shows the state of the color shift of each color before control in Example 1. FIG. The figure which shows the pattern which detects the color shift in Example 1. FIG. 6 is a diagram illustrating a state in which color misregistration of each color after phase control of the photosensitive drum in Example 1 is eliminated. The figure which shows the pattern for position shift detection in Example 1, and its example of arrangement | positioning. FIG. 5 is a longitudinal sectional view showing the main configuration of a color image forming apparatus that is Embodiment 2.

Explanation of symbols

1 Photosensitive drum (image carrier)
7 Process cartridge 11 Transfer material conveyance belt (conveyance means, endless belt)
42 Phase detector 44 Image detection sensor

Claims (3)

A plurality of image forming units having an optical unit and an image carrier;
A plurality of transfer means for transferring an image on a conveying means for forming an endless belt that sequentially passes through the plurality of image forming sections, or on a recording material placed and conveyed on the conveying means;
A pattern forming unit for forming a dual-purpose pattern for detecting a stationary position shift in the transport direction and a position shift that varies periodically on the transport unit;
Pattern detecting means for detecting a pattern formed by the pattern forming means;
A calculation means for calculating a steady position shift in the transport direction and a position shift that varies periodically based on the detection result of the pattern detection means;
A positional deviation correction means for correcting the positional deviation based on the positional deviation calculated by the computing means;
A color image forming apparatus comprising: The color image forming apparatus according to claim 1.
Comprising an exchange detection means for detecting the exchange of the image carrier;
When the replacement detection unit detects the replacement of the image carrier, the correction unit newly calculates a positional shift using the pattern forming unit, the pattern detection unit, and the calculation unit, and based on the calculated positional shift. A color image forming apparatus that performs correction of misregistration. The color image forming apparatus according to claim 2.
The color image forming apparatus according to claim 1, wherein when the replacement detection unit does not detect the replacement of the image carrier, the correction unit corrects the position shift based on the position shift already calculated by the calculation unit.

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