JP5812717B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that corrects color misregistration in color image formation.

  In a color image forming apparatus adopting the tandem method, in order to correct the deviation of the image forming position for each color from the target position, a pattern for color misregistration correction is formed by each image forming unit corresponding to each color and detected. Thus, the color misregistration correction is performed by deriving the color misregistration amount. The light output from the light emitting element is reflected by the pattern formed on the intermediate transfer member and received by the light receiving element. According to Patent Document 1, an invention has been proposed in which color misregistration is detected using a light receiving element that receives specularly reflected light from a pattern and a light receiving element that receives diffusely reflected light.

  An error in pattern detection timing may occur between the two light receiving elements. Due to machine differences that occur when the two light receiving elements are assembled or attached to the main body, the timing at which the two light receiving elements output signals is deviated even though the same pattern is detected. According to Patent Document 1, it is described that the same pattern is read by two light receiving elements, an offset amount between detection timings is determined, and the detection timings of the two light receiving elements are corrected according to the offset amount.

JP 2007-156159 A

  Usually, the pattern can be recognized because there is a difference between the amount of specular reflection from the intermediate transfer member and the amount of specular reflection from the toner. The same applies to the amount of irregularly reflected light. However, if the intermediate transfer member is worn by rubbing against a cleaning device or a transfer device, the pattern cannot be detected. This is because the surface state of the intermediate transfer member changes and the surface gloss decreases. Thus, when the gloss reduction occurs, the number of toner patterns that can be detected by both the regular reflection light detection unit and the irregular reflection light detection unit is reduced.

  For example, before the gloss reduction, the regular reflection detection unit can detect yellow, magenta, cyan, and black toner patterns, and the irregular reflection detection unit can detect yellow, magenta, and cyan toner patterns. Therefore, before the gloss reduction, a detection timing error between the regular reflection detection unit and the irregular reflection detection unit can be corrected by using a toner pattern of yellow, magenta, or cyan. On the other hand, after the gloss reduction, the regular reflection detection unit can detect only black, and the irregular reflection detection unit can detect only yellow, magenta, and cyan toner patterns. Therefore, there is no toner pattern that can be detected in common between the regular reflection detection unit and the irregular reflection light detection unit. That is, the invention described in Patent Document 1 has a problem that it does not function after the gloss is lowered.

  Accordingly, an object of the present invention is to detect and correct color misregistration even when the surface state of an image carrier deteriorates.

According to the present invention,
First image forming means for forming a first toner image using black toner;
A second image forming means for forming a second toner image using a color toner different from the black toner;
An image carrier to which the first toner image and the second toner image are transferred;
First measuring means for measuring specularly reflected light from a toner pattern formed on the image carrier;
A second measuring means for measuring irregularly reflected light from the toner pattern formed on the image carrier;
Correction condition deriving means for obtaining a correction condition for aligning the positions of the first toner image and the second toner image based on the measurement result of the first measurement means and the measurement result of the second measurement means;
Based on the measurement result of the first measurement unit and the measurement result of the second measurement unit with respect to the same timing correcting toner pattern, the difference between the measurement timing of the first measurement unit and the measurement timing of the second measurement unit is corrected. Correction condition determining means for obtaining correction conditions;
The correction condition determining means is a single color toner pattern using the color toner without using the black toner as the timing correction toner pattern based on the measurement result of the surface of the image carrier by the first measuring means. Or a multi-color toner pattern using the black toner and the color toner is determined.
An image forming apparatus is provided.

According to the present invention, it is possible to detect and correct color misregistration even if the surface state of the image carrier deteriorates .

Schematic illustrating the configuration of an image forming unit in the image forming apparatus The figure which shows the optical relationship between a light emitting element, a regular reflection light receiving element, and a irregular reflection light receiving element Control block diagram (A) is a diagram showing a sensor output signal when a pattern is detected before the endurance of the intermediate transfer belt, and (b) is a diagram showing a sensor output signal when a pattern is detected after the endurance of the intermediate transfer belt. (A) is a diagram showing a signal obtained by binarizing the signal detected by the regular reflection light receiving element, and (b) is a diagram showing a signal obtained by binarizing the signal detected by the irregular reflection light receiving element. The figure which shows the timing which switches the pattern which detects the offset value between light-receiving parts. (A) is a figure which shows detection timing correction between two light-receiving parts in a single color pattern, (b) is a figure which shows detection timing correction between two light-receiving parts in a several color pattern FIG. 5A is a timing chart for forming a detection timing correction pattern in a single color, and FIG. 5B is a timing chart for forming a detection timing correction pattern in a plurality of colors. (A) is a flowchart showing the printing operation of the copying machine, (b) is a flowchart showing the offset detection operation between the light receiving sections, (c) is a flowchart showing the color misregistration correction operation (auto registration)

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified.

  In FIG. 1, an image forming apparatus 100 includes four image forming stations arranged in the order of yellow (Y), cyan (C), magenta (M), and black (K). Of reference numerals, YMCK is omitted when describing common items. One image forming station includes a laser writing unit 15, a photosensitive drum 1 as an image carrier, and a developing device 16. The laser writing unit 15 exposes the surface of the photosensitive drum 1 to form a latent image. The developing device 16 develops the latent image using toner of a predetermined color to form a visible image (toner image). The toner images of the respective colors formed on the photosensitive drums 1Y, 1M, 1C, and 1K are sequentially superimposed and transferred onto the intermediate transfer belt 5. Thereby, a color toner image 6 is formed. The color toner image 6 is transferred onto the paper at the junction (transfer position) between the belt support roller 3 and the transfer roller 4. The sheet is sent to the fixing unit by the conveyance belt 12. The fixing unit fixes the toner image on the paper. The pattern detection sensor 7 is arranged in the vicinity of the intermediate transfer belt 5, reads the color misregistration correction pattern of each color formed on the intermediate transfer belt 5, and outputs a signal corresponding to the reading level.

  As shown in FIG. 2, the pattern detection sensor 7 detects the color misregistration amount using both the regular reflection light receiving element 201 and the irregular reflection light receiving element 202. As described above, depending on the color of the toner, the difference between the regular reflection light amount from the intermediate transfer belt 5 and the regular reflection light amount from the toner cannot be detected. Further, depending on the color of the toner, there may be a case where the difference between the amount of irregularly reflected light from the intermediate transfer belt 5 and the amount of irregularly reflected light from the toner cannot be detected. Therefore, all patterns can be detected by using both the regular reflection light receiving element 201 and the irregular reflection light receiving element 202. Since all patterns can be detected, color misregistration between colors can be detected. Color misregistration is a phenomenon in which the image forming position of each color deviates from the target position.

  The light emitting element 200 is an example of a light emitting unit that emits light to a plurality of patterns of different colors formed on a target member. The incident angle θ1 of the light emitted from the light emitting element 200 to the surface of the intermediate transfer belt 5 is equal to the reflection angle θ2 of the regular reflected light. The regular reflection light receiving element 201 is disposed at a position where it can receive regular reflection light reflected by the pattern. The irregular reflection light receiving element 202 is arranged at a position where irregular reflection light can be received from the surface of the intermediate transfer belt 5. The reflection angle θ3 of the irregular reflection light is different from the reflection angle θ2 of the regular reflection light. Usually, in order to receive regular reflection light and irregular reflection light from the same pattern at the same timing, the optical path length of regular reflection light and the optical path length of irregular reflection light are equal to each other. The diffusely reflected light receiving element 202 is positioned.

  When the pattern detection sensor 7 is assembled, the optical axes of the respective light emitting elements 200, regular reflection light receiving elements 201 and irregular reflection light receiving elements 202 are adjusted. However, since this optical axis adjustment is based on the design value, there is actually a machine difference. Therefore, the optical axis shift occurs. When the optical axis is shifted, there is a time lag between the detection timing of the regular reflection light receiving element 201 and the detection timing of the irregular reflection light receiving element 202 even though the same pattern is detected. Due to such a detection timing shift, the detection result of the color misregistration correction pattern is not a pure color shift but a blur that includes a detection timing shift in addition to the color shift. Therefore, the detection timing deviation is corrected by the control described later.

  In FIG. 2, the pattern detection sensor 7 converts the amount of light received from the surface of the intermediate transfer belt 5 or the toner pattern formed thereon into a voltage and outputs the voltage. An output signal output from the regular reflection light receiving element 201 is input to the first signal generation comparator 203. The output signal output from the irregularly reflected light receiving element 202 is input to the second signal generation comparator 204. The first signal generation comparator 203 outputs a first digital signal binarized according to whether or not the voltage level of the input signal exceeds a predetermined threshold value. The first signal generation comparator 203 is an example of second signal generation means that generates and outputs an output signal when the signal level of the signal output from the second light receiving element exceeds a second threshold value. The second signal generation comparator 204 outputs a second digital signal binarized according to whether or not the voltage level of the input signal is below a predetermined threshold. The second signal generation comparator 204 is an example of first signal generation means that generates and outputs an output signal when the signal level of the signal output from the first light receiving element is lower than the first threshold value. The regular reflection light receiving element 201 and the first signal generation comparator 203 are first light receiving means for receiving a first reflection component from the pattern. The irregularly reflected light receiving element 202 and the second signal generation comparator 204 are second light receiving means for receiving a second reflection component having a reflection angle different from that of the first reflection component.

  The control block in an Example is demonstrated using FIG. The output signal from the regular reflection light receiving element 201 and the output signal from the irregular reflection light receiving element 202 are also input to the A / D converter 315. The A / D converter 315 converts analog output signals from the regular reflection light receiving element 201 and the irregular reflection light receiving element 202 into digital signals and outputs them to the ASIC 301 and the CPU 309.

  The ASIC 301 is a digital integrated circuit having a plurality of functions. The pattern generation unit 302 generates image data of a toner pattern generated by pattern detection control. The reading control unit 303 reads the binarized output signals of the regular reflection light receiving element 201 and the irregular reflection light receiving element 202 and temporarily stores the data. The color misregistration deriving unit 304 derives the color misregistration amount for each color based on the data stored in the reading control unit 303. That is, the color misregistration deriving unit 304 determines the color misregistration amount corresponding to the output signal output from the first light receiving unit and the output signal output from the second light receiving unit, and data indicating the determined color misregistration amount. It functions as a color misregistration amount determining means for outputting.

  The color misregistration correction unit 305 corrects the writing timing and the like based on the color misregistration amount derived by the color misregistration deriving unit 304.

  The gloss level deriving unit 306 derives the gloss level from the level of regular reflection light from the surface of the intermediate transfer belt 5. As shown in FIG. 6, the offset detection unit 307 derives a detection timing shift between the two light receiving elements from the read result of the detection timing correction pattern as an offset value and stores it. The offset detector 307 determines an offset value indicating an offset value indicating a deviation from the temporal center of the output signal output from the first light receiving unit to the temporal center of the output signal output from the second light receiving unit. Function as. The pattern switching unit 308 switches whether the detection timing correction pattern is a single color pattern or a multiple color pattern according to the glossiness of the surface of the intermediate transfer belt 5. The CPU 309 is the center of the control system, and controls each part of the image forming apparatus 100 based on a program stored in the ROM 310. Note that the color misregistration deriving unit 304 and the color misregistration correction unit 305 output the output signal output from the first light receiving unit or the output signal output from the second light receiving unit as much as the offset value determined by the offset detection unit 307. It functions as an adjusting means for adjusting automatically. Note that the offset value may be added to or subtracted from the color misregistration amount, or may be added to or subtracted from data indicating the detection timing stored in the reading control unit 303. This is because the same adjustment result can be obtained no matter which calculation step the offset value is applied.

  The voltage level of the output signal output from the pattern detection sensor 7 when the patterns of the respective colors formed on the intermediate transfer belt 5 are detected will be described with reference to FIGS. 4 (a) and 4 (b). FIG. 4A assumes that the intermediate transfer belt 5 has a high surface gloss. The voltage level of the output signal of the regular reflection light receiving element 201 is Rout, and the voltage level of the output signal of the irregular reflection light receiving element 202 is Iout.

  The regular reflection components of the yellow, magenta, cyan, and black patterns formed on the intermediate transfer belt 5 are smaller than the regular reflection components of the intermediate transfer belt 5. Therefore, the sensor output Rout for the intermediate transfer belt 5 becomes high, and the sensor output Rout for the yellow, magenta, cyan, and black patterns formed on the intermediate transfer belt 5 becomes low. Therefore, all color patterns such as yellow, magenta, cyan, and black can be detected from the voltage level Rout of the output signal of the regular reflection light receiving element 201.

  On the other hand, the irregular reflection component of the yellow, magenta, and cyan patterns formed on the intermediate transfer belt 5 is larger than the irregular reflection component of the intermediate transfer belt 5. Therefore, the sensor output Iout for the intermediate transfer belt 5 is low, and the sensor output Iout for the yellow, magenta, and cyan patterns formed on the intermediate transfer belt 5 is high. Here, since the black pattern has a small amount of irregular reflection components, the sensor output of the irregular reflection light receiving element 202 is low, and is almost equal to the sensor output of the irregular reflection component from the intermediate transfer belt 5. Therefore, the yellow, magenta, and cyan patterns can be detected from the voltage level Iout of the output signal of the irregularly reflected light receiving element 202, but the black pattern cannot be detected.

  Thus, if the glossiness of the intermediate transfer belt 5 is high, it is between the voltage level Rout corresponding to the regular reflection light from the surface of the intermediate transfer belt 5 and the voltage level Rout corresponding to the regular reflection light from the toner image. There are significant differences. Therefore, if the glossiness of the intermediate transfer belt 5 is high, the regular reflection light receiving element 201 can detect patterns of all colors such as yellow, magenta, cyan, and black. If the glossiness is high, the regular reflection light receiving element 201 and the irregular reflection light receiving element 202 can detect patterns of the same color (yellow, magenta, cyan). That is, if a pattern of any one of yellow, magenta, and cyan is used, a time difference between the output timing of the output signal of the regular reflection light receiving element 201 and the output timing of the output signal of the irregular reflection light receiving element 202 is detected. it can.

  If the glossiness of the intermediate transfer belt 5 is high, the reflected light from the intermediate transfer belt 5 received by the irregularly reflected light receiving element 202 has less diffused reflection components and the voltage level Iout becomes lower. When yellow, magenta, and cyan toner images are present on the intermediate transfer belt 5, the irregular reflection component increases in the reflected light received by the irregular reflection light receiving element 202, and the voltage level Iout becomes relatively high. Here, since the reflected light from the black pattern has few irregular reflection components, the voltage level Iout becomes low. That is, there is no significant difference between the voltage level Iout for the black pattern and the voltage level Iout of the irregular reflection component from the surface of the intermediate transfer belt 5. Therefore, the irregularly reflected light receiving element 202 can detect yellow, magenta, and cyan patterns, but cannot detect black patterns.

  FIG. 4B is based on the premise that the intermediate transfer belt 5 has a low surface gloss. The regular reflection component from the surface of the intermediate transfer belt 5 when the surface glossiness of the intermediate transfer belt 5 is low is less than the regular reflection component from the surface of the intermediate transfer belt 5 when the surface glossiness is high. Therefore, the voltage level Rout of the output signal corresponding to the intermediate transfer belt 5 output from the regular reflection light receiving element 201 is lowered. Therefore, the difference between the voltage level Rout of the output signal corresponding to the intermediate transfer belt 5 and the voltage level Rout of the output signal corresponding to the yellow, magenta, and cyan toner images formed on the intermediate transfer belt 5 becomes small. Here, the voltage level Rout of the black pattern is further lower than the voltage level Rout of regular reflection light from the intermediate transfer belt 5 when the surface glossiness is low. Therefore, the regular reflection light receiving element 201 cannot detect the yellow, magenta, and cyan patterns, but can still detect the black pattern. As described above, when the glossiness becomes low, the regular reflection light receiving element 201 cannot detect the yellow, magenta, and cyan patterns.

  Since the irregular reflection component of the reflected light from the surface of the intermediate transfer belt 5 is small, the voltage level Iout of the output signal output from the irregularly reflected light receiving element 202 is low. As described above, since the color toner image formed on the intermediate transfer belt 5 has many irregular reflection components, the voltage level Iout of the output signal output from the irregular reflection light receiving element 202 is high. Since the reflected light from the black pattern has few irregular reflection components, the voltage level Iout is low. As a result, there is no significant difference between the voltage level Iout for the black pattern and the voltage level Iout of the irregular reflection component for the reflected light from the surface of the intermediate transfer belt 5.

  As described above, when the glossiness decreases, the irregularly reflected light receiving element 202 can detect the yellow, magenta, and cyan patterns, but cannot detect the black pattern. This means that a common pattern cannot be detected by the regular reflection light receiving element 201 and the irregular reflection light receiving element 202. That is, no matter what color is used, the time difference between the output timing of the output signal of the regular reflection light receiving element 201 and the output timing of the output signal of the irregular reflection light receiving element 202 cannot be detected. Therefore, when the glossiness is lowered, a special pattern capable of detecting this time difference is required.

  As shown in FIG. 5A, the analog output signal Rout is binarized by determining whether or not the analog output signal Rout from the regular reflection light receiving element 201 is lower than a predetermined threshold Thr. 1 digital signal Rout_d is output. As shown in FIG. 5B, the analog output signal Iout is binarized by determining whether or not the analog output signal Iout from the irregularly reflected light receiving element 202 exceeds a predetermined threshold value Thi. A digital signal Iout_d is output.

  FIG. 6 is a graph showing changes in the voltage level Rout according to the amount of regular reflection from the surface of the intermediate transfer belt 5 with respect to the endurance time. In the present embodiment, when the glossiness is lower than the threshold value Th, the mode for deriving the offset value is changed from the second mode using a single color pattern of yellow, magenta, or cyan to a multi-color pattern combining yellow and black. Switch to the first mode to be used.

  The first mode is a mode in which a color misregistration amount is determined using a first pattern and a second pattern (multiple color pattern) formed to overlap the center of the first pattern. The second mode is a mode for determining the color misregistration amount of each color using a single color pattern. The determination regarding the glossiness is, for example, determining whether or not the voltage level Rout for the regular reflection light from the surface of the intermediate transfer belt 5 exceeds a predetermined threshold value Th.

  When the voltage level Rout corresponding to the regular reflection light from the surface of the intermediate transfer belt 5 exceeds the threshold value Th, the regular reflection light receiving element 201 can detect all the single-color patches of the four colors described above. The irregularly reflected light receiving element 202 can detect yellow, magenta, and cyan patterns. On the other hand, when the voltage level Rout corresponding to the regular reflection light from the surface of the intermediate transfer belt 5 is equal to or smaller than the threshold value Th, the regular reflection light receiving element 201 cannot detect the above-described yellow, magenta, and cyan patterns. That is, the threshold value Th is determined from the viewpoint of whether at least one color pattern of yellow, magenta, and cyan can be detected.

  The determination regarding the glossiness may be, for example, a determination as to whether or not the endurance time has exceeded a threshold time Th_time. As long as the endurance time does not exceed the threshold time Th_time, the regular reflection light receiving element 201 can detect all three colors described above. When the durability time exceeds the threshold time Th_time, the regular reflection light receiving element 201 cannot detect yellow, magenta, and cyan patterns. As described above, any parameter may be used as long as it has a correlation with the glossiness. In addition, what is necessary is just to determine these threshold values by experiment or simulation at the time of factory shipment. This is because the threshold value varies depending on the material of the intermediate transfer belt 5, the performance of the pattern detection sensor 7, and the reflectance of the toner.

  FIG. 7A shows a second mode using a single color pattern of yellow, magenta, and cyan. Here, for convenience of explanation, it is assumed that yellow is used. In the second mode, a yellow single color pattern is formed on the surface of the intermediate transfer belt 5 and detected by both the regular reflection light receiving element 201 and the irregular reflection light receiving element 202. The distance from the center of gravity of the digital output signal Rout_D of the monochromatic pattern from the regular reflection light receiving element 201 to the center of gravity of the digital output signal Iout_D of the monochromatic pattern from the irregular reflection light receiving element 202 is shifted in detection timing due to an optical axis misalignment (offset). Value).

  Therefore, in this embodiment, the time difference between the output timing of the barycentric position of the output signal of the monochromatic pattern from the regular reflection light receiving element 201 and the output timing of the barycentric position of the output signal of the monochromatic pattern from the irregular reflection light receiving element 202 is offset. Determine as value.

FIG. 7B shows a first mode using a plurality of color patterns. This multiple color patterns, and colors of different first patterns respectively, than the first pattern includes a small second pattern area, the second pattern in the center of the first pattern is superposition. Here, the color of the first pattern is a color that is more likely to be diffusely reflected than the color of the second pattern, and the color of the second pattern is a color that is more likely to be regularly reflected than the color of the first pattern.

  Here, as an example, a multi-color pattern in which black is superimposed on yellow is employed, but magenta or cyan may be employed instead of yellow. As shown in FIG. 7B, when the black pattern is formed on the yellow pattern, the yellow pattern is arranged on both sides of the black pattern in the conveyance direction of the intermediate transfer belt 5. That is, the black pattern is sandwiched by the yellow pattern. As a result, as shown in FIG. 7B, the digital output signal Iout_d output from the irregularly reflected light receiving element 202 when detecting a plurality of color patterns becomes two pulses. The reason why two pulses are formed is that the yellow pattern is divided into two by the black pattern. That is, a section in which the level of the digital output signal Iout_d decreases corresponds to a black pattern. Therefore, the distance from the center of gravity of the digital output signal Rout_D to the center of gravity of the section where the level of the digital output signal Iout_d has decreased (the center of gravity of the two pulses) indicates a detection timing shift (offset value) due to an optical axis shift or the like. Yes.

  FIG. 8A shows the timing at which an image signal for forming a single color (yellow) pattern is sent to the laser writing unit 15. FIG. 8B shows the timing at which an image signal for forming a multi-color (yellow and black) pattern is sent to the laser writing unit 15. By sending the image signal in this way, a single color pattern and a plurality of color patterns are formed on the surface of the intermediate transfer belt 5. Here, by making the yellow image formation time β longer than the black image formation time α, the area of the black toner image can be made smaller than the area of the yellow toner image. That is, the width of the black toner image is narrower than the width of the yellow toner image in the transport direction. The distance from the center of the image signal corresponding to the yellow toner image to the center of the image signal corresponding to the width of the black toner image is γ. This γ is a time corresponding to the distance from the transfer position of the yellow toner image to the transfer position of the black toner image. That is, when the image signal shown in FIG. 8B is used, a black pattern is formed so as to overlap with the center of the yellow pattern.

  A printing operation of the image forming apparatus 100 will be described with reference to FIG. In step S901, the CPU 309 determines whether a print job has been input from the host computer or the operation unit. When a print job is made, the process proceeds to S902. In step S902, the CPU 309 determines whether a condition for deriving an offset value is satisfied. The offset value deriving conditions include, for example, that the image forming apparatus 100 has been assembled at the factory, the pattern detection sensor 7 has been replaced, and the intermediate transfer belt 5 has been replaced. Assume that the image forming apparatus 100 is assembled at the factory, for example, a code indicating that is input to the CPU 309 from the operation unit. Also, the replacement of the pattern detection sensor 7 means that a code indicating that is input to the CPU 309 from the operation unit. Similarly, when the intermediate transfer belt 5 is replaced, it is assumed that a code indicating that is input to the CPU 309 from the operation unit. Note that the presence or absence of replacement of these units may be detected by the CPU 309 using a dedicated sensor. If the offset derivation condition is satisfied, the process proceeds to S903. On the other hand, if the offset derivation condition is not satisfied, S903 is skipped and the process proceeds to S904.

  In step S <b> 903, the CPU 309 outputs a command for instructing to derive an offset value to the ASIC 301. When the ASIC 301 receives this command, the ASIC 301 executes the offset derivation process shown in FIG.

  In step S904, the CPU 309 executes a print job and controls each unit of the image forming apparatus 100 so that an image corresponding to the input image data is formed on a sheet.

  In step S905, the CPU 309 determines whether the number of prints has exceeded a predetermined threshold number. The number of prints is the number of prints since the previous auto registration was executed. Auto-registration is color misregistration correction processing. When the number of prints exceeds a predetermined threshold number, the process proceeds to S906. On the other hand, if the number of prints does not exceed the predetermined threshold number, S906 is skipped and the print process is terminated.

  In step S906, the CPU 309 instructs the ASIC 301 to execute auto registration. Auto registration (auto registration) is a so-called color misregistration correction process. Details of the auto register will be described later with reference to FIG.

  The offset derivation process will be described with reference to FIG. In step S <b> 911, the reading control unit 303 of the ASIC 301 detects the gloss level of the surface of the intermediate transfer belt 5. For example, the reading control unit 303 drives the light emitting element 200 to irradiate the surface of the intermediate transfer belt 5 with light, and the regular reflection light receiving element 201 detects the regular reflection component of the reflected light. Here, the voltage level of the output signal corresponding to the regular reflection component is Rout. That is, Rout is a parameter indicating the glossiness. The glossiness deriving unit 306 may derive the glossiness from the voltage level Rout of the output signal. The glossiness corresponds to an integral value of the voltage level Rout_d. Therefore, the glossiness deriving unit 306 derives the glossiness by integral calculation. However, in the following, the voltage level Rout is used to simplify the description.

  In S922, the pattern switching unit 308 determines whether or not the voltage level Rout_d of the regular reflection component exceeds the threshold value Th. This determination is determination processing for selecting the first mode or the second mode described above. If the voltage level Rout_d exceeds the threshold value Th, the glossiness of the intermediate transfer belt 5 is sufficient. Therefore, the second mode for forming the monochromatic pattern is selected, and the process proceeds to S923.

  In step S923, the pattern generation unit 302 generates an image signal of a single color pattern according to the derivation result of the glossiness deriving unit 306. The monochromatic pattern image signal is the image signal shown in FIG. Thereafter, the process proceeds to S925.

  On the other hand, if the voltage level Rout_d of the regular reflection component does not exceed the threshold value Th in S922, the glossiness is not sufficient. Therefore, the first mode for forming a multi-color pattern is selected, and the process proceeds to S924. In step S924, the pattern generation unit 302 generates an image signal having a plurality of color patterns according to the derivation result of the glossiness deriving unit 306. The image signal of the multi-color pattern is the image signal shown in FIG. Thereafter, the process proceeds to S925.

  In step S <b> 925, the offset detection unit 307 detects the pattern formed on the surface of the intermediate transfer belt 5 using the regular reflection light receiving element 201 and the irregular reflection light receiving element 202.

  In S926, the offset detection unit 307 calculates the offset value. For example, the offset detection unit 307 calculates the center of gravity of the output signal voltage level Rout_d for the regular reflection light receiving element 201 and the center of gravity of the output signal voltage level Iout_d for the irregular reflection light receiving element 202. Further, the offset detection unit 307 calculates the calculated distance between the two centroids as an offset value. The method for calculating the offset value for the monochromatic pattern is as shown in FIG. The offset value calculation method for the multi-color mode is as shown in FIG. The multi-color pattern is a pattern in which a pattern (black) having a large regular reflection component is superimposed on a pattern (for example, yellow) having a large irregular reflection component. Therefore, even if the glossiness (gloss) of the intermediate transfer belt 5 is lowered, the presence of this pattern can be detected by both the regular reflection light receiving element 201 and the irregular reflection light receiving element 202.

  The auto registration will be described with reference to FIG. In S931, the pattern generation unit 302 generates an image signal of a pattern of four colors as shown in FIG. As a result, a pattern of four colors is ideally formed at regular intervals on the surface of the intermediate transfer belt 5. Note that, under the condition that color misregistration occurs, the interval between at least two patterns out of the four color patterns deviates from the target interval.

  In step S <b> 932, the reading control unit 303 detects the black pattern using the regular reflection light receiving element 201 and detects the yellow, magenta, and cyan patterns using the irregular reflection light receiving element 202. Data binarized by the first signal generation comparator 203 and data binarized by the second signal generation comparator 204 are temporarily stored in a storage unit included in the reading control unit 303. That is, these data are data indicating the detection timing of each pulse corresponding to each pattern.

  In step S933, the color misregistration deriving unit 304 determines the time misregistration with respect to the target timing as the color misregistration amount for the color of the second pattern with respect to the timing of the output signal output from the first signal generating means. Further, the color misregistration deriving unit 304 determines a time misregistration with respect to the target timing as the color misregistration amount for the first pattern color with respect to the timing of the output signal output from the second signal generating means. More specifically, the color misregistration deriving unit 304 reads detection timing data from the reading control unit 303 and derives the color misregistration amount. Generally, the writing timing of the laser writing units 15Y, 15M, 15C, and 15K is adjusted so that the distance between the patterns becomes a constant target distance. In the color misregistration correction, the writing timing of the remaining colors is corrected for one reference color. Here, when black is used as a reference color, the deviation of the distance between black and yellow with respect to the target distance is the amount of color deviation between black and yellow. Similarly, when black is used as the reference color, the deviation of the distance between black and magenta with respect to the target distance is the amount of color deviation between black and magenta. Similarly, when black is used as the reference color, the deviation of the distance between black and cyan with respect to the target distance is the amount of color deviation between black and cyan.

  In step S934, the color misregistration deriving unit 304 performs offset correction for the detection timing between the light receiving elements by adding or subtracting the above-described offset value to the calculated color misregistration amount. Note that the color misregistration amount may be obtained after offset correction is performed on data before the color misregistration amount is calculated.

  In step S <b> 935, the color misregistration correction unit 305 corrects the writing timing of the laser writing unit 15 using the color misregistration amount that is offset-corrected for the remaining colors excluding the reference color.

  As described above, according to the present embodiment, the pattern for correcting the detection timing between the two light receiving elements is formed by superimposing the first pattern and the second pattern having different colors, respectively. The offset value of the detection timing is determined by reading. In particular, a second pattern having a relatively small area is superimposed on the center of the first pattern. That is, the second pattern is sandwiched by the first pattern. As described above, when the glossiness of the intermediate transfer belt 5 decreases, one of the first light receiving element and the second light receiving element can detect the second pattern, and the other cannot detect the second pattern. . Actually, the section sandwiched between the first patterns and undetectable by the other light receiving element is the section of the second pattern. Therefore, the section in which the second pattern cannot be detected may be recognized as the second pattern section. Therefore, the distance between the temporal center of the output signal output from the first light receiving element and the temporal center of the output signal output from the second light receiving element indicates a shift in detection timing. That is, this distance is an offset value for correcting the detection timing between the two light receiving elements. As described above, according to the present invention, even if there is no toner pattern that can be detected in common between the regular reflection light receiving element 201 and the irregular reflection light receiving element 202, the regular reflection light receiving element 201 and the irregular reflection light receiving element. The detection timing error 202 can be corrected.

  In this embodiment, a pattern was formed on the intermediate transfer belt, and auto registration was performed. However, automatic registration may be performed by forming a pattern on a continuous sheet or by forming a pattern on a sheet conveyed by a sheet conveying belt. In the 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 also be applied to, for example, an ink jet printing apparatus.

  In the present embodiment, the configuration in which the pattern is detected by the regular reflection light receiving element 201 and the irregular reflection light receiving element 202 is adopted, but the density of this pattern may be detected. That is, the density of the yellow, magenta, and cyan patterns can be detected from the amount of light incident on the irregularly reflected light receiving element 202. Further, the density of the black pattern can be detected from the amount of light incident on the regular reflection light receiving element 201.

  In this embodiment, as shown in FIGS. 5A and 5B, the analog signal waveform indicating the amount of light detected by the regular reflection light receiving element 201 and the irregular reflection light receiving element 202 is compared with a threshold value. A pulse is generated. And it demonstrated as what auto-registration is performed by deriving the gravity center position of this pulse. However, a pulse signal indicating the peak value of the analog signal waveform may be generated, and auto registration may be performed based on this peak value. This is because the pulse duration and the peak value are in a proportional relationship.

  In this embodiment, the description has been made on the assumption that the glossiness of the surface of the intermediate transfer belt 5 is detected by the regular reflection light receiving element 201. However, the parameter indicating the surface state is not limited to the glossiness, and other parameters indicating the surface state may be adopted. Further, in order to detect the glossiness, the irregular reflection light receiving element 202 may be employed instead of the regular reflection light receiving element 201. Alternatively, both the regular reflection light receiving element 201 and the irregular reflection light receiving element 202 may be used. In this case, the average value of the output result of the regular reflection light receiving element 201 and the output result of the irregular reflection light receiving element 202 is defined as the glossiness.

  In this embodiment, it is assumed that the glossiness of the surface decreases depending on the durability of the intermediate transfer belt 5. However, the present invention can also be applied to the intermediate transfer belt 5 that employs a material whose surface glossiness increases due to durability or the intermediate transfer belt 5 that employs a material whose glossiness does not change linearly. This is because the present invention does not depend on the temporal change rate of the glossiness.

  In this embodiment, the detection timing deviation between the light receiving elements is caused by the optical axis deviation, but may be a detection timing deviation depending on characteristics of the light receiving elements, circuit characteristics, and the like. This is because the present invention does not depend on the cause of the deviation in detection timing.

Claims (4)

  First image forming means for forming a first toner image using black toner;
  A second image forming means for forming a second toner image using a color toner different from the black toner;
  An image carrier to which the first toner image and the second toner image are transferred;
  First measuring means for measuring specularly reflected light from a toner pattern formed on the image carrier;
  A second measuring means for measuring irregularly reflected light from the toner pattern formed on the image carrier;
  Correction condition deriving means for obtaining a correction condition for aligning the positions of the first toner image and the second toner image based on the measurement result of the first measurement means and the measurement result of the second measurement means;
  Based on the measurement result of the first measurement unit and the measurement result of the second measurement unit with respect to the same timing correcting toner pattern, the difference between the measurement timing of the first measurement unit and the measurement timing of the second measurement unit is corrected. Correction condition determining means for obtaining correction conditions;
  The correction condition determining means is a single color toner pattern using the color toner without using the black toner as the timing correction toner pattern based on the measurement result of the surface of the image carrier by the first measuring means. Or an image forming apparatus that determines whether a multi-color toner pattern using the black toner and the color toner is to be formed.   First image forming means for forming a first toner image using black toner;
  A second image forming means for forming a second toner image using a color toner different from the black toner;
  An image carrier to which the first toner image and the second toner image are transferred;
  First measuring means for measuring specularly reflected light from a toner pattern formed on the image carrier;
  A second measuring means for measuring irregularly reflected light from the toner pattern formed on the image carrier;
  Correction condition deriving means for obtaining a correction condition for aligning the positions of the first toner image and the second toner image based on the measurement result of the first measurement means and the measurement result of the second measurement means;
  Based on the measurement result of the first measurement unit and the measurement result of the second measurement unit with respect to the same timing correcting toner pattern, the difference between the measurement timing of the first measurement unit and the measurement timing of the second measurement unit is corrected. Correction condition determining means for obtaining correction conditions;
  The correction condition determining means may form a single color toner pattern using the color toner without using the black toner as the timing correction toner pattern based on the usage time of the image carrier, An image forming apparatus that determines whether to form a multi-color toner pattern using black toner and the color toner.   The multi-color toner pattern is obtained by forming a toner pattern using the black toner in a smaller area on a toner pattern formed using the color toner. The image forming apparatus according to 2.   In the multi-color toner pattern, a toner pattern formed using the color toner is exposed on both sides of the toner pattern formed using the black toner,
  The correction condition determining unit outputs an output signal output by the first measuring unit measuring the single color toner pattern, and an output signal output by the second measuring unit measuring the single color toner pattern. The correction condition is determined by calculating the difference from the output timing of
  The correction condition determining unit uses an output timing of an output signal output by the first measuring unit measuring a toner pattern formed using the black toner among the plurality of color toner patterns, and the black toner. Output of two output signals output by the second measuring means measuring the first toner pattern and the second toner pattern formed using the color toner exposed on both sides of the formed toner pattern The image forming apparatus according to claim 3, wherein the correction condition is determined by obtaining a difference from a timing center.

Images