JP2003266787A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct position shift of an image of each color with high accuracy. <P>SOLUTION: This color image forming apparatus forms images of a plurality of colors by a laser beam deflected by a deflector. Measurement pattern images of the colors are formed on a transferring belt and the positions thereof in a sub-scanning direction are detected by a sensor 27, and then an amount of shift of each of the images from a reference position is calculated by a counter 29 and a comparing/calculating circuit 30. The shift is corrected by adjusting an image-writing timing and displacing the projection position of the beam in the sub-scanning direction by moving the optical axis of the laser beam. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color copying machine,
The present invention relates to a color image forming apparatus such as a color printer, and more particularly to a technique for preventing the occurrence of color misregistration when forming a color image in these color image forming apparatuses.

[0002]

2. Description of the Related Art There are various types of conventional color image forming apparatuses, and among them, there is an electrophotographic color image forming apparatus using a semiconductor laser (laser light emitting element) as a light source. In this type of color image forming apparatus, a laser beam modulated according to a color image signal obtained by reading and scanning an original is applied to a photosensitive drum or a photosensitive belt to form an electrostatic latent image, and The electrostatic latent image is developed with toner of a corresponding color and then transferred to a transfer paper. In addition, there is a type of color copying machine that uses an electrophotographic system, in which a color image is formed by an independent image forming unit for each color.
Generally, it is called a 4-tandem engine because it has four image forming units corresponding to each color of black, yellow, magenta, and cyan.

In such a color image forming apparatus, images of four colors are formed on one recording sheet (for example, transfer paper) in an overlapping manner, but at this time, the positional deviation of the images of each color, that is, the color deviation is a problem. Becomes The cause of this positional shift (color shift) is, for example, in the case of a digital color copying machine,
There are deviations in the mounting position and peripheral speed of each photoconductor, deviations in the exposure position with respect to the photoconductors, and deviations in the linear velocity of the endless transfer belt that conveys the transfer paper. To reduce this misalignment,
Conventionally, this has been dealt with by increasing the precision of each component and the precision of mounting each component, but in this case, there is a problem that the component cost and the assembly cost are high and the productivity is poor. In addition, there is also a problem that readjustment is necessary because there is a change with time of each component and a variation due to component replacement. As a solution to such a problem, for example, Japanese Patent Publication No. 7-19083 and Japanese Patent No. 2765626 disclose a measurement pattern image for each color and detect it to shift the image formation timing of each color. An image forming apparatus is disclosed that includes a unit that measures the amount and corrects the writing timing of the image of each color based on the amount of deviation.

[0004]

However, in these devices, the writing for each color is performed by using a deflector such as a polygon mirror, and these deflectors are used before the start of writing an image for each color. It is necessary to control the rotation phase of the deflector so that the deflector can be accurately rotated at a constant rotation during image formation. Therefore, when the deviation of the image of each color is corrected only at the writing start timing, it can be corrected only at the timing of an integral multiple of the time required for one scanning. Then, in order to perform correction with a finer precision than the time required for one scan, it is necessary to adjust the rotation phase of the deflector. In order to adjust the rotation phase of the deflector, it is necessary to adjust the rotation while temporarily performing acceleration / deceleration, but since the deflector is rotating at high speed, it takes time to adjust the phase. There was a problem that it was technically difficult and very expensive.

Although the above publication does not disclose in detail the correction with a precision smaller than the time required for one scanning,
For this reason, there is a problem in that the correction cannot be performed with a precision smaller than the time required for one scan, and a shift corresponding to that amount occurs. In addition, in order to reduce the cost of the device, 1
In an image forming apparatus in which a laser beam that forms an image of each color is deflected by only one deflector, the writing phase of each color is always the same, so phase adjustment cannot be performed and the positional deviation of each color is written out. There is also a problem in that the correction can be performed only in the unit of time required for one scan when the correction is performed only by itself. The present invention has been made in view of the above problems, and in a color image forming apparatus that writes an image of each color by a laser beam, it is possible to correct the positional deviation of the image of each color in the sub-scanning direction with higher accuracy. The aim is to improve reliability and image quality.

[0006]

In order to achieve the above object, the present invention forms a latent image on a photoconductor by a laser beam which is emitted from a laser light emitting element and is deflected by a deflector through a coupling optical system. Writing means for writing, and a plurality of developing means for developing the latent image to form a visible image of each color,
A color image forming apparatus for forming a color image by superimposing on the recording medium the visualized images of the respective colors developed by the plurality of developing means, which conveys the recording medium onto which the visualized image is transferred. A pattern image forming means for forming a measurement pattern image of each color on the conveying means via a photoconductor by a laser beam from a laser light emitting element, a detecting means for detecting the measurement pattern image, and the detecting means Of the measured pattern images of the respective colors, the distance between the reference one measured pattern image and the measured pattern image of the other color is measured to calculate the deviation amount of the measured pattern images of the other colors in the sub-scanning direction. And an optical axis moving means for displacing the optical axis of the laser beam from the laser light emitting element to displace the beam irradiation position on the photoconductor in the sub-scanning direction. Based on the shift amount for each color of the measurement pattern image obtained by the calculating means, the optical axis moving means is driven to displace the beam irradiation position on the photoconductor in the sub-scanning direction to shift the image position of each color. There is provided a color image forming apparatus provided with an image position deviation correcting means for correcting the above.

In the color image forming apparatus, an LD unit in which a laser light emitting element and a coupling optical system are held by a holding member is provided, and the optical axis is exposed to an optical housing holding the LD unit. The beam irradiation position on the body is attached so as to be movable in the direction of displacement in the sub-scanning direction, and the optical axis moving means displaces the optical axis by moving the LD unit to sub-scan the beam irradiation position on the photoconductor. It may be a means for displacing in the direction. In the color image forming apparatus, the LD unit is rotatably attached to the optical housing, and the rotation center axis of the LD unit is in the main scanning direction with respect to the optical axis of the laser beam emitted by the laser light emitting element. It is better to shift them. The center axis of rotation of the LD unit may be made to substantially coincide with the optical axis of the laser beam emitted by the laser light emitting element on the deflecting surface of the deflector.

Further, a pattern image forming means for forming a measurement pattern image of each color on a conveying means via a photoconductor by a laser beam from a laser emitting element, a detecting means for detecting the measurement pattern image, and the detecting means. By measuring the interval between one reference measurement pattern image of each color of the measurement pattern images detected and the measurement pattern image of another color, the deviation amount of the measurement pattern images of the other colors in the sub-scanning direction can be determined. A laser light emitting element and a coupling optical system are held by a holding member to form an LD unit, and the LD unit is rotatably attached to an optical housing having an aperture for shaping the shape of a laser beam. Along with the mounting, a drive means for rotating the LD unit is provided, and the LD unit is connected to the rotation center axis. The optical axis of the laser beam emitted by the laser light emitting element is shifted in the main scanning direction, and the driving means is driven based on the deviation amount for each color of the measurement pattern image obtained by the arithmetic means. The color image forming apparatus may be configured by providing a beam position adjusting unit for adjusting the position in the sub-scanning direction for each laser beam of each color with which the laser light emitting element is moved by rotating the LD unit to irradiate the photoconductor. . In the color image forming apparatus, the image writing timing by the laser beam corresponding to each color according to the deviation amount in the sub-scanning direction between one reference measurement pattern image obtained by the calculation means and the measurement pattern image of another color It is advisable to provide an adjusting means for adjusting.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing the configuration of a main part of a writing means included in a color image forming apparatus according to the present invention, and FIG. 2 is an overall configuration diagram showing a digital color copying machine which is also an example of the color image forming apparatus. . A digital color copying machine which is a color image forming apparatus shown in FIG. 2 has a laser light emitting element (hereinafter referred to as LD) 6 shown in FIG.
By the laser beam which is irradiated from 2 and is deflected by the deflector 50 through the collimator lens 63, the aperture 53 and the cylinder lens 52 which are coupling optical systems,
Photoreceptor drums 14C, 14M, 14Y, 14 shown in FIG.
Laser light emitting devices 12C, 12M, 12 constituting writing means for writing latent images for cyan (C), magenta (M), yellow (Y) and black (BK) colors on BK.
Y, 12BK and a developing device 16 which is a plurality of developing means for developing each latent image and forming a visible image (toner image) of each color.
C, 16M, 16Y, and 16BK, and a transfer belt 21 that serves as a transporting unit that transports a transfer sheet P that is a recording medium that transfers the above-mentioned visible image.
This is a color image forming apparatus for forming a color image by superposing on the transfer paper P the visible images of the respective colors developed by 16Y and 16BK. In addition, the plurality of photosensitive drums 14C, 1
4M, 14Y, 14BK, and the laser light emitting device 12C,
12M, 12Y, 12BK and developing devices 16C, 16
M, 16Y, and 16BK are 1 for specific colors among them.
Except when referring to one, the photosensitive drum 1 is generically referred to below
4, laser light emitting device 12 and developing device 16.

This digital color copying machine has a scanner section 1 for reading a document and an image processing section 2 for electrically processing an image signal output as a digital signal from the scanner section 1. Based on the image data of each color output from the image processing unit 2, the image forming unit 3
An image is formed on the transfer paper P which is a recording medium. The scanner unit 1 has a lamp 5 which is, for example, a fluorescent lamp for scanning and illuminating an original on the original table 4. And that lamp 5
The reflected light from the original illuminated by the mirrors 6, 7,
It is reflected by 8 and enters the imaging lens 9. The reflected light is reflected by the imaging lens 9 to the dichroic prism 10
Is imaged on, for example, red R, green G, and blue B light of three kinds of wavelengths are separated, and for each wavelength of light, the red CCD 11R, the green CCD 11G, and the blue C
It is incident on each light receiver of the CD 11B. Each CCD 11R, 1
1G and 11B convert incident light into a digital signal and output it, and the output is subjected to necessary signal processing in the image processing unit 2, and image data of each color, for example, black (hereinafter referred to as B
K (abbreviated as K), yellow (abbreviated as Y), magenta (abbreviated as M), and cyan (abbreviated as C) are converted into image data for image formation.

Although FIG. 2 shows an example of forming four color images of BK, Y, M and C, it is also possible to form a color image with only three colors. In that case, the number of recording devices can be reduced by one as compared with the example shown in FIG. The signal from the image processing unit 2 is input to the image forming unit 3 and sent to the laser light emitting devices 12BK, 12Y, 12M, 12C that emit laser beams corresponding to the respective colors. In the image forming unit 3, four sets of recording devices 13C, 13M, 13Y, and 13BK are arranged in a line in this image forming apparatus, and each of them is composed of the same member. Therefore, the cyan recording device 13C will be described as a representative of those, and description of other colors will be omitted. It should be noted that, hereinafter, except for the case of referring to the recording device for a specific color, the recording device is generically referred to as the recording device 13. The recording device 13C includes a laser beam emitting device 12C that constitutes a writing unit and a photoconductor drum 14C. Around the photosensitive drum 14C, a charging charger 15C, a developing device 16C, a transfer charger 17C, etc. are arranged. A latent image of a cyan image is formed on the surface of the photoconductor drum 14C uniformly charged by the charging charger 15C by exposure by the laser light emitting device 12C, and the latent image is developed by the developing device 16C. It becomes a visible image (toner image).

On the other hand, the transfer paper P is supplied from one of the two paper supply cassettes 19 as a paper supply unit by the paper supply roller 18 and is sent to the transfer belt 21 by the registration rollers 20 at the same timing. The transfer paper P is electrostatically attracted to the transfer belt 21, and is accurately conveyed at the speed of the transfer belt 21. The transfer paper P is formed on the photoconductor drum 14 on which a visible image corresponding to each color is formed.
The images are sequentially sent to BK, 14Y, 14M, and 14C, where they are transferred by the transfer charger 17 so that the visible images (toner images) of different colors on the photoconductor drums are sequentially superimposed. After that, the transfer paper P is sent to the fixing roller 22 to fix the formed visible image, and is discharged by the paper discharge roller 23. As shown in FIG. 3, the transfer belt 21 is supported by a belt drive roller 24 and a driven roller 25, moves in the direction of arrow A, and conveys the transfer paper electrostatically adsorbed thereto. Further, one reflection type sensor 27 which is a detecting means for detecting a measurement pattern image of each color described later is provided so as to face the outer surface of the transfer belt 21 on the left side in FIG. Further, the cleaning unit 26 for removing the detected measurement pattern image from the transfer belt 21.
Is provided on the right side in FIG. As shown in FIG. 3, the cleaning unit 26 and the sensor 27 are located on the conveyance path of the transfer belt 21 and separated from each other on substantially opposite sides. By doing so, the cleaning unit 2
It is possible to prevent the fine powder toner scattered during the operation of 6 from adhering to the detection surface of the sensor 27 and lowering the detection sensitivity, whereby the reliability of the sensor 27 is maintained for a long period of time.

Next, the registration of the images of the respective colors performed in this digital color copying machine will be described. In this digital color copying machine, recording devices 13BK, 13Y, 13M and 13C for BK, Y, M and C are used for measuring pattern images 28B of respective colors BK, Y, M and C as shown in FIG.
K, 28Y, 28M, and 28C (hereinafter, collectively referred to as a measurement pattern image 28 if one is not specified) are laser light emitting elements 62 (shown in FIG. 1) of each laser emitting device 12 (hereinafter, LD 62). (Hereinafter, referred to as “the laser beam”) from the transfer belt 2 via each photoconductor drum 14
1 on each. That is, in this embodiment, each recording device 13BK, 13Y, 13M, 13C
Functions as a pattern image forming unit. The measurement pattern image 28 of each color is formed outside the area of the transfer belt 21 where the transfer paper is conveyed. Then, the respective measurement pattern images 28 are arranged at intervals of a (mm) in the order of BK, Y, M, and C in the direction of arrow A, which is the transport direction of the transfer belt 21, and they are in the transport direction of the transfer belt 21. It is formed as a linear pattern extending in a direction substantially orthogonal to.
Then, each measurement pattern image 28 is transferred to the transfer belt 2
By passing under the sensor 27 as 1 moves in the direction of arrow A, it is sequentially detected by the sensor 27.

In this digital color copying machine, one of the measurement pattern images 28 of each color detected by the sensor 27, which serves as a reference, is used as a reference measurement pattern image for BK (measurement pattern images of other colors are used as references). Of the measurement pattern image of another color (other than BK in this example) in the sub-scanning direction indicated by arrow A in FIG. Is provided with a calculation means (in this embodiment, a comparison calculation circuit 30 described later in FIG. 9 corresponds thereto). Further, in this digital color copying machine, as shown in FIG. 5, the optical axis of the laser beam from the LD 62 of each laser beam emitting device 12 is in the direction of the arrow B around the axis 66 formed on the holding member 67. 6 to displace the beam irradiation position Lp on the photosensitive drum 14 in the sub-scanning direction as shown in FIG.
That is, the optical axis moving means for displacing from the position shown by the solid line to the position shown by the broken line is provided. The optical axis moving means is a motor 34 shown in FIG. 5, which will be described later, a lead screw 75, and a holding member that is rotatable about a shaft 66 in a state where the lead screw 75 is screwed into a female screw portion 67a. For example, the member 67 is configured. Also, in this digital color copying machine, the optical axis moving means is driven based on the deviation amount for each color of the measurement pattern image 28 obtained by the calculating means, and the beam irradiation position Lp on the photosensitive drum 14 is moved. Image position deviation correction means (in this embodiment, which corresponds to the beam position displacement control circuit 33 described later in FIG. 9) for correcting the image position deviation of each color by displacing in the sub-scanning direction is also provided.

Each measurement pattern image 28 shown in FIG.
The interval a is a numerical value that can be arbitrarily set by setting the exposure timing for each recording device 13 in advance, and the linear velocity of the transfer belt 21 is V ₂ (mm / se).
c), the measurement pattern images 28BK, 28 of each color
The detection time difference between Y, 28M and 28C is a / V ₂ (sec)
Becomes To form the respective measurement pattern images 28 so as to be arranged in the sub-scanning direction of the arrow A at intervals a,
If there is no deviation in the formation timing, it may be formed at the following timing. That is, as shown in FIG. 7, the length along the outer peripheral surface of each photosensitive drum 14 from the exposure position to the transfer position is L ₁ (mm).
4 is V ₁ (mm / sec) and the distance between the photoconductor drums is L ₂ (mm), the required time T ₁ from exposure to transfer is T ₁ = L for each photoconductor drum 14. ₁
It becomes the same value as / V ₁ (sec). Then, the time T ₂ required for the transfer belt 21 to move between the respective photoconductor drums 14
Is T ₂ = L ₂ / V ₂ (sec). Therefore,
When it is desired to form the measurement pattern image 28 at the interval a, the measurement pattern image 28 of each color may be written at the next timing with reference to BK. That is, the cyan write timing is TC = (L ₂ + a) / V ₂ (sec)
The writing timing of magenta is TM = 2 (L ₂ +
The writing timing of a) / V ₂ (sec) yellow may be delayed by TY = 3 (L ₂ + a) / V ₂ (sec).

However, in practice, each photosensitive drum 1
4 due to variations in position, variations in exposure position with respect to the photoconductor drum 14, variations in linear velocity of the photoconductor drum 14 and the transfer belt 21, variations in phase of the deflecting means of each laser light emitting device 12, etc. Even if the writing is instructed, the intervals a of the measurement pattern image 28 actually formed on the transfer belt 21 deviate from the set value, so that the color image in the four-color overlapping image formed on the transfer paper is colored. It will appear as a gap. That is, as shown in FIG. 8, the detection timing of each measurement pattern image 28 by the sensor 27 may be a solid line timing slightly deviated from the theoretical value indicated by the broken line. The detection signal from the sensor 27 is input to the counters 29Y, 29M and 29C shown in FIG. If the timing of forming each measurement pattern image 28 is set as described above, even if the position of each measurement pattern image 28 is slightly shifted, the order does not change. Therefore, the first detection signal is the detection signal of BK Subsequent detection signals are Y,
It can be recognized as a detection signal of M and C.

The counters 29C, 29M and 29Y are all reset by the detection signal of BK and start counting. Then, for example, the counter 29C stops counting by the detection signal of C. The other counters 29M and 29Y stop counting by the detection signals of M and Y, respectively.
The operation of each of the following circuits is the same for C, M, and Y, so C will be described as a representative. In this digital color copying machine, as described above, the position of the image of each color is first aligned with the position of the image of BK forming the measurement pattern image 28 as a reference. After the count is stopped, the count value of the counter 29C is output to the comparison calculation circuit 30 which is calculation means, and the comparison calculation circuit 30 calculates the amount of deviation from the preset set value in terms of time. That is, the count clock frequency is M (H
z), where the actual count value is KC and the set value of the count value is KCs, the difference ΔT with the set value TKC = KCs / M
Calculate C = KC / M-KCs / M. This ΔTC is BK
The amount of deviation of the interval between the measurement pattern image of C and the measurement pattern image of C with respect to the set interval is shown.

Here, the deflector 50 shown in FIG. 1 of the recording device 13 is a polygon mirror having, for example, six polygon surfaces 51 serving as reflecting surfaces, which are rotated at 20,000 rpm and have a pixel density of 600 dpi. Image of single beam L
When the image is formed at D, the linear velocity V ₁ of the photosensitive drum 14 is 84.67 mm / s, and an image is formed.
If writing is performed with two beams, the linear velocity of the photosensitive drum 14 is 169.33 mm / s. Here, for example, BK
Amount ΔT of the measurement pattern image of C and C with respect to the set interval
When C is calculated to be 4.8 ms, the beam irradiation position adjustment value ΔX is ΔX = ΔTC × V ₁ = 4.8 ms × 84.67 mm / s.
= 0.406 mm. Based on this value, the beam position displacement control circuit 33 drives the motor 34 that displaces the optical axis of the laser beam, and displaces the irradiation position of the laser beam onto the photosensitive drum 14 by 0.406 mm in the sub-scanning direction. Then, the deviation amount is corrected. Similarly, each of the M and Y measurement pattern images 28
With respect to M and 28Y as well, the shift amounts ΔTM and ΔTY are calculated, and the optical axes of the laser beams are respectively displaced according to the shift amounts to correct the shift amounts. By controlling in this way, in this digital color copying machine, even if the rotation phases of the respective deflectors do not match,
The positional deviation amount can be corrected exactly. Although not shown here, such a correction is performed by a single L
The same can be applied to a color image forming apparatus that writes an image of each color using a D unit and a deflector.
As a result, precise alignment can be performed.

Next, FIG. 5 shows an example of the optical axis moving means.
Will be described in detail with reference to. The optical axis moving means for rotating the LD unit 60 to displace the optical axis of the laser beam is
For example, as shown in FIG. 5, the holding member 67 has a female screw portion 67a formed at one end, a lead screw 75 screwed into the holding member 67, and a motor 34 having the lead screw 75 fixed to a rotating shaft. . The motor 34
Is rotationally driven in response to a drive signal from the beam position displacement control circuit 33 shown in FIG. 9, and the lead screw 75 that rotates thereby pushes up or pushes down the female screw portion 67a to hold it. The member 67 rotates around the shaft 66 as a rotation center, and the entire LD unit 60 rotates in the same direction. As the motor 34, for example, a stepping motor having 20 pulses per rotation is used. By using the optical axis moving means having such a configuration, the beam position displacement control circuit 33 (FIG. 9) sends a signal corresponding to the displacement amount to the motor 34 based on the beam irradiation position correction value ΔX described above. Then, the LD unit 60 is rotated by driving the motor 34 to rotate L
The optical axis of D62 can be displaced from the position shown by the solid line to the position shown by the broken line as shown in FIG. As a result, as shown in FIG. 6, the beam irradiation position Lp on the photosensitive drum 14 is displaced in the sub-scanning direction.

In FIG. 6, the beam irradiation position (beam spot position) Lp on the photosensitive drum 14 by the laser beam from the LD 62 is from the center of rotation when the optical axis of the laser beam is displaced to the main scanning direction. The beam irradiation position which is the farthest position is shown by hatching. Further, the beam irradiation positions Lp indicated by broken lines above and below the beam irradiation positions Lp respectively indicate the beam irradiation positions after being displaced in the sub-scanning direction when the optical axis is displaced with the rotation center as the fulcrum. The position of the LD 62 when the correction value of the beam irradiation position is 0 may be set so that the beam irradiation position formed by the laser beam emitted from the LD 62 is the beam irradiation position hatched in FIG. The change of the beam irradiation position on the photoconductor drum 14 due to the displacement of the optical axis when the LD unit 60 is rotated is shown in FIG. 11 as the rotation angle of the LD unit and the displacement amount of the beam irradiation position on the photoconductor drum 14. Is as shown.

In this embodiment, since the stepping motor is used as the motor 34 as described above, the displacement amount in the sub-scanning direction on the photosensitive drum 14 at the beam irradiation position due to the rotation per pulse thereof is as follows. It was about 5 μm, which was a sufficient resolution. Further, since the displacement in the main scanning direction on the photosensitive drum 14 at the beam irradiation position when the LD unit 60 is rotated is extremely small as compared with the displacement in the sub scanning direction, there is no problem. As for the displacement in the main scanning direction, the laser light emitting device 12 is provided with the synchronization detection unit 58 as shown in FIG. 12, and the scanning position in the main scanning direction is corrected by this, so that the image quality is improved. Will not cause any problems. As described above, according to this embodiment, the beam irradiation position on the photoconductor drum 14 can be accurately corrected in the sub-scanning direction with high resolution. In this embodiment, the optical axis moving means using the motor 34 performs alignment with the position of the measurement pattern image 28BK for BK (black) color shown in FIG. 4 as a reference. The recording device 13BK for the BK does not need to be provided with the optical axis moving means, and the recording devices 13C, 13M, 13Y for the other colors.
It is necessary to provide only for.

The reference measurement pattern image is not limited to the BK color, but other C, M, Y
Either of them may be used as a reference. In that case, the optical axis moving means is not provided for the recording apparatus corresponding to the reference color, but the optical axis moving means is provided for all the recording apparatuses corresponding to other colors. Further, the arrangement order of the recording devices 13 of each color and the formation order of the measurement pattern image 28 of each color are not limited to those in the above-described embodiment. Further, in principle, the deviation of the beam irradiation position of each color can be corrected only by the correction of the beam irradiation position due to the displacement of the optical axis described above. Since the spot diameter may change and affect the image quality, the image writing timing generation circuit 31 and the LD modulation circuit 32 are provided as shown in FIG. 9 to correct the writing timing of the laser beam for each color. It is preferable to do this together. Also, L
If the D unit 60 is rotatably attached to an optical housing (not shown) that holds the deflector 50 and the like shown in FIG. 1 without providing a dedicated supporting member that rotatably supports the D unit 60, the dedicated D unit 60 is provided. Eliminates the need for additional support members.

Further, in this embodiment, the LD unit 6 is used.
The rotation center axis line La of 0 is shifted in the main scanning direction (left and right direction in FIG. 1) with respect to the optical axis Lb of the laser beam emitted by the LD 62. The rotation center axis La of the LD unit 60 is the optical axis Lb of the laser beam emitted by the LD 62.
And a polygonal surface 51, which is a deflecting surface of the deflector 50, are substantially aligned with each other. By doing so, when the beam irradiation position on the photosensitive drum 14 is displaced, the amount of change in the optical characteristics due to the change in the optical path can be reduced, so that the change in spot diameter and the like can be reduced and the image quality can be improved. The decrease can be prevented. If you do this, LD
The intersection point of the laser beam from 62 on the polygonal surface 51 is
As shown in FIG. 10B, even if the optical axis is displaced, it does not move, but the moving direction of the LD unit 60 and the moving direction of the beam irradiation position on the photosensitive drum are opposite. On the other hand, as shown in FIG.
When the LD unit 60 in which the D62 and the collimator lens 63 are fixed to the holding member is moved in the sub-scanning direction while keeping the direction of the optical axis of the LD 62, the moving direction of the LD unit 60 and the position on the photoconductor drum. It coincides with the moving direction of the beam irradiation position.

FIG. 13 is a plan view similar to FIG. 1, showing a recording apparatus in a color image forming apparatus according to another embodiment of the present invention, and the portions corresponding to those in FIG. 1 are designated by the same reference numerals. The recording apparatus of the color image forming apparatus according to this embodiment is different from the recording apparatus described in FIGS.
The only difference is that the D unit 60 is rotatably attached to the side surface of an optical housing 80 to which an aperture 53 for shaping the shape of a laser beam is fixed. Therefore, in the digital color copying machine which is the color image forming apparatus according to this embodiment, the laser beam emitted from the LD 62 passes through the collimator lens 63 which is the coupling optical system and is deflected by the deflector 50 onto the photosensitive drum. Writing means for writing a latent image on the recording medium, a plurality of developing means for developing the latent image to form a visible image of each color, and a transfer means for transferring a transfer paper which is a recording medium for transferring the visible image. The point of having a belt is the same as that of the digital color copying machine described in FIGS. 1 to 12. The copying machine is also provided with a sensor 27 for detecting the measurement pattern image 28 for each color described in FIG. 4, and one measurement pattern serving as a reference among the measurement pattern images 28 for each color detected by the sensor 27. An arithmetic means is provided for measuring the distance between the image (for example, a BK color image) and the measurement pattern image of another color to calculate the shift amount of the measurement pattern image for the other color in the sub-scanning direction. The point is the same.

In this embodiment, the LD unit 60 holding the LD 62 and the collimating lens 63 on the holding member 67 is attached to the side surface of the optical housing 80 to which the aperture 53 for shaping the shape of the laser beam is fixed as described above. It is attached rotatably. Further, similarly to the digital color copying machine described with reference to FIGS. 1 to 12, a motor (similar to the motor 34 described with reference to FIG. 5) for rotating the LD unit 60 is provided, and the LD unit 60 is provided with the rotation center axis line La thereof. And the optical axis Lb of the laser beam emitted by the LD 62 are shifted from each other in the main scanning direction, and the motor is driven to drive the LD unit based on the shift amount for each color of the measurement pattern image obtained by the calculating means. By rotating 60, the LD 62 is moved to provide beam position adjusting means for adjusting the position in the sub-scanning direction for each laser beam for each color that is irradiated onto the photosensitive drum. In this embodiment also, the optical axes Lb and Lb of the laser beam are
The rotation center axis line La of the D unit 60 is made to substantially coincide with the polygon surface 51 serving as the deflection surface of the deflector 50. As a result, the amount of change in optical characteristics is reduced, and the amount of change in beam spot diameter can be reduced, so that a high-quality image can be obtained.

By the way, in a recording apparatus using a laser beam, an aperture for shaping the shape of the laser beam is generally attached to the LD unit in many cases. In such a configuration, when the laser light emitting element (LD) is moved, the amount of movement of the beam irradiation position on the photoconductor that moves due to this increases in the sub-scanning direction. Therefore, in such a configuration, the beam irradiation position on the photoconductor cannot be adjusted in the sub-scanning direction in units of several μ. However, in the digital color copying machine according to this embodiment, since the LD unit 60 is rotatably attached to the optical housing 80 to which the aperture 53 is fixed as described above, even if the LD unit 60 is rotated, the aperture 53 is rotated. The light flux passing thereafter does not change significantly. Therefore, the beam irradiation position on the photosensitive drum of the laser beam emitted from the LD 62 can be accurately adjusted in the sub-scanning direction in units of several μm. For the correction of the beam irradiation position, the beam position control circuit (similar to the beam position control circuit 33 described in FIG. 9) uses a signal corresponding to the displacement amount based on the above-described correction value ΔX of the beam irradiation position. Is output to the motor that rotates the LD unit 60, and the motor is rotated. In this way, when the LD unit 60 is rotated, the LD 62 is displaced by rotating around the rotation center axis line La of the LD unit 60, so that the optical axis Lb of the laser beam is displaced. As a result, similarly to the case described with reference to FIG. 6, the beam irradiation position on the photosensitive drum is displaced in the sub scanning direction.

Also in this embodiment, the motor for rotating the LD unit 60 is a stepping motor having 20 pulses per rotation. Then, the stepping motor was actually used to measure the relationship between the rotation angle of the LD unit 60 and the displacement amount of the beam irradiation position on the photoconductor drum in an actual machine. The displacement amount was 20 μm / motor rotation, and the displacement amount of the beam irradiation position was about 1 μm per one pulse of the motor, and the beam irradiation position could be adjusted with extremely high accuracy. On the other hand, when the aperture 53 was attached to the LD unit 60 side and checked with an actual machine, the beam irradiation position was displaced on the photosensitive drum by about 300 μm per one rotation of the motor. Furthermore, the movement was not linear and the accuracy was insufficient. The LD unit 6
Since the displacement of the beam irradiation position on the photosensitive drum in the main scanning direction when 0 is rotated is very small compared to the displacement in the sub scanning direction as in the case described with reference to FIG. 6, there is no problem. I won't. The slight deviation of the beam irradiation position in the main scanning direction can be corrected by the correction of the write timing using the synchronization detection unit 58 shown in FIG. 12, so that there is no problem in image quality.

Although it depends on the correction amount, in principle, it is possible to correct the positional deviation of the beam irradiation position only by correcting the beam irradiation position by the displacement of the optical axis. However, if the deviation of the beam irradiation position of each color is corrected by both the correction of the beam irradiation position by displacing the optical axis Lp by the rotation of the LD unit 60 described above, the correction by adjusting the writing timing is also performed. Good. As means for displacing the beam irradiation position in the sub-scanning direction in each of the above-described embodiments, not only the method of rotating the LD unit 60 as described in each of the embodiments, but also illustration of the inside of the writing device is omitted. There is also a method of displacing the beam irradiation position by changing the angle of the folding mirror. However, in the case of this method, the beam irradiation position is largely changed due to a slight angle change of the folding mirror, which is not suitable for practical use due to accuracy problems. As another method, it is possible to dispose a plate glass-like object in front of the deflector with respect to the laser beam and change the angle to change the beam irradiation position in the sub-scanning direction. As the number of parts increases, there is a risk that the beam imaging performance will be adversely affected depending on the surface accuracy of the plate glass to be added. Therefore, the beam irradiation position on the photosensitive drum is adjusted in the sub-scanning direction by adjusting the LD unit 60 as in the above-described embodiments.
It is most effective to rotate by.

[0029]

As described above, according to the color image forming apparatus of the present invention, the positional deviation of the image of each color in the sub-scanning direction can be corrected with higher accuracy, so that a high quality image is formed. You can

[Brief description of drawings]

FIG. 1 is a plan view showing a configuration of a main part of a writing unit included in a color image forming apparatus according to the present invention.

FIG. 2 is an overall configuration diagram showing a digital color copying machine which is also an example of the color image forming apparatus.

FIG. 3 is a front view showing the transfer belt of the digital color copying machine together with a plurality of photosensitive drums.

FIG. 4 is a plan view showing the vicinity of an end portion of the transfer belt for explaining the measurement pattern image formed on the transfer belt.

5 is a rear view showing an LD unit provided in the writing means of FIG. 1 and a mechanism portion for rotating the LD unit. FIG.

FIG. 6 is an explanatory diagram for explaining a change in a beam irradiation position on a photosensitive drum.

FIG. 7 is a diagram for explaining setting of a measurement pattern image formation interval for the transfer belt of FIG. 3;

FIG. 8 is a diagram for explaining the detection timing of the measurement pattern image similarly.

9 is a block diagram showing a control system for aligning images of respective colors, which the digital color copying machine shown in FIG. 2 has.

10 is a diagram showing how the optical axis of the laser light emitting device changes when the LD unit of FIG. 5 is moved.

FIG. 11 is a diagram showing a relationship between a rotation angle of the LD unit and a displacement amount of a beam irradiation position on the photosensitive drum.

12 is a plan view showing a configuration of a laser light emitting device included in the digital color copying machine of FIG. 2 in a state in which an upper lid is opened.

FIG. 13 is a plan view similar to FIG. 1, showing a configuration of a main part of a writing unit included in a color image forming apparatus according to another embodiment of the present invention.

[Explanation of symbols]

12BK, 12Y, 12M, 12C: Laser light emitting devices 13BK, 13Y, 13M, 13C: Recording devices 14BK, 14Y, 14M, 14C: Photosensitive drums 16BK, 16Y, 16M, 16C: Developing device (developing means) 21: Transfer Belt (conveying means) 27: Sensor (detecting means) 28BK, 28Y, 28M, 28C: Measurement pattern image 30: Comparison calculation circuit (calculation means) 31: Image writing timing generation circuit 32: LD modulation circuit 33: Beam position displacement control Circuit (image position deviation correcting means) 34: Motor (optical axis moving means) 50: Deflector 51: Polygon surface (deflection surface) 53: Aperture 60: LD unit 62: LD (laser light emitting element) 63: Collimator lens (cup) Ring optical system) 67: Holding member 75: Lead screw 80: Optical housing : Transfer paper (recording medium)

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/01 G03G 15/01 112A 5C072 112 15/04 5C074 15/04 H04N 1/23 103C 21/14 1/29 G H04N 1/04 B41J 3/00 D 1/113 G03G 21/00 372 1/23 103 H04N 1/04 104A 1/29 DF Term (reference) 2C362 AA43 AA49 BB50 CA18 CA23 CA39 CB73 2H027 DA21 DE02 DE07 DE10 EC03 EC06 ED04 2H045 AA01 BA22 BA33 BA34 CA45 CA88 DA02 2H076 AB05 AB12 AB18 AB68 EA01 2H300 EA06 EB04 EB07 EB12 EF02 EF06 EF09 EG03 EH16 EH35 EH36 EJ09 FF05 GG23 HH16 RR20 RR38 TT04 5C072 AA03 BA04 BA19 HA02 HA13 HB08 QA14 QA17 RA18 UA13 XA01 5C074 AA02 AA10 BB17 CC22 CC26 DD15 EE02 EE04 HH02

Claims (6)

[Claims] 1. A writing unit for writing a latent image on a photosensitive member by a laser beam which is emitted from a laser light emitting element and is deflected by a deflector through a coupling optical system, and a latent image is developed to develop a latent image of each color. It has a plurality of developing means for forming a visible image and a conveying means for conveying a recording medium to which the visible image is transferred, and superimposes the visible images of the respective colors developed by the plurality of developing means on the recording medium. A color image forming apparatus for forming a color image by means of a pattern image forming means for forming a measurement pattern image of each color on the conveying means via the photoconductor by a laser beam from the laser light emitting element; Between the detection means for detecting the pattern image and one measurement pattern image as a reference among the measurement pattern images of each color detected by the detection means and the measurement pattern image of another color Calculating means for respectively calculating the amount of deviation of the measurement pattern image of the other color in the sub-scanning direction by measuring the distance, and displacing the optical axis of the laser beam from the laser light emitting element on the photoreceptor. An optical axis moving means for displacing the beam irradiation position in the sub-scanning direction, and an optical axis moving means for driving the optical axis moving means on the basis of the shift amount for each color of the measurement pattern image obtained by the calculating means. And an image position deviation correcting unit that corrects the image position deviation of each color by displacing the beam irradiation position in the sub-scanning direction. 2. The color image forming apparatus according to claim 1, further comprising an LD unit holding the laser light emitting element and the coupling optical system in a holding member, and the LD unit holding the deflector and the like. The optical axis is attached to the housing so as to be movable in the direction in which the beam irradiation position on the photoconductor is displaced in the sub-scanning direction, and the optical axis moving means displaces the optical axis by moving the LD unit. And a means for displacing the beam irradiation position on the photoconductor in the sub-scanning direction. 3. The color image forming apparatus according to claim 2, wherein the LD unit is rotatably attached to the optical housing, and the central axis of rotation of the LD unit is irradiated by the laser light emitting element. A color image forming apparatus, which is deviated in a main scanning direction with respect to an optical axis of a laser beam. 4. The color image forming apparatus according to claim 3, wherein the rotation center axis of the LD unit is substantially coincident with the optical axis of the laser beam emitted by the laser light emitting element on the deflecting surface of the deflector. A color image forming apparatus characterized in that 5. Writing means for writing a latent image on a photoconductor by a laser beam emitted from a laser light emitting element and deflected by a deflector through a coupling optical system, and developing means for developing the latent image to develop a latent image of each color. It has a plurality of developing means for forming a visible image and a conveying means for conveying a recording medium to which the visible image is transferred, and superimposes the visible images of the respective colors developed by the plurality of developing means on the recording medium. A color image forming apparatus for forming a color image by means of a pattern image forming means for forming a measurement pattern image of each color on the conveying means via the photoconductor by a laser beam from the laser light emitting element; Between the detection means for detecting the pattern image and one measurement pattern image as a reference among the measurement pattern images of each color detected by the detection means and the measurement pattern image of another color A calculation unit that calculates the amount of deviation of the measurement pattern image of the other color in the sub-scanning direction by measuring the distance is provided, and the laser light emitting element and the coupling optical system are held by a holding member. An LD unit, the LD unit being rotatably attached to an optical housing having an aperture for shaping the shape of a laser beam rotatably provided, and driving means for rotating the LD unit is provided, and the LD unit is provided with the rotation center axis and the laser. The optical axis of the laser beam emitted by the light emitting element is shifted in the main scanning direction, and the driving means is driven based on the shift amount for each color of the measurement pattern image obtained by the computing means. By rotating the LD unit, the laser light emitting element is moved to irradiate the photoconductor with the laser beam of each color. Color image forming apparatus characterized in that a beam position adjusting means for adjusting the sub-scanning direction located in and. 6. The color image forming apparatus according to claim 5, according to a deviation amount in the sub-scanning direction between one reference measurement pattern image and the other color measurement pattern images obtained by the calculation means. A color image forming apparatus comprising an adjusting means for adjusting an image writing timing by a laser beam corresponding to each color.