JP2001265086A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To distinguish a normal pattern and a noise pattern from each other, to accurately correct color slippage and to obtain an image of high printing quality without forming and detecting a registration pattern detected with dust and dirt and scratches again at forming the registration pattern on an intermediate transfer belt. SOLUTION: The color image forming device is provided with a registration pattern forming means for forming the registration pattern capable of correcting all the error factors with a single detecting operation on plural exposure means, a color slippage detecting means for forming the registration pattern formed on plural image stations on a transfer material and then detecting the color slippage of the image, a noise filtering means for removing scratches and powdery dust on the transfer material from detection data, and a noise distinguishing means for removing the noise component which drop from the noise filtering means and which is judged as an effective signal, then, the registration is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for detecting color misregistration in an electrophotographic color image forming apparatus having a plurality of photoconductors and performing accurate color matching on a recording medium.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus employing an electrophotographic system, a photoconductor as an image carrier is charged by a charger, and the photoconductor is irradiated with light according to image information to form a latent image. An image formed by forming the latent image and developing the latent image by a developing device is transferred to a sheet material or the like to form an image.

On the other hand, a plurality of image forming stations for performing the above-described image forming processes are provided with the colorization of the images, and each of the color images of cyan, magenta, yellow, and preferably black is carried on each image. Formed on the body,
A tandem-type color image forming apparatus that forms a full-color image by superimposing and transferring each color image on a sheet material at a transfer position of each image carrier has also been proposed. Such a tandem-type color image forming apparatus has an image forming unit for each color, which is advantageous for speeding up.

However, there is a problem of how to properly perform registration (registration) of images formed by different image forming units. This is because the shift of the image forming positions of the four colors transferred to the sheet material finally appears as a color shift or a change in color tone.

FIG. 5 is a diagram showing types of color misregistration. As the types of the color shift of the transfer material, (a) of FIG.
As shown in (b), (c), (d), and (e), the displacement in the transfer material transfer direction (the direction of the arrow S in the drawing) (hereinafter, referred to as the sub-scanning displacement) (FIG. 5A )), Misalignment in the scanning direction (direction orthogonal to the direction of arrow S in the figure) (hereinafter, referred to as main scanning misalignment) (FIG. 5B), misalignment in the oblique direction (hereinafter, referred to as skew error) (FIG. 5 (c)), deviation of magnification error (FIG. 5 (d)), deviation of bending error (FIG.
(E)), and in fact, the one in which the above five types of shifts are superimposed appears.

[0006] Then, the mounting displacement of the scanning optical system and
This is a shift in the attachment of a lens or a mirror (not shown) in the scanning optical system, and the same applies to a shift in the main scanning position in FIG. 5B.

The inclination shift in the oblique direction in FIG. 5C is the angle shift of the rotating shaft of the photosensitive drum of the image forming station and the mounting angle shift of the scanning optical system.
The shift due to the magnification error in (d) is caused by the shift in the scanning line length due to the error in the optical path length from each scanning optical system to the photosensitive drum of the image forming station.
The displacement due to the curvature error in (e) is due to a displacement of the lens and the like in each scanning optical system.

[0008] Therefore, a pattern (hereinafter referred to as a registration pattern) is drawn in advance for the above five types of shifts, a registration pattern is detected by a plurality of sensors (color shift detection), and the shift amount is calculated from the result. Then, it is necessary to perform position adjustment (color shift correction) of each image according to the shift amount.

Hereinafter, the operation of the conventional color image forming apparatus and the operation of detecting and correcting color misregistration will be described. FIG. 6 shows a configuration diagram of a conventional color image forming apparatus.

In FIG. 6, the image forming apparatus includes four image forming stations 3a, 3b, 3c, and 3d.
Each of the image forming stations 3a, 3b, 3c, 3d includes a photosensitive drum 32a, 32b, 32c, 3 as an image carrier.
Each has 2d.

Also, a dedicated charging means 33 is provided therearound.
a, 33b, 33c, 33d, and an exposure unit 2 and a developing unit 34 of a scanning optical system for irradiating the photosensitive drums 32a, 32b, 32c, 32d with light corresponding to image information.
a, 34b, 34c, 34d, transfer device 3 in transfer means 4
5a, 35b, 35c, and 35d, and photosensitive drum cleaning means 36a, 36b, 36c, and 36d are provided, respectively.

Here, the image forming stations 3a, 3
b, 3c, 3d represent a black image, a cyan image,
A magenta image and a yellow image are to be formed.

On the other hand, each image forming station 3a, 3
b, 3c, 3d, the photosensitive drum 32
An endless intermediate transfer belt 4 is disposed below a, 32b, 32c, and 32d, and moves in the direction of arrow S.

In the above arrangement, first, a latent image of a black component color of image information is formed on the photosensitive drum 32a by a known electrophotographic process means such as the charging means 33a of the first image forming station 3a and the exposure means 2. Is formed, the latent image is visualized as a black toner image by a developing material having black toner by a developing unit 34a, and the black toner image is transferred to the intermediate transfer belt 4 by a transfer unit 35a.

On the other hand, while the black toner image is being transferred to the intermediate transfer belt 4, the second image forming station 3
In b, a latent image of a cyan component color is formed, and subsequently, a cyan toner image by cyan toner is obtained by the developing unit 34b.
The cyan toner image is transferred by the transfer means 35b of the second image forming station 3b to the intermediate transfer belt 4 whose transfer has been completed in the first image forming station 3a, and is superimposed on the black toner image.

Thereafter, an image is formed on the magenta toner image and the yellow toner image in the same manner, and when the superposition of the four color toner images on the intermediate transfer belt 4 is completed, the paper feed cassette 39 is fed by the paper feed roller 39. The toner images of four colors are collectively transferred and conveyed by a sheet material transfer roller 42 onto a sheet material 40 such as paper fed from a fixing unit 4.
3 to form a full-color image on the sheet material 40.

The photosensitive drums 32a, 32b, 32c, and 32d, to which the transfer has been completed, have their residual toner removed by the photosensitive drum cleaning means 36a, 36b, 36c, and 36d. The residual toner is removed by the belt cleaning means 44,
The printing operation is completed.

Here, when the power is turned on, the image forming stations 3a, 3b, 3c, 3d are exchanged, or the image forming station or the scanning optical system is misplaced due to a change in the temperature of the inside of the apparatus or the installation state of the image forming apparatus. Misalignment occurs.

Therefore, a color misregistration detection / correction operation is performed when the power is turned on, when each image forming station 3a, 3b, 3c, 3d is replaced or when the temperature inside the apparatus changes.

The color misregistration of the color image device is detected by the exposure means 2 shown in FIG.
After the image is formed on the intermediate transfer belt 2 and the registration pattern of the toner drawn on the intermediate transfer belt 4 is detected by the color misregistration detecting means 5, the color misregistration amount calculating means 6 calculates.

As shown in FIG. 7, CCDs arranged in a line in the main scanning direction are used for the color misregistration detecting means.
When the registration patterns 51, 52, 53, and 54 of the respective toners formed on the intermediate transfer belt 4 pass below the cells of the CCD, the change of the electric signal corresponding to the change in the amount of reflected light is determined for each cell. Was detected.

FIG. 8 shows a change in the output of the registration pattern detected for each cell. The registration pattern is formed by a straight line in the main scanning direction. The deviation X in the main scanning direction depends on the presence or absence of a signal for each cell as shown in FIGS. As shown in c), the calculation is based on the time difference ΔT detected between the CCD units and for each cell.

FIG. 9 shows the inside of the color shift detecting means 5 of the CCD system. Using a CCD 47 as a light receiving unit, light emitted from a light source 48 is reflected by the intermediate transfer belt 4 and condensed on the CCD 47 through a selfoc lens array 49.

However, in the configuration of the CCD system, the accumulation time of the light incident on the CCD 47 is required to be about 1 msec in order to detect a change in the registration pattern formed on the intermediate transfer belt conveyed at high speed.

A feature of the tandem type color image forming apparatus is that a high-speed color image can be formed by providing an image forming section for each color. Therefore, in order to detect a registration pattern formed on an image carrier conveyed at high speed with high accuracy, it is necessary to shorten the accumulation time to about several μsec. In other words, measures such as increasing the illuminance of the light source 31 or using a high-sensitivity CCD have been taken, but have caused a problem of cost increase.

On the other hand, there is a method in which the conveyance speed of the intermediate transfer belt is switched to a low speed only when detecting the conveyance speed of the intermediate transfer belt for the purpose of accumulating the accumulation time of the CCD system. Since the vibration error component of each drive system is different from the normal moving speed, an error occurs in the registration pattern detection, and high-precision correction cannot be performed at the normal moving speed. Had occurred.

Therefore, instead of the CCD system, a laser system capable of shortening the storage time to about several nsec as shown in FIG. 10 has been proposed.

The laser beam emitted from the semiconductor laser 13 is applied to the intermediate transfer belt 4 through the condenser lens 14. The reflected light enters the PIN photodiode 16 through the condenser lens 15. As in the CCD system, when the registration pattern passes through the position of the intermediate transfer belt 4 on the laser beam path, the amount of reflected light changes, and the pattern position can be detected.

The semiconductor laser 13 continues to emit light while the registration pattern on the intermediate transfer belt 4 passes through the entire area irradiated with the laser. The light emission amount becomes a constant light amount by the light emission amount setting means 11 and the light emitting circuit 12. The signal photoelectrically converted by the PIN photodiode 16 is amplified by the amplifying unit 17 (Vs), and the threshold setting unit 18 sets a threshold level to the variation width of the light amount in advance.
The comparison circuit 19 compares the threshold value (Vr) with the threshold value (Vr), and detects the edge of the compared signal (Vo) as the position of the registration pattern.

In the laser system, compared to the CCD system,
The light collecting property is high, the detection area can be reduced, and the registration pattern can be detected with high accuracy.

Further, since the S / N ratio of incident light is high,
By drawing a grayscale image having a gradation on the intermediate transfer belt 4, it can be used as a density detecting unit.

The toner on the intermediate transfer belt 4 after the detection is not transferred to the sheet material 40 such as paper, and the toner is removed by the intermediate transfer belt cleaning means 44.

[0033]

However, according to the above-mentioned conventional method of detecting a registration pattern formed on an image carrier on an intermediate transfer belt and correcting the registration pattern, scratches, dust, etc. on the intermediate transfer body are required. Is detected in the same manner as the registration pattern, so that the burden on the software such as entrusting the analysis of the correction data including the noise component after the detection to software processing increases. In addition, registration pattern detection / correction processing is performed again, and so on.
There have been problems such as spending more time than necessary for the detection and correction operation, and naturally increasing the toner consumption due to re-detection.

According to the present invention, in order to solve such a problem, a low-cost detecting means is constituted, and a curving error including various color misregistration errors is accurately detected, and a noise component is removed by one detecting operation. It is another object of the present invention to provide a color image forming apparatus capable of shortening the detection correction time and reducing the toner consumption.

[0035]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a registration pattern for causing a plurality of exposure means to generate a registration pattern capable of correcting all error factors in one detection operation. Generating means, color misregistration detecting means for forming a registration pattern formed in the plurality of image forming stations on a transfer material and detecting color misregistration of an image, and detection data for scratches and dust on the transfer material. By performing high-accuracy registration detection with a detection configuration having a noise filtering means for removing noise components, and a noise discriminating means for removing noise components determined as effective signals spilled from the noise filtering means. Color shift correction can be performed accurately and in a short time, and an image with high print quality can be obtained.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, a registration pattern formed from each image forming station by a registration pattern generating means has a predetermined interval, angle, thickness, and width. The main scanning position deviation and the sub-scanning position deviation can be detected and corrected with a single detection operation by using at least two or more straight lines, and an image with high print quality can be obtained. .

According to a second aspect of the present invention, there is provided at least two or more color misregistration detecting means, and the registration pattern is bilaterally symmetric with respect to the vertical direction in the transfer material transport direction according to the number of the detecting means. Or, by forming the same pattern and detecting it by the detecting means, it is possible to detect a main scanning position deviation, a sub-scanning position deviation, a magnification error, a skew error, and a bending error at a time with high accuracy, and to obtain accurate color. The shift can be corrected and an image with high print quality can be obtained.

The invention according to claim 3 of the present invention comprises a noise filtering means for the signal component detected by the detecting means, and performs a highly accurate detection by removing the noise component. Color misregistration correction can be performed, and an image with high print quality can be obtained.

According to a fourth aspect of the present invention, a time margin of a theoretical value of a registration pattern formed at a predetermined interval and thickness by a registration pattern generating means is provided, and a thickness within the time margin is provided. If the interval between the next pattern and the next pattern is shorter than the time margin, noise is applied. If the interval is longer than the time margin, effective detection data is used. An image with high print quality can be obtained.

(Embodiment 1) An embodiment of the present invention will be described below.

As shown in FIG. 1, the registration pattern is formed by forming at least two or more straight lines having predetermined intervals, angles, thicknesses, and widths on the intermediate transfer belt. Even if you lose some,
The position can be detected by another registration pattern.

The laser is irradiated on the lines LA and LB on the intermediate transfer belt. The angle of the pattern is such that the extended lines of the pattern intersect at 90 degrees, and the width of the pattern in the main scanning direction is a predetermined minimum width in the main scanning direction (W in the figure) determined by the intersection of the color misregistration detecting means. Form. The thickness of the pattern is made larger than the diameter of the laser beam applied to the intermediate transfer belt. By making the size larger, it becomes easier to distinguish between the intermediate transfer body and the registration pattern formed by the toner. In addition, by making W as small as possible and not making the pattern orthogonal on the transfer material,
It is possible to virtually increase the interval between the intersection on the extension line of the pattern and the color misregistration detection point. As a result, it is possible to improve the detection accuracy and reduce the toner consumption.

Also, instead of forming the registration patterns arranged in the main scanning direction in different directions of “<” and “>” as shown in FIGS.
As shown in 24, 25, 26, and 27, by forming them in the same direction such as ">" and ">" or "<" and "<", the interval between the patterns in the main scanning direction is kept within a certain width. This makes it possible to simplify the memory capacity and the hardware configuration for generating the detection pattern in the main scanning direction.

When a flaw, dust, or the like is generated on the intermediate transfer belt 4 as shown in FIG. 2A, a noise component is also detected by the color misregistration detecting means 5 as in the case of the registration pattern. However, the present invention proposes a method of providing a noise filtering unit and removing a noise component as described below.

FIG. 2B shows a signal that should be detected when there is no noise such as dust.

Here, assuming that noise such as dust smaller than the pattern width is generated between the registration patterns, a signal as shown in FIG. In this case, the signal 28 corresponds to noise other than the registration pattern.

[0047] In order to remove the noise, the present invention previously sets a time margin W _v of the theoretical value of the registration pattern width and stored. The counting is started from the beginning of the registration pattern, and an effective area signal having a width _Wv is obtained. Compared to the original detection signal, if less than the width W _v, it is possible to determine the signal as noise, it is removed.

Similarly, when noise such as dust that is larger than the pattern width occurs between the registration patterns, a signal as shown in FIG. The noise 30 corresponds to noise other than the registration pattern.

In order to remove this noise, in the present invention, the time margin Wb of the theoretical value of the blank width between the registration patterns is set in advance and stored. From the time when the registration pattern has passed, an invalid area signal having a width Wb is obtained. During the invalid area, the data is masked, and the signal detected during Wb can be determined as noise and removed.

In this manner, the minimum value is set for the pattern width, and a pattern smaller than the minimum value is determined to be noise, and a specified value is also provided to the pattern cycle width, and a signal detected during that period is determined to be noise. By removing noise, highly accurate detection can be performed, and by performing accurate color misregistration correction, an image with high print quality can be obtained.

In the case where the noise is leaked even if the noise filtering means is used and the registration pattern is blurred or partially formed for some reason, the present invention provides the following effective area discriminating circuit. Can be used to discriminate between a regular registration pattern and noise and compensate for it.

The time from the earlier falling edge of the change time of the registration pattern detection signal to the later falling edge is defined as Margin by the color misregistration detecting means 5 arranged in two or more in the main scanning direction. Stipulate. Also, the time from the falling edge of the later change time of the detection signal to the earlier falling edge of the change time of the next registration pattern detection signal is Ne.
Defined as "gativeMargin". Margi
The states of n and NegativeMargin are repeated with each other, and the color misregistration detecting means under detection is Margin and Negative.
activeMargin. However, in a normal state, Margin <Negati
veMargin status.

When only one of the registration patterns is detected for some reason by two or more color misregistration detecting means, it is detected with a time change as shown in FIGS. 3 (a) and 3 (b). .

Margin, NegativeMarg
In, the state changes as shown in the figure, and from the time when the normal registration pattern was not detected, Mar
gin <NegativeMargin.

By forming at least two or more registration patterns, Margin <Negat
From the status of liveMargin, select Margin> Neg
The point in time when the state becomes activeMargin can be determined, and a normal registration pattern and noise can be determined from the subsequent pattern.

In this way, by managing the registration pattern in the state of Margin and NegativeMargin, a normal component and a noise component can be discriminated by one detection.

FIG. 4 shows a functional block diagram. As shown in the drawing, a toner image of each color is formed in each image forming station 3 from a registration pattern generating means 1 through an exposure means 2, and the toner is superimposed on the intermediate transfer belt 4.

The color misregistration amount of the formed toner is detected by the color misregistration detecting means 5, the ineffective component of the detection signal is removed by the noise filtering means 7,
The CPU 9 calculates a color shift amount.

[0059]

As described above, according to the present invention, a registration pattern generating means for generating a registration pattern capable of correcting all error factors in a plurality of exposure means by one detection operation; A color misregistration detecting means for forming a registration pattern formed in the image forming station on the transfer material and detecting color misregistration of the image; and a noise for removing scratches and dust on the transfer material from the detection data. Filtering means, comprising a noise determination means for removing a noise component determined as a valid signal spilled from the noise filtering means, by performing a highly accurate registration detection,
Color shift correction can be performed accurately and in a short time, and an image with high print quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a layout diagram of a registration pattern and a color misregistration detection unit on an intermediate transfer belt in a transfer unit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a registration pattern including an abnormality on an intermediate transfer belt according to an embodiment of the present invention.

FIG. 3 is a timing chart for detecting a registration pattern including an abnormality on an intermediate transfer belt according to an embodiment of the present invention.

FIG. 4 is a functional block diagram of an embodiment of the present invention.

FIG. 5 is a diagram showing types of color misregistration.

FIG. 6 is a configuration diagram of a conventional color image forming apparatus.

FIG. 7 is a layout diagram of a conventional color misregistration detecting means and a registration pattern.

FIG. 8 is a diagram showing a signal detected by a conventional color shift detecting unit.

FIG. 9 is a configuration diagram of a conventional color shift detecting unit.

FIG. 10 is a configuration diagram of a conventional color shift detecting unit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Registration pattern generation means 2 Exposure means 3a, 3b, 3c, 3d Image forming station 4 Intermediate transfer belt 5 Color misregistration detection means 6 Color misregistration amount calculation means 7 Noise filtering means 8 Discrimination circuit 9 CPU 10 Memory 11 Light emission amount setting means Reference Signs List 12 light emitting circuit 13 semiconductor laser 14, 15 condensing lens 16 PIN photodiode 17 amplifying means 18 level setting means 19 comparing means 20a, 20b, 21a, 21b, 22a, 22b, 2
3a, 23b, 24a, 24b, 25a, 25b, 26
a, 26b, 27a, 27b Registration patterns 32a, 32b, 32c, 32d Photoconductor drums 33a, 33b, 33c, 33d Charging means 34a, 34b, 34c, 34d Developing means 35a, 35b, 35c, 35d Transfer means 36a, 36b , 36c, 36d Photoconductor drum cleaning means 37 Intermediate transfer belt driving roller 38 Intermediate transfer belt driven roller 39 Paper feed roller 40 Sheet material such as paper 41 Paper feed cassette 42 Sheet material transfer roller (paper transfer means) 43 Fixing means 44 Intermediate Transfer belt cleaning means 45a, 45b, 45c, 45d Optical path correction means 46a, 46b, 46c, 46d Laser light 47 CCD 48 Light source 49 Selfoc lens array 51, 52, 53, 54 Registration pattern

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2C362 BA52 CA22 CA23 CA39 CB73 2H027 EB04 EC03 2H030 AA01 AB02 AD16 BB42 BB56 5C074 AA07 AA10 BB03 BB26 CC26 DD21 DD24 EE04 EE11 FF15 GG02 GG09 GG12 GG14 9A001

Claims (4)

[Claims] A plurality of image forming stations including an exposure unit, a photosensitive member on which a latent image is formed by the exposure unit, and a developing unit for developing the latent image formed on the photosensitive member as a toner image Transfer means for transferring and conveying the toner images formed in the plurality of image forming stations to a transfer material, and color shift detection means for detecting a color shift that occurs when the toner images are sequentially superimposed on the transfer material. A color image forming apparatus for forming a composite image, wherein the exposure means has a registration pattern generating means for generating a registration pattern in order to detect the generated color shift. If the registration pattern detected by the color misregistration detecting means is at least two or more straight lines having a predetermined interval, angle, thickness, and width. Becomes, the color image forming apparatus, characterized in that not orthogonal on the transfer material. 2. The apparatus according to claim 2, wherein said registration pattern has at least two or more color misregistration detecting means, and said registration pattern forms a pattern which is symmetrical in the vertical direction with respect to the conveyance of said transfer material or the same pattern as the left and right in accordance with the number of detecting means. 2. The color image forming apparatus according to claim 1, wherein the color image is detected by a detecting unit. 3. The method according to claim 1, wherein a characteristic of a registration pattern formed at a predetermined interval and thickness by said registration pattern generating means is used, and a noise filtering means is used for a signal detected by said detecting means. Item 2. A color image forming apparatus according to Item 1. 4. The color image forming apparatus according to claim 1, further comprising an effective area discriminating circuit for noise remaining after using a noise filtering means on the registration pattern detected by said detecting means.