JPH06246975A - Color image forming apparatus - Google Patents

Abstract

PURPOSE:To achieve the enhancement of quality and the shortening of a color shift adjusting time without requiring a precise adjusting mechanism by providing a plurality of laser beam generating means corresponding to respective color components, a plurality of scanners independently deflecting the laser beam generating means, a plurality of recording media and the rotary phase control means of the respective scanners. CONSTITUTION:Independent scanners 5a, 5b are provided to scanning systems of respective colors and, by controlling the rotary phases of them, a laser exposure interval L of respective colors can be adjusted to accuracy of a scanning pitch or less on recording media 7a, 7b. That is, when the rotary phases of the scanners 5a, 5b rotating in the same number of rotations of the scanning systems of respective colors are adjusted at every colors, the scanning start positions on the continuously rotating recording media 7a, 7b can be shifted and the color shift in a sub-scanning direction generated when the recording media are superposed one upon another is corrected. If shift quantity is once measured, the angle-of-rotation phase adjusting quantity corresponding to correction quantity can be electrically adjusted and, therefore, it is certainly and simply adjusted. That is, by shifting a rotary phase without shifting an exposure position, color shift is easily corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus for forming a color image using a laser beam.

[0002]

2. Description of the Related Art A conventional color image forming apparatus will be described with reference to FIG.
0 is a plurality of independently modulatable laser light sources, for example, four laser light sources are combined into one component,
The laser beam from each laser light source is converted into a light ON / OFF signal by a laser driver (not shown) that operates based on the color-separated image information. 15
Denoted at 18 is a collimator lens attached to each laser light source, and each laser beam is emitted as parallel light.

The laser light source on the side of the collimator lens 15 is turned on and off based on the image information obtained by the color separation of black.
It is deflected by the rotating polygon mirror 70 while repeating F,
The light enters the condensing lens 65, further passes through the bending mirror 45, and then enters the first color recording medium 55 to form a one-dimensional fine light spot on the first color recording medium 55. Since the first-color recording medium 55 is continuously rotating, black-separated image information is recorded as two-dimensional fine optical information on the first-color recording medium 55. This optical information is
Then, as in a normal electrophotographic process, the image is visualized and transferred to form a black image on the recording paper.

Similarly, on the other second-color recording mediums 56 to 58, the image information obtained by color separation of red, yellow, and indigo is recorded as two-dimensional fine optical information. Then, these optical information is also visualized and transferred, so that images of red, yellow, and indigo are recorded on the recording paper. In this way, the four color images are recorded on the recording paper in an overlapping manner.

[0005]

The above-mentioned conventional color image forming apparatus has the following problems. That is, normally, when a color image is created, it is necessary to superimpose an image created independently for each color of black, crimson, yellow, and indigo on a correct position on the recording paper. In order to superimpose the image of each color on the accurate position on the recording paper, the recording start position of the image of each color on the recording media 55 to 58 in the scanning direction and the sub-scanning direction must be accurately adjusted.

Regarding the adjustment of the scanning direction, the laser scanning start position is always detected by the detector, and the delay amount of the recording timing of the recording data is adjusted for each color so that the exposure device and the recording medium position in the device can be adjusted. It is already known that, even if it is roughly mounted, color misregistration does not occur when images of respective colors are superposed. However, in order to correct the color misregistration in the vertical direction, the recording medium 55
Since it is necessary to keep the laser beam irradiation position on ~ 58 at L = np (L: laser beam irradiation position interval of each color, n: integer, p: scanning pitch), simultaneous scanning of each color is performed using the scanner 24 common to each color. By doing so, the recording medium 5 of each color
5 to 58 are recorded at the same scanning frequency to adjust the timing of the scanning line for each color.

However, in this method, since the recording is performed at the scanning frequency of the same phase, it is impossible to correct the color misregistration of one scanning pitch or less, which is an obstacle to improving the printing quality. In order to further improve the color misregistration correction by this method, it is necessary to mechanically adjust the exposure position by the color misregistration amount of 1 scanning pitch or less by the folding mirrors 45 to 48. The size of the color image forming apparatus is increased because a precise mechanical adjustment mechanism capable of adjusting various color shifts is required. Increase the cost. It requires a lot of color misregistration adjustment time. There is a problem that maintenance is difficult because mechanical adjustment work is required.

The present invention has been proposed in view of the above problems, and the object thereof is to improve print quality without requiring a precise mechanical adjustment mechanism. Another object of the present invention is to provide a color image forming apparatus that does not require a precise mechanical adjustment mechanism and can achieve downsizing of the apparatus, cost reduction, shortening of color misregistration adjustment time, and improvement of maintainability.

[0009]

In order to achieve the above object, a color image forming apparatus of the present invention comprises a plurality of laser beam generating means corresponding to each color component and a plurality of laser beams which are independently deflected. Multiple scanners to
It is provided with a plurality of recording media for recording image information for each color by each of the laser beams, and a rotation phase control means of each of the scanners.

[0010]

The color image forming apparatus of the present invention is configured as described above, and the rotational phase of the scanner of each color is controlled by the rotational phase control means without changing the exposure position of each color on each recording medium. Since the recording start position in the sub-scanning direction is adjusted, the print quality is improved without requiring a precise mechanical adjustment mechanism. Further, it is possible to achieve downsizing of the apparatus, cost reduction, shortening of color misregistration adjustment time, and improvement of maintainability without requiring a precise mechanical adjustment mechanism.

[0011]

【Example】

(First Embodiment) Next, a color image forming apparatus of the present invention will be described with reference to FIG.
1a and 1b are delay elements, 2a and 2b are phase comparators, 3a and 3b are low-pass filters, 4a and 4b are scanner motor drivers (rotational phase control means of the scanner), 5a, 5b is a scanner, 5a ', 5b' is a scanner motor, 7a, 7
b is a recording medium, 8 is the same reference clock, 11a, 11
Reference numeral 8 is a laser light source (laser beam generating means), and the same reference clock 8 is provided with different delay elements 1a, 1b → phase comparators 2a, 2b → scanner motor drivers corresponding to respective colors so that color deviation does not occur for each color. 4a and 4b, the rotational phases of the scanners 5a and 5b are controlled, and the laser exposure interval L of each color on the recording media 7a and 7b is adjusted to an accuracy of the scanning pitch or less.

(Second Embodiment) FIG. 2 shows a second embodiment in which 9a and 9b are frequency dividers, 2a and 2b are phase comparators, 3a and 3b are low-pass filters, and 4a and 4b are scanners. Motor driver (rotational phase control means of the scanner), 5a ′, 5b ′ are scanner motors, 8 is the same reference clock, and the common reference clock 8 is a frequency divider 9a,
9b, and by shifting the reset timing temporally, the rotational phase of each scanner (see 5a and 5b in FIG. 1) is controlled, and the laser exposure interval L of each color on the recording media 7a and 7b is set to the scanning pitch. The accuracy is adjusted to the following.

Next, the operation of the color image forming apparatus shown in FIGS. 1 and 2 will be specifically described. By providing independent scanners 5a and 5b in the scanning system for each color and controlling the rotational phase of the scanners 5a and 5b, the laser exposure interval L of each color on the recording media 7a and 7b can be set to an accuracy of the scanning pitch or less. It is adjustable. That is, the scanning start position on the continuously rotating recording media 7a and 7b is shifted by adjusting the rotational phase of 5a and 5b rotating at the same number of revolutions in the scanning system for each color for each color. This makes it possible to correct the color misregistration in the sub-scanning direction when superposed.

Further, once the shift amount is measured, the rotation angle phase adjustment amount according to the correction amount can be adjusted electrically, so that it can be adjusted reliably and easily. That is, in the conventional color image forming apparatus, since the speed of the recording paper is constant as shown in FIG. 5, it is necessary to adjust the recording start position of the recording media 55 to 58 for forming an image for each scanning system. In order to correct the deviation accurately, it is necessary to shift the exposure positions on the recording media 55-58 by the bending mirrors 45-48 to correct the recording start position.

For example, if the exposure position is 200 mm from the folding mirrors 45 to 48 and the color misregistration correction amount is 50 μm, an angular resolution of 25 seconds is required for the mirror adjustment, and a very high precision adjustment is required. Configuration becomes complicated,
Maintenance becomes difficult, and the cost of the device itself increases. On the other hand, in the color image forming apparatus of the present invention, the color misregistration can be easily corrected by shifting the rotational phase of the scanners 5a and 5b for each color as shown in FIGS. 1 and 2 without shifting the exposure position. To be done. That is, with a six-sided scanner, 10.000 RPM, scanning pitch 100 μm
When scanning with, the color shift between the first and second colors is 50μ
When m is corrected (see FIG. 3), the color misregistration is corrected by shifting the rotational phase of the scanner 5b by 30 ° with respect to the rotational phase of the scanner 5a.

At this time, when the reference frequency of the reference clock 8 is 1 KHZ, it is sufficient to use the delay element 1b of 50 μsec. Similarly, in the case of FIG. 2 as well, when the scanners 5a and 5b are rotated by the feedback signal of 1KHZ and the common reference frequency of the scanners 5a and 5b is 20KHZ, the frequency division timing is shifted by 1/2 by the reset signal. As a result, it becomes possible to correct the rotational phase of the scanner 5b by 30 ° as in the case of FIG. (See Figure 3). That is, since the scanner 5b rotates 30 ° later than the scanner 5a, the writing start position on the recording medium 7 is ½ of one scanning pitch of 100 μm (= 30 ° / 60).
.Degree.), That is, a delay of 50 .mu.m, and it becomes possible to correct the color shift when superposed.

From the reference frequency, the delay elements 1a, 1b,
Alternatively, the reference signals of the scanner motors 5a ′ and 5b ′, which are slightly shifted (50 μm in FIGS. 1 and 2) corresponding to the color shift through the frequency dividers 9a and 9b, are the phase comparators 2a and 2b.
b, and is compared with the encoder motors of the scanner motors 5a ', 5b' or the feedback signal in the scanning tamming detection signal, and the low-pass filter 3 is used to match the rotation of the scanner motors 5a ', 5b' with the reference signal.
The rotational speeds of the scanner motors 5a 'and 5b' are accurately controlled via a, 3b and the motor drivers 4a, 4b.

As described above, by controlling the phases of the scanners 5a and 5b of the respective colors for the correction of the color shift less than the scanning pitch, the color shift on the recording media 7a and 7b can be performed without the need for a precise mechanical adjustment mechanism. Correction is possible. Figure 4
In this case, each color is simultaneously scanned by a plurality of beams, and in this case, one scanning of the scanner records a scanning pitch of three lines, and a large color shift occurs as compared with one-beam scanning. In FIG. 4, one scanning pitch is 100 μm,
When the horizontal line is recorded with three beams and the write tamming of the first color and the second color is 1/2 scanning misalignment, the misregistration amount when the colors are overlapped is 150 μm.
If the number of recording beams is large as described above, the amount of color misregistration is large, which is a major factor in image quality deterioration. Even in such a case, the color misregistration is completely corrected by adding a 30 ° phase delay to the second color and controlling the timing.

[0019]

As described above, the color image forming apparatus of the present invention controls the rotational phase of the scanner for each color by the rotational phase control means so as to change the exposure position of each color on each recording medium in the sub-scanning direction. Since the recording start position of is adjusted, the print quality can be improved without requiring a precise mechanical adjustment mechanism.

Further, without requiring a precise mechanical adjusting mechanism, it is possible to achieve downsizing of the apparatus, cost reduction, shortening of color misregistration adjusting time, and improvement of maintainability.

[Brief description of drawings]

FIG. 1 is a system diagram showing a first embodiment of a color image forming apparatus of the present invention.

FIG. 2 is a system diagram showing a second embodiment of the color image forming apparatus of the invention.

FIG. 3 is a diagram illustrating the principle of color misregistration correction of the color image creating apparatus.

FIG. 4 is a principle explanatory diagram of color misregistration correction when a plurality of simultaneous beam scans are performed by the color image forming apparatus.

FIG. 5 is a perspective view showing a conventional color image forming apparatus.

[Explanation of symbols]

 1a to 4a Rotational phase control means of scanner 5a 1b to 4b Rotational phase control means of scanner 5b 5a Scanner 5b 〃 7a Recording medium 7b 〃 11a Laser beam generation means 11b 〃

Claims (1)

[Claims] 1. A plurality of laser beam generating means corresponding to each color component, a plurality of scanners for independently deflecting the plurality of laser beams, and a plurality of recordings for recording image information by each laser beam for each color. A color image forming apparatus comprising a medium and rotation phase control means of each of the scanners.