JP7549623B2 - Color image forming device - Google Patents

Description

The present invention relates to a color misregistration correction technique for a color image forming apparatus that uses an electrophotographic process.

A color image forming apparatus (hereinafter, simply referred to as an image forming apparatus) that forms an image using toners of multiple colors performs color shift correction control to maintain the quality of the image it forms. Specifically, the image forming apparatus forms an inspection image for detecting the amount of color shift on an image carrier such as an intermediate transfer belt, and determines and obtains the amount of color shift by detecting the inspection image using a reflective optical sensor. The image forming apparatus then corrects the image formation conditions, such as the timing of image formation, so as to reduce the color shift based on the obtained amount of color shift. Here, if the image carrier is scratched, the inspection image may be erroneously detected, reducing the accuracy of obtaining the amount of color shift. For this reason, Patent Document 1 discloses a method for avoiding erroneous detection of the inspection image due to scratches on the image carrier.

JP 2019-164248 A

However, if the inspection image is formed on the image carrier so that it is in contact with the scratch, the configuration of Patent Document 1 cannot detect the presence of the scratch, and the effect of the scratch causes the formation position of the inspection image to be erroneously detected, thereby reducing the accuracy of obtaining the amount of color shift. Furthermore, in an image carrier such as an intermediate transfer belt, there may be areas where the reflectance varies locally due to manufacturing reasons. With the configuration of Patent Document 1, even if the inspection image is in contact with this area where the reflectance varies, the formation position of the inspection image may be erroneously detected due to the variation in reflectance, thereby reducing the accuracy of obtaining the amount of color shift.

The present invention provides a technology that suppresses the decrease in accuracy of obtaining the amount of color shift.

According to one aspect of the present invention, an image forming apparatus includes an image carrier, an image forming means for forming an image on the image carrier using toners of a plurality of colors, and a detection means for detecting an inspection image formed on the image carrier by the image forming means, the inspection image including a pair of a first pattern and a second pattern of the same color for each of the plurality of colors, the first pattern and the second pattern of the pair being patterns having the same shape, and being linear patterns extending in a direction different from a transport direction of the image carrier and a width direction perpendicular to the transport direction, and detection of the inspection image by the detection means. the image forming apparatus is provided with an acquisition means for acquiring an amount of color shift based on the detection result of the inspection image by the detection means, and a determination means for acquiring the distance in the transport direction between the first pattern and the second pattern of the pair based on the detection result of the inspection image by the detection means, and determining that there is a local abnormality in the surface reflectance of the image carrier in contact with the inspection image if the distance is not within a predetermined range , wherein the image forming means forms the first pattern and the second pattern of the pair at different positions in the transport direction, and does not form the first pattern or the second pattern of another pair between the first pattern and the second pattern of the pair in the transport direction .

This invention makes it possible to suppress a decrease in the accuracy of obtaining the amount of color shift.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 4 is a block diagram of a control unit according to one embodiment. FIG. 4 is a control block diagram of an optical sensor according to one embodiment. 1 illustrates an inspection image according to one embodiment. FIG. 13 illustrates a V-shaped pattern in an inspection image used to detect the relative color shift of two colors, according to one embodiment. 6A and 6B are explanatory diagrams illustrating degradation of detection accuracy of the formation position of a straight line pattern due to imprint defects of an image carrier according to an embodiment. 6 is an explanatory diagram of deterioration in detection accuracy of the formation position of a straight line pattern due to a scratch on an image carrier according to an embodiment. 11 is a flowchart of a process for acquiring a color misregistration amount according to an embodiment. FIG. 13 illustrates a pair of two straight line patterns used to determine degradation of detection accuracy of a formation position, according to one embodiment. 6A and 6B are explanatory diagrams illustrating degradation of detection accuracy of the formation position of a straight line pattern due to imprint defects of an image carrier according to an embodiment. 11 is a flowchart of a process for acquiring a color misregistration amount according to an embodiment. FIG. 13 illustrates a pair of two straight line patterns used to determine degradation of detection accuracy of a formation position, according to one embodiment. 6A and 6B are explanatory diagrams illustrating erroneous detection of the formation position of a straight line pattern due to imprint defects on an image carrier according to an embodiment.

The following embodiments are described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe multiple features, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicate explanations are omitted.

First Embodiment
FIG. 1 is a schematic diagram of an image forming apparatus 700 according to the present embodiment. In FIG. 1, the letters Y, M, C, and K at the end of the reference symbols indicate that the colors of the toner images formed by the members indicated by the reference symbols are yellow, magenta, cyan, and black, respectively. In the following description, when it is not necessary to distinguish the colors, reference symbols without the letters Y, M, C, and K at the end are used. The photoconductor 701 of the image forming unit 705 is rotated clockwise in the figure during image formation. The charging unit 702 charges the surface of the rotating photoconductor 701 to a uniform potential. The exposure unit 707 exposes the surface of each photoconductor 701 to light to form an electrostatic latent image on each photoconductor 701. The developing unit 703 develops the electrostatic latent image on the photoconductor 701 with toner to form a toner image on the photoconductor 701. The primary transfer roller 706 transfers the toner image on the photoconductor 701 to the intermediate transfer belt 20, which is an image carrier. During image formation, the intermediate transfer belt 20 is driven to rotate in a counterclockwise direction in the figure. The toner images on the photoconductors 701 are transferred onto the intermediate transfer belt 20 in a superimposed state, forming a full-color toner image on the intermediate transfer belt 20. The toner image on the intermediate transfer belt 20 is transported to a position facing the secondary transfer roller 711 by the rotation of the intermediate transfer belt 20.

The recording material in cassette 713 is transported by transport rollers 714, 715, and 716 along transport path 709 to a position facing secondary transfer roller 711. Secondary transfer roller 711 transfers the toner image on intermediate transfer belt 20 to the recording material. The recording material to which the toner image has been transferred is transported to fixing section 717. Fixing section 717 heats and presses the recording material to fix the toner image to the recording material. The recording material is then discharged to the outside of image forming apparatus 700 by discharge rollers 720.

The control unit 500 includes a microcomputer (hereafter referred to as the microcomputer) 501, and controls the entire image forming apparatus 700. The optical sensor 30 detects an inspection image formed on the intermediate transfer belt 20 for detecting the amount of color shift and density, and outputs the detection result to the microcomputer 501. The microcomputer 501 performs color shift correction control and density correction control based on the detection result. The direction of movement of the surface of the intermediate transfer belt 20 is called the sub-scanning direction or transport direction, and the direction perpendicular to the sub-scanning direction is called the main scanning direction or width direction.

2 is a functional block diagram of the control unit 500 related to color shift correction control. Each functional block in the microcomputer 501 in FIG. 2 is realized by the microcomputer 501 executing a control program stored in a storage device (not shown) of the control unit 500. When color shift correction control is executed, the image control unit 506 outputs image data of the inspection image to the print control unit 502. The print control unit 502 outputs image data of the inspection image to the exposure unit 707 and controls each member in FIG. 1 to form an inspection image on the intermediate transfer belt 20. The inspection image includes a plurality of pattern images (hereinafter simply referred to as patterns), the details of which will be described later. The print control unit 502 controls the sensor control unit 503 to cause the optical sensor 30 to detect the inspection image on the intermediate transfer belt 20. A detection signal indicating the detection result of the inspection image by the optical sensor 30 is output to the color shift detection unit 510 of the microcomputer 501 via the sensor control circuit 50.

The position detection unit 511 of the color shift detection unit 510 detects the passing timing of each pattern of the inspection image based on the detection signal from the optical sensor 30, and thereby detects the formation position on the intermediate transfer belt 20 in the conveying direction for each pattern of the inspection image. The color shift amount calculation unit 512 judges the amount of color shift based on the formation position of each pattern detected by the position detection unit 511. The color shift detection unit 510 outputs the judged amount of color shift to the color shift correction unit 505. The color shift correction unit 505 determines the correction amount of the control parameter used in the print control unit 502 based on the amount of color shift, and sets the correction amount in the print control unit 502. The control parameters include the writing timing of the electrostatic latent image in the main scanning direction and the sub-scanning direction, the magnification in the main scanning direction, etc. In actual image formation, the print control unit 502 controls image formation according to the correction amount of each control parameter. This makes it possible to form an image with reduced color shift.

The abnormality determination unit 515 determines whether or not there has been a deterioration in the detection accuracy of the formation position of each pattern included in the inspection image. Some of the causes of the deterioration in the detection accuracy of the formation position of each pattern included in the inspection image and a method of determining whether or not there has been a deterioration in the detection accuracy will be described later.

Figure 3 shows the control configuration of the optical sensor 30. The light source 31 of the optical sensor 30 emits light toward the intermediate transfer belt 20. The light emission of the light source 31 is controlled by the microcomputer 501 via the drive circuit 40 of the sensor control circuit 50. The light receiving element 32 is arranged to receive the specular reflected light of the light emitted by the light source 31 at the intermediate transfer belt 20. The light receiving element 32 mainly receives the specular reflected light, but also receives the scattered reflected light at the same angle as the specular reflected light. The light receiving element 33 is arranged to receive the scattered reflected light of the light emitted by the light source 31 at the intermediate transfer belt 20 or the image formed thereon. The member 34 is provided to narrow down the light emitted by the light source 31 and the light received by the light receiving elements 32 and 33.

The light receiving elements 32 and 33 output currents corresponding to the amount of light received to the IV conversion units 51a and 51b, respectively. The IV conversion units 51a and 51b convert the input currents into voltages and output them to the gain adjustment amplifier units 52a and 52b, respectively. The gain adjustment amplifier units 52a and 52b amplify the input voltages and output analog detection signals S1a and S1b to the comparators 53a and 53b, respectively. The gains in the gain adjustment amplifier units 52a and 52b are set by the microcomputer 501.

The comparators 53a and 53b use a threshold value to perform binarization processing of the detection signals S1a and S1b to generate the detection signals S2a and S2b. The detection signals S2a and S2b are input to a terminal having an input capture function (not shown) of the microcomputer 501. The microcomputer 501 detects the passing timing of each pattern of the inspection image based on the timing of the rising and falling edges of the detection signals S2a and S2b. Then, based on this passing timing, the formation position of each pattern on the intermediate transfer belt 20 in the conveying direction (hereinafter simply referred to as the formation position). Note that the reflection positions in the main scanning direction on the intermediate transfer belt 20 of the reflected light received by the light receiving element 32 and the light receiving element 33 are predetermined positions, and are hereinafter referred to as the sensing position Pos_a and the sensing position Pos_b, respectively.

Figure 4 shows an inspection image. The up-down direction in Figure 4 corresponds to the transport direction (sub-scanning direction), and the left-right direction corresponds to the width direction (main scanning direction). The optical sensors 30 are arranged near both ends of the intermediate transfer belt 20 in the width direction. In the following description, the optical sensor 30 arranged on the left end side in the moving direction of the surface of the intermediate transfer belt 20 is referred to as the optical sensor 30L, and the optical sensor 30 arranged on the right end side is referred to as the optical sensor 30R. The two optical sensors 30L and 30R are collectively referred to as the optical sensor 30. The sensing positions Pos_a and Pos_b of the optical sensor 30L are referred to as the sensing positions Pos_La and Pos_Lb, and the sensing positions Pos_a and Pos_b of the optical sensor 30R are referred to as the sensing positions Pos_Ra and Pos_Rb.

Optical sensor 30L detects each pattern of the inspection image passing through sensing positions Pos_La and Pos_Lb. Similarly, optical sensor 30R detects each pattern of the inspection image passing through sensing positions Pos_Ra and Pos_Rb. In the following, sensing positions Pos_La and Pos_Lb are collectively referred to as sensing positions (L), and sensing positions Pos_Ra and Pos_Rb are collectively referred to as sensing positions (R). Pattern sets 11L, 12L, 21L, 22L, 31L, and 32L are formed at sensing position (L). Similarly, pattern sets 11R, 12R, 21R, 22R, 31R, and 32R are formed at sensing position (R).

Each pattern set includes a plurality of V-shaped first patterns or a plurality of inverted V-shaped second patterns. Specifically, in FIG. 4, pattern sets 11L, 11R, 21L, 21R, 31L, and 31R include the same plurality of second patterns (inverted V-shaped). Also, in FIG. 4, pattern sets 12L, 12R, 22L, 22R, 32L, and 32R include the same plurality of first patterns (V-shaped). In FIG. 4, the plurality of first patterns included in pattern set 12L are each a shape obtained by inverting the plurality of second patterns of pattern set 11L in the width direction. In the following description, the first pattern and the second pattern are collectively referred to as a "V-shaped pattern." The V-shaped pattern is composed of two straight line patterns, and each straight line pattern is formed in one color.

In FIG. 4, each linear pattern is given a reference code to distinguish each linear pattern. The first letters Y, M, C, and K of the reference code of the linear pattern indicate that the color of the linear pattern is yellow, magenta, cyan, and black. The second letter "a" of the reference code indicates that the linear pattern is formed at the sensing position Pos_a, and the letter "b" indicates that the linear pattern is formed at the sensing position Pos_b. The first two digits and the last letter of the three-digit number of the reference code of the linear pattern correspond to the reference code of the pattern set to which the linear pattern belongs. For example, the reference code of each linear pattern of the pattern set 11L is "xx11xL". The letter "x" differs depending on the linear pattern. The last number of the three-digit number of the reference code of the linear pattern is "0", which indicates that the V-shaped pattern composed of the linear pattern is composed of only one color. On the other hand, when the last digit of the three-digit reference code for a straight line pattern is "1," this indicates that the V-shaped pattern made up of that straight line pattern is made up of two colors. The light receiving element 33 that detects the straight line pattern formed at the sensing position Pos_b receives scattered reflected light. For this reason, the black straight line pattern is formed on top of another color, for example, yellow, so that the black straight line pattern can be detected by the light receiving element 33. An example of this is the straight line pattern Kb110L in FIG. 4.

Figure 5(A) shows pattern set 11L. The relative color shift amount of two colors, a first color and a second color, is determined from a V-shaped pattern consisting of only the first color, a V-shaped pattern consisting of only the second color, and a V-shaped pattern consisting of the first color and the second color. Figure 5(B) shows three V-shaped patterns used to determine the color shift amount of yellow relative to magenta. Figure 5(C) shows three V-shaped patterns used to determine the color shift amount of magenta relative to cyan. Figure 5(D) shows three V-shaped patterns used to determine the color shift amount of cyan relative to black.

In the following, the first color is yellow, the second color is magenta, and a method for calculating the color shift amount of magenta relative to yellow is described. Note that the formation position of a straight line pattern detected based on detection signals S2a and S2b (see FIG. 3) is expressed by adding the letter "d" before the reference symbol of the straight line pattern. For example, the formation position detected for straight line pattern Ya110L is expressed as dYa110L.

The color shift amount daYM11L of yellow relative to magenta at the sensing position Pos_La is expressed as follows:
daYM11L=dYa110L-dYb110L+dYb111L-dMa111L
The color misregistration amount dbYM11L of yellow relative to magenta at the sensing position Pos_Lb is calculated as follows:
dbYM11L=dYb111L-dMa111L+dMa110L-dMb110L
Therefore, the color misregistration amount YMp11L of yellow in the sub-scanning direction relative to magenta in the pattern set 11L is given by
YMp11L=(daYM11L+dbYM11L)/2
Furthermore, the color misregistration amount YMs11L of yellow relative to magenta in the main scanning direction in the pattern set 11L is calculated as follows:
YMs11L=(daYM11L-dbYM11L)/2
The same applies to other color combinations. Also, the inclination in the sub-scanning direction and the magnification in the main scanning direction can be obtained from the relative relationship between the amount of color shift at the sensing position (L) and the amount of color shift at the sensing position (R).

In this manner, in this embodiment, the formation position of each straight line pattern is detected based on the detection signals S2a and S2b, and the amount of color shift is determined based on the detected formation position. Note that since there is unevenness in the rotation period of rotating members such as the intermediate transfer belt 20, the formation position of each straight line pattern is shifted due to the unevenness in the rotation period of the rotating members. For this reason, in this embodiment, as shown in FIG. 4, multiple pattern sets are formed in sequence along the conveying direction of the intermediate transfer belt 20 to suppress the effects of unevenness in the rotation period of the intermediate transfer belt 20. In other words, the average value of the color shift amounts calculated from each pattern set is used as the final color shift amount, thereby suppressing the effects of unevenness in the rotation period, and the amount of color shift is determined with high accuracy.

However, if the reflectance of the surface of the intermediate transfer belt 20 in the area adjacent to the formation position of the linear pattern is extremely different from that of the other areas, the detection accuracy of the formation position of the linear pattern deteriorates, and the difference between the actual formation position and the detected formation position becomes large. In the following description, a state in which the error of the detected formation position from the actual formation position is larger than a predetermined value is expressed as "misdetection of the formation position". For example, a local change in the reflectance of the surface of the intermediate transfer belt 20 is caused by so-called "imprinting loss". Specifically, in recent years, a nanoimprint belt has been proposed that forms a micron-pitch groove shape on the surface of the intermediate transfer belt 20 for the purpose of simplifying the conventional wrapping prescription process, reducing the frictional force on the intermediate transfer belt 20, and improving durability. If foreign matter adheres during the manufacturing of the mold for the nanoimprint belt, the formation of the grooves may be hindered. As a result, a spot site (imprinting loss) with an abnormally high reflectance occurs on the intermediate transfer belt 20. In addition, if there is a scratch on the surface of the intermediate transfer belt 20 and this scratch is in contact with the linear pattern, erroneous detection of the formation position may occur.

Below, we will explain why imprint defects cause erroneous detection of the formation position. Imprint defects affect the specularly reflected light from the intermediate transfer belt 20, and therefore affect the detection of the linear pattern formed at the sensing position Pos_a. Figure 6 (A) shows seven linear patterns of pattern set 11L formed at sensing position Pos_La. Since no color shift occurs between two linear patterns of the same color, the distance in the transport direction between two linear patterns of the same color (hereinafter, the distance in the transport direction will be simply referred to as "distance") is approximately equal to the design value.

Strictly speaking, the formation position of each linear pattern is shifted due to the unevenness of the rotation period of the rotating member, so that even between linear patterns of the same color, the distance between them may deviate from the design value. The closer the phase of the rotation period at the target formation position of two linear patterns of the same color is, the smaller the deviation from the design value becomes. Therefore, in this embodiment, two linear patterns of the same color formed close to each other in the same pattern set are paired, and the distance between the two linear patterns of the pair is determined. Then, whether or not an erroneous detection of the formation position due to imprint defects has occurred is determined depending on whether or not the distance is within a predetermined range based on the design value. In this embodiment, as shown in FIG. 6A, each pattern set includes two linear patterns, that is, one pair, for magenta, cyan, and black. On the other hand, each pattern set includes only one linear pattern for yellow. Therefore, in this embodiment, one yellow inspection pattern is added to each pattern set to determine whether or not an erroneous detection of the formation position for yellow has occurred.

Figure 6 (B) shows the waveform of the detection signal S1a (see Figure 3) when the optical sensor 30 detects the straight line pattern of Figure 6 (A), and Figures 6 (C) and 6 (D) show the waveform of the detection signal S2a (see Figure 3) obtained by binarizing the detection signal S1a. The detection signal S1a is a detection signal that mainly contains specularly reflected light, and while the straight line pattern is in the detection area of the optical sensor 30, the detection level of the detection signal S1a drops significantly. The detection signal S2a shown in Figures 6 (C) and 6 (D) is the detection signal S1a of Figure 6 (B) binarized with the threshold voltage Vth, and its waveform edges correspond to the edges of the straight line pattern. Therefore, the formation position of the straight line pattern can be determined based on the detection timing of the waveform edges.

As shown in FIG. 6(A), it is assumed that an imprint gap 61 exists at a position tangent to the straight line pattern Ca111L. The dashed line 61s1 in FIG. 6(B) shows the detection signal S1a when the imprint gap 61 exists. The dashed line 62s2 in FIG. 6(C) and FIG. 6(D) shows the detection signal S2a when the imprint gap 61 exists.

The detection position dCA111L of the straight line pattern Ca111L is determined based on the detection timing of the two edges of the straight line pattern Ca111L. The detection position dCA111L in FIG. 6(C) is a value obtained when the imprint missing 61 does not exist, that is, when the detection signal S2a is as shown by the solid line. On the other hand, the detection position dCA111L' in FIG. 6(D) is a value obtained when the imprint missing 61 exists, that is, when the detection signal S2a fluctuates as shown by the dashed line. As is clear from FIG. 6(C) and FIG. 6(D), when the imprint missing 61 exists, the formation position of the detected straight line pattern Ca111L will differ from the actual formation position, and if this difference is equal to or greater than a predetermined value, the formation position will be erroneously detected. Note that since the formation position of the detected straight line pattern Ca111L differs from the actual formation position, the distance between the two straight line patterns Ca111L and Ca110L also varies from the design value. In FIG. 6(C), the distance between the two straight line patterns Ca111L and Ca110L is the difference between dCA111L and dCA110L.

Figure 7(A) shows a case where scratch 71 occurs at a position where it contacts straight line pattern Ca111L. Figure 7(B) shows detection signal S1a, with dashed line 71s1 showing a case where scratch 71 occurs. Figure 7(C) shows detection signal S2a, with dashed line 71s2 showing a case where scratch 71 occurs. As is clear from Figure 7(C), scratch 71 causes the distance between straight line patterns Ca111L and Ca110L to vary from the design value, just as in the case of imprint defects. It is also possible to determine whether or not the straight line patterns are affected by scratches, imprint defects, etc., based on their width.

Figure 8 is a flowchart of a process for acquiring the amount of color shift in the color shift correction control according to this embodiment. When the color shift correction control starts, the control unit 500 forms an inspection image on the intermediate transfer belt 20 in S10, and detects the formation position of each straight line pattern of the inspection image using the optical sensor 30. In S11, the control unit 500 obtains the distance between the two straight line patterns of the pair. As described above, the two straight line patterns of the pair are two straight line patterns of the same color in the same pattern set. In S12, the control unit 500 determines whether the distance between the pair of straight line patterns is within a predetermined range. The predetermined range is determined based on the design value of the distance between the two straight line patterns of the pair, and is stored in advance in the control unit 500. If there is no distance between the pair of straight line patterns that is outside the predetermined range, the control unit 500 determines the overall amount of color shift based on the color shift of each pattern set in S13.

On the other hand, if the distance between the paired straight line patterns is outside the predetermined range in S12, the control unit 500 determines in S14 whether the number of repetitions of the process in FIG. 8 has reached a predetermined number N. If the predetermined number N has not been reached, the control unit 500 repeats the process from S10. On the other hand, if the predetermined number N has been reached, the control unit 500 excludes the pattern set including the pair whose distance is outside the predetermined range in S15, and determines the overall color shift amount based on the color shift amount of the remaining pattern sets. For example, it is assumed that the pattern set 11L is excluded from the inspection image shown in FIG. 4. In this case, the control unit 500 calculates the color shift amount of each color in the main scanning direction and the sub-scanning direction on the sensing position (L) side by averaging the five pattern sets 21L, 31L, 12L, 22L, and 32L. The control unit 500 calculates the amount of color misregistration in the main scanning direction and sub-scanning direction on the sensing position (R) side as an average of the six pattern sets 11R, 21R, 31R, 12R, 22R, and 32R. The control unit 500 then calculates the writing position and inclination in the sub-scanning direction and the writing position and magnification in the main scanning direction from the relative relationship between the amount of color misregistration at the sensing position (L) and the amount of color misregistration at the sensing position (R).

As described above, according to this embodiment, the distance in the transport direction between two straight line patterns of the same color in a pattern set for calculating the amount of color shift is compared with a design value to determine whether or not an erroneous detection of the formation position has occurred. Then, the amount of color shift is determined by excluding the pattern set in which an erroneous detection of the formation position has occurred. This configuration makes it possible to suppress deterioration in the accuracy of obtaining the amount of color shift.

Second Embodiment
Next, the second embodiment will be described focusing on the differences from the first embodiment. In this embodiment, in order to detect the occurrence of erroneous detection of the formation position, a linear pattern at the sensing position Pos_La and a linear pattern at the sensing position Pos_Ra that is approximately the same position in the sub-scanning direction as the linear pattern and has the same color are used. Since no color shift occurs between linear patterns of the same color, if they are formed at approximately the same position in the sub-scanning direction, the influence of the shift in the image formation position due to the rotation period unevenness is reduced.

Figure 9 shows the yellow linear patterns formed at sensing positions Pos_La and Pos_Ra extracted from the inspection image shown in Figure 4. At sensing positions Pos_La and Pos_Ra, two linear patterns that are approximately the same in the sub-scanning direction form one pair. For example, linear pattern Ya110L of pattern set 11L and linear pattern Ya110R of pattern set 11R form one pair. More specifically, one first pattern set at sensing position (L) is associated with one second pattern set at sensing position (R). One second pattern set associated with one first pattern set at sensing position (L) is the second pattern set that is the shortest distance from the first pattern set in the transport direction among the multiple second pattern sets at sensing position (R). One straight line pattern of the first pattern set and a straight line pattern of the same color of the second pattern set that corresponds to the first pattern set form one pair. Therefore, in Fig. 9, there are a total of six pairs. dY11_LaRa, dY21_LaRa, dY31_LaRa, dY12_LaRa, dY22_LaRa, and dY32_LaRa in Fig. 9 are the distance in the sub-scanning direction between the formation positions of the two straight line patterns of each pair.

Figure 10 (A) shows the pair of straight line patterns Ya110L and Ya110R in Figure 9. Figures 10 (B) and 10 (C) show the detection signal S1a and detection signal S2a when straight line pattern Ya110L passes through the detection area of optical sensor 30L. The same is true for the detection signal S1a and detection signal S2a when straight line pattern Ya110R passes through the detection area of optical sensor 30R. As shown in Figure 10 (A), if an imprint defect 62 occurs at a position adjacent to straight line pattern Ya110L, the detection signal S1a changes as shown by dashed line 62s1 due to the influence of the imprint defect 62, and the detection signal S2a changes as shown by dashed line 62s2. Therefore, as explained in the first embodiment, the detected formation position of the straight line pattern Ya110L is shifted from the actual formation position, and therefore an error occurs in the distance dY11_LaRa between the straight line pattern Ya110L and the straight line pattern Ya110R. The same applies when there is a scratch adjacent to the straight line pattern.

In the first embodiment, two straight patterns formed at the same sensing position in the main scanning direction are paired, and the distance between the two straight patterns of the pair in the sub-scanning direction and the design value are compared to determine whether or not the formation position is erroneously detected. However, in this embodiment, the optical sensors 30 that detect the two straight patterns that constitute the pair are different. Even if there is no error in the formation position of the straight pattern detected by each optical sensor 30, the obtained distance may deviate from the design value due to individual variations in the optical sensors 30L and 30R, and variations in the installation position and direction on the image forming device 700. In other words, in this embodiment, it is difficult to determine whether or not the formation position is erroneously detected by comparing the distance between the two straight patterns in the sub-scanning direction and the design value, as in the first embodiment. For this reason, in this embodiment, the average value of the distances obtained for pairs of the same shape is used as a reference value, and the distance of each pair is compared with the reference value to determine whether or not the formation position is erroneously detected. Note that a pair of the same shape means that, among multiple pairs of the same color, one of the two linear patterns has the same shape of the first linear pattern, and the other has the same shape of the second linear pattern.

Specifically, as shown in FIG. 9, the shapes of the two straight line patterns of the pair Ya110L and Ya110R, the pair Ya210L and Ya210R, and the pair Ya310L and Ya310R are the same. Therefore, the average value of dY11_LaRa, dY21_LaRa, and dY31_LaRa is calculated as the reference value dY1LRave. Then, the deviation amount, which is the difference between the distance of the pair Ya110L and Ya110R and the reference value, is calculated as |dY11_LaRa-dY1LRave|. The deviation amount is calculated in the same manner for the pair Ya210L and Ya210R, and the pair Ya310L and Ya310R. Then, if the deviation amount is greater than a predetermined value, it is determined that an erroneous detection of the formation position has occurred.

As shown in FIG. 9, the shapes of the two straight line patterns of the pair Ya120L and Ya120R, the pair Ya220L and Ya220R, and the pair Ya320L and Ya320R are the same. Therefore, the average value of dY12_LaRa, dY22_LaRa, and dY32_LaRa is calculated as the reference value dY2LRave. The deviation amount of the pair Ya120L and Ya120R is calculated as |dY12_LaRa-dY2LRave|. The deviation amount is calculated in the same manner for the pair Ya220L and Ya220R, and the pair Ya320L and Ya320R. If the deviation amount is greater than a predetermined value, it is determined that an erroneous detection of the formation position has occurred.

Figure 11 is a flowchart of a process for acquiring the amount of color shift in the color shift correction control according to this embodiment. When the color shift correction control starts, the control unit 500 forms an inspection image on the intermediate transfer belt 20 in S20, and detects the formation position of each straight line pattern of the inspection image using the optical sensor 30. The control unit 500 obtains the distance between the two straight line patterns of the pair in S21. The control unit 500 obtains the average value of the distances of the same type pairs in S22 and sets it as a reference value, and obtains the deviation amount of the distance of each pair from the reference value in S23. Note that a same type pair means a pair in which the two straight line patterns included in the pair have the same color and shape. The control unit 500 determines whether the deviation amount is within a predetermined value in S24. The predetermined value is stored in the control unit 500 in advance. If there is no deviation amount outside the predetermined value, the control unit 500 determines the overall amount of color shift based on the color shift amount of each pattern set in S25.

On the other hand, if the deviation amount is outside the predetermined value in S24, the control unit 500 determines in S26 whether the number of repetitions of the process in FIG. 11 has reached a predetermined number N. If the predetermined number N has not been reached, the control unit 500 repeats the process from S20. On the other hand, if the predetermined number N has been reached, the control unit 500 excludes the pattern set including the pair of straight line patterns whose deviation amount is outside the predetermined value in S27, and determines the overall color shift amount based on the color shift amount of the remaining pattern sets. For example, if the deviation amount of the pair of straight line patterns Ya110L and Ya110R shown in FIG. 9 is outside the predetermined value, the pattern sets 11L and 11R are not used to determine the overall color shift amount.

In this embodiment, the two straight line patterns included in one pair have the same shape, but the two straight line patterns included in one pair do not have to have the same shape. Specifically, the two straight line patterns of the pair Ya110L and Ya110R are both straight lines that slope upward as they move to the right, as shown in FIG. 5. However, it is also possible to pair a straight line pattern that slopes upward as it moves to the right, and a straight line pattern that slopes downward as it moves to the right. In the first embodiment, the pattern set includes only one yellow straight line pattern, so only one yellow straight line pattern was added for inspection. However, in this embodiment, there is no need to add a straight line pattern for inspection.

Third Embodiment
Next, the third embodiment will be described focusing on the differences from the first and second embodiments. In this embodiment, two straight line patterns of the same color that constitute a V-shaped pattern are paired, and whether or not erroneous detection of the formation position has occurred is determined based on the distance in the sub-scanning direction between the formation positions of the two straight line patterns in the pair.

As described above, the imprint defects or scratches on the intermediate transfer belt 20 affect the specularly reflected light from the intermediate transfer belt 20, and therefore cause an abnormality in the detection waveform of the light receiving element 32 that receives the specularly reflected light from the sensing position Pos_a. On the other hand, the imprint defects or scratches on the intermediate transfer belt 20 do not have much effect on the detection waveform of the light receiving element 33 that receives the diffusely reflected light from the sensing position Pos_b. For this reason, in this embodiment, whether or not the formation position is erroneously detected is determined based on the distance in the sub-scanning direction between the two straight patterns of the same color that constitute the V-shaped pattern. Since there is no color shift between the straight patterns of the same color, the deviation of the formation position of the two straight patterns of the same color that constitute the V-shaped pattern due to the unevenness in the rotation period of the intermediate transfer belt 20 is small. However, as in the second embodiment, since the distance of the formation position is obtained by two different light receiving elements 32 and 33, it is not compared with the design value, but rather the deviation from the average value of multiple distances is used to determine whether or not the formation position is erroneously detected.

Figure 12 shows a V-shaped pattern consisting of only yellow straight line patterns extracted from the inspection image shown in Figure 4. In Figure 12, for each V-shaped pattern, the distance in the sub-scanning direction between one straight line pattern and the other straight line pattern is represented by a symbol beginning with "d."

Figure 13 (A) shows a V-shaped pattern composed of a straight line pattern Ya110L and a straight line pattern Yb110L. Figures 13 (B) and 13 (D) show the detection signal S1a and the detection signal S2a of the light receiving element 32 when the straight line pattern Ya110L passes through the detection area of the optical sensor 30L. Similarly, Figures 13 (C) and 13 (E) show the detection signal S1b and the detection signal S2b of the light receiving element 33 when the straight line pattern Yb110L passes through the detection area of the optical sensor 30L. Note that while the straight line pattern Yb110L is in the detection area of the optical sensor 30L, the scattered reflected light received by the light receiving element 33 increases. The control unit 500 determines the middle of the two edges of the detection signal S2a from the light receiving element 32 when the straight line pattern Ya110L passes through the detection area of the optical sensor 30L as the formation position of the straight line pattern Ya110L. Similarly, the control unit 500 determines the middle point between the two edges of the detection signal S2b from the light receiving element 33 when the straight line pattern Yb110L passes through the detection area of the optical sensor 30L as the formation position of the straight line pattern Yb110L. As shown in FIG. 13A, if an imprint defect 63 occurs at a position adjacent to the straight line pattern Ya111L, the detection signal S1a of the light receiving element 32 changes as shown by the dashed line 63s1 and the detection signal S2a changes as shown by the dashed line 63s2 due to the influence of the imprint defect 63. Therefore, as explained in the first embodiment, the formation position of the detected straight line pattern Ya110L is shifted from the actual formation position, and therefore an error also occurs in the distance dY11_LaLb between the straight line pattern Ya110L and the straight line pattern Yb110L. The same applies when there is a scratch adjacent to the straight line pattern.

As described above, in this embodiment, as in the second embodiment, the average value of the distances of each homogeneous pair is set as the reference value, and the deviation from the reference value is calculated. In this embodiment, one pair is two straight line patterns of the same color that constitute one V-shaped pattern. Also, homogeneous pairs are pairs of the same color that are detected by the same optical sensor 30 and have the same V-shaped direction. For example, a V-shaped pattern including a straight line pattern Ya110L, a V-shaped pattern including a straight line pattern Ya210L, and a V-shaped pattern including a straight line pattern Ya310L detected by the optical sensor 30L are homogeneous pairs. Similarly, a V-shaped pattern including a straight line pattern Ya120L, a V-shaped pattern including a straight line pattern Ya220L, and a V-shaped pattern including a straight line pattern Ya320L detected by the optical sensor 30L are homogeneous pairs. The V-shaped pattern including the straight line pattern Ya110L and the V-shaped pattern including the straight line pattern Ya120L are not a homogeneous pair because the orientation of the V is different.

In terms of the distances shown in Figure 12, one reference value dY1LLave of the distance of the V-shaped pattern detected by optical sensor 30L is the average value of dY11_LaLb, dY21_LaLb, and dY31_LaLb. Another reference value dY2LLave of the distance of the V-shaped pattern detected by optical sensor 30L is the average value of dY12_LaLb, dY22_LaLb, and dY32_LaLb. Another reference value dY1RRave of the distance of the V-shaped pattern detected by optical sensor 30R is the average value of dY11_RaRb, dY21_RaRb, and dY31_RaRb. Furthermore, another reference value dY2RRave of the distance of the V-shaped pattern detected by the optical sensor 30R is the average value of dY12_RaRb, dY22_RaRb, and dY32_RaRb. Therefore, for example, the deviation amount of the V-shaped pattern composed of the straight line pattern Ya110L and the straight line pattern Yb110L is the difference between the reference value dY1LLave and dY11_LaLb.

The flowchart of the process for acquiring the color shift amount in this embodiment is basically the same as that in the second embodiment. However, the two straight line patterns in the pair in FIG. 11 are two straight line patterns of the same color that form a V-shaped pattern.

In addition, in this embodiment, there is no need to add a linear inspection pattern as in the first embodiment.

＜Other＞
In the above-described embodiments, the color shift amount is obtained by excluding the pattern set in which the erroneous detection of the formation position occurs. However, when the erroneous detection of the formation position occurs, the entire sequence of obtaining the color shift amount may be invalidated, and the process may be terminated without obtaining the entire color shift amount. In this case, the user may be notified of the abnormality of the intermediate transfer belt 20 and prompted to replace it. Furthermore, in the above-described embodiments, when the erroneous detection of the formation position occurs, the color shift amount is obtained by excluding the entire pattern set including the pair in which the erroneous detection of the formation position is detected, regardless of the color of the linear pattern of the pair in which the erroneous detection of the formation position is detected. However, the color shift amount for the color of the linear pattern of the pair in which the erroneous detection of the formation position occurs may be excluded, and the entire color shift amount may be obtained without excluding the color shift amount of the other colors of the pattern set including the pair. Furthermore, the number of repetitions N in the processes of FIG. 8 and FIG. 11 may be 0. In other words, when the erroneous detection of the formation position occurs, the process of S15 or S27 may be immediately executed.

[Other embodiments]
The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

The present disclosure includes the following configurations.
(Configuration 1)
An image carrier;
an image forming means for forming an image on the image carrier using toners of a plurality of colors;
a detection unit for detecting an inspection image formed on the image carrier by the image forming unit;
an acquisition unit that acquires a color shift amount based on a detection result of the inspection image by the detection unit;
Equipped with
the inspection image includes a first pattern and a second pattern of the same color that are formed at different positions in a transport direction of the image carrier,
The acquisition means acquires the distance between the first pattern and the second pattern in the transport direction based on the detection result of the inspection image by the detection means, and if the distance is not within a predetermined range, notifies of an abnormality in the image carrier, or does not use the detection result by the detection means of the first pattern and the second pattern whose distance is not within the predetermined range to acquire the amount of color shift.
(Configuration 2)
the inspection image includes a plurality of pattern sets that are sequentially formed on the image carrier along the transport direction,
Each of the plurality of pattern sets includes a pair of the first pattern and the second pattern,
2. The image forming apparatus according to claim 1, wherein the acquiring unit determines whether or not the distance is within the predetermined range for each of the pairs in the plurality of pattern sets.
(Configuration 3)
each of the plurality of pattern sets includes the pair for each of the plurality of colors;
The image forming apparatus according to configuration 2, wherein the acquisition means determines whether the distance is within the specified range for each pair of the plurality of colors in each of the plurality of pattern sets, and does not use a detection result by the detection means for a pattern set including a pair whose distance is not within the specified range to acquire the amount of color shift.
(Configuration 4)
The detection unit includes a light emitting unit that emits light toward the image carrier;
a light receiving element configured to receive light emitted by the light emitting means and specularly reflected at a predetermined position on the image carrier in a width direction perpendicular to the transport direction;
Equipped with
4. The image forming apparatus according to any one of configurations 1 to 3, wherein the first pattern and the second pattern are formed at the predetermined position on the image carrier.
(Configuration 5)
5. The image forming apparatus according to any one of configurations 1 to 4, wherein the first pattern and the second pattern are linear patterns in a direction different from the transport direction and a width direction perpendicular to the transport direction, respectively.
(Configuration 6)
An image carrier;
an image forming means for forming an image on the image carrier using toners of a plurality of colors;
a detection unit for detecting an inspection image formed on the image carrier by the image forming unit;
an acquisition unit that acquires a color shift amount based on a detection result of the inspection image by the detection unit;
Equipped with
the test image includes a plurality of pairs;
each of the plurality of pairs includes a first pattern and a second pattern of the same color that are formed at different positions in a width direction perpendicular to a transport direction of the image carrier;
the acquisition means acquires the distance between the first pattern and the second pattern in the transport direction for each of the plurality of pairs based on the detection result of the inspection image by the detection means, acquires a reference value based on the distance acquired for each of the plurality of pairs, acquires a difference value between the distance and the reference value for each of the plurality of pairs, and if any of the difference values acquired for each of the plurality of pairs is greater than a predetermined value, notifies of an abnormality in the image carrier, or does not use the detection result by the detection means of the first pattern and the second pattern of a pair among the plurality of pairs whose difference value is greater than the predetermined value to acquire the amount of color misalignment.
(Configuration 7)
7. The image forming apparatus of claim 6, wherein the first pattern of each of the plurality of pairs has the same shape, and the second pattern of each of the plurality of pairs has the same shape.
(Configuration 8)
the inspection image includes a plurality of first pattern sets formed in sequence on the image carrier along the transport direction, and a plurality of second pattern sets formed in sequence on the image carrier along the transport direction at positions different from the positions of the plurality of first pattern sets in the width direction,
the detection means includes first detection means for detecting the plurality of first pattern sets and second detection means for detecting the plurality of second pattern sets;
8. The image forming apparatus of claim 6 or 7, wherein the first pattern of a pair is included in one first pattern set of the plurality of first pattern sets, and the second pattern of the pair is included in a second pattern set corresponding to the one first pattern set of the plurality of second pattern sets.
(Configuration 9)
9. The image forming apparatus according to claim 8, wherein the second pattern set corresponding to the first pattern set is the second pattern set among the plurality of second pattern sets that has a smallest distance from the first pattern set in the transport direction.
(Configuration 10)
the inspection image includes the plurality of pairs for each of the plurality of colors;
The image forming apparatus of configuration 8 or 9, wherein the acquisition means acquires the reference value for each of the plurality of colors and determines whether there is a pair whose difference value is greater than the specified value, and does not use the detection results by the detection means of the first pattern set and the second pattern set including the first pattern and the second pattern of the pair whose difference value is greater than the specified value to acquire the amount of color shift.
(Configuration 11)
the first detection means includes a first light emitting means that emits light toward the image carrier, and a first light receiving element that is configured to receive light that is emitted by the first light emitting means and specularly reflected at a first predetermined position of the image carrier in the width direction,
the second detection means includes a second light emitting means that emits light toward the image carrier, and a second light receiving element that is configured to receive light that is emitted by the second light emitting means and specularly reflected at a second predetermined position of the image carrier in the width direction,
11. The image forming apparatus of any one of configurations 8 to 10, wherein the first pattern of the pair is formed at the first predetermined position of the image carrier, and the second pattern of the pair is formed at the second predetermined position of the image carrier.
(Configuration 12)
12. The image forming apparatus according to any one of configurations 6 to 11, wherein the first pattern and the second pattern are linear patterns in directions different from the transport direction and the width direction, respectively.
(Configuration 13)
the inspection image includes a plurality of pattern sets that are sequentially formed on the image carrier along the transport direction,
each of the plurality of pattern sets includes the pair;
8. The image forming apparatus of claim 6 or 7, wherein the first pattern and the second pattern of the pair form a V-shaped pattern.
(Configuration 14)
each of the plurality of pattern sets includes the pair for each of the plurality of colors;
The image forming apparatus of configuration 13, wherein the acquisition means acquires the reference value for each of the plurality of colors and determines whether there is a pair whose difference value is greater than the specified value, and does not use the detection result by the detection means of the pattern set including the pair whose difference value is greater than the specified value to acquire the color shift amount.
(Configuration 15)
the detection means includes a light emitting means for emitting light toward the image carrier, a first light receiving element configured to receive light emitted by the light emitting means and reflected specularly at a first predetermined position of the image carrier in the width direction, and a second light receiving element configured to receive light emitted by the light emitting means and reflected diffusely at a second predetermined position of the image carrier in the width direction,
15. The image forming apparatus of claim 13, wherein the first pattern of the pair is formed at the first predetermined position of the image carrier, and the second pattern of the pair is formed at the second predetermined position of the image carrier.

The invention is not limited to the above-described embodiment, and various modifications and variations are possible without departing from the spirit and scope of the invention. Therefore, the following claims are appended to disclose the scope of the invention.

20: intermediate transfer belt, 705Y, 705M, 705C, 705K: image forming unit, 30: optical sensor, 500: control unit

Claims (4)

An image carrier;
an image forming means for forming an image on the image carrier using toners of a plurality of colors;
a detection means for detecting an inspection image formed on the image carrier by the image forming means , the inspection image including a pair of a first pattern and a second pattern of the same color for each of the plurality of colors, the first pattern and the second pattern of the pair being patterns having the same shape, and being linear patterns extending in a direction different from a transport direction of the image carrier and a width direction perpendicular to the transport direction;
an acquisition unit that acquires a color shift amount based on a detection result of the inspection image by the detection unit;
a determination means for obtaining a distance between the first pattern and the second pattern of the pair in the transport direction based on a detection result of the inspection image by the detection means, and determining that there is a local abnormality in the surface reflectance of the image carrier in contact with the inspection image when the distance is not within a predetermined range;
Equipped with
an image forming device, wherein the image forming means forms the first pattern and the second pattern of the pair at different positions in the transport direction, and does not form either the first pattern or the second pattern of another pair between the first pattern and the second pattern of the pair in the transport direction . the inspection image includes a plurality of pattern sets that are sequentially formed on the image carrier along the transport direction,
each of the plurality of pattern sets includes the pair of the first pattern and the second pattern;
The image forming apparatus according to claim 1 , wherein the determining unit determines whether or not the distance is within the predetermined range for each of the pairs in the plurality of pattern sets. each of the plurality of pattern sets includes the pair for each of the plurality of colors;
the determining means determines whether or not the distance is within the predetermined range for each of the pairs of the plurality of colors in each of the plurality of pattern sets;
3. The image forming apparatus according to claim 2, wherein the acquisition unit does not use a detection result by the detection unit of a pattern set including a pair whose distance is not within the predetermined range for acquiring the amount of color misregistration. The detection unit includes a light emitting unit that emits light toward the image carrier;
a light receiving element configured to receive light emitted by the light emitting means and specularly reflected at a predetermined position on the image carrier in a width direction perpendicular to the transport direction;
Equipped with
The image forming apparatus according to claim 1 , wherein the first pattern and the second pattern are formed at the predetermined position on the image carrier.

Images