JP2013238671A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that allows stable registration control irrespective of the remaining amount of developer.SOLUTION: An image forming apparatus includes: image forming means for forming a detection pattern on an image carrier; sampling means for irradiating the image carrier with light, sampling the amount of light reflected on the image carrier, and acquiring sampling values; determination means for determining a sampling value corresponding to reflection light from a patch from among the acquired sampling values on the basis of a predetermined first threshold; decision means for deciding a first value corresponding to the amount of reflection light from a developer image in a first color and a second value corresponding to the amount of reflection light from a developer image in a second color on the basis of the sampling value corresponding to the reflection light from the patch, and deciding a second threshold that is a value between the first value and the second value; and detection means for detecting a boundary between the developer image in a first color and the developer image in a second color on the basis of the second threshold.

Description

  The present invention relates to a color misregistration control technique in an image forming apparatus.

  Currently, printers as image output terminals are rapidly spreading due to advances in computer network technology. In recent years, with the progress of colorization of output images, there is an increasing demand for improving the stability of image quality of color printers. In particular, with regard to the overlay accuracy (color registration) between colors, a high degree of stability is required regardless of changes in the installation environment, changes over time, or differences in the characteristics of individual devices. However, in the image forming apparatus, color registration is fluctuated due to variation in color registration due to wear deterioration due to continuous use of each driving member or image forming member, and temperature change in the apparatus. Therefore, in order to keep color registration optimal, it is common to perform correction control by detecting a color shift or a position shift. The positional deviation detection is performed by, for example, forming a test developer image (hereinafter referred to as a detection pattern) on a circulating moving body such as a photoconductor, an intermediate transfer body, a transfer conveyance belt, and the relative position of the detection pattern. Is measured by a sensor. Control target that controls color registration based on the measurement results and conditions when the detection pattern is formed, so that color registration is appropriate during actual printing, for example, exposure write position when forming a latent image And image forming magnification.

  Patent Document 1 discloses a technique related to registration control using such a detection pattern. Patent Document 2 discloses a technique in which diffuse reflected light that is not easily affected by the surface state of a circulating moving body on which a detection pattern is formed is received by a light receiving element, and positional deviation is corrected.

Japanese Patent Laid-Open No. 2002-023445 JP 2009-093155 A

  In the configuration of Patent Document 2, a black developer image with little diffusely reflected light is superimposed on a color developer image with much diffusely reflected light. When the amount of developer, which is a consumable item, decreases, the detection pattern also becomes thin. However, the behavior of the detection signal of the sensor differs when the color developer decreases and the black developer decreases. Specifically, when the color developer is decreased, the influence of the circulating moving body as the base appears in the sensor signal. On the other hand, when the amount of black developer is reduced, the influence of the color developer as the base appears in the sensor signal. In either case, registration control can become unstable.

  An object of the present invention is to provide an image forming apparatus that enables stable registration control regardless of the remaining amount of developer.

  According to one aspect of the present invention, the image forming apparatus forms a second color developer image having a reflected light amount different from that of the first color developer image on the first color developer image. An image forming apparatus that corrects misregistration using a detection pattern including a patch, image forming means for forming the detection pattern on an image carrier, and irradiating light toward the image carrier, and sampling the amount of reflected light A sampling means for acquiring a sampling value; a determination means for determining a sampling value corresponding to the reflected light from the patch among the acquired sampling values based on a predetermined first threshold; and the first A first value corresponding to the amount of reflected light from the color developer image and a second value corresponding to the amount of reflected light from the second color developer image are sampled corresponding to the reflected light from the patch. Determine based on value Determining means for determining a second threshold value that is a value between the first value and the second value; and the developer image of the first color and the second color based on the second threshold value. And detecting means for detecting a boundary with the developer image.

  The boundary position of the detection pattern can be detected stably even if the developer of either color or black is decreased.

1 is a configuration diagram of an image forming unit of an image forming apparatus according to an embodiment. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment. The figure which shows the relationship between the sensor and intermediate transfer belt by one Embodiment. The block diagram of the sensor by one Embodiment. The figure which shows the structure between the sensor and DC controller by one Embodiment. The figure which shows the output signal of the sensor by one Embodiment. The flowchart of the determination process of the detection pattern position by one Embodiment. The figure which shows the detection pattern by one Embodiment. The figure which shows the output signal of the sensor at the time of the detection pattern detection by one Embodiment. The figure which shows the output signal of the sensor at the time of the detection pattern detection in which a black area | region is darker than FIG. The figure which shows the detection pattern by one Embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

<First embodiment>
FIG. 1 is a configuration diagram of an image forming unit of the image forming apparatus according to the present exemplary embodiment. In FIG. 1, the constituent elements to which the letters a, b, c, and d are attached to the reference numerals correspond to the constituent elements of the first station, the second station, the third station, and the fourth station, respectively. In the present embodiment, each of the first to fourth stations uses a toner image that is a developer image of yellow (Y), magenta (M), cyan (C), and black (K) as an image carrier. This is an image forming station formed on an intermediate transfer belt 80. The first station to the fourth station have the same configuration except for the color of the toner that is the developer of each, and in the following description, when it is not necessary to distinguish the colors, the letters a, b, c, Use the reference signs excluding d.

  The charging roller 2 is in contact with the photosensitive member 1 rotating in the direction indicated by the arrow, and charges the surface of the photosensitive member 1 to a negative polarity. The exposure unit 11 scans the photoconductor 1 with the scanning beam 12 modulated based on the image signal, and forms an electrostatic latent image on the photoconductor 1. The developing unit 8 has toner of a corresponding color, and develops the electrostatic latent image on the photoreceptor 1 with toner by a developing bias applied to the developing roller 4 to form a toner image. The primary transfer roller 81 applies a DC bias having a reverse polarity (that is, positive polarity) to the toner, and transfers the corresponding toner image on the photoreceptor 1 to the intermediate transfer belt 80. Further, the cleaning unit 3 cleans the toner that is not transferred to the intermediate transfer belt 80 but remains on the photoreceptor 1. In this embodiment, the photosensitive member 1, the developing unit 8, the charging roller 2, and the cleaning unit 3 are an integrated process cartridge 9 that is detachable from the image forming apparatus.

  The intermediate transfer belt 80 is supported by three rollers, that is, a secondary transfer counter roller 86, a driving roller 14, and a tension roller 15 as a stretching member, and an appropriate tension is maintained. By driving the drive roller 14, the intermediate transfer belt 80 moves in the forward direction with respect to the photoreceptor 1 at substantially the same speed in the direction of the arrow in the figure. From the first station to the fourth station, the toner images of the respective colors are superimposed and transferred onto the intermediate transfer belt 80, whereby a color image is formed on the intermediate transfer belt 80. The toner image transferred to the intermediate transfer belt 80 is transferred to the recording material conveyed through the conveyance path 87 by the secondary transfer roller 82. The toner image transferred to the recording material is then fixed on the recording material by a fixing unit (not shown). In the present embodiment, the sensor unit 60 is provided downstream of the fourth station in the conveyance direction of the intermediate transfer belt 80.

  FIG. 2 is a block diagram of the image forming apparatus according to this embodiment. The PC 271 serving as the host computer outputs a print command to the formatter 273 inside the image forming apparatus 1 and transfers the image data of the print image to the formatter 273. The formatter 273 converts the image data from the PC 271 into exposure data and transfers it to the exposure control unit 277 of the DC controller 274. The exposure control unit 277 is controlled by the CPU 276 to turn on / off exposure data and control the exposure unit 11. When receiving a print command from the formatter 273, the CPU 276 starts control for image formation. The memory 275 is a work area for the CPU 276.

  Further, the CPU 276 receives a signal detected by the sensor unit 60. As shown in FIG. 2, the sensor unit 60 includes two sensors 61 and 62. Here, the sensor 61 detects a detection pattern formed near one end of the intermediate transfer belt 80 in a direction orthogonal to the moving direction of the intermediate transfer belt 80, and the sensor 62 is positioned near the other end. The formed detection pattern is detected.

  Next, registration control will be described. Registration control is performed in order to adjust the relative toner image formation position of each image forming station, and aims to eliminate so-called color misregistration and obtain good printing results. In the registration control, for example, a detection pattern is formed on the intermediate transfer belt 80, and the relative positional deviation amount of the toner image formed by each image forming station is measured and corrected. In the registration control, detection patterns formed on the intermediate transfer belt 80 are read by the sensors 61 and 62, and signals output from the sensors are stored in the memory 275 via the CPU 276 and processed by the CPU 276.

  Next, adjustment of the toner image formation position will be described. The DC controller 274 can adjust the toner image formation position by changing the exposure speed and exposure timing of the exposure unit 11. For example, when the polygon mirror type exposure unit 11 is used, the DC controller 274 outputs exposure data of one scanning line synchronized with the reference pulse received from the exposure unit 11 to the exposure unit 11 during image formation. By changing the timing at which exposure data is sent after receiving the reference pulse for a time of about several dots for each image forming station, the writing position of each scanning line can be changed by about several dots. As a result, the writing position in the main scanning direction can be adjusted. For example, if the writing timing of one scanning line is delayed, the entire scanning line can be shifted to the sub scanning direction side, and the position in the sub scanning direction can be adjusted. Further, by controlling the rotational phase difference of the polygon mirror between the image forming stations, it is possible to perform alignment not more than the interval between adjacent scanning lines in the sub-scanning direction. Furthermore, the magnification in the main scanning direction can be adjusted by changing the clock frequency of the exposure data.

  As described above, the color misregistration amount (registration) can be corrected by adjusting the image forming position by changing the image forming timing and the exposure speed (clock frequency) regarding the color misregistration between the image forming stations. is there. Registration control is performed in order to measure a relative color shift amount for determining these adjustment amounts.

  FIG. 3 is a diagram illustrating the relationship between the intermediate transfer belt 80 and the sensors 61 and 62. Reference numeral 238 indicates the moving direction of the intermediate transfer belt 80, that is, the sub-scanning direction. In this embodiment, at the time of registration control, a detection pattern 235 is formed on each side of the intermediate transfer belt 80, and the position of the detection pattern (sensor detection) is detected by two sensors 61 and 62 provided on each side of the intermediate transfer belt 80. (Area passing time) is detected.

  The configurations of the sensors 61 and 62 are the same, and the sensor 61 will be described below as a representative. The sensor 61 irradiates light 233 from the emission hole 231 toward the intermediate transfer belt 80. Reference numeral 237 indicates an irradiation spot of the light 233. For example, the irradiation spot 237 has a substantially circular shape with a diameter of 3 mm. Reflected light from the intermediate transfer belt 80 or the detection pattern 235 formed on the surface thereof passes through the light receiving hole 232 and reaches the light receiving element in the sensor 61. The light receiving element generates a voltage signal corresponding to the amount of received light.

  FIG. 4 is a cross-sectional view of the sensor 61. The configuration of the sensor 62 is the same. The sensor 61 includes, for example, a light emitting element 242 such as an LED and a light receiving element 244 such as a phototransistor. Light from the light emitting element 242 passes through the light guide path 241 and is applied to the intermediate transfer belt 80. The light receiving element 244 receives reflected light passing through the light guide path 245. In the present embodiment, the light guide paths 241 and 245 are provided so that the light irradiated by the light emitting element 242 and regularly reflected by the surface of the intermediate transfer belt 80 or the detection pattern 235 does not enter the light guide path 245 on the light receiving side. In FIG. 4, the light guide path 241 is provided so as to be in the normal direction of the intermediate transfer belt 80, and the light guide path 245 is provided so as to be at an angle of 45 degrees with respect to the normal direction of the intermediate transfer belt 80. Yes.

  The wavelength of the light emitted from the light emitting element 242 is from ultraviolet to infrared as long as the wavelength is absorbed by the black (second color) detection pattern and diffusely reflected by the color (first color) detection pattern. Any wavelength of can be used. That is, it is possible to use arbitrary wavelengths having different amounts of diffuse reflection between the black and color toner images. In this embodiment, an infrared LED having a wavelength of 950 nm is used. In addition, if there is a large amount of diffuse reflection on the surface of the intermediate transfer belt 80, which is the base, it is difficult to detect the detection pattern.

  FIG. 5 is a block diagram relating to signal processing between the sensor 61 and the DC controller 274. The same applies to the sensor 62 and the DC controller 274. The CPU 276 controls the amount of light emitted from the light emitting element 242. The light receiving element 244 converts the optical signal into an electric signal, and the amplifier 293 amplifies the electric signal output from the light receiving element 244 into an electric signal having an appropriate amplitude. An electric signal corresponding to the amount of light received by the light receiving element 244 output from the amplifier 293 is taken into the CPU 276 through two paths. One path is a path directly input from the amplifier 293 to the AD conversion port of the CPU 276. The AD conversion port samples the voltage value of the input electrical signal at regular intervals. Each sampling value is stored in the memory 275. That is, the CPU 276 and the sensor constitute a sampling unit that irradiates light toward the carrier, samples the amount of reflected light, and acquires a sampling value. The other path is a path that passes through the comparator 295. The comparator 295 compares the reference voltage with the voltage of the electric signal output from the amplifier 293. When the electric signal is equal to or higher than the reference voltage, the comparator 295 outputs a “high” level signal. The signal is output to the interrupt port of the CPU 276. The CPU 276 constantly monitors the state of the interrupt port, and if there is an interrupt whose state changes from “high” to “low” and / or “low” to “high”, it immediately records the time. As described above, the CPU 276 has a configuration capable of performing both time measurement with high time resolution by the interrupt port and relatively coarse time measurement by the AD conversion port in parallel.

  FIG. 6 is a diagram for explaining the output characteristics of the output signals of the sensors 61 and 62. FIG. 6 shows output signals from the sensors 61 and 62 when a detection pattern having a uniform density is passed through the irradiation spot. Note that Vth in the figure is a reference voltage used by the comparator 295. Actually, the detection pattern 235 moves and the irradiation spot is a fixed position. However, in FIG. 6, the irradiation spot indicated by a circle moves relative to the position of the detection pattern 235. It shows. The output signal level when there is no detection pattern 235 in the irradiation spot is equivalent to the dark voltage of the light receiving element 244 and is at a low level. When the detection pattern 235 starts to enter the irradiation spot at time t1, the output signal of the sensor starts to rise. At time t3, after the detection pattern 235 enters the entire range of the irradiation spot, the output signal becomes constant. The time required for the rise of the output signal is substantially equal to the time obtained by dividing the diameter of the irradiation spot by the moving speed of the intermediate transfer belt 80. When the detection pattern 235 starts to come off from the irradiation spot at time t4, the output signal of the sensor starts to fall. At time t6, when the detection pattern 235 is removed from the irradiation spot, the output signal returns to the dark voltage. The time required for the fall of the output signal is the same as the time required for the rise.

  In registration control, in order to detect the position of the detection pattern, the time when the output signal of the sensor crosses the reference voltage Vth of the comparator 295 is recorded. For example, the intersection time between the rising edge of the output signal and the reference voltage Vth is the time t2 when the leading edge of the detection pattern is detected, and the intersection time between the falling edge of the output signal and the reference voltage Vth is the time t5 when the trailing edge of the detection pattern is detected. And the average time is recorded as the position of the detection pattern. By using the average time of the front end and the rear end as the position, there is an advantage that the position of the detection pattern to be measured is not affected even if the threshold value or the output signal level changes.

  The method of detecting the position of the detection pattern by detecting the diffuse reflected light as in this embodiment does not affect the diffuse reflected light so much even if the intermediate transfer belt 80 as a base is scratched. Has the advantage of being stable. There is also an advantage that the detection accuracy does not change over a long period of use.

  Next, registration control in the present embodiment will be described with reference to FIG. In S10, the CPU 276 of the image forming apparatus starts registration control. In S10, each actuator is operated to prepare for image formation as in normal printing. Further, the sensor output when the light emitting element 242 of the sensors 61 and 62 is turned off, that is, the dark voltage of the light receiving element 244 is measured for each sensor. Next, the light emitting elements 242 of the sensors 61 and 62 are caused to emit light with a predetermined light amount. Since it takes several seconds until the light output of the light emitting element 242 is stabilized, the light emission may be started sufficiently before the actual measurement is started.

  The CPU 276 forms a detection pattern on the intermediate transfer belt 80 in S11. FIG. 8 is a diagram showing a part of the detection pattern 235 according to the present embodiment. As already described, detection patterns 235 as shown in FIG. 8 are created on each side of the intermediate transfer belt 80. 8B is a plan view of the detection pattern 235 formed on the surface of the intermediate transfer belt, and FIG. 8A is a cross-sectional view taken along the line AA in FIG. 8B. In the figure, a patch image 211 is a patch image in which a diamond-shaped patch image with black toner is formed on a diamond-shaped patch image with yellow toner. Note that the diamond-shaped patch image using black toner is smaller than the diamond-shaped patch image using yellow toner. The patch image 212 is a rhombus image using magenta toner, and the patch image 213 is a rhombus image using cyan toner. The patch images 214, 215, and 216 are obtained by reversing the order of the patch images 211, 212, and 213 and the rhombus direction. Each patch image can be a so-called solid image having a large amount of toner and a high density in order to ensure contrast in reading by the sensors 61 and 62. The detection pattern 235 is detected by the sensors 61 and 62 from the patch image 211 on the front side in the traveling direction of the intermediate transfer belt 80.

  In S <b> 12, the CPU 276 samples the output signals of the sensors 61 and 62 and stores the sampling value in the memory 275. FIG. 9 shows an example of sampling values stored when the patch images 211 and 212 in FIG. 8 pass through the detection range of the sensor 61 or 62. FIG. 9 shows a case where sampling is performed every 6 milliseconds, and black dots indicate sampling points and sampling values. Each sensor provided in the vicinity of both ends of the intermediate transfer belt 80 starts storing the sampling value before the detection pattern reaches, and the CPU 276 performs sampling while all the detection patterns pass through the detection range of the sensor. The value is stored in the memory 275.

  Thereafter, in S13 to S16, the CPU 276 specifies the yellow toner image area of the patch image 211, that is, the background area and the black area of the patch image 211. Details will be described below. In the sampling value stored in the memory 275, the CPU 276 first starts from the sampling point 209 immediately after exceeding the first threshold (line 311 in FIG. 9), and the sampling value is equal to or greater than the first threshold. The sampling point 210 immediately before the search is searched. That is, the sampling values near the front end and the rear end of the patch image 211 are determined. The search range should be provided with a margin that takes into account variations in manufacturing and changes due to the operating temperature environment from the time when generation of the electrostatic latent image starts until the detection pattern reaches the detection range of the sensor. Can be determined. In this embodiment, the rising search range is set to a range of 0 to 0.08 seconds, and the falling search range is set to a range of 0.19 to 0.27 seconds. Further, the first threshold value can be determined in advance as a value higher than the dark voltage of the light receiving element 244 and sufficiently lower than the maximum output during detection pattern detection. When the surface of the intermediate transfer belt 80 is partially contaminated, the output of the portion increases by about 0.1 to 0.2 V. Therefore, in this embodiment, the darkness of the intermediate transfer belt is reduced to 0.1 V. In order to prevent the influence, 0.4V obtained by adding 0.3V is set as the first threshold value.

  In S14, the CPU 276 outputs the Y level (first value) corresponding to the diffuse reflected light from the yellow area of the patch image 211 and the K level as the output level corresponding to the diffuse reflected light from the black area. (Second value) is determined. The sampling points 209 and 210 specified in S13 are sampling points near the front end and the rear end of the patch image 211, respectively. As already described, it takes time depending on the spot diameter to rise and fall of the output signal of the sensor. Therefore, the predetermined number of sampling values corresponding to the rising and falling times can be excluded from the determination of the Y level because the output signal is not stable. Specifically, the sampling level corresponding to the time (about 20 milliseconds) required to move from the first sampling point 209 from the patch image 211 by a distance corresponding to the spot diameter is the Y level. It can be set as the structure which is not used for determination of this. Similarly, the sampling value between the last sampling point 210 of the patch image 211 and the previous sampling point 202 of about 20 milliseconds may be configured not to be used for determining the Y level. That is, between the sampling point 201 and the sampling point 202, the Y level is determined from the sampling value excluding the sampling value corresponding to the reflected light from the partial black region where the sampling value is relatively low.

  For example, an average of sampling values of a predetermined number thereafter including, for example, three sampling points including the sampling point 201 can be set as the Y level. The predetermined number can be determined on the basis of the number of sampling points within this length by calculating the minimum length in the sub-scanning direction of the underlying yellow region when the color shift of the black region is maximum. . More simply, the sampling point corresponding to the maximum value between the sampling point 201 and the sampling point 202 can be set to the Y level. It should be noted that the average of the sampling values of a predetermined number of sampling points including the sampling point 202 can be set to the Y level.

  In the present embodiment, the sampling point 203 corresponding to the minimum sampling value from the sampling point 201 to the sampling point 202 is stored as the K level. Note that an average of sampling values within a predetermined time range near the center in time from the sampling point 201 to the sampling point 202 may be set as the K level. Further, a predetermined number lower than the Y level selected from the sampling values within a predetermined time range, for example, an average of three sampling values may be set as the K level.

  In S15, the CPU 276 determines a second threshold value for determining the boundary between the yellow area and the black area of the patch image 211. In FIG. 9, the line 204 represents the second threshold value. At the boundary between the yellow area and the black area, the output signal of the sensor changes sharply. In order to specify the boundary position as accurately as possible, it is preferable to measure the time when the output signal changes steeply. In the present embodiment, the average value of the Y level and the K level determined in S14 is set as the second threshold value. However, any value between the Y level and the K level can be used. By measuring the time when the output signal of the sensor crosses the second threshold value, the boundary between the yellow region and the black region can be specified with high accuracy.

  In S16, the CPU 276 specifies the position of the black area. In FIG. 9, sampling points 205 and 206 are the sampling points before and after the second threshold value 204 is straddled at the falling edge. Further, sampling points 208 and 207 before and after the second threshold value 204 is straddled at the rising edge. For example, among sampling points that exceed the second threshold, the sampling point 205 that is closest to the position where the output signal intersects the second threshold and the sampling point 207 that is closest to the position where the output signal intersects at the rising edge are defined as the boundaries of the black region. can do. Alternatively, a sampling point that falls below the second threshold can be selected, and in this case, the sampling points 206 and 208 are the boundaries of the black region. Further, a sampling point having a small difference between the second threshold value among the sampling points 205 and 206 and a sampling point having a small difference between the second threshold values among the sampling points 207 and 208 may be set as the position of the black region. Further, linear interpolation is performed between the sampling point 205 and the sampling point 206, and linear interpolation is performed between the sampling points 208 and 207, and the time when the rising and falling portions of the output signal obtained thereby intersect the second threshold value 204. May be the boundary of the black region. Thereby, the boundary of the black region can be estimated with high accuracy.

  Thereafter, in S17, the CPU 276 specifies the areas of the patch images 212 to 215 and the boundaries of the yellow area and the black area of the patch image 216, respectively. The determination of the boundary between the yellow area and the black area of the patch image 216 is the same as that for the patch image 211. Further, the boundaries of the patch images 212 to 215 can be specified by the first threshold value. Alternatively, the patch images 212 to 215 can specify the boundary by determining the corresponding color level in the same manner as the determination of the yellow level and setting a threshold value based on the average value of the level and the dark voltage level. .

  As described above, in this embodiment, each threshold value is determined and the boundary of the patch image is specified. For example, when the amount of black toner decreases, the black detection pattern may become lighter. In this case, the diffuse reflected light from the black region also increases, and therefore the output signal level of the sensor does not decrease sufficiently.

  For example, FIG. 10 shows the output signal of the sensor when the black toner amount of the patch image 211 is sufficient, and FIG. 9 shows the output signal of the sensor when the black toner amount of the patch image 211 is smaller than that of FIG. 9 and 10, the line indicated by Vth is the reference voltage Vth (third threshold value) of the comparator 295. As shown in FIG. 10, when the amount of toner in the black area is sufficient, the output signal of the sensor also becomes sufficiently low, and an interrupt occurs at times t2 and t3 corresponding to the boundary between the yellow area and the black area. The CPU 276 can record the time. On the other hand, in FIG. 9, since the amount of toner in the black area is small, the output signal of the sensor is larger than the reference voltage Vth while the black area is detected. It cannot be detected. In this embodiment, since the threshold value is adaptively changed, the black region can be specified even if the amount of black toner changes.

  For example, the registration control using the comparator 295 is normally executed, and when the position measurement of the detection pattern by the comparator 295 is not successful, the position measurement using the sampling value can be executed. . This is because the accuracy of position measurement of each color region by the comparator 295 is high, and this configuration enables stable registration control even when the amount of toner is reduced. In the method of this embodiment, since the position can be specified by processing the sampling value stored in the memory 275 later, the position measurement is performed based on the sampling value even after the position measurement by the comparator 295 is determined. There is an advantage that can be done. In the position measurement by the comparator 295, since the number of times that an interrupt is generated is known according to the detection pattern, it can be determined that the position measurement by the comparator 295 has not been successful if the number of generated interrupts is different from the required number.

  As described above, in the present embodiment, the position of the detection pattern can be specified even if the pattern of any one of the toners becomes thin, and the color misregistration amount can be measured and corrected.

<Second embodiment>
Next, the second embodiment will be described focusing on the differences from the first embodiment. FIG. 11 shows detection patterns used in the present embodiment. In the present embodiment, registration control and density correction control are executed in a continuous sequence. Accordingly, as shown in FIG. 11, in addition to the registration control patch images 211 to 216, patch images 217 to 220 constituting a density control detection pattern are formed on the intermediate transfer belt 80 as in the first embodiment. To do. As a set of patch images 211 to 220 shown in FIG. 11, a plurality of sets of detection patterns are formed on the intermediate transfer belt 80 within one turn of the intermediate transfer belt 80. The patch images 217 to 220 are formed of yellow (Y), magenta (M), cyan (C), and black (K) toners, respectively. In the present embodiment, each color patch image for density control uses three different densities, but the number of density gradations is an example, and there are a plurality of density correction patch images. It is possible to form with any gradation. In order to perform density control, it is necessary to detect regular reflection light from the ground of the detection pattern. Accordingly, the sensor includes a light emitting element, a light receiving element that receives the light that is emitted from the light emitting element and diffusely reflected by the intermediate transfer belt, and a light receiving element that receives the light regularly reflected by the intermediate transfer belt. Is used.

  Since each patch image of the detection pattern for density control may vary in density at the front and rear ends due to the edge effect, it is preferable to measure the density at the center of the patch image of each density. For this purpose, it is necessary to roughly know the positional deviation amount of the detection pattern for density control. For this, the detection pattern position specifying method described in the first embodiment can be used.

  For example, the position of each black area of the patch images 211 and 216 shown in FIG. 11 is measured by the method described in the first embodiment. An average value of the positions of the two black areas is A. In this case, the average value A and the distance or time to the patch image 220 for black density control are fixed because they are the same color. Therefore, by measuring the time of A and using the sampling value after a predetermined time from A, the central portion of each color of the patch image 220 for black density control is used regardless of the amount of displacement of the black toner image. It becomes possible to measure the concentration. The same applies to other colors. Further, the configuration may be such that the position of the black density control patch image 220 is specified with reference to the position of one of the black areas of the patch images 211 and 216.

  As described above, in the present embodiment, when the density control and the registration control are performed in the same sequence, the density control can be accurately performed regardless of the relative positional deviation amount of each color. If the density control is successful, the subsequent registration control can be performed with high accuracy, so that it is possible to realize calibration that is resistant to changes.

<Other embodiments>
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (23)

Image formation for correcting misregistration by a detection pattern including a patch on which a second color developer image having a reflected light amount different from that of the first color developer image is formed on the first color developer image. A device,
An image forming means for forming the detection pattern on an image carrier;
Sampling means for irradiating the image carrier with light, sampling the amount of reflected light, and obtaining a sampling value;
Determination means for determining a sampling value corresponding to the reflected light from the patch among the acquired sampling values based on a predetermined first threshold;
The first value corresponding to the amount of reflected light from the developer image of the first color and the second value corresponding to the amount of reflected light from the developer image of the second color are reflected light from the patch. Determining means for determining a second threshold value that is a value between the first value and the second value, based on a sampling value corresponding to
Detecting means for detecting a boundary between the developer image of the first color and the developer image of the second color based on the second threshold;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the detection unit detects a boundary between the image carrier and the first color developer image based on the first threshold. The second value is determined from a sampling value within a predetermined time range among sampling values corresponding to reflected light from the patch.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The predetermined time range is a time range including a sampling value centered in time of a sampling value corresponding to the reflected light from the patch,
The image forming apparatus according to claim 3. The second value is a minimum value of sampling values within the predetermined time range.
The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus. The second value is an average value of sampling values selected from sampling values within the predetermined time range.
The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus. Among the sampling values corresponding to the reflected light from the patch, the first value is a first predetermined number of sampling values in time, a last predetermined number of sampling values in time, and a predetermined time range. Determined from the sampling value excluding the sampling value,
The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus. Among the sampling values corresponding to the reflected light from the patch, the first value is a first predetermined number of sampling values in time, a last predetermined number of sampling values in time, and a predetermined time range. The maximum sampling value excluding the sampling value,
The image forming apparatus according to claim 7. Among the sampling values corresponding to the reflected light from the patch, the first value is a first predetermined number of sampling values in time, a last predetermined number of sampling values in time, and a predetermined time range. The average value of the sampling values selected from the sampling values excluding the sampling values.
The image forming apparatus according to claim 7. The first predetermined number in time and the last predetermined number in time are sampled while the image carrier moves by a distance corresponding to the spot diameter of the light irradiated by the sampling means on the image carrier. Corresponding to the number,
The image forming apparatus according to claim 7, wherein the image forming apparatus is an image forming apparatus. The detecting means detects a boundary between the developer image of the first color and the developer image of the second color based on a predetermined third threshold value, and develops the first color based on the third threshold value. When the boundary between the developer image and the developer image of the second color cannot be detected, the developer image of the first color and the development of the second color based on the second threshold determined by the determination unit Detect the boundary with the agent image,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The image forming means continuously forms the detection pattern for detecting displacement and a pattern for density correction on the image carrier,
The detection means detects the position of the developer image of the second color included in the pattern for density correction and the position of the developer image of the first color of the patch detected by the detection means and the second color. Determined based on the boundary with the developer image of the color of
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Image formation for correcting misregistration by a detection pattern including a patch on which a second color developer image having a reflected light amount different from that of the first color developer image is formed on the first color developer image. A device,
An image forming means for forming the detection pattern on an image carrier;
Sampling means for irradiating the image carrier with light, sampling the amount of reflected light, and obtaining a sampling value;
If the boundary cannot be detected by a predetermined threshold for detecting the boundary between the developer image of the first color and the developer image of the second color, the developer image of the first color A first value corresponding to the amount of reflected light and a second value corresponding to the amount of reflected light from the developer image of the second color are determined based on a sampling value corresponding to the reflected light from the patch, Determining means for determining a threshold value which is a value between the first value and the second value;
An image forming apparatus comprising:   The developer image of the first color and the developer image of the second color are set according to the predetermined threshold value or a threshold value that is a value between the first value and the second value. The image forming apparatus according to claim 13, further comprising detection means for detecting a boundary. The second value is determined from a sampling value within a predetermined time range among sampling values corresponding to reflected light from the patch.
The image forming apparatus according to claim 13, wherein the image forming apparatus is an image forming apparatus. The predetermined time range is a time range including a sampling value centered in time of a sampling value corresponding to the reflected light from the patch,
The image forming apparatus according to claim 15. The second value is a minimum value of sampling values within the predetermined time range.
The image forming apparatus according to claim 15, wherein the image forming apparatus is an image forming apparatus. The second value is an average value of sampling values selected from sampling values within the predetermined time range.
The image forming apparatus according to claim 15, wherein the image forming apparatus is an image forming apparatus. Among the sampling values corresponding to the reflected light from the patch, the first value is a first predetermined number of sampling values in time, a last predetermined number of sampling values in time, and a predetermined time range. Determined from the sampling value excluding the sampling value,
The image forming apparatus according to claim 15, wherein the image forming apparatus is an image forming apparatus. Among the sampling values corresponding to the reflected light from the patch, the first value is a first predetermined number of sampling values in time, a last predetermined number of sampling values in time, and a predetermined time range. The maximum sampling value excluding the sampling value,
The image forming apparatus according to claim 19. Among the sampling values corresponding to the reflected light from the patch, the first value is a first predetermined number of sampling values in time, a last predetermined number of sampling values in time, and a predetermined time range. The average value of the sampling values selected from the sampling values excluding the sampling values.
The image forming apparatus according to claim 19. The first predetermined number in time and the last predetermined number in time are sampled while the image carrier moves by a distance corresponding to the spot diameter of the light irradiated by the sampling means on the image carrier. Corresponding to the number,
The image forming apparatus according to claim 19, wherein the image forming apparatus is an image forming apparatus. The image forming means continuously forms the detection pattern for detecting displacement and a pattern for density correction on the image carrier,
The detection means detects the position of the developer image of the second color included in the pattern for density correction and the position of the developer image of the first color of the patch detected by the detection means and the second color. Determined based on the boundary with the developer image of the color of
The image forming apparatus according to claim 14, wherein the image forming apparatus is an image forming apparatus.

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