JP2003156905A - Color image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming apparatus that securely detects the position of toner even in the case of toner having high reflectance, prevents erroneous detection of a pattern which is caused by a change in the surface of a body to be subjected to transfer or scratch on the surface of the body, detects a reliable amount of color slippage and therefore, forms a color image of high image quality. SOLUTION: At least, out of color slippage detection images in separate colors, the color of reference value setting images (13a, 14a, 15a, and 16a) for the color slippage detection image in a color having the lowest light reflectance is made different from the color of reference value setting images (13b, 14b, 15b, and 16b) for the color slippage detection images in the other colors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer or a copying machine using an electrophotographic system or an electrostatic recording system, and more particularly to a multicolor image forming apparatus having a plurality of image forming units. The present invention relates to a color image forming apparatus that can be formed.

[0002]

2. Description of the Related Art Conventionally, an electrostatic latent image is formed on an image carrier by an electrophotographic system or an electrostatic recording system, and the electrostatic latent image is developed as a toner image by a toner included in a developer by a developing device. There is an image forming apparatus that obtains an image by transferring a toner image onto a recording material.

Particularly, in an electrophotographic color image forming apparatus, a plurality of image forming sections are provided for speeding up.
Various methods have been proposed in which images of different colors are sequentially transferred onto a recording material held on a conveyor belt. In such a color image forming apparatus, each image forming unit serves as an image bearing member, for example, a drum type electrophotographic photosensitive member, that is,
A toner image formed on each photosensitive drum by the electrophotographic image forming process is provided as a recording material carrier, for example, a recording material that is conveyed to each image forming unit on a conveyor belt that moves endlessly. Transfer to form a color image.

By the way, as a problem of a color image forming apparatus having a plurality of image forming portions, due to mechanical precision and the like, the plurality of photosensitive drums and the conveyance belt are unevenly moved, and the photosensitive drums at the transfer positions of the respective image forming portions are caused. For example, the relationship between the outer peripheral surface and the movement amount of the conveyor belt may be different for each color, and when the images are superposed, they do not coincide with each other and a color shift occurs.

In particular, in an apparatus having a photosensitive drum and a plurality of image forming sections having a laser scanner as an exposing means for forming an electrostatic latent image on the photosensitive drum, each image forming section has a space between the laser scanner and the photosensitive drum. If there is an error in the distance and the error differs between the image forming units, a difference occurs in the scanning width of the laser on the photosensitive drum and a color shift occurs.

FIG. 16 shows an example of color shift. In the figure, the original image position 7 and the image position 8 when the color shift occurs
(8a, 8b, 8c, 8d) are shown. FIG.
Although (a), (b), and (c) show color misregistration in the main scanning direction (direction orthogonal to the recording material conveyance direction), two lines are drawn separately in the conveyance direction for the sake of explanation. is there.

FIG. 16 (a) shows the deviation of the main scanning line inclination, which occurs when there is an inclination between the optical section and the photosensitive drum. For example, by adjusting the positions of the optical unit and the photosensitive drum and the position of the lens, the correction is performed in the arrow direction.

FIG. 16B shows a color shift due to a variation in the main scanning line width, which is caused by a difference in the distance between the optical section and the photosensitive drum. This is likely to occur when the optical unit is a laser scanner. For example, by finely adjusting the image frequency, that is, when the scanning width is too long, the frequency is increased to change the length of the scanning line, thereby correcting in the arrow direction.

FIG. 16C shows a writing position error in the main scanning direction. For example, if the optical unit is a laser scanner,
It is corrected in the direction of the arrow by adjusting the writing timing from the beam detection position.

FIG. 16D shows a writing position error in the recording material conveyance direction. For example, the writing timing of each color from the detection of the leading edge of the sheet is adjusted to correct the arrow direction.

Conventionally, in order to correct these color misregistrations, the image forming apparatus uses a color misregistration detection pattern for each color as an image for color misregistration detection by a toner image formed in each image forming unit on the conveyor belt 3. And a pair of optical sensors 6a provided on both sides of the downstream side of the transport belt 3 in the recording material transport direction (in the vicinity of both ends in the direction orthogonal to the recording material transport direction).
6b (FIG. 9), and depending on the detected deviation amount,
It has a color misregistration correction means for performing various adjustments as described above. As a result, the image forming position is corrected.

FIG. 10 shows an example of a conventional color shift detection pattern. As shown in FIG. 10, patterns 9 (9a to 9d) and 10 (10a to 10d) for recording material conveyance direction for detecting the amount of color misregistration in the recording material conveyance direction (sub-scanning direction).
And main scanning direction patterns 11 (11a to 11d) and 12 (12a to 1) for detecting the color misregistration amount in the main scanning direction.
2d) is formed. In this example, the main scanning direction patterns 11 and 12 are formed with an inclination of 45 degrees with respect to the transport belt moving direction. Pattern 9 for recording material conveyance direction,
10 and main scanning direction patterns 11 and 12, a to d are black (Bk), yellow (Y), magenta (M), and cyan (C) patterns, respectively. Also, in the figure, tsf1-4, tmf1-4,
tsr1 to 4 and tmr1 to 4 indicate the detection timing of each pattern, and the arrow indicates the moving direction of the conveyor belt 3.

Here, the moving speed of the conveyor belt 3 is vmm.
/ S, with black as the reference color, black recording material conveying direction patterns 9a and 10a and patterns 9b to 9 of each color.
The theoretical distance between d, 10b and 10d is
Ymm, dsMmm, dsCmm. Further, the recording material conveying direction patterns 9a to 9d of each color on the left side when viewed from the upstream side in the conveying belt moving direction and the main scanning direction pattern 11a.
Measured distances between 11d and 11d are dmfBkm and
m, dmfYmm, dmfMmm, dmfCmm,
Recording material conveying direction patterns 10a to 10d for each color on the right side
And the measured distances between the main scanning direction patterns 12a to 12d are dmrBkm, dmrYmm, and dmr, respectively.
Mmm and dmrCmm. If black is the reference color, the misregistration amount δes of each color in the recording material transport direction
Is δesY = v × {(tsf2-tsf1) + (tsr2-tsr1)} / 2-dsY (1) δesM = v × {(tsf3-tsf1) + (tsr3-tsr1) / 2-dsM (2) δesC = v × {(tsf4-tsf1) + (tsr4-tsr1)} / 2-dsC (3) Further, with respect to the main scanning direction, the positional deviation amounts δemf and δemr of the respective colors of the left and right are: dmfBk = v × (tmf1-tsf1) ... (4) dmfY = v × (tmf2-tsf2) ... (5) dmfM = vx (tmf3-tsf3) ... (6) dmfC = vx (tmf4-tsf4) ... (7) and dmrBk = vx (tmr1-tsr1) ... (8) dmrY = vx (Tmr2-tsr2) ... (9) dmrM = v * (tmr3-tsr3) ... (10) dmrC = v * (tmr4-tsr4) ... (11) From [delta] emfY = dmfY-dmfBk ... -(11) deltaemfM = dmfM-dmfBk ... (12) deltaemfC = dmfC-dmfBk ... (13) and deltaemrY = dmrY-dmrBk ... (14) deltae rM = dmrM-dmrBk ··· (15) δemrC = dmrC-dmrBk ··· (16), and the direction shifted from the positive and negative calculation result can be determined. Then, the writing position is calculated from δemf as δemr−δemf
The main scanning width is corrected from. When there is an error in the main scanning width, the writing position is calculated not only by δemf but also by taking into account the amount of change in the image frequency that has changed due to the main scanning width correction.

FIG. 11 shows the pattern detecting section (optical sensor) 6 of the color shift detecting means. The pattern detection unit 6 has a light emitting element 51 such as an LED serving as a light emitting means, and a light receiving element 52 such as a photo sensor serving as a light receiving means. The pattern detection unit 6 detects the color misregistration detection patterns 9, 10, 11, 12 formed on the conveyor belt 3. That is, the emitted light 53 is emitted from the light emitting element 51,
The conveyor belt 3 or the color shift detection patterns 9, 10, 11,
Of the reflected light from 12, the received light 54 is received by the light receiving element 52. The light emitting element 51 and the light receiving element 52 are configured by a regular reflection optical system with the conveyor belt 3 as a reflection surface.
The position of the color misregistration detection pattern is detected based on the difference in reflectance of the regular reflection light between the conveyor belt 3 and the color misregistration detection pattern, that is, the difference in reflectance.

FIG. 12 shows a pattern reading processing section for processing the pattern detection signal by the color shift detecting means. The pattern reading processing unit includes a light emitting element 51 and a light receiving element 51.
And the like, a calculation unit 61 that calculates the color shift amount and the correction value by calculating the detection data, and an image output unit 6 that forms an image according to the calculation result.
2, and a timer 63 and a CPU 64 for adjusting the timing of each part and performing various settings. The arithmetic unit 61, the timer, the CPU 64, and the like constitute a unit that controls the image forming position of each color image based on the pattern detection signal for detecting the color misregistration.

FIG. 13 shows a circuit configuration of the light receiving element 52 included in the pattern detecting section 6 of the color shift detecting means shown in FIG. The detected current from the light receiving element 52 is converted into a voltage by the I / V conversion circuit 55, and the upper peak hold circuit 56a and the lower peak hold circuit 56b as means for storing the maximum value and the minimum value of the output of the light receiving element 52. The maximum value and the minimum value are respectively detected by the first resistor 57a,
The voltage is divided by the second resistor 57b. The first and second resistors 57a,
57b constitutes a reference value generating means for generating a reference value (pulse conversion reference voltage) determined by the maximum value and the minimum value. Thus, the maximum / minimum value detection circuit 50 of the output of the light receiving element 52 is configured. Then, the output waveform of the I / V conversion circuit 55, the first resistor 57a, and the second resistor 57
A comparison circuit (comparator) 58 as a comparison means determines the magnitude relationship between the voltage value divided in b and a pulse signal is generated. Further, such a circuit operates on the basis of a reset signal from the CPU 64, and the upper peak hold circuit 56a operates.
And a function of resetting the information held in the lower peak hold circuit 56b.

Here, in order for the upper peak hold circuit 56a and the lower peak hold circuit 56b to obtain the maximum value and the minimum value respectively, the line (pattern) is set to 1 in advance.
Need to be read. A pulse conversion reference voltage is created from the maximum and minimum values obtained from this line.
That is, in the color misregistration detection pattern shown in FIG. 10, just before the recording material conveyance direction patterns 9a and 10a,
It is necessary to form maximum value / minimum value acquisition patterns (hereinafter, referred to as “minimum value reading patterns”) 13 and 14 as reference value setting images.

With reference to FIG. 14, a detection waveform when the color shift detection pattern is detected by the pattern detection unit 6 shown in FIG. 11 will be described. In FIG. 14, the horizontal axis represents time t. FIG. 14A shows the color shift detection patterns 9, 10, 11, and 12 detected by the light receiving element 52. FIG. 14 (b)
Shows the output waveform of the light receiving element 52. FIG. 14C shows
The pulse conversion reference voltage (threshold value, slice level) that is generated from the output of the maximum value / minimum value detection circuit and serves as the reference of the comparison circuit 58. FIG. 14D shows the output (position information pulse) of the comparison circuit 58. is there.

The conveyor belt 3 has a high reflectance and emits the emitted light 5.
Most of 3 becomes regular reflection light 54, which is received by the light receiving element 52. Color shift detection patterns 9 and 1 which are toner images
The reflectances of 0, 11, and 12 are low, most of the emitted light 53 is scattered, and the specularly reflected light 54 received by the light receiving element 52 is small. The output waveform (b) is high when the conveyor belt 3 is detected and is low when the color shift detection pattern is detected. The value of the reference voltage (c) is the first resistance 57a, the second
It is determined by the voltage division ratio of the resistor 57b. This relationship is expressed by the following equation.

A: B = first resistance: second resistance

To facilitate understanding, among the color shift detection patterns shown in FIG. 10, the recording material conveying direction patterns 9a to 9d on the left side when viewed from the upstream side in the moving direction of the conveying belt 3 are shown.
For example, first, the black, yellow, magenta, and cyan color shift detection patterns 9a to 9d shown in FIG. 10 are formed on the transport belt 3, and the pattern detection unit 6 of the color shift detection means shown in FIG. 11 is formed. Detected at. The light receiving element 52 of the pattern detection unit 6 outputs four waveforms corresponding to FIG. The first corresponds to the color shift detection pattern of black, the second to yellow, the third to magenta, and the fourth to cyan color misregistration detection patterns.

At this time, the waveforms for detecting the four color patterns show the same shape. That is, the first to fourth valleys are lower than the reference voltage (c), and the pulse corresponding to FIG. 7D is output from the comparison unit. The calculation unit shown in FIG.
The center position of each of the first to fourth pulses in (d) is obtained, and the time difference between the center positions is further obtained. The color shift amount is calculated from the difference between the calculated time difference and the preset time difference value.

[0023]

However, the four color toners have different light reflectances, and the black reflectance is almost 0% as shown in FIG. The reflectance of the toner is 20% to 40%. Therefore, in order to detect four color toners using the same reference voltage (threshold value), it is necessary to set the reference voltage on the sufficiently bright side (the side of the amount of light reflected by the conveyor belt 3). Here, in the following description, the reflectance is high, that is, the conveyor belt 3
The side of the reflected light amount due to is simply referred to as the “bright side”, and the side of low reflectance such as magenta is simply referred to as the “dark side”.

However, when the reference voltage is set to the bright side, the output waveform of the pattern detection unit 6 due to the change of the light amount due to the scratches on the conveyor belt 3 or the surface variation of the conveyor belt is changed to the reference voltage as shown in FIG. 15B. There is a problem that there is a high possibility that an erroneous detection will occur.

In the above description, the color image forming apparatus in which the toner image is transferred from the photosensitive drum to the recording material conveyed on the conveyor belt has been described as an example, but the same problem also exists in the intermediate transfer type color image forming apparatus. To do. An intermediate transfer type color image forming apparatus multiple-transfers toner images of a plurality of colors from a photosensitive drum to an intermediate transfer body, and then secondarily transfers the toner images from the intermediate transfer body to a recording material at once to form a color image. Form. Even in such an intermediate transfer type image forming apparatus, in order to correct the positional deviation (color misregistration) of the toner images of a plurality of colors which are superimposed on the intermediate transfer body, the intermediate transfer body is subjected to the same operation as in the case of the conveyor belt. A color shift detection pattern and a minimum value reading pattern are formed and detected.

Therefore, an object of the present invention is to reliably detect the position of an image for detecting a color shift formed by a developer having a high light reflectance, and to transfer a transfer means such as a conveying means or an intermediate transfer body. It is possible to prevent erroneous detection of color misregistration detection images due to surface fluctuations on the body or scratches on the surface of the transferred material, and it is possible to form a high-quality color image by detecting an appropriate amount of color misregistration. Another object of the present invention is to provide a color image forming apparatus.

Another object of the present invention is to achieve the above object,
In addition, the usability can be improved by shortening the detection time and the calibration time, and the accuracy of the color misregistration correction can be improved by obtaining the accurate position information of the color misregistration pattern. A color image forming apparatus is provided.

[0028]

The above object can be achieved by a color image forming apparatus according to the present invention. In summary, the present invention forms images of different color developer images on a plurality of image bearing members, and transfers images of the developer images to form a plurality of color developer images on a transfer target. Forming means; conveying means for conveying the recording material, to which the developer is transferred from the plurality of image carriers, to the plurality of image carriers, and detecting means for detecting the developer image on the conveying means. Detecting means for detecting positional information of the developer image on the conveying means by comparison with a reference value set based on an output signal when the reference value setting image formed on the conveying means is detected. In the color image forming apparatus having: and, the reference value setting image for the color shift detection image of the color having the lowest light reflectance among the color shift detection images of the plurality of colors, and the other color Reference value setting image for color shift detection image That bets with different colors is a color image forming apparatus according to claim.

According to another aspect of the present invention, the developer images of different colors are sequentially formed on the image bearing member, and the developer images are transferred to form a plurality of color developer images on the transferred material. An image forming unit for forming; an intermediate transfer member on which a developer is sequentially transferred from the image carrier; a detecting unit for detecting a developer image on the intermediate transfer member, which is formed on the intermediate transfer member. Detecting means for detecting positional information of the developer image on the intermediate transfer member by comparison with a reference value set based on an output signal when the reference value setting image is detected; and the image forming means. Means for controlling the image forming position of each color of the image forming means based on the result of detecting the position information of the color shift detection images of a plurality of forces formed on the intermediate transfer member by the detecting means. In the color image forming apparatus having At least a reference value setting image for the color shift detection image of the color having the lowest light reflectance among the color shift detection images of the plurality of colors, and a reference for the color shift detection images of other colors. There is provided a color image forming apparatus having a color different from that of the value setting image.

According to each of the above embodiments of the present invention, a reference value setting image for at least a black color misregistration detection image and a reference value setting image for a color misregistration detection image of any other color And a different color. According to a preferred embodiment, the reference value setting image for the color misregistration detection image of black is formed in black, and the reference value image for the color misregistration detection image of a color other than black is of a color other than black. Of these, the color having the lowest light reflectance is formed.

According to each of the above-described other embodiments of the present invention, reference setting images of different colors are formed for the color shift detection images of the respective colors. According to a preferred embodiment, the plurality of color misregistration detection images are arranged such that different colors are not continuous.

In each of the above-mentioned present inventions, according to one embodiment, the detection means receives the reflected light of the light emitted from the light emitting means and the conveying means or the intermediate transfer member by the light emitting means and determines the received light amount. Light receiving means for outputting a proportional voltage, means for storing the maximum value of the output of the light receiving means,
Means for storing the minimum value of the output of the light receiving means, reference value generating means for generating the reference value determined by the maximum value and the minimum value, and the magnitude of the output of the light receiving means and the reference value Comparing means for generating a pulse signal for comparison, the maximum value is determined by the amount of light reflected from the surface of the conveying means or the intermediate transfer member, and the minimum value is reflected from the reference value setting image. The configuration is determined by the amount of light.

[0033]

DETAILED DESCRIPTION OF THE INVENTION A color image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 8 shows a schematic configuration of an embodiment of a color image forming apparatus to which the present invention can be applied. In the color image forming apparatus of this embodiment, in accordance with a signal from an external device such as a personal computer communicatively connected to the apparatus main body, a toner image of each color corresponding to the color-separated image information is electronically displayed in each image forming unit. The color laser beam printer is capable of forming a full-color image of four colors by being formed by a photographic image forming process and transferred onto a recording material.

First, with reference to FIG. 8, the overall structure of the color image forming apparatus 100 of the present embodiment will be described. The color image forming apparatus 100 serves as four color image forming means.
Black (Bk), yellow (Y), magenta (M), and cyan (C) image forming portions Pa, Pb, Pc,
Has Pd. Each of the image forming units Pa to Pd is a drum type electrophotographic photosensitive member as an image bearing member, that is, the photosensitive drum 1.
a, 1b, 1c, 1d, around which the photosensitive drum 1 is provided.
Charging roller 2 as charging means for uniformly charging a to 1d
1a to 21d, the photosensitive drums 1a to 1 according to the image signal
Laser scanners 2a to 2d as exposure means (latent image forming means) for exposing d to form electrostatic latent images on the photosensitive drums 1a to 1d, and electrostatic latent images formed on the photosensitive drums 1a to 1d. Developing devices 22a to 22d, which are developing means, which supply toner included in the developer to visualize the toner image.
Cleaning devices 24a to 24d for removing and cleaning the toner adhering to the photosensitive drums 1a to 1d are provided.

Further, the recording material P is set to the image forming portions Pa to P of the respective colors.
An endless conveyor belt 3 as a conveyor for sequentially conveying the sheet to the photosensitive drums 1a to 1d is provided so as to face the photosensitive drums 1a to 1d. The conveyor belt 3 is stretched around the driving roller 4 and the driven roller 5, and moves (rotates) in the direction of the arrow in the figure. The drive roller 4 is connected to a drive means including a motor, a gear, etc., and drives the conveyor belt 3. Driven roller 5
Rotates according to the movement of the conveyor belt 3 and applies a constant tension to the conveyor belt 3. Inside the conveyor belt 3, the transfer member 23a is provided so as to face the photosensitive drums 1a to 1d.
23 to 23d are arranged in contact with the conveyor belt 3. A transfer bias voltage is applied to the transfer members 23a to 23d during transfer, and a transfer bias having a polarity opposite to that of the toner is applied to the recording material P carried on the conveyor belt 3 via the conveyor belt 3. In this way, the conveyor belt 3 also functions as a transfer belt as a transfer unit.

Furthermore, the color image forming apparatus 100 includes a cassette 25a for containing the recording material P and a recording material supply roller 25.
b, a recording material supply device 25 including a conveyance roller (not shown), a guide (not shown), a registration roller 25c, and the like. Further, on the downstream side of the conveying belt 3 in the recording material conveying direction, a fixing device 2 for fixing the unfixed toner image transferred onto the recording material P in each of the image forming portions Pa to Pd onto the recording material P.
6 is provided.

The color image forming apparatus 100 having such a configuration.
When data to be image-formed is sent from an external device such as a personal computer and image information processing according to the printer engine system is completed and the image can be formed, recording is performed by the recording material supply roller 25b from the cassette 25a. The material P is supplied and reaches the conveyor belt 3. Then, the recording material P is sequentially conveyed by the conveying belt 3 to the image forming portions Pa to Pd of the respective colors. The image signals of the respective colors are sent to the respective laser scanners 2 in synchronism with the conveyance of the recording material P by the conveyance belt 3, and electrostatic latent images are formed on the photosensitive drums 1a to 1d. This electrostatic latent image is developed by the developing devices 22a to 22d and then transferred to the transfer members 23a to 23d.
The image is transferred onto the recording material P in an overlapping manner by d. In the image forming apparatus of this embodiment, images are sequentially formed in the order of cyan, magenta, yellow, and black.

After that, the recording material P is separated from the conveyor belt 3, and the toner image is fixed on the recording material P by heat by the fixing device 26 and discharged to the outside of the apparatus.

Since the operations of the image forming sections Pa to Pd are the same, the black image forming section Pa will be described as an example. The surface of the photosensitive drum 1a which is rotationally driven in the direction of the arrow in the figure is uniformly moved by the charging roller 21a. Is charged. A laser scanner 2a scans and exposes the surface according to black image information color-separated into image information to form an electrostatic latent image on the photosensitive drum 1a. Next, the photosensitive drum 1
The electrostatic latent image formed on a is visualized as a toner image by supplying toner by the developing device 22a. The developing device 22a is mainly provided with, for example, resin toner particles (toner) and magnetic carrier particles (carrier) as a developer, and the developer carrier holds the developer up to a developing area facing the photosensitive drum 1a. The electrostatic latent image on the photosensitive drum 1a is developed by carrying and carrying it and by applying to the developer carrying body a developing bias in which an AC voltage and a DC voltage are usually superposed.

On the other hand, from the cassette 25a to the supply roller 25
The recording material P supplied by b or the like and electrostatically attracted to the conveyor belt 3 is conveyed in synchronization with the formation of the toner image in each of the image forming portions Pa to Pd. Then, in the transfer region where the photosensitive drum 1a and the transfer member 23a face each other via the conveyor belt 3, the transfer bias applied to the transfer member 23a causes the toner image to be transferred from the photosensitive drum 1a to the recording material P.

Next, the recording material P is separated from the conveyor belt 3 and conveyed to the fixing device 26. Here, the toner image is fixed on the recording material P and becomes a permanent image. After that, the recording material P is discharged to a recording material discharge tray (not shown) provided outside the apparatus. After the transfer of the toner image, the cleaning device 24a removes the transfer residual toner adhering to the surface of the photosensitive drum 1a to prepare for the subsequent image formation.

The color shift detecting means and the color shift detecting pattern in this embodiment will be described below.

The color image forming apparatus 100 of this embodiment is
A color shift correction unit is provided to correct various color shifts as described with reference to FIG. Since the basic configuration and operation of the color misregistration correction means are the same as those of the conventional one described above, elements having the same function and configuration are denoted by the same reference numerals, and redundant description will be omitted. Only the characteristic parts of the example will be described in detail below.

That is, in order to reduce the color misregistration, the color misregistration detection pattern and the minimum value reading pattern shown in FIG. 1 are formed on the conveyor belt 3. Then, a pair of patterns of the color misregistration detecting means, which are provided side by side in the main scanning direction on both sides of the conveyor belt 3 on the downstream side of the black image forming portion Pa in the recording material conveying direction of the conveyor belt 3, are provided with these patterns. Detection unit (optical sensor) 6a, 6b
Read to detect the amount of color misregistration between each color. The image forming position is corrected by performing the above-described various preparations according to the detected shift amount.

As shown in FIG. 1, the color misregistration detection pattern is located on the left side and the right side when viewed from the upstream side in the moving direction of the conveyor belt 3, and black, yellow, magenta, and cyan recording material conveying direction patterns 9a to 9d. And 10a to 10d. Also, the recording material conveying direction patterns 9a to 9d,
Main scanning direction patterns 11a to 11d and 12a to 12d on the left side and the right side of the moving belts 10a to 10d in the moving direction of the conveying belt 3 when viewed from the moving direction upstream side of the black, yellow, magenta, and cyan conveying belts 3. Have.

In addition to these color misregistration detection patterns, in the pattern detection order, at least a pair of minimum value reading patterns (made up of black toner) preceding (immediately before) the black recording material conveying direction patterns 9a and 10a ( Toner surface reflected light reading pattern) 13
a and 14a are provided, and at least a pair of minimum value reading patterns 15a and 16a are provided before (immediately before) the black main scanning direction patterns 11a and 12a.

Immediately after the black recording material conveying direction patterns 9a and 10a, that is, the recording material conveying direction patterns 9b to 9 formed by toners of colors other than black.
d, 10b to 10d (in this embodiment, immediately before the yellow recording material conveyance direction patterns 9b and 10b), at least a pair of minimum value reading patterns 13b and 14b made of toner other than black toner are provided. Immediately after the black main scanning direction patterns 11a and 12a, that is, the recording material conveying direction patterns 11b to 11d and 12b to 1 formed by toners of colors other than black.
Prior to 2d (in this embodiment, immediately before the yellow main scanning direction patterns 11b and 12b), at least a pair of minimum value reading patterns 15b and 16b made of toner other than black are provided.

Next, the color misregistration detection pattern detection operation of this embodiment will be described in detail with reference to the operation algorithm of this embodiment shown in FIG. 2 and the operation timing chart of FIG. 2 shown in FIG. Here, in order to facilitate understanding, among the color shift detection patterns and the minimum value reading patterns shown in FIG. 1, the recording material conveyance direction patterns 9a to 9d on the left side when viewed from the upstream side in the movement direction of the conveyance belt 3 are shown. The minimum value reading patterns 13a and 13b will be described as an example.

Before the color shift correction is executed, the upper peak hold circuit 56a and the lower peak hold circuit 56b are in the reset state. The reset state that can be placed in the upper peak hold state is a state in which the lowest voltage that the circuit can take is fixed. On the other hand, the reset state that can be placed in the lower peak hold state is a state in which the highest voltage that the circuit can take is fixed.

When the color misregistration correction is started, the light emitting element (LED in this embodiment) 51 is caused to emit light (S1). The light emitting element 51 is turned on and off by turning on the light emitting element 51 and a power source or GND.
This can be done by turning on / off a switch placed in between by a signal from the CPU 64.

Next, the reset of the upper peak hold circuit 56a and the lower peak hold circuit 56b is released (S2). Next, the color shift detection patterns 9a to 9a shown in FIG.
9d, minimum value reading patterns 13a and 13b are formed. During this time, since the light receiving element (PD in this embodiment) 52 of the color shift detecting means is looking at the surface of the conveyor belt 3 having a high reflectance, the upper peak hold circuit 56a corresponds to the reflectance of the conveyor belt 3. A large voltage is sampled (S3). This voltage is applied to the lower peak hold circuit 56.
Since it is equal to or lower than the reset level of b, the lower peak hold circuit 56b also samples the same voltage.

After a lapse of time, the conveyor belt 3 moves, and the light receiving element 52 reflects from the minimum value reading pattern 13a formed of black toner, which precedes the color shift detection pattern 9a formed of black toner. Light enters. The reflectance of the minimum value reading pattern 13a formed of black toner is determined by the conveyance belt 3
Since it is lower, the upper peak hold circuit 56a does not change, and the lower peak hold circuit 56b samples the voltage corresponding to the reflectance of the minimum value reading pattern 13a formed by black toner (S4). In this way, when the maximum value and the minimum value are sampled by the upper peak hold circuit 56a and the lower peak hold circuit 56b, respectively, the slice level of the comparison circuit 58 is changed by the resistance division by the first resistance and the second resistance. Determined (S
5).

When the conveyor belt 3 further advances (during this time, the light from the conveyor belt 3 enters the light receiving element 52 (S6)).
Reflected light from the color shift detection pattern 9a formed of black toner is incident on the light receiving element 52. When the black color misregistration detection pattern 9a is read in this way, the output of the light receiving element 52 crosses the slice level.
The comparison circuit 58 is inverted and a position information pulse is obtained (S
7). Thereafter, the CPU 64 resets the hold voltage of the upper and lower peak hold circuits 56a and 56b to reset the reference voltage for black toner (S).
8).

Subsequently, when the conveyor belt 3 further advances (during this time, the light from the conveyor belt 3 enters the light receiving element 52 (S
9)), the reflected light from the minimum value reading pattern 13b formed of toner other than black (here, yellow toner) is received prior to the color shift detection pattern 9b formed of toner other than black. Element 5
It is incident on 2 (S10). Here, the slice level of the comparison circuit 58 is determined as in the case of black (S1).
1).

After that, when the conveyor belt 3 further advances (during this time, the light from the conveyor belt 3 enters the light receiving element 52 (S
12)), yellow, magenta, and cyan color shift detection patterns 9b, 9c, and 9d are read one by one. When the color misregistration detection patterns 9b to 9d are read, the output of the light receiving element 52 crosses the slice level, so the comparison circuit 58 is inverted to obtain the position information pulse (S13).
-1).

When all the color patterns have been read (S1
3-2), the calculation unit 61 obtains, for example, the center position of the rising edge and the falling edge as the position of each toner from the obtained position information pulse, and calculates the above formulas (1) to (16).
The color shift amount of each color is calculated by (S14), and the timer 6
3. The CPU 64 or the like performs color misregistration correction such as fine adjustment of the image frequency and adjustment of the writing start timing (S1
5).

As described above, when the reflectances of the black toner and the yellow, magenta, and cyan toners are greatly different, the minimum value reading pattern 13a using the black toner and the minimum value reading pattern using the non-black toner are used. 13b is formed, and the reference voltage (threshold value) can be made different between the black toner and the non-black toner. As a result, the ratio of the reference voltage to the upper peak voltage and the lower peak voltage can be made closer to the lower peak voltage on the toner side, and due to surface fluctuations of the conveyor belt 3 and scratches on the surface of the conveyor belt 3. It is possible to avoid erroneous detection of noise as a color shift detection pattern.

As described above, according to this embodiment, the maximum value and the minimum value of the signal from the light receiving element of the color shift detecting means are held in the two peak hold circuits, and the comparison circuit for detecting the position information based on this signal is held. In the color misregistration correction unit of the color image forming apparatus that determines the slice level of the color misregistration detecting unit, the slice level of the comparison circuit is reset for black and a color other than black, so that the light reception of the color misregistration detection unit due to the difference in reflectance of each color toner It prevents the problem that the element output does not cross the slice level. Further, by slicing the slice level from the maximum value corresponding to the reflectance of the surface of the conveyor belt, erroneous detection due to surface fluctuations and scratches on the conveyor belt can be prevented. As a result, accurate position information of the color misregistration pattern can be obtained, and deterioration of the color misregistration correction accuracy can be prevented.

Embodiment 2 Next, another embodiment of the present invention will be described. The basic configuration and operation of the color image forming apparatus of this embodiment are the same as those of the first embodiment.
Since they are the same as those described above, the elements having the same functions and configurations are designated by the same reference numerals, and detailed description thereof will be omitted.

The color shift detecting means and the color shift detecting pattern in this embodiment will be described below.

As shown in FIG. 14, the reflectance differs depending on the color of the toner. This difference becomes noticeable when the reflectance of the surface of the conveyor belt 3 is close to the reflectance of the toner. Therefore, when the difference in reflectance between the toners other than the black toner is large, even if the reference voltage for the toners other than the black toner is set as in the first embodiment, the output of the light receiving element 52 does not exceed the reference voltage. It is assumed that toner of a color that does not traverse appears and the pattern cannot be detected correctly.

In view of this, the present embodiment is characterized in that when the reflectances of toners other than black toner differ greatly, the reference voltage for toners other than black is set for each color toner.

FIG. 4 shows the color shift detection pattern and the minimum value reading pattern of this embodiment. As shown in FIG.
In this embodiment, the color misregistration detection pattern is the same set as that of the first embodiment shown in FIG. In addition to this color misregistration detection pattern, the black recording material conveyance direction pattern 9 is used in the pattern detection order as in the first embodiment.
Prior to (a immediately before) a and 10a, at least a pair of minimum value reading patterns 13a and 1 made of black toner.
4a is provided, and at least a pair of minimum value reading patterns 15a and 16a are provided (immediately before) to the black main scanning direction patterns 11a and 12a.

Further, in the present embodiment, the patterns 9b to 9d, 1 for the recording material conveyance direction of yellow, magenta and cyan are used.
Prior to (immediately before) each of 0b to 10d, at least a pair of minimum value reading patterns 13b and 14b made of yellow toner and at least a pair of minimum value reading patterns 13c and 14 made of magenta toner, respectively.
c, at least a pair of minimum value reading patterns 13d and 14d composed of cyan toner are provided, and the main scanning direction pattern 11 of yellow, magenta and cyan is provided.
Prior to (immediately before) b to 11d and 12b to 12d, at least a pair of minimum value reading patterns 15b and 16b made of yellow toner, at least a pair of minimum value reading patterns 15c and 16c made of magenta toner, and a cyan toner. There is provided at least a pair of minimum value reading patterns 15d and 16d.

Next, the detection operation of the color misregistration detection pattern in this embodiment will be described in detail with reference to the operation algorithm of this embodiment shown in FIG. Here, in order to facilitate understanding, among the color misregistration detection patterns and the minimum value reading patterns shown in FIG. 4, the recording material conveyance direction patterns 9a to 9L on the left side when viewed from the upstream side in the movement direction of the conveyance belt 3 are described.
9d and the minimum value reading patterns 13a and 13b will be described as an example.

Before the color shift correction is executed, the upper peak hold circuit 56a and the lower peak hold circuit 56b are in the reset state. When the color misregistration correction is started, the light emitting element (LED in this embodiment) 51 is caused to emit light (S
1).

Next, the reset of the upper peak hold circuit 56a and the lower peak hold circuit 56b is released (S2). Next, the color shift detection patterns 9a to 9a shown in FIG.
9d, minimum value reading patterns 13a to 13d are formed. During this time, since the light receiving element (PD in this embodiment) 52 of the color shift detecting means is looking at the surface of the conveyor belt 3 having a high reflectance, the upper peak hold circuit 56a corresponds to the reflectance of the conveyor belt 3. A large voltage is sampled (S3). This voltage is applied to the lower peak hold circuit 56.
Since it is equal to or lower than the reset level of b, the lower peak hold circuit 56b also samples the same voltage.

After a lapse of time, the conveyor belt 3 moves, and the light receiving element 52 reflects from the minimum value reading pattern 13a formed by black toner, which precedes the color shift detection pattern 9a formed by black toner. Light enters. The reflectance of the minimum value reading pattern 13a formed of black toner is determined by the conveyance belt 3
Since it is lower, the upper peak hold circuit 56a does not change, and the lower peak hold circuit 56b samples the voltage corresponding to the reflectance of the minimum value reading pattern 13a formed by black toner (S4). In this way, when the maximum value and the minimum value are sampled by the upper peak hold circuit 56a and the lower peak hold circuit 56b, respectively, the slice level of the comparison circuit 58 is changed by the resistance division by the first resistance and the second resistance. Determined (S
5).

When the conveyor belt 3 further advances (during this time, the light from the conveyor belt 3 enters the light receiving element 52 (S6)),
Reflected light from the color shift detection pattern 9a formed of black toner is incident on the light receiving element 52. When the black color misregistration detection pattern 9a is read in this way, the output of the light receiving element 52 crosses the slice level.
The comparison circuit 58 is inverted and a position information pulse is obtained (S
7). Thereafter, the CPU 64 resets the hold voltage of the upper and lower peak hold circuits 56a and 56b to reset the reference voltage for black toner (S).
2).

Subsequently, when the conveyor belt 3 further advances (during this time, the light from the conveyor belt 3 enters the light receiving element 52 (S
3)), the reflected light from the minimum value reading pattern 13b formed of yellow toner, which precedes the color shift detection pattern formed of yellow toner, is received by the light receiving element 5;
It is incident on 2 (S4). Here, the slice level of the comparison circuit 58 is determined as in the case of black (S5).

After that, when the conveyor belt 3 further advances (during this time, the light from the conveyor belt 3 enters the light receiving element 52 (S
6)), the reflected light from the color shift detection pattern 9b formed of yellow toner is incident on the light receiving element 52. When the yellow color shift detection pattern 9b is read in this way, the output of the light receiving element 52 crosses the slice level, so the comparison circuit 58 is inverted and a position information pulse is obtained (S7). Thereafter, the CPU 64 resets the hold voltage of the upper and lower peak hold circuits 56a and 56b, and resets the reference voltage for yellow toner (S2). Thereafter, the operations of (S2) to (S7) are similarly repeated for magenta and cyan.

When the patterns of all colors have been read (S
8), the calculation unit 61 obtains the position of the center of the rising and falling edges as the position of each toner from the obtained position information pulse, and calculates the color misregistration of each color by the above formulas (1) to (16). Calculate the amount (S9), timer 63, CPU
The color misregistration correction such as the fine adjustment of the image frequency and the adjustment of the writing start timing is performed by 64 (S10).

As described above, when the reflectances of the black, yellow, magenta, and cyan toners are greatly different, the minimum value reading pattern is formed for each toner, and the reference voltage (threshold value) is different for each toner. Can be made. This makes it possible to make the ratio of the reference voltage to the upper peak voltage and the lower peak voltage sufficiently close to the toner side, especially when the reflectances of toners other than black are greatly different from each other, and the surface fluctuation of the transport belt 3 is caused. Also, it is possible to prevent erroneous detection of noise due to scratches on the surface of the conveyor belt 3 as a color misregistration detection pattern.

As described above, according to this embodiment, the maximum value and the minimum value of the signal from the light receiving element of the color shift detecting means are held in the two peak hold circuits, and the comparator for detecting the position information based on this signal is held. In the color misregistration correction means of the color image forming apparatus for determining the slice level of the color image forming apparatus, by resetting the slice level of the comparison circuit for each color, the output of the light receiving element of the color misregistration detection means is sliced due to the difference in reflectance of each color toner. Prevent problems such as not crossing the level.
Further, by slicing the slice level from the maximum value corresponding to the reflectance of the surface of the conveyor belt, erroneous detection due to surface fluctuations and scratches on the conveyor belt can be prevented. As a result, accurate position information of the color misregistration pattern can be obtained, and deterioration of the color misregistration correction accuracy can be prevented.

Embodiment 3 Next, still another embodiment of the present invention will be described. Since the basic configuration and operation of the color image forming apparatus of this embodiment are the same as those of the first and second embodiments, elements having the same functions and configurations will be assigned the same reference numerals and detailed description thereof will be omitted.

In the second embodiment, when the reflectances of the respective toners are greatly different, particularly when the reflectances of the toners other than the black toner are greatly different, the reference voltage is set for each color toner to set the reference voltage of each color toner. The method for surely detecting the color shift detection pattern has been described. However, in the case of the pattern of the first embodiment shown in FIG. 4, each detection pattern (recording material conveyance direction pattern, main scanning direction pattern)
It is necessary to form a minimum value reading pattern for each
The disadvantages are that the entire pattern becomes long and the detection time increases, or the detection interval becomes long and the detection accuracy deteriorates proportionately.

In view of this, in this embodiment, the color misregistration detection patterns (recording material conveying direction pattern, main scanning direction pattern) are collected at one location for each color, and the number of minimum value reading patterns is minimized. , And shortens the entire length of the detection pattern.

FIG. 6 shows a color shift detection pattern and a minimum value reading pattern in this embodiment. As shown in FIG. 6, in the present embodiment, the same color of the color misregistration detection pattern is collected at one place, and the minimum value reading pattern formed by the toner of each color is formed at the beginning thereof.

That is, the minimum value reading patterns 13a and 14a formed of black toner and the black recording material are formed on the left side and the right side as viewed from the upstream side in the moving direction of the conveying belt 3 from the front in the moving direction of the conveying belt 3. Conveyance direction patterns 9a and 10a and black main scanning direction patterns 11a and 12a are provided as a set for one color. Subsequent to the black pattern set, a set of yellow toner, a set of magenta toner, and a set of cyan toner, which are similarly set for one color, are formed.

Next, the color misregistration detection pattern detection operation in this embodiment will be described in detail with reference to the operation algorithm of this embodiment shown in FIG. Here, in order to facilitate understanding, the color misregistration detection pattern and the minimum value reading pattern shown in FIG. 6 include black, yellow, magenta on the left side when viewed from the upstream side in the moving direction of the conveyor belt 3,
A cyan pattern set will be described as an example.

Before the color shift correction is executed, the upper peak hold circuit 56a and the lower peak hold circuit 56b are in the reset state. When the color misregistration correction is started, the light emitting element (LED in this embodiment) is caused to emit light (S1).

Then, the reset of the upper peak hold circuit 56a and the lower peak hold circuit 56b is released (S2). Next, the color shift detection pattern 9a shown in FIG.
11a, the minimum value reading pattern 13a is formed.
During this period, the light receiving element of the color misregistration detecting means (P in the present embodiment,
D) 52 is looking at the surface of the conveyor belt 3 having a high reflectance, and therefore the upper peak hold circuit 56a is
Sampling a large voltage corresponding to the reflectance of
3). Since this voltage is equal to or smaller than the reset level of the lower peak hold circuit 56b, the lower peak hold circuit 56b also samples the same voltage.

After a lapse of time, the conveyor belt 3 moves, and the light receiving element 52 reflects from the minimum value reading pattern 13a formed of black toner, which precedes the color shift detection pattern 9a formed of black toner. Light enters. The reflectance of the minimum value reading pattern 13a formed of black toner is determined by the conveyance belt 3
Since it is lower, the upper peak hold circuit 56a does not change, and the lower peak hold circuit 56b samples the voltage corresponding to the reflectance of the minimum value reading pattern 13a formed by black toner (S4). In this way, when the maximum value and the minimum value are sampled by the upper peak hold circuit 56a and the lower peak hold circuit 56b, respectively, the slice of the comparison circuit 58 is sliced by the resistance division by the first resistor 57a and the second resistor 57b. The level is decided (S5).

When the conveyor belt 3 further advances (during this time, the light from the conveyor belt 3 enters the light receiving element 52 (S6)),
Reflected light from the color misregistration detection pattern (recording material conveyance direction pattern) 9a formed of black toner is incident on the light receiving element 52. When the black recording material conveyance direction pattern 9a is read in this way, the output of the light receiving element 52 crosses the slice level, so the comparison circuit 58 is inverted and a position information pulse is obtained (S7). Subsequently, the reflected light from the color misregistration detection pattern (main scanning direction pattern) 11 a formed of black toner is received by the light receiving element 5.
Incident on 2. When the black main scanning direction pattern 11a is read in this way, the output of the light receiving element 52 crosses the slice level, so the comparison circuit 58 is inverted and a position information pulse is obtained (S8). After that, the CPU 64 resets the hold voltage of the upper and lower peak hold circuits 56a and 56b, and resets the reference voltage for black toner (S2).

Then, when the conveyor belt 3 further advances (during this time, the light from the conveyor belt 3 enters the light receiving element 52 (S
3)), the reflected light from the minimum value reading pattern 13b formed by the yellow toner enters the light receiving element 52 (S4). Here, the slice level of the comparison circuit 58 is determined as in the case of black (S5).

After that, when the conveyor belt 3 further advances (during this time, the light from the conveyor belt 3 enters the light receiving element 52 (S
6), on the light receiving element 52, a color misregistration detection pattern (recording material conveyance direction pattern) formed by yellow toner
The reflected light from 9b enters. When the yellow recording material conveyance direction pattern 9b is read in this way, the light receiving element 52
Since the output of the crosses the slice level, the comparison circuit 5
8 is inverted and a position information pulse is obtained (S7). Subsequently, the reflected light from the color shift detection pattern (main scanning direction pattern) 11b formed by the yellow toner is incident on the light receiving element 52. When the yellow main scanning direction pattern 11b is read in this way, the output of the light receiving element 52 crosses the slice level, so the comparison circuit 58 is inverted and a position information pulse is obtained (S8). Then CP
U64 is the upper and lower peak hold circuits 56a, 56.
The hold voltage of b is reset and the reference voltage for yellow toner is reset (S2). Thereafter, the operations of (S2) to (S8) are similarly repeated for magenta and cyan.

When all the color patterns have been read (S
9), the calculation unit 61 obtains, for example, the center position of the rising edge and the falling edge as the position of each toner from the obtained position information pulse, and the color misregistration of each color is calculated by the above formulas (1) to (16). Calculate the amount (S10), timer 63, CP
Color misregistration correction such as fine adjustment of the image frequency and adjustment of the writing start timing is performed by U64 or the like (S11).

As described above, when the reflectances of the black, yellow, magenta, and cyan toners are greatly different, the minimum value reading pattern is formed for each toner, and the reference voltage (threshold) is different for each toner. Can be made. This makes it possible to make the ratio of the reference voltage to the upper peak voltage and the lower peak voltage sufficiently close to the toner side, especially when the reflectances of toners other than black are greatly different from each other, and the surface fluctuation of the transport belt 3 is caused. Also, it is possible to prevent erroneous detection of noise due to scratches on the surface of the conveyor belt 3 as a color misregistration detection pattern.
Further, the length of the entire pattern at that time can be set to the shortest length to shorten the time required for pattern detection, and the detection error proportionally increasing due to the wider pattern interval can be suppressed.

As described above, according to the present embodiment, the patterns for each color are gathered in one place, and the number of toner patterns for reading the minimum value is minimized. Can be shortened. Therefore, the usability is improved by shortening the calibration time. Further, since the detection error which increases proportionally due to the widening of the pattern interval can be suppressed small, it is possible to obtain accurate position information of the color misregistration pattern and improve the accuracy of color misregistration correction.

In each of the above embodiments, the case where the principle of the present invention is applied to the color image forming apparatus having the conveyor belt 3 also serving as the transfer belt has been described.
The present invention is equally applicable to an image forming apparatus having an intermediate transfer member instead of the above, and a paper conveying system separately provided, and similar effects can be obtained.

FIG. 17 shows a schematic structure of a color laser beam printer 200 as an example of an intermediate transfer type color image forming apparatus to which the present invention can be applied. In FIG. 17, elements having the same functions and configurations as those of the color image forming apparatus of each of the above-described embodiments are designated by the same reference numerals. The color image forming apparatus 200 sequentially forms an electrostatic latent image on the photosensitive drum 17 as an image carrier according to the color-separated image information.
This latent image is applied to developing devices 22a, 22b, 22c, 2 for a plurality of colors (for example, black, yellow, magenta, and cyan).
By using the rotary developing device 80 that holds 2d on the rotating body 81, the development is sequentially performed with a developer of a desired color. Then, the toner images formed on the photosensitive drum 1 are sequentially transferred as an intermediate transfer member onto, for example, an intermediate transfer drum 70 in which a sheet is stretched over a frame body and formed into a drum shape by the action of the primary transfer unit 71. To do. After that, the toner images that have been multiple-transferred onto the intermediate transfer drum 70 are secondarily collectively transferred onto the recording material P that is conveyed on the conveyor belt 73 that is a conveyor by the action of the secondary transfer device 72.

Also in the color image forming apparatus 200 of such an intermediate transfer system, by forming the color shift detection pattern and the minimum value reading pattern of a plurality of colors on the intermediate transfer member and detecting the position information, each color is detected. Correct the image misregistration (color misregistration). The color misregistration detection pattern, the minimum value reading pattern, and the detection method of these patterns can be the same as those in each of the above embodiments. Therefore, here, the color misregistration detection pattern and the minimum value reading pattern are replaced with those to be formed on the intermediate transfer member, and the whole description in each of the above-mentioned embodiments is incorporated.

In each of the above embodiments, the minimum value reading pattern is provided one by one, but it goes without saying that a plurality of minimum value reading patterns may be provided. However, if the width of the minimum value reading pattern (the length in the recording material conveyance direction) is less than or equal to the width of the color misregistration detection pattern, the signal held in the lower peak hold circuit 56b is less than the actual color misregistration detection pattern. May be small. Therefore, the position detection and the lower peak hold circuit 5 are performed by the first color misregistration detection pattern.
Since 6b is sampled at the same time and its value is changed, the comparison circuit 58 for generating the position information detection signal for the first and second color misregistration detection patterns and the first color misregistration detection pattern. The slice level will change.
For this reason, an error may occur in the obtained position information, which may deteriorate the accuracy of color misregistration correction. Therefore, the minimum value reading pattern is preferably equal to or wider than the width of the color shift detection pattern. Further, in the first embodiment, for the same reason, when there is a difference in the reflectance of the toners of colors other than black, it is desirable to form the minimum value reading pattern with the toner of the lowest reflectance.

[0095]

As described above, according to the present invention,
The position can be reliably detected even in a color shift detection image formed by a developer having a high light reflectance, and the surface variation of the transfer target such as the transporting means and the intermediate transfer member and the surface of the transfer target can be detected. It is possible to prevent erroneous detection of the color misregistration detection image due to a scratch or the like, and it is possible to detect a proper color misregistration amount and form a high-quality color image. Further, according to the present invention, it is possible to shorten the detection time and the calibration time, improve the usability, and obtain accurate position information of the color misregistration pattern while achieving the above-described effects. The accuracy of color misregistration correction can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining an embodiment of a color shift detection pattern and a minimum value reading pattern according to the present invention.

FIG. 2 is a flow chart diagram for explaining one embodiment of the operation of the color misregistration detection means according to the present invention.

FIG. 3 is a timing chart diagram for explaining an embodiment of the operation of the color misregistration detection means according to the present invention.

FIG. 4 is an explanatory diagram for explaining another embodiment of the color shift detection pattern and the minimum value reading pattern according to the present invention.

FIG. 5 is a flow chart diagram for explaining another embodiment of the operation of the color misregistration detection means according to the present invention.

FIG. 6 is an explanatory diagram for explaining still another embodiment of the color shift detection pattern and the minimum value reading pattern according to the present invention.

FIG. 7 is a flow chart for explaining still another embodiment of the operation of the color misregistration detection means according to the present invention.

FIG. 8 is a schematic sectional view showing a schematic configuration of an example of a color image forming apparatus to which the present invention can be applied.

FIG. 9 is a schematic diagram showing an embodiment of the arrangement configuration of a pattern detection unit.

FIG. 10 is an explanatory diagram illustrating an example of a conventional color shift detection pattern.

FIG. 11 is a schematic diagram for explaining a pattern detection unit of a color shift detection unit.

FIG. 12 is a schematic diagram for explaining a circuit configuration of a color shift detection pattern reading processing unit of the color shift detection unit.

FIG. 13 is a schematic circuit diagram showing a circuit configuration of a light receiving element included in the pattern detection unit of the color shift detection unit.

FIG. 14 is an explanatory diagram for explaining an output waveform of the pattern detection unit of the color shift detection unit.

FIG. 15 is an explanatory diagram for explaining a problem of the conventional color shift detection method.

FIG. 16 is an explanatory diagram for explaining various color misregistrations.

FIG. 17 is a schematic sectional view of another example of a color image forming apparatus to which the present invention can be applied.

[Explanation of symbols]

1 Photosensitive drum (image carrier) 2 Laser scanner (exposure means) 3 Conveyor belt (transfer target) 6 Optical sensor (pattern detector) 9-12 color shift detection pattern 13-16 Minimum value reading pattern 51 light emitting element 52 Light receiving element

Claims (12)

[Claims] 1. An image forming unit for forming developer images of different colors on a plurality of image carriers, and transferring the developer images to form developer images of a plurality of colors on a transfer target. A transport means for transporting a recording material onto which a developer image is transferred from the plurality of image carriers to the plurality of image carriers, and a detection means for detecting the developer image on the transport means, Detection means for detecting positional information of the developer image on the conveying means by comparison with a reference value set based on an output signal when detecting the reference value setting image formed on the conveying means, Means for controlling the image forming position of each color of the image forming means based on the result of detecting the position information of the color shift detection images of a plurality of colors formed on the conveying means by the image forming means by the detecting means. And a color image forming apparatus having At least the reference value setting image for the color shift detection image of the color having the lowest light reflectance among the color shift detection images of the plurality of colors, and the color shift detection image of the other colors. A color image forming apparatus having a different color from the reference value setting image. 2. A color different from a reference value setting image for at least a black color misregistration detection image and a reference value setting image for other color misregistration detection images. The color image forming apparatus according to claim 1. 3. The reference value setting image for the color misregistration detection image of black is formed in black, and the reference value image for the color misregistration detection image of a color other than black is the most of the colors other than black. The color image forming apparatus according to claim 2, wherein the color image forming apparatus is formed of a color having a low light reflectance. 4. The color image forming apparatus according to claim 1, wherein a reference setting image of a different color is formed for each color misregistration detection image. 5. The color shift detection images of the plurality of colors are arranged such that different colors are not continuous.
Color image forming apparatus. 6. The detecting means includes a light emitting means, a light receiving means for receiving the reflected light of the light emitted onto the conveying means by the light emitting means and outputting a voltage proportional to the amount of the received light, and the light receiving means of the light receiving means. Means for storing the maximum value of the output, means for storing the minimum value of the output of the light receiving means, reference value generating means for generating the reference value determined by the maximum value and the minimum value, and the light receiving means Comparing means for generating a pulse signal by comparing the magnitude of the output and the reference value, the maximum value is determined by the amount of light reflected from the surface of the conveying means, the minimum value is the reference value 2. It is determined by the amount of reflected light from the setting image.
5. The color image forming apparatus according to any one of items 5 to 5. 7. An image forming means for sequentially forming developer images of different colors on an image carrier, and transferring the developer images to form developer images of a plurality of colors on a transferred body. An intermediate transfer member on which a developer image is sequentially transferred from the image carrier, and a detection unit for detecting the developer image on the intermediate transfer member, for setting a reference value formed on the intermediate transfer member. Detecting means for detecting positional information of the developer image on the intermediate transfer body by comparison with a reference value set based on an output signal when the image is detected; and on the intermediate transfer body by the image forming means. A color image forming apparatus having means for controlling the image forming position of each color of the image forming means based on the result of detecting the position information of the color misregistration detection images of a plurality of colors formed by the detecting means. , At least the multiple colors The reference value setting image for the color deviation detection image of the color having the lowest light reflectance among the color deviation detection images and the reference value setting image for the color deviation detection images of the other colors are displayed. A color image forming apparatus having different colors. 8. A color different from a reference value setting image for at least a black color misregistration detection image and a reference value setting image for other color misregistration detection images. The color image forming apparatus according to claim 7. 9. The reference value setting image for the color misregistration detection image of black is formed in black, and the reference value image for the color misregistration detection image of a color other than black is the most of the colors other than black. The color image forming apparatus according to claim 8, wherein the color image forming apparatus is formed of a color having a low light reflectance. 10. The color image forming apparatus according to claim 7, wherein different color reference setting images are formed for each color misregistration detection image. 11. The color image forming apparatus according to claim 10, wherein the color misregistration detection images of the plurality of colors are arranged such that different colors are not continuous. 12. The detecting means includes a light emitting means, a light receiving means for receiving the reflected light of the light emitted onto the intermediate transfer member by the light emitting means and outputting a voltage proportional to the amount of the received light, and the light receiving means. Means for storing the maximum value of the output of the light receiving means, means for storing the minimum value of the output of the light receiving means, reference value generating means for generating the reference value determined by the maximum value and the minimum value, and the light receiving Comparing means for comparing the output of the means and the reference value to generate a pulse signal,
The maximum value is determined by the amount of reflected light from the surface of the intermediate transfer member, and the minimum value is determined by the amount of reflected light from the reference value setting image. The color image forming apparatus according to any one of 1.