JP6798240B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

An image forming apparatus for color printing is provided with a photoconductor and a developing device for each color, forms a single-color toner image on each photoconductor, and sequentially transfers each toner image to record a color image on transfer paper. The tandem method is the mainstream.

In the tandem image forming apparatus, the toner image is formed on the transfer belt by the developing unit, and the toner image on the transfer belt is collectively transferred onto the transfer paper by the secondary transfer apparatus. At this time, since the photoconductors of each color are arranged in series with respect to the traveling direction of the transfer belt, the toner image formed on the transfer belt has a transfer timing of each color when a slight change in the transfer belt occurs. It fluctuates and causes color shift in the sub-scanning direction, leading to deterioration of image quality. The cause of the change in the transfer belt is that the belt rotates, and the belt is displaced due to slippage in the main scanning direction of image formation, or the belt is wavy.

A technique for correcting a color shift caused by such a transfer belt is known. For example, in Japanese Patent No. 5773612 (Patent Document 1), the position where a pattern for correction is formed is changed and the pattern is detected. A technique for reducing color shift by correcting the color shift is disclosed. However, in Patent Document 1, it is not possible to deal with the waviness of the belt generated at the timing of reading the pattern, and erroneous correction is performed due to the reading error, which may cause color shift.

Further, in Japanese Patent Application Laid-Open No. 2015-082076 (Patent Document 2), when the inclination amount of the roller for rotating the transfer belt becomes a certain value or more, the wave regulation roller arranged so as to come into contact with the transfer belt is provided. The image forming apparatus having is disclosed. However, in Patent Document 2, when a wave suddenly occurs during the correction of the color shift, a time difference until the operation of the roller occurs, and the color shift may also occur due to the erroneous correction.

Therefore, the correction of color shift by the above-mentioned conventional technique is not sufficient, and there has been a demand for a technique capable of appropriately correcting color shift even in a state where a waviness phenomenon due to the belt is generated.

The present invention has been made in view of the above problems in the prior art, and provides an image forming apparatus capable of appropriately correcting color shift even in a state where waviness occurs in the transfer belt. The purpose.

That is, according to the present invention, it is an image forming apparatus that prints a color image by forming a toner image of a plurality of colors on a transfer belt.
A test pattern generating means for forming a pattern for detecting misalignment on the transfer belt, and
Two or more test pattern detecting means for detecting the falling edge and the rising edge of the output signal reading the pattern, and
A waviness determining means for determining whether or not the transfer belt has waviness based on the detection result by the test pattern detecting means,
Including a correction processing means for correcting the color shift of the toner image by a predetermined correction value,
The correction processing means
When the waviness determination means determines that the transfer belt has no waviness, a correction value is calculated based on the detection result.
When the waviness determining means determines that the transfer belt has waviness, a correction value is calculated by adding the influence of the waviness to the detection result.
An image forming apparatus is provided.

As described above, according to the present invention, there is provided an image forming apparatus capable of appropriately correcting color shift even in a state where waviness occurs in the transfer belt.

The figure which shows the structure of the image forming apparatus of this embodiment. The figure which shows the structure of the detection sensor included in the image forming apparatus of this embodiment. The figure which shows the example of the image pattern formed on the transfer belt. The figure which shows the hardware composition included in the image forming apparatus of this embodiment. The software block diagram included in the image forming apparatus of this embodiment. The figure which shows the example of the timing chart which generates the pattern for misalignment detection. The figure explaining the method of calculating the deviation amount from the position deviation detection pattern in this embodiment. The figure which shows the example which detects the pattern on the transfer belt in this embodiment. The figure explaining the sensor-to-sensor deviation amount of the detection sensor of this embodiment. The flowchart of the process which performs the color shift correction of this embodiment. The figure explaining the example of correcting the detection result of the detection sensor in this embodiment.

Hereinafter, the present invention will be described with reference to embodiments, but the present invention is not limited to the embodiments described later. In each of the figures referred to below, the same reference numerals are used for common elements, and the description thereof will be omitted as appropriate.

FIG. 1 is a diagram showing a configuration of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 includes a writing unit 101, an image forming unit 102, and a transfer unit 103. The writing unit 101 includes optical elements such as a semiconductor laser, an LED, and a polygon mirror, and enables image-like exposure for image formation. The image forming unit 102 includes a photoconductor drum, a charging device, a developing device, and the like, and forms an electrostatic latent image on the photoconductor drum and visualizes the toner image on the photoconductor drum in a transfer process. Is transferred to the transfer belt 130.

Further, the writing unit 101 deflects a light beam emitted from a light source such as a semiconductor laser (not shown) by a polygon mirror 110 and causes the light beam to enter the fθ lens 111. The light beam is indicated by the arrow A, and in the illustrated embodiment, a number corresponding to each color of cyan (C), magenta (M), yellow (Y), and black (K) is generated, and the fθ lens 111 is generated. After passing through, it is reflected by the reflection mirror 112.

After shaping the light beam, the WTL lens 113 deflects the light beam toward the reflection mirrors 114 and 115, and uses the photoconductor drums 120c, 120m, 120k, and 120y of each color as the light beam used for exposure. Image-irradiate the light beam. Since the irradiation of the photoconductor drums 120c, 120m, 120k, and 120y with the light beam is performed using a plurality of optical elements as described above, timing synchronization is performed with respect to the main scanning direction and the sub-scanning direction. ..

Hereinafter, the main scanning direction is defined as the scanning direction of the light beam, and the sub-scanning direction is a direction orthogonal to the main scanning direction. In many image forming apparatus 100, the photoconductor drums 120c, 120m, 120k, It is defined as the direction of rotation of 120y.

The photoconductor drum 120 includes a photoconducting layer including at least a charge generating layer and a charge transporting layer on a conductive drum such as aluminum. The photoconducting layer is arranged corresponding to the photoconductor drums 120c, 120m, 120k, 120y, respectively, and is surface-charged by the chargers 122c, 122m, 122k, 122y including the corotron, the scorotron, or the charging roller. Is given.

The electrostatic charges applied to the photoconductor drums 120c, 120m, 120k, 120y by the respective chargers 122c, 122m, 122k, 122y are image-exposed by the light beam to form an electrostatic latent image. The electrostatic latent image formed on the photoconductor drums 120c, 120m, 120k, 120y is developed by a developing device 121c, 121m, 121k, 121y including a developing sleeve, a developing agent supply roller, a regulating blade, etc. Is formed.

The developer supported on the photoconductor drums 120c, 120m, 120k, 120y is transferred onto the transfer belt 130 moving in the direction of the arrow B by the transport rollers 131a, 131b, 131c. The transfer belt 130 is conveyed to the secondary transfer unit while carrying the developing agents C, M, Y, and K. The secondary transfer unit includes a secondary transfer belt 133 and transfer rollers 134a and 134b. The secondary transfer belt 133 is conveyed in the direction of the arrow C by the conveying rollers 134a and 134b. The image receiving material 150 such as high-quality paper and a plastic sheet is supplied to the secondary transfer unit from the image receiving material accommodating unit 140 such as a paper feed cassette by the transport roller 135.

A plurality of detection sensors 200 for detecting a pattern image for correcting the formation condition of the image formed on the transfer belt 130 are arranged in the vicinity of the transfer roller 131a. The pattern image described above includes, for example, a test pattern image for position shift correction, a test pattern image for density correction, and the like. As the detection sensor 200, a reflection type detection sensor including a known reflection type photo sensor can be used, and based on the detection result of each detection sensor 200, the skew (tilt) of each color with respect to the reference color and the deviation of the main scanning resist are used. Various deviation amounts including the amount, the sub-scanning resist deviation amount, the main scanning magnification error, and the like can be calculated. The image forming apparatus 100 can correct various deviation amounts related to image quality adjustment based on the calculated values, and can correct the image forming conditions when forming an image on the transfer belt 130. The configuration of the detection sensor 200 will be described in detail later.

The secondary transfer unit applies a secondary transfer bias to transfer the multicolor developer image supported on the transfer belt 130 to the image receiving material 150 adsorbed and held on the secondary transfer belt 133. The image receiving material 150 is supplied to the fixing device 136 together with the transfer of the secondary transfer belt 133. The fixing device 136 is configured to include a fixing member 137 such as a fixing roller containing silicone rubber, fluorine rubber, etc., and pressurizes and heats the image receiving material 150 and the multicolor developer image to form a printed matter 160 as an image forming device 100. Output to the outside of. The transfer belt 130 after transferring the multicolor developer image is supplied to the next image forming process after the transfer residual developer is removed by the cleaning unit 139 including the cleaning blade.

Next, the details of the detection sensor 200 will be described. FIG. 2 is a diagram showing a configuration of a detection sensor 200 included in the image forming apparatus 100 of the present embodiment. The detection sensor 200 includes one light emitting element 201, two light receiving elements 202 and 203, and a condenser lens 204. As the light emitting element 201, for example, an infrared light LED that emits infrared light or a laser light emitting element can be used. Further, the light receiving element 202 is a specular light receiving element, and the light receiving element 203 is a diffuse reflection type light receiving element, and a phototransistor or a combination of a photodiode and an amplifier circuit can be used, respectively.

In the detection sensor 200, the infrared light L1 emitted by the light emitting element 201 passes through the condenser lens 204 and reaches the transfer belt 130. The infrared light L1 that has reached the transfer belt 130 is reflected by the test pattern forming region on the transfer belt 130 and the toner layer in the test pattern forming region. Of the infrared light L1, the specularly reflected light L2 is detected by the light receiving element 202 after retransmitting the condensing lens 204 as the specular reflected light L2. Further, among the infrared light L1, the diffusely reflected light is retransmitted through the condenser lens 204 as the diffuse reflected light L3 and detected by the light receiving element 203.

In this way, the detection sensor 200 reads the test pattern formed on the transfer belt 130 and calculates the parameters for correcting the color shift and the like. Therefore, next, a test pattern formed during the printing operation will be described. FIG. 3 is a diagram showing an example of an image pattern formed on the transfer belt 130.

In FIG. 3, an image 310 transferred to the image receiving material 150 and a misalignment detection pattern 320 are formed on the transfer belt 130. It is preferable that a plurality of misalignment detection patterns 320 are formed in order to correct the waviness of the belt due to the belt approach. Therefore, the detection sensor 200 is arranged at a position corresponding to the misalignment detection pattern 320. The detection sensors 200a and 200c are arranged at positions where the vicinity of the end of the transfer belt 130 can be read, and the detection sensors 200b are arranged at positions where the vicinity of the center of the transfer belt can be read.

An image to be transferred is formed at the position read by the detection sensor 200b during the printing operation, and by forming the misalignment detection pattern 320 at a timing other than the printing operation, the detection result of the detection sensor 200b can also be obtained. It is possible to make corrections including.

The misalignment detection pattern 320 is a pattern of each color corresponding to the photoconductor drum 120, and preferably includes a pattern parallel to the main scanning direction and a pattern inclined with respect to the main scanning direction. It is preferable to form a plurality of identical patterns in the scanning direction. By forming the pattern in this way, it is possible to perform correction for reducing color shift even if there is waviness in the belt.

Up to this point, the pattern for performing correction formed by the image forming apparatus 100 has been described. Next, the data processing system of the present embodiment will be described based on the hardware configuration of the image forming apparatus 100. FIG. 4 is a diagram showing a hardware configuration included in the image forming apparatus 100 of the present embodiment.

As described with reference to FIG. 2, the detection sensor 200 receives the reflected light of the light emitted by the light emitting element 201 by the light receiving elements 202 and 203, and outputs an analog detection signal according to the intensity of the received light. The analog detection signal is amplified by the amplification unit 440, and only the line detection signal component is passed by the filter 442.

After that, the A / D conversion unit 444 converts the analog data into digital data. The sampling of the A / D conversion data is controlled by the sampling control unit 446. The digital detection data sampled by the A / D converter 444 is stored in the FIFO (First In First Out) memory 448.

When the detection of one set of patterns is completed, the sampling control unit 446 outputs the detection data from the FIFO memory 448 to the CPU 410 and the RAM 412 via the I / O port 420. The CPU 410 performs a predetermined arithmetic process according to the program stored in the ROM 411, and calculates a correction amount for correcting the color shift and the like. In addition to the above-mentioned programs, the ROM 411 can store programs for controlling various hardware included in the image forming apparatus 100.

The CPU 410 can monitor the detection data from the light receiving elements 202 and 203 at an appropriate timing and generate a control signal for controlling the intensity of the infrared light L1 emitted by the light emitting element 201. The control signal is output to the light emitting amount control unit 430 via the I / O port 420, and the light emitting amount control unit 430 controls the light emitting amount of the light emitting element 201 according to the control signal. By controlling the amount of light emitted in this way, the level of the detection data output by the light receiving elements 202 and 203 can be made constant.

Further, the CPU 410 calculates a correction amount for correcting the color shift amount calculated from the detection result of the position shift detection pattern 320. Based on the calculated correction amount, the CPU 410 changes the timing of starting writing of drawing data, the pixel clock frequency, and the like, outputs the data to the writing control unit 413, and sets the timing.

The write control unit 413 has a configuration in which the output frequency can be set with high accuracy, such as a clock generator using a VCO (Voltage Controlled Oscillator), and this output can be used as a pixel clock. The write control unit 413 drives the LD lighting control unit 415 according to the drawing data output by the controller 414 with reference to the pixel clock. By operating the LD lighting control unit 415, an image is formed on the photoconductor drum 120 shown in FIG. 1, and by rotating, an image is sequentially formed on the transfer belt 130.

As described above, the writing control unit 413 controls the timing of writing the drawing data based on the correction amount obtained by the CPU 410, so that an image that appropriately reflects the state of the transfer belt 130 can be formed. Color shift can be reduced.

The hardware configuration included in the image forming apparatus 100 of the present embodiment has been described above. Next, the functional means executed by each hardware in the present embodiment will be described with reference to FIG. FIG. 5 is a software block diagram included in the image forming apparatus 100 of the present embodiment.

The image forming apparatus 100 of the present embodiment includes a light irradiation unit 510, a transfer image forming unit 520, a transfer unit 530, a correction processing unit 540, a test pattern detection unit 550, and a storage unit 560. The details of each functional block will be described below.

The light irradiation unit 510 is a means for irradiating the photoconductor drum 120 with light for forming a transfer image, and includes a plurality of semiconductor laser light sources such as a laser diode. The transfer image forming unit 520 is a means for forming an image on the photoconductor drum 120 by the light beam emitted by the light irradiation unit 510. The transfer image forming unit 520 includes a test pattern forming unit 521, and can form a misalignment detection pattern 320 or the like in addition to the image included in the drawing data.

The transfer unit 530 is a means for transferring the image formed on the photoconductor drum 120 to the transfer belt 130 and further transferring the image onto the image receiving material 150 such as plain paper. The image of the image receiving material 150 that has been secondarily transferred is fixed by the fixing device 136, and the image is output as a printed matter 160.

The correction processing unit 540 is a means for correcting the color shift of the image, and includes a waviness determination unit 541 and a correction value calculation unit 542. The wavy determination unit 541 determines the wavy state of the transfer belt 130 based on the pattern detected by the detection sensor 200. The correction value calculation unit 542 calculates the amount of color shift based on the result output by the wave wave determination unit 541, and calculates the correction amount of the color shift.

The test pattern detection unit 550 is a means for detecting the misalignment detection pattern 320, and includes a detection sensor 200. The test pattern detection unit 550 transmits the detected result to the correction processing unit 540. The storage unit 560 is a means for storing various programs executed by each hardware of the image forming apparatus 100 of the present embodiment, various correction values for correcting an image, and the like. The storage unit 560 may include, for example, an HDD (Hard Disk Drive) in addition to the FIFO memory 448 and the ROM 411.

The software block described above corresponds to a functional means realized by the CPU 410 executing the program of the present embodiment to make each hardware function. Further, all of the functional means shown in each embodiment may be realized by software, or some or all of them may be implemented as hardware that provides equivalent functions.

Up to this point, the configuration of the software block of the image forming apparatus 100 of the present embodiment has been described. Next, the correction process according to the present embodiment will be specifically described with reference to FIGS. 6 to 11. In the following description, the misalignment detection pattern 320 of the present embodiment includes four colors of yellow (Y), black (K), magenta (M), and cyan (C) in the same direction as the main scanning direction. It is composed of a horizontal line pattern and an oblique line pattern inclined by a predetermined angle with respect to the main scanning direction, but the configuration of the misalignment detection pattern 320 is not limited. Further, in the following description of the embodiment, the case where the diagonal line pattern is inclined by 45 ° with respect to the main scanning direction will be described as an example.

FIG. 6 is a diagram showing an example of a timing chart for generating a pattern for detecting misalignment, and FIGS. 6A to 6D form images of each color (Ye, Bk, Ma, Cy), respectively. It shows the timing. The fgate_n is a signal indicating an image region (a period for writing the image data) of each color, and the image data is written to the photoconductor drum 120 at the timing when the fgate_n is Low.

Further, in FIG. 6, the writing timing of each color is deviated by the distance between the photoconductor drums because the photoconductor drums 120 of each color are arranged side by side with respect to the transport direction of the transfer belt 130. By shifting the writing timing by the amount, an image in which the toner images of each color are superimposed on the transfer belt 130 is formed. Although the misalignment detection pattern 320 is shown up to the third set in FIG. 6, the number of sets of patterns may be changed according to the belt length and the photoconductor length.

By forming the horizontal line pattern and the diagonal line pattern as shown in FIG. 6, the position shift detection pattern 320 as shown in FIG. 3 is formed on the transfer belt 130. In the present embodiment, the amount of color shift can be calculated by detecting the pattern, and the correction process is performed.

FIG. 7 is a diagram illustrating a method of calculating the displacement amount from the misalignment detection pattern 320 in the present embodiment, and shows how the detection sensor 200 reads the misalignment detection pattern 320 formed on the transfer belt 130. It shows.

The detection sensor 200 reads the misalignment detection pattern 320 at a predetermined sampling interval as the transfer belt 130 is conveyed, and outputs the detection result to the CPU 410 via the I / O port 420. When the CPU 410 receives the notification of the pattern detection result, it corresponds to the distance between the horizontal line patterns and the horizontal line pattern and the horizontal line pattern of each color based on the detection result, the sampling interval described above, and the transfer speed of the transfer belt 130. Calculate the distance from the diagonal line pattern. By comparing the distances calculated in this way, the amount of misalignment can be obtained, and the value for correcting the color misalignment can be obtained.

First, the calculation of the amount of misalignment in the sub-scanning direction will be described. The amount of misalignment in the sub-scanning direction can be obtained from the distance between the horizontal line patterns, and is calculated based on the distance between the reference horizontal line pattern and the horizontal line pattern of each target color. In FIG. 7, the reference horizontal line pattern is K, and the distances between K and the horizontal line patterns of each color are calculated as y1, c1, and m1. Then, by comparing with the ideal distances y0, c0, and m0 between the horizontal line patterns of each color when there is no misalignment, the difference between the two can be obtained as the amount of misalignment. That is, the amount of misalignment of Y, C, and M with respect to the reference color K in the sub-scanning direction is y1-y0, c1-c0, and m1-m0, respectively.

Next, the calculation of the amount of misalignment in the main scanning direction will be described. Since the diagonal line pattern is inclined at a predetermined angle with respect to the main scanning direction, if there is a positional deviation in the main scanning direction, the diagonal line pattern is also displaced with respect to the sub scanning direction. In particular, in the present embodiment, since the diagonal line pattern is inclined by 45 ° with respect to the main scanning direction, the amount of misalignment in the sub-scanning direction of the diagonal line pattern is the same as the amount of misalignment in the main scanning direction. Become. Therefore, the amount of misalignment in the main scanning direction can be obtained based on the distance between the horizontal line pattern and the diagonal line pattern.

In FIG. 7, the distances y2, k2, c2, and m2 between the horizontal line pattern and the corresponding diagonal line pattern of the same color are obtained. Then, using an arbitrary color as the reference color, the difference between the inter-pattern distance of the reference color and the inter-pattern distance of the non-reference color is obtained. For example, assuming that K is a reference color, k2-y2, k2-m2, and k2-c2 can be obtained as the amount of misalignment in the main scanning direction, respectively.

In this way, the amount of misalignment in the sub-scanning direction and the main scanning direction of each color can be obtained. Further, by obtaining the above-mentioned misalignment amount for each detection sensor 200, it is possible to obtain skew and scanning magnification error, and it is possible to obtain correction parameters when forming an image. For example, the skew component of the displacement amount can be calculated from the difference in the displacement amount in the sub-scanning direction detected by the detection sensors 200a, 200b, and 200c, respectively.

Based on the various displacement amounts obtained as described above, the correction process for forming an image on the transfer belt 130 can be performed. In the correction process, the image forming apparatus 100 is adjusted so that the amount of misalignment of each color matches. For example, the amount of misalignment of each color can be matched by adjusting the emission timing of the light beam irradiating the photoconductor drum 120 of each color or adjusting the rotation speed of the photoconductor drum 120. Further, the angle of the mirror that reflects the light beam can be corrected by adjusting it with a stepping motor or the like. Further, the misalignment can be corrected by changing the image data such as adding a white line to the formed image.

The above-mentioned misalignment is also caused by the waviness of the transfer belt 130 as shown in FIG. FIG. 8 is a diagram showing an example of detecting a pattern on the transfer belt 130 in the present embodiment. FIG. 8A shows a case where the transfer belt 130 is not wavy, FIG. 8B shows a case where the transfer belt 130 is wavy, and the CPU 410 has a falling edge of the light receiving level. The presence / absence of the misalignment detection pattern 320 is detected based on the above and the rising edge.

In FIG. 8A, since the transfer belt 130 has no waviness, the pattern on the transfer belt 130 is also flat, and the light receiving level detected as having a pattern also maintains a constant value. On the other hand, in FIG. 8B, since the transfer belt 130 is wavy, the pattern on the transfer belt 130 is also wavy, and the distance between the sensor and the pattern differs depending on the position. Therefore, there is a difference in the reflection level between the place where the distance between the sensor and the pattern is short and the place where the distance is far, and the correct position cannot be detected. In particular, in the diagonal line pattern, since the pattern shifts in the main scanning direction due to the waviness of the transfer belt 130, the timing of detecting the falling edge and the rising edge changes, and erroneous detection may occur.

As described above, if there is an erroneous detection of a pattern due to the waviness of the transfer belt 130, it is not possible to perform an appropriate correction only by correcting the misalignment, and the image quality is deteriorated due to the color misalignment. Therefore, the color shift can be reduced by evaluating the waviness state of the transfer belt 130 and, if there is a waviness, correcting the wavy state in consideration of the waviness state. The wave of the transfer belt 130 can be determined from the pattern detection result for each detection sensor 200, that is, the amount of deviation between the sensors.

FIG. 9 is a diagram illustrating an amount of misalignment between the sensors of the detection sensor 200 of the present embodiment. FIG. 9 illustrates two detection sensors 200a and 200c that read the vicinity of both ends of the transfer belt 130. FIG. 9A shows the detection sensor 200a, and FIG. 9B shows the detection sensor 200c, respectively. Shown. Further, a case where the transfer belt 130 of FIG. 9 is wavy and the misalignment detection pattern 320 is also misaligned will be described as an example.

As shown in FIG. 9A, the distances a1 and b1 between the two patterns are detected based on the output signal of the detection sensor 200a. a1 is the distance from the falling edge of the first set of diagonal line patterns to the falling edge of the second set of diagonal line patterns of the same color, and b1 is 2 from the rising edge of the first set of diagonal line patterns. It is the distance to the rising edge of the diagonal line pattern of the same color in the set. Similarly, as shown in FIG. 9B, based on the output signal of the detection sensor 200c, the rising edge of the diagonal line pattern of the first set to the rising edge of the diagonal line pattern of the same color in the second set. The distance a2 to the falling edge and the distance b2 from the rising edge of the first set of diagonal line patterns to the rising edge of the second set of diagonal line patterns of the same color are detected.

Here, it is ideal that a1 and b1 and a2 and b2 have the same value, respectively, and the value is determined by the writing timing of the first set pattern and the second set pattern. However, as described above, appropriate pattern detection may not be possible due to the waviness of the transfer belt 130, and it is necessary to evaluate the amount of misalignment between the two detection sensors 200. Assuming that the amount of misalignment between the sensors on the front edge side of the detection sensors 200a and 200c is S21 and the amount of misalignment between the sensors on the rear end side edge is K21, the amount of misalignment between the sensors can be calculated by the following equation 1.

The amount of misalignment between the sensors is caused by fluctuations in the transport speed of the transfer belt 130 and an error during reading by the sensor. When waviness occurs in the transfer belt 130, the values of S21 and K21 become large, and the difference between the two is also the difference in the detected pattern width, so that the amount of color shift detection becomes large. Therefore, in the correction process, the values of S21 and K21 are evaluated, and if the values are equal to or higher than a certain value, the color shift correction is performed in consideration of the amount of shift between the sensors.

In the above description, the amount of sensor misalignment was calculated from the patterns of the first set and the second set, but similarly, the sensor misalignment from the patterns of the second set and the third set, and the patterns of the third set and the fourth set. By calculating the amount, fluctuations in the transport speed and reading errors can be detected. In the example of FIG. 9, the edge spacing is obtained from the adjacent patterns, but when the edge spacing is obtained from the distant patterns, the long-period error of the transfer belt 130 and the influence of the rotation unevenness of the photoconductor drum 120 are affected. Therefore, it is preferable to obtain the edge spacing from adjacent sets of patterns. Further, it is preferable to obtain the edge spacing from the pattern within one rotation of the photoconductor drum 120.

Further, in FIG. 9, a case where the sensor misalignment amount is detected from two diagonal line patterns is shown as an example, but the embodiment of the present invention is not limited, and for example, the sensor misalignment amount including the horizontal line pattern is shown. May be detected. However, since it is difficult to detect the deviation in the main scanning direction only with the horizontal line pattern, it is preferable to include at least one diagonal line pattern. Further, since the timing of forming an image differs for each color, it is preferable to detect the amount of misalignment between the sensors for each color. By detecting the amount of misalignment between sensors for each color, the effects of color misalignment and skew can be reduced.

Next, the processing performed by the image forming apparatus 100 of the present embodiment will be described. FIG. 10 is a flowchart of a process for performing color shift correction according to the present embodiment.

First, the image forming apparatus 100 starts the process of correcting the color shift from step S1000. Next, in step S1001, a misalignment detection pattern 320 is formed on the transfer belt 130. The pattern formed in step S1001 is a pattern as shown in FIG. 3, and is arranged at a position that can be detected by two or more sensors in order to determine the waviness of the transfer belt 130, and in particular, the transfer belt 130. It is preferably formed near the end.

After that, in step S1002, the detection sensor 200 reads the misalignment detection pattern 320, and in step S1003, the amount of misalignment between the sensors (S21, K21) described in FIG. 9 is calculated based on the reading result. After that, in step S1004, the calculated amount of misalignment between the sensors is compared with a predetermined value set in advance, and the presence or absence of waviness of the transfer belt 130 is determined.

Since it is very difficult for the color image forming apparatus to make the amount of color shift of each color zero, in the processing of the present embodiment, the correction value is calculated so that the amount of color shift is equal to or less than the standard value. , Make corrections. For example, if the difference between S21 and K21 is larger than the standard value, an abnormal image with color shift occurs, so the amount of shift between the sensors is corrected. Although the standard value has been described here as an example, the user, the service person, or the like may change the standard value to an arbitrary value based on the data at the time of design. In particular, in the shipping inspection process of a manufacturer or the like, since the device is immediately assembled, the belt is largely displaced, so that it is preferable to detect the pattern with higher accuracy than usual.

If the amount of misalignment between the sensors is equal to or less than the specified value in step S1004, it is determined that the transfer belt 130 has no waviness, and the process proceeds to step S1005. In step S1005, the amount of color shift described with reference to FIG. 7 is calculated from the detection result of the detection sensor 200, and in step S1006, a correction value for correcting the color shift is calculated.

If the amount of misalignment between the sensors is larger than the specified value in step S1004, it is determined that the transfer belt 130 has waviness, and the process proceeds to step S1007. In step S1007, a value for correcting the deviation of the detection result due to the wave (hereinafter referred to as a detection result correction value) is calculated based on the amount of deviation between the sensors and the detection result of the detection sensor 200. After that, in step S1008, a correction value for correcting the color shift amount is calculated based on the detection result correction value calculated in step S1007 and the detected color shift amount. Therefore, the correction value of the amount of color shift calculated in step S1008 is obtained as a value in which the waviness of the transfer belt 130 is added.

Here, the correction of the detection result when the amount of deviation between the sensors is large will be described. 11A and 11B are views for explaining an example of correcting the detection result of the detection sensor 200 in the present embodiment. FIG. 11A shows the output signal of the detection sensor 200a, and FIG. 11B shows the detection sensor 200c. 11 (c) illustrates the corrected output signal of the detection sensor 200c, respectively. Further, FIG. 11 is a diagram assuming a case where diagonal line patterns of specific colors in the first and second sets are read, and other horizontal line patterns and diagonal line patterns are omitted.

The error at the time of pattern detection compares the difference between the pattern width of the first set and the ideal pattern width and the difference between the pattern width of the second set and the ideal pattern width, and the error is larger for the pattern with the larger difference. It can be determined that it is large. That is, from the above comparison, the pattern formed at the ideal position can be determined. Further, by comparing the errors of the two detection sensors 200a and 200c, the direction closer to the belt can be determined. Further, since the waviness of the belt is generated at the end in the belt traveling direction, it is possible to detect a change in the total of the pattern width of the first set and the pattern width of the second set. Here, assuming that the difference between the front end side edge and the rear end side edge in the two detection sensors 200a and 200c is C1sk21 and C2sk21, respectively, the values of both are expressed by the following equation 2.

Here, the absolute values of C1sk21 and C2sk21 are compared, and the detection sensor 200 having a small absolute value has less variation in the reading result. Therefore, the detection result of each color is corrected based on the detection sensor 200 having a small error. For example, when S21-K21 is equal to or higher than a certain value and the absolute value of C1sk21 is smaller than the absolute value of C2sk21, the detection result correction value d can be obtained from the following equation 3.

In the above equation 3, the detection result correction value d is obtained from the signal assert width of each detection sensor 200. Further, when the absolute value of S21 is larger than the absolute value of K21, the rear end side edge spacing is closer to the ideal value than the front end side edge spacing, and the absolute value of S21 is smaller than the absolute value of K21. Means that the leading edge spacing is closer to the ideal value than the trailing edge spacing. Therefore, the reference detection sensor 200 can be selected by comparing the absolute values.

Further, when the value of S21 is negative, the timing at which the edge on the tip end side of the first set of patterns falls is different from the ideal value, and when the value of S21 is zero or more, the tip end side of the second set of patterns The timing at which the edge falls will differ from the ideal value. Therefore, by determining whether the value of S21 is positive or negative, it is possible to perform a process of correcting the edge of the corresponding pattern. For example, when the value of S21 is negative, the amount of deviation is calculated so that the edge on the tip end side of the first set of patterns is shifted forward by d.

In the above description, the correction amount is calculated from the amount of displacement between the sensors, but it may be calculated by a method other than the above method. For example, based on the detection result of the horizontal line pattern, the detection difference d'of the pattern width for each sensor is calculated as in the following formula (4-1) in the same manner as in the formula (3). Then, as in the following equation (4-2), the difference generated between the sensors can be removed by subtracting d'from the detection difference of the diagonal line pattern obtained by the equation (3), and the correction amount is calculated. can do. In addition, a1', a2', b1', b2' in the following formula (4-1) are the distance between the front edge side and the distance between the rear end side edge of the horizontal line pattern detected by each detection sensor 200, respectively. ..

Since the horizontal line pattern is not easily affected by the waves, the variation between the two detection sensors 200 can be obtained by obtaining it by the above equation (4), and it is corrected together with the detection result of the diagonal line pattern. The amount can be calculated.

As described above, by calculating the deviation amount from the edge timing in which the edge spacing of the pattern is corrected, the correction value excluding the influence of the wave of the transfer belt 130 can be obtained.

The explanation is returned to FIG. After calculating the correction value in step S1006 or S1008, in step S1009, the color shift correction process is performed based on the calculated correction value. Then, in step S1010, the image forming apparatus 100 ends the process.

By the processing described so far, the waviness state of the transfer belt 130 can be determined from the value of the amount of misalignment between the sensors, and by calculating the correction value according to the waviness state, appropriate color misalignment correction is performed. be able to.

According to the embodiment of the present invention described above, it is possible to provide an image forming apparatus capable of appropriately correcting color shift even in a state where waviness occurs in the transfer belt.

Each function of the embodiment of the present invention described above can be realized by a device executable program described in C, C ++, C #, Java (registered trademark), etc., and the program of the present embodiment is a hard disk device, a CD-. It can be stored and distributed in a device-readable recording medium such as ROM, MO, DVD, flexible disk, EEPROM, EPROM, and can be transmitted via a network in a format that other devices can.

Although the present invention has been described above with embodiments, the present invention is not limited to the above-described embodiments, and as long as the present invention exerts its actions and effects within the range of embodiments that can be inferred by those skilled in the art. , Is included in the scope of the present invention.

100 ... image forming apparatus, 101 ... writing unit, 102 ... image forming unit, 103 ... transfer unit, 110 ... polygon mirror, 111 ... fθ lens, 112 ... reflective mirror, 113 ... WTL lens, 114, 115 ... reflective mirror, 120 ... Photoreceptor drum, 121 ... Developer, 122 ... Charger, 130 ... Transfer belt, 131 ... Transfer roller, 133 ... Secondary transfer belt, 134, 135 ... Transfer roller, 136 ... Fixing device, 137 ... Fixing member, 139 ... Cleaning unit, 140 ... Image receiving material accommodating unit, 150 ... Image receiving material, 160 ... Printed matter, 200 ... Detection sensor, 201, 202 ... Light emitting element, 203 ... Light receiving element, 204 ... Condensing lens, 310 ... Image, 320 ... Position shift detection pattern, 410 ... CPU, 411 ... ROM, 412 ... RAM, 413 ... write control unit, 414 ... controller, 415 ... LD lighting control unit, 420 ... I / O port, 430 ... light emission amount control unit, 440 ... Amplification unit, 442 ... Filter, 444 ... A / D conversion unit, 446 ... Sampling control unit, 448 ... FIFA memory, 510 ... Light irradiation unit, 520 ... Transfer image forming unit, 521 ... Test pattern forming unit, 530 ... Transfer unit, 540 ... Correction processing unit, 541 ... Wave determination unit, 542 ... Correction value calculation unit, 550 ... Test pattern detection unit, 560 ... Storage unit

Japanese Patent No. 5773612 JP-A-2015-082076

Claims (8)

An image forming apparatus that prints a color image by forming a toner image of multiple colors on a transfer belt.
A test pattern generating means for forming a pattern for detecting misalignment on the transfer belt, and
Two or more test pattern detecting means for detecting the falling edge and the rising edge of the output signal reading the pattern, and
The distance between the rising edge of the pattern of a specific color and the rising edge of the pattern of the same color as the specific color detected by the test pattern detecting means, the falling edge of the pattern of the specific color, and the above. By calculating the difference between the falling edges of the pattern of the same color as the specific color and the distance between the falling edges and comparing the value of the difference with the standard value, it is possible to determine whether the transfer belt has waviness. Judgment, wave judgment means,
A correction processing means for correcting the color shift of the toner image by a correction value calculated based on the distance between rising edges and the distance between falling edges is included.
The correction processing means
When the waviness determination means determines that the transfer belt has no waviness, a correction value is calculated based on the detection result.
When the waviness determining means determines that the transfer belt has waviness, a correction value is calculated by adding the influence of the waviness to the detection result.
Image forming device. The pattern is formed in the vicinity of both ends of the transfer belt.
The image forming apparatus according to claim 1 . The distance between rising edges and the distance between falling edges are calculated from a set of patterns including one or more diagonal line patterns.
The image forming apparatus according to claim 1 . The distance between rising edges and the distance between falling edges are calculated from a set of adjacent patterns.
The image forming apparatus according to claim 1 . The standard value to be compared in the wave determination means can be changed to any value.
The image forming apparatus according to claim 1 . The waviness determining means determines whether or not the transfer belt has waviness based on the amount of deviation between the sensors.
When the transfer belt has waviness, the correction processing means calculates a correction value in which the amount of deviation between the sensors is added to the detection result.
The image forming apparatus according to claim 1 . The amount of misalignment between the sensors is calculated based on the result of detecting the horizontal line pattern.
When the transfer belt has waviness, the correction processing means calculates a correction value in which the amount of deviation between the sensors is added to the detection result.
The image forming apparatus according to claim 6 . When the transfer belt has waviness, the correction processing means calculates a correction value by correcting the detection timing of the rising edge or the falling edge.
The image forming apparatus according to claim 6 or 7 .