JP2004098558A - Color image formation apparatus and image formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image formation apparatus which can highly precisely correct a color shift caused by a change of a process speed, and to provide an image formation method. <P>SOLUTION: When the change of the process speed is started (S101), it is checked whether an inclination correction value of a beam scanning line corresponding to the process speed to be changed is recorded (S102). The step moves to a step 105 when the value is recorded. When the value is not recorded, a shift amount of the inclination of the beam scanning line is detected (S103), and the correction value is calculated on the basis of the detected shift amount (S104), when the step moves to the step 105. A stepping motor for changing the position of an f-θ lens is rotated on the basis of the correction value, whereby the inclination of the beam scanning line is corrected (S105). A printing operation is carried out in a correction state (S106). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a color image forming apparatus, such as a color printer, a color copying machine, and a color facsimile apparatus, which has a plurality of image forming units and draws an image with a beam, and particularly relates to the prevention of color misregistration.
[0002]
[Prior art]
An electrophotographic color image forming apparatus has a plurality of image forming units for speeding up, and sequentially transfers images of different colors onto a recording material held on a transport belt or onto an intermediate transfer belt. Various schemes have been proposed.
[0003]
In such a configuration, the rotation speed of an optical scanning device (hereinafter, referred to as a scanner) has been increased in order to further reduce the image forming time. Usually, a rotating polygon mirror (hereinafter, referred to as a polygon mirror) is used in the scanner, and an error in the deflection angle of the polygon mirror causes a change in position on the photoconductor due to the optical path length of the beam. For this reason, it is necessary that each surface of the polygon mirror has a very small inclination error, and that vibration due to high-speed rotation is small.
[0004]
Therefore, in order to obtain a stable rotation of the polygon mirror, the polygon mirror needs to be accurately tilted, and precision machining technology is required. Therefore, the polygon mirror is very expensive. An image forming apparatus equipped with a plurality of such scanners is large and expensive.
[0005]
Therefore, in order to reduce the cost, a configuration in which a common scanner is used for a plurality of image forming units is disclosed in Patent Document 1 below. In Patent Document 1, two beams are deflected and scanned by one polygon mirror. The two beams scan the corresponding photoconductors in opposite directions.
[0006]
Further, among color image forming apparatuses, there is an image forming apparatus that changes a process speed according to a type of a transfer material. In such an image forming apparatus, the process speed is switched, for example, to normal speed for plain paper, 1/2 speed for thick paper, and 1/4 speed for OHT sheets. In the above-mentioned Patent Document 1, when the rotation speed (process speed) of the photoconductor is changed without changing the scanning speed, a color shift occurs in principle.
[0007]
FIG. 12 is a diagram for explaining that when the process speed is changed without changing the scanning speed, a color shift due to the inclination of the beam scanning line occurs.
[0008]
In FIG. 12, reference numerals 1k and 1c denote photosensitive drums which rotate in the illustrated direction. Reference numeral 2ck denotes a laser beam scanner that scans 1k and 1c in opposite directions. Reference numeral 3 denotes a transport belt which rotates in the direction shown. Reference numeral 50 denotes a beam scanning line when the photosensitive drum 1c does not rotate. Reference numeral 52 denotes a C beam scanning line when the photoconductor rotates at a normal process speed. Since the photosensitive drum 1c rotates during scanning, the photosensitive drum 1c tilts by about one dot. Reference numeral 51 denotes a beam scanning line when the photosensitive drum 1c rotates at half the process speed of a normal process. Due to the rotation of the photosensitive drum 1c during scanning, the photosensitive drum 1c is inclined by about 1/2 dot.
[0009]
In the photosensitive drum 1k, the scanning is performed in the reverse direction, so that the photosensitive drum 1k is tilted in the opposite direction to the photosensitive drum 1c.
[0010]
FIG. 11 shows a state in which the scanning lines shown above have been developed and printed on paper. 60C and 60K are obtained by printing straight lines in the beam scanning direction on paper at process speeds of normal speeds of C (cyan) and K (black), respectively. Originally, 60C and 60K are exactly overlapped, but are drawn slightly shifted up and down for convenience of illustration. Arrows indicate the beam scanning direction, which is overwritten for convenience of explanation. In this figure, the inclination is correct, and no color shift occurs. Next, straight lines printed at the half process speed as they are are 61C and 61K. Even if the process speed is changed, the beam scanning speed is not changed, so that the inclination of C and K is shifted as described with reference to FIG. 12, and the center is aligned in the paper transport direction. A shift of 1/2 dot occurs.
[0011]
A method for reducing the occurrence of color misregistration due to such switching of the process speed is disclosed in Patent Document 2 below. In Patent Document 2, for example, when there are two types of process speeds, that is, a normal speed and a half speed, the scanning angle is adjusted so that color misregistration is not conspicuous at any speed. In other words, the configuration is such that the inclination of the beam scanning line is set in advance so that the color shift slightly occurs at each process speed so that the process speed at which the color shift is extremely large does not occur.
[0012]
Another claim of Patent Document 2 also states that "when the process speed is changed to a predetermined process speed, a color image forming position shift caused by the change in the process speed is corrected". I have.
[0013]
[Patent Document 1]
Japanese Patent Publication No. 4-51829
[Patent Document 2]
JP 2001-265090 A
[0014]
[Problems to be solved by the invention]
However, the configuration of the above-described conventional example has the following problems.
[0015]
In the configuration disclosed in Patent Document 2 in which the inclination of the scanning line is adjusted so that the color shift is small at any process speed, although the color shift is reduced, the color shift still occurs in principle. For example, when there is a normal speed and a 1/2 speed, a color shift of about 1/4 dot or more occurs in principle. Further, when the process speed is more than two types, the color shift is further increased. For example, when there are a normal speed, a 1/2 speed, and a 1/4 speed, a color shift of about 3/8 dot or more occurs in principle.
[0016]
Also, another configuration of Patent Literature 2 is configured such that “when the process speed is changed to a predetermined process speed, the color image forming position shift caused by the change in the process speed is corrected”. Although this is an effective configuration, no specific configuration is shown for color misregistration caused by the inclination of the scanning line.
[0017]
The present invention has been made under such circumstances, and an object of the present invention is to provide a color image forming apparatus and an image forming method capable of correcting a color shift caused by a change in process speed with high accuracy.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, a color image forming apparatus is configured as in the following (1) to (10), and an image forming method is configured as in the following (11) and (12).
[0019]
(1) a plurality of image forming units for forming an electrostatic latent image corresponding to image information on a photosensitive member by scanning a beam, and developing the electrostatic latent image;
A process speed changing means for switching to a plurality of process speeds by changing a moving speed of the intermediate transfer body or the transfer material conveying body;
Means for changing the number of writing lines of the beam without changing the rotation speed of the rotating polygon mirror when changing the process speed by the process speed changing means,
In a color image forming apparatus, a beam scanning direction of at least one image forming unit in the plurality of image forming units is different from other image forming units.
Inclination changing means for changing the inclination of the beam scanning line;
When the process speed is changed by the process speed changing unit, the control unit controls to correct the tilt of the beam scanning line by the tilt changing unit,
A color image forming apparatus comprising:
[0020]
(2) In the color image forming apparatus according to (1),
A color image forming apparatus having a configuration in which one rotary polygon mirror deflects and scans beams corresponding to two or more image forming units.
[0021]
(3) In the color image forming apparatus according to (1) or (2),
A deviation detecting unit that detects a deviation amount of the inclination of the beam scanning line,
The color image forming apparatus according to claim 1, wherein said control means detects a deviation amount of the inclination by said deviation detecting means every time the process speed is changed, and performs control to correct the inclination of the beam scanning line based on the detected deviation amount.
[0022]
(4) In the color image forming apparatus according to (1) or (2),
Deviation detecting means for detecting the deviation amount of the inclination of the beam scanning line;
A detection recording unit that detects a deviation amount of the inclination by the deviation detection unit for each process speed, and records a correction value for each process speed;
With
The color image forming apparatus, wherein when the process speed is changed by the process speed changing unit, the control unit changes the inclination of the beam scanning line based on a value recorded in the detection recording unit.
[0023]
(5) In the color image forming apparatus according to (1) or (2),
Recording means for recording a beam scanning line inclination correction value for each process speed, wherein the control means performs beam scanning based on the value recorded in the recording means when the process speed is changed by the process speed changing means. A color image forming apparatus that controls so as to change the inclination of a line.
[0024]
(6) In the color image forming apparatus according to (1) or (2),
When the process speed is changed by the process speed changing unit, the calculation unit calculates a tilt of the beam scanning line such that color shift does not occur,
A color image forming apparatus for controlling, when the process speed is changed by the process speed changing means, a control to change a tilt of a beam scanning line based on a calculation result of the calculation means.
[0025]
(7) In the color image forming apparatus according to any one of (1) to (6),
A color image forming apparatus, wherein at least one of the image forming units does not correct a tilt of a beam scanning line.
[0026]
(8) In the color image forming apparatus according to any one of (1) to (7),
A color image forming apparatus, wherein the inclination changing unit is a unit that moves an optical element in an optical system that scans the beam.
[0027]
(9) In the color image forming apparatus according to (8),
The color image forming apparatus, wherein the optical element is a refractive optical element, a diffractive optical element, a composite optical element combining a refractive optical element and a diffractive optical element, or a reflecting mirror.
[0028]
(10) In the color image forming apparatus according to any one of (1) to (7),
The color image forming apparatus, wherein the inclination changing unit is a unit that moves the photoconductor.
[0029]
(11) An image forming method in a color image forming apparatus including a plurality of image forming units in which directions of beam scanning lines are different from each other,
Step A for changing the process speed;
Correcting the inclination of the beam scanning line when the process speed is changed in step A;
Step C of forming an image in the corrected state of Step B;
An image forming method comprising:
[0030]
(12) The image forming method according to (11),
When the power is turned on for the first time after the photosensitive drum or the scanner unit is replaced in the color image forming apparatus, a step D for measuring the inclination of the beam scanning line and obtaining a correction value used in the step B is provided. Image forming method.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to examples of a color image forming apparatus. The present invention is not limited to the form of the apparatus, but can be implemented in the form of a method, supported by the description of the embodiments.
[0032]
【Example】
(Example 1)
In the first embodiment, an example will be described in which the amount of inclination correction of the beam scanning line is determined by performing color shift detection, and the inclination of the beam scanning line is corrected every time the process speed is changed.
[0033]
FIG. 1 is a diagram illustrating the entire “color image forming apparatus” according to the first embodiment.
[0034]
The present embodiment includes image forming units for four colors, that is, yellow (hereinafter, referred to as Y), magenta (hereinafter, referred to as M), cyan (hereinafter, referred to as C), and black (hereinafter, referred to as K). In FIG. 1, reference numerals 1y, 1m, 1c, and 1k denote photosensitive drums for forming electrostatic latent images, which are Y, M, C, and K photosensitive drums, respectively. Reference numeral 2 denotes a laser scanner that performs exposure according to an image signal and forms an electrostatic latent image on the photosensitive drum 1. Reference numeral 2ym denotes a laser scanner that scans the Y and M photoconductor drums, and 2ck denotes a laser scanner that scans the C and K photoconductor drums, each of which exposes two image forming units. The configuration of the laser scanner will be described later.
[0035]
Reference numeral 3 denotes an endless conveyance belt that also serves as a transfer belt and sequentially conveys a sheet to an image forming unit of each color. Reference numeral 4 denotes a driving roller which is connected to driving means including a motor and gears (not shown) and drives the transport belt 3. Reference numeral 5 denotes a driven roller that rotates according to the movement of the conveyor belt 3 and applies a constant tension to the conveyor belt 3.
[0036]
Hereinafter, the operation of the present embodiment will be described.
[0037]
Data to be printed is sent from the host computer or the like to the color image forming apparatus of the present embodiment, preparation for image formation according to the printing method is completed, and when printing is possible, paper is supplied from a paper cassette (not shown). The sheet arrives at the transport belt 3, and the paper is sequentially transported by the transport belt 3 to the image forming units of each color. Image signals of each color are sent to each laser scanner 2 (2ck, 2ym) in synchronism with the sheet conveyance by the conveyance belt 3, and an electrostatic latent image is formed on the photosensitive drum 1, and toner is formed by a developing unit (not shown). Is developed and transferred onto a sheet at a transfer section. In FIG. 1, images are sequentially formed in the order of Y, M, C, and K. Thereafter, the sheet is separated from the transport belt, the toner image is fixed on the sheet by heat in a fixing device (not shown), and the sheet is discharged out of the color image forming apparatus.
[0038]
FIG. 2 shows a schematic perspective view of the scanner optical system. The same components as those in FIG. 1 are denoted by the same reference numerals. In the description, the scanner 2ck will be described, but the scanner 2ym has the same configuration.
[0039]
201c and 201k are laser beam light sources (usually laser diodes) corresponding to the C image forming unit and the K image forming unit, respectively.
[0040]
The laser beam emitted from the laser 201k is collimated by the collimator lens 205k and then scanned by the polygon mirror 203ck. The scanned beam is corrected in scanning speed by the f-θ lens 206k, is reflected by the return mirror 202k, and finally forms a latent image corresponding to an image signal on the photoconductor 1k. The image clock is synchronized with a horizontal synchronization signal (hereinafter, referred to as BD signal) (not shown) output from a sensor (hereinafter, referred to as BD sensor) 204k which is a beam detection means for detecting the timing of writing an image signal on the photoconductor k. (Hereinafter referred to as BD synchronization). After synchronizing the image clock with the BD, a certain time is delayed and writing of the image signal is started. Further, using the BD signal, rotation speed control is performed so that the motor connected to the polygon mirror 203ck rotates at a specified rotation speed.
[0041]
The laser beam emitted from the laser 201c is similarly deflected and scanned by the polygon mirror 203ck, and forms a latent image corresponding to the image signal on the photoconductor 1c. The BD sensor corresponding to the laser 201c is 204c.
[0042]
As can be seen from FIG. 2, the scanning direction on the photoconductor is reversed between C and K. For this reason, as described in the conventional example, unless the inclination angle of the beam scanning line is changed every time the process speed is changed, color shift occurs at both ends of the scanning line.
[0043]
Next, a configuration for correcting the inclination of the beam scanning line will be described. FIG. 3 is a diagram illustrating a configuration of a drive unit that corrects the position of an optical element (f-θ lens) in order to correct the inclination of a beam scanning line. The inclination correction of the beam scanning line in the K image forming unit will be described with reference to FIG. The correction of the inclination of the beam scanning line in the Y, M, and C image forming units has the same configuration and operation. In this embodiment, the inclination is corrected in all the image forming units Y, M, C, and K. However, the scanning direction is set to one direction, for example, the direction of the Y and C scanning lines. Alternatively, the inclination of the M and K scanning lines in the other scanning direction may be corrected.
[0044]
In FIG. 3, reference numeral 801 denotes a stepping motor; 802, a lead screw-shaped motor shaft; 803, a head for pressing the f-θ lens 206k; 804, a stay of the head; 805, a pole for guaranteeing the straight movement of the stay; A spring 807 for holding the f-θ lens 206k is a rotation fulcrum when the f-θ lens 206k moves.
[0045]
Hereinafter, the operation of the driving unit will be described.
[0046]
The stay 804 is pushed by the lead screw 802 by rotating the stepping motor 801 at a predetermined number of revolutions or a predetermined angle, and the stay 804 moves up and down along the pole 05, and f-θ is set by the head 803 attached to the stay 804. The lens 206k is pushed, and the f-θ lens 206k rotates around the rotation fulcrum 807. At this time, the f-θ lens 206k rotates while being held by the spring 806 and the head 803, and is fixed by the spring stress at the position where the movement of the head 803 is stopped. By moving the f-θ lens 06k about the illustrated rotation fulcrum 807, the image position in the image forming unit can be adjusted about the rotation fulcrum 807 as shown by 901 in FIG. For this reason, by changing the position of the f-θ lens 206k so as to correct the position shift amount, optical scanning is performed at a desired position, and color shift due to image inclination is corrected.
[0047]
FIG. 4 is a diagram illustrating a change in the inclination of the scanning line when the f-θ lens 206k illustrated in FIG. 3 is moved. When the f-θ lens 206k is at the position indicated by 811 in FIG. 3, the inclination of the beam scanning line becomes the angle indicated by 901 in FIG. When the f-θ lens 206k is at the position shown by 812 in FIG. 3, the inclination of the beam scanning line becomes the angle shown by 902 in FIG. When the f-θ lens 206k is at the position shown by 813 in FIG. 3, the inclination of the beam scanning line becomes the angle shown by 903 in FIG. By setting the position of the f-θ lens 206k to an appropriate position, it is possible to correct the inclination of the beam scanning line so that color shift does not occur.
[0048]
Next, a method for detecting the inclination of the beam scanning line will be described.
[0049]
A pattern for detecting the inclination of the beam scanning line is formed on the conveyor belt 3 and read by a pair of optical sensors 10A and 10B provided on both sides of the conveyor belt 3 to detect the inclination of the beam scanning line of each color. I do.
[0050]
FIG. 5 is a diagram illustrating a pattern for detecting the inclination of the beam scanning line. In the figure, 20Y, 20M, 20C and 20K are linear patterns extending in the beam scanning directions of Y, M, C and K, respectively. Reference numerals 10A and 10B denote optical sensors for detecting displacement, which are referred to as registration detection sensors. Output signals of the registration detection sensors 10A and 10B are input to a controller unit 30 including a CPU and the like.
[0051]
The transport belt 3 moves in the transport belt moving direction shown in the figure. With the movement of the transport belt, the registration detection sensors 10A and 10B sequentially detect the linear patterns 20Y, 20M, 20C and 20K and output signals. The controller unit measures the intervals T_YMA, T_MCA, T_CKA, T_YMB, T_MCB, and T_CKB of the respective linear patterns from the signals output from the registration detection sensors 10A and 10B. In the figure, T_YMA represents the interval between the linear patterns 20Y and 20M in the registration detection sensor 10A. Similarly, T_MCA is the interval between 20M and 20C in the registration detection sensor 10A, T_CKA is the interval between 20C and 20K in the registration detection sensor 10A, T_YMB is the interval between 20Y and 20M in the registration detection sensor 10B, and T_MCB is the registration detection sensor 10B. Represents the interval between 20M and 20C, and T_CKB represents the interval between 20C and 20K at the registration detection sensor 10B.
[0052]
The controller unit 30 calculates the rotation amount (or the number of steps) of the stepping motor such that T_CKA and T_CKB match from the relationship between the rotation amount of the stepping motor 801 and the inclination of the beam scanning line. Similarly, the amount of rotation of the stepping motor that moves the f-θ lens of the C image forming unit so that T_MCA and T_MCB match, and the f-θ lens of the C image forming unit that matches T_YMA and T_YMB move Calculate the rotation amount of the stepping motor. These rotation amounts become the correction amounts for the inclination correction of the beam scanning line.
[0053]
In addition, the writing position of the Y, M, C, and K in the moving direction of the conveyor belt is adjusted by the image data and the phase of the polygon mirror so that T_YMA, T_MCA, and T_CKA match.
[0054]
Next, a method of changing the process speed will be described.
[0055]
The present image forming apparatus is configured such that when printing on thick paper or an OHT sheet, the process speed can be switched to improve fixability. Normal speed is set for plain paper, 1/2 speed for thick paper, and 1/4 speed for OHT sheets.
[0056]
At 1/2 speed, the photosensitive drums 1y, 1m, 1c, 1k and the conveyor belt 3 rotate at 1/2 speed of the normal speed. By fixing the fixing device at half speed, the fixing property is improved. Also, the rotation speed of the polygon mirror is not changed. A normal image can be formed by repeatedly outputting one line of image data and not outputting the next one line. This means that the number of writing lines of the beam has been changed.
[0057]
At 1/4 speed, the photosensitive drums 1y, 1m, 1c, 1k and the conveyor belt 3 rotate at 1/4 the normal speed. The fixing device also has a 1/4 speed to improve the fixing property. Also, the rotation speed of the polygon mirror is not changed. By repeating outputting one line of image data and not outputting the next three lines, a normal image can be formed.
[0058]
The operation of this embodiment will be described with reference to FIGS.
[0059]
FIG. 6 is a block diagram illustrating a main configuration of the first embodiment. Reference numeral 30 denotes a control unit also shown in FIG. 1, which controls the printer unit. Reference numeral 31 denotes a CPU in the control unit 30, which performs calculations for controlling the printer unit. Reference numeral 32 denotes a non-volatile memory, which is used by the CPU 31 to record the inclination correction amount and other information regarding the printer unit. 10A and 10B are registration detection sensors. Reference numeral 801 denotes a stepping motor whose rotation is controlled by the CPU 31 via a motor driver.
[0060]
FIG. 7 is a flowchart illustrating processing when the process speed is changed in the present embodiment. When a process speed change is started in step 101 (in the figure, denoted as S101, the same applies hereinafter), first, it is checked whether or not the tilt correction value of the beam scanning line corresponding to the process speed to be changed is recorded in the nonvolatile memory 32. The inclination correction value is a rotation position of the stepping motor 801 such that color shift due to inclination of the beam scanning line does not occur at a corresponding process speed. If the correction value has not been recorded, in step 103, the amount of color misregistration caused by the inclination of the beam scanning line is detected as described above. In step 104, a correction value that does not cause color shift is calculated from the detected color shift amount, and is recorded in the nonvolatile memory 32 as a corresponding process speed correction value. If the correction value has been recorded, or after recording the correction value in step 104, the stepping motor 801 is rotated based on the correction value recorded in step 105 so as to eliminate the color shift. As described above, the color shift caused by the beam scanning line inclination is corrected. Then, a necessary printing operation is performed (step 106), and the process ends.
[0061]
Separately from this sequence, when the power is turned on for the first time in the present color image forming apparatus, or when the power is turned on for the first time after the photosensitive drum 1 or the scanner unit 2 is replaced, the inclination deviation amount of the beam scanning line is detected. May be. Alternatively, initially, only the correction value at the normal speed may be determined, and the correction values for other process speeds may be made before printing for the first time at that process speed.
[0062]
In the present embodiment, a configuration is described in which the inclination correction value is recorded for each process speed, and the inclination is corrected based on the recorded value each time the process speed is changed. Alternatively, each time the process speed is changed, the amount of color misregistration may be detected, and the inclination may be corrected based on the result.
[0063]
Further, in the present embodiment, the configuration has been described in which the position of the f-θ lens, which is a refractive optical element, is corrected for correcting the inclination of the beam scanning line. Alternatively, tilt correction may be performed by correcting the position of a diffractive optical element, a composite optical element combining a refractive optical element and a diffractive optical element, or the position of a reflecting mirror. Alternatively, the inclination may be corrected by moving the photosensitive drum.
[0064]
Further, in this embodiment, a configuration in which one polygon mirror scans beams corresponding to a plurality of image forming units has been described. In addition, the present invention is effective even in a configuration in which one polygon mirror scans a beam corresponding to one image forming unit as long as there is an image forming unit whose scanning direction is opposite to that of another image forming unit. is there.
[0065]
With the above configuration, color shift due to process speed can be reduced. In addition, since the amount of color misregistration can be measured, the amount of color misregistration can be reduced even when the tilt amount of the beam scanning line is changed due to replacement of the optical system or the photosensitive drum, and high-quality images can be obtained. Can output.
[0066]
(Example 2)
In the “color image forming apparatus” according to the second embodiment, measured values are measured in advance and recorded in a non-volatile memory, and each time the process speed is changed, the beam scanning line is determined based on the recorded values. An example of correcting the inclination will be described. The overall configuration of the present embodiment is the same as that of the first embodiment.
[0067]
FIG. 8 is a block diagram illustrating a main configuration of the present embodiment. Except for 35 and 36, it is the same as FIG. 6 described in the first embodiment.
[0068]
An interface 36 of the color image forming apparatus is connected to an input terminal 35 such as a personal computer (PC). As the interface, a general-purpose interface such as a printer port or a network port which is usually mounted on a printer, or a dedicated interface for connecting a jig or the like is used. The input terminal 35 can communicate with the control unit 30 via the interface 36, and can record the beam scanning line inclination correction value in the nonvolatile memory.
[0069]
First, after assembling in a factory or repairing in the market, a test chart is printed for each process speed to check the inclination correction value of each process speed. The test chart prints each of Y, M, C, and K so that the value to be set as the correction value can be visually recognized. Alternatively, the test chart may be read by a dedicated device to determine a tilt correction value.
[0070]
The result is input from the input terminal 35, and the correction value is written into the nonvolatile memory 32 via the CPU 31 in the control unit 30 for each process speed.
[0071]
FIG. 9 is a flowchart showing the processing when changing the process speed in the present embodiment. In step 201, the process speed change is started. Next, the inclination correction value of the beam scanning line corresponding to the process speed to be changed, which is to be changed, is read from the nonvolatile memory 32, and the stepping motor is rotated based on the correction value so as to eliminate the color shift (step 202). ). As described above, the color shift caused by the beam scanning line inclination is corrected. Then, a necessary printing operation is performed (step 203), and the process ends.
[0072]
With the above configuration, color shift due to process speed can be reduced, and a high-quality image can be output. Further, since a sensor for measuring the amount of color misregistration is not required, the configuration can be made at low cost.
[0073]
(Example 3)
In the “color image forming apparatus” according to the third embodiment, an example will be described in which the correction amount is predicted from the process speed to correct the beam scanning line inclination angle.
[0074]
In the present embodiment, the overall configuration is the same as in the first embodiment.
[0075]
In the case of the configuration of the drive unit for correcting the position of the optical element shown in FIG. 3, the rotation amount of the stepping motor 801 and the change amount of the inclination of the beam scanning line are almost proportional.
[0076]
FIG. 10 is a diagram for explaining the amount of change in inclination of the beam scanning line. Reference numeral 101 denotes a scanning line before changing the inclination (or a straight line in the beam scanning direction printed on paper), and reference numeral 102 denotes a scanning line after changing the inclination (or a straight line in the beam scanning direction printed on paper). Reference numeral 103 denotes a prescribed width, for example, using the maximum paper size of the printer unit. At this time, the length of 104 is called the amount of change in the inclination of the beam scanning line. In FIG. 3, the amount of rotation of the stepping motor 801 and the amount of vertical movement of the head, that is, the amount of vertical movement of the right end of the f-θ lens 206k is proportional, and the amount of vertical movement of the right end of the f-θ lens 206k and the beam scanning line Is proportional to the slope change amount. Therefore, the rotation amount of the stepping motor 801 is proportional to the inclination change amount of the beam scanning line.
[0077]
Therefore, the amount of change Δ in inclination of the beam scanning line when the stepping motor 801 is rotated by one step is determined in advance. The calculation method may be a design value, or the measurement may be performed for each scanner unit, and the result may be recorded in a nonvolatile memory or the like.
[0078]
As shown above, if the inclinations of the C and K beam scanning lines match at the normal speed (there is no color shift due to the inclination), if the process speed is reduced to ず without performing the inclination correction, The two ends of the line are shifted by ド ッ ト dot.
[0079]
FIG. 11 illustrates this. 60C and 60K are obtained by printing straight lines in the beam scanning direction on paper at process speeds of normal speeds of C and K, respectively. Originally, 60C and 60K are exactly overlapped, but are drawn slightly shifted up and down for convenience of illustration. Arrows indicate the beam scanning direction, which is overwritten for convenience of explanation. In this figure, the inclination is correct, and no color shift occurs. Next, the straight lines printed at the process speed of 1/2 without performing the inclination correction are 61C and 61K. Even if the process speed changes, the beam scanning speed does not change, so that the inclination of C and K is shifted, and when the position is adjusted in the paper transport direction at the center, a shift of 1/2 dot occurs at both ends of the straight line. That is, the stepping motor 801 may be rotated so as to correct the inclination of 1/2 dot. To be precise, although the shift amount is reduced by the time from the end of the scanning line on the photosensitive member 1 to the leading end of the next scanning line, it is assumed that the shift amount is 1/2 dot for the sake of simplicity. To calculate accurately, the amount of deviation may be calculated in consideration of the time from the end of the scanning line on the photoconductor 1 to the leading end of the next scanning line.
[0080]
Considering the case of 600 dpi, one dot is about 42.3 μm, and the rotation amount (the number of steps) of the stepping motor is given by the following equation.
Δ / 42.3 μm / 2
The rotation direction of the motor 801 is set such that both C and K move in directions indicated by arrows 62C and 62K in FIG.
[0081]
By performing such an operation when the process speed is changed from the normal speed to a half speed, it is possible to eliminate a color shift caused by the inclination of the beam scanning line. When the process speed is changed from the half speed to the normal speed, the rotation direction of the stepping motor may be reversed and the same rotation may be performed.
[0082]
Further, it is not always necessary to move the f-θ lens 206 for both C and K. For example, even in a configuration in which only the f-θ lens 206k for K is moved, the inclination can be corrected by changing the amount of movement. is there.
[0083]
If the inclination of the f-θ lens 206 is increased, the bending of the beam scanning line, the magnification, and the spot shape of the laser beam are adversely affected. Therefore, the operation amount of the f-θ lens 206 needs to be limited to a range where image quality can be guaranteed. From the calculation result of the correction value, when the operation amount of the f-θ lens 206 exceeds the guaranteed range, it is necessary to make the correction amount fall within the guaranteed range.
[0084]
With the above configuration, the inclination can be corrected by calculation, so that a nonvolatile memory is not required, and the inclination can be corrected at low cost. Alternatively, since it is not necessary to measure the amount of deviation of the inclination, the calibration time of the printer unit can be shortened.
[0085]
【The invention's effect】
As described above, according to the present invention, a color shift caused by a change in process speed can be corrected with high accuracy.
[0086]
More specifically, according to the first, second, and eleventh aspects of the present invention, the beam scanning direction is reversed by the photoconductor, so that when the process speed changes, color misregistration due to the beam scanning line inclination occurs. Even if the process speed is changed, color shift does not occur, and a high-quality image can be obtained.
[0087]
According to the third and fourth aspects of the present invention, since the inclination can be corrected based on the color misregistration detection result, even when the inclination is misaligned due to an environment such as a temperature or replacement of a replacement part, high quality without color misregistration is obtained. Can obtain a perfect image.
[0088]
According to the fifth aspect of the present invention, since there is data in which an inclination correction value is recorded for each process speed, there is no need for a color misregistration detection function, and the configuration can be made at low cost.
[0089]
According to the sixth aspect of the present invention, the inclination correction value can be obtained based on the calculation, so that the configuration can be made inexpensively.
[0090]
According to the seventh aspect of the present invention, at least one image forming unit does not have a tilt correction function, and thus can be configured at a low cost.
[0091]
According to the eighth to tenth aspects of the present invention, the inclination can be corrected by moving the optical system and the photosensitive member, so that a high-quality image with little color shift can be obtained.
[0092]
According to the twelfth aspect, even when the photosensitive drum or the scanner unit is replaced, a high-quality image with little color shift can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an entire color image forming apparatus according to a first embodiment.
FIG. 2 is a perspective view showing a configuration of a scanner optical system.
FIG. 3 is a diagram illustrating a configuration of a drive unit that performs position correction of an optical element.
FIG. 4 is a diagram for explaining a scanning line inclination change amount when an optical element is driven.
FIG. 5 is a view for explaining a beam scanning line inclination detection pattern;
FIG. 6 is a block diagram showing a configuration of a main part of the first embodiment;
FIG. 7 is a flowchart showing processing when changing a process speed in the first embodiment.
FIG. 8 is a block diagram illustrating a configuration of a main part of a second embodiment.
FIG. 9 is a flowchart illustrating processing when a process speed is changed in the second embodiment.
FIG. 10 is a view for explaining an amount of change in inclination of a beam scanning line in the third embodiment.
FIG. 11 is a view for explaining a scanning line inclination change amount when the process speed is set to a half speed.
FIG. 12 is a view for explaining a color shift caused by a tilt of a beam scanning line.
[Explanation of symbols]
1y, 1m, 1c, 1k photoreceptor
2ck, 2ym laser scanner optical system
10A, 10B Registration detection sensor
30 Control unit
31 CPU

Claims (12)

Forming a plurality of electrostatic latent images corresponding to the image information on the photosensitive member by scanning the beam, and developing the electrostatic latent images;
A process speed changing means for switching to a plurality of process speeds by changing a moving speed of the intermediate transfer body or the transfer material conveying body;
Means for changing the number of writing lines of the beam without changing the rotation speed of the rotating polygon mirror when changing the process speed by the process speed changing means,
In a color image forming apparatus, a beam scanning direction of at least one image forming unit in the plurality of image forming units is different from other image forming units.
Inclination changing means for changing the inclination of the beam scanning line;
When the process speed is changed by the process speed changing unit, the control unit controls to correct the tilt of the beam scanning line by the tilt changing unit,
A color image forming apparatus comprising: The color image forming apparatus according to claim 1,
A color image forming apparatus, wherein one rotary polygon mirror deflects and scans beams corresponding to two or more image forming units. The color image forming apparatus according to claim 1, wherein
A deviation detecting unit that detects a deviation amount of the inclination of the beam scanning line,
The color control method, wherein the control means detects a deviation amount of the inclination by the deviation detection means each time the process speed is changed, and performs control so as to correct the inclination of the beam scanning line based on the detected deviation amount. Image forming device. The color image forming apparatus according to claim 1, wherein
Deviation detecting means for detecting the deviation amount of the inclination of the beam scanning line;
In advance, a detection recording unit that detects a deviation amount of the inclination by the deviation detection unit for each process speed, and records a correction value for each process speed,
With
The color image, wherein the control means controls to change the inclination of the beam scanning line based on a value recorded in the detection recording means when the process speed is changed by the process speed changing means. Forming equipment. The color image forming apparatus according to claim 1, wherein
Recording means for recording a beam scanning line inclination correction value for each process speed, wherein the control means performs beam scanning based on the value recorded in the recording means when the process speed is changed by the process speed changing means. A color image forming apparatus which controls so as to change the inclination of a line. The color image forming apparatus according to claim 1, wherein
When the process speed is changed by the process speed changing unit, the calculation unit calculates a tilt of the beam scanning line such that color shift does not occur,
The color image forming apparatus according to claim 1, wherein when the process speed is changed by the process speed changing unit, the control unit changes the inclination of the beam scanning line based on a calculation result of the calculation unit. The color image forming apparatus according to any one of claims 1 to 6,
A color image forming apparatus, wherein at least one of the image forming units does not correct a tilt of a beam scanning line. The color image forming apparatus according to any one of claims 1 to 7,
A color image forming apparatus, wherein the inclination changing means is means for moving an optical element in an optical system for scanning the beam. The color image forming apparatus according to claim 8,
The color image forming apparatus, wherein the optical element is a refractive optical element, a diffractive optical element, a composite optical element combining a refractive optical element and a diffractive optical element, or a reflecting mirror. The color image forming apparatus according to any one of claims 1 to 7,
The color image forming apparatus according to claim 1, wherein the inclination changing unit is a unit that moves the photoconductor. An image forming method in a color image forming apparatus including a plurality of image forming units in which directions of beam scanning lines are different from each other,
Step A for changing the process speed;
Correcting the inclination of the beam scanning line when the process speed is changed in step A;
Step C of forming an image in the corrected state of Step B;
An image forming method comprising: The image forming method according to claim 11, wherein
When the power is turned on for the first time after the photosensitive drum or the scanner unit is replaced in the color image forming apparatus, a step D for measuring the inclination of the beam scanning line and obtaining a correction value used in the step B is provided. An image forming method.

Images