JP2007240592A - Image forming apparatus and displacement correction method for image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of detecting the amount of displacement even when a sensor the resolution of which is relatively low is used. <P>SOLUTION: The color pattern 1 is a rectangular image. A black pattern 2 is a mask image including a triangular window. The black pattern 2 is superimposed on the upper layer of the color pattern 1. Diffused reflection light, obtained when the superimposed pattern is illuminated with a detecting illumination light source, is captured with a light receiving element. On the basis of its quantity, the position of the color pattern relative to the black pattern is calculated to obtain the amount of displacement. As shown in FIG. 1(B), in the case where the color pattern 1 is formed on an image carrier such that it is displaced in the direction of arrow T, the detected quantity of diffused reflection light is small. As shown in FIG. 1(C), in the case where the color pattern 1 is formed such that it is displaced in the direction of arrow U, the detected quantity of diffused reflection light is large. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine.

In this type of image forming apparatus, when a color image is printed, a positional shift may occur between the colors. Therefore, it is necessary to detect such a displacement amount.
Patent Document 1 discloses a technique for improving position detection accuracy by arranging thin line patterns for position detection in a process direction at regular intervals.
Patent Document 2 discloses a technique for improving the position detection accuracy by making the position detection fine line pattern L-shaped.

JP 2001-281195 A JP 2001-277599 A

  However, in these methods, it is necessary to use a sensor having a high position resolution or time resolution (detecting a movement amount in the process direction as a passage time).

  The present invention has been made from the background described above, and it is an object of the present invention to provide an image forming apparatus capable of detecting a positional deviation amount even when a sensor having a relatively low position resolution or time resolution is used. To do.

  In order to achieve the above object, an image forming apparatus according to the present invention includes an image carrier, a light source, a first pattern on the image carrier, and a second pattern having a color different from the first pattern. A pattern forming unit that overlaps with the pattern, a sensor that detects the amount of light reflected from the light source and reflected from the first pattern and the second pattern formed by the pattern forming unit, and the sensor And calculating means for calculating the amount of color image misregistration based on the amount of light detected by.

Preferably, the pattern forming unit forms a black pattern as the second pattern, and the sensor detects the amount of diffusely reflected light with respect to a pattern other than black.
Preferably, the pattern forming unit forms a black pattern as the first pattern, and the sensor detects the amount of light regularly reflected by the image carrier having a substantially mirror surface.
Preferably, the pattern forming unit forms a second pattern larger than the first pattern on the first pattern.
Preferably, the pattern forming unit forms at least one of the first pattern and the second pattern with a coverage of approximately 100%.

  Preferably, at least one of the first pattern and the second pattern formed by the pattern forming unit is different from a region covered with the second pattern in a region where the first pattern is formed. It consists of a shape that linearly changes the area of the region and the amount of displacement calculated by the calculating means.

  Preferably, at least one of the first pattern and the second pattern formed by the pattern forming unit is different from a region covered with the second pattern in a region where the first pattern is formed. It has a shape in which the area of the region and the positional deviation amount calculated by the calculation means are changed nonlinearly.

Preferably, the calculation means calculates a positional deviation amount further based on density information of a pattern acquired in advance.
Preferably, the calculation means calculates a positional deviation amount based further on the reflected light amount information of the black pattern acquired in advance.
Preferably, the image processing apparatus further includes a correction unit that corrects the image based on the positional deviation amount calculated by the calculation unit.

  In the image forming apparatus according to the present invention, there is provided an image forming apparatus comprising: an image carrier; a light source having a plurality of spectra; and a color sensor that detects the amount of light irradiated and reflected from the light source. A first pattern is formed on the image carrier, and then a second pattern having a color different from the first pattern is overlaid, and the amount of light reflected from the formed first pattern is changed to the amount of light reflected from the formed first pattern. Detection is performed using a color sensor, and a positional deviation amount of the color image is calculated based on the detected light amount.

  According to the image forming apparatus of the present invention, it is possible to detect the amount of positional deviation even when a relatively low resolution sensor is used.

First, the outline of the present invention will be described in order to facilitate understanding of the present invention.
FIG. 1 is a diagram for explaining a test pattern used in the present invention and a detected positional deviation amount.
FIG. 1A shows a color pattern 1 and a black pattern 2 used in the present invention. As shown in FIG. 1A, the color pattern 1 is a rectangular image, and the black pattern 2 is a mask image having a shape including a triangular window. A region S indicates a detection area where diffuse reflected light is detected by the light receiving element.

  In the image forming apparatus according to the present invention, yellow (Y), magenta (M), cyan (C), and black (K) test patterns (color pattern 1 and black pattern 2) are formed on the image carrier, When light is irradiated from an illumination light source provided obliquely above, light diffused through the test pattern is collected by a lens and read by a light receiving element. The image carrier is a photosensitive member or a transfer member (intermediate transfer belt or the like) having a substantially mirror surface. On such an image carrier, diffuse reflected light corresponding to the exposure area of the pattern is detected in the case of color toners such as YMC (yellow, magenta, cyan), while in the case of black (K) toner, Since almost no light is reflected, as a result, only diffusely reflected light from the color toner is detected.

In the present invention, the second pattern is superimposed on the upper layer of the first pattern, and the diffuse reflected light when the superimposed pattern is illuminated by the detection illumination light source is captured by the light receiving element, and the second pattern is based on the amount of the reflected light. By calculating the first pattern position with respect to the position, a positional deviation amount is obtained. The color of the first pattern is not limited to any of YMC, but the color of the second pattern is preferably black. In this case, position information of each color of YMC with respect to the black position is obtained.
Note that when the first pattern is black (K) due to restrictions on the printing order, as shown in FIG. 12, the image carrier, which is a substantially mirror surface, was not concealed by the first and second patterns. Since the amount of specularly reflected light at the portion is captured by the light receiving element and the second pattern position relative to the first pattern position is calculated based on the amount, the positional deviation amount can be obtained. Even if there are restrictions, the present invention functions effectively. Each configuration shown in FIG. 12 is substantially the same as each configuration described later with reference to FIG.
The direction of the positional deviation to be detected is arbitrarily set depending on the orientation of the black pattern 2 or the like. For example, the misregistration direction is set to the main scanning direction or the process direction. In the example of FIG. 1A, the black pattern 2 and the like are set to the direction in which the misregistration in the main scanning direction is detected. The black pattern 2 is preferably larger than the color pattern 1.

  FIG. 1B and FIG. 1C show superimposed patterns of the color pattern 1 and the black pattern 2 formed on the image carrier when a positional deviation occurs. As shown in FIG. 1B, when the color pattern 1 is formed on the image carrier in the direction of the arrow T in the figure, the amount of diffusely reflected light detected is small. In this case, the larger the positional deviation amount, the smaller the diffuse reflection light amount.

  As shown in FIG. 1C, when the color pattern 1 is formed so as to be shifted in the direction of the arrow U in the figure, the diffuse reflection light to be detected becomes large. In this case, the larger the positional deviation amount, the larger the diffuse reflection light amount. Therefore, the image forming apparatus according to the present invention detects the direction and size of the positional deviation of the color pattern 1 with respect to the black pattern 2 by detecting the amount of diffusely reflected light.

  In addition, at least one of the color pattern 1 and the black pattern 2 has an area of a region different from the region covered with the black pattern 2 in the region where the color pattern 1 is formed, and a detected positional deviation amount. It has a shape that changes non-linearly. In this example, since the window portion of the black pattern 2 is a triangle, when the color pattern 1 is shifted in the direction of the arrow T, the diffuse reflected light decreases nonlinearly with respect to the positional shift amount, and the color pattern 1 is changed to the arrow. When it shifts in the direction of U, the diffusely reflected light increases nonlinearly with respect to the positional shift amount. At this time, the rate of increase is greater than the rate when increasing linearly (ie, the slope). For this reason, even when a relatively low position resolution or time resolution sensor such as a process control sensor (ADC) or an unevenness detection sensor is used, the amount of displacement can be detected effectively. In addition, at least one of the color pattern 1 and the black pattern 2 is preferably formed with a coverage of approximately 100%. This is because the change in the diffuse reflection light amount or the regular reflection light amount becomes remarkable, and the change can be easily detected.

FIG. 2 is a diagram showing a test pattern in the case of detecting a positional deviation amount in the sub-scanning direction.
As shown in FIG. 2, the amount of positional deviation in the sub-scanning direction is detected by changing the direction in which the color pattern 1 and the black pattern 2 shown in FIG. 1 are formed on the image carrier.
In this manner, the image forming apparatus according to the present invention detects the amount of misregistration with respect to black (K) of each color of YMC in the main scanning direction and the sub-scanning direction.

Next, the image forming apparatus 10 according to the embodiment of the present invention will be described.
FIG. 3 is a diagram showing a configuration of the tandem type image forming apparatus 10 according to the embodiment of the present invention.
As shown in FIG. 3, the image forming apparatus 10 includes an image reading unit 12, an image forming unit 14, an intermediate transfer belt 16, a paper tray 17, a paper transport path 18, a fixing device 19, an image processing device 20, and a reflected light amount detection device. 26. The image forming apparatus 10 has a function as a full-color copying machine using the image reading unit 12 and a function as a facsimile in addition to a printer function for printing image data received from a personal computer (not shown). It may be a multifunction machine.

  In the image forming apparatus 10, the image reading unit 12 reads an image displayed on the document 30 and outputs it to the image processing apparatus 20. The image processing device 20 performs predetermined image processing on image data input from the image reading unit 12 or image data input from a personal computer or the like via a network line such as a LAN, and performs image processing. The image forming unit 14 is controlled based on the applied image data.

  Below the image reading unit 12, a plurality of image forming units 14 are arranged corresponding to the colors constituting the color image. In this example, the first image forming unit 14K, the second image forming unit 14Y, and the third image forming corresponding to each color of black (K), yellow (Y), magenta (M), and cyan (C). The unit 14M and the fourth image forming unit 14C are arranged horizontally along the intermediate transfer belt 16 with a certain interval. The intermediate transfer belt 16 rotates as an intermediate transfer member in the direction of the arrow A in the figure, and these four image forming units 14C, 14M, 14Y, and 14K are arranged in accordance with the image data input from the image processing apparatus 20 according to the respective colors. The toner images are sequentially formed and transferred (primary transfer) to the intermediate transfer belt 16 at a timing at which the plurality of toner images are superimposed on each other. In this way, the image forming unit 14 forms a pattern in which the first pattern and the second pattern having a color different from the first pattern are superimposed on the intermediate transfer belt 16 as the image carrier. Forming means;

  The sheet conveyance path 18 is disposed below the intermediate transfer belt 16. The recording paper 32 supplied from the paper tray 17 is transported on the paper transport path 18, and the toner images of each color transferred onto the intermediate transfer belt 16 are collectively transferred (secondary transfer). The transferred toner image is fixed by the fixing device 19 and discharged to the outside along the arrow B.

Next, each configuration of the image forming apparatus 10 will be described in detail.
The first image forming unit 14C, the second image forming unit 14M, the third image forming unit 14Y, and the fourth image forming unit 14K are arranged and formed in parallel at regular intervals in the horizontal direction. The configuration is almost the same except that the color of the image is different. Accordingly, the first image forming unit 14C will be described below. The configuration of each image forming unit 14 is distinguished by attaching C, M, Y, or K.
The image forming unit 14 </ b> C forms an electrostatic latent image by an optical scanning device 140 </ b> C that scans a laser beam in accordance with image data input from the image processing device 20 and a laser beam scanned by the optical scanning device 140 </ b> C. And an image forming apparatus 150C.

  The optical scanning device 140C modulates the semiconductor laser 142C according to cyan (C) image data and emits laser light from the semiconductor laser 142C according to the image data. The laser light emitted from the semiconductor laser 142C is applied to the photosensitive drum 152C of the image forming apparatus 150C via the first reflection mirror 143C, the second reflection mirror 144C, and the like.

The image forming apparatus 150C includes a photosensitive drum 152C as an image carrier that rotates at a predetermined rotational speed in the direction of arrow A, and primary charging as a charging unit that uniformly charges the surface of the photosensitive drum 152C. For example, a developing device 156C for developing the electrostatic latent image formed on the photosensitive drum 152C, and a cleaning device 158C. The photosensitive drum 152C is uniformly charged by the scorotron 154C, and an electrostatic latent image is formed by the laser beam irradiated by the optical scanning device 140C. The electrostatic latent image formed on the photoreceptor drum 152C is developed with cyan (C) toner by the developing unit 156C and transferred to the intermediate transfer belt 16. Residual toner, paper dust, and the like adhering to the photosensitive drum 152C after the toner image transfer process are removed by the cleaning device 158C.
The other image forming units 14M, 14Y, and 14K also form magenta (M), yellow (Y), and black (K) toner images in the same manner as described above, and intermediately transfer the formed toner images of the respective colors. Transfer to belt 16.

  The intermediate transfer belt 16 is driven to circulate at a predetermined speed in the direction of arrow A when the drive roll 164 is rotationally driven by a drive motor (not shown). The intermediate transfer belt 16 includes a first primary transfer roll 162C, a second primary transfer roll 162M, a third primary transfer roll 162Y, and a position facing the image forming units 14C, 14M, 14Y, and 14K. A fourth primary transfer roll 162K is disposed, and the toner images of the respective colors formed on the photosensitive drums 152C, 152M, 152Y, and 152K are transferred onto the intermediate transfer belt 16 in a multiple manner by these primary transfer rolls 162. The The residual toner adhering to the intermediate transfer belt 16 is removed by a cleaning blade or brush of a belt cleaning device 189 provided downstream of the secondary transfer position.

  The reflected light amount detection device 26 is for reading a toner image formed on the intermediate transfer belt 16, for example. In the present embodiment, the reflected light amount detection device 26 is downstream of the image forming unit 14K and reads a toner image before transfer. The reflected light amount detection device 26 will be described in detail later.

In the paper transport path 18, a paper feed roller 180 for taking out the recording paper 32 from the paper tray 17, a first roller pair 181, a second roller pair 182 and a third roller pair 183 for paper transport, and a recording paper A registration roll 184 is provided that conveys 32 to the secondary transfer position at a predetermined timing.
In addition, a secondary transfer roll 185 that is in pressure contact with the backup roll 168 is disposed at the secondary transfer position on the paper transport path 18, and each color toner image transferred onto the intermediate transfer belt 16 is Secondary transfer is performed on the recording paper 32 by the pressing force and electrostatic force of the secondary transfer roll 185. The recording paper 32 onto which the toner image of each color is transferred is conveyed to the fixing device 19 by the first conveyance belt 186 and the second conveyance belt 187.
The fixing device 19 melts and fixes the toner to the recording paper 32 by performing heat treatment and pressure treatment on the recording paper 32 to which the toner images of the respective colors are transferred.

FIG. 4 is a diagram showing details of the reflected light amount detection device 26.
As shown in FIG. 4, the reflected light amount detection device 26 includes an illumination light source 260, a lens 262, and a light receiving element 264. The illumination light source 260 is arranged so that light is emitted at an angle θ with respect to the vertical line of the intermediate transfer belt 16. As the light emitted from the illumination light source 260, white light or infrared light can be used. The lens 262 collects the diffusely reflected light emitted from the illumination light source 260 and reflected by the color pattern 1 formed on the intermediate transfer belt 16, and causes the light receiving element 264 to read it.

  When the color pattern 1 is formed on the intermediate transfer belt 16 and the black pattern 2 having the mask portion 28 and the window portion 29 (triangular portion in FIG. 1) is further formed thereon, the surface of the color pattern 1 is formed. Is masked by the mask part 28 of the black pattern 2, the light emitted from the illumination light source 260 is reduced in the amount of diffuse reflection and the amount of light received by the light receiving element 264 is reduced accordingly.

  For this reason, as the color pattern shifts in the direction of arrow T in the figure, the portion hidden by the mask portion 28 of the black pattern 2 increases, and the amount of light received by the light receiving element 264 decreases. On the other hand, as the color pattern shifts in the direction of arrow U in the figure, the portion hidden by the mask portion 28 of the black pattern 2 becomes smaller, and the amount of light received by the light receiving element 264 increases.

  The color of the pattern 2 having the mask portion 28 is not limited to black (K), and may be a pattern having a color different from that of the color pattern 1. Since the spectral reflected light amounts of cyan (C), magenta (M), and yellow (Y) are different from each other, the positional deviation amount can be obtained from the detected spectral reflected light amount based on the difference between the reflected light amounts. For example, the first pattern (C) is formed on the intermediate transfer belt 16 and then the second pattern (M) having a different color from the first pattern is overlaid to form the first pattern (C). And irradiating light including at least the R component from the illumination light source 260 through the intermediate transfer belt 16 on which the second pattern (M) is formed, and detecting the R spectral reflection light quantity by the first pattern (C), Based on the detected spectral reflection light quantity, the amount of positional deviation of the first color image (C) with respect to the second pattern (M) may be calculated. In order to detect the amount of spectral reflected light, a commonly used method such as a method using an RGB light source or a sensor combining a white light illumination and a light receiving element with a spectral filter may be used.

FIG. 5 is a block diagram illustrating a functional configuration of the image processing apparatus 20.
As shown in FIG. 5, the image processing apparatus 20 includes an image signal conversion unit 200, a test pattern generation circuit 210, a selector 220, and a correction calculation circuit 230. Each of the above-described components included in the image processing apparatus 20 may be realized by software such as a CPU, a memory, and a program, or may be realized by hardware such as an ASIC.

The image signal conversion unit 200 includes a memory that stores a positional deviation amount for each color calculated by a correction arithmetic circuit 230 described later, and acquires and acquires CMYK color image data from a DFE such as a computer or a server (not shown). A position shift correction process is performed on each color of the image data (CMYK), and the result is output to the selector 220. The image signal converter 200 will be described in detail later.
The test pattern generation circuit 210 generates test pattern data for forming a test pattern (FIGS. 1 and 2) for each color of CMYK and outputs the test pattern data to the selector 220.

  The selector 220 is a mode for printing an image according to the CMYK color image data acquired from the DFE by the image forming apparatus 10 (normal print mode), or a mode for correcting a positional deviation of the printed image (test mode). The setting indicating in which mode the operation should be performed is acquired via, for example, a user interface (not shown), and the image data selected according to the acquired setting is output to the image forming unit 14. That is, the selector 220 selects and outputs the image data input from the image signal conversion unit 200 when acquiring the setting to operate in the normal print mode, and acquires the setting to operate in the test mode. The test pattern data input from the test pattern generation circuit 210 is selected and output.

  The correction calculation circuit 230 includes, for example, a CPU, inputs the reflected light amount detected by the reflected light amount detection device 26, and calculates the positional deviation amount of each color based on the reflected light amount information of each color stored in advance. Output to the image signal converter 200. The correction arithmetic circuit 230 will be described in detail later.

FIG. 6 is a diagram illustrating details of the image signal conversion unit 200.
As illustrated in FIG. 6, the image signal conversion unit 200 includes a positional deviation amount storage unit 202 and a position information conversion unit 204. The misregistration amount storage unit 202 stores the misregistration amount for each color calculated by the correction arithmetic circuit 230. The misregistration amount storage unit 202 is realized by a memory, a hard disk drive, or the like. The position information conversion unit 204 receives the CMYK color image data constituting the image data, corrects the pixel position based on the color misregistration amount stored in the misregistration amount storage unit 202, and supplies the data to the selector 220. Output.

FIG. 7 is a diagram showing details of the correction arithmetic circuit 230.
As illustrated in FIG. 7, the correction calculation circuit 230 includes a reflected light amount information storage unit 232 and a positional deviation amount calculation unit 234. The reflected light amount information storage unit 232 stores the relationship between the diffuse reflected light amount and the area of a region different from the region covered with the black pattern 2 in the region where the color pattern 1 is formed for each color. The reflected light amount information storage unit 232 stores the diffusely reflected light amount of the black pattern 2 measured in advance. Here, the diffuse reflection light amount of the black pattern 2 is obtained by detecting the diffuse reflection light amount in a state where the color pattern 1 is not formed on the intermediate transfer belt 16 and only the black pattern 2 is formed.

  The misregistration amount calculation unit 234 inputs the detected diffuse reflection light amount, and the black pattern of each color pattern 1 based on the relationship between the diffuse reflection light amount and the area stored in the reflection light amount information storage unit 232. 2 is calculated.

  Further, the positional deviation amount calculation unit 234 corrects the diffuse reflection light amount from the color pattern 1 based on the diffuse reflection light amount of the black pattern 2 stored in the reflected light amount information storage unit 232, and then the color pattern. A positional deviation amount of 1 may be calculated. In this case, the misregistration amount calculation unit 234 sets a value obtained by subtracting the stored diffuse reflection light amount of the black pattern 2 from the detected diffuse reflection light amount as the diffuse reflection light amount of the color pattern 1. Thereby, the positional deviation amount can be detected with higher accuracy.

  Further, the positional deviation amount calculation unit 234 acquires the density information of the color pattern 1 acquired by an ADC sensor (not shown) or the like, corrects the area of the color pattern 1 based on the density information, and then corrects the color pattern 1. A positional deviation amount may be calculated. For example, the coverage of the color pattern 1 is approximately 100%. Here, the ADC sensor optically measures the density of a pattern formed on an image carrier such as the intermediate transfer belt 16. The misregistration amount calculation unit 234 may correct the area using the process control information.

FIG. 8 is a flowchart showing the positional deviation amount calculation processing (S10) by the image forming apparatus 10.
As shown in FIG. 8, in the test mode, a test pattern is formed on the intermediate transfer belt 16 in step 100 (S100). Here, the test patterns are the color pattern 1 (FIG. 1) and the black pattern 2 stored in the test pattern generation circuit 210 (FIG. 5) of the image processing apparatus 20, and the color pattern 1 is applied to the intermediate transfer belt 16. After the formation, the black pattern 2 is formed on the upper layer.

  In step 102 (S102), the illumination light source 260 of the reflected light amount detection device 26 (FIG. 4) emits light, and the light receiving element 264 detects the diffuse reflected light amount by the test pattern formed on the intermediate transfer belt 16. The reflected light amount detection device 26 outputs the detected diffuse reflected light amount to the image processing device 20.

In step 104 (S104), the correction calculation circuit 230 of the image processing device 20 (FIG. 5) calculates the amount of positional deviation based on the diffused reflected light amount input from the reflected light amount detection device 26, and the image signal converting unit 200 Output.
In step 106 (S106), the image signal conversion unit 200 stores the calculated displacement amount.
The image forming apparatus 10 performs the above-described processing on the color pattern 1 of cyan (C), magenta (M), and yellow (Y), thereby obtaining the amount of misregistration of each color with respect to black (K). it can.

FIG. 9 is a flowchart showing the overall operation (S20) of the image forming apparatus 10 in the normal printing mode.
As shown in FIG. 9, in step 200 (S200), the image forming apparatus 10 inputs image data of CMYK colors from a computer or the like (not shown). This image data is input to the image processing apparatus 20.

In step 202 (S202), the image signal conversion unit 200 of the image processing apparatus 20 refers to the stored misregistration amounts of cyan, magenta, and yellow.
In step 204 (S204), the image signal conversion unit 200 corrects the pixel position for each of cyan, magenta, and yellow based on the amount of displacement.

  In step 206 (S206), the corrected image data is selected and output by the selector 220, and transferred to the intermediate transfer belt 16 by the image forming unit 14 (FIG. 3). Further, the transferred toner images of respective colors are transferred and fixed on the recording paper 32, and an image is formed on the recording paper 32.

  As described above, the image forming apparatus according to the present invention includes an image carrier, a light source, and a pattern forming unit that forms the first pattern and the second pattern on the image carrier, A sensor for detecting the amount of light reflected from the light source with respect to the first pattern and the second pattern formed by the pattern forming means, and a positional deviation amount of the color image based on the amount of light detected by the sensor. Calculating means for calculating. Thereby, even when a sensor with a relatively low position resolution or time resolution is used, the amount of positional deviation can be detected. Therefore, since the sensor for a control computer (ADC) or the unevenness detection sensor can also be used, the number of sensors can be reduced and the cost can be reduced.

  Preferably, one of the first pattern and the second pattern is a black pattern, and the amount of diffuse reflection with respect to a pattern other than black is detected. Thereby, since the change in the amount of diffuse reflection light of a color different from that of the black pattern becomes significant, the position of the color image with respect to black can be detected more effectively.

Next, a modification of the test pattern will be described with reference to FIGS.
FIG. 10 is a diagram showing a first modification of the test pattern used in the present invention.
FIG. 10A shows a case where the positions of the color pattern 1 and the black pattern 2 are both as defined. As shown in FIG. 10A, the color pattern 1 and the black pattern 2 may both be rectangular images. In this case, the shape of these patterns linearly changes the area of a region different from the region covered with the black pattern 2 in the region where the color pattern 1 is formed and the amount of misalignment detected. It is.

Therefore, as shown in FIG. 10B, when the color pattern 1 is formed on the image carrier in the direction of arrow T in the figure, the amount of diffuse reflection detected is proportional to the amount of positional deviation. Become smaller. Further, the larger the positional deviation amount, the smaller the diffuse reflection light amount.
On the other hand, as shown in FIG. 10C, when the color pattern 1 is formed so as to be shifted in the direction of the arrow U in the drawing, the diffuse reflection light to be detected increases in proportion to the amount of positional shift. Further, the greater the amount of displacement, the greater the amount of diffuse reflection.

FIG. 11 is a diagram showing a second modification of the test pattern used in the present invention.
FIG. 11A shows a case where the positions of the color pattern 1 and the black pattern 2 are both as defined. As shown in FIG. 11A, the shape of the black pattern 2 is a rectangle, and the shape of the color pattern 1 is different from the region covered with the black pattern 2 in the region where the color pattern 1 is formed. The area of the region and the detected displacement amount may be changed nonlinearly.

Therefore, as shown in FIG. 11B, when the color pattern 1 is formed on the image carrier with a shift in the direction of the arrow T in the figure, the amount of diffuse reflection detected is the position of the color pattern 1. Smaller at a rate greater than the rate of change. Further, the larger the positional deviation amount, the smaller the diffuse reflection light amount.
On the other hand, as shown in FIG. 11C, when the color pattern 1 is formed so as to be shifted in the direction of the arrow U in the figure, the detected diffuse reflected light is larger than the rate at which the position of the color pattern 1 changes. Increase in proportion. Further, the greater the amount of displacement, the greater the amount of diffuse reflection.
Due to the shapes of the color pattern 1 and the black pattern 2 as described above, a change in the position of the color pattern 1 can be detected with higher sensitivity as a change in the amount of diffusely reflected light.

It is a figure explaining the test pattern used in this invention, and the amount of displacement detected. It is a figure which shows the test pattern in the case of detecting the positional offset amount in a subscanning direction. 1 is a diagram illustrating a configuration of a tandem-type image forming apparatus 10 according to an embodiment of the present invention. It is a figure which shows the detail of the reflected light amount detection apparatus 26. FIG. 3 is a block diagram illustrating a functional configuration of the image processing apparatus 20. FIG. 3 is a diagram showing details of an image signal conversion unit 200. FIG. 5 is a diagram showing details of a correction arithmetic circuit 230. FIG. 5 is a flowchart showing a positional deviation amount calculation process (S10) by the image forming apparatus 10. 4 is a flowchart illustrating an overall operation (S20) of the image forming apparatus 10 in a normal print mode. It is a figure which shows the 1st modification of the test pattern used in this invention. It is a figure which shows the 2nd modification of the test pattern used in this invention. It is a figure which shows the modification of the reflected light amount detection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st pattern 2 2nd pattern 10 Image formation apparatus 14 Image formation unit 16 Intermediate transfer belt 20 Image processing apparatus 26 Reflected light quantity detection apparatus 28 Mask part 29 Window part 200 Image signal conversion part 202 Position shift amount memory | storage part 204 Position Information conversion unit 210 Test pattern generation circuit 220 Selector 230 Correction calculation circuit 232 Reflected light quantity information storage unit 234 Position shift amount calculation unit 260 Illumination light source 262 Lens 264 Light receiving element

Claims (11)

An image carrier;
A light source;
Pattern forming means for forming a first pattern and a second pattern having a color different from the first pattern on the image carrier;
A sensor for detecting the amount of light irradiated and reflected from the light source to the first pattern and the second pattern formed by the pattern forming means;
An image forming apparatus comprising: a calculation unit that calculates a positional deviation amount of a color image based on a light amount detected by the sensor. The pattern forming means forms a black pattern as the second pattern,
The image forming apparatus according to claim 1, wherein the sensor detects the amount of diffusely reflected light with respect to a pattern other than black. The pattern forming unit forms a black pattern as the first pattern,
The image forming apparatus according to claim 1, wherein the sensor detects an amount of light that is regularly reflected by an image carrier having a substantially mirror surface. The image forming apparatus according to claim 1, wherein the pattern forming unit forms a second pattern that is larger than the first pattern on the first pattern. The image forming apparatus according to claim 1, wherein the pattern forming unit forms at least one of the first pattern and the second pattern with a coverage of approximately 100%. At least one of the first pattern and the second pattern formed by the pattern forming unit has an area of a region different from a region covered with the second pattern in a region where the first pattern is formed. The image forming apparatus according to any one of claims 1 to 5, wherein the image forming apparatus has a shape that linearly changes a displacement amount calculated by the calculation unit. At least one of the first pattern and the second pattern formed by the pattern forming unit has an area of a region different from a region covered with the second pattern in a region where the first pattern is formed. The image forming apparatus according to claim 1, wherein the image forming apparatus has a shape that nonlinearly changes a positional deviation amount calculated by the calculation unit. The image forming apparatus according to claim 1, wherein the calculation unit calculates a positional deviation amount further based on density information of a pattern acquired in advance. The image forming apparatus according to claim 1, wherein the calculation unit calculates a positional deviation amount further based on information on the amount of reflected light of a black pattern acquired in advance. The image forming apparatus according to claim 1, further comprising a correction unit that corrects an image based on the amount of misregistration calculated by the calculation unit. In an image forming apparatus having an image carrier, a light source having a plurality of spectra, and a color sensor that detects the amount of light irradiated and reflected from the light source,
A first pattern is formed on the image carrier, and then a second pattern having a color different from the first pattern is overlaid,
Detecting the amount of light reflected from the formed first pattern using the color sensor;
A positional deviation correction method for an image forming apparatus, which calculates a positional deviation amount of a color image based on the detected light amount.

Images