JP2012159605A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that detects a color-shift detecting pattern more accurately.SOLUTION: In order to correct color-shift that occurs in superimposing images formed in a plurality of image forming parts for forming images of different colors, a color-shift detecting pattern is formed in each image forming part, transferred onto an intermediate transfer belt 5 and read by a detection sensor 7 having a regular reflection light receiving part 201 and a diffused reflection light receiving part 202. Whether the voltage output from the regular reflection light receiving part 201 can detect the color-shift detecting patterns for all colors is determined. When the determination is affirmative, only the regular reflection light receiving part 201 is used for color-shift correction. When the determination is negative, both the regular reflection light receiving part 201 and the diffused reflection light receiving part 202 are used for color-shift correction. The regular reflection light receiving part 201 or the diffused reflection light receiving part 202 is selected therefor.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that performs color image formation, and more particularly to a technique for accurately detecting a color misregistration detection pattern according to the surface state of an image carrier.

  Conventionally, in color image forming apparatuses such as copiers, printers, and facsimiles that employ a tandem method, in order to correct a color shift, which is a shift in the relative formation position of toner images formed on a plurality of photosensitive members, Execute the process. First, the control unit that controls the image forming unit for each color forms a pattern for correcting color misregistration for each color on an image carrier such as an intermediate transfer member (intermediate transfer belt) or a carrier (conveyor belt) that conveys a recording medium. To do.

  The color misregistration detection pattern thus formed is detected by an optical sensor, and the control unit calculates a relative misregistration amount of the color misregistration detection pattern on the image carrier based on the detection result. The control unit controls the image forming timing of the image forming unit for each color based on the calculation result.

  As a method for detecting a color misregistration detection pattern, a method is known in which an optical sensor is disposed in the vicinity of an intermediate transfer member, and the color misregistration detection pattern formed on the intermediate transfer member is detected by the optical sensor. Specifically, the optical sensor irradiates light onto the intermediate transfer member from the light emitting element provided in the optical sensor, and the optical sensor detects the difference in the amount of reflected light between the surface of the intermediate transfer member and the color misregistration detection pattern transferred onto the intermediate transfer member. The color misregistration detection pattern is recognized by detecting it with a photo sensor. As a method for detecting reflected light, there are a regular reflection light detection method and a diffuse reflection light detection method.

  In order to accurately detect the color misregistration detection pattern, it is desirable to detect the color misregistration detection pattern using a single detection means (photosensor). This is because the position (relative position) of the color misregistration correction patterns of a plurality of colors can be accurately and simultaneously detected by using a single detection means (photosensor).

  However, depending on the color of the toner, it may be impossible to detect the color misregistration detection pattern by either the regular reflection light detection method or the irregular reflection light detection method. For example, there is a case where the gloss (surface glossiness) of the intermediate transfer member is reduced by the frictional wear of the intermediate transfer member with a cleaning device or a transfer device. In this case, the regular reflection light detection method cannot detect a color misregistration detection pattern for colors other than black (K) (yellow (Y), magenta (M), cyan (C)). This is due to the following reason.

  That is, the amount of regular reflection from the region where the color misregistration detection pattern is formed is smaller than the amount of regular reflection from the intermediate transfer member itself. Here, the amount of decrease in the amount of specular reflection in the region where the detection patterns for Y, M, and C are formed is smaller than the amount of decrease in the amount of specular reflection in the region where the detection pattern for K is formed. . On the other hand, when the surface glossiness of the intermediate transfer member decreases, the amount of specular reflection from the intermediate transfer member itself decreases. Therefore, when the amount of decrease in the amount of specular reflection in the region where the detection patterns for Y, M, and C are formed becomes equal to the amount of decrease in the amount of specular reflection from the intermediate transfer body itself, The detection pattern cannot be detected.

  Therefore, the specular reflection light detection method and the diffuse reflection light detection method are used in which the specular reflection light detection method is used for black color shift detection pattern detection and the irregular reflection light detection method is used for color shift detection pattern detection for colors other than black. The technique used together is proposed (refer patent document 1).

JP 2007-156159 A

  In the technique described in Patent Document 1, since the regular reflection light detection method and the irregular reflection light detection method are used together, it is possible to detect a color misregistration detection pattern for each color even when the surface glossiness is lowered. However, the technique described in Patent Document 1 uses both the regular reflection light detection method and the irregular reflection light detection method even when the surface state of the intermediate transfer body is capable of pattern detection only by the regular reflection light detection method. Therefore, in order to accurately detect the color misregistration detection pattern, it is not possible to satisfy the demand that it is desirable to perform color misregistration detection pattern detection using a single detection means.

  An object of the present invention is to provide an image forming apparatus that can detect a color misregistration detection pattern more accurately by switching between using a single detection unit or a plurality of detection units.

  An image forming apparatus according to the present invention is an image forming apparatus comprising: an image carrier; and a plurality of image forming units that form toner images of a plurality of colors using different color toners on the image carrier. The plurality of image forming units respectively form a plurality of color misregistration detection patterns for correcting the formation positions of the plurality of color toner images using the different color toners on the image carrier. A light emitting means for irradiating light to the image carrier and the color misregistration detection patterns for a plurality of colors; and regular reflection light from the image carrier and the color misregistration detection patterns for a plurality of colors. Regular reflection light receiving means for outputting a signal corresponding to the intensity of the regular reflection light, and irregular reflection light from the image carrier and the color misregistration detection patterns for a plurality of colors, and the intensity of the received irregular reflection light. Random to output a signal according to the height And detecting the relative positional relationship of the color misregistration detection patterns of a plurality of colors on the image carrier based on a signal output from the regular reflection light reception unit or the irregular reflection light reception unit. Based on the relative positional relationship detected by the detection means, the detection means and the plurality of colors on the image carrier so as to reduce the deviation between the toner images of the plurality of colors on the image carrier. And a correction unit that corrects the formation position of the toner image, and the correction unit outputs a signal output from the regular reflection light receiving unit in response to receiving the regular reflection light from the image carrier. When the output level is equal to or higher than a predetermined level, the formation positions of the toner images of a plurality of colors are corrected based on the relative positional relationship detected based only on the signal from the regular reflection light receiving unit, When the output level is less than the predetermined level, the toner images of a plurality of colors according to the relative positional relationship detected based on the signal from the regular reflection light receiving unit and the signal from the irregular reflection light receiving unit It is characterized in that the formation position of is corrected.

  According to the present invention, when the color misregistration detection patterns for all colors can be detected from the output of the regular reflection light receiving means, only the regular reflection light receiving means is used. Thereby, highly accurate color misregistration correction can be performed. On the other hand, if the color misregistration detection patterns for all colors cannot be detected from the output of the regular reflection light receiving means, color misregistration detection for all colors using the regular reflection light receiving means and the irregular reflection light receiving means. Detect the pattern. Thereby, it is possible to appropriately cope with color misregistration correction when the surface glossiness of the image carrier is lowered. In this way, it becomes possible to continuously perform high-quality image formation.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an exemplary embodiment. FIG. 2 is a diagram illustrating a schematic configuration of a detection sensor included in the image forming apparatus. 2 is a block diagram illustrating an outline of a control system of the image forming apparatus. FIG. FIG. 4 is a diagram illustrating an output voltage signal when a detection sensor detects a color misregistration detection pattern formed on an intermediate transfer belt, and (a) is a diagram when the surface glossiness of the intermediate transfer belt is high, and (b). FIG. 4 is a view when the surface glossiness of the intermediate transfer belt is lowered. It is a figure which shows the signal which binarized the output voltage signal from a pattern detection sensor, (a) is a figure in the case of the output voltage signal from a regular reflection light light-receiving part, (b) is the output from a irregular reflection light light-receiving part. It is a figure in the case of a voltage signal. It is a figure which shows the shift | offset | difference of the detection timing in the signal which binarized the output voltage signal from a pattern detection sensor. It is a figure which shows typically the operation | movement aspect of the switching part with which an image forming apparatus is provided. 3 is a flowchart illustrating a control flow of the image forming apparatus. It is a flowchart which shows the processing flow of the auto registration (step S4) in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, a digital color multifunction peripheral (MFP) using an electrophotographic system is taken up as an image forming apparatus according to the present invention. Note that the dimensions, materials, shapes, relative arrangements, and the like of the components of the image forming apparatus described in the present embodiment are not limited to the forms shown below unless otherwise specified.

<Schematic configuration of image forming apparatus>
FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present embodiment. The image forming apparatus includes a plurality of image forming units for forming a color image by a quadruple tandem method. That is, the image forming apparatus has an equivalent structure for forming toner images of different colors, that is, yellow (Y), cyan (C), magenta (M), and black (K) in order from the left side of FIG. Are formed in a line. In each image forming unit, an electrostatic latent image is formed on the photosensitive drums 1a, 1b, 1c, and 1d by the laser writing units 15a, 15b, 15c, and 15d, and the formed electrostatic latent images are developed by the developing devices 16a, 16b, The toner is developed by 16c and 16d to form a toner image.

  The Y, C, M, and K toner images respectively formed on the photosensitive drums 1a to 1d are sequentially superimposed and transferred onto the image carrier. In the present embodiment, the image carrier is the intermediate transfer belt 5. Accordingly, the Y, C, M, and K toner images are sequentially transferred onto the intermediate transfer belt 5 so as to form a color toner image 6. The color toner image 6 is transferred onto the paper P that has been transported through the paper transport path at the contact portion (transfer position) between the belt support roller 3 and the transfer roller 4. The paper P onto which the color toner image 6 has been transferred in this manner is sent to a fixing unit (not shown) by the transport belt 12, where the toner image is fixed on the paper P, and then discharged outside the image forming apparatus. (Discharged).

  In the image forming apparatus according to the present embodiment, a color misregistration correction pattern image (hereinafter referred to as “color misregistration detection pattern”) for correcting the formation position of each color toner image at each image forming unit at a predetermined timing. Are transferred onto the intermediate transfer belt 5. The predetermined timing is, for example, when the number of printed sheets reaches a predetermined fixed number.

  A detection sensor 7 for detecting a color misregistration detection pattern is disposed in the vicinity of the intermediate transfer belt 5. The detection sensor 7 detects (reads) the color misregistration detection pattern transferred onto the intermediate transfer belt 5 and obtains the relative positional relationship between the color misregistration detection patterns. Based on the result, as will be described later, color misregistration correction (auto registration) is performed in each image forming unit so as to correct the toner image forming position of each color so that the misregistration between toner images is reduced.

<Schematic configuration of detection sensor 7>
FIG. 2 is a diagram showing a schematic configuration of the detection sensor 7. The detection sensor 7 receives a light emitting element 200 as a light emitting unit that emits light to the irradiation target, a regular reflection light receiving unit 201 that receives regular reflection light from the irradiation target, and irregular reflection light from the irradiation target. A diffusely reflected light receiving unit 202. In this embodiment, the irradiation target is the intermediate transfer belt 5 and the color misregistration detection pattern transferred onto the intermediate transfer belt 5.

  In the detection sensor 7, the incident angle and the reflection angle are equal so that the regular reflection light receiving unit 201 can receive regular reflection light when light is emitted from the light emitting element 200 to the intermediate transfer belt 5 at a constant angle. The light emitting element 200 and the regular reflection light receiving unit 201 are arranged at the position. Further, the irregular reflection light receiving unit 202 is disposed at a position where the incident angle and the reflection angle are not equal so that irregular reflection light from the intermediate transfer belt 5 can be received.

  An analog voltage signal corresponding to the amount of reflected light received from the surface of the intermediate transfer belt 5 itself and the color misregistration detection pattern formed on the surface of the intermediate transfer belt 5 is output from the detection sensor 7 by photoelectric conversion. Is output. The first signal generation comparator 203 that is the first signal generation unit and the second signal generation comparator 204 that is the second signal generation unit illustrated in FIG. 2 will be described later with reference to FIG.

  When the detection sensor 7 is assembled, the optical axes of the light emitting element 200, the regular reflection light receiving unit 201, and the irregular reflection light receiving unit 202 are adjusted. However, the optical axis adjustment at the time of assembling the detection sensor 7 is an adjustment based on the design value. Actually, variations due to machine differences (optical axis deviation) occur, and when the color deviation is corrected, the regular reflection light receiving unit 201 and the irregular reflection light are corrected. There is a possibility that the detection timing is deviated from the light receiving unit 202. In the present embodiment, as described later, a detection timing shift (optical axis shift amount) due to an optical axis shift is held as an offset and used for signal correction in color shift correction.

<Control system of image forming apparatus>
FIG. 3 is a block diagram illustrating an outline of a control system of the image forming apparatus. The CPU 109 is the center of the control system and controls various commands. The control of the CPU 109 is performed based on program data stored in the ROM 110.

  As described above, the detection sensor 7 is a reflective optical sensor for detecting a color misregistration detection pattern formed by toner of each color (Y, M, C, K) on the intermediate transfer belt 5, and is a regular reflection. The light receiving unit 201 and the irregular reflection light receiving unit 202 are provided. As shown in FIG. 2, the output voltage signal from the regular reflection light receiving unit 201 is input to the first signal generation comparator 203, and the output voltage signal from the irregular reflection light reception unit 202 is input to the second signal generation comparator 204. Is done.

  The first signal generation comparator 203 compares the magnitude (output level) of the output voltage signal input from the regular reflection light receiving unit 201 with a predetermined threshold value (first threshold value), and binarizes the first signal generation comparator 203. 1 digital signal is output. Similarly, the second signal generation comparator 204 compares the magnitude (output level) of the output voltage signal input from the irregularly reflected light receiving unit 202 with a predetermined threshold value (second threshold value), and binarizes it. The second digital signal is output. Details of these processes will be described later with reference to FIG.

  As shown in FIG. 3, both the output voltage signal from the regular reflection light receiving unit 201 and the output voltage signal from the irregular reflection light receiving unit 202 are input to the A / D converter 205. The A / D converter 205 converts an analog output voltage signal input from the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 into a digital signal.

  The ASIC 101 is a digital integrated circuit including various arithmetic units for performing color misregistration correction based on the detection result of the detection sensor 7. The ASIC 101 includes a pattern generation unit 102, a pattern reading control unit 103, a color misregistration amount calculation unit 104, a color misregistration correction unit 105, a surface state calculation unit 106, an offset detection unit 107, and a switching unit 108.

  The pattern generation unit 102 generates image data of a color misregistration detection pattern that is generated when auto-registration is executed. The pattern reading control unit 103 reads binary output signals (first digital signal and second digital signal) output from the first signal generation comparator 203 and the second signal generation comparator 204, respectively, and temporarily Store data in. A method of generating the first digital signal and the second digital signal in the first signal generation comparator 203 and the second signal generation comparator 204 will be described later with reference to FIGS.

  The color misregistration amount calculation unit 104 calculates a color misregistration detection pattern misregistration (color misregistration amount) for each color based on the read pattern data. The pattern data is a first digital signal and a second digital signal output from the first signal generation comparator 203 and the second signal generation comparator 204. In the color misregistration correction unit 105, based on the color misregistration amount calculated by the color misregistration amount calculation unit 104, the laser writing units 15a, 15b, 15c, and 15d apply electrostatic latent images to the photosensitive drums 1a, 1b, 1c, and 1d. The write timing or the like for forming the pattern is corrected. As a result, the toner image formation position on each of the photosensitive drums 1a, 1b, 1c, and 1d is corrected.

  The surface state calculation unit 106 calculates the surface glossiness of the intermediate transfer belt 5 based on the digital signal acquired from the A / D converter 205. As will be described later, the surface glossiness is a value that is compared with a switching criterion for determining whether the area is a pattern detectable area or a pattern undetectable area. As will be described later with reference to FIG. 5, the offset detection unit 107 reads the same color misregistration detection pattern by the light receiving unit (the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202) of the detection sensor 7. The detection timing shift between the light receiving units is calculated and stored.

  The switching unit 108 performs color misregistration correction by detecting a color misregistration detection pattern using only the regular reflection light receiving unit 201 based on the calculated value of the surface state calculation unit 106, or the regular reflection light receiving unit 201 and the irregular reflection light receiving unit. In 202, the color misregistration detection pattern is detected and the color misregistration correction is switched. Details of the switching control by the switching unit 108 will be described later with reference to FIGS.

<Output signal from detection sensor 7>
FIG. 4 is a diagram illustrating an output voltage signal when the detection sensor 7 detects a color misregistration detection pattern formed on the intermediate transfer belt 5. FIG. 7A shows a case where the surface glossiness of the intermediate transfer belt 5 is high, and FIG. 7B shows a case where the surface glossiness of the intermediate transfer belt 5 is low.

  As shown in FIG. 4A, when the surface glossiness of the intermediate transfer belt 5 is high, the reflected light from the surface of the intermediate transfer belt 5 itself has a large amount of specularly reflected light components. The output voltage (analog output) from becomes larger. On the other hand, since the specular reflection light component is reduced where the Y, M, C, and K color misregistration detection patterns are formed, the output voltage from the specular reflection light receiving unit 201 becomes small, and the K color misregistration detection is performed. In particular, the output voltage is reduced where the use pattern is formed.

  Further, when the surface glossiness of the intermediate transfer belt 5 is high, the reflected light from the surface of the intermediate transfer belt 5 itself has a small amount of irregularly reflected light components, so the output voltage from the irregularly reflected light receiving unit 202 becomes small. Here, when the color misregistration detection patterns of Y, M, and C are formed, the output voltage from the irregularly reflected light receiving unit 202 increases because the irregularly reflected light component increases. On the other hand, where the K color misregistration detection pattern is formed, there is less diffuse reflection light component than where the other color misregistration detection patterns are formed. Therefore, the output voltage from the irregular reflection light receiving unit 202 corresponding to the place where the K color misregistration detection pattern is formed is from the irregular reflection light receiving unit 202 corresponding to the irregular reflection light component from the surface of the intermediate transfer belt 5 itself. The output voltage is almost the same.

  As shown in FIG. 4B, when the surface glossiness of the intermediate transfer belt 5 is low, the reflected light component from the surface of the intermediate transfer belt 5 itself has less specularly reflected light components. The output voltage from the light receiving unit 201 becomes small. Here, when the Y, M, and C color misregistration detection patterns are formed on the intermediate transfer belt 5, the specular reflection light component is reduced. Therefore, the output voltage from the regular reflection light receiving unit 201 corresponding to the position where the Y, M, and C color misregistration detection patterns are formed is regular reflection with respect to the regular reflection light component from the surface of the intermediate transfer belt 5 itself. The output voltage from the light receiving unit 201 is almost equal to the output voltage. On the other hand, the output voltage from the regular reflection light receiving unit 201 corresponding to the place where the K color misregistration detection pattern is formed is the regular reflection light receiving unit 201 for the regular reflection light component from the surface of the intermediate transfer belt 5 itself. The output voltage is further smaller than the output voltage.

  In addition, when the surface glossiness of the intermediate transfer belt 5 is low, the reflected light from the surface of the intermediate transfer belt 5 itself has a small amount of irregularly reflected light components, so the output voltage from the irregularly reflected light receiving unit 202 becomes small. Here, where the Y, M, and C color misregistration detection patterns are formed on the intermediate transfer belt 5, the irregular reflection light component increases, and the output voltage from the irregular reflection light receiving unit 202 increases. On the other hand, where the K color misregistration detection pattern is formed, there is less diffuse reflection light component than where the other color misregistration detection patterns are formed. Therefore, the output voltage from the irregular reflection light receiving unit 202 corresponding to the place where the K color misregistration detection pattern is formed is from the irregular reflection light receiving unit 202 corresponding to the irregular reflection light component from the surface of the intermediate transfer belt 5 itself. The output voltage is almost the same.

  The first threshold value and the second threshold value shown in FIG. 4 will be described below with reference to FIG.

<Binarization of output voltage signal from detection sensor 7>
FIG. 5 is a diagram showing a signal obtained by binarizing the output voltage signal from the detection sensor 7. FIG. 5A shows the output voltage signal from the regular reflection light receiving unit 201, and FIG. 5B shows the irregular reflection light receiving unit. Each of the output voltage signals from 202 is shown. As described above, the process of binarizing the output voltage signal from the detection sensor 7 is executed by the first signal generation comparator 203 and the second signal generation comparator 204.

  As previously shown in FIG. 4, the magnitude of the specular reflection light component of the reflected light from the surface of the intermediate transfer belt 5 itself changes under the influence of the surface glossiness of the intermediate transfer belt 5, so that the regular reflection The magnitude of the output voltage (output voltage value) from the light receiving unit 201 indicates a value reflecting this change. Therefore, as shown in FIG. 5A, the output voltage value from the regular reflection light receiving unit 201 accompanying the detection of the regular reflection light component of the reflected light from the surface of the intermediate transfer belt 5 itself is the first voltage value. As a threshold setting reference, a first threshold value smaller than this is set.

  Since the output voltage value from the regular reflection light receiving unit 201 serving as the first threshold setting reference changes according to the change in the amount of regular reflection light component from the surface of the intermediate transfer belt 5 itself, the absolute value of the first threshold value is As the absolute value of the first threshold setting reference changes, the difference changes so as to be constant. That is, the absolute value of the first threshold is not always constant, and as shown in FIGS. 4A and 4B, the difference between the first threshold setting reference and the first threshold is always constant. Is set.

  The first signal generation comparator 203 determines whether or not the peak value of the output voltage value from the regular reflection light receiving unit 201 is equal to or less than the first threshold value. In this case, the first digital signal binarized to “0” is output.

  Similarly, as shown in FIG. 5B, the output voltage value from the irregularly reflected light receiving unit 202 when the irregularly reflected light component of the reflected light from the surface of the intermediate transfer belt 5 itself is detected is set to the second threshold value. As a setting reference, the second threshold is set to a value larger than this. Similar to the first threshold, the absolute value of the second threshold is not always constant, and is set so that the difference between the second threshold setting reference and the second threshold is always constant. As shown in a) and (b), the change in the absolute value of the second threshold is extremely small compared to the change in the absolute value of the first threshold. The second signal generation comparator 204 determines whether or not the peak value of the output voltage value from the irregularly reflected light receiving unit 202 is equal to or greater than the second threshold value. Outputs a second digital signal binarized to “0”.

<Correction of detection timing shift in detection sensor 7>
FIG. 6 illustrates a binarized signal (first and second) based on a detection timing shift between the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 when the detection sensor 7 detects a color misregistration detection pattern. It is a figure which shows the shift | offset | difference of the detection timing in (digital signal).

  The color misregistration correction is performed based on the detection timing when the regular reflection light receiving unit 201 reads the color misregistration detection pattern and the detection timing when the irregular reflection light receiving unit 202 reads the color misregistration detection pattern. Here, as described above, due to the optical axis shift or the like in the detection sensor 7, the detection timing when one color shift detection pattern is read by the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 is shifted. Sometimes. In this case, if the detection timing is not corrected, the misregistration detection pattern whose position is shifted although the specular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 detect the same misregistration detection pattern. Therefore, accurate color misregistration correction cannot be performed. Therefore, a detection timing shift caused by an optical axis shift or the like is held as an offset and used for color shift correction.

  Specifically, as shown in FIG. 6, the difference between the center of gravity of the pulse (“1” signal) in the first digital signal and the center of gravity of the pulse (“1” signal) in the second digital signal. Is calculated as an offset value, and the value is held.

<Switching of light receiving part in detection sensor 7>
FIG. 7 is a diagram schematically illustrating the operation of the switching unit 108, that is, the operation mode of switching the light receiving unit used for color misregistration correction between the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 of the detection sensor 7. is there.

  The magnitude of the output voltage from the regular reflection light receiving unit 201 representing the surface glossiness of the intermediate transfer belt 5 decreases with the passage of the endurance time (that is, over time as the image forming apparatus is used). To go. For this reason, in the pattern detectable region where the magnitude of the output voltage from the regular reflection light receiving unit 201 is such that the color misregistration detection patterns for all colors can be detected, the output voltage from the regular reflection light receiving unit 201. Auto register using only the signal. On the other hand, when the output voltage signal from the regular reflection light receiving unit 201 is not large enough to detect the color misregistration detection patterns for all colors, the regular reflection light receiving unit 201 and the irregular reflection are not detected. Auto-registration is performed using voltage signals respectively output from the light receiving unit 202.

  A switching reference (predetermined level) for determining whether the area is a pattern detectable area or a pattern undetectable area is predetermined in the image forming apparatus. As described above, the output voltage signal from the regular reflection light receiving unit 201 is input to the A / D converter 205, and the A / D converter 205 converts the input output voltage signal into a digital signal to the CPU 109 and the ASIC 101. Output. The surface state calculation unit 106 of the ASIC 101 calculates the surface glossiness, and the CPU 109 determines whether or not the surface glossiness is equal to or higher than the switching reference.

  Based on the determination result by the CPU 109, the switching unit 108 performs auto registration using only the output voltage signal from the regular reflection light receiving unit 201, or is output from the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202, respectively. Switch between using voltage signal. Note that the switching unit 108 may determine whether the magnitude of the output voltage signal from the regular reflection light receiving unit 201 is greater than or equal to the switching reference.

<Control of image forming apparatus>
FIG. 8 is a flowchart showing a control flow of the image forming apparatus. Control of the image forming apparatus is realized by causing the CPU 109 to execute a program stored in the ROM 110 on the RAM and executing various controlled units constituting the image forming apparatus in accordance with commands from the CPU 109. The

  First, the CPU 109 determines whether or not a print job has been input in order to detect the start of the print job (step S1). If no print job has been input (“YES” in S1), input of the print job is awaited in step S1, and if a print job has been input (“YES” in S1), the printing operation is started (step S2). .

  After starting the printing operation, the CPU 109 determines whether or not the total number of prints (the total number of prints including the number of print jobs before the print job) has reached a predetermined fixed number (step S3). When the predetermined number is reached (“YES” in S3), the CPU 109 performs auto registration (step S4). When auto registration is performed, the count of the total number of prints is reset to zero. When the predetermined number of sheets has not been reached (“NO” in S3) and after the end of auto registration, the CPU 109 determines whether or not the print job has ended (step S5). If the print job is finished (“YES” in S5), the process is finished. If the print job is not finished (“NO” in S5), the process is returned to step S3, and the remaining print job A printing operation is executed for.

<Auto cash register processing flow>
FIG. 9 is a flowchart showing a processing flow of the automatic registration (step S4) in FIG. When auto registration is started, first, the surface state of the intermediate transfer belt 5 is detected, and the surface state calculation unit 106 obtains the surface glossiness of the intermediate transfer belt 5 (step S11). Specifically, first, the regular reflection light receiving unit 201 detects specular reflection light from the surface of the intermediate transfer belt 5 when the light is emitted from the light emitting element 200 to the intermediate transfer belt 5. The output voltage from 201 is converted into a digital signal by the A / D converter 205. The surface state calculation unit 106 obtains the surface glossiness from this digital signal.

  Next, the CPU 109 determines whether or not the surface glossiness obtained in step S11 is greater than or equal to the switching reference (step S12). When the surface glossiness is equal to or higher than the switching reference (“YES” in S12), the control of “first auto registration control” is performed in which only the regular reflection light receiving unit 201 is used to detect the color misregistration detection pattern and perform auto registration. enter. On the other hand, when the surface glossiness is less than the switching reference (“NO” in S12), the color registration detection pattern is detected using both the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 to perform auto registration. The control enters "second auto registration control". Switching between using only the regular reflection light receiving unit 201 or using both the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 is performed by the switching unit 108 that receives a command from the CPU 109.

[First auto register control]
Whether or not the offset detection unit 107 holds an offset value between these light receiving units in order to confirm whether or not there is a deviation in the detection timing of each of the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 Is confirmed (step S13).

  When the offset value is held (“YES” in S13), since the misregistration detection patterns for all colors can be detected only by the regular reflection light receiving unit 201, only the regular reflection light receiving unit 201 is used. Use it for auto register. As the procedure, first, a color misregistration detection pattern for each color is formed on the intermediate transfer belt 5 (step S14), and the color misregistration detection pattern is detected using the regular reflection light receiving unit 201 (step S15).

  The output voltage signal output from the regular reflection light receiving unit 201 is binarized by the first signal generation comparator 203 and converted into a first digital signal. The first digital signal is temporarily stored in the pattern reading control unit 103, and the color misregistration amount is determined using the offset value held in the offset detection unit 107 and the read pattern data (first digital signal). Calculated (step S16). Based on the color misregistration amount thus calculated, the writing timing is corrected (step S17), and thus the auto registration is completed.

  If the offset value between the light receiving portions is not held (“NO” in S13), a color misregistration detection pattern for each color is formed on the intermediate transfer belt 5 (step S18). Subsequently, a color misregistration detection pattern is detected using the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 (step S19). The output voltage signal from the regular reflection light receiving unit 201 is binarized by the first signal generation comparator 203 and converted into a first digital signal, and the output voltage signal from the irregular reflection light reception unit 202 is converted to the second signal generation comparator 204. Is binarized and converted into a second digital signal.

  The first digital signal is temporarily stored in the pattern reading control unit 103, and the color misregistration amount is calculated based on the read pattern data (first digital signal) (step S20). Based on the color misregistration amount thus calculated, the writing timing is corrected (step S21). Further, the offset detection unit 107 compares the first digital signal and the second digital signal to obtain a detection timing shift amount between the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202, and the offset. It holds as a value (step S22).

[Second auto register control]
In the second auto registration control, first, a color misregistration detection pattern for each color is formed on the intermediate transfer belt 5 (step S23). Subsequently, the K color misregistration detection pattern is detected using the regular reflection light receiving unit 201, and the Y, M, and C color misregistration detection patterns are detected using the irregular reflection light receiving unit 202 (step S24). . The output voltage signal from the regular reflection light receiving unit 201 is binarized by the first signal generation comparator 203 and converted into a first digital signal, and the output voltage signal from the irregular reflection light reception unit 202 is converted to the second signal generation comparator 204. Is binarized and converted into a second digital signal.

  The first digital signal and the second digital signal are temporarily stored in the pattern reading control unit 103, and the amount of color misregistration is based on the read pattern data (first digital signal and second digital signal). Calculated (step S25). Next, the detection timing is corrected using the offset value derived during the first auto registration control (step S26), and the writing timing is corrected based on the corrected color misregistration amount (step S27). .

  As described above, in the image forming apparatus according to the present embodiment, when the regular reflection light amount detected by the regular reflection light receiving unit 201 is larger than a predetermined value, automatic registration is performed based only on the detected regular reflection light amount. . As a result, it is possible to eliminate the influence of the optical axis deviation between the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202, and to detect a color misregistration detection pattern with high accuracy, and as a result, high image quality. Image formation can be performed.

  Further, by detecting the same color misregistration detection pattern by the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 during the first auto registration control, the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 are detected. An offset value is detected by detecting a shift in the detection timing. As a result, it is not necessary to perform a special process for detecting a shift in the detection timing, and therefore no increase in downtime occurs.

<Modification of Image Forming Apparatus>
In the above-described embodiment, the method of forming a color misregistration detection pattern on the intermediate transfer belt 5 and performing automatic registration has been described. However, the present invention is not limited to this, and a method for creating a color misregistration detection pattern on continuous paper and performing auto registration, and a method for creating a color misregistration detection pattern on paper conveyed by a paper conveyance belt and performing auto registration, The present invention is applicable. In the above embodiment, an image forming apparatus that performs printing using an electrophotographic process has been described as an example. However, the present invention is not limited to this, and can be applied to, for example, an inkjet image forming apparatus. It is.

  Furthermore, in the above-described embodiment, the configuration for detecting the color misregistration detection pattern is performed by the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202. However, the density of the color misregistration detection pattern may be detected. That is, the density detection of each of the Y, M, and C color misregistration detection patterns is performed by the amount of light incident on the irregular reflection light receiving unit 202, and the density detection of the K color misregistration detection pattern is incident on the regular reflection light receiving unit 201. Depending on the amount of light to be used, a method may be employed.

  In the above-described embodiment, a digital signal binarized based on a preset threshold value is generated from the output voltage signals from the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202, and the barycenter of the pulse in this digital signal is generated. Auto-registration was performed by calculating the position. However, the present invention is not limited to this, and a configuration may be adopted in which automatic registration is performed by detecting the peak value of the output voltage signal from the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 and generating a binarized digital signal. .

  In the above-described embodiment, the surface glossiness of the intermediate transfer belt 5 is detected by the regular reflection light receiving unit 201. However, the surface property detection target is not limited to the glossiness. The unit 202 may be used, or a detection unit may be provided separately. Furthermore, in the above-described embodiment, the surface glossiness that has decreased with time, such as the intermediate transfer belt 5, is detected, but the surface glossiness increases with time. A detection target that does not change linearly can also be used. Furthermore, in the above embodiment, the detection timing shift between the regular reflection light receiving unit 201 and the irregular reflection light receiving unit 202 is caused by the shift of the optical axis. However, the light receiving elements used in these light receiving units The detection timing may be shifted due to characteristics or circuit characteristics.

<Other embodiments>
Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. Furthermore, each embodiment mentioned above shows only one embodiment of this invention, and it is also possible to combine each embodiment suitably.

  The present invention can also be realized by executing the following processing. That is, software (program) for realizing the functions of the above-described embodiments is supplied to the image forming apparatus via a network or various storage media, and the computer (or CPU, MPU, etc.) of the image forming apparatus reads the program code. It is a process to be executed. In this case, the program and the storage medium storing the program constitute the present invention.

1a, 1b, 1c, 1d Photosensitive drum 5 Intermediate transfer belt 7 Pattern detection sensor 101: ASIC
DESCRIPTION OF SYMBOLS 102 Pattern production | generation part 103 Pattern reading control part 104 Color misregistration amount calculation part 105 Color misregistration correction part 106 Surface state calculation part 108 Switching part 109 CPU
201 specular reflection light receiving unit 202 irregular reflection light receiving unit 203 first signal generation comparator 204 second signal generation comparator

Claims (5)

An image forming apparatus comprising: an image carrier; and a plurality of image forming units that form toner images of a plurality of colors using different color toners on the image carrier,
Each of the plurality of image forming units forms a plurality of color misregistration detection patterns for correcting the formation positions of the plurality of color toner images on the image carrier using the different color toners.
Light emitting means for irradiating light to the image carrier and the color misregistration detection patterns of a plurality of colors; and regular reflection light from the image carrier and the color misregistration detection patterns of a plurality of colors are received and the received positive Regular reflection light receiving means for outputting a signal corresponding to the intensity of the reflected light, and irregular reflection light from the image carrier and the color misregistration detection pattern for a plurality of colors are received, and the intensity of the received irregular reflection light is measured. An irregular reflection light receiving means for outputting a corresponding signal, and the color misregistration detection pattern of a plurality of colors on the image carrier based on the signal output from the regular reflection light reception means or the irregular reflection light reception means Detecting means for detecting the relative positional relationship between
Based on the relative positional relationship detected by the detection means, the toner images of the plurality of colors on the image carrier are reduced based on the relative positional relationship detected by the detection unit so that the deviation between the toner images of the plurality of colors on the image carrier is reduced. Correction means for correcting the formation position,
When the output level of a signal output from the regular reflection light receiving unit in response to receiving regular reflection light from the image carrier is equal to or higher than a predetermined level, the correction unit receives the regular reflection light receiving unit. When the output positions of the toner images of a plurality of colors are corrected based on the relative positional relationship detected based only on the signal from the output signal and the output level is less than the predetermined level, the regular reflected light receiving unit An image forming apparatus that corrects the formation positions of the toner images of a plurality of colors in accordance with the relative positional relationship detected based on the signal of 1 and the signal from the irregularly reflected light receiving means.   The predetermined level is a magnitude indicating that an output level of a signal output from the regular reflection light receiving unit cannot detect the color misregistration detection pattern by the regular reflection light receiving unit. The image forming apparatus according to claim 1, wherein:   When the output level of the signal output from the regular reflection light receiving unit when the regular reflection light receiving unit detects reflected light from the image carrier itself is equal to or higher than the predetermined level, An offset that is detected by using the regular reflection light receiving means and the irregular reflection light receiving means, and that is held as an offset value, by detecting the amount of detection timing shift caused by the optical axis deviation between the regular reflection light receiving means and the irregular reflection light receiving means. The image forming apparatus according to claim 1, further comprising a detection unit.   When the output level of the signal output from the regular reflection light receiving means when the regular reflection light receiving means detects reflected light from the image carrier itself is smaller than the predetermined level, the correction means 4. The image according to claim 3, wherein a deviation in detection timing between the regular reflection light receiving means and the irregular reflection light receiving means is corrected using the offset value held in the offset detection means. Forming equipment. The plurality of colors are yellow, magenta, cyan, black,
The detection means detects the formation position of the black color misregistration detection pattern by the regular reflection light receiving means when the output level of the signal output from the regular reflection light receiving means is less than the predetermined level. 5. The image forming apparatus according to claim 1, wherein the formation positions of the respective color misregistration detection patterns of yellow, yellow, magenta, and cyan are detected by the irregularly reflected light receiving unit.

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