JPH02297574A - Color image forming device - Google Patents

Abstract

PURPOSE:To correct color slippage caused by the bending of the locus of a beam scanning line by detecting the positions of pattern images in the sub- scanning direction at plural locations in the main scanning direction of these pattern images and correcting the bending of the beam scanning lines of laser beam scanners. CONSTITUTION:Based on a signal from an image forming signal generating means, the pattern images for measurement are formed on a transfer belt 21, and a position detecting means detects the positions in the sub-scanning direction of the pattern images 48BK, 48Y, 48M and 44C, at plural locations in the main scanning direction thereof. A control means operates a bending correction means correcting the bending of the beam scanning lines of the laser beam scanners 12C, 12M, 12Y and 12BK, based on a detecting signal from the position detecting means. Consequently, the bending of the beam scanning lines are corrected and the color slippage can be prevented even if the beam scanning lines are bent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image forming apparatus configured to form a color image by overlapping and transferring developed images of each color onto a transfer paper.

[Prior art] A color image forming apparatus uses C (cyan), 2M (magenta),
, Y (yellow), and BK (black), and electrostatic latent images are formed on the plurality of photoreceptors by a light beam modulated with color signals corresponding to these photoreceptors. Form. Then, the electrostatic latent image on each photoreceptor is developed to form a developed image of each color, and a color image is formed by superimposing and transferring the developed images of each color onto the same transfer paper.

Therefore, if the transferred image position due to transfer performed at the position of the photoreceptor corresponding to each color deviates from the ideal setting position, the image intervals of different colors may shift or overlap, resulting in a difference in one color or color shift. occurs and the quality of the color image deteriorates.

In order to prevent such transfer misalignment, Japanese Unexamined Patent Publication No. 63-4
In Japanese Patent No. 3172, visualized pattern images corresponding to each color are formed outside the transfer paper area, and these pattern images are detected by a sensor.

An image forming apparatus has been proposed that corrects the positional deviation by changing the writing timing of each color based on the detection signal.

Furthermore, in Japanese Patent Application Laid-Open No. 63-271275, an image register mark is formed on a transfer material to detect the image position, and one image is transferred based on a detection signal obtained by detecting this image register mark with a sensor. A multiplex image forming apparatus has been proposed that corrects at least two of the following: positional deviation in the material movement direction, image magnification, and image tilt.

According to these proposed methods, it is possible to form a high-quality color image by correcting the deviation in the sub-scanning direction (transfer material moving direction) of the image corresponding to each color.

[Problems to be Solved by the Invention] Generally, in a color image forming apparatus, a shift may occur in the position of a lens or a light source in a laser beam scanning device due to temperature changes or the like. If the position of the lens or light source within the laser beam scanning device is shifted in this way, the locus of the scanning line of the laser beam will be curved.

If the locus of the scanning line of the laser beam is curved, color shift cannot be prevented simply by aligning the positions of the images corresponding to each color in the sub-scanning direction, as in the above-mentioned method of discarding.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color image forming apparatus that is capable of correcting color shift caused by curved locus of a scanning line of a laser beam due to temperature changes or the like.

[Means for Solving the Problems] The above object is to provide a color image forming apparatus with an image forming signal generating means for forming a pattern image for measurement on a transfer belt, and a main unit for generating a pattern image formed on the transfer belt. A position detection means for detecting positions in the sub-scanning direction at multiple locations in the scanning direction, a curvature correction means for correcting the curvature of the beam scanning line of the laser beam scanning device, and a detection signal from the position detection means to perform the curvature correction. This is achieved by providing a control means for controlling the means.

[Operation] A pattern image for measurement is formed on the transfer belt based on the signal from the image forming signal generating means, and one position detection means detects the pattern image in the sub-scanning direction at a plurality of locations in the main-scanning direction of the pattern image. The position of is detected.

Based on the detection signal of the position detection means, the curvature correction means for correcting the curvature of the beam scanning line of the laser beam scanning device is operated by the control means, the curvature of the beam scanning line is corrected, and the curvature of the beam scanning line is corrected. Even if color misregistration occurs, the occurrence of color misregistration is prevented.

[Example code] Embodiments of the present invention will be described below with reference to the drawings.

Prior to a detailed description of the embodiment, a color image forming apparatus, which is the basis of the embodiment, will be explained.

FIG. 16 is an explanatory diagram showing the overall configuration of a color image forming apparatus that is the basis of an embodiment of the present invention, in which 1 is a scanner section, 2 is an image processing section, 3 is a printer section, L is an optical system, 1
2C, 12M, 12Y, 128 are laser beam scanning devices, 13G, 13M.

13Y and 13BK are recording devices, 14C and 14M.

14Y, 14BK are photoreceptors, 15C, 15M, 15Y
, 158 are chargers, 16C, 16M.

16Y and 16BK are developing devices, 17C and 17M.

17Y and 17BK are transfer chargers, and 19 is a paper feed section.

The copying machine shown in FIG. 16 includes a scanner unit 1 for reading originals, an image processing unit 2 that electrically processes image signals output as digital signals from the scanner unit 1, and a It has a printer section 3 that forms an image on transfer paper based on image recording information of each color.

The scanner section 1 has a lamp 5, such as a fluorescent lamp, that scans and illuminates the document on the document table 4.

The reflected light from the document when illuminated by the fluorescent lamp 5 is
The light is reflected by mirrors 6, 7, and 8 of the optical system and enters the imaging lens 9. The image light is focused on the Leibreuzk prism 10 by the imaging lens 9, and the image light is, for example, red R,
The light is separated into three wavelengths: green G and blue B.
A light receiver 11 for each wavelength light, for example, a red CCDIL
R, C for green: CD11G, CCD for blue], I
It is incident on B.

Each CCDIIR, IIG, and IIB converts the incident light into a digital signal and outputs it, and the output is subjected to necessary processing in the image processing section 2 to produce recorded color information for each color, such as black (hereinafter abbreviated as BK). The signals are converted into signals for recording of each color: yellow (abbreviated as Y), magenta (abbreviated as M), and cyan (abbreviated as C).

Although FIG. 16 shows an example of forming four colors, BK, Y, M, and C, it is also possible to form a color image using only three colors.

In that case, the number of recording devices can be reduced by one compared to the example shown in FIG.

The signal from the image processing section 2 is input to the printer section 3, and the laser beam scanning devices 12BK, 12G,
Sent to 12M and 12Y.

In the illustrated example, the printer unit 3 includes four sets of recording devices 13C,
1, 3M, 13Y, and 13BK are arranged side by side.

Since each recording device 13 is made of the same constituent members, in order to simplify the explanation, the recording device for C will be explained, and the explanations for other colors will be omitted. Note that for each hue, the same parts are given the same reference numerals, and in order to distinguish the composition of each color, a subscript indicating each color is added to the reference numbers.

The recording device 13C has a photoreceptor 14G, for example, a photoreceptor drum, in addition to the laser beam scanning device 12C. Photoreceptor 14
C is provided with a charger 15c, an exposure position by a laser beam scanning device f12c, a developing device 16C, a transfer charger 17C, and the like in the same manner as in a known copying apparatus.

Photoreceptor 1 uniformly charged by charger 15C
4C forms a cyan latent image by exposure with a laser beam scanning device [12G], and develops it with a developing device 116c to form we. The paper feed section 1 is fed by the paper feed roller 18.
9. For example, the leading edge of the transfer paper fed from either of the two paper cassettes is aligned by the registration roller 20,
The images are sent to the transfer belt 21 at the same timing. The transfer paper conveyed by the transfer belt 21 is transferred to photoreceptors 14BK, 14Y, 14M, and 14(
: and the developed image is transferred under the action of the transfer charger 17. The transferred paper is fixed by a fixing roller 22 and discharged by a paper discharge roller 23.

The transfer paper is electrostatically attracted to the transfer belt 21 and is conveyed with high precision at the speed of the transfer belt.

17 and 18 are a perspective view and a sectional view illustrating the laser beam scanning device of FIG. 16. In these figures, 14BK is a photoreceptor, 24BK is a beam, 25BK is a laser unit, 26BK is a motor, 27BK is a polygon mirror, 288 is a condenser lens, 29BK is an fθ lens, and 30BK.

31BK is a mirror, 328 is a dustproof glass, 33BK is an optical housing, and 34BK is a cover.

In FIGS. 17 and 18, B
Only the one for K will be explained.

In FIG. 17, 25BK is a laser unit,
It is equipped with a semiconductor laser and a condensing lens, and a collimated beam 24BK is emitted from a laser unit 25BK. The beam 24BK is linearly focused by a cylindrical condensing lens 28BK onto a polygon mirror 27BK driven by a motor 26BK. The laser beam 24BK reflected by the polygon mirror 27BK is directed to the photoreceptor 14B by the fθ lens 29BK.
The image is formed on K, and by rotation of the polygon mirror 27BK,
The photoreceptor 14BK is scanned. Also, here, the beam reflected by the polygon mirror 27BK passes through the two mirrors 30
It is reflected by BK and 31BK and guided onto photoreceptor 14BK.

As shown in FIG. 18, the condenser lens 28BK, fθ
The lens 29BK, the polygon mirror 27BK, and the folding mirrors aoBK and 318 are housed in an optical housing 338, and a dustproof glass 32BK is provided at the beam exit portion. and optical housing 3
A cover 348K is attached to the 3BK, and the inside of the housing has a sealed structure. The optical housing 33BK is fixed to front and rear side plates of the main body (not shown).

FIG. 19 is an explanatory diagram showing another example of the laser beam scanning device of the color image forming apparatus that is the basis of the embodiment, and in the same figure, 14C, 14M, and 14Y.

14BK is photoreceptor, 21 is transfer belt, 29C229M
, 29Y, and 29BK are fθ lenses, 37 is a polygon mirror, and 38 is a mirror.

As shown in FIG. 19, the laser beam scanning device may be of a type in which one or two polygon mirrors 37 driven by one motor (not shown) are used to scan a plurality of laser beams. Note that the beam light source and cylindrical lens are not shown in FIG. 19.

Next, a description will be given of the fact that the beam scanning line in the laser beam scanning device of the color image forming apparatus has a curved shape.

FIGS. 20 to 22 are explanatory diagrams showing the state of beam scanning lines in a laser beam scanning device.

Fig. 20 is an explanatory diagram showing the optical system under normal conditions, Fig. 21 is an explanatory diagram showing the optical system when there is a deviation, and Fig. 22 is the scanning line of the beams in Figs. 20 and 21. In these figures, 14 is a photoreceptor, 25 is a laser unit, 28 is a condensing lens, 29 is an fθ lens, and 4
0 is a semiconductor laser.

41 is a collimating lens, 42 is a laser beam, and 43 is a polygon mirror surface.

As shown in FIG. 20, in the initial state, the collimating lens 4
1. When the light sources of the condenser lens 28, fθ lens 29, and laser unit 25 are arranged on the optical axis in a nearly ideal state, the locus of the scanning line of the beam becomes a straight line as shown in FIG. 22(a). becomes.

However, the optical housing deforms due to temperature changes, etc.
As shown in FIG. 21, the condenser lens 28 and fθ lens 29
However, if it is tilted or deviated from the optical axis, or if the polygon mirror surface 43 or the optical axis itself is tilted, the locus of the scanning line of the beam becomes curved as shown in FIG. 22(b). .

FIG. 23 is a system block diagram of a color image forming apparatus that is the basis of the embodiment, in which 1 is a scanner section;
2 is an image processing section, and 3 is a printer section.

SY is a system controller, and P is an operation panel.

In FIG. 23, a system controller SY controls each module of a scanner section 1, an image processing section 2, and a printer section 3. The control contents include display control and key manual processing on the operation panel P, start signals to the scanner section 1 and printer section 3 corresponding to the mode set on the operation panel P, and sending of a magnification ratio designation signal to the 5 image processing sections. Sending image processing mode designation signals (color conversion, masking, trimming, mirroring) to 2, abnormal signals and operating status signals (wait, ready) from each module
.

5top) to control the entire system.

The scanner unit l scans the original at a scanning speed corresponding to the magnification specified by the start signal from the system controller SY, reads this original with a sensor such as a CCD, and scans the original with R (red), G (green), B (Blue) Each 8-bit image data is sent to the image processing unit 2 in synchronization with 5-LSYNC (horizontal synchronization signal), S-8TROBE (image clock) and FGATE (vertical synchronization signal) from the image processing unit 2.
supply to.

The image processing unit 2 receives R, G,
Image processing such as γ correction (gradation characteristic correction), UCR processing that removes play from the three color toners and replaces them with a small amount of black toner, and color correction is applied to the 8-bit image data for each B, and Y, M, C,
It is converted into 3-bit BK image data and supplied to the printer section 3. In addition, the image processing unit performs scaling processing, masking processing, etc. according to commands from the system controller SY.
Editing processes such as trimming, color conversion, and mirroring are performed. This image processing section is equipped with a buffer memory for outputting Y, M, C, and BK image data shifted by the distance between the photosensitive pairs of the printer section 3.

The printer section 3 receives 5-LSYNCC (horizontal synchronization signal), S
-3 TROBE (Image clock) The laser beam emitting device is modulated by the image data supplied from the image processing unit 2 in synchronization with the image clock, and a copy image is formed on the transfer paper by an electrophotographic process.

FIG. 24 is an explanatory diagram of the transfer belt portion of the color image forming apparatus which is the basis of the embodiment.
M, 14Y, 148 are photosensitive pairs, 21 is a transfer belt, 4
4 is a driving roller, 45 is a driven roller, 46 is a cleaning unit, and 47 is a reflective sensor as a position detecting means.

As shown in FIG. 24, the transfer belt 21 is connected to the drive roller 4.
5 and a driven roller 45, and is transported in the six directions of arrows in the figure to convey the transfer paper. A cleaning unit 46 provided upstream of the transfer belt 21 removes toner adhering to the transfer belt 21. Then, the reflection type sensor 47 detects the transfer belt 21 as described below.
The position of the pattern image formed thereon is detected.

FIG. 25 is an explanatory diagram of pattern image detection in the color image forming apparatus which is the basis of the embodiment.
1 is a transfer belt 5T is a transfer paper, 44 is a drive roller, 47
is a reflective sensor, 48BK.

48Y, 48M, and 48C are pattern images.

As shown in FIG. 25, a pattern image 488 48Y, 48
M, 48G are arrayed at one interval d (am). These pattern images 48BK.

48Y, 48M, and 48C are sequentially detected by the reflective sensor 47 as the transfer belt 21 moves.

In this case, pattern images 48BK, 48Y, 48M, 4
The interval d of the 8C array is selectively set by setting the exposure timing for each color recording device in advance.

FIG. 26 is a block diagram showing the configuration of an image forming signal generating circuit of a color image forming apparatus which is the basis of the embodiment, in which 80 is a rising detection circuit, 81a to 81d are pattern signal generating means, and 82b to B2d. is buffer memory,
83b-83d are address counters, 84b-84d are comparators, 85b-85d are address setters, 86b-8
6d is a delay device, and 87a to 87d are OR circuits.

As shown in Figure 26, FGATE (vertical synchronization signal)
is input to the rising edge detection circuit 80, and the rising edge detection circuit 8
The output terminal of 0 is connected to the input terminal of the pattern signal generating means 8La and the input terminals of the OR circuits 88b to 88d,
The output terminal of the pattern signal generating means 81a is the OR circuit 87.
The BK input signal is connected to one input terminal of the OR circuit 87a, and the BK input signal is input to the other input terminal of the OR circuit 87a.
A BK output signal is extracted from a.

The circuits corresponding to Y, M, and C have the same configuration, so to explain the circuit corresponding to Y, the output terminal of the above-mentioned OR circuit 88b is connected to the reset terminal of the address counter 83b, and the address counter 83b is connected to the buffer memory 82.
A Y input signal is input to the buffer memory 82b, and an output terminal of the buffer memory 82b is connected to one input terminal of the OR circuit 87b.
A Y output signal is taken out from the OR circuit 87b.

The output terminal of the address counter 83b is connected to a comparator 84b, and the output terminal of an address setter 85b to which the Y correction signal is input is connected to the comparator 84b. Further, the output terminal of the comparison @84b is connected to the other input terminal of the above-mentioned OR circuit 88b and the delay device 86b, and the output terminal of the delay device 186b is connected to the input terminal of the pattern signal generating means 81b, and the pattern signal The output terminal of the generating means 81b is connected to the other input terminal of the OR circuit 87a.

FIG. 27 is a signal waveform diagram showing the operation of FIG. 26, and in the same figure, t. 9 is the setting value of address setting 8ij85b,
tDM is the set value of the address setter 85c, toc is the set value of the address setter 85d, and tPY is the delay device 186b.
, tPM is the setting time of delay device 1186c, and tPc is the delay bag! This is the setting time of 1i86d.

In the color copying machine shown in FIG. 16, BK is used.

The recording devices are arranged in the order of Y, M, and C.

BK image data is processed by the image processing unit and output as is, and Y, M, and C image data are output with a delay of uDY+jDM+toe, respectively, with respect to the BK image data.

FIG. 28 is an explanatory diagram showing the arrangement of photoreceptors in the color image forming apparatus which is the basis of the embodiment.
14Y, 14M, and 14C are photoreceptors.

21 is a transfer belt.

As shown in FIG. 28, the length from the exposure position to the transfer position for each photoreceptor 14 is Ql (am), the linear velocity of the photoreceptor is v L (am/5ee), and the distance between the photoreceptors is Ql (@ )
.

When the linear velocity of the transfer belt is v, (+u+/5ec), the time t1 required from exposure to transfer has the same value for each photoreceptor and is given by the following equation.

t, = Q, / V l (see)
・= ・= (1) Travel time t2 between each photoreceptor
It is given by the following equation.

t, = Q, /V, (see)...
...(2) Then, in order to form images of each color at the same position on the transfer paper, jDYp jDM+ as described in -
jDC is given by equation (:3).

toy=” (see) ■2 tDM-1 Kurenai (see) ・・・・
...(3)■. . =2 (-ao) (2) Now, the operation of FIG. 26 will be explained for BK and Y, taking into account the sameness of the circuit configuration. .

A rise detection circuit 80 detects the rise of the vertical synchronization signal FGATE sent from the scanner section 1 .

BK, Y, M, C input signals and F G A T E
are input at the same time, the output of the rising edge detection circuit 80 is a signal representing the start of BK image writing.

The output signal of the rising edge detection circuit 80 is input to the BK pattern signal generation means, and outputs a detection pattern. In other words, in the case of BK, the leading edge of the image and the pattern position are the 25th
As shown in the figure, it is the same in the moving direction of the transfer belt.

The output signal of the rising edge detection circuit 80 is input to the reset terminal of the address counter Y83b via the OR circuit 88b, and resets the address counter Y83b. Y according to the count value of address counter 83b
The input image data of is stored in the buffer memory: Y82b.

On the other hand, the output of the address counter 83b is the comparator: Y8
4b, the output of the address counter 83b is compared with the set value of the address setting II: Y85b, and when the output of the address counter 83b matches the set value of the address setter 85b, the comparator 84b outputs a match signal. This match signal is transmitted to the buffer memory 82b.
is input to the reset terminal of address counter 83b via OR circuit 88b, and resets the output of address counter 83b to "φ".

The address φ of the buffer memory 82b is accessed again. After reading the already stored image data, the buffer memory 82b writes newly inputted image data to the same address.

Here, if the setting value of the address setting device 85b is set to the drum interval (t Dy) of BK and Y, the B
An image can be created by aligning the K and Y images.

The match signal of comparator Y84b is also input to delay device [:Y86b, triggering delay device 86b, and comparator 84b.
Pattern signal generation means: Y after a certain period of time from the matching signal of
81b outputs a detection pattern.

Since the coincidence signal of the comparator Y84b is output at the same time as the leading edge of the Y image, the Y detection pattern is outputted with a delay of the delay time (tpy) by the delay device i: Y86b from the leading edge of the image. Here, if the delay time of the delay device fit: Y86b is set to the time required for the transfer belt 21 to move d (m11), as shown in FIG.
The Y detection pattern can be created with a delay of d (Ilm) from the leading edge of the image.

The same goes for M and C, setting the value of the address setter 85C to tD□, and setting the value of the address setter 85d to t.
oc, and the setting time of the delay device 86G is t PM=
2 d/Vz It knee, delay device 186d (7
[If you set the fixed time to t pc = 3 d / Vz,
The leading edge of the image can be matched in each color, and at the same time the pattern image for detection can be made in d (mm) as shown in Figure 25.
It can be output in pitch.

Here, if the BK, Y, M, and C image positions shift on the transfer paper due to variations in the position of each photoconductor, variations in the exposure position to the photoconductor, and variations in the linear speed of the photoconductor and transfer belt, the detection The detection pattern also shifts accordingly, and by measuring the interval between the detection patterns, the amount of positional shift of the image can be detected.

FIG. 29 is a circuit diagram showing the configuration of a pattern detection circuit of a color image forming apparatus which is the basis of the embodiment, in which 27 is a reflective sensor, C2 is a capacitor, 90 is a voltage follower, 91 is an inverting amplifier, 92 is a comparator.

As shown in FIG. 29, the LED and phototransistor P
The output terminal of the reflective sensor 27 constituted by h is connected to the input terminal of the voltage follower 90 via the capacitor C2, and the output terminal of the voltage follower 90 is connected to the input terminal of the inverting amplifier 91. An output terminal of the comparator 92 is connected to an input terminal of the comparator 92.

30(a) to 30(d) are signal waveform diagrams explaining the operation of FIG. 29, in which FIG. 30(a) is a waveform diagram of the signal Fi1 at the output terminal of the reflective sensor 27, and FIG. 30(b) is a waveform diagram of the signal F,2 at the input terminal of the voltage follower 90, (c)
is a waveform diagram of the signal F14 at the output terminal of the inverting amplifier 91, and (d) is a waveform diagram of the signal F14 at the output terminal of the comparator 92.

As shown in Fig. 29, the output current of the phototransistor ph of the reflective sensor 27 is converted into voltage by the resistor R, and in Fig. 30 (,) the DC component is cut off by the capacitor C2 and only the AC component is taken out. (Figure 30(b))
, this signal is input to the inverting amplifier 91 via the voltage follower 90 and amplified to an appropriate voltage level (FIG. 30(c)).The output of the inverting amplifier 91 is determined by the comparator 92 and resistors R1 and R9. . Threshold voltage V
TM and a rectangular wave output signal is obtained (FIG. 30(d)).

Therefore, if the pitch of this rectangular wave output signal is measured, as shown in FIG. 25, pattern images 48BK, 4. You can know the intervals of BY, 48M, and 48C.

FIG. 31 is a block diagram showing the configuration of a pattern image interval measuring circuit of a color image forming apparatus, which is the basis of the embodiment.
In the figure, 93, 94a to 94C are counters, 95 is a data selector, 96 is a CPU, 97 is an AND circuit, 9
8.99 is an OR circuit.

As shown in FIG. 31, the A terminal of the counter 93 is AND
Circuit 97. The B terminal of the counter 93 is connected to one input terminal of the OR circuit 98 and the OR circuit 99.
A through the other input terminal of 8.99 and the inverting circuit 100.
It is connected to the other input terminal of the ND circuit 97. AN
D circuit 97. The output terminals of the OR circuit 98 and the OR circuit 99 are connected to the EN terminals of the counters 94a, 94b, and 94c, respectively, the data selector 95 is connected to the output terminals of the counters 94a, 94b, and 94c, and the output terminal of the data selector 95 C, PU96 is connected.

The CPU 96 is configured to output a clear signal to the counters 93, 94a to 94c, and output a select signal to the data selector 95.

FIG. 32 is a signal waveform diagram illustrating the operation of FIG. 31.

In FIG. 31, before measuring the pattern image interval, the CPU
A clear signal is output from 96, and the counter 93.94a
~94c is cleared. The output signal of the pattern detection circuit shown in FIG. 29 is input to the CK terminal of the counter 93, and the signals shown in FIG. 32 are output from the counter 93A terminal and B terminal, respectively.

The A terminal signal of the counter 93 and the inverted B terminal signal A
When ND is determined by the AND circuit 97, a signal indicating the pattern interval between BK and Y is obtained.

Also, by calculating the exclusive OR of the A terminal signal of the counter 93 and the B terminal No. 4a in the OR circuit 98, BK and M
A signal indicating the pattern spacing is obtained. Then, the logical sum of the A terminal signal and the B terminal signal of the counter 93 is ORed.
By determining this in the circuit 99, a signal indicating the BK and C pattern spacing is obtained.

BK and Y, BK and M, and BK obtained in this way
The signals indicating the pattern intervals of
The reference clock is counted, and binary data proportional to the pattern intervals of BK and Y, BK and M, and BK and C are output from the counters 94a to 94c.

When the counting operations of these counters 94a to 94c are completed, a select signal is supplied from the CPU 96 to the data selector 95, and the binary data of the counters 94a to 94c is taken in from the data selector 95.

In the CPU 96, the captured binary data is compared with a reference value, the difference between the reference value and the measured value is calculated, and correction signals ΔY and ΔM are generated to correct the difference.

ΔC is output from the CPU 96.

Then, this correction signal is sent to the address setters: Y, M, C86b to 85d shown in FIG. 26, and by changing the writing timing of the image for BK, the position of the image of each color in the sub-scanning direction can be corrected. .

However, as already shown in FIG. 22(b).

When the optical housing deforms due to temperature changes, etc.

The trajectory of the scanning line of the beam becomes curved.

FIG. 33 is a diagram illustrating image deviation due to curvature of the locus of the scanning line of the beam in the color image forming apparatus which is the basis of the embodiment, in which 101 is an image of C, 102
are BK, Y, and M images, 103 is the maximum deviation amount, and T is the transfer paper.

As shown in Fig. 33, if the scanning line of a beam of a certain color is curved, color shift cannot be prevented even if the correction described above is performed (in Fig. 33, the scanning line of a beam of C is curved). are doing).

Now, a specific embodiment of the present invention will be explained, and first, a method for correcting the curvature of the scanning line of the beam will be explained.

First, a case will be described in which the curvature of the scanning line of the beam is corrected by curving one reflection mirror.

FIGS. 3(a), 3(b), and 3(c) are explanatory diagrams showing the trajectory of the reflecting mirror of the optical system 1 and the scanning line, respectively, when the reflecting mirror in the embodiment is in the normal position.

Figure 4 (a), (b), (c) and Figure 5 (a)
), (b), (c).

FIG. 6 is an explanatory diagram showing an optical system, a reflecting mirror, and a scanning locus when the reflecting mirror in the example is curved.

In these figures, 14 is a photoreceptor, M is a reflection mirror,
24 is a beam, 24a is a beam reflected at the center, 24
b is the beam reflected at the periphery, LL, L2. L3 is the locus of the scanning line on the photoreceptor 14.

Figures 3 (a), (b), (e) to Figure 5 (a)
), (b), and (c), when the mirror M curves, the locus of the scanning line curves accordingly. Fourth
Figures (a) to (c) are explanatory views when the reflecting mirror M is curved in the direction of the reflecting surface from the state shown in Fig. 3 (8). At this time, the reflection position of the beam changes between the central part and the peripheral part of the mirror M, and the locus of the scanning line curves as shown by L2.

FIGS. 5(a) to 5(c) are explanatory diagrams when the one-reflection mirror M is curved in the opposite direction to the reflecting surface, contrary to FIGS. 4(a) to (e). At this time, the locus of the scanning line curves in the opposite direction to that in FIG. 4(C), as indicated by L3.

As is clear from this, when the locus of the scanning line on the photoreceptor 14 is curved, the curvature of the scanning line is corrected by deforming (deflecting) the first reflecting mirror M in the normal direction of the reflecting surface. can do.

Next, an example of a mechanism for deforming the reflecting mirror M as shown in FIGS. 4(b) and 5(b) will be described with reference to the drawings.

FIG. 6(a) is an explanatory diagram showing the configuration of the reflecting mirror deformation stirring mechanism in the embodiment, and FIG. 6(b) is a sectional view taken along the line AA in FIG. 6(a). In these figures, 51 is a reflecting mirror; 52
53 is a support member for the mirror, 53 is a stay that also holds down the mirror, 54 and 55 are elastic members, 56 and 57 are screws, 58 is a suppressing member that presses the mirror, and 59 is an adjustment screw equipped with a worm wheel portion. .

In FIGS. 6(a) and 6(b), the stay 53 is fixed with the screw 56.
By fixing the reflection mirror 51 at 57°, both ends of the reflection mirror 51 are pressed against the support member 52 by elastic members 54 and 55. Also, a suppressing member is provided in the longitudinal center of the reflection mirror 51 to deform the reflection mirror 51. 58 are provided. Further, a male thread is attached to this suppressing member. The male thread fits into the female thread of the adjustment screw 59, and the female thread of the adjustment screw 59 fits into the female thread provided at the longitudinal center of the stay 53. Further, the part of the adjusting screw indicated by 60 in the figure is a worm wheel, which meshes with a worm gear 62 attached to a stepping motor 61. By driving this stepping motor 61, the adjusting screw 59 rotates, and according to the principle of a differential screw, the suppressing member 58 is moved as shown by the arrow B in the figure.
move in the direction.

The reflecting mirror 51 can be modified as shown in FIGS. 4 and 5.

Next, as another example of correcting the curvature of the scanning line, a method will be described in which the curvature of the scanning line is corrected by changing the inclination of a transparent parallel plate (glass) placed on the optical path of the beam.

First, the principle of changing the curvature of the scanning line by tilting the parallel plate with respect to the optical axis will be explained.

FIGS. 7(a) and 7(b) are a perspective view and a side view, respectively, when the parallel plates in the example are in the normal position.

FIGS. 8(a) and 8(b) are a perspective view and a side view, respectively, when the parallel flat plate in the example is tilted.

FIGS. 9 to 11 are explanatory diagrams showing the displacement of the beam after passing through a parallel plate in the example.

FIG. 12 is an explanatory diagram showing the relationship between the inclination of the parallel plate and the locus of the scanning line in the example.

In these figures, TP is a transparent parallel plate, B is the beam, DP is the deflection plane of the laser beam, BO is the beam optical axis toward the image height of 0, TLO is the locus of the scanning line when Y=0°, TL30 is the locus of the scanning line when γ=30°.

Figures 7(a) and (b) show the transparent parallel plate T as described above.
This is a diagram showing a state in which the normal line of P and the beam optical axis BO toward the image height O are -M, and at this time, the beam B
does not deviate in the sub-scanning direction before and after passing the parallel plate TP, and FIGS. 8(a) and (b) are similar to FIG. 7(a).

It is a diagram showing a state in which the parallel plate TP is rotated from the state of (b) around an axis substantially parallel to the main scanning direction, and at this time, the beam B has passed through the parallel plate TP.

Displaced in the sub-scanning direction from the position before passing. This amount of displacement is indicated by C in FIG. 8(b).

By the way, this displacement l:〇 is different from the image height to which the beam B is directed. (This is because the beam incidence angle of the parallel plate TP/\ differs depending on the image height.) An example will be given below for explanation. As shown in FIG. 9, on the deflection plane, the angle formed by the beam heading towards image height 0 and the beam heading towards image height +150 is defined as ψ.

Also, as shown in Fig. 10, let the angle of incidence of the beam toward the image height O on the parallel plate be γ.Then, in this state, the angle of incidence of the beam toward the image height 150 on the parallel plate −〇 is as follows. It is given by Eq.

θ=”'-” L + tan β”; tan y ) (4
) However, in equation (4), β=jan-''±4ren.

C01iγ Furthermore, where the thickness of the parallel plate TP is d and the refractive index is n, there is a relationship between the incident angle i and the axis deviation C as shown in equation (5).
(See Figure 11).

COSθ C=dsini(1, z sin' 0 )
(5) If the axis deviation of the beam heading towards image height 0 is 00, and the axis deviation of the beam heading towards image height 150 is C15°, then
(6).

Equation (7) is obtained.

C,=dsinY(12-z) (
6) n −5in γ COSθ C□,. = d sinθ(1-nz-5in” B
) (7) Furthermore, the amount of axis deviation only in the sub-scanning direction is set to eo+80. . Then, (i
s), formula (9) is obtained.

eo=C,...(8) C,,osin"η+C082η"CO9λe"ll"
cos fJ (cos rt +sln q ・t
an B ) (9) tanψ However, in equation 9, λ=:tan-' ((an
y ), rr = tan-' (tan y 11c
osλ).

- Example Toshite, ψ=20°, y=30°, d=5mm.

e from (8), (9) as n =],,5. and e
ls. Find e, = 0.967 (mm), 8
1SO=1.064 (11111).

This revealed that the amount of axis deviation in the sub-scanning direction is different between the beam heading toward image height 0 and the beam heading toward image height 150.

In this case, e, , -so=0.095(mm
), and as shown in FIG. 12, it can be seen that the scanning line is curved by tilting the parallel plate. The amount of curvature changes by changing the inclination γ of the parallel plate, and the direction of curvature changes depending on the direction of the parallel plate.

Next, an example of a mechanism for changing the inclination of the parallel plates will be explained.

FIGS. 13 and 14 are explanatory diagrams of a mechanism that uses the dustproof glass in the laser beam scanning device as a parallel flat plate for correcting curvature. In these figures, 32 is the dustproof glass, 33 is the dustproof glass.
6 is an optical housing, 63 is a holder, 64 is a support member, 6
5 is a stepping motor, and 66 is a worm gear.

As shown in FIGS. 13 and 14, the dustproof glass 32 is held in a holder 63 whose outer shape forms part of a cylinder.
The holder 63 is supported by a support member 64 fixed to the optical housing 33.

Further, a worm wheel 64 is attached to the end of the holder 63, and a worm gear 66 is attached to the rotating shaft of a stepping motor 65 fixed to the optical housing 33.
They are intertwined. Then, by driving the stepping motor 64, the dustproof glass 32 is rotated in the direction of the arrow in the figure.

Furthermore, another method for correcting the curvature of the scanning line is to take advantage of the fact that the scanning line is curved due to the positional shift or tilt of the lens, which has already been explained with reference to FIG.

There are ways to move or rotate the lens.

FIG. 15 is an explanatory diagram showing the adjustment mechanism of the fθ lens in the example, and in the same figure, 29 is the fθ lens system;
3 is an optical housing, 67 is a laminated piezoelectric actuator, and 68 and 69 are fO lenses.

As shown in FIG. 15, the fθ lens 68 of the fθ lens system 29 is held in the optical housing 33, and the fθ lens 69
is held in the optical housing 33 via a laminated piezoelectric actuator 67.

With such a configuration, the laminated piezoelectric actuator 67
By varying the voltage applied to.

The fθ lens 69 moves in the direction of the arrow in FIG.

Scan line curvature is corrected.

Next, detection of a pattern image in an embodiment of the present invention will be described.

FIG. 1 is an explanatory diagram of the pattern image detection method in the embodiment, and in the figure, 21 is a transfer belt.

T is transfer paper, 44 is a drive roller, 70.71 is a sensor,
72BK, 72Y, 72M, 72G, 738, 73Y
, 73M, and 73C are pattern images.

In the embodiment, as shown in FIG.
A distance d in the main scanning direction on the upstream side of the image forming area 1 near the side edge. (mm), pattern images 73BK, 73Y, 73M, and 73C of each color are formed, and these pattern images are detected by a sensor 71 disposed opposite the upstream end of the transfer belt 21. Also, in the sub-scanning direction, pattern images 73BK, 73Y, 73M, 73
At positions corresponding to C, pattern images 72BK, 72Y, 72M,
72C are formed at a distance d, (am) adjacent to each other, and these pattern images are detected by a sensor 70 disposed facing the center of the upper end of the transfer belt 21.

When detecting these pattern images, the 29th
The pattern detection circuit and pattern image interval measurement circuit described in FIG. 3 and FIG. 31 are used.

Next, a method of changing the curvature of the scanning line and the timing of writing the image based on the detected interval between the pattern images will be described. Here, a case will be described in which curvature is corrected by rotating the dustproof glass shown in FIGS. 13 and 14.

First, the detection time difference corresponding to the pre-known intervals d, 2d, and 3d between the BK pattern image and the Y, M, and C pattern images is t, Y, tOM (=2xt, Y).

death. Let C (=3Xt, Y). And actually sensor 7
BK pattern image detected by 0 and Y.

The intervals between the pattern images of M and C are tlY, tlM, and t.

C. BK pattern image detected by sensor 71;
The interval between Y, M, and C pattern images is t2Y.

Let t, M, and t2C. Also, the rotation angle γ and the axis deviation amount e of the scanning line when the dustproof glass is rotated. and the amount of curvature δ (=
e-engineering. -e, , ) can be obtained as described above, so these relationships are stored in a ROM table or the like.

The respective correction methods will be explained for various cases.

(1) In the case of t-work Y=t, Y#t, Y In this case, it can be concluded that the amount of curvature of the BK scanning line and the Y scanning line is the same, but the BK image forming position and the Y image forming position is shifted in the sub-scanning direction. Therefore, by inputting the correction signal corresponding to the toy-t machine Y to the address setter Y85b shown in FIG.

Correct the position of the Y image in the sub-scanning direction.

(2) When t, M=t-work M≠t, M In this case,
The BK images overlap in the center of the image area. However, B.K.
The amount of curvature of the scanning line of and the amount of curvature of the scanning line of M are different.

In this case, first, the curvature correction amount δM (=
t 2 M t M) is calculated, and then the curvature correction amount δ,
The rotation angle γ of the dustproof glass corresponding to . is read from the ROM table. Also, the axis deviation amount e corresponding to the rotation angle γ. M is also read from the ROM table. Then, a signal corresponding to the rotation angle γ□ is inputted to the drive circuit of the stepping motor 66 corresponding to M shown in FIG. 85
By inputting to c, the image of BK and the image of M can be superimposed.

(3) If t, C≠LLC≠ and 2C, then,
The BK image and the C image are different in amount of curvature and position in the sub-scanning direction. At this time as well, the curvature correction amount δc (=t2C-t, C) of the scanning line C is first determined, and the curvature correction amount δ is obtained. The rotation angle γ of the dustproof glass corresponding to . is read from the ROM table. In addition, the axis deviation amount eoc corresponding to the rotation angle Yc is also RO
Read from M table. Then, a signal corresponding to the rotation angle γc is inputted to the drive circuit of the stepping motor 66 corresponding to C shown in FIG.
By inputting a correction signal obtained from a value obtained by comparing the times corresponding to C to the address setter C85d shown in FIG. 26, the C image can be superimposed on the BK image.

FIG. 2 is an explanatory diagram of another method of detecting a pattern image in the embodiment, in which 21 is a transfer belt, T is a transfer paper, 44 is a drive roller, 70, 71° 74 is a sensor, 72
BK, 72Y, 72M, 72C, 73BK, 73Y, 7
3M, 73C, 75BK, 75Y, 75M, and 75C are pattern images.

In the above description, an example has been described in which the pattern image on the transfer belt is detected at two locations, one at the center of the image area and one at one end, and the curvature of the scanning line and the shift in the sub-scanning direction are corrected.

On the other hand, in the case of Fig. 2, sensors 70, 71, and 74 are provided at three locations at the center of the five image areas and at the edge of the surface, and the pattern image is detected at these three locations. .

In this case, for example, the difference δ7 in the amount of curvature between the BK scanning line and the Y scanning line is obtained from equation (10).

Y+t, Y (10)δY””
2 In the formula (10), t and Y are the distance between the BK image and the Y image detected by the sensor 70, and t□Y is the distance between the BK image and the Y image detected by the sensor 71. The distance t, Y is the distance between the BK image and the Y image detected by the sensor 74.

Furthermore, by making it possible to detect the shift of images of each color at both ends of the image area, it is possible to also correct the inclination of the scanning line, as described in Japanese Patent Laid-Open No. 63-271275. It is.

As described above, according to the embodiment, the amount of curvature of the scanning line of the beam and the deviation in the sub-scanning direction are detected by detecting the pattern image formed on the conveyor belt 21 at a plurality of positions in the main-scanning direction. By controlling the curvature correction means in accordance with this detected value, color shift in the formed color image is prevented.

[Effects of the Invention] According to the present invention, color shift caused by curving of the locus of the scanning line of the laser beam due to temperature changes or the like is also corrected, and a high-quality color image is formed.

[Brief explanation of drawings]

1 to 15 are diagrams explaining the present invention in detail, FIG. 1 is an explanatory diagram of a pattern image detection method, FIG. 2 is an explanatory diagram of another pattern image detection method, and FIG. 3 is an explanatory diagram of a pattern image detection method. Optical system when the reflecting mirror is in the normal position. Explanatory diagrams showing the reflection mirror and the trajectory of the scanning line, FIGS. 4 and 5 are optical systems when the reflection mirror is curved. Explanatory diagram showing the locus of the reflection mirror and the scanning line, Fig. 6(a)
) is an explanatory diagram of the reflection mirror deformation mechanism, and the same figure (b) is the same figure (
AA sectional view of a), Figure 7 (aL (b) is a perspective view and side view, respectively, when the parallel plate is in the normal position, Figures 8 (a) and (b) are when the parallel plate is tilted) FIGS. 9 to 11 are explanatory diagrams showing the displacement of the beam after passing through the parallel plates. FIG. 12 is an explanatory diagram showing the relationship between the inclination of the parallel plates and the locus of the scanning line. , FIGS. 13 and 14 are explanatory diagrams of a mechanism that uses the dustproof glass in the laser beam scanning device as a parallel flat plate for curvature correction, FIG. 15 is an explanatory diagram of the fθ lens adjustment mechanism, and FIGS. 33
The figure is a diagram for explaining a color image forming apparatus which is the basis of an embodiment of the present invention, Figures 1 and 6 are explanatory diagrams showing the overall configuration, and Figures 17 and 18 are the laser beam scanning device of Figure 16. FIG. 19 is an explanatory diagram showing another example of the laser beam scanning device, FIG. 20 is an explanatory diagram showing the optical system of the laser beam scanning device in normal operation, and FIG. 21 is an explanatory diagram showing the optical system of the laser beam scanning device in normal operation. FIG. 22 is an explanatory diagram showing the beam scanning lines of FIGS. 20 and 21; FIG. 23 is a system block diagram;
FIG. 24 is an explanatory diagram of the transfer belt portion, FIG. 25 is an explanatory diagram of pattern image detection, and FIG. 26 is a block diagram showing the configuration of the image creation signal generation circuit.5 FIG. 27 is a signal diagram showing the operation of FIG. 26 Waveform diagram, FIG. 28 is an explanatory diagram showing the arrangement of the photoreceptor, FIG. 29 is a circuit diagram showing the configuration of the pattern detection circuit, and FIGS. 30(a) to (d) are signals explaining the operation of FIG. 29. FIG. 31 is a block diagram showing the configuration of the pattern image interval measuring circuit, FIG. 32 is a signal waveform diagram explaining the operation of FIG. 31, and FIG. It is a figure explaining a shift. 1... Scanner section, 2... Image processing section, 3... Printer section, 12C, 12M, 12Y
, 12BK... Laser beam scanning device, 13C
, 13M, 13Y, 13 B K --- Recording device, 14 G, 14 M, 14 Y, 14 B K ---
--- Photoreceptor, 16C, 16M, 16Y, 1.6
B K------Developing device, ]-7C, 17M, 17
Y, 178K...Transfer charger, 258K.
...Laser unit, 278K...Polygon mirror, 28BK...Condensing lens, 29B
K... fθ lens, 30BK, 318K...
... folding mirror, 32BK ... dustproof glass, 338K ... housing, 44 ...
・Drive roller, 47... Reflective sensor, 488
, 48Y, 48M, 48C...---Pattern image, 70.71...Sensor, 72BK, 72Y. 72M, 72C, 73BK, 73Y, 73M, 73C・
...Pattern image, 758, 75Y, 75M. 75C...Pattern image, 80...Rise detection circuit, 818-81d...Pattern signal generation means. 82b~82d...Buffer memory, 83b~
83d...Address counter, 84b to 84d
......Comparator, 85b-85d...Address setter, 86b-86d...Delay device, 8
7a-87d...OR circuit, 90...
Voltage follower, 91...Inverting amplifier, 9
2... Comparator, 93.94a to 94c.
...Counter, 95...Data selector, 96...CPU. Go to Figure 1 Figure 2 State praise and hate play E
- Fig. 7 Main scanning direction 1 Fig. 8 (a) Fig. 9 Electron, f[IO Fig. 11 Fig. 12: Machine height -150 1 Elephant height○ (
Aircraft height +150 Fig. 13 Fig. 14 Fig. 15 Fig. 916g Fig. 17 Fig. 18 Fig. 19 Fig. 20 Fig. 21 Fig. O Fig. 22 , j U Fig. 24 Fig. 25 Fig. 30 (a) EIK Y MC ＞ Σ Q ＜＜＜

Claims (1)

[Claims] A plurality of photoconductors and a photoconductor provided corresponding to these photoconductors,
a laser beam scanning device that forms an electrostatic latent image on the photoconductor using light beams modulated with different color signals; and a developing device that visualizes the electrostatic latent image formed on the photoconductor. A collar comprising: a transfer means for transferring the developed image obtained by visualizing the electrostatic latent image by the developing means onto a transfer paper; and a transfer belt for moving the transfer paper along the photoreceptor. The image forming apparatus includes an image forming signal generating means for forming a pattern image for measurement on the transfer belt, and a position of the pattern image formed on the transfer belt in the sub-scanning direction at a plurality of locations in the main scanning direction. It is characterized by having a position detection means for detecting a position, a curvature correction means for correcting curvature of a beam scanning line of the laser beam scanning device, and a control means for controlling the curvature correction means based on a detection signal of the position detection means. Color image forming apparatus.