JP6834806B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

Conventionally, in the positional relationship detection method of each color drum for color shift correction in an image forming apparatus, the position is determined by an optical means of a method of reflecting or transmitting a pattern for position detection on a transfer belt (intermediate transfer belt). Detected and indexed.

However, when the position of the pattern is detected, if the transfer belt is scratched, it may be mistaken as a pattern. Further, as a pattern detection omission, if the patterns are overlapped and imaged, or if the pattern cannot be detected for some reason, a malfunction may occur in the adjustment amount indexing operation. Therefore, based on these problems, a color matching control method that prevents erroneous detection due to scratches on the transfer belt and malfunction due to omission of pattern detection in the color image forming apparatus and realizes accurate color shift correction control at low cost is already known. Has been done. As an example, there is a "color matching control method in an image forming apparatus" (see Patent Document 1).

The above-mentioned technique according to Patent Document 1 aims to prevent erroneous detection of scratches on the transfer belt and malfunction due to omission of detection of patterns. Therefore, if the count value of the different pattern detected between the detection of the pattern of the specific reference color and the detection of the pattern of the next specific reference color is different from the predetermined amount, the reliability of the detection position signal is considered to be low. As a result, it is not adopted as a detection signal for executing color matching control.

Specifically, in this color matching control method, a set of eight pattern groups consisting of horizontal lines and diagonal lines of four colors related to yellow (Y), black (K), magenta (M), and cyan (C) is formed. The number of pattern groups used in one-time color matching control is eight. In such a case, for a pattern group in which there is an erroneous detection of scratches on the transfer belt or omission of pattern detection between the detection of the pattern of the specific reference color and the detection of the pattern of the next specific reference color, all one set is for misalignment detection. Exclude from the calculation target of the pattern correction value of.

However, if all one set is excluded from the calculation of the pattern correction value for misalignment detection in this way, the pattern group used for the calculation is reduced from 8 sets to 7 sets, and the accuracy of the calculated pattern correction value for misalignment detection is reduced. There is a problem that it falls.

The present invention has been made to solve such a problem, and the technical problem thereof is a pattern correction value for accurately misalignment detection without reducing the pattern group used for calculation and without reducing the accuracy. The purpose is to provide an image forming apparatus capable of calculating.

In order to solve the above technical problems, in one embodiment of the present invention, a plurality of first image carriers and a plurality of first image carriers are exposed to form a latent image, and the plurality of first image carriers are exposed. An image forming means for developing each latent image of the first image carrier with different colors to form an image of each color, and a plurality of first image carriers driven by a predetermined speed by the image forming means. The second image carrier, in which the images of the respective colors formed on the image are aligned and transferred, and the image of each color, which is superimposed and transferred on the second image carrier, are transferred to the transfer material. An image forming means for forming an image, and a pattern generating means for generating a test pattern image for detecting misalignment, which is formed by a plurality of first image carriers and transferred to the second image carrier. A pattern detection means that detects the test pattern image transferred to the second image carrier and outputs a test pattern detection signal, and a correction value calculation means that calculates a pattern correction value of the test pattern image based on the test pattern detection signal. The image forming apparatus is provided with, and the pattern generating means can generate a test pattern image in a constant width or a constant amount of change in the driving direction of the second image carrier. There are a width calculation means that calculates the width of the test pattern image from the falling and rising edges of the test pattern detection signal, and a width change amount calculating means that calculates the amount of change in the width of the test pattern image calculated by the width calculation means. , A test pattern image with a constant width based on the detection result by the width calculation means, and a test pattern image with a width showing a constant change amount on the detection result by the width change amount calculation means are set as the calculation target of the pattern correction value, and the constant change. A selection means for selecting to exclude a test pattern image having a width indicating no amount from the calculation target of the pattern correction value is provided, and the correction value calculation means performs pattern correction for the test pattern image selected by the selection means. It is characterized by calculating a value.

According to the present invention, the above configuration makes it possible to accurately calculate the pattern correction value for misalignment detection without reducing the pattern group used for the calculation and without degrading the accuracy. Issues, configurations and effects other than those described above will be clarified by the following description of the embodiments.

It is the schematic which showed the basic structure of the image forming apparatus which concerns on embodiment of this invention. It is a figure which showed the schematic structure of the inside of the detection sensor provided in the image forming apparatus shown in FIG. It is a schematic diagram which showed the appearance that the test pattern image for the position deviation detection was transferred and formed with respect to the intermediate transfer belt in the image forming apparatus shown in FIG. A block diagram showing a configuration of a control system circuit related to generation of a test pattern image for position shift detection based on a test pattern detection signal from a detection sensor in the image forming apparatus shown in FIG. 1 and calculation of a pattern correction value of the test pattern image. Is. FIG. 5 is a schematic diagram of a test pattern image showing a method of calculating the amount of misalignment at the time of detecting a test pattern image for detecting misalignment of a CPU in the control system circuit shown in FIG. It is a flowchart which shows the whole operation processing which concerns on a CPU in the control system circuit shown in FIG. It is a figure which illustrated the test pattern image for the position shift detection in the pattern width change mode included in the operation process of FIG. 6, and the waveform of the test pattern detection signal from the detection sensor. (A) is a diagram showing a first aspect, (b) is a diagram showing a second aspect, (c) is a diagram showing a third aspect, (d) is a diagram showing a fourth aspect, and (e) is a fifth aspect. It is a figure which shows the aspect. The method of calculating the amount of misalignment at the time of detecting the test pattern image for detecting misalignment in the pattern width change mode included in the operation process of FIG. 6 is compared between the case where the pattern width is the same and the case where the pattern width is changed to be constant. It is a schematic diagram of the pattern image shown by. 6 is a flowchart showing detailed processing of the operation processing related to the CPU after shifting to the pattern width change mode included in the operation processing of FIG. In the pattern width change mode included in the operation process of FIG. 6, the pattern for detecting the misalignment between the case where the patterns are connected in the pattern width change mode and the case where the pattern is taken as a countermeasure are compared with the waveform of the test pattern detection signal from the detection sensor. It is a figure illustrated by. (A) is a diagram showing a pattern connection mode and a countermeasure mode, and (b) is a diagram showing a pattern width change for the countermeasure mode.

Hereinafter, the image forming apparatus of the present invention will be described in detail with reference to the drawings with reference to examples.

FIG. 1 is a schematic view showing a basic configuration of an image forming apparatus 100 according to an embodiment of the present invention. With reference to FIG. 1, the image forming apparatus 100 is of a digital multifunction device (MFP: Multifunction Peripheral) specification in which a plurality of functions such as a printer, a copying machine, a scanner, and a facsimile are integrated in one housing. ..

Specifically, the image forming apparatus 100 is configured to include an optical apparatus 101, an image forming unit 102, and a transfer unit 103 so as to perform a function as an image forming means and a function as a pattern image forming means. .. Of these, the optical device 101 is configured to include optical elements such as a semiconductor laser light source and a polygon mirror 110. The image forming unit 102 includes a drum-shaped photoconductor (hereinafter, referred to as a photoconductor drum), a charging device, a developing device, and the like. The transfer unit 103 includes a transfer belt (intermediate transfer belt) and the like.

To explain in detail, in the optical device 101, the light beam BM emitted from a plurality of light sources which are semiconductor laser light sources including a laser diode (LD) is deflected by the polygon mirror 110, and the scanning lenses 111a and 111b including the fθ lens are deflected. To be incident on. The number of these light beam BMs corresponding to the images of each color of yellow (Y), black (K), magenta (M), and cyan (C) is generated, and after passing through the scanning lenses 111a and 111b, respectively, It is reflected by the reflection mirrors 112y, 112k, 112m, 112c. For example, the yellow (Y) light beam BM passes through the scanning lens 111a, is reflected by the reflection mirror 112y, and is incident on the long toroidal lens (hereinafter, referred to as WTL lens) 113y. Similarly, the black (K) light beam BM passes through the scanning lens 111a, is reflected by the reflection mirror 112k, and is incident on the WTL lens 113k. The magenta (M) light beam BM passes through the scanning lens 111b, is reflected by the reflection mirror 112m, and is incident on the WTL lens 113m. Similarly, the cyan (C) light beam BM passes through the scanning lens 111b, is reflected by the reflection mirror 112c, and is incident on the WTL lens 113c.

The WTL lenses 113y, 113k, 113m, and 113c shape the incident light beam BM of each color, and then deflect the light beam BM of each color toward the reflection mirrors 114y, 114k, 114m, and 114c. The light beam BMs of each of these colors are further reflected by the reflection mirrors 115y, 115k, 115m, and 115c, and image-illuminate the photoconductor drums 120y, 120k, 120m, and 120c as the light beam BMs used for exposure, respectively. Will be done. The irradiation of the photoconductor drums 120y, 120k, 120m, and 120c with the light beam BM is performed using a plurality of optical elements as described above. Therefore, timing synchronization is performed with respect to the main scanning direction and the sub-scanning direction with respect to the photoconductor drums 120y, 120k, 120m, and 120c. Hereinafter, the main scanning direction with respect to the photoconductor drums 120y, 120k, 120m, and 120c is defined as the scanning direction of the optical beam BM. Further, the sub-scanning direction is defined as the direction orthogonal to the main scanning direction and the rotation direction of the photoconductor drums 120y, 120k, 120m, and 120c.

The photoconductor drums 120y, 120k, 120m, and 120c are configured to include 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 120y, 120k, 120m, 120c of each color, respectively, and is composed of a charger 122y, 122k, 122m, 122c including a corotron, a scorotron, a charging roller, or the like. Surface charge is applied.

The electrostatic charges applied to the photoconductor drums 120y, 120k, 120m, and 120c by the chargers 122y, 122k, 122m, and 122c of each color are image-exposed by the light beam BM, respectively. As a result, an electrostatic latent image is formed on the scanned surface of the chargers 122y, 122k, 122m, and 122c of each color. The electrostatic latent images formed on the scanned surfaces of the photoconductor drums 120y, 120k, 120m, and 120c are respectively produced by the developing devices 121y, 121k, 121m, 121c including the developing sleeve, the developing agent supply roller, the regulating blade, and the like. It is developed. As a result, a developer image is formed on the surface to be scanned of the photoconductor drums 120y, 120k, 120m, 120c, and the photoconductor drums 120y, 120k, 120m, 120c function as the first image carrier. The optical device 101 and the image forming unit 102 expose the first image carrier to form a latent image, develop each latent image of the first image carrier in a different color, and develop an image of each color. It functions as an image forming means for forming the above.

Each developer supported on the surface to be scanned of the photoconductor drums 120y, 120k, 120m, and 120c is transferred onto the intermediate transfer belt 130 that moves in the direction of arrow D by the transport rollers 131a, 131b, and 131c. The photoconductor drums 120y, 120k, 120m, and 120c are provided with primary transfer rollers 132y, 132k, 132m, and 132c at positions facing each other with the intermediate transfer belt 130 interposed therebetween. The intermediate transfer belt 130 is conveyed to the secondary transfer unit in a state where the developer of each color transferred from the surface to be scanned of the photoconductor drums 120y, 120k, 120m, and 120c is carried. That is, the intermediate transfer belt 130 corresponds to the intermediate transfer body, and images of each color formed on each of the first image carriers by the image forming means are aligned and superposed by being driven at a predetermined speed. It functions as a second image carrier to be transferred.

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 arrow E by the conveying rollers 134a and 134b. A recording medium P, which is an image receiving material, is supplied to the secondary transfer unit by a transfer roller 135 from a recording medium storage unit T such as a paper feed cassette for storing high-quality paper and a sheet storage unit for storing plastic sheets. In the secondary transfer unit, a secondary transfer bias is applied to transfer the multicolor developer image supported on the intermediate transfer belt 130 to the recording medium P adsorbed and held on the secondary transfer belt 133. The recording medium P is supplied to the fixing device 136 together with the transfer of the secondary transfer belt 133. The secondary transfer unit functions as an image forming means for performing image formation by transferring an image of each color superimposed and transferred on the second image carrier to a recording medium P as a transfer material.

The fixing device 136 is configured to include a fixing member 137 provided with a fixing roller containing silicone rubber, fluororubber, and the like. The fixing device 136 pressurizes and heats the recording medium P and the multicolor developer image, and the paper ejection roller 138 discharges the recording medium P as printed matter P'to the outside of the image forming apparatus 100. Incidentally, the intermediate 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.

Further, in the vicinity of the transport roller 131a, three detection sensors 5a and 5b for detecting a test pattern image for correcting the image formation condition when forming the color image formed on the intermediate transfer belt 130. 5c is provided. This test pattern image includes a test pattern image for position shift correction and a test pattern image for density correction. The detection sensors 5a, 5b, and 5c function as pattern detection means for detecting the test pattern image transferred to the second image carrier and outputting the test pattern detection signal. For these, a reflective detection sensor including a known reflective photo sensor may be used. The control means mounted on the image forming apparatus has various deviations including the skew (tilt) of each color with respect to the reference color, the amount of deviation of the main scanning resist, the amount of deviation of the sub-scan resist, and the error of the main scanning magnification based on the detection results. Calculate the amount. Further, the control means corrects various deviation amounts related to image quality adjustment based on the calculation results, and performs position deviation correction and density correction, which are image formation conditions when forming a color image on the intermediate transfer belt 130. Do. In this way, various processes related to the generation of the test pattern image at the time of image adjustment are executed.

The control means here is a general term for the arithmetic function of the CPU, which will be described later, and the functions of various control units including the arithmetic function of the controller. That is, the control means has a function as a pattern generation means for generating a test pattern image for detecting misalignment, which is formed by the first image carrier and transferred to the second image carrier. In addition, the control means has a function as a correction value calculation means for calculating a pattern correction value of the test pattern image based on the test pattern detection signal. Details will be explained later.

FIG. 2 is a diagram showing a schematic configuration inside the detection sensor 5a provided in the image forming apparatus 100 shown in FIG. The internal configurations of the other detection sensors 5b and 5c are also common.

Referring to FIG. 2, the detection sensor 5a includes one light emitting unit 10a, two light receiving units 11a, 12a, and one condenser lens 13a. The light emitting unit 10a is a light emitting element that emits light, and examples thereof include the case where an infrared light emitting diode (LED) that generates infrared light is used. As the light emitting element, a laser light emitting element or the like may be used instead of the infrared light emitting diode. Further, for example, a case where a specular reflection type light receiving element is used for the light receiving unit 11a and a diffuse reflection type light receiving element is used for the light receiving unit 12a can be exemplified. Although it is assumed that a phototransistor is used for each of these light receiving units 11a and 12a, a type composed of a photodiode, an amplifier circuit, or the like may be used.

In this detection sensor 5a, when the light L1 emitted from the light emitting unit 10a passes through the condenser lens 13a and then reaches the test pattern of the intermediate transfer belt 130, a part of the light L1 is a toner in the test pattern forming region or the test pattern forming region. Specular reflection in the layer. The specularly reflected light passes through the condenser lens 13a and is received by the light receiving unit 11a as the specularly reflected light L2. Further, the other part of the light L1 is diffusely reflected by the toner layer in the test pattern forming region and the test pattern forming region. The diffusely reflected light passes through the condenser lens 13a and is received by the light receiving unit 12a as diffusely reflected light L3. The specular reflected light L2 received by the light receiving unit 11a and the diffuse reflected light L3 received by the light receiving unit 12a are photoelectrically converted and output as a test pattern detection signal.

FIG. 3 is a schematic view showing how a test pattern image for detecting misalignment is transferred and formed on the intermediate transfer belt 130 in the image forming apparatus 100 shown in FIG. FIG. 3 shows a state in which a test pattern image for detecting misalignment is formed in a row corresponding to the detection sensors 5a, 5b, and 5c on the intermediate transfer belt 130. However, when color shift correction is performed at the timing during printing operation, a test pattern image is not formed in the row corresponding to the detection sensor 5b, and only in the rows corresponding to the detection sensors 5a and 5c at both ends thereof. A test pattern image is formed.

FIG. 4 relates to the generation of a test pattern image for detecting misalignment based on the test pattern detection signals from the detection sensors 5a, 5b, and 5c in the image forming apparatus 100 shown in FIG. 1 and the calculation of the pattern correction value of the test pattern image. It is a block diagram which showed the structure of the control system circuit.

Referring to FIG. 4, in this control system circuit, the test pattern detection signal obtained from the light receiving units 11a and 12a of the detection sensors 5a, 5b and 5c is amplified by the amplification unit 201, and then the line detection signal is detected by the filter 202. Only the ingredients are allowed to pass. After that, the analog / digital (A / D) conversion unit 203 converts the analog data into digital data, and then the sampling control unit 204 controls the sampling of the test pattern image. The data of the test pattern image sampled by the sampling control unit 204 is stored in the first-in first-out (FIFO) memory 205. After the detection of the set of test pattern images for detecting misalignment is completed, the data of the test pattern images stored in the first-in first-out memory 205 is connected by the data bus via the input / output (I / O) port 206. It is loaded into the CPU 209 and RAM 208. The CPU 209 performs a predetermined arithmetic process to obtain the various deviation amounts described above.

In addition, the ROM 207 is connected to the CPU 209 and the RAM 208 and the input / output port 206 by the data bus. The ROM 207 stores a program for calculating various deviation amounts described above, and various programs for controlling position deviation correction (calculation of pattern correction value) and image formation. Further, the CPU 209 monitors the test pattern detection signals from the light receiving units 11a and 12a at appropriate timings. As a result, the CPU 209 controls the light emitting amount of the light emitting unit 10a by the light emitting amount control unit 213 so that the test pattern image can be reliably detected even if the intermediate transfer belt 130 or the light emitting unit 10a deteriorates. .. As a result of controlling the amount of light emitted by the CPU 209, the level of the test pattern detection signal from the light receiving units 11a and 12a is controlled to be always constant.

As described above, the CPU 209 and the ROM 207 have a function of controlling the overall operation of the image forming apparatus 100. Further, the CPU 209 sets the writing start timing, the pixel clock frequency change, and the like in the writing control unit 210 based on the obtained pattern correction values of various deviation amounts. The write control unit 210 includes a clock generator or the like using a VCO (Voltage Controlled Oscillator) as a device capable of setting the output frequency very finely, and uses this output as an image clock. An image is written to the recording medium P by driving the LD (laser diode) lighting control unit 212 according to the image data sent from the controller 211 with the pixel clock as a reference. The write control unit 210 controlled by the CPU 209 and the controller 211 and the LD lighting control unit 212 controlled by the write control unit 210 cooperate with each other to perform a test for detecting misalignment transferred to the second image carrier. It functions as a pattern generation means for generating a pattern image.

FIG. 5 is a schematic diagram of a test pattern image showing a method of calculating the amount of misalignment at the time of detecting a test pattern image for detecting misalignment related to CPU 209 in the control system circuit shown in FIG. However, in FIG. 5, the case where the mark sequence of the test pattern image for detecting the misalignment is detected by the detection sensor 5a will be described, but the same applies to the other detection sensors 5b and 5c. Here, it is premised that the CPU 209 activates the function of the pattern generating means based on the program of the ROM 207 to generate a test pattern image in the driving direction of the intermediate transfer belt 130 with a constant width. Further, it is also premised that the CPU 209 activates the function of the distance calculation means based on the program of the ROM 207 and calculates the distance between the test pattern images with reference to the center of the test pattern image shown in the test pattern detection signal.

The detection sensor 5a targets the mark sequence of the test pattern image for detecting misalignment as a detection target, and when a mark (same as the test pattern image) is detected at a predetermined fixed sampling time interval, the detection sensor 5a notifies the CPU 209 as a test pattern detection signal. To do. In the following, the test pattern image is simply simplified as a pattern. When the CPU 209 sequentially receives notifications of mark detection by the test pattern detection signal from the detection sensor 5a, the distances y1, m1, and c1 between the horizontal line patterns are calculated based on the notification interval of each detection and the sampling time interval. To do. Similarly, the distances y2, k2, m2, and c2 between each horizontal line pattern and the corresponding diagonal line patterns of the same color are calculated. In this way, the distances y1, m1, c1 between the horizontal line patterns in the mark sequence and the distances y2, k2, m2, c2 between each horizontal line pattern and the diagonal line patterns of the same color corresponding to them are obtained. .. After that, the amount of misalignment can be calculated by comparing the obtained distances y1, m1, c1, y2, k2, m2, and c2, respectively.

More specifically with reference to FIG. 5, first, in the calculation of the amount of misalignment in the sub-scanning direction, a horizontal line pattern is used, and black (K), which is a reference color, and yellow (Y), which is a target color thereof, are used. The distances (y1, m1, c1) of each pattern from magenta (M) and cyan (C) are calculated. Next, these distances (y1, m1, c1) are compared with the ideal distances (y0, m0, c0) stored in advance, and the distance y1-ideal distance y0, the distance m1-ideal distance m0, From the value of the distance c1-ideal distance c0, the amount of misalignment of the target colors yellow (Y), magenta (M), and cyan (C) with respect to the reference color black (K) can be calculated.

In calculating the amount of misalignment in the main scanning direction, first, the distance between the horizontal line pattern and the diagonal line pattern of each color of yellow (Y), black (K), magenta (M), and cyan (C) (y2, k2, m2). , C2) is calculated. Next, using the calculated distances (y2, k2, m2, c2), the difference value between the distance of the reference color black (K) and the distance of the target color is calculated. These difference values correspond to the amount of misalignment in the main scanning direction. The reason is that the diagonal line pattern is tilted with respect to the main scanning direction by, for example, a predetermined angle (for example, 45 degrees can be exemplified). Therefore, when the position is displaced in the main scanning direction, the distance from the horizontal line pattern is increased. This is because it expands or narrows more than the distance for other colors. That is, the amount of misalignment in the main scanning direction of black (K) and yellow (Y), black (K) and magenta (M), and black (K) and cyan (C) is distance k2-distance y2, distance k2-. It is obtained by the distance m2 and the distance k2-distance c2. In this way, the amount of misalignment in the sub-scanning direction and the main scanning direction can be obtained.

Further, the skew component and the main scanning magnification error can be calculated based on the detection results of different detection sensors 5a, 5b, and 5c. The skew component can be calculated by calculating the difference in the amount of misalignment in the sub-scanning direction based on the test pattern detection signals from the detection sensors 5a and 5c by the CPU 209. Then, based on the various displacement amounts acquired as described above, a correction process for correcting the image formation conditions when forming a color image on the intermediate transfer belt 130 is executed. As this correction process, for example, the emission timing of the light beam BM corresponding to each color with respect to the photoconductor drums 120y, 120k, 120m, and 120c is adjusted so that the amount of misalignment substantially matches, so that the main scanning direction and the sub scanning direction Adjusts the misalignment and the overall magnification of the main scan.

Regarding the adjustment of the misalignment in the sub-scanning direction, the amount of misalignment with respect to the photoconductor drum 120k is corrected by finely adjusting the rotation speeds of the photoconductor drums 120y, 120k, 120m, and 120c. Further, the stepping motor is driven to adjust the inclination of the reflection mirrors 112y, 112k, 112m, 112c, 114y, 114k, 114m, 114c, 115y, 115, 115m, 115c with respect to the light beam BM. In addition, the amount of misalignment can be corrected even if the image data is changed, such as by adding a white line. Incidentally, the correction of various misalignment amounts described with reference to FIG. 5 indicates that the pattern correction value for misalignment detection is calculated.

FIG. 6 is a flowchart showing the overall operation processing related to the CPU 209 in the control system circuit shown in FIG.

Referring to FIG. 6, in the overall operation processing of the CPU 209, first, the function of the pattern generating means for generating the pattern in the driving direction of the intermediate transfer belt 130 with a constant width is activated by the initial setting. In the operation process, the writing control unit 210 controlled by the controller 211 is instructed to control the LD lighting control unit 212, and the pattern for detecting the misalignment is output in the drive direction of the intermediate transfer belt 130 with a constant width ( Step S1) and transfer to the intermediate transfer belt 130. Next, the pattern for detecting the displacement of the intermediate transfer belt 130 is detected by the detection sensors 5a, 5b, and 5c (step S2). Normally, the detected pattern is a set of eight horizontal line patterns and diagonal line patterns of four colors of yellow (Y), black (K), magenta (M), and cyan (C), and one color. There are a total of 64 patterns with 8 pattern groups used in the matching control. Further, the CPU 209 functions as a width calculation means for calculating the width of the pattern from the falling / rising edges of the test pattern detection signal based on the program of the ROM 207. As a result, the process of calculating the width of the pattern from the falling and rising edges of the detected pattern (step S3) is performed.

After that, the CPU 209 functions as a determination means for determining whether or not the number of patterns is appropriate based on the test pattern detection signal based on the program of the ROM 207. As a result, it is determined whether or not the number of detected patterns is appropriate (step S4). By the way, the CPU 209 has a function as a selection means for calculating a pattern correction value for a pattern having a certain width as a detection result by the width calculation means based on the program of the ROM 207. Further, the CPU 209 has a function as a correction value calculation means for calculating a pattern correction value of a pattern based on a test pattern detection signal based on a program of ROM 207.

Therefore, as a result of the determination (step S4) as to whether or not the number of detected patterns described above is appropriate, if the number of patterns is appropriate, the function of the selection means is activated to determine whether or not the width of the pattern is constant. The determination (step S5) is performed. As a result of this determination, if the width of the pattern is constant, the function of the distance calculation means and the function of the correction value calculation means described with reference to FIG. 5 are used to calculate the pattern correction value for position deviation detection (step S6). ). After that, the pattern correction value for detecting the misalignment is stored in, for example, a RAM 208 (step S7), and then the operation process is terminated.

On the other hand, as a result of determining whether or not the number of detected patterns described above is appropriate (step S4), if it is not appropriate, the width of the scratches on the intermediate transfer belt 130 (hereinafter referred to as belt scratches) is grasped. Since it is necessary to keep it, the width of the belt scratch is stored in the RAM 208 or the like (step S8). That is, the inappropriate number here means a case where the number of patterns reaches a predetermined value and becomes unsuitable, including the case where the belt is scratched. After that, the operation process ends after shifting to the pattern width change mode (step S9). Further, even if the number of detected patterns is appropriate, as a result of determining whether or not the width of the pattern is constant (step S5), if the width of the pattern is not constant, it can be considered that there is a belt scratch or an abnormality. Therefore, even in such a case, by the function as the selection means, it is regarded as noise such as belt scratches, excluded from the calculation target of the pattern correction value, and the mode is shifted to the pattern width change mode (step S9), and then the operation process is terminated. Incidentally, in the pattern width changing mode, as will be described later, the pattern generating means generates the test pattern image by changing the width by a constant amount of change instead of generating the test pattern image in the driving direction of the intermediate transfer belt 130 with a constant width.

FIG. 7 is a diagram illustrating a pattern for detecting misalignment in the pattern width change mode included in the operation process of FIG. 6 and a waveform of a test pattern detection signal (denoted as a sensor output signal) from the detection sensor 5a. .. 7 (a) shows a first aspect, FIG. 7 (b) shows a second aspect, FIG. 7 (c) shows a third aspect, and FIG. 7 (d) shows a fourth aspect. FIG. 7 (e) is a diagram showing a fifth aspect. However, although the case where the horizontal line pattern is detected as the pattern for detecting the positional deviation by the detection sensor 5a is shown here, the same processing is performed for the detection of the diagonal line pattern. Further, the same processing is performed for the detection of the horizontal line pattern and the detection of the diagonal line pattern by the other detection sensors 5b and 5c.

Incidentally, in relation to the pattern width change mode of FIG. 7, the CPU 209 has a function as a width change amount calculation means for calculating the change amount of the pattern width calculated by the width calculation means based on the program of the ROM 207. Further, the CPU 209 has a function of selecting a width pattern showing a constant change amount in the detection result by the width change amount calculation means as a pattern correction value calculation target as a function of the selection means described above based on the program of the ROM 207. .. Further, it has a function of selecting a width pattern that does not show a constant change amount in the detection result by the width change amount calculation means to be excluded from the calculation target of the pattern correction value. In addition, the function of the width change amount calculating means calculates the change amount of the width of the pattern from the difference between the width of the pattern of interest and the width of the pattern immediately before in the generation order adjacent to the pattern of interest. However, if it is assumed that the width of the previous pattern is due to a belt scratch, it is calculated from the difference from the width of the previous pattern in the order of generation. It is assumed that each of these functions is provided.

Specifically, the first aspect of FIG. 7A corresponds to the case where there is no belt scratch in any of the nth group and the n + 1th group of the pattern group. In the four-color test pattern detection signal, the rising edge is detected from the falling edge, and the width of each pattern is specified by the CPU 209. It is detected that the width from the falling edge to the rising edge of each of the four color test pattern detection signals in the nth group of the pattern group is formed by a constant amount of change for each color at y3, k4, m5, and c6. Will be done. The width from the falling edge to the rising edge of each of the four color test pattern detection signals in the n + 1th set of the pattern group is also formed with a constant amount of change for each color at y7, k8, m9, and c10. Detected.

Further, it is shown that the width of the pattern has a constant amount of change even when straddling the nth set and the n + 1st set of the pattern group. The amount of change in the width of each pattern is the width of the pattern (k4-y3), (m5-k4), (c6-m5), (y7-c6), (k8-y7), (m9-k8), (c10). It is obtained by the difference of −m9). That is, the amount of change calculated by the difference between the pattern of interest here and the width of the pattern immediately before in the order of generation adjacent to the pattern of interest is constant, and if not, the pattern of interest is a belt scratch. It can be determined that there is.

The second aspect of FIG. 7B corresponds to the case where there is a belt scratch in the n + 1 group of the pattern group. The widths of the patterns detected in the nth set of the pattern group are y3, k4, m5, and c6 as in FIG. 7A. Here, in the n + 1 group of the pattern group, it is assumed that there is a noise width x1 due to the first belt scratch pattern between yellow (Y) and black (K). The widths of the patterns detected at this time are y7, x1, k8, m9, and c10, which are larger than the number of appropriate patterns. The amount of change in the width of each pattern can be calculated from the difference between the width of the pattern of interest and the width of the pattern immediately before in the order of generation adjacent to it, and can be calculated from (y7-c6), (x1-y7), (k8-x1). ), (M9-k8), (c10-m9). Here, assuming that the amount of change is a, the relationship of the amount of change is (y7-c6) = a, (x1-y7) ≠ a, (k8-x1) ≠ a, (m9-k8) = a, (c10). −M9) = a.

From this result, it can be determined that the pattern detected as the noise width x1 due to the first belt scratch pattern is the belt scratch, so that the pattern is excluded from the calculation target of the pattern correction. In such a case, if the difference between the pattern width k8 and the width y7 of the previous pattern in the order of generation is calculated, (k8-y7) = a, which is constant and is used as the calculation target of the pattern correction. be able to. As a result, the function as the correction value calculating means calculates the pattern correction value for detecting the misalignment with respect to the pattern selected by the function of the selecting means.

The third aspect of FIG. 7C corresponds to the case where there is a belt scratch in the nth group of the pattern group. Here, in the nth group of the pattern group, there is a noise width x2 due to the second belt scratch pattern between black (K) and magenta (M), and the width x2 is the pattern width y3, k4, m5, c6. It is assumed that it is the same as any of the above. Specifically, it is assumed that the width is the same as the pattern width k4. The widths from the falling edge to the rising edge of each of the four color test pattern detection signals in the nth set of the pattern group detected at this time are y3, k4, x2, m5, and c6, and are of appropriate patterns. More than a number are detected.

When the noise width x2 due to the second belt scratch pattern is the same as the pattern width k4, k4 and x2 are continuously different (x2-k4) = 0. In such a case, the pattern having the widths k4 and x2 of the pattern is excluded from the calculation target of the pattern correction. If the same width is not continuous, the noise width x2 due to the second belt scratch pattern is determined as the belt scratch and excluded from the calculation target of the pattern correction in the same manner as in the procedure of FIG. 7B. Incidentally, the widths of the patterns detected in the n + 1th set are y7, k8, m9, and c10 as in FIG. 7A.

The fourth aspect of FIG. 7D corresponds to the case where there is a belt scratch in the n + 1 group of the pattern group. The widths of the patterns detected in the nth set of the pattern group are y3, k4, m5, and c6 as in FIG. 7A. Here, it is assumed that the width k8 of the n + 1th set of black (K) patterns in the pattern group is overlapped with the width x3 of the noise due to the third belt scratch pattern (k8 = x3). At this time, the widths of the patterns detected in the n + 1th set of the pattern group are y7, x3, m9, and c10, and the number of patterns is appropriate.

The amount of change is calculated from the difference in the width of the pattern as before. Assuming that the amount of change is a, the relationship of the amount of change is (y7-c6) = a, (x3-y7) ≠ a, (m9-x3) ≠ a, (c10-m9) = a. From this result, it can be determined that the pattern detected as the noise width x3 due to the third belt scratch pattern is the belt scratch, so that the pattern is excluded from the calculation target of the pattern correction. In such a case, the pattern width m9 is calculated as a difference from the width y7 of the previous pattern in the order of generation, and (m9-y7) = a, which is constant and is used as a pattern correction calculation target.

The fifth aspect of FIG. 7 (e) corresponds to the case where there is a belt scratch in the n + 1 group of the pattern group. The widths of the patterns detected in the nth set of the pattern group are y3, k4, m5, and c6 as in FIG. 7A. Here, it is assumed that the width k8 of the n + 1th set of black (K) patterns in the pattern group overlaps so as to include the noise width x4 due to the fourth belt scratch pattern (k8> x4). At this time, the widths of the patterns detected in the n + 1th set of the pattern group are y7, x8, m9, and c10, and the number of patterns is appropriate. In this case, since it is considered that there is no belt scratch, the selection of the calculation target of the pattern correction is not affected.

From the relationship between the amount of change in the width of the pattern and the number of patterns based on the test pattern detection signals from the detection sensors 5a, 5b, and 5c by the functional processing described with reference to FIGS. 7 (a) to 7 (e). The calculation target of the pattern correction can be accurately selected. This makes it possible to accurately calculate the pattern correction value for misalignment detection without reducing the pattern group used for the calculation and without degrading the accuracy.

FIG. 8 shows a pattern image in which the method of calculating the amount of misalignment at the time of detecting the pattern for detecting misalignment in the above-mentioned pattern width change mode is compared between the case where the width of the pattern is the same and the case where the width is constantly changed. It is a schematic diagram.

With reference to FIG. 8, even if the widths of the patterns are the same or different, the widths of the patterns are changed with reference to the center of each pattern, so that the distances between the patterns are the same. Therefore, as in the case of the method described with reference to FIG. 5, the distances y1, m1, c1 between the horizontal line patterns in the mark sequence, the horizontal line patterns, and the diagonal line patterns of the same color corresponding to them are used. Various misalignment amounts can be calculated by obtaining the distances y2, k2, m2, and c2 between them and comparing the obtained distances y1, m1, c1, y2, k2, m2, and c2, respectively. The specific content is omitted because the explanation is duplicated.

FIG. 9 is a flowchart showing detailed processing of the operation processing related to the CPU 209 after shifting to the pattern width change mode described above.

Referring to FIG. 9, in the detailed processing of the CPU 209, first, the function of the pattern generating means for generating a pattern in the driving direction of the intermediate transfer belt 130 with a constant amount of change is activated by setting the pattern width changing mode. In the operation process, the writing control unit 210, which is controlled by the controller 211, is instructed to control the LD lighting control unit 212, and the pattern for detecting the misalignment is widened in the drive direction of the intermediate transfer belt 130 by a constant amount of change. Is changed and output (step S1). As a result, the pattern whose width is changed by a constant amount of change is transferred to the intermediate transfer belt 130. However, it is assumed that the width of the pattern to be written here is wider than the width of the belt scratches memorized by the operation process in FIG. The reason is that if there is a belt scratch having the same width as the pattern, it is not possible to distinguish between the belt scratch and the pattern. Therefore, if the width of the belt scratch is stored as described with reference to FIG. 6 and the pattern is formed with a width larger than the width, the pattern correction value can be calculated without excluding the pattern.

Next, the pattern for detecting the displacement of the intermediate transfer belt 130 is detected by the detection sensors 5a, 5b, and 5c (step S102). Further, the function as the width calculation means is activated, the width of the pattern is calculated from the falling / rising edges of the test pattern detection signal (step S103), and then the function of the width change amount calculating means is activated. As a result, the width of the pattern of interest is compared with the width of the previous pattern in the order of generation, and the amount of change in the width of the pattern is calculated (step S104). If the previous pattern is regarded as noise such as belt scratches and is excluded, the width of the previous pattern is compared with the width of the previous pattern in the order of generation.

After that, the CPU 209 activates the function of the selection means and determines whether or not the amount of change is constant (step S105). As a result of this determination, if the amount of change in the width of the pattern is not constant, it is subsequently determined whether or not the number of detected patterns is appropriate (step S106). As a result of this determination, if it is appropriate, a pattern in which the amount of change in the width of the pattern is not constant is excluded (step S107), and if it is not appropriate, it is determined whether or not the width of the same pattern continues (step S108). I do. As a result of this determination, if the widths of the same patterns are continuous, the continuous patterns are excluded (step S109). On the other hand, if the number of detected patterns is not appropriate and the widths of the same patterns are not continuous, patterns in which the amount of change in the width of the patterns is not constant are excluded (step S107).

After any pattern exclusion, as a result of subsequent determination of whether or not the amount of change is constant (step S105), the pattern for detecting misalignment is the same as when the amount of change is constant. The process shifts to the process of calculating the correction value (step S110). Here, too, the function of the distance calculation means and the function of the correction value calculation means are activated. Further, the pattern correction value for detecting the misalignment is stored in, for example, a RAM 208 (step S111), and then the number of excluded patterns is counted (step S112). This count number is also stored in, for example, RAM 208. Finally, the CPU 209 determines whether or not the count number is less than the predetermined value by determining whether or not the count number is less than the predetermined value (step S113). As a result of this determination, if the count number is less than the predetermined value, the operation process is terminated, but if the count number is greater than or equal to the predetermined value, the user is notified of the belt replacement (step S114), and then the operation process is terminated. ..

By the detailed processing shown in FIG. 9, the pattern correction is calculated based on the change amount of the pattern width, the number of patterns, and the state of the pattern width based on the test pattern detection signals from the detection sensors 5a, 5b, and 5c. Can be selected accurately. This makes it possible to accurately calculate the pattern correction value for misalignment detection without reducing the pattern group used for the calculation and without degrading the accuracy.

FIG. 10 shows a pattern for detecting a positional deviation between a case where the patterns are connected in the above-mentioned pattern width change mode and a case where the pattern is taken as a countermeasure, and a waveform of a test pattern detection signal (denoted as a sensor output signal) from the detection sensor 5a. It is a figure illustrated in comparison. FIG. 10A is a diagram showing a pattern connection mode and a countermeasure mode, and FIG. 10B is a diagram showing a pattern width change for the countermeasure mode. However, in each case, the case where the horizontal line pattern is detected as the pattern for detecting the positional deviation by the detection sensor 5a is shown, but the detection of the diagonal line pattern is also processed in the same manner. Further, the detection of the horizontal line pattern and the detection of the diagonal line pattern by the other detection sensors 5b and 5c are also processed in the same manner.

Incidentally, in relation to the countermeasure mode of the pattern width change mode of FIG. 10, when the number of patterns determined by the determination means based on the program of the ROM 207 becomes equal to or less than a predetermined value, the CPU 209 will be described below as the pattern generation means. Have a processing function to do. In the outline, it is to have a function to change the width of the pattern from a mode in which a large amount of change is generated to a mode in which a small amount of change is generated. Basically, if the preformed patterns overlap, the width of the pattern is generated small by a certain amount of change, and if they do not overlap, the width of the pattern is generated large by a constant amount of change. Just do it.

With reference to FIG. 10A, for example, when the width of the patterns is increased by a certain amount of change as described with reference to FIG. 7A, the patterns directly overlap each other or due to belt scratches between the patterns. The number of detected patterns may decrease due to the connection of patterns. Specifically, the widths of the original patterns m5 and c6 are connected by the width of the fifth belt scratch pattern between the nth set of magenta (M) and cyan (C), and the integrated pattern width x5 is obtained. It is formed and detected. That is, in such a case, the widths of the patterns of each color in the nth set of the pattern group are y3, k4, and x5, and the number of detected patterns is reduced. Such continuous patterns are excluded from the calculation target of pattern correction. Therefore, when the number of detected patterns in the nth group decreases in this way, the width of the pattern may be reduced by a constant amount of change from the n + 1th group of the pattern group. Further, when the width of the pattern is reduced, the width of the pattern may be increased when the width of the pattern is reduced to the minimum width that can be detected by the detection sensor 5a.

With reference to FIG. 10B, when the amount of change is a, the interval hn from the rising edge to the falling edge of the next pattern can be calculated by the relational expression hn = h1- (n-1) a. .. If the mode is switched to a mode in which the width of the pattern is increased in the range where the patterns do not overlap (hn> 0) and the width of the pattern is decreased before hn <0, the pattern can be changed as in the connection of the patterns in FIG. 10A. The pattern correction value for detecting the misalignment can be calculated without wasting it. In this way, the function of the pattern generating means is to generate a small pattern width with a constant amount of change if the patterns formed in advance in the pattern width change mode overlap, and to keep the pattern width constant within the range where they do not overlap. It is preferable to generate a large amount by the amount of change in.

In short, in the image forming apparatus according to the embodiment, the number of patterns is belted based on the test pattern detection signal in which the CPU 209 detects a pattern having a constant width in the driving direction of the intermediate transfer belt 130 from the detection sensors 5a, 5b, and 5c. Judge that it is not appropriate to include scratches. In such a case, the writing control unit 210 and the LD lighting control unit 212 are instructed to change the width with a constant amount of change with respect to the driving direction of the intermediate transfer belt 130 to generate a pattern. Then, the pattern is transferred and formed on the intermediate transfer belt 130 while increasing the width of the pattern of each color in order, and the pattern correction is calculated from the relative amount of change in the width of the pattern based on the test pattern detection signal at that time. Select a pattern. At this time, if it does not correspond to the amount of change in the width of the pattern of each color, it is regarded as a belt scratch and excluded from the calculation target of the pattern correction, and only the part where the pattern is generated is calculated as the pattern correction value for misalignment detection. Reflect in. This makes it effective to apply to a color matching control method that can prevent erroneous detection of belt scratches and malfunctions due to omission of pattern detection and can accurately realize color shift correction control. As a result, it becomes possible to accurately calculate the pattern correction value for misalignment detection without reducing the pattern group used for the calculation.

The following is a comprehensive list of the functional features of the various means of the CPU 209 in the image forming apparatus according to the embodiment and their effects.

First, the CPU 209 pays attention to a width pattern in which the calculation result by the width change amount calculation means does not show a constant change amount as a function of the selection means. Specifically, when the number of patterns is not appropriate in the determination result by the determination means and the widths of the same pattern are continuous in the detection result by the width calculation means, the pattern correction value is calculated for both consecutive same pattern images. Exclude from the target. As a result, if there is a belt scratch with the same width as the pattern between the patterns, it is not possible to distinguish between the belt scratch and the pattern. In such a case, both the noise due to the belt scratch and the pattern should be excluded from the correction value calculation. Can prevent false positives.

Secondly, as a function of the selection means, the CPU 209 pays attention to a width pattern in which the calculation result by the width change amount calculation means does not show a constant change amount. Specifically, the amount of change between the case where the number of patterns is appropriate in the judgment result by the judgment means and the case where the widths of the same pattern are not continuous in the detection result by the width calculation means even if the number of patterns is not appropriate. Excludes patterns for which is not constant from the calculation target of the pattern correction value. As a result, even if the belt scratches overlap and become the same width as the other patterns, it is possible to accurately determine which color pattern cannot be used, and the pattern correction value for misalignment detection without excluding the pattern. Can be calculated.

Thirdly, the CPU 209 counts the number of excluded patterns and stores the count number in the storage means (RAM 208), and notifies the notification means when the count number in the storage means exceeds a predetermined value. As a result, the user can be notified when the count number of the patterns excluded as noise due to belt scratches reaches a predetermined value, and the timing of replacement of the intermediate transfer belt 130 can be notified.

Fourth, as a function of the pattern generating means, the CPU 209 generates a test pattern image having a certain width by default, and reaches a predetermined value including the case where the number of patterns is a belt scratch in the judgment result by the judgment means. The mode shifts to the pattern width change mode when the pattern width is no longer appropriate and when the pattern width is not constant in the detection result by the width calculation means even if the number of patterns is appropriate. Here, the presence or absence of belt scratches is assumed by counting the number of patterns with a certain width detected by the initial setting, and if belt scratches are assumed, the toner consumption is suppressed by shifting to the pattern width change mode. be able to.

Fifth, the CPU 209 continues to increase the pattern width by a constant amount of change in the pattern width change mode as a function of the pattern generation means. As a result, the belt scratch and the pattern can be accurately distinguished from the amount of change in the width of the pattern that has been made constant.

Sixth, the CPU 209 stores the width of the test pattern image excluded by the selection means in the storage means (RAM 208), and as a function of the pattern generation means, stores the pattern with a width larger than the width of the pattern stored in the storage means. appear. As a result, if there is a belt scratch having the same width as the pattern between the patterns, it is possible to separately implement a countermeasure that makes it impossible to distinguish between the belt scratch and the pattern. That is, by storing the width of the belt scratch and forming the pattern with a width larger than the width, it is possible to calculate the pattern correction value for detecting the misalignment without unnecessarily excluding the pattern.

Seventh, as a function of the width change amount calculation means, the CPU 209 determines the amount of change in the width of the pattern from the difference between the width of the pattern of interest and the width of the pattern immediately before in the generation order adjacent to the pattern of interest. calculate. Alternatively, if the width of the pattern one before is assumed to be due to a belt scratch, it is calculated from the difference from the width of the pattern one before one in the order of generation. Here, if the pattern detected as the comparison target of the change amount of the pattern width is a belt scratch, the change amount of the pattern of interest is not an appropriate value, so the belt is further changed from the change amount of the previous pattern. Determine if it is a scratch.

Eighth, as a function of the pattern generating means, the CPU 209 is from a mode in which when the number of patterns determined by the determining means in the pattern width changing mode becomes equal to or less than a predetermined value, the pattern width is greatly generated by a constant amount of change. Change to a mode that generates a small amount with a certain amount of change. This makes it possible to deal with the problem that if the widths of the patterns are constantly increased, the patterns overlap each other, or the patterns are connected due to belt scratches between the patterns and the pattern correction value for detecting misalignment cannot be calculated. That is, if it is determined that the patterns overlap by reducing the number of patterns detected by the function of the determination means and the width of the subsequent patterns is formed small, it is possible to avoid the pattern overlap and connection.

Ninth, as a function of the pattern generation means, the CPU 209 generates a small pattern width with a constant amount of change if the preformed patterns overlap in the pattern width changing mode, and if the patterns do not overlap, the CPU 209 generates a small pattern width. A large width is generated with a constant amount of change. If the range in which the patterns do not overlap is calculated in advance in this way, the pattern correction value for position shift correction can be accurately calculated without the patterns overlapping and forming a useless pattern.

It should be noted that the present invention is not limited to the gist described in the examples in the above-described embodiment, and various modifications can be made without departing from the technical gist thereof, and the technical idea described in the claims can be applied. All of the technical matters included are the subject of the present invention. Although the above examples show suitable examples, those skilled in the art can realize various modifications from the disclosed contents, but these are described in the attached claims. Included in the technical scope.

5a, 5b, 5c Detection sensor 10a Light emitting part 11a, 12a Light receiving part 13a Condensing lens 100 Image forming device 101 Optical device 102 Image forming part 103 Transfer part 110 Polygon mirror 111a, 111b Scanning lens 112y, 112k, 112m, 112c, 114y , 114k, 114m, 114c, 115y, 115k, 115m, 115c Reflective mirror 113y, 113k, 113m, 113c WTL lens 120y, 120k, 120m, 120c Photoreceptor drum 121y, 121k, 121m, 121c Developer 122y, 122k, 122m, 122c Charger 130 Intermediate transfer belt 131a, 131b, 131c, 134a, 134b, 135 Transfer roller 132y, 132k, 132m, 132c Primary transfer roller 133 Secondary transfer belt 136 Fixing device 139 Cleaning unit 201 Amplification unit 202 Filter 203 Analog / Digital (A / D) converter 204 Sampling control unit 205 First-in first-out (FIFA) memory 206 Input / output (I / O) port 207 ROM
208 RAM
209 CPU
210 Write control unit 211 Controller 212 LD (laser diode) lighting control unit 213 Light emission control unit P Recording medium P'Printed matter T Recording medium storage unit

JP-A-2003-098793

Claims (10)

The plurality of first image carriers and the plurality of first image carriers are exposed to form a latent image, and the latent images of the plurality of first image carriers are displayed in different colors. An image forming means for developing to form an image of each color and an image of each color formed with respect to each of the plurality of first image carriers by the image forming means driven at a predetermined speed are positioned. A second image carrier that is superimposed and transferred together, and an image forming means that transfers an image of each color that is superimposed and transferred on the second image carrier to a transfer material to form an image. The pattern generating means for generating a test pattern image for detecting misalignment formed by the plurality of first image carriers and transferred to the second image carrier, and the second image carrier It is provided with a pattern detection means that detects the transferred test pattern image and outputs a test pattern detection signal, and a correction value calculation means that calculates a pattern correction value of the test pattern image based on the test pattern detection signal. It is an image forming device
The pattern generating means can generate the test pattern image by changing the width in the driving direction of the second image carrier with a constant width or a constant amount of change.
A width calculation means for calculating the width of the test pattern image from the falling / rising edges of the test pattern detection signal, and a width change amount calculation for calculating the change amount of the width of the test pattern image calculated by the width calculation means. The pattern correction value is calculated for the means, a test pattern image having a constant width based on the detection result by the width calculation means, and a test pattern image having a width showing a constant change amount based on the detection result by the width change amount calculation means. Moreover, it is provided with a selection means for selecting a test pattern image having a width that does not show a constant amount of change so as to be excluded from the calculation target of the pattern correction value.
The correction value calculation means is an image forming apparatus characterized in that a pattern correction value is calculated for the test pattern image selected by the selection means. In the image forming apparatus according to claim 1,
A determination means for determining whether or not the number of test pattern images is appropriate based on the test pattern detection signal is provided.
The selection means has an inappropriate number of test pattern images in the determination result by the determination means and the width of the test pattern image having a width whose calculation result by the width change amount calculation means does not show a constant amount of change. An image forming apparatus characterized in that when the widths of the same test pattern images are continuous in the detection result by the calculation means, both of the continuous same test pattern images are excluded from the calculation target of the pattern correction value. In the image forming apparatus according to claim 2,
The selection means refers to a case where the number of test pattern images is appropriate in the judgment result by the determination means for a test pattern image having a width whose calculation result by the width change amount calculation means does not show a constant amount of change. Even if the number of test pattern images is not appropriate, if the width of the same test pattern image is not continuous in the detection result by the width calculation means, the amount of change is not constant. The test pattern image is the target for calculating the pattern correction value. An image forming apparatus characterized by excluding from. In the image forming apparatus according to claim 2 or 3.
It is characterized by including a storage means for counting the number of excluded test pattern images and storing the count number, and a notification means for notifying when the count number in the storage means exceeds a predetermined value. Image forming device. In the image forming apparatus according to claim 4,
The pattern generating means generates a test pattern image having a certain width by default, and the determination result by the determining means determines that the number of the test pattern images is a scratch on the second image carrier. The pattern width change mode is entered when the value is reached and becomes inappropriate, and when the width of the test pattern image is not constant in the detection result by the width calculation means even if the number of the test pattern images is appropriate. An image forming apparatus characterized in that. In the image forming apparatus according to claim 5,
The pattern generating means is an image forming apparatus characterized in that the width of the test pattern image is continuously increased by a constant amount of change in the pattern width changing mode. In the image forming apparatus according to claim 6,
The width of the test pattern image excluded by the selection means is stored in the storage means,
The image forming apparatus is characterized in that the pattern generating means generates the test pattern image with a width larger than the width of the test pattern image stored in the storage means. In the image forming apparatus according to claim 7,
The width change calculation means is the difference between the width of the test pattern image of interest and the width of the test pattern image immediately preceding in the generation order adjacent to the test pattern of interest with respect to the amount of change in the width of the test pattern image. If it is assumed that the width of the test pattern image immediately before is due to the scratches on the second image carrier, it is calculated from the difference from the width of the test pattern image immediately before one in the order of generation. An image forming apparatus characterized by In the image forming apparatus according to claim 5,
The pattern generating means is a mode in which when the number of the test pattern images determined by the determining means in the pattern width changing mode becomes equal to or less than a predetermined value, the width of the test pattern images is greatly generated by a constant amount of change. An image forming apparatus characterized by changing from a mode to a mode in which a small amount of change is generated from the image. In the image forming apparatus according to claim 9,
In the pattern width changing mode, the pattern generating means generates a small width of the test pattern image with a constant amount of change if the test pattern images formed in advance overlap, and the test is performed within a range in which the test pattern images do not overlap. An image forming apparatus characterized in that a large width of a pattern image is generated with a constant amount of change.

Images