JP2024030132A - Image forming device - Google Patents

Abstract

An object of the present invention is to suppress a decrease in detection accuracy of an inspection image by the sensor even when a sensor installation error occurs. An optical sensor (30) detects a linear inspection image formed by an image forming section (5) using a detection spot on an intermediate transfer belt (20). The control unit 10 acquires the amount of color shift, which is the amount of shift between the formation positions of images of different colors, based on the detection result of the inspection image by the optical sensor 30, and uses the image forming unit 5 to determine the amount of color shift based on the amount of color shift. Correct the color shift of the formed image. The control unit 10 further determines the relationship between the plurality of test images of the same color and the detection spot in the main scanning direction based on the detection results of the plurality of test images of the same color formed at different angles with respect to the main scanning direction. The relative positional deviation amount is acquired, and the formation position of the inspection image by the image forming unit 5 in the main scanning direction is corrected according to the relative positional deviation amount. [Selection diagram] Figure 14

Description

The present invention relates to a technique for detecting the amount of color misregistration in an image forming apparatus.

Image forming apparatuses that form color images are required to have little color shift. Color misregistration is a phenomenon in which the formation position of a toner image of a certain color is shifted from the formation position of a toner image of another color. Patent Documents 1 and 2 propose a technique of detecting the amount of color shift by forming a plurality of chevron marks as an inspection image using toners of different colors, and detecting the inspection image with a sensor. There is.

Japanese Unexamined Patent Publication No. 6-118735 Japanese Patent Application Publication No. 11-84759

In the above-mentioned conventional technology, a sensor that detects the right ridgeline of the chevron mark formed as an inspection image and a sensor that detects the left ridgeline are used. However, no consideration is given to the fact that if these sensors are installed at a position shifted from the ideal position (nominal position) assumed in advance in the design, a detection error of the inspection image by the sensor may occur.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a technique for suppressing a decrease in the detection accuracy of an inspection image by the sensor even when a sensor installation error occurs.

An image forming apparatus according to one aspect of the present invention includes: an image bearing member that is rotationally driven; an image forming unit that forms an image on the image bearing member using toner of a plurality of colors; A detection means detects the linear inspection image obtained by using a detection spot on the image carrier, and a detection means detects the formation position of the image of a different color based on the detection result of the inspection image by the detection means. a first acquisition unit that acquires a color shift amount, which is a shift amount; a first correction unit that corrects a color shift of an image formed by the image forming unit based on the color shift amount; and a detection unit. Inspecting the plurality of same colors in the main scanning direction based on detection results of a plurality of inspection images of the same color formed at different angles with respect to the main scanning direction perpendicular to the moving direction of the surface of the image carrier. a second acquisition means for acquiring a relative positional deviation amount between an inspection image and the detection spot; and a formation position of an inspection image by the image forming means in the main scanning direction according to the relative positional deviation amount; and a second correction means for correcting.

According to the present invention, even when a sensor installation error occurs, it is possible to suppress a decrease in the detection accuracy of an inspection image by the sensor.

FIG. 7 is a diagram showing an example of a pattern group for detecting the amount of color shift. FIG. 7 is a diagram showing an example of a pattern group for detecting the amount of color shift. FIG. 7 is a diagram showing an example of a pattern group for detecting the amount of color shift. The figure which shows the example of the relationship between a pattern group and a detection error. FIG. 6 is a diagram illustrating an example of a change in the detection error of the amount of color shift. FIG. 7 is a diagram showing an example of the relationship between the amount of deviation dP and the detection error of the amount of color deviation. FIG. 7 is a diagram showing an example of a pattern group for detecting the amount of color shift. The figure which shows the example of the relationship between a pattern group and a detection error. FIG. 7 is a diagram illustrating an example of a change in the detection error of the amount of color shift. FIG. 7 is a diagram showing an example of the relationship between the amount of deviation dP and the detection error of the amount of color deviation. The figure which shows the example of the relationship between a pattern group and a detection error. The figure which shows the example of the relationship between a pattern group and a detection error. The figure which shows the example of the detection of the shift amount of a sensing position. FIG. 3 is a block diagram showing a configuration example of a control unit. 5 is a flowchart showing an example of a color shift detection sequence. 5 is a flowchart showing an example of a color shift detection sequence. FIG. 2 is a perspective view and a cross-sectional view showing a configuration example of an optical sensor. FIG. 1 is a cross-sectional view showing an example of the hardware configuration of an image forming apparatus. FIG. 3 is a diagram showing an example of the positional relationship between a pattern group on an intermediate transfer belt and an optical sensor.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the claimed invention. Although a plurality of features are described in the embodiments, not all of these features are essential to the invention, and the plurality of features may be arbitrarily combined. Furthermore, in the accompanying drawings, the same or similar components are designated by the same reference numerals, and redundant description will be omitted.

[First embodiment]
<Image forming device>
FIG. 18 is a cross-sectional view showing an example of the hardware configuration of the image forming apparatus 100 according to the embodiment of the present disclosure. The image forming apparatus 100 is a color printer that forms a toner image on a sheet 11 using an electrophotographic process. The image forming apparatus 100 includes image forming sections 5Y, 5M, 5C, and 5K that form yellow, magenta, cyan, and black toner images, respectively. Y, M, C, and K added to the end of the reference numerals are abbreviations for yellow, magenta, cyan, and black. If there is no need to distinguish between colors, the letters Y, M, C, and K are omitted from the reference numerals. The image forming section 5 includes a photoreceptor 1, a charger 2, a developer 3, and a primary transfer roller 6, which are provided corresponding to each color. The image forming apparatus 100 also includes an exposure device 7. Note that in the following description, when the image forming section 5 is referred to as the image forming section 5, the exposure device 7 is also included in the image forming section 5.

The charger 2 uniformly charges the surface of the photoreceptor 1. The exposure device 7 irradiates the photoreceptor 1 with laser light according to the image signal (image data) supplied from the control unit 10 to form an electrostatic latent image on the photoreceptor 1 corresponding to the image signal. . The developing device 3 develops the electrostatic latent image using toner of a corresponding color to form a toner image on the photoreceptor 1. The primary transfer roller 6 transfers the toner image from the photoreceptor 1 to the intermediate transfer belt 20 .

The intermediate transfer belt 20 is rotationally driven so that the surface of the intermediate transfer belt 20 moves in the V direction in FIG. 18 . Yellow, magenta, cyan, and black toner images formed on the photoreceptors 1Y, 1M, 1C, and 1K, respectively, are transferred onto the intermediate transfer belt 20 so as to be superimposed on each other. The intermediate transfer belt 20 conveys the toner image to the secondary transfer section as it moves in the V direction.

The sheet cassette 13 is a storage that accommodates a large number of sheets 11. Conveyance rollers 14 , 15 , and 16 convey the sheet 11 housed in the sheet cassette 13 through the conveyance path 9 to the secondary transfer section. A secondary transfer roller 12 provided in the secondary transfer section transfers the toner image on the intermediate transfer belt 20 to the sheet 11. The fixing device 17 applies heat and pressure to the toner image and the sheet 11 to fix the toner image on the sheet 11. The discharge roller 21 discharges the sheet 11 to the outside of the image forming apparatus 100 .

The transfer position of the toner image depends on the timing at which the exposure device 7 starts writing the laser beam. The laser beam is started in synchronization with a main scanning synchronizing signal in the main scanning direction and with a sub scanning synchronizing signal in the sub scanning direction. When the writing timings of the YMCK laser beams are not mutually appropriate, so-called color shift occurs. Color misregistration is a phenomenon in which the formation position of a toner image of a certain color is shifted from the formation position of a toner image of another color. More specific examples of color misregistration include, for example, the position at which the toner image is formed may shift in the main scanning direction, and the position at which the toner image is formed may shift in the sub-scanning direction. Further, as the amount of color shift, the magnification of the toner image in the main scanning direction may deviate from the ideal magnification, and the toner image may be tilted from the sub-scanning direction (the inclination of the toner image may be deviated from the sub-scanning direction).

An optical sensor 30 is provided at a position facing the intermediate transfer belt 20. The optical sensor 30 is a sensor that detects a toner image (inspection image) formed on the intermediate transfer belt 20. In a color shift detection sequence for detecting the amount of color shift, the control section 10 controls the image forming section 5 to form a test image on the intermediate transfer belt 20, and the optical sensor 30 detects the test image. The control unit 10 can, for example, correct the aforementioned color shift of the toner image and correct the density of the toner image based on the detection result of the inspection image. Hereinafter, the moving direction of the surface of the intermediate transfer belt 20 will be referred to as the "V direction," "sub-scanning direction," or "conveyance direction," and the direction orthogonal to the sub-scanning direction will be referred to as the "H direction," "main-scanning direction." ” or “width direction”.

Note that in this embodiment, the intermediate transfer belt 20 is an example of an image carrier that is rotationally driven. Further, the image forming section 5 (image forming sections 5Y, 5M, 5C, 5K, and exposure device 7) is an example of an image forming means that forms an image on an image carrier using toner of a plurality of colors.

<Optical sensor>
FIG. 19 shows an example of the positional relationship between the pattern group Pg formed on the intermediate transfer belt 20 and the optical sensor 30. As shown in FIG. 19, the optical sensor 30 is composed of optical sensors 30L and 30R arranged at different positions in the main scanning direction. In the present embodiment, the optical sensor 30L detects an inspection image formed on one end region of the intermediate transfer belt 20 in the main scanning direction using two or more detection spots on the intermediate transfer belt 20. This is an example of the first sensor. Further, the optical sensor 30R is configured to detect an inspection image formed on the other end region of the intermediate transfer belt 20 in the main scanning direction using two or more detection spots on the intermediate transfer belt 20. This is an example of a sensor.

In the example of FIG. 19, the optical sensor 30L is arranged to detect a pattern group Pg (inspection image group) formed in one end region of the intermediate transfer belt 20 in the main scanning direction. The optical sensor 30R is arranged to detect a pattern group Pg (inspection image group) formed on the other end region of the intermediate transfer belt 20 in the main scanning direction. The pattern group Pg includes a plurality of patterns P. If sensors are placed at multiple positions in the main scanning direction, the amount of color shift in the main scanning direction and sub-scanning direction detected at those sensing positions will be determined by the magnification shift in the main scanning direction and the tilt in the sub-scanning direction, which will be described later. It becomes possible to detect the deviation of the

FIG. 17(A) is a perspective view showing a configuration example of the optical sensor 30. FIG. 17(B) is a cross-sectional view showing a configuration example of the optical sensor 30. The optical sensor 30 includes a light emitting element (LED 32) and a light receiving element (PD 35, 36) provided on a printed circuit board 31. Note that LED is an abbreviation for light emitting diode, and PD is an abbreviation for photodetector or photodiode. The optical sensor 30 has a diaphragm member 37 provided so as to cover the LED 32 and PDs 35 and 36. The aperture member 37 has apertures 40, 41, 45 for constricting and restricting the light beam path.

The light emitted from the LED 32 passes through the openings 40 and 41 and is irradiated onto the intermediate transfer belt 20. The light emitted from the LED 32 and passed through the opening 40 is irradiated onto the detection area 50 of the intermediate transfer belt 20 . The PD 35 is arranged to mainly receive light (specularly reflected light 60) that is specularly reflected by the detection area 50 and passes through the aperture 45. Further, the light emitted from the LED 32 and passed through the opening 41 is irradiated onto the detection area 51 of the intermediate transfer belt 20 . The PD 36 is arranged so as to mainly receive light (diffusely reflected light 61) that is diffusely reflected by the detection area 51 and passed through the aperture 45.

The sensing position Pos_a is a position in the main scanning direction corresponding to the detection area 50 (reflection position). The sensing position Pos_b is a position in the main scanning direction corresponding to the detection area 51 (reflection position). The sensing positions Pos_a and Pos_b correspond to detection spots on the intermediate transfer belt 20 that are used by the optical sensor 30 to detect the linear inspection image formed by the image forming unit 5. A pattern consisting of sub-pattern Pa and sub-pattern Pb is configured so as to pass through sensing positions Pos_a and Pos_b, respectively. The sub-patterns Pa and Pb each correspond to a linear inspection image, and constitute two line segments of a V-shaped pattern. The optical sensor 30 uses the PD 35 to detect specularly reflected light from a linear inspection image (sub-pattern Pa) passing through the sensing position Pos_a, and detects the regular reflection light from the linear inspection image (sub-pattern Pb) passing through the sensing position Pos_b. The PD 36 detects the diffusely reflected light from the sensor.

When the sub-pattern Pa passes through the detection area 50, the amount of light received by the PD 35 (output signal level) changes. The control unit 10 measures the time during which the amount of light received by the PD 35 is changing (the passage time of the sub-pattern Pa), and determines the middle (center) timing of the passage time as the detection timing of the sub-pattern Pa. Similarly, when the sub-pattern Pb passes through the detection area 51, the amount of light received by the PD 36 (output signal level) changes. The control unit 10 measures the time during which the amount of light received by the PD 36 is changing (the passage time of the sub-pattern Pb), and determines the middle (center) timing of the passage time as the detection timing of the sub-pattern Pb. Based on the detection timings of the sub-patterns Pa and Pb obtained in this manner, it is possible to detect the amount of color misregistration of the toner image.

Furthermore, in order to detect the density of a toner image, both the amount of light received by the PD 35 and the amount of light received by the PD 36 are required. Although the PD 35 is provided at a position where it can receive the specularly reflected light 60 from the detection area 50, the diffusely reflected light generated by the intermediate transfer belt 20 (or the toner image formed thereon) also enters the PD 35. In other words, the amount of light received by the PD 35 also includes a component of diffusely reflected light. Therefore, the control unit 10 reduces the diffusely reflected light component included in the amount of light received by the PD 35 and extracts only the specularly reflected component, based on the amount of diffusely reflected light received by the PD 36. Based on the area gradation determined from the specular reflection component, the density of the toner image can be detected with high accuracy.

<Configuration of inspection pattern>
FIG. 1 shows an inspection pattern for detecting the amount of color misregistration in this embodiment. The test pattern includes one or more basic patterns, and each basic pattern is composed of one pattern group Pg (first pattern group) and one pattern group Ng (second pattern group). FIG. 1(A) shows a pattern group Pg for detecting the amount of color shift, and FIG. 1(B) shows a pattern group Ng for detecting the amount of color shift. As shown in FIG. 1, the pattern group Pg and the pattern group Ng included in the inspection pattern are formed at different positions in the V direction (the moving direction of the surface of the intermediate transfer belt 20).

As shown in FIG. 1(A), the pattern group Pg includes a first sub-pattern group Pga and a second sub-pattern group Pgb. Each sub-pattern group Pga includes a plurality of linear sub-patterns Pa. Each sub-pattern group Pgb includes a plurality of linear sub-patterns Pb. The sub-pattern Pa and the sub-pattern Pb have a one-to-one correspondence relationship. One V-shaped pattern (inverted V-shaped chevron pattern) is formed by one set of linear patterns of the sub-pattern Pa and the corresponding sub-pattern Pb. As shown in FIG. 1A, the pattern group Pg includes a plurality of V-shaped patterns formed at different positions in the V direction. The two line segments of each V-shaped pattern are composed of two linear inspection images (subpatterns) formed at different angles with respect to the H direction (main scanning direction).

As for the angle (θ) with respect to the H direction, sub-pattern Pb is tilted by +45 degrees with respect to the H direction, and sub-pattern Pa is tilted with −45 degrees with respect to the H direction. In other words, the angle formed by sub-pattern Pa and sub-pattern Pb is 90 degrees. However, this angle is only an example, and other angles may be used. Further, the pattern formed by the sub-pattern Pa and the corresponding sub-pattern Pb does not necessarily have to have an accurate V-shape. Further, the sub-pattern Pa and the sub-pattern Pb may be joined to each other or may be separated from each other. Alternatively, the sub-pattern Pa and the sub-pattern Pb may overlap near the joint.

Each sub-pattern (linear pattern) of the pattern group Pg is written as a pattern "PxAB". Here, "x" is "a" or "b". "A" and "B" are either Y, M, C, or K. The fact that “x” is “a” indicates that the subpattern belongs to the subpattern group Pga, and the fact that “x” is “b” indicates that the subpattern belongs to the subpattern group Pgb. Show that you belong. "A" indicates the color of sub-pattern Pa, and "B" indicates the color of sub-pattern Pb. For example, the sub-pattern PaKC indicates a black sub-pattern Pa belonging to the sub-pattern group Pga, and indicates that the color of the sub-pattern Pb paired with this sub-pattern Pa is cyan.

Each sub-pattern Pa (linear pattern) belonging to the sub-pattern group Pga is formed so as to pass through the sensing position Pos_a. Each sub-pattern Pb (linear pattern) belonging to the sub-pattern group Pgb is formed so as to pass through the sensing position Pos_b. PD 35 receives specularly reflected light 60 generated in detection area 50 through which sub-pattern Pa passes. The PD 36 receives diffusely reflected light 61 generated in the detection area 51 through which the sub-pattern Pb passes.

Note that the amount of diffusely reflected light on the surface of the intermediate transfer belt 20 and the black (achromatic color) toner pattern is relatively small. Therefore, the sub-pattern PbKK is formed, for example, on a yellow (chromatic color) toner pattern (base image). The diffusely reflected light generated by the yellow toner pattern is stronger than the diffusely reflected light generated by the black toner pattern. Therefore, the amount of light received by the PD 36 when the sub-pattern PbKK passes through the detection area 50 due to movement of the surface of the intermediate transfer belt 20 in the V direction increases due to the preceding yellow toner pattern. Furthermore, it decreases with the black toner pattern and increases again with the subsequent yellow toner pattern. The control unit 10 detects the sub-pattern PbKK by measuring the time during which the amount of light received by the PD 36 (output signal level) decreases below the threshold value.

As shown in FIG. 1B, the pattern group Ng is, to put it simply, the V-shaped patterns of the pattern group Pg, which are symmetrically reversed with the main scanning direction as the axis. That is, the pattern group Ng includes a plurality of V-shaped patterns obtained by symmetrically inverting each of the V-shaped patterns included in the pattern group Pg about the V direction (main scanning direction). The pattern group Ng includes a first sub-pattern group Nga and a second sub-pattern group Ngb. Each subpattern group Nga includes a plurality of linear subpatterns Na. Each subpattern group Ngb includes a plurality of linear subpatterns Nb. The sub-pattern Na and the sub-pattern Nb have a one-to-one correspondence relationship. One V-shaped pattern is formed by a set of linear patterns including the sub-pattern Na and the corresponding sub-pattern Nb. As shown in FIG. 1(B), the pattern group Ng includes a plurality of V-shaped patterns.

Regarding the angle (θ) with respect to the H direction, subpattern Na is inclined by +45 degrees with respect to the H direction, and subpattern Pb is inclined by −45 degrees with respect to the H direction. That is, the angle formed by the sub-pattern Na and the sub-pattern Nb is 90 degrees. However, this angle is only an example, and other angles may be used. Furthermore, the pattern formed by the sub-pattern Na and the corresponding sub-pattern Nb does not necessarily have to have an accurate V-shape. Further, the sub-pattern Na and the sub-pattern Nb may be joined to each other or may be separated from each other. Alternatively, the sub-pattern Na and the sub-pattern Nb may overlap near the joint.

Note that, as shown in FIG. 1B, each linear pattern of the pattern group Ng is expressed as a pattern "NxAB". Note that the usage of "x", "A", and "B" is the same as in pattern group Pg. Further, pattern NbKK is also formed on the yellow toner pattern similarly to pattern PbKK.

FIG. 2A shows an example of one basic pattern composed of a pattern group Pg and a pattern group Ng. Note that in FIGS. 2A to 2D, "x" is omitted from the notation of patterns "PxAB" and "NxAB". FIG. 2B shows three patterns used to detect the amount of color shift between black and cyan when black is the reference color and cyan is the detection target color. Similarly, FIG. 2C shows three patterns used to detect the amount of color shift between black and magenta. FIG. 2(D) shows three patterns used to detect the amount of color shift between black and yellow.

Further, in FIGS. 2A to 2D, identification information indicating each V-shaped pattern is written as "PAB". "A" indicates the color of the subpattern Pa. "B" indicates the color of the subpattern Pb. For example, the V-shaped pattern PKC is composed of a black sub-pattern Pa and a cyan sub-pattern Pb. The amount of color shift of the detection target color Z with respect to the reference color is detected using three V-shaped patterns shown in FIGS. 2(B) to 2(D), respectively. In this embodiment, the detection target color Z is set to Y, M, or C, and the reference color is set to black K. These three V-shaped patterns are a pattern PZZ consisting only of the detection target color Z, a pattern PKK consisting only of the reference color black K, and a pattern consisting of the detection target color Z and black K. Contains pattern PKZ.

As shown in FIG. 2(D), the control unit 10 calculates the amount of deviation in the detection timing in the V direction of the sub-pattern Pb with respect to the sub-pattern Pa in one V-shaped pattern based on the detection results of the pattern group Pg. Detect. When the detection timing of sub-pattern Pb is shifted in the −V direction with respect to the detection timing of sub-pattern Pa, the detection timing shift amount dP is a positive value. On the other hand, when the detection timing of sub-pattern Pb is shifted in the +V direction with respect to the detection timing of sub-pattern Pa, the shift amount dP becomes a negative value.

For example, the control unit 10 obtains the following deviation amount dP for the detection target color Y (the same applies to the other detection target colors M and C).
- Displacement amount dPKK of sub-pattern PbKK with respect to sub-pattern PaKK in V-shaped pattern PKK.
- Displacement amount dPYY of sub-pattern PbYY with respect to sub-pattern PaYY in V-shaped pattern PYY.
- Displacement amount dPKY of sub-pattern PbKY with respect to sub-pattern PaKY in V-shaped pattern PKY.

Note that in FIGS. 2A to 2D, the identification information of each V-shaped pattern in the pattern group Ng is written as "NAB". "A" indicates the color of the subpattern Na. "B" indicates the color of the subpattern Nb. Similarly to the pattern group Pg, for example, dNKK, dNYY, and dNKY are determined by the control unit 10 for the detection target color Y (the same applies to the other detection target colors M and C).

<How to find the amount of color shift>
In this embodiment, an example will be described in which the amount of color shift of the detection target color with respect to the reference color is determined when magenta, cyan, and yellow are the detection target colors and black is the reference color. However, although the method for determining the amount of color shift for yellow will be described below, the same applies to other colors (magenta and cyan).

FIG. 3 shows only the inspection pattern used in determining the amount of yellow color misregistration out of one basic pattern. In this embodiment, inspection patterns are formed near both ends (end regions) of the intermediate transfer belt 20 in the main scanning direction. As shown in FIG. 3, the position where the approximate center of the inspection pattern is formed in the left end region is denoted as position L, and the position where the approximate center of the inspection pattern is formed in the right end region of the figure. is written as position R. Further, the character "(L)" is added to the notation "PxAB" of the inspection pattern passing through the sensing positions Pos_a and Pos_b at position L. The character "(R)" is added to the notation "PxAB" of the inspection pattern passing through the sensing positions Pos_a and Pos_b at position R.

The optical sensor 30 detects the linear inspection image formed by the image forming unit 5 using detection spots (sensing positions Pos_a and Pos_b) on the intermediate transfer belt 20. Specifically, the optical sensor 30L detects the inspection image formed on one end region of the intermediate transfer belt 20 in the main scanning direction using sensing positions Pos_a and Pos_b (detection spots) at position L. do. The optical sensor 30R detects the inspection image formed on the other end region of the intermediate transfer belt 20 in the main scanning direction using sensing positions Pos_a and Pos_b (detection spots) at position R. The control unit 10 acquires the amount of color shift based on the detection result of the inspection image by the optical sensor 30.

The control unit 10 determines the color shift amount LaPKY at the sensing position Pos_a and the color shift at the sensing position Pos_b based on the three shift amounts dPKK(L), dPYY(L), and dPKY(L) shown in FIG. 2(D). Find the amount LbPKY.
LaPKY (L) = dPKY (L) - dPYY (L) (1)
LbPKY(L)=dPKY(L)-dPKK(L) (2)

The control unit 10 determines the amount of color shift LsPKY in the main scanning direction and the amount LpPKY of color shift in the sub-scanning direction.
LsPKY(L) = (LaPKY(L) - LbPKY(L))/2 (3)
LpPKY(L)=(LaPKY(L)+LbPKY(L))/2 (4)

Based on the detection result of the pattern group Pg formed at the position R, the control unit 10 similarly calculates the following color shift amount for the position L.
LaPKY (R) = dPKY (R) - dPYY (R) (5)
LbPKY(R) = dPKY(R) - dPKK(R) (6)
LsPKY(R) = (LaPKY(R) - LbPKY(R))/2 (7)
LpPKY(R)=(LaPKY(R)+LbPKY(R))/2 (8)

The control unit 10 determines four color shift amounts Ps1, Ps2, Pp1, and Pp2 using the following equations based on the color shift amounts obtained using equations (3), (4), (7), and (8).
Ls1PKY= (LsPKY(L)+LsPKY(R))/2 (9)
Ls2PKY=-(LsPKY(L)-LsPKY(R)) (10)
Lp1PKY= (LpPKY(L)+LpPKY(R))/2 (11)
Lp2PKY= (LpPKY(L)-LpPKY(R)) (12)

Ls1PKY is the amount of deviation of the writing start position in the main scanning direction (hereinafter referred to as main scanning position deviation amount). Ls2PKY is the amount of deviation in the length of the image in the main scanning direction (hereinafter referred to as main scanning length deviation amount). Lp1PKY is the amount of deviation of the writing start position in the sub-scanning direction (hereinafter referred to as sub-scanning position deviation amount). Lp2PKY is the amount of tilt of the image in the sub-scanning direction (hereinafter referred to as tilt shift amount).

The control unit 10 further similarly obtains the following deviation amounts for the pattern group Ng.
LaNKY (L) = dNKY (L) - dNYY (L) (13)
LbNKY(L) = dNKY(L) - dNKK(L) (14)
LsNKY(L)=-(LaNKY(L)-LbNKY(L))/2 (15)
LNNKY(L)=(LaNKY(L)+LbNKY(L))/2 (16)
LaNKY (R) = dNKY (R) - dNYY (R) (17)
LbNKY(R) = dNKY(R) - dNKK(R) (18)
LsNKY(R)=-(LaNKY(R)-LbNKY(R))/2 (19)
LpNKY(R)=(LaNKY(R)+LbNKY(R))/2 (20)
Ls1NKY=(LsNKY(L)+LsNKY(R))/2 (21)
Ls2NKY=-(LsNKY(L)-LsNKY(R)) (22)
Lp1NKY=(LpNKY(L)+LpNKY(R))/2 (23)
Lp2NKY=(LpNKY(L)−LpNKY(R)) (24)

Equations (13) to (24) correspond to Equations (1) to (12), respectively, and are based on the detection results of pattern group Ng, and "P" in Equations (1) to (12) is replaced by "N ”. Note that equations (15) and (19) are obtained by inverting the signs of equations (3) and (7) in order to adjust the positive/negative of the deviation amount. The control unit 10 calculates the amounts of black and yellow color shift using the following equations based on the values obtained using equations (9) to (12) and the values obtained using equations (21) to (24).
Ls1=(Ls1PKY+Ls1NKY)/2 (25)
Ls2=(Ls2PKY+Ls2NKY)/2 (26)
Lp1=(Lp1PKY+Lp1NKY)/2 (27)
Lp2=(Lp2PKY+Lp2NKY)/2 (28)

S1 is the main scanning positional deviation amount, and S2 is the main scanning length deviation amount. Furthermore, P1 is the sub-scanning positional deviation amount, and P2 is the tilt deviation amount. Equations (25) to (28) are used to calculate the average value of the four color shift amounts obtained using the pattern group Pg and the corresponding color shift amounts among the four color shift amounts obtained using the pattern group Ng. be. Note that although the yellow color shift amount is calculated here, by changing Y in the above equation to C or M, the cyan color shift amount and the magenta color shift amount can be calculated respectively.

<Control unit>
FIG. 14 is a block diagram showing a configuration example of the control unit 10 that executes the color shift detection sequence according to the present embodiment. Control unit 10 includes a CPU 1100 and a storage unit 1200. By the CPU 1100 executing the control program stored in the storage unit 1200, each function shown in FIG. 14 is realized as a function of the CPU 1100. The storage unit 1200 includes a non-volatile storage medium such as a read-only memory (ROM) and a volatile storage medium such as a random access memory (RAM), and serves as a storage location for programs and data, and a place where the CPU 1100 executes the programs. It is used as a working space.

The CPU 1100 includes a pattern generator 1101, a print control section 1102, a sensor control section 1103, an ADC (analog-to-digital converter) 1104, a correction section 1105, and a color shift detection section 1110. The color shift detection section 1110 includes a position detection section 1111, a shift amount calculation section 1112, a La/Lb calculation section 1113, and an Ls/Lp calculation section 1113.

A pattern generator 1101 generates an image signal (image data) for forming an inspection pattern and supplies it to a print control unit 1102. The print control unit 1102 performs image formation so as to form a toner image (inspection pattern) on the intermediate transfer belt 20 (image carrier) based on the image data for each of the toner colors Y, M, C, and K. 5.

More specifically, the print control unit 1102 uses the correction amount (correction data) set by the correction unit 1105 to correct the control parameters for image formation, so that the image formed by the image forming unit 5 Correct color shifts in images. Corrections by the print control unit 1102 include correction of the writing start timing in the main scanning direction, correction of the writing start timing in the sub-scanning direction, and correction of the magnification (adjusted by the image clock) in the main scanning direction. The print control unit 1102 supplies the corrected image data for each of the toner colors Y, M, C, and K to the image forming unit 5 (exposure device 7) so as to form an electrostatic latent image on the photoreceptor 1. Controls the image forming section 5 (exposure device 7). The print control unit 1102 further controls the developer 3 to develop the electrostatic latent image on the photoreceptor 1 with toner of a corresponding color, thereby forming a toner image (inspection pattern) on the photoreceptor 1. do.

The sensor control unit 1103 controls the optical sensors 30 (30L, 30R) to detect the inspection pattern on the intermediate transfer belt 20. The optical sensors 30 (30L, 30R) are configured to use at least sensing positions Pos_a or Pos_b (sensing spots) arranged at different positions in the main scanning direction.

The optical sensors 30L and 30R detect the inspection pattern on the intermediate transfer belt 20 and output a detection signal. The CPU 1100 uses an input capture function (not shown) to obtain the measured time by measuring the time based on the rising edge and falling edge of the detection signals input from the optical sensors 30L and 30R. This measurement time corresponds to the transit time during which the sub-patterns Pa, Pb, Na, and Nb of the inspection pattern pass through the sensing position Pos_a or Pos_b. Note that the detection signals input from the optical sensors 30L and 30R are input to the ADC 1104 and converted from analog signals to digital signals. The CPU 1100 measures the above-described time based on the detection signal after conversion into a digital signal.

The color shift detection unit 1110 is configured to obtain a color shift amount, which is the shift amount of the formation position of images of different colors, based on the detection results of the inspection images (subpatterns Pa and Pb) by the optical sensor 30. Ru. In the color shift detection unit 1110, the position detection unit 1111 acquires the detection timing of the sub-patterns Pa, Pb, Na, and Nb of the inspection pattern at the sensing position Pos_a or Pos_b based on the above-mentioned measurement time. The deviation amount calculation unit 1112 calculates the deviation amount dP as the difference between the detection timing of the sub-pattern Pa and the detection timing of the sub-pattern Pb, which are output from the position detection unit 1111. The deviation amount calculation unit 1112 further calculates the deviation amount dN as the difference between the detection timing of the sub-pattern Na and the detection timing of the sub-pattern Nb. (Hereinafter, the amount of deviation dP and the amount of deviation dN will be collectively referred to as the amount of deviation d.)

The La/Lb calculation unit 1113 uses the deviation amount d obtained by the deviation amount calculation unit 1112 to calculate the color deviation amount La at the sensing position Pos_a and the color deviation amount Lb at the sensing position Pos_b. The Ls/Lp calculation unit 1114 calculates the color deviation amounts Ls and Lp using the color deviation amounts La and Lb calculated by the La/Lb calculation unit 1113. The calculated color shift amounts Ls and Lp are passed to the correction unit 1105.

The correction unit 1105 determines the correction amount of the control parameter used by the print control unit 1102 based on the color shift amounts Ls and Lp output from the color shift detection unit 1110 (Ls/Lp calculation unit 1114). The correction unit 1105 sets the determined correction amount to the print control unit 1102.

<Detection error of color shift amount>
Next, a periodic shift in the toner image transfer position (image forming position) that occurs in the image forming apparatus 100 will be explained.

The image forming apparatus 100 includes many rotating members and motors, gears, etc. that drive them. There are irregularities in the rotation period of the rotating member. The uneven rotation period is caused by eccentricity of the rotating members (for example, the drive roller of the intermediate transfer belt 20 and the photoreceptor 1), eccentricity of the gear that drives the rotating members, and variations in the film thickness of the intermediate transfer belt 20. Occur. Such unevenness in the rotation period of the rotating member causes a dynamic shift in the transfer position of the toner image (dynamic color shift).

In the image forming apparatus 100, dynamic color shift can be reduced by forming a plurality of pattern groups Pg at positions on the intermediate transfer belt 20 where the unevenness of the rotation period is canceled out. However, in order to cancel out all of the plurality of rotation period components and their higher-order period components, the total length of the pattern Pg becomes long.

Therefore, the control unit 10 of this embodiment is configured to measure the pattern of the reference color and the pattern of the comparison color (detection target color) at timings as close as possible when measuring the amount of color shift. Specifically, the control unit 10 is configured to reduce the difference between the arrangement phase of the reference color and the arrangement phase of the comparison color with respect to the rotation period of the rotating member described above. In short, the distance between the reference color pattern and the comparison color pattern in the sub-scanning direction is set short. As a result, if the sensing position Pos_a and the sensing position Pos_b are ideal positions (nominal positions) in the main scanning direction, the detection result of the amount of color shift between the reference color and the comparison color will have a dynamic detection error. Almost never occurs. On the other hand, if the sensing position Pos_a and the sensing position Pos_b are shifted from the nominal position in the main scanning direction, a detection error occurs.

FIG. 4A shows an example of a dynamic variation in the amount of positional deviation that occurs at the formation position of the test pattern on the intermediate transfer belt 20 when the test pattern of this embodiment is used. FIG. 4(A) shows that a dynamic formation position shift of up to ±100 μm in the sub-scanning direction occurs in one rotation period of the rotating member (intermediate transfer belt 20) with respect to the ideal formation position of the inspection pattern. This is a simple example of the case where In this case, a dynamic detection error of +1.5 μm occurs in the deviation amount dPKK of the sub-pattern PbKK with respect to the sub-pattern PaKK. A detection error of -15.8 μm occurs in the deviation amount dPYY of sub-pattern PbYY with respect to sub-pattern PaYY. A detection error of -17.4 μm occurs in the deviation amount dPKY of sub-pattern PbKY with respect to sub-pattern PaKY. However, these detection errors change depending on which phase in the rotation period of the rotating member the timing at which the test pattern is detected is located.

FIG. 5A shows an example of changes in detection errors of the deviation amounts dPKY, dPYY, and dPKK. This example shows a case where the phase of the positional shift amount of the inspection pattern corresponding to the timing at which the pattern PaKY in FIG. 4(A) is detected is expressed as 180°. FIG. 5(B) shows an example of changes in the color shift amounts LaPKY and LbPKY at the sensing positions Pos_a and Pos_b, which are calculated based on the shift amounts dPKY, dPYY, and dPKK. FIG. 5C shows an example of changes in the color shift amounts LsPKY and LpPKY in the main scanning direction and the sub-scanning direction, which are calculated based on the color shift amounts LaPKY and LbPKY.

As shown in FIG. 5C, the maximum value of the detection error of the color shift amount LsPKY in the main scanning direction is 10.0 μm. The maximum value of the detection error of the color shift amount LpPKY in the sub-scanning direction is 14.9 μm. Note that the larger the deviation amount dPYY, the larger the phase difference with respect to periodic drive unevenness of the intermediate transfer belt 20. As a result, the error in detecting the amount of color shift increases. This relationship is shown in FIG. The maximum values of 14.9 μm and 10.0 μm shown in FIG. 5(C) are the maximum values of the above-mentioned dynamic positional deviation amounts in all phases when the deviation amount dPYY is 2 mm.

Although the patterns PKY, PYY, and PKK having an inverted V shape have been described in FIGS. 4 and 5, the same applies to the patterns NKY, NYY, and NKK having a V shape. That is, when the sensing positions Pos_a and Pos_b deviate from the ideal position (nominal position) in the main scanning direction, a dynamic detection error similarly occurs in the deviation amounts LaNKY and LbNKY, and the maximum error is shown in FIG. 5 (C ) is the same as the value shown in ).

In this way, when the sensing positions Pos_a and Pos_b are deviated from the nominal position as shown in FIG. The dynamic shift causes an error in detecting the amount of color shift.

<Detection error detection correction method>
In this embodiment, in the color shift detection sequence, the relative positional shift amount (positional relationship) of the sensing positions Pos_a and Pos_b in the main scanning direction with respect to the V-shaped pattern passing through the sensing positions Pos_a and Pos_b is detected. To detect the relative positional deviation amount, a V-shaped pattern (for example, PYY, PKK, NYY, etc.) having a pair of sub-patterns of the same color is used among the plurality of V-shaped patterns included in the inspection pattern. . Furthermore, in subsequent color shift detection sequences, the formation position of the V-shaped pattern (inspection image) in the main scanning direction is corrected according to the detected relative positional shift amount. Specifically, the inspection pattern is shifted in the main scanning direction (by correcting the image writing timing) according to the relative positional shift amount. This suppresses the above-mentioned error in detecting the amount of color shift.

The inspection pattern shown in FIG. 4A shows a state where there is no static color shift. However, the sensing positions Pos_a and Pos_b are shifted from the predetermined positions of the sub-patterns Pa and Pb. Therefore, even if the actual amount of color misregistration is zero, a dynamic detection error occurs in the detected amount of color misregistration as described above. Here, if the formation position of the V-shaped pattern PYY can be shifted to the right in FIG. Become.

FIG. 4B shows an example in which the formation position of the inspection pattern is shifted to a position where the deviation amount dPYY is zero. In this case, the sub-pattern PaYY detected at the sensing position Pos_a and the sub-pattern PbYY detected at the sensing position Pos_b are detected in the same phase of the dynamic shift amount caused by periodic drive unevenness of the intermediate transfer belt 20. be done. As a result, the amount of deviation dPYY detected using the V-shaped pattern PYY (sub-patterns PaYY and PbYY) is zero.

In this way, by bringing the amount of deviation dP (dPYY) detected using the V-shaped pattern P closer to zero, the error in detecting the amount of color deviation becomes smaller, as shown in FIG.

Therefore, in this embodiment, in order to bring the deviation amount dPYY detected using the V-shaped pattern PYY, which is included in the inspection pattern and is composed of sub-patterns of the same color, close to zero, the V-shaped pattern PYY is Shift it in the H direction. The amount of shift (image shift amount) of the V-shaped pattern PYY in the H direction is set by the following equation.
Image shift amount = dPYY×tan(90-θ)÷2 (29)

In the case of FIG. 4A, the difference (distance) in the main scanning direction between the sensing position Pos_a and the sensing position Pos_b is 7 mm, dPYY is 2 mm, and θ is 45°. Therefore, by setting the image shift amount to the following value, it is possible to bring the above-mentioned color shift amount detection error close to zero.
Image shift amount = 2mm x tan45° ÷ 2 = 1mm (30)

Further, as shown in FIG. 19, when the inspection patterns are formed on both ends of the intermediate transfer belt 20, the above-mentioned image shift amount is set by the following equation.
Image shift amount = {dPYY(L)+dPYY(R)}
×tan(90-θ)÷4 (31)

In this case, the average of the deviation amounts dPYY for both positions L and R will be brought close to zero. Note that, as shown in the following equation, the V-shaped pattern NYY of the pattern group Ng may also be used to set the image shift amount. Thereby, it is possible to further reduce the detection error due to the averaging effect.
Image shift amount = {dPYY(L)-dNYY(L)+dPYY(R)-dNYY(R)}
×tan(90-θ)÷8 (32)

In the above example, among the V-shaped patterns composed of sub-patterns of the same color included in the inspection pattern, yellow V-shaped patterns PYY and NYY are used, but V-shaped patterns of other colors are used. It is also possible to use similar patterns (PKK, NKK, etc.).

<Color shift detection sequence>
FIG. 15 is a flowchart illustrating an example of the procedure of the above-described color misregistration detection sequence executed by the CPU 1100 in the image forming apparatus 100 of this embodiment. The processing of each step in FIG. 15 is executed in the image forming apparatus 100 by the CPU 1100 executing a control program for executing the color misregistration detection sequence stored in the storage unit 1200.

When the execution conditions for detecting the amount of color misregistration are satisfied, the CPU 1100 starts executing the following process. The execution conditions include, for example, that the image forming apparatus 100 has been started, that the image forming apparatus 100 has continuously formed a predetermined number of images, and that the temperature within the image forming apparatus 100 has changed significantly (for example, a change in temperature). the amount exceeds a predetermined amount). In order to simplify the explanation, the detection of the amount of color misregistration between black and yellow will be described below as an example, but in reality, detection is performed similarly for magenta and cyan.

In step S<b>1201 , the CPU 1100 obtains the color misregistration correction amount that was determined from the previous time or a predetermined color misregistration detection sequence and is stored in the storage unit 1200 . The CPU 1100 further performs color misregistration correction by applying the obtained color misregistration correction amount to the control parameters used by the print control unit 1102.

In step S1202, the CPU 1100 obtains the setting value of the image shift amount for the color shift detection sequence stored in the storage unit 1200. Note that the set values for the color shift correction amount (S1201) and the image shift amount (S1202) at the time of executing the color shift detection sequence for the first time are, for example, zero. In S1203, the CPU 1100 corrects the timing of the main scanning synchronization signal (image writing timing) in order to shift the inspection pattern formed in S1204 in the main scanning direction according to the acquired image shift amount setting value. .

Next, in S1204, the CPU 1100 controls the image forming unit 5 to form an inspection pattern on the intermediate transfer belt 20. After forming the test pattern, in step S1205, the CPU 1100 detects the test pattern on the intermediate transfer belt 20 using the optical sensor 30. In S1206, the CPU 1100 determines the amount of deviation d (dP, dN) based on the detection result of the inspection pattern by the optical sensor 30. For example, as shown in FIG. 3, for yellow and black, the deviation amounts dPYY, dPKY, dPKK, dNYY, dNKY, and dNKK are determined.

Thereafter, in S1207, the CPU 1100 calculates color shift amounts La and Lb (LaKY, LbKY) at the sensing positions Pos_a and Pos_b (detection spots) based on the shift amount d. Furthermore, in S1208, the CPU 1100 determines the color shift amounts Ls and Lp (LsKY, LpKY) in the main scanning direction and the sub-scanning direction based on the color shift amounts La and Lb. Note that it is also possible to calculate the following as in equations (9) to (12) and (21) to (24) above.
- Shift amount Ls1 of the writing start position in the main scanning direction.
- Amount of deviation Ls2 in the length (magnification) of the image in the main scanning direction.
- Amount of deviation Lp1 of the writing start position in the sub-scanning direction.
- The amount of tilt Lp2 of the image in the sub-scanning direction.

In S1209, the CPU 1100 calculates the correction amount (color shift correction amount) of control parameters such as the writing start position and image clock to correct the color shift based on the obtained color shift amounts Ls and Lp (LsKY, LpKY). . CPU 1100 stores the obtained color shift correction amount in storage unit 1200.

In S1210, the CPU 1100 calculates the relative positional deviation amount between the plurality of sub-patterns (inspection images) of the same color (yellow) and the sensing position (detection spot) in the main scanning direction based on the deviation amount dPYY (and dNYY). get. Thereby, the CPU 1100 sets the image shift amount of the inspection pattern for correcting the formation position of the inspection image in the main scanning direction according to the relative positional shift amount. The image shift amount is set using, for example, the above equation (29), equation (31), or equation (32). The CPU 1100 stores the set value of the image shift amount in the storage unit 1200, and ends the processing according to the procedure of FIG. 15.

Note that the optical sensor 30 of this embodiment detects the sub-pattern Pa by its specularly reflected light, and detects the sub-pattern Pb by its scattered reflected light. Therefore, when the color of the sub-pattern Pb is black, a chromatic-colored base image is required to detect the sub-pattern Pb. The color of the base image may be yellow, magenta, or cyan. For example, the control unit 10 may check the remaining amount of yellow, magenta, and cyan toner, and form the base image using the toner of the color with a large remaining amount.

The optical sensor 30 may be configured to detect the sub-pattern Pa using specularly reflected light, and also detect the sub-pattern Pb using specularly reflected light. In this case, the base image becomes unnecessary.

In this embodiment, a V-shaped pattern is used as the inspection pattern in order to detect the amount of color shift in the main scanning direction and the sub-scanning direction, but this is only an example. For example, when detecting the amount of color shift only in the sub-scanning direction, a pattern of horizontal lines parallel to the main-scanning direction may be employed as the inspection pattern.

As described above, in the present embodiment, the optical sensor 30 detects the linear inspection images (subpatterns Pa, Pb) formed by the image forming section 5 at the detection spot (sensing position) on the intermediate transfer belt 20. Pos_a, Pos_b). The control unit 10 (CPU 1100) obtains the amount of color shift, which is the amount of shift between the formation positions of images of different colors, based on the detection result of the inspection image by the optical sensor 30. The control unit 10 corrects the color shift of the image formed by the image forming unit 5 based on the obtained color shift amount. The control unit 10 further detects the plurality of test images of the same color in the main scanning direction based on the detection results of the plurality of test images of the same color formed at different angles with respect to the main scanning direction by the optical sensor 30. and the detection spot. The control unit 10 corrects the formation position of the inspection image by the image forming unit 5 in the main scanning direction in accordance with the obtained relative positional deviation amount.

In one aspect of the present embodiment, the optical sensor 30 is configured to use at least a first detection spot (sensing position Pos_a) and a second detection spot (sensing position Pos_b) arranged at different positions in the main scanning direction. Ru. A plurality of inspection images of the same color are formed at different positions in the main scanning direction, and are a first inspection image (e.g. sub-pattern PaYY) and a second inspection image (e.g. sub-pattern PaYY) that constitute two line segments of a V-shaped pattern. Example: subpattern PbYY). The control unit 10 detects the detection result of the first inspection image (e.g. sub-pattern PaYY) using the first detection spot and the detection result of the second inspection image (e.g. sub-pattern PbYY) using the second detection spot. Based on the result, the above-mentioned relative positional shift amount is obtained.

In one aspect of the present embodiment, the control unit 10 controls the amount of shift in the main scanning direction of the inspection images (subpatterns Pa, Pb) formed by the image forming unit 5 according to the determined relative positional deviation amount. By setting , the formation position of the inspection image in the main scanning direction may be corrected. The control unit 10 may also correct the formation position of the inspection image in the main scanning direction by correcting the timing at which the image forming unit 5 starts writing the image in the main scanning direction according to the set value of the shift amount. good.

In this way, in this embodiment, the amount of positional deviation when the optical sensor 30 is installed deviated from the ideal position is specified as the amount of relative positional deviation between the plurality of inspection images of the same color and the detection spot. , the formation position of the inspection image is corrected accordingly. Thereby, even if an installation error of the optical sensor 30 occurs, it is possible to suppress a decrease in the detection accuracy of the inspection image by the optical sensor 30.

[Second embodiment]
The second embodiment will be described using an example of a test pattern different from the first embodiment. In the following, description of parts common to the first embodiment will be omitted, and parts different from the first embodiment will be mainly described.

FIG. 7(A) shows a test pattern of the second embodiment. The amount of color shift of the detection target color (first color) is determined by the following: a V-shaped pattern consisting only of the first color, a V-shaped pattern consisting only of a second color different from the first color, and a V-shaped pattern consisting only of the second color different from the first color. It is determined from the color and the V-shaped pattern made up of the second color. In the V direction, a V-shaped pattern of only the first color, a V-shaped pattern of the first and second colors, and a V-shaped pattern of only the second color are arranged in this order. FIG. 7 shows an example in which the first color is yellow, the second color is magenta, the third color is cyan, and the fourth color is black.

FIG. 7B shows three V-shaped patterns belonging to pattern group Pg and three V-shaped patterns belonging to pattern group Ng for obtaining the amount of color shift of magenta with respect to yellow. FIG. 7C shows three V-shaped patterns belonging to pattern group Pg and three V-shaped patterns belonging to pattern group Ng for obtaining the amount of color shift of cyan with respect to magenta. FIG. 7(D) shows three V-shaped patterns belonging to pattern group Pg and three V-shaped patterns belonging to pattern group Ng for obtaining the amount of color shift of black with respect to cyan. For example, by using the pattern group shown in FIG. 7(D), the deviation amounts dPCC, dPKC, dPKK, dNCC, dNKC, and dNKK can be determined.

FIG. 8A shows an example of a dynamic variation in the amount of positional deviation occurring at the formation position of the test pattern on the intermediate transfer belt 20 when the test pattern of this embodiment is used. Similar to FIG. 4(A), FIG. 8(A) shows a dynamic side effect of up to ±100 μm in one rotation period of the rotating member (intermediate transfer belt 20) with respect to the ideal formation position of the inspection pattern. A case in which a formation position shift in the scanning direction occurs is simply illustrated. In this case, a dynamic detection error of -23.5 μm occurs in the deviation amount dPKK of the sub-pattern PbKK with respect to the sub-pattern PaKK. A detection error of -13.0 μm occurs in the deviation amount dPCC of the sub-pattern PbCC with respect to the sub-pattern PaCC. A detection error of -19.0 μm occurs in the deviation amount dPKC of sub-pattern PbKC with respect to sub-pattern PaKC. However, these detection errors change depending on which phase in the rotation period of the rotating member the timing at which the test pattern is detected is located.

FIG. 9A shows an example of changes in detection errors of the deviation amounts dPKC, dPCC, and dPKK. This example shows a case where the phase of the positional shift amount of the inspection pattern corresponding to the timing at which the pattern PaKY in FIG. 9(A) is detected is expressed as 180°. FIG. 9B shows an example of changes in the color shift amounts LaPKC and LbPKC at the sensing positions Pos_a and Pos_b (detection spots), which are calculated based on the shift amounts dPKC, dPCC, and dPKK. FIG. 9C shows an example of changes in the color shift amounts LsPKC and LpPKC in the scanning direction and the sub-scanning direction, which are calculated based on the color shift amounts LaPKC and LbPKC. As shown in FIG. 8C, the maximum value of the detection error of the color shift amount LsPKC in the main scanning direction is 10.0 μm. The maximum value of the detection error of the color shift amount LpPKY in the sub-scanning direction is 3.0 μm. Note that the larger the deviation amount dPCC, the larger the phase difference with respect to periodic drive unevenness of the intermediate transfer belt 20. As a result, the error in detecting the amount of color shift increases. This relationship is shown in FIG. The maximum values of 10.0 μm and 3.0 μm shown in FIG. 9(C) are the maximum values of the above-mentioned positional deviation amounts in all phases when the deviation amount dPCC is 2.8 mm.

Although the patterns PKC, PCC, and PKK having an inverted V shape have been described in FIGS. 8 and 9, the same applies to the patterns NKC, NCC, and NKK having a V shape. In other words, when the sensing positions Pos_a and Pos_b (detection spots) deviate from the ideal position (nominal position) in the main scanning direction, a dynamic detection error similarly occurs in the deviation amounts LaPKC and LbPKC, and the maximum error is This is the same value as shown in FIG. 10(C).

In this way, when the sensing positions Pos_a and Pos_b are deviated from the nominal position as shown in FIG. The dynamic shift causes an error in detecting the amount of color shift.

In the inspection pattern of the second embodiment (FIG. 7), three V-shaped patterns are arranged in the sub-scanning direction in each of pattern groups Pg and Ng, compared to the inspection pattern of the first embodiment (FIG. 2). placed close to each other. Therefore, it is possible to reduce the detection error of the amount of color shift compared to the first embodiment. The maximum detection error of the amount of color shift when using the inspection pattern of the first embodiment has the characteristics shown in FIG. On the other hand, the maximum detection error of the amount of color shift when using the inspection pattern of the second embodiment has the characteristics shown in FIG. In this way, by using the inspection pattern of the second embodiment, it is possible to further suppress errors in detecting the amount of color shift.

In the first embodiment, the main scanning synchronization signal is shifted with respect to the average value of the deviation amount at a total of four sensing positions in the main scanning direction (sensing positions Pos_a and Pos_b of positions L and R, respectively). As a result, the entire inspection pattern is shifted. In this case, if the degree of manufacturing variation in the sensing positions is different for each sensing position, the effect of suppressing the amount of color shift may be limited.

In the present embodiment, in the color misregistration detection sequence, the relative amount of misalignment between the sensing position Pos_a and the sub-pattern Pa and the relative amount of misalignment between the sensing position Pos_b and the sub-pattern Pb are individually detected. A V-shaped pattern (for example, PCC) having a pair of sub-patterns of the same color is used to detect these relative positional deviation amounts. That is, the optical sensor 30 is configured to use a plurality of detection spots (sensing positions Pos_a and Pos_b) arranged at different positions in the main scanning direction, and the control unit 10 controls the relative Obtain the amount of positional deviation.

In the present embodiment, the image forming positions of the pattern group Pga and the pattern group Pgb are further corrected individually in the next color misregistration detection sequence based on the relative positional deviation amounts of the individually detected sensing positions Pos_a and Pos_b. That is, the control unit 10 controls the inspection images (subpatterns Pa, Pb) corresponding to each detection spot according to the relative positional deviation amount acquired for each of the plurality of detection spots (sensing positions Pos_a and Pos_b). ) is corrected. This further suppresses the above-mentioned error in detecting the amount of color shift.

FIG. 11B shows an example in which correction is performed to shift the formation position of the inspection pattern to a position where the deviation amount dPCC detected using the V-shaped pattern PCC becomes zero. FIG. 11(A) shows a state before correction of the formation position of the inspection pattern, and is similar to FIG. 8(A). In FIG. 11(B), the arrangement interval in the main scanning direction between the sub-pattern group Pga and the sub-pattern group Pgb is different from that in FIG. 11(A). This is due to the correction of the formation positions of the sub-pattern groups Pga and Pgb (inspection image group) that pass through the sensing positions Pos_a and Pos_b, respectively. In this embodiment, the formation position correction is performed for individual test image groups formed for each of the positions L and R of the intermediate transfer belt 20. This makes it possible to bring the deviation amounts dPCC(L) and dPCC(R) close to zero. In this way, by bringing the deviation amount d close to zero, the main scanning width of the inspection pattern (between the sub-pattern groups Pga and Pgb, respectively) can be narrowed to the minimum, as shown in FIG. 11(C). It becomes possible.

Further, FIG. 12 shows, as an example of correction for shifting the formation position of the inspection pattern, a correction for narrowing the arrangement interval of sub-pattern groups Pga and Pgb passing through sensing positions Pos_a and Pos_b, respectively. FIG. 12(A) shows the state before correction of the formation position of the inspection pattern. FIG. 12(B) shows the state after correction of the formation position of the inspection pattern, and FIG. 12(C) shows an example in which the main scanning width of the inspection pattern sub-pattern groups Pga and Pgb is set to the minimum. show. 11(B), FIG. 11(C), FIG. 12(B), and FIG. 12(C) all show that the pattern PaCC detected at the sensing position Pos_a and the pattern PbCC detected at the sensing position Pos_b are intermediate The amount of dynamic positional deviation caused by periodic driving unevenness of the transfer belt 20 is detected in the same phase. As a result, the amount of deviation dPCC detected using the V-shaped pattern PCC (sub-patterns PaCC and PbCC) is zero.

In this way, by bringing the amount of deviation dP (dPCC) detected using the V-shaped pattern P closer to zero, the error in detecting the amount of color deviation becomes smaller, as shown in FIG.

Therefore, in this embodiment, as will be described below with reference to FIG. Detect the amount (positional relationship).

FIG. 13A shows a case where the sensing positions Pos_a and Pos_b of the optical sensor 30 are deviated from the ideal position (nominal position). FIG. 13(B) shows a case where the sensing positions Pos_a and Pos_b of the optical sensor 30 are at the nominal position. In FIGS. 13(A) and (B), a V-shaped (inverted V-shaped) pattern PYY passes through each of the sensing positions Pos_a (L), Pos_b (L), Pos_a (R), and Pos_b (R). It shows the distance dPN in the sub-scanning direction between the sub-pattern belonging to the V-shaped pattern NYY and the sub-pattern belonging to the V-shaped pattern NYY. Note that the V-shaped patterns PYY and NYY are both composed of sub-patterns of the same color (yellow). Further, dPN (ref) shown in FIG. 13(B) is an ideal value (nominal value) and is determined in advance in design.

For example, the distance dPN in the sub-scanning direction between the sub-pattern PaYY (L) of the inverted V-shaped pattern PYY and the sub-pattern NaYY (L) of the V-shaped pattern NYY, which pass through the sensing position Pos_a (L), is , is obtained as follows.
dPN_aYY(L) = NaYY(L) - PaYY(L) (33)
In this way, subpattern PaYY(L) (first inspection image) and subpattern NaYY(L) (third inspection image) are detected using the same detection spot (sensing position Pos_a(L)). ) is calculated. The control unit 10 of the present embodiment detects the plurality of inspection images of the same color in the main scanning direction based on the difference between the distance thus obtained and a reference value (nominal value dPN (ref) to be described later). Obtain the amount of positional deviation relative to the spot.

When dPN_aYY(L) is smaller than the nominal value dPN(ref) (dPN_aYY(L)<dPN(ref)), the sensing position Pos_a(L) is relatively shifted to the left in FIG. 13. On the other hand, when dPN_aYY(L) is larger than the nominal value dPN(ref) (dPN_aYY(L)<dPN(ref)), the sensing position Pos_a(L) is relatively shifted to the right in FIG. 13.

Furthermore, the distance dPN in the sub-scanning direction between the sub-pattern PbYY(L) of the inverted V-shaped pattern PYY and the sub-pattern NbYY(L) of the V-shaped pattern NYY, which pass through the sensing position Pos_b(L), is , is obtained as follows.
dPN_bYY(L) = NbYY(L) - PbYY(L) (34)

When dPN_bYY(L) is smaller than the nominal value dPN(ref) (dPN_bYY(L)<dPN(ref)), the sensing position Pos_b(L) is relatively shifted to the right in FIG. 13. When dPN_bYY(L) is larger than the nominal value dPN(ref) (dPN_bYY(L)>dPN(ref)), the sensing position Pos_b(L) is relatively shifted to the left in FIG. 13.

The set value of the image shift amount in this embodiment is set as follows. Let Sa be the set value of the image shift amount for the sub-pattern groups Pga and Nga, and Sb be the set value of the image shift amount for the sub-pattern groups Pgb and Ngb. In this case, Sa(L) and Sb(L) at position L and Sa(R) and Sb(R) at position R are individually set as follows.
Sa(L) = {dPN_aYY(L)-dPN(ref)}×tan(90-θ)÷4 (35)
Sb(L)=-{dPN_bYY(L)-dPN(ref)}×tan(90-θ)÷4 (36)
Sa(R) = {dPN_aYY(R)-dPN(ref)}×tan(90-θ)÷4 (37)
Sb(R)=-{dPN_bYY(R)-dPN(ref)}×tan(90-θ)÷4 (38)

<Color shift detection sequence>
FIG. 16 is a flowchart illustrating an example of the procedure of the above-described color misregistration detection sequence executed by the CPU 1100 in the image forming apparatus 100 of this embodiment. The processing of each step in FIG. 16 is executed in the image forming apparatus 100 by the CPU 1100 executing a control program for executing the color misregistration detection sequence stored in the storage unit 1200.

When the execution conditions for detecting the amount of color misregistration are satisfied, the CPU 1100 starts executing the following process. The execution conditions include, for example, that the image forming apparatus 100 has been started, that the image forming apparatus 100 has continuously formed a predetermined number of images, and that the temperature within the image forming apparatus 100 has changed significantly (for example, a change in temperature). the amount exceeds a predetermined amount). In order to simplify the explanation, the detection of the amount of color misregistration between black and cyan will be described below as an example, but in reality, the detection is performed similarly for yellow and magenta.

In step S<b>1201 , the CPU 1100 obtains the color misregistration correction amount that was determined from the previous time or a predetermined color misregistration detection sequence and is stored in the storage unit 1200 . The CPU 1100 further performs color misregistration correction by applying the obtained color misregistration correction amount to the control parameters used by the print control unit 1102.

In step S1202, the CPU 1100 obtains the setting value of the image shift amount for the color shift detection sequence stored in the storage unit 1200. Note that the set values for the color shift correction amount (S1201) and the image shift amount (S1202) at the time of executing the color shift detection sequence for the first time are, for example, zero. In S1211, the CPU 1100 corrects the image data used for image formation for each sensing position (detection spot) according to the acquired image shift amount setting value. Thereby, the formation position of the inspection image (sub-pattern) corresponding to each detection spot is corrected according to the relative positional deviation amount acquired for each of the plurality of sensing positions (detection spots).

Next, in S1204, the CPU 1100 controls the image forming unit 5 to form an inspection pattern on the intermediate transfer belt 20. After forming the test pattern, in step S1205, the CPU 1100 detects the test pattern on the intermediate transfer belt 20 using the optical sensor 30. In S1206, the CPU 1100 determines the amount of deviation d (dP, dN) based on the detection result of the inspection pattern by the optical sensor 30. For example, as shown in FIG. 7, for cyan and black, the deviation amounts dPCC, dPKC, dPKK, dNCC, dNKC, and dNKK are determined.

Thereafter, in S1207, the CPU 1100 calculates color shift amounts La and Lb (LaKC, LbKC) at the sensing positions Pos_a and Pos_b (detection spots) based on the shift amount d. Furthermore, in S1208, the CPU 1100 determines the color shift amounts Ls and Lp (LsKC, LpKC) in the main scanning direction and the sub-scanning direction based on the color shift amounts La and Lb. Note that it is also possible to calculate the following as in equations (9) to (12) and (21) to (24) above.
- Shift amount Ls1 of the writing start position in the main scanning direction.
- Amount of deviation Ls2 in the length (magnification) of the image in the main scanning direction.
- Amount of deviation Lp1 of the writing start position in the sub-scanning direction.
- The amount of tilt Lp2 of the image in the sub-scanning direction.

In S1209, the CPU 1100 calculates the correction amount (color shift correction amount) of control parameters such as the writing position and image clock to correct the color shift based on the obtained color shift amounts Ls and Lp (LsKC, LpKC). . CPU 1100 stores the obtained color shift correction amount in storage unit 1200.

In S1212, the CPU 1100 sets the image shift amount of the inspection pattern for each sensing position (detection spot) based on dPN_aYY and dPN_bYY using equations (33) to (36) described above. The CPU 1100 stores the individual setting value of the image shift amount for each sensing position (detection spot) in the storage unit 1200, and ends the processing according to the procedure of FIG. 16. In this way, the optimum position of the test pattern for each sensing position is detected.

As described above, in the present embodiment, the optical sensor 30 detects the linear inspection image (e.g. sub-patterns Pa, Na) formed by the image forming unit 5 at the detection spot ( Example: Detect using sensing position Pos_a). The control unit 10 (CPU 1100) obtains the amount of color shift, which is the amount of shift between the formation positions of images of different colors, based on the detection result of the inspection image by the optical sensor 30. The control unit 10 corrects the color shift of the image formed by the image forming unit 5 based on the obtained color shift amount. The control unit 10 further detects the plurality of test images of the same color in the main scanning direction based on the detection results of the plurality of test images of the same color formed at different angles with respect to the main scanning direction by the optical sensor 30. and the detection spot. The control unit 10 corrects the formation position of the inspection image by the image forming unit 5 in the main scanning direction in accordance with the obtained relative positional deviation amount.

In one aspect of the present embodiment, the plurality of inspection images of the same color include a first inspection image (eg, sub-pattern PaYY) and a third inspection image (eg, sub-pattern NaYY). The first inspection image and the third inspection image are formed at different positions in the sub-scanning direction and at different angles with respect to the main scanning direction. Based on the detection results of the first inspection image (e.g. sub-pattern PaYY) and the third inspection image (e.g. sub-pattern NaYY) obtained using the same detection spot, the control unit 10 , obtain the above-mentioned relative positional deviation amount.

In one aspect of the present embodiment, the control unit 10 calculates the distance between the first test image and the third test image that are detected using the same detection spot, and calculates the difference between the distance and the reference value. Based on this, the relative positional deviation amount is obtained. Further, the optical sensor 30 may be configured to use a plurality of detection spots (sensing positions Pos_a and Pos_b corresponding to positions L and R, respectively) arranged at different positions in the main scanning direction. In that case, the control unit 10 acquires the relative positional shift amount for each of the plurality of detection spots. Furthermore, the control unit 10 corrects the formation position of the inspection image corresponding to each detection spot according to the relative positional deviation amount acquired for each of the plurality of detection spots.

In this way, in this embodiment, the amount of positional deviation when the optical sensor 30 is installed deviated from the ideal position is specified as the amount of relative positional deviation between the plurality of inspection images of the same color and the detection spot. , the formation position of the inspection image is corrected accordingly. Thereby, even if an installation error of the optical sensor 30 occurs, it is possible to suppress a decrease in the detection accuracy of the inspection image by the optical sensor 30.

Note that if the sensing position deviates significantly from the ideal position (nominal position), detection may only be possible with Sa(L), Sb(L), Sa(R), or Sb(R). is assumed. In such a case, if correction is performed according to the result of the inspection pattern at the detected main scanning position, the large amount of deviation will be coarsely adjusted, so in the next color deviation detection sequence, all inspection patterns will be In many cases, it becomes possible to detect

Further, in general, the amount of color shift is about several hundred μm even before correction. Once the color misregistration detection and correction is performed, the variation level of the amount of color misregistration thereafter becomes a variation level of several tens of micrometers. On the other hand, manufacturing variations of approximately several hundred μm to 1 mm occur in the sensing positions Pos_a and Pos_b of the optical sensor 30 in the main scanning direction. Therefore, the main purpose of the above-described embodiments is to correct the influence of mechanical manufacturing variations in optical sensors. Further, in color shift correction, image forming positions of other colors are corrected using one of the colors as a reference. Therefore, for the reference color for which the image forming position is not corrected, if the setting value of the individual image shift amount for each sensing position is calculated using equations (35) to (38), the transition of the individual image shift amount This has the advantage of making it easier to understand.

The disclosure herein includes the following image forming apparatus.
(Item 1)
an image carrier that is rotationally driven;
an image forming means for forming an image on the image carrier using toner of a plurality of colors;
a detection means for detecting a linear inspection image formed by the image forming means using a detection spot on the image carrier;
a first acquisition unit that acquires a color shift amount, which is a shift amount of the formation position of images of different colors, based on a detection result of the inspection image by the detection unit;
a first correction means for correcting color misregistration of an image formed by the image forming means based on the amount of color misregistration;
Based on the detection results of a plurality of inspection images of the same color formed at different angles with respect to the main scanning direction perpendicular to the moving direction of the surface of the image carrier by the detection means, a second acquisition means for acquiring a relative positional shift amount between a plurality of inspection images of the same color and the detection spot;
a second correction means for correcting a position at which an inspection image is formed by the image forming means in the main scanning direction in accordance with the relative positional deviation amount;
An image forming apparatus comprising:
(Item 2)
The detection means is configured to use at least a first detection spot and a second detection spot arranged at different positions in the main scanning direction,
The plurality of inspection images of the same color are formed at different positions in the main scanning direction and include a first inspection image and a second inspection image that constitute two line segments of a V-shaped pattern,
The second acquisition means is configured to obtain the relative The image forming apparatus according to item 1, wherein the image forming apparatus obtains a positional deviation amount.
(Item 3)
Item 1 or 2 characterized in that the second correction means sets a shift amount in the main scanning direction of the inspection image formed by the image forming means according to the relative positional deviation amount. The image forming apparatus described in .
(Item 4)
The image forming apparatus according to item 3, wherein the second correction means corrects the timing at which the image forming means starts writing the image in the main scanning direction, according to the set value of the shift amount.
(Item 5)
The plurality of inspection images of the same color include a first inspection image and a third inspection image, which are formed at different positions in the movement direction and at different angles with respect to the main scanning direction. ,
The second acquisition means acquires the relative positional deviation amount based on the detection result of the first inspection image and the detection result of the third inspection image obtained using the same detection spot. The image forming apparatus according to item 1, characterized in that:
(Item 6)
The second acquisition means determines a distance between the first inspection image and the third inspection image detected using the same detection spot, and based on the difference between the distance and a reference value, The image forming apparatus according to item 5, wherein the relative positional shift amount is acquired.
(Item 7)
The detection means is configured to use a plurality of detection spots arranged at different positions in the main scanning direction,
The image forming apparatus according to item 5 or 6, wherein the second acquisition unit acquires the relative positional shift amount for each of the plurality of detection spots.
(Item 8)
The second correction means corrects the formation position of the inspection image corresponding to each detection spot according to the relative positional deviation amount acquired for each of the plurality of detection spots. The image forming apparatus according to item 7.
(Item 9)
An item characterized in that the second correction means corrects image data used for image formation by the image forming means according to the relative positional deviation amount acquired for each of the plurality of detection spots. 8. The image forming apparatus according to 8.
(Item 10)
further comprising a control means for controlling the image forming means to form an inspection pattern on the image carrier for detecting the amount of color misregistration;
The inspection pattern includes a first pattern group and a second pattern group formed at different positions in the moving direction,
The first pattern group includes a plurality of V-shaped patterns formed at different positions in the moving direction, and two line segments of each V-shaped pattern are formed at different angles with respect to the main scanning direction. It consists of two linear inspection images,
From item 1, wherein the second pattern group includes a plurality of V-shaped patterns obtained by symmetrically inverting each V-shaped pattern included in the first pattern group with the main scanning direction as an axis. 9. The image forming apparatus according to any one of 9.
(Item 11)
The detection means includes:
a first sensor that detects the inspection image formed on one end region of the image carrier in the main scanning direction using two or more detection spots on the image carrier;
a second sensor that detects the inspection image formed on the other end region of the image carrier in the main scanning direction using two or more detection spots on the image carrier;
The image forming apparatus according to any one of items 1 to 10, characterized in that the image forming apparatus has:

The invention is not limited to the embodiments described above, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the following claims are hereby appended to disclose the scope of the invention.

100: Image forming device, 1: Photoreceptor, 5: Image forming section, 7: Exposure device, 10: Control section, 30: Optical sensor, 1100: CPU

Claims (11)

an image carrier that is rotationally driven;
an image forming means for forming an image on the image carrier using toner of a plurality of colors;
a detection means for detecting a linear inspection image formed by the image forming means using a detection spot on the image carrier;
a first acquisition unit that acquires a color shift amount, which is a shift amount of the formation position of images of different colors, based on a detection result of the inspection image by the detection unit;
a first correction means for correcting color misregistration of an image formed by the image forming means based on the amount of color misregistration;
Based on the detection results of a plurality of inspection images of the same color formed at different angles with respect to the main scanning direction perpendicular to the moving direction of the surface of the image carrier by the detection means, a second acquisition means for acquiring a relative positional shift amount between a plurality of inspection images of the same color and the detection spot;
a second correction means for correcting a position at which an inspection image is formed by the image forming means in the main scanning direction in accordance with the relative positional deviation amount;
An image forming apparatus comprising: The detection means is configured to use at least a first detection spot and a second detection spot arranged at different positions in the main scanning direction,
The plurality of inspection images of the same color are formed at different positions in the main scanning direction and include a first inspection image and a second inspection image that constitute two line segments of a V-shaped pattern,
The second acquisition means is configured to obtain the relative The image forming apparatus according to claim 1, wherein the image forming apparatus acquires a positional deviation amount. 2. The second correction means sets a shift amount in the main scanning direction of the inspection image formed by the image forming means in accordance with the relative positional deviation amount. 2. The image forming apparatus according to 2. 4. The image forming apparatus according to claim 3, wherein the second correcting means corrects the timing at which the image forming means starts writing the image in the main scanning direction according to the set value of the shift amount. The plurality of inspection images of the same color include a first inspection image and a third inspection image, which are formed at different positions in the movement direction and at different angles with respect to the main scanning direction. ,
The second acquisition means acquires the relative positional deviation amount based on the detection result of the first inspection image and the detection result of the third inspection image obtained using the same detection spot. The image forming apparatus according to claim 1, characterized in that: The second acquisition means determines a distance between the first inspection image and the third inspection image detected using the same detection spot, and based on the difference between the distance and a reference value, The image forming apparatus according to claim 5, wherein the relative positional shift amount is acquired. The detection means is configured to use a plurality of detection spots arranged at different positions in the main scanning direction,
The image forming apparatus according to claim 5 or 6, wherein the second acquisition unit acquires the relative positional shift amount for each of the plurality of detection spots. The second correction means corrects the formation position of the inspection image corresponding to each detection spot according to the relative positional deviation amount acquired for each of the plurality of detection spots. The image forming apparatus according to claim 7. The second correction means corrects the image data used for image formation by the image forming means according to the relative positional deviation amount acquired for each of the plurality of detection spots. The image forming apparatus according to item 8. further comprising a control means for controlling the image forming means to form an inspection pattern on the image carrier for detecting the amount of color misregistration;
The inspection pattern includes a first pattern group and a second pattern group formed at different positions in the moving direction,
The first pattern group includes a plurality of V-shaped patterns formed at different positions in the moving direction, and two line segments of each V-shaped pattern are formed at different angles with respect to the main scanning direction. It consists of two linear inspection images,
1 . The second pattern group includes a plurality of V-shaped patterns obtained by symmetrically inverting each V-shaped pattern included in the first pattern group with the main scanning direction as an axis. Or the image forming apparatus according to 2. The detection means includes:
a first sensor that detects the inspection image formed on one end region of the image carrier in the main scanning direction using two or more detection spots on the image carrier;
a second sensor that detects the inspection image formed on the other end region of the image carrier in the main scanning direction using two or more detection spots on the image carrier;
The image forming apparatus according to claim 1 or 2, characterized in that the image forming apparatus has:

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