JPH09267512A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to accurately and effectively sense and measure relative color drift by forming a deviation measuring pattern to hold or surround the color for measuring the positional deviation with the color of reference, and sensing the deviation of the colors by using the pattern. SOLUTION: A color 2 is disposed in an area held by a color 1 without superposing with the color 1 in the pattern of the case that the colors 1 and 2 are not deviated to be intended to be formed by an image forming apparatus. If the gap widths 1a, 1b are set to the allowable limit of the color drift at an output signal from a pattern sensor in the case of sensing the pattern, the output of the pattern sensor of the case that the deviation exceeding the range occurs becomes 0 level output at only one place, and hence abnormal deviation can be effectively and easily sensed. If the colors 1 and 2 are positionally deviated, the relative positional deviation of the color 2 to the color 1 in the sensing direction is observed from the output signal from the pattern sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is applicable to color image forming apparatuses such as color copying machines, printers and facsimiles.
In particular, the present invention relates to a color misregistration prevention technique which is most suitable for a so-called electrophotographic digital image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in order to obtain a color image, an image forming device for each color of cyan, magenta, yellow and, if necessary, black is provided, and an image forming device for each color is formed on a recording medium such as paper or an intermediate transfer member. Image of each color is overlaid and recorded by the image device,
A technique for creating a color image is known. In such a color image forming technique, a technique of adjusting the image forming timing on the recording medium of each color image forming apparatus is indispensable in order to accurately superpose the color images. In order to adjust the image forming timing, it is necessary to measure the deviation between the colors of the formed image on the recording medium by each color image forming device. For this reason, the recording medium, especially the endless conveying means (transfer belt,
There is known a technique of forming a pattern for measuring deviation on a (conveying belt) and detecting the pattern to measure the color deviation.

[0003]

The pattern for measuring the deviation formed on the recording medium, particularly on the endless conveying means (transfer belt, conveying belt) is a toner (powder) image which has not been subjected to the fixing process. The detection means such as a sensor for detecting this, from the disturbance such as scratches and dirt on the endless conveying means,
It is necessary to detect the pattern accurately and surely. Therefore, the present invention has been made in view of the above points, and can accurately or reliably detect or measure the deviation of the image of each color, and based on this, image formation on the recording medium of each color image forming apparatus. An image forming apparatus capable of adjusting a timing and forming a color image without color misregistration.

[0004]

In order to achieve the above object, the first invention of the present invention comprises a plurality of image forming devices corresponding to respective colors and an endless conveying means for supplying recording paper to the image forming device. An image forming apparatus for forming an image by superimposing images of respective colors on one recording sheet, wherein a measurement color for each color is provided on the endless conveying means, and a reference for sandwiching the measurement color in at least the sub-scanning direction. A pattern forming means for forming a measurement pattern composed of a color and a detecting means for detecting the pattern and detecting a deviation amount of the measurement color, and writing timing of each image forming device based on the deviation amount. And an image writing timing generating means for generating the writing timing corrected. Second
The invention according to claim 1 is the image forming apparatus according to claim 1, wherein the pattern forming means forms a measurement pattern with a reference color of black. A third aspect of the invention is the first aspect of the invention, in which the measurement pattern has an overlapping width or a gap width between the measurement color and the reference color that is equal to or less than the maximum allowable deviation amount of each color. The image forming apparatus according to claim 1, wherein

[0005]

According to the first aspect of the invention, the pattern for measuring the amount of deviation is formed such that the reference color (color 1) sandwiches or surrounds the color (colors 2, 3, 4) for measuring the positional deviation. Since the positional deviation of each color is detected using this measurement pattern, relative color misalignment can be detected and measured accurately and reliably. In the second aspect of the invention, the reference color (color 1) of the deviation measuring pattern is black, so that the pattern detecting device 12, which is an optical sensor, can detect and measure more accurately and reliably. Also, since the deviation of each color is corrected with black as the reference,
Even if the permissible deviation amount of each color is set to be relatively large, the deviation of the entire image can be made inconspicuous. In the third invention,
In the deviation amount measurement pattern, the width of the overlapping portion of the color (color 2, 3, 4) for measuring the positional deviation and the reference color (color 1) that is sandwiched, or the width of the gap, is formed to be less than the allowable deviation amount. Therefore, when the color misregistration exceeds the permissible amount, it can be detected reliably with high sensitivity.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below. FIG.
FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus that performs multicolor superposition using the pattern detection device of the present invention. In the figure, reference numeral 1 is a transfer paper, 2 is a transfer paper transport belt, and 3 to 6 are, for example, black. (Bk), magenta (M), yellow (Y), and cyan (C) image forming devices, 7 is a transfer paper separating device, 7a is separating claws, and 8a to 8d.
Is a drum-shaped photoconductor installed in each of the image forming devices 3 to 6, and 9
a to 9b are transfer devices for transferring the images of the respective colors formed on the photoconductors 8a to 8d of the image forming devices 3 to 6 to the transfer paper 1, and 10a is a drive for rotationally driving the transfer paper transport belt 2. Rollers, 10b are driven rollers, 11a and 11b are belt charge eliminating devices, 12 is a pattern detecting device, and 14 is a registration roller.

In FIG. 1, a transfer sheet 1 is sent from a sheet feeding device (not shown) to a transfer sheet conveying belt 2 via a conveying path and a registration roller 14, and is adsorbed on the surface of the transfer sheet conveying belt 2 and conveyed. . The transfer paper 1 on the transfer paper transport belt 2 passes from the first image forming device 3 to the fourth image forming device 6, during which the toner images on the photoconductors 8a to 8d are transferred by the transfer devices 9a to 9b. The images are sequentially superposed and transferred, separated from the transfer paper transport belt 2 by the transfer paper separating device 7, the image is fixed through a fixing device (not shown), and sent to a paper discharging device (not shown).

In each of the image forming devices 3 to 6, the drum-shaped photoconductor 8 is used.
A charging device, an exposure device (optical writing device), a developing device, a cleaning device, and a destaticizing device, which are not shown, are arranged around a to 8d, and the photoconductors 8a to 8d are rotationally driven in the clockwise direction to charge, Each color toner image is formed on each photoconductor 8a to 8d through each process of exposure and development. When the transfer sheet 1 conveyed by the transfer sheet conveying belt 2 passes from the first image forming device 3 to the fourth image forming device 6, the toner images on the photoconductors 8a to 8d of the respective stations are changed. The images are sequentially transferred onto the transfer paper 1 by the transfer devices 9a to 9d. After the transfer process, the residual toner and the like adhering to the surfaces of the photoconductors 8a to 8d are removed and cleaned by a cleaning device (not shown), and the residual electrification is neutralized by the neutralization device.

The transfer sheet conveying belt 2 is rotationally driven by a driving roller 10a, and after the conveyed transfer sheet 1 is separated at a transfer sheet separating position 7, belt cleaning is performed downstream of the belt charge eliminators 11a and 11b in the belt traveling direction. Means are provided so that the toner adhering to the belt during the transfer and the pattern image described later can be deleted. The image forming devices 3 to 6 form images by using toners of different colors, for example, black, magenta, yellow, and cyan. Then, in order to detect the deviation of the image forming position in each of the image forming apparatuses 3 to 6, a pattern image for measuring the deviation is formed on the transfer paper conveyance belt 2 by the toner in each of the image forming apparatuses 3 to 6,
This pattern image formed on the transfer paper transport belt 2 is detected by the pattern detection device 12.

The pattern for measuring the amount of deviation according to the present invention is
As shown in FIG. 2, a pattern in which color 2 (measurement color) is sandwiched by color 1 (reference color), or as shown in FIG. 3, color 2 (measurement color) is surrounded by color 1 (reference color) It is a pattern.
In this case, if the color 1 is the reference color, for example, black, the color 2 is the measurement color of magenta, yellow, or cyan. Then, as shown in FIG. 4, the positional deviation between each measurement color of color 2 (magenta, yellow, cyan) and color 1 (black) which is the reference color is measured and detected.

In detail, FIG. 4 shows a color shift amount measuring method using the shift amount measuring pattern shown in the center of FIG. FIG.
The pattern for measuring the deviation amount in the middle is arranged such that the color (color 2 (magenta), color 3 (yellow), color 4 (cyan)) for measuring the deviation amount is sandwiched by the reference color (color 1 (black)). Pattern. As in the example described later, a reflection type sensor is used in the pattern detection device 12 so that the output signal becomes 0 level when detecting the background of the transfer paper transport belt and the output signal becomes negative level when detecting the colored pattern. By setting to, the pattern position on the transfer paper transport belt is recognized.
In this case, it is possible to set the background color of the transfer paper transport belt to white. In the pattern, when there is no positional deviation of each of the other colors with respect to the reference color, the entire area of the pattern is colored, so that the output of the detection device 12 is always at a negative level in the pattern area. On the other hand, if there is a positional deviation of the other colors (color 2 (magenta), color 3 (yellow), color 4 (cyan)) from the reference color (color 1 (black)),
As shown in (1), for example, an overlapping portion of color 1 (black) and color 2 (magenta) is formed, and a belt background having a considerable width appears as a deviation in the pattern area. Therefore, the output signal from the detection device 12 becomes an output signal in which a 0-level signal having a width corresponding to the deviation amount appears in the negative-level signal representing the pattern area. The image forming timing of the magenta image forming device 4 is corrected by an amount corresponding to the width of the 0 level output. If the same timing correction is performed for yellow and cyan, a color image having no color shift can be formed when an actual image is formed.

FIG. 7 shows an image forming timing correcting means when a laser diode (LD) is used as an exposure device (optical writing device) of the image forming devices 3 to 6. As for the output from the pattern detection device 12, a 0 level signal is detected by the 0 level detection means 13. On the basis of this 0 level signal, the deviation amount measuring means 14 measures the deviation amount. The image writing timing generation circuit 15 changes the image signal generation timing based on the shift amount. This makes it possible to change the writing timing in accordance with the image writing start timing in accordance with the amount of positional deviation after transfer. The above timing correction is performed for each of the magenta, yellow, and cyan exposure devices (optical writing devices).

FIG. 5 shows a specific example on the left side of FIG. 2 and shows a deviation amount measuring pattern arranged in a region sandwiched by color 1 (reference color). The upper left side of FIG. 5 is a pattern in the case where there is no positional deviation between color 1 and color 2 that the image forming apparatus is going to form, and color 2 is arranged in a region sandwiched by color 1 without overlapping with color 1. Has been done. The lower left part of FIG. 5 is an output signal from the pattern detection device 12 when the pattern is detected. Here, if the clearance widths la and lb are set to the permissible limits of the color misregistration amount, the output of the pattern detection device 12 when the misregistration exceeds the permissible range is output as a 0 level output as shown in the lower right part of FIG. Since there is only one location, abnormal deviation can be detected reliably and easily, which is preferable.

The center and the right side of FIG. 5 show the pattern actually formed when color 1 and color 2 are misaligned.
It is an output signal from the pattern detection device 12 when the pattern is detected. As can be seen from the figure, in the center of FIG. 5, when the color 2 does not overlap with the color 1 in the area sandwiched by the color 1 (reference color), la′-la or l
b-lb 'is a relative positional deviation amount of the color 2 with respect to the color 1 (reference color) in the detection direction (usually the sub-scanning direction).
Further, as shown on the right side of FIG. 5, when color 2 overlaps color 1 (reference color), (-la '')-la or lb-
lb ″ is the relative positional deviation amount of the color 2 with respect to the color 1 (reference color) in the detection direction (usually the sub-scanning direction).

FIG. 6 shows a specific example on the right side of FIG.
In this arrangement, the color 2 (measurement color) is sandwiched by the color 1 (reference color), and the color 2 overlaps with the left and right color 1 regions to measure the amount of deviation. The upper part of the left side of FIG. 6 is a pattern in the case where there is no positional deviation between color 1 and color 2 that the image forming apparatus tries to form, and color 2 is arranged in the area sandwiched between color 1 and left and right color 1 And evenly overlap. The lower left part of FIG. 6 is an output signal from the pattern detection device 12 when the pattern is detected. Here, if the widths lc and ld of the overlapping portions are set to the permissible limits of the color misregistration amount, the output of the pattern detection device 12 when the misregistration exceeds the permissible range, as shown in the middle and right side of FIG. Since 0 level output is generated, the abnormal deviation can be detected reliably and easily, which is preferable.

The center and the right side of FIG. 6 show the pattern actually formed when the color 1 and the color 2 are misaligned.
It is an output signal from the pattern detection device 12 when the pattern is detected. As can be seen from the figure, in the center of FIG. 6, when the color 2 (measurement color) overlaps the left side of the color 1 in the area sandwiched by the color 1 (reference color), -lc-l
c ′ or −ld ″ + ld is the relative positional deviation amount of the color 2 with respect to the color 1 (reference color) in the detection direction (usually the sub-scanning direction). Also, as shown on the right side of FIG. 6, color 2 is color 1.
In the area sandwiched by (reference colors), when overlapping with the right side of color 1, when color 2 overlaps, ld + ld '' or lc'-lc is the detection direction of color 2 with respect to color 1 (reference color). It is the amount of relative positional deviation in (usually the sub-scanning direction).

If la and lb are set as the allowable deviation amounts on the left side of FIG. 5, and if a positional deviation exceeding the allowable deviation amount occurs, the output signal from the pattern detection device 12 is changed to the right side of FIG. As shown, the 0 level peak is 1
It becomes a point. Similarly, on the left side of FIG. 6, lc, ld
Is set as the allowable deviation amount, and if a positional deviation exceeding the allowable deviation amount occurs, the output signal from the pattern detection device 12 has one 0 level peak as shown on the right side in the middle of FIG. Become.

[0018]

As described above, in the first invention,
A pattern for measuring the amount of displacement is formed by sandwiching or enclosing the color (color 2, 3, 4) for measuring the displacement with the reference color (color 1), and the position of each color is determined using this measurement pattern. Since the shift is detected, the relative color shift can be detected and measured accurately and reliably. In the second aspect of the invention, the reference color (color 1) of the deviation measuring pattern is black, so that the pattern detecting device 12, which is an optical sensor, can detect and measure more accurately and reliably. Further, since the deviation of each color is corrected with reference to black, the deviation of the entire image can be made inconspicuous even if the allowable deviation amount of each color is relatively large. In the third invention, the pattern for measuring the amount of deviation is
The width of the overlapping part or the width of the gap between the color (color 2, 3 and 4) for measuring the positional deviation and the reference color (color 1) to be sandwiched,
Since the amount of misregistration is less than or equal to the permissible amount, it is possible to reliably detect with high sensitivity when the color misregistration exceeds the permissible amount.

[0019]

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus that performs multicolor superposition according to the present invention.

FIG. 2 is a diagram showing an example of a measurement pattern of the present invention.

FIG. 3 is a diagram showing another embodiment of the measurement pattern of the present invention.

FIG. 4 is a diagram showing an example of a measurement pattern when a positional deviation occurs.

FIG. 5 is a diagram showing a change when a positional deviation occurs with the measurement pattern of the present invention.

FIG. 6 is a diagram showing another measurement pattern of the present invention and a change when a positional deviation occurs.

FIG. 7 is a schematic diagram of an image forming timing correction unit of the present invention.

[Explanation of symbols]

 1. Recording paper 2. Endless transport means 3, 4, 5, 6. Imaging device 12. Pattern detection device 15. Image writing timing generation means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04N 1/46 H04N 1/46 Z

Claims (3)

[Claims] 1. An image for forming an image by superposing images of respective colors on one recording sheet, the image forming apparatus having a plurality of image forming apparatuses corresponding to the respective colors, and an endless conveying means for supplying the recording sheet to the image forming apparatus. A forming device, a pattern forming means for forming a measurement pattern on the endless conveying means, each of which includes a measurement color for each color and a reference color sandwiching the measurement color in at least the sub-scanning direction; A detection unit for detecting a deviation amount of the measurement color, and an image writing timing generation unit for generating a writing timing in which the writing timing of each of the image forming devices is corrected based on the shifting amount. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the pattern forming unit forms a measurement pattern with a reference color of black. 3. The image according to claim 1, wherein the measurement pattern has an overlapping width or a gap width between the measurement color and the reference color is equal to or less than the maximum allowable deviation amount of each color. Forming equipment.