JP5731769B2 - Image forming apparatus and control method thereof - Google Patents

Description

  The present invention relates to an image forming apparatus such as a color printer or a color copying machine employing an electrophotographic system, and a control method thereof. In particular, the present invention relates to an image forming apparatus having a function of correcting a color shift amount between a plurality of images having different colors and a control method thereof.

  In recent years, image forming apparatuses such as color printers and color copiers adopting an electrophotographic system are increasingly adopting a so-called tandem system that is advantageous for high speed and high productivity. In an image forming apparatus adopting this tandem system, for example, a plurality of image forming stations corresponding to each color such as yellow, magenta, cyan, and black are arranged in series. Then, images of each color such as yellow, magenta, cyan, and black formed by the plurality of image forming stations are primarily transferred in a state of being superimposed on each other on the intermediate transfer belt. Next, a color image output product is obtained by fixing the images of multiple colors, such as yellow, magenta, cyan, and black, transferred onto the intermediate transfer belt in a secondary transfer onto a recording sheet, and then fixing the images. Is obtained.

  In such a tandem image forming apparatus, it is important in terms of product quality that images of each color such as yellow, magenta, cyan, and black formed at each image forming station are accurately printed at predetermined positions. Is done. That is, it is important that no color misregistration occurs. Therefore, the conventional image forming apparatus is provided with a measuring mechanism for forming a toner mark of yellow, magenta, cyan, black, etc., and measuring the relative color misregistration amount between the toner images of each color, and the color misregistration from the measured value. It has a mechanism for correcting the image forming position so that the amount is small. However, in the color misregistration correction operation, it is necessary to perform toner mark formation, toner mark cleaning, and the like, and during this time, a downtime during which the user cannot print is caused. This is not preferable because it reduces the productivity of image formation.

  In response to this contradictory problem, the change in the environment that causes the variation in the color misregistration amount is detected, and the color misregistration amount is predicted from the output of the environment sensor and corrected without performing the time-consuming color misregistration measurement operation. A method has been proposed. For example, Patent Documents 1 and 2 disclose techniques for predictive correction of the color misregistration amount. According to these, by calculating the color misregistration amount instantaneously by the arithmetic unit in the image forming apparatus, the downtime for measuring the actual color misregistration amount is omitted, and the productivity is improved.

JP-A-63-307481 Japanese Patent Laid-Open No. 1-96665

  However, the above prior art has the following problems. The following configurations are disclosed in Patent Document 1 and Patent Document 2 described above. That is, the temperature inside the apparatus is detected by the temperature detecting means, and the irradiation position of the laser beam in the scanning direction on the photosensitive member is changed or the writing of the optical writing means is started based on the detection result of the temperature detecting means. Control timing.

  However, the amount of deformation of individual components that affect the color shift differs depending on the heat generated from the heat source in the machine and the exchange of heat with the environment. In the prior art described above, there is a case where the correlation between the temperature detection value of the temperature detection means for detecting the environmental temperature and the actual color misregistration amount does not hold. For example, when the image forming apparatus repeatedly operates and stops, and the internal temperature repeatedly rises and falls before reaching a steady state, the temperature of the component that contributes to the color misregistration amount changes with a heat transfer delay. The transient state in which the color misregistration amount changes every moment continues. In such a case, it is difficult to predict the color misregistration amount. In such a situation, there is a problem that the color misregistration cannot be corrected and the image quality is deteriorated.

  On the other hand, when color misregistration correction with toner mark formation is performed, even though it is possible to prevent the image quality from being deteriorated, the downtime is increased and the productivity of the image forming apparatus is lowered.

  The present invention provides an image forming apparatus that accurately corrects color misregistration while maintaining productivity by minimizing downtime for measuring the color misregistration amount, and a control method thereof.

The present invention can be realized as an image forming apparatus, for example. The image forming apparatus according to an embodiment of the present invention is based on the detection result of detecting the toner marks of the respective colors, a measuring means for measuring a relative color misregistration amount of the toner image of each color, the color shift amount measured an image forming apparatus having a color shift correcting means for correcting the relative color shift of each color toner images on the basis, in the timing of the color misregistration correction, to form a toner mark of all colors for each color, each color Measuring means for measuring a relative color misregistration amount of the toner image and determining whether or not a condition for correcting the color misregistration is satisfied, and when the determination means determines that the condition is not satisfied, the measuring means Measures the relative color misregistration amount between the reference color and the other one color, and the color misregistration correction means calculates the relative color misregistration between the measured reference color and the other one color. Based on the quantity, the reference color and the color other than one other color A predicting unit that predicts a color misregistration amount, corrects a color misregistration of another one color based on the color misregistration amount measured by the measuring unit, and based on the color misregistration amount predicted by the prediction unit The image forming apparatus corrects a color misregistration of a color other than one other color, and the image forming apparatus includes a storage unit that stores another color when the color misregistration correcting unit performs the color misregistration correction at the first timing. In addition, when the color misregistration correction unit performs color misregistration correction at a second timing after the first timing, the measurement unit is configured to make a relative color with respect to a reference color for a color different from the stored color. And the predictor measures the relative color between the reference color and a color other than the different color based on the relative color shift amount between the measured reference color and a different color. It is characterized by predicting a deviation amount .
An image forming apparatus according to another aspect of the present invention includes a forming unit that forms a toner mark of a reference color and a toner mark of another color, and a detection result obtained by detecting the formed toner mark. Based on the measurement means for measuring the relative color shift amount between the reference color and the other one color, and the relative color shift amount between the measured reference color and the other one color. On the basis of a relative color shift amount between a reference color and a color other than one other color, and correcting a color shift of the other color based on the measured color shift amount; and A color misregistration correction unit that corrects color misregistration of a color other than one other color based on the predicted color misregistration amount, and another color when the color misregistration correction unit performs color misregistration correction. And a storage unit that performs the color misregistration correction at the first timing. The toner mark of the reference color and the toner mark of one other color are formed, and the measuring unit measures the relative color misregistration amount between the reference color and the other one color, When the color misregistration correction unit performs the color misregistration correction at the second timing after the timing, the forming unit performs the toner mark of the color different from the toner mark of the reference color and the color stored at the first timing And the measurement means measures a relative color shift amount between a reference color and a different color.

  According to the present invention, by measuring the color misregistration amount between two colors and predicting other color misregistration amounts, the color misregistration is suppressed while minimizing downtime for measuring the color misregistration amount and maintaining productivity. Can be corrected with high accuracy.

  Furthermore, since only the amount of color misregistration between two colors is measured, image formation can be performed between patch pattern formations, and downtime is minimized to maintain productivity.

1 is a diagram illustrating a configuration example of an image forming apparatus according to a first embodiment. FIG. 2A is a block diagram illustrating a control configuration example of the image forming apparatus according to the first exemplary embodiment, and FIG. 2B is a diagram illustrating a configuration example of a patch sensor. It is a block diagram which shows the structural example of DC controller of Fig.2 (a). 6 is a diagram illustrating an example of a large-scale color misregistration adjustment pattern used in Embodiment 1. FIG. 6 is a diagram illustrating an example of a small-scale color misregistration adjustment pattern used in Embodiment 1. FIG. FIG. 6 is a diagram illustrating a relationship between the number of printed sheets when color misregistration adjustment is not performed and a color misregistration amount based on black (K). 6A is a diagram illustrating a relationship between a color misregistration amount of magenta (M) and a color misregistration amount of cyan (C) and a prediction formula of the first embodiment, which is created from the relationship of FIG. It is. (B) is a diagram showing the relationship between the color misregistration amount of magenta (M) and the color misregistration amount of yellow (Y) based on black (K) created from the relationship of FIG. It is. 3 is a flowchart illustrating a procedure example of color misregistration adjustment according to the first exemplary embodiment. It is a flowchart which shows the example of a procedure of Embodiment 1 of the small color misregistration adjustment (S80) of FIG. 6 is a diagram illustrating a result of color misregistration adjustment according to Embodiment 1. FIG. It is a figure which shows the comparative example 1 of color misregistration adjustment when only large-scale color misregistration adjustment is performed. FIG. 6 is a diagram illustrating a relationship between a fixing rotation time (in-machine temperature increase) and a color misregistration amount based on black (K) when no color misregistration adjustment is performed. It is a figure which shows the comparative example 2 of color misregistration adjustment at the time of performing color misregistration prediction of all the colors based on the in-machine temperature rise of FIG. (A) is a diagram showing the relationship between the color misregistration amount of magenta (M) and the color misregistration amount of yellow (Y) based on black (K) during continuous printing, and the prediction formula of the second embodiment. FIG. 7B is a diagram illustrating a relationship between a color misregistration amount of magenta (M) and a color misregistration amount of yellow (Y) with black (K) as a reference at the time of intermittent printing, and a prediction formula of the second embodiment. FIG. 10 is a diagram illustrating a result of color misregistration adjustment according to the second embodiment. (A) is a diagram showing the color misregistration amount due to thermal expansion of the driving roller, (b) is a diagram showing the color misregistration amount due to the temperature rise of the scanner, and (c) is a continuous print in which (a) and (b) are added together. It is a figure which shows the color shift amount equivalent to the color shift change at the time. (A) shows the relationship between the color misregistration amount of magenta (M) and the color misregistration amount of cyan (C) or yellow (Y) based on black (K) created from the relationship of FIG. FIG. FIG. 15B shows the color misregistration amount of magenta (M) and the color misregistration of cyan (C) or yellow (Y) with reference to black (K) assumed in the continuous printing created from the relationship of FIG. It is a figure which shows the relationship with quantity.

[Embodiment 1]
<Example of Configuration of Image Forming Apparatus of Present Embodiment>
As shown in FIG. 1, the image forming apparatus 1000 is a tandem type color image forming apparatus including four image forming stations. From the upstream side of the intermediate transfer belt 13 in the rotational direction, the first image forming station is formed with yellow (Y), the second image forming station is magenta (M), and the third image forming station is cyan (C). The fourth image forming station is black (K). The first image forming station will be described as a representative. The first image forming station includes an OPC photosensitive drum 1a as an image carrier. Further, the first image forming station includes a charging roller 2a as a charging unit, a cleaning unit 3a for cleaning residual toner on the photosensitive drum 1a, and a developing unit 8a as a developing unit. The developing unit 8a includes a developing sleeve 4a, a nonmagnetic one-component developer 5a, and a developer coating blade 7a. The above-described 1a to 8a are configured as an integrated process cartridge 9a and are detachable from the image forming apparatus. The exposure unit 11a is composed of a scanner unit or LED array that scans user light with a polygon mirror, and irradiates a scanning beam 12a modulated based on an image signal onto the photosensitive drum 1a.

  Next, an image forming operation of the image forming apparatus 1000 will be described. When the image forming operation starts, the photosensitive drums 1a to 1d, the intermediate transfer belt 13 and the like start to rotate in the arrow direction at a predetermined process speed. The photosensitive drum 1a is uniformly charged negatively by the power supply 20a to the charging roller 2a, and then an electrostatic latent image according to the image information is formed by the scanning beam 12a from the exposure unit 11a. The toner 5a in the developing unit 8a is charged to a negative polarity by the developer applying blade 7a and applied to the developing sleeve 4a. The developing sleeve 4a is supplied with a bias from a developing bias power source 21a. When the photosensitive drum 1a rotates and the electrostatic latent image formed on the photosensitive drum 1a reaches the developing sleeve 4a, the electrostatic latent image is visualized as a toner image by the negative polarity toner, and the electrostatic latent image is visualized on the photosensitive drum 1a. A toner image of the first color (Y in this embodiment) is formed. Since the second to fourth image forming stations have the same configuration as the first image forming station, the description thereof is omitted.

  On the other hand, the intermediate transfer belt 13 which is a toner image carrier is disposed so as to abut against all four photosensitive drums 1a to 1d. The intermediate transfer belt 13 is supported by three rollers, that is, an auxiliary roller 24, a driving roller 15, and a tension roller 14 as a stretching member. A spring force acts on the tension roller 14 to maintain an appropriate tension on the intermediate transfer belt. By driving the driving roller 15, the intermediate transfer belt 13 moves in the forward direction at substantially the same speed with respect to the photosensitive drums 1a to 1d. As the intermediate transfer belt moves, the tension roller 14 is driven to rotate in the direction of the arrow. The primary transfer member 10a is disposed on the opposite side of the photosensitive drum 1a with the intermediate transfer belt 13 interposed therebetween. The charging roller 2a is connected to a charging bias power source 20a that is a voltage supply unit to the charging roller 2a. The developing sleeve 4a is connected to a developing power source 21a that is a voltage supply unit to the developing sleeve 4a. The primary transfer member 10a is connected to a primary transfer power source 22a that is a voltage supply unit to the primary transfer member 10a. The secondary transfer roller 25 is connected to a secondary transfer power supply 26. Primary transfer members 10a to 10d are arranged around the intermediate transfer belt 13 and opposed to the photosensitive drums 1a to 1d so as to correspond to the respective photosensitive drums 1a to 1d. Depending on the distance between the primary transfer positions of each color, an electrostatic latent image by exposure is formed on each photosensitive drum 1a to 1d while delaying a write signal from a controller (not shown) at a certain timing for each color. . A voltage having a polarity opposite to that of the toner is applied from the primary transfer power sources 22a to 22d to the corresponding primary transfer members 10a to 10d. Through the above steps, a toner image of each color is sequentially transferred to the intermediate transfer belt 13, thereby forming a multiple image on the intermediate transfer belt 13. Note that the patch sensor 28 can detect the presence / absence of toner on the belt and the passage time by irradiating the intermediate transfer belt 13 with light.

  In parallel with the movement of the toner image formed on the intermediate transfer belt, the transfer material P loaded on the transfer material cassette 16 is picked up by the paper feed roller 17, and the position of the registration roller 18 by the conveyance roller (not shown). It is conveyed to. The transfer material P is formed by the intermediate transfer belt 13 and the secondary transfer roller 25 by the registration roller 18 in synchronization with the timing so that the tip of the toner image on the intermediate transfer belt 13 matches the tip of the transfer material P. It is conveyed to the contact part. Thereafter, a voltage having a polarity opposite to that of the toner is applied from the secondary transfer power source 26 to the secondary transfer roller 25, so that the four-color multiple toner images carried on the intermediate transfer belt 13 are transferred onto the transfer material P. Secondary transfer is performed at once. On the other hand, after the secondary transfer, the transfer residual toner remaining on the intermediate transfer belt 13 and the paper powder transferred from the transfer material P onto the intermediate transfer belt 13 are disposed in contact with the intermediate transfer belt 13. The belt cleaning unit 27 removes and collects the surface. After the completion of the secondary transfer, the transfer material is conveyed to a fixing unit (fixing device) 19 where the toner image is fixed and is discharged out of the image forming apparatus as an image formed product (print, copy).

  In addition, the image forming apparatus 100 according to the present exemplary embodiment is provided with a fixing temperature sensor 29 that measures a fixing temperature around the fixing device and an environmental temperature sensor 30 that measures an environmental temperature near the image forming station and the intermediate transfer belt 13. ing.

(Control configuration example of image forming apparatus)
The above-described image forming operation will be described with reference to the block diagram of FIG. The host computer 40 is responsible for issuing a print command to the image forming apparatus 1000 and transferring the image data of the print image to the interface board 41. The interface board 41 converts the image data from the host computer 40 into exposure data and issues a print command to the DC controller 200. The DC controller 200 operates with power supplied from the low-voltage power supply 43. Upon receiving a print command, the DC controller 200 starts an image forming sequence while monitoring the state of various sensors 53. As will be described later with reference to FIG. 3, the DC controller 200 is equipped with a CPU, a memory, and the like, and performs a pre-programmed operation. Specifically, the operations of various driving units 1a to 1d, 24 such as a main motor, a developing unit, and a photosensitive drum driving unit are controlled in synchronization with outputs of various sensors 53 and internal timers. Further, the color mode and the mono mode are identified, and the operations of the development separation unit 61 of the black development unit and the color development separation unit 60 of the color development unit are controlled. The DC controller 200 controls the high-voltage power supply with a pre-programmed control voltage, control current, and timing while monitoring applied voltages and currents of a plurality of high-voltage power supplies provided in the high-voltage power supply 44.

  Various functional parts that control image formation are connected to the high-voltage power supply. The photosensitive member charging members 2a to 2d provided in each station play a role of charging the surface of the photosensitive drum to a uniform potential by receiving a high voltage from the high voltage power supply 44 and contacting or approaching the photosensitive drum of each station. . The charging potential is controlled by the DC controller 200 controlling the high voltage generated in the high voltage power supply 44. Similarly, a high voltage is supplied from a high voltage power supply 44 to the developing rollers 4 a to 4 d provided at each station and the primary transfer members 10 a to 10 d provided at each station and the secondary transfer member 25. The applied voltage and applied current are controlled by the DC controller 200 so as to obtain appropriate secondary transfer characteristics. Further, the power control unit 57 connected to the fixing unit 19 is controlled to perform power control so that the temperature of the fixing unit 19 maintains a predetermined temperature. Further, the DC controller 200 can correct the color misregistration by adjusting the timing at the same time as controlling the exposure units 11a to 11d so that the scanning speed becomes a predetermined value and the exposure light quantity becomes a predetermined value. For example, in the case of an image forming apparatus having a polygon mirror type exposure unit, the DC controller 200 counts the write reference pulse from the exposure unit to generate an image leading edge signal and sends it to the interface board 41 at the time of image formation. In synchronization with the signal, exposure data is sent from the interface board 41 to the exposure unit via the DC controller 200 for each line (one surface of the polygon mirror). By changing the timing of outputting the image leading edge signal to the DC controller 200 for about several dots for each image forming station, the writing timing of each line can be changed by several dots. Thereby, the writing start position in the main scanning direction can be adjusted. Further, for example, if the writing start timing for one line is delayed, the entire image can be shifted by one line in the conveyance direction, so that the writing position adjustment in the sub-scanning direction can be performed in units of one line. Further, by controlling the rotational phase difference of the polygon mirror, which is a polygon mirror of the scanner, between the image forming stations, it is possible to align one line or less in the sub-scanning direction. Furthermore, the main scanning magnification can be corrected by changing the clock frequency that is the reference for turning on / off the exposure data. As described above, the color misregistration amount can be corrected by adjusting the image forming timing and the reference clock regarding the color misregistration between the image forming stations. At this time, in order to determine the timing shift amount and the reference clock change amount, a color shift adjustment sequence (color shift adjustment control) for measuring the relative color shift amount is performed. In the color misregistration adjustment sequence, a color misregistration detection pattern (toner mark) for each color is formed on the intermediate transfer belt 13, and a pair of optical sensors (patch sensors) provided on both sides of the intermediate transfer belt 13 downstream portion. In 28), the toner mark is detected. Further, based on the detection result, the relative color misregistration amount of each color toner image is measured, and the color misregistration correction of the output image is performed according to the measured color misregistration amount.

(Configuration example of patch sensor 28)
FIG. 2B shows a configuration example of the patch sensor 28, which includes a light emitting element and a light receiving element. The light emitting element 65 is, for example, an LED. An optical path is provided in the sensor housing 66 so that light is incident at an angle θ (= 15 °) with respect to the perpendicular of the intermediate transfer belt 13. The light emitting element 65 is disposed at a distance of Ls1 (= 10 mm) from the surface of the intermediate transfer belt 13. The light receiving element 67 is, for example, a phototransistor. The phototransistor 67 is disposed at a position that mainly receives light at an angle of ψ (= 15 °) with respect to the perpendicular of the intermediate transfer belt 13 and at a distance of Ls2 (= 10 mm) from the belt, and receives light. The light intensity is converted into an electrical signal. By setting θ and ψ to the same angle, more regular reflection light (not diffuse reflection light) from the intermediate transfer belt 13 can be taken in by the phototransistor 67. In actual use, the patch sensor 28 is traversed in a state where a color misregistration detection pattern (toner mark) (not shown) is placed on the intermediate transfer belt 13. The range irradiated by the LED 65 is a substantially circular shape having a diameter of about 3 mm on the intermediate transfer belt 13. The phototransistor 67 measures reflected light from a substantially circular region having a diameter of about 1 mm near the center of the irradiation range of the LED 65. The amount of light received by the phototransistor 67 varies depending on whether the toner image is present in the measurement range of the phototransistor 67, whereby the passage of toner can be converted into an electrical signal. In addition, by recording the time when the amount of received light changes, the passage time of the toner image can be measured.

<Configuration Example of DC Controller 200>
FIG. 3 shows a configuration block of the DC controller 200. The same components as those in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof is omitted to avoid duplication. 210 is a CPU for arithmetic processing. A ROM 220 stores a boot program used by the CPU 210 and fixed parameters. A RAM 230 is used as a temporary storage while the CPU 210 executes the program. Reference numeral 240 denotes a mass storage unit such as a program executed by the CPU 210 or a disk for storing parameters in a nonvolatile manner. Reference numeral 260 denotes an input interface for input from various sensors 53 including, for example, the patch sensor 28, the fixing temperature sensor 29, and the environmental temperature sensor 30. Reference numeral 270 denotes an output interface for a control signal to each processing unit shown in FIG.

  In the RAM 230 of this embodiment, an area for storing the following data is secured. 231 stores a color misregistration adjustment condition flag indicating the result of determining the timing for performing color misregistration adjustment based on the elapsed time from the previous color misregistration adjustment and the number of prints. Reference numeral 232 stores a timer for measuring an elapsed time from the previous print, a fixing temperature detected by the fixing temperature sensor 29, and an environmental temperature detected by the environmental temperature sensor 30. Furthermore, an initial state flag indicating the result of determining whether to perform large-scale color misregistration adjustment or small-scale color misregistration adjustment from these values is stored. 233 stores a continuous print / intermittent print flag indicating the determination result of whether the current print state is continuous print or intermittent print, which is used in the second embodiment. In 234, a color misregistration detection pattern (toner mark) which is patch data printed at the time of color misregistration adjustment is stored. In 235, pattern reading data obtained by reading the formed color misregistration detection pattern with the patch sensor 28 is stored. In 236, relative color misregistration data of magenta, cyan and yellow detected from the pattern read data with reference to black is stored. Here, in the small-scale color misregistration adjustment of the first embodiment, the color misregistration amount data predicted from the magenta color misregistration amount data is stored as cyan and yellow color misregistration amount data. 237 stores color misregistration adjustment data in the main scanning direction and the sub scanning direction calculated from the measured or predicted color misregistration amount data. Reference numeral 238 denotes a program load area into which a program stored in the large-capacity storage unit 240 is loaded, and is executed by the CPU 210. Each of the above-described areas is a data area specific to the present embodiment, and a description of a general-purpose data area is omitted.

  An area for storing the following data is secured in the large-capacity storage unit 240 of the present embodiment. Reference numeral 241 holds image data formed by the image forming apparatus. 242 stores patch data for large-scale color misregistration adjustment used when the initial state flag 232 indicates large-scale color misregistration adjustment. 243 stores patch data for small-scale color misregistration adjustment used when the initial state flag 232 indicates small-scale color misregistration adjustment. In 244, a color misregistration determination condition is stored as a threshold value serving as a determination criterion for the color misregistration adjustment condition flag 231. 245 stores an initial state determination condition as a threshold value serving as a determination reference regarding the initial state flag 232. 246 stores a prediction formula for predicting the CK (cyan based on black) color shift amount from the MK (magenta based on black) color shift amount. 247 stores a prediction formula for predicting the YK (yellow based on black) color shift amount from the MK (magenta based on black) color shift amount. In the case of the second embodiment, 246 and 247 have a prediction equation for continuous printing and a prediction equation for intermittent printing. Reference numeral 251 stores an image forming processing program for controlling the image forming processing of the image forming apparatus. A color misregistration adjustment program for controlling color misregistration adjustment according to the present embodiment, which will be described below with reference to FIG. 253 stores a large-scale color misregistration adjustment module that controls large-scale color misregistration adjustment. 254 stores a small-scale color misregistration adjustment module that controls small-scale color misregistration adjustment according to the present embodiment, which will be described below with reference to FIG. Note that the above-mentioned area is mainly a data and program area specific to the present embodiment, and a description of general-purpose data and program areas is omitted.

(Large-scale color misregistration adjustment pattern)
FIG. 4 shows an example of a color misregistration detection pattern used in a large-scale color misregistration adjustment sequence, which is patch-formed on the intermediate transfer belt 13. Reference numerals 101 and 102 denote patterns for detecting the color misregistration amount in the transfer material conveyance direction (sub-scanning direction), and 103 and 104 denote patterns for detecting the color misregistration amount in the main scanning direction orthogonal to the transfer material conveyance direction. . The subscripts Y, M, C, and B indicate toner images formed at the image forming stations for yellow, magenta, cyan, and black, respectively. Reference numerals tsf1 to 4, tmf1 to 4, tsr1 to 4, and tmr1 to 4 indicate times when each pattern is detected by the patch sensor 28, and arrows indicate the moving direction of the transfer belt 9a.

First, a method for correcting the amount of color misregistration in the sub-scanning direction of the large-scale color misregistration adjustment sequence will be described. The moving speed of the intermediate transfer belt 13 is v (mm / s), and K is a reference color for relative color shift. Further, the theoretical distance between the transfer material conveyance direction pattern (tsf2 to 4 and tsr2 to 4) and the K pattern (tsf1, tsr1) is dsY (mm), dsM (mm), dsC (mm), and K is a reference color. To do. At that time, with respect to the transport direction, the color misregistration amount δes of each color is
δesY = v * {(tsf2-tsf1) + (tsr2-tsr1)} / 2-dsY (Equation 1)
δesM = v * {(tsf3-tsf1) + (tsr3-tsr1)} / 2-dsM (Expression 2)
δesC = v * {(tsf4-tsf1) + (tsr4-tsr1)} / 2-dsC (Equation 3)
It becomes. The direction of deviation is known from the positive and negative of the calculation result. δes is a color shift in the sub-scanning direction. Adjustment in line units (about 40 μm at 600 dpi) can be realized by shifting the writing start timing by the number of lines, and adjustment for one line or less can be realized by changing the rotational phase of the polygon mirror of each color.

  Next, a correction method using a color misregistration adjustment sequence in the main scanning direction will be described. The measured distance between the transfer material conveyance direction pattern and the main scanning direction pattern for each color is dmfK (mm), dmfY (mm), dmfM (mm), dmfC (mm), dmrK (mm), dmrY (mm), dmrM (mm), and dmrC (mm). Regarding the main scanning direction, the color misregistration amounts δemf and δemr for each of the left and right colors are as follows.

δemfY = dmfY−dmfK (Formula 4)
δemfM = dmfM−dmfK (Formula 5)
δemfC = dmfC−dmfK (Formula 6)
δemrY = dmrY−dmrK (Expression 7)
δemrM = dmrM−dmrK (Equation 8)
δemrC = dmrC−dmrK (Formula 9)
Where dmfK = v * (tmf1-tsf1) (Equation 10)
dmfY = v * (tmf2-tsf2) (Formula 11)
dmfM = v * (tmf3-tsf3) (Formula 12)
dmfC = v * (tmf4-tsf4) (Formula 13)
dmrK = v * (tmr1-tsr1) (Formula 14)
dmrY = v * (tmr2-tsr2) (Formula 15)
dmrM = v * (tmr3-tsr3) (Formula 16)
dmrC = v * (tmr4-tsr4) (Expression 17)
It was. Since δemfM is the left main scanning color shift and δemrM is the right main scanning color shift, when the reference position is the center, for example, by shifting the main scanning writing position by the average value of δemfM and δemrM, The position in the scanning direction is corrected. Further, from δemrM−δemfM, the shift amount of the main scanning width can be known. The main scanning width can be corrected by changing the user lighting frequency of the main scanning.

  Incidentally, it is known that the color misregistration amount δes in the sub-scanning direction is affected by the eccentricity of the drum and the eccentricity of the driving roller. In order to cope with this, for example, in order to reduce the influence of the eccentricity of the drum, it is effective to form a plurality of sets of color misregistration patterns and average δes obtained from each set. In order to reduce the influence of drum eccentricity, a plurality of sets of color misregistration patterns are formed, and δes obtained from each set is averaged. Assuming that the interval between the first set and the second set is L1, L1 is arranged at a position that is half the odd number of times of the circumference of the drum. Thus, δes calculated from the first set and δes calculated from the second set are obtained by measuring the color misregistration amount at a position shifted by exactly 180 ° in the rotational phase of the drum, and the average of both is calculated. Thus, the influence of the eccentricity of the drum can be reduced. In this example, L1 is 37.68 mm, which is half the circumference of the photosensitive drum. The combination of the second set is the first set, and a total of four sets are arranged. The interval between the first patch pattern of the first set and the second patch pattern of the second set is L2, the interval between the first set and the second set of the second set is L3, and L3 is L1. And the same distance. By setting L2 to a distance that is half the length of one circumference of the driving roller × odd multiple, the first and second sets of patches are exactly 180 ° out of phase with the rotational phase of the driving roller. In this example, it is 84.78 mm which is 3/2 of the driving roller. By averaging these δes, the influence of the eccentricity of the drive roller can be reduced. The total length of the detection pattern used in the large-scale color misregistration adjustment sequence was 154.46 mm.

(Small color shift adjustment pattern)
A small-scale color misregistration adjustment sequence in this embodiment will be described. The small-scale color misregistration adjustment sequence executes a color misregistration measurement sequence with a short required time between printing operations when the large-scale color misregistration adjustment sequence is performed in the initial state described above. FIG. 5 shows an example of a color misregistration detection pattern used for the small-scale color misregistration adjustment sequence formed on the intermediate transfer belt 13 as a patch. Here, the subscripts M and K indicate toner images formed at the magenta and black image forming stations, respectively. The patterns 120 and 121 are linear patterns with a width of 1 mm and a length of 10 mm in the main scanning direction. The same color patterns 120 and 121 are arranged on the same straight line in the main scanning direction. 120K and 120M are formed with an interval of 2 mm in design. 122 and 123 are linear patterns formed with an inclination of 45 ° with respect to the main scanning direction. 120 and 121 are patterns for detecting a color misregistration amount in the transfer material conveyance direction (sub-scanning direction), and 122 and 123 are patterns for detecting a color misregistration amount in the main scanning direction orthogonal to the transfer material conveyance direction. It is. The two vertical dotted lines represent the lines detected by the two patch sensors. As the intermediate transfer belt moves, the toner crosses the detection position of the fixed non-contact patch sensor, and the patch passes. Detect time. “tsf1,” “tsf2,” “tsm1,” “tsm2,” “tsr1,” “tsr2,” “tmr1,” and “tmr2” indicate times when each pattern is detected by the patch sensor. The eight lines formed by these 120, 121, 122, and 123 form a first set. From this first set, it is possible to measure the relative printing accuracy between two colors, such as a deviation in the main scanning direction, a deviation in the sub-scanning direction, a magnification in the main scanning direction, and parallelism. The moving speed of the transfer belt B is v [mm / s], K is the reference color, and the theoretical distance between the transfer material conveyance direction pattern and the K pattern is dsM [mm] (in this example, the design value as described above) 2), the measured distance between the pattern for the transfer material for each color and the pattern for the main scanning direction is dmfK (mm), dmfM (mm), dmrK (mm), dmrM (mm ). With K as the reference color, the color misregistration amount δesM in the transport direction is
δesM = v * {(tsf2−tsf1) + (tsr2−tsr1)} / 2−dsM (Expression 18)
It becomes. Regarding the main scanning direction, the color misregistration amounts δemfM and δemrM of the respective colors on the left and right sides are as follows.

δemfM = dmfM−dmfK (Equation 19)
δemrM = dmrM−dmrK (Equation 20)
However,
dmfK = v * (tmf1-tsf1) (Formula 21)
dmfM = v * (tmf2-tsf2) (Formula 22)
dmrK = v * (tmr1−tsr1) (Equation 23)
dmrM = v * (tmr2-tsr2) (Equation 24)
It is. Subsequent 124, 125, 126, and 127 are the second set of color misregistration detection patterns, and the same patterns as 120 to 123 are formed with a predetermined interval L4. L4 is set to a distance (= 37.68 mm) half of the circumference of the photosensitive drum (= 75.36 mm). The first set and the second set are formed at positions that differ by approximately 180 ° in the phase of the rotation angle of the photosensitive drum. By averaging the deviation amounts obtained from the respective sets, the influence of the eccentricity of the photosensitive drum is reduced. The length of the first set is 20 mm, and the pattern set having a length of 57.68 mm together with the second set is referred to as the first set. Measurement of the first set of color misregistration patterns can reduce the influence of the rotational phase of the photosensitive drum. The third set and the fourth set constituting the second set are also formed at an interval of 37.68 mm. The distance between the second patch pattern of the second group and the first patch pattern of the first group is formed with a distance of L5. L5 is preferably n / 2 times the circumference of the drive roller (where n is an odd number). The circumference of the drive roller in this example was 56.52 mm, and L5 was 367.38 mm (13/2 times the circumference of the drive roller). Reference numeral 136 denotes a printing area of A4 (length 297 mm). A print image to be printed on paper is formed between the first set of color shift detection patterns and the second set of color shift detection patterns. For example, when the print image is A3, L5 is changed to 536.96 mm (19/2 times the circumference of the drive roller), and the formation position of the second color misregistration detection pattern is recorded according to the recording paper length. It needs to be changed in conjunction with the total length of the paper. In some cases, the total length can be reduced by canceling the drive roller eccentricity between the first set and the second set and canceling the influence of the photosensitive drum eccentricity between the first set and the second set. It is preferable to select a method with good space efficiency depending on the configuration of the image forming apparatus and the size of the recording paper.

(Comparison between large-scale color shift adjustment and small-scale color shift adjustment)
When measuring the color misregistration amount after reducing the influence of the eccentricity of the photosensitive drum and the eccentricity of the driving roller for all colors as in the large-scale color misregistration adjustment sequence, the total number of necessary patches increases. Therefore, the downtime required for the sequence becomes long. By dividing the color misregistration detection pattern and inserting it before and after the print image as in this embodiment, the print image is output while detecting the color misregistration detection pattern, and the user feels a waiting time. The color misregistration adjustment sequence can be performed without doing so. Here, the extra length required on the belt before the printed image can be reduced to 57.68 mm in one set. While the paper passes through the fixing device and is discharged to the outside, post-processing such as image formation, reading, and development separation of the second set can be completed. Therefore, for example, when the process speed is 50 mm / sec, the color misregistration detection is performed by delaying only the time for forming the image for one set, that is, the time for discharging the printed image from the image forming apparatus by 1.2 seconds. It can be performed. On the other hand, when a large-scale color misregistration adjustment sequence is performed, more time of 3.1 seconds is required for the pattern formation time alone. In addition, during the large-scale color misregistration adjustment sequence, the printing voltage adjustment, drum potential stabilization, and developer contact / separation operations are performed as preparations for image formation, even though printing on paper is not performed. It will take time. Eventually, it takes about 30 seconds, so paper printing cannot be performed, and downtime in which the user cannot use the image forming apparatus takes a long time. In this embodiment, since the color misregistration detection pattern is formed in front of the image printed on the recording paper, the color misregistration detection pattern may be in direct contact with the secondary transfer roller, so that the secondary transfer roller may become dirty. In order to avoid this as much as possible, while the color misregistration detection pattern is passing, a voltage in the reverse direction (for example, -2 kV) is applied to the secondary transfer roller so that toner is not attached as much as possible. preferable. Alternatively, when the secondary transfer roller has a mechanism capable of separating from the intermediate transfer member, it is preferable to separate the rollers.

(Prediction formula for CK and YK deviation from MK deviation)
By forming a color misregistration detection pattern (toner mark) of only magenta and black as in this embodiment, the total number of color misregistration detection patterns is reduced. Furthermore, the time required for color misregistration adjustment control can be shortened by dividing the image into a plurality of sets and inserting them between printed images. However, in this case, although the relative color misregistration amount relating to magenta and black as the measurement colors can be measured, the relative color misregistration amount between the image forming station of the measurement color and the image forming station of the color other than the measurement color cannot be measured. In this embodiment, by predicting the relative color misregistration amount for the image forming station of colors other than the measurement color from the relative color misregistration amounts of magenta and black, the color misregistration can be reduced while reducing the time required for the color misregistration adjustment control. Suppress.

  FIG. 6 shows the transition of the color misregistration amount with respect to the number of sheets passing in various sheet passing modes when the color misregistration adjustment control is not performed. FIG. 6A shows the relative color shift amount between M and K. FIG. In this figure, if printing is continued continuously, printing is performed at one output pace per minute, printing is performed at one output pace per 5 minutes, and one sheet is printed every 10 minutes. This shows the transition of the color misregistration amount when printing is continued at an output pace of. FIG. 6B shows the transition of the relative color shift amount between C and K, and FIG. 6C shows the transition of the relative color shift amount between Y and K. In FIG. 6B, when one sheet is printed per minute, the color misregistration amount once changes in the positive direction and then tends to decrease when printing is further continued. When the temperature in the image forming apparatus rises due to the operation of the fixing device or the heat generated from the electric substrate of the image forming apparatus, and the outer diameter of the drive roller changes, the CK color shift changes in the negative direction. On the other hand, when the temperature of the scanner as the exposure apparatus rises, the irradiation position changes, and the color shift of CK changes in the positive direction. Since the time required for the heat from the fixing device to be transmitted to the drive roller and the exposure device is different, the temperature rise curves of the respective parts with respect to the operation time of the image forming apparatus are different, and further, the temperature rise is started. The time lag is also different. As a result, the amount of color misregistration, which is the result of adding the change in the negative direction caused by the thermal expansion of the drive roller and the change in the positive direction caused by the temperature rise of the exposure apparatus, once changed to a positive value and then changed to a negative value. It turns. In particular, while the image forming apparatus is once in operation and stopped, the temperature changes as follows. The temperature of the fixing unit is maintained higher than that of other members for a while, and the drive roller and exposure device are slowly moved by complicated heat transfer paths such as radiant heat, direct heat transfer through the frame, and radiant heat from the frame. Be warmed up. Further, the distance from the main heat source in the image forming apparatus representing the fixing device differs depending on the exposure device of each color, and the temperature increase rate also differs for each image forming station. Since the temperature rise rate of each member with respect to the number of printed sheets is affected by the history such as the ratio between the operation time and the downtime, the amount of color misregistration is similarly the operation time per unit time, the width and length of the recording paper, It depends on the type of thickness.

  FIG. 7 shows a statistical tendency regarding the transition of the relative color misregistration amount in the sub-scanning direction for each printing mode of FIG. FIG. 7A plots the amount of color misregistration (vertical axis) in the sub-scanning direction between C and K with respect to the amount of color misregistration in the sub-scanning direction between M and K (horizontal axis). Similarly, FIG. 7B plots the amount of color misregistration (vertical axis) in the sub-scanning direction between Y and K with respect to the amount of color misregistration in the sub-scanning direction between M and K (horizontal axis). is there. As shown in FIG. 7, it can be seen that there is a correlation between the M-K color shift amount and the C-K color shift amount statistically. As shown in FIG. 1, in the case of a main body configuration in which an intermediate transfer belt that receives a transfer from a plurality of image forming stations by a driving roller is rotated, a change in the peripheral speed due to thermal expansion of the driving roller due to a temperature rise in the apparatus causes all image formation. It affects the color misregistration amount of the station. When there is an element that changes the relative color shift amount of all image forming stations due to thermal expansion of not only the driving roller but also a single component, the relative color shift amount between the reference image forming station and one image forming station is measure. For this reason, it is possible to predict the color misregistration amount of other image forming stations to some extent.

In this example, when the CK color misregistration amount y1 (μm) is set to x (μm),
y1 = 0.5521x + 24.311
Was used as a prediction formula. In addition, regarding the YK color misregistration amount y2 (μm), when the MK color misregistration amount is x (μm),
y2 = 0.9695x + 25.731
Was used as a prediction formula.

  The color misregistration amount measurement sequence between M and K in this example can be executed more frequently without increasing the downtime that the user cannot print because the execution time per time is shorter than in the comparative example. In the present embodiment, every time 30 preset printings are executed, the color misregistration amount measurement sequence between M and K is executed. Further, the above y1 and y2 are immediately obtained from the measured color misregistration amount x between M and K. Furthermore, M is x (μm), C is y1 (μm), and Y is y2 (μm) from the reference position measured in the initial state stored in the non-volatile memory, in the sub-scanning direction of the subsequent print. Only correct. Thereafter, the correction value is continuously maintained until the next color misregistration amount adjustment sequence is executed.

<Operation Example of Image Processing Device of First Embodiment>
In the color misregistration adjustment sequence of this embodiment, one specific color is defined as a reference color (for example, K), and the amount of relative color misregistration with the reference color is measured. There are two types of color misregistration adjustment sequences. The first color misregistration adjustment sequence is a large-scale color misregistration adjustment sequence for measuring the relative color misregistration amount between the image forming station for the reference color and all other image forming stations. The second color misregistration adjustment sequence is a small-scale color misregistration adjustment sequence for measuring a relative color misregistration amount between an image forming station of the reference color and one other image forming station. The image forming apparatus according to the present embodiment executes a large-scale color misregistration adjustment sequence in an initial state in which the image forming apparatus is not in operation and is sufficiently familiar with the temperature and humidity of the surrounding environment, and thereby, color misregistration of all colors. Is stored as a reference position. Here, when the image forming apparatus is operated and the in-machine temperature rises, color misregistration starts to occur, and when the operation of the image forming apparatus is stopped, the color misregistration amount tends to return to the reference position as the apparatus is gradually cooled. is there. In the initial state, the image forming apparatus is based on output values such as a temperature detection element in the fixing device in the apparatus, a sensor for detecting the environmental temperature, and a timer for measuring the elapsed time from the last printing end. Judge whether there is. In the initial state, a large-scale color misregistration adjustment sequence is executed, and the reference position is stored in a nonvolatile memory inside the image forming apparatus. In the image forming apparatus, for example, a condition that a difference between an environmental temperature and a fixing device temperature is within a predetermined temperature (for example, within 5 ° C.) and a predetermined time or more (for example, 2 hours or more) has passed since the previous printing. When (initial state determination condition) is satisfied, it is determined that the current state is the initial state. The image forming apparatus sets the corrected position of the large-scale color misregistration adjustment sequence executed in the initial state as the reference position.

(Example of processing procedure of DC controller 200)
A processing procedure example of the DC controller 200 of the image forming apparatus 1000 will be described with reference to FIGS. Such processing procedure is executed by the CPU 210. FIG. 8 shows a procedure example of the color misregistration adjustment program 252 and shows only a portion related to the present invention. First, in S82, the CPU 210 performs large-scale color misregistration adjustment at power-on. When the large-scale color misregistration adjustment is completed, the CPU 210 starts image print processing in S84. Next, in S86, the CPU 210 determines whether or not to perform the color misregistration adjustment by determining the color misregistration adjustment conditions (30 prints in this example) and determining whether it is the timing for performing the color misregistration adjustment. Determine whether. If it is determined that color misregistration adjustment is not performed, S86 is repeated. As described above, the printing process is executed in parallel with the above process. If it is determined that the color misregistration adjustment is to be performed, the process proceeds to S88. In S88, the CPU 210 determines whether the image forming apparatus is in an initial state. This determination is a condition for determining whether or not it is in the initial state (in this example, whether or not the difference between the fixing temperature and the environmental temperature is within 5 ° C. within 2 hours from the last print. ) Is used. This condition corresponds to a condition for executing large-scale color misregistration adjustment. If the initial state is determined, the process proceeds to S90, where the CPU 210 interrupts the printing process, executes a large-scale color misregistration adjustment in S92, confirms the end of the large-scale color misregistration adjustment, and resumes the printing process in S94. To do. On the other hand, if it is determined that the current state is not the initial state, the process advances to step S100, and the CPU 210 executes small-scale color misregistration adjustment according to the present embodiment, which will be described later with reference to FIG. Finally, in S96, the CPU 210 determines that the image forming apparatus is powered off. If not, the CPU 210 returns to S86 and continues the processing. If the power is off, the CPU 210 ends the process.

  FIG. 9 is a processing procedure for small-scale color misregistration adjustment in S100. In S102, the CPU 210 temporarily suspends the print process. In S <b> 104, the CPU 210 transfers the first set of first patch patterns onto the intermediate transfer belt 13. In S106, the CPU 210 resumes the printing process. That is, in the small-scale color misregistration adjustment, there is no need to wait in an idle state until the adjustment is completed. In S <b> 108, the CPU 210 reads the first set of first patch patterns on the intermediate transfer belt 13 by the patch sensor 28. In S110, the CPU 210 calculates an (M−K) color shift amount from the read pattern data. In S112, based on the calculated (M−K) color shift amount, the CPU 210 predicts the (C−K) color shift amount and the (Y−K) color shift amount using the prediction formula shown in FIG. In S114, the CPU 210 corresponds to the measured (M−K) color shift amount and the predicted (C−K) color shift amount and (Y−K) color shift amount, in the main scanning direction, the sub scanning direction, and the drum eccentricity. Perform color misregistration adjustment. In S <b> 116, the CPU 210 transfers the second set of second patch patterns onto the intermediate transfer belt 13. This timing is a timing at an interval that is an integral multiple of one rotation of the drive roller. A normal image can be formed between the first set of first patch patterns and the second set of second patch patterns. In S <b> 118, the CPU 210 reads the second set of second patch patterns on the intermediate transfer belt 13 by the patch sensor 28. In S120, the CPU 210 calculates an (M−K) color misregistration amount from the read pattern data. In S <b> 122, the CPU 210 predicts the (C−K) color shift amount and the (Y−K) color shift amount based on the calculated (M−K) color shift amount and the prediction formula shown in FIG. 7. In S <b> 124, the CPU 210 adjusts the color misregistration of the driving roller in accordance with the measured (M−K) color misregistration amount and the predicted (CK) color misregistration amount and (YK) color misregistration amount. Then, the process returns to FIG.

<Example and Effect of Color Shift Adjustment of First Embodiment>
When the color misregistration adjustment as in Embodiment 1 is performed, for example, the result applied to the color misregistration data without the color misregistration adjustment in FIG. 6 is shown in FIG. According to the color misregistration correction control of the first embodiment, the color misregistration amount is 45 μm between M and K, 34 μm between C and K, and 73 μm between Y and K. The effect of the first embodiment becomes more apparent in comparison with the image forming apparatuses of Comparative Examples 1 and 2 below.

(Comparative Example 1)
As a comparative example 1, a case where only the large-scale color misregistration adjustment sequence is executed once for every 100 printed sheets will be exemplified. A large-scale color misregistration adjustment sequence that measures the color misregistration amount of all colors has a long downtime, so it is not preferable for the user to perform it frequently. For this reason, it is executed periodically with a period of time so as not to impair the print quality rather than every print, and color misregistration is corrected. FIG. 11 shows how the color misregistration transition of FIG. 6 becomes when the large-scale color misregistration adjustment sequence is executed once for 100 sheets. The maximum amount of color misregistration without color misregistration was 101 μm between M and K, 52 μm between C and K, 102 μm between Y and K, and 101 μm between M and K, C—K. There was no change in the maximum value of the color misregistration amount of 52 μm between them and 102 μm between Y and K.

(Comparative Example 2)
Next, color misregistration adjustment in the image forming apparatus of Comparative Example 2 will be described. When the image forming apparatus is operated continuously and the temperature inside the image forming apparatus changes, the optical unit parts that affect the image forming position are deformed by thermal expansion, and the frame that is the frame of the apparatus, and deformation by thermal expansion of the drive roller. Etc. occur. As a result, the image forming positions of the respective image forming stations are relatively displaced, and if image formation is performed in this state, color misregistration occurs. For this reason, the amount of color misregistration due to the temperature rise of the image forming apparatus is predicted. FIG. 12 shows how the color misregistration amount changes with respect to the operation time of the fixing device with respect to the data in FIG. Rather than correcting the amount of color misregistration based on the number of printed sheets, the amount of color misregistration is easier to predict because the operating time of the fixing device, which is the main heat source for increasing the temperature inside the apparatus, has a higher correlation with the temperature inside the image forming apparatus. A prediction curve showing the transition of the color misregistration amount with respect to the fixing rotation time obtained by averaging the color misregistration amounts in the respective sheet passing modes is shown in FIG. FIG. 13 shows the transition of color shift when the writing position is corrected for each print along the prediction curve shown in FIG. 12 using the color shift data of FIG. The maximum color misregistration amount was 56 μm between M and K, 41 μm between C and K, and 82 μm between Y and K. When the image forming apparatus repeatedly stops operating and repeatedly increases and decreases in the in-machine temperature before reaching the steady state, the transition of the color misregistration amount varies greatly depending on the mode in which the sheet is passed. For this reason, a place where the difference between the color misregistration amount predicted from the fixing rotation time and the actual color misregistration amount becomes large occurs.

  In such a transient state in which the temperature state in the image forming apparatus continues to change, color misregistration adjustment as in this embodiment is advantageous. That is, only the relative color misregistration amount between two stations having a larger thermal fluctuation than the prediction of all colors is measured, and so to speak, the degree of influence of the temperature rise in the apparatus on the color misregistration is directly measured. The remaining image forming stations can improve the correction accuracy by predicting the color misregistration amount.

[Embodiment 2]
The image forming apparatus of this example is the same as that exemplified in the first embodiment, and the color misregistration detection pattern used in the color misregistration adjustment sequence is also the same. The timing for executing the color misregistration adjustment sequence is also the same. As long as there is no notice, the same structure as Embodiment 1 is used. However, the second embodiment is different in the method of predicting the color misregistration amount of other image forming stations from the relative color misregistration amount between M and K. The method will be described below.

(Prediction formula of YK deviation amount of continuous / intermittent printing from MK deviation amount)
FIG. 7B shows the correlation between the data obtained by continuous printing and the data obtained by intermittent printing at 1 sheet / minute, 1 sheet / 5 minutes, and 1 sheet / 10 minutes. 14 plotted. FIG. 14A shows the correlation between the color misregistration amount between M and K and the color misregistration amount between Y and K during continuous printing, and the color misregistration between Y and K with respect to the color misregistration amount between M and K. It can be seen that the quantities are not very correlated. FIG. 14B shows the correlation between the M-K color shift amount and the Y-K color shift amount during intermittent printing. It can be seen that there is a strong correlation between the color shift amount between M and K and the color shift amount between Y and K during intermittent printing. Therefore, when the prediction formula described in the first embodiment is different from that for intermittent printing and continuous printing, it is possible to predict with higher accuracy. That is, the printing interval of 30 sheets until the color misregistration adjustment sequence is executed (for example, the timing at which the feeding roller feeds the recording paper or the timing at which the recording paper is discharged from the fixing device) is recorded, and the following two sheets are recorded. Calculate and record the time interval. When the average print interval of 30 sheets is shorter than twice the assumed value of continuous printing, for example, by recording such a printing frequency, it is determined that the printing is substantially continuous printing, and the following prediction formula is used.

Regarding the YK color misregistration amount y3 (μm), when the MK color misregistration amount is x (μm),
y3 = 0.5046x−0.9432
Is used as a prediction formula.

Regarding the CK color shift amount y4 (μm), when the M-K color shift amount is x (μm),
y4 = 0.317x + 5.3444
Is used as a prediction formula. When the average print interval from the recorded print frequency is twice or more that during continuous printing, it is regarded as a substantial intermittent print, and the following prediction formula is used.

Regarding the YK color misregistration amount y5 (μm), when the MK color misregistration amount is x (μm),
y5 = 1.139x−34.37
Is used as a prediction formula.

Regarding the CK color shift amount y6 (μm), when the M-K color shift amount is x (μm),
y6 = 0.4802x + 31.112
Is used as a prediction formula.

(Example of processing procedure of Embodiment 2)
The processing procedure of the second embodiment is basically the same as that shown in FIGS. However, before the color misregistration amount prediction (S112 and S122) in FIG. 9 is performed, it is determined whether the print is continuous print or intermittent print, and the prediction formula to be used is selected as shown in FIG. It is different. In this embodiment, every time 30 sheets set in advance are printed, the color misregistration amount measurement sequence between M and K is executed. Further, the above y is immediately obtained from the measured color misregistration amount between M and K. In the case of continuous printing from the reference position measured in the initial state stored in the non-volatile memory in the sub-scan direction in the subsequent print, M is x (μm), C is y3 (μm), and Y is y4. Correct by (μm). On the other hand, in the case of intermittent printing, M is corrected by x (μm), C is corrected by y5 (μm), and Y is corrected by y6 (μm). The correction value is maintained until the next color misregistration amount adjustment sequence is executed.

(Explanation of color shift between continuous print and intermittent print)
Next, the reason why the correlation is different between continuous printing and intermittent printing will be described. FIG. 16A shows how the color misregistration amount due to thermal expansion of the driving roller changes as the number of printed sheets increases. Continuous printing was performed, the belt driving speed was measured with a user Doppler speedometer, and curve fitting was performed to remove noise. K is farthest from the fixing device, which is a major factor for temperature rise in the apparatus, and is in a position where the temperature rise is difficult. There is a tendency that the color misregistration amount increases as the station (for example, Y) is closer to the fixing device. FIG. 16B shows how the color misregistration amount changes with the temperature rise of the scanner. The displacement of the irradiation position on the photosensitive drum of the scanner is continuously measured, the displacement amount is converted into a color misregistration amount, and curve fitting is performed to remove noise. FIG. 16C is a combination of the color deviation due to the scanner and the color deviation due to the drive roller. The color shift change during continuous printing can be roughly explained by the superposition of the above two factors.

  Next, FIG. 17B plots the correlation between the M-K color misregistration amount and other color misregistration amounts with respect to the graph at the time of continuous printing in FIG. 16C. It can also be seen from this figure that there is little direct correlation between the color shift amount between M and K and the color shift amount of other stations during continuous printing. On the other hand, FIG. 17A plots the correlation between the color shift amount between M and K and other color shift amounts with respect to the graph of FIG. It can be seen that there is a strong linear correlation between the color misregistration amount between M and K and other color misregistration amounts with respect to the color misregistration due to the thermal expansion factor of the driving roller. In the image forming apparatus of this example, as shown in FIG. 1, the driving roller 15 also serves as a secondary transfer facing member. During continuous printing, the recording paper P having a temperature relatively lower than the internal temperature is continuously nipped and conveyed between the secondary transfer roller 25 and the driving roller 15. At that time, the recording paper P serves to cool the drive roller 15. On the other hand, during intermittent printing, the amount of recording paper passing per unit time is drastically reduced. Therefore, it is considered that the temperature rise of the drive roller 15 occurs earlier due to heat transfer from the fixing device 19. Therefore, the change in the color misregistration amount during intermittent printing is dominated by the driving roller rather than the color misregistration change amount due to the temperature rise of the scanner. As described above, when a color shift occurs between a plurality of image forming stations due to a temperature change of one component and the contribution of the component becomes high, a strong correlation between colors is obtained as shown in FIG. To have. Therefore, it is possible to predict and correct the color misregistration amount with relatively high accuracy. In the second embodiment, the amount of color misregistration between M and K is actually measured, and other image forming stations are predicted from the prediction formula. The image forming station to be actually measured is preferably the image forming station having the largest color misregistration amount due to the temperature rise. It is difficult to capture the exact state of the in-flight temperature rise only by prediction without actual measurement. Therefore, by selectively measuring the color misregistration amount of the image forming station that is most affected by the temperature rise, the measured value is less likely to be buried in the measurement error, and it is possible to know the state of the image forming apparatus more accurately and correct with high accuracy. It can be performed.

<Example of Result of Color Shift Adjustment of Embodiment 2>
When the color misregistration adjustment of the second embodiment is performed, for example, the result when applied to the color misregistration data of FIG. 9 is shown in FIG. According to the color misregistration correction control according to the second embodiment, the color misregistration amount can be reduced to 45 μm at maximum between M and K, 31 μm at maximum between CK, and 63 μm at maximum between Y and K. According to the second embodiment, the total number of color misregistration detection patterns is reduced by forming a limited size pattern for detecting the relative color misregistration amount only between M and K, and it is easier to insert between print images. In addition, the time required for color misregistration adjustment control is shortened. In addition, the frequency of printing, such as intermittent printing and continuous printing, and using different prediction formulas in the recording results improve the prediction accuracy, suppress color misregistration, and achieve good image quality A device is provided.

[Other Embodiments]
(Selection example for large-scale color shift adjustment)
In the above-described embodiment, the configuration in which the color misregistration amount between M and K is actually measured and the color misregistration amounts of other image forming stations are predicted and corrected is illustrated. As another embodiment, first, a small color misregistration adjustment sequence for measuring a relative color misregistration amount between two image forming stations is executed. Then, whether to execute a large-scale color misregistration adjustment sequence for measuring the color misregistration amounts of all colors from the measured values, or to execute the color misregistration adjustment sequence after a predetermined number of sheets again without executing the large-scale color misregistration adjustment sequence. You may provide the step which judges whether it is. By doing so, it is possible to delay the execution of a large-scale color misregistration adjustment sequence with a long downtime, so that there is an effect that productivity can be maintained.

  In addition, as a criterion for performing the large-scale color misregistration adjustment sequence, it may be performed when it can be assumed that the image forming apparatus has some significant color misregistration change. For example, this is a case where the color misregistration amount between two stations is larger than a specific threshold and is assumed to deviate beyond the normal range. In addition, there is a case where there is a difference greater than a specific threshold between the previous color misregistration amount measurement result and the current color misregistration amount measurement result. Further, this is a case where the color shift is on the side opposite to the assumed color shift direction and more than a specific threshold. In such a case, a large-scale color misregistration adjustment sequence is performed. By providing such a determination criterion, it is possible to determine when the color misregistration has changed significantly due to factors other than temperature rise in the apparatus, such as when the process CRG has been replaced or when the use environment of the image forming apparatus has changed significantly. As described above, it is possible to quickly detect a case where it is not appropriate to perform the predictive control, and to correct the color misregistration by the large-scale color misregistration adjustment sequence to maintain the print quality.

(Example of changing the measurement color for small color shift adjustment)
When a color shift between M and K is detected in the small-scale color shift adjustment sequence, the color to be measured may be changed after the next time. For example, the color shift between C and K may be detected in the next small color shift adjustment sequence, and the color shift between Y and K may be detected in the next small color shift adjustment sequence. In this way, when the superscale color misregistration adjustment sequence is executed three times, correction based on the actual measurement value of each color can be performed. In other words, since one large-scale color misregistration adjustment sequence can be divided into three small-scale color misregistration adjustment sequences, downtime of the image forming apparatus can be distributed over a long period of time, thereby reducing stress on the user. .

  Further, in this example, since the color shift between M and K is most strongly affected by the temperature rise, a method of measuring the color shift between M and K every time in the color shift adjustment sequence for each regular number of sheets is illustrated. However, for example, when both M-K and Y-K are strongly affected by the temperature rise, the following method may be used. First, M-K is measured in the first color misregistration adjustment sequence, Y-K is measured in the next color misregistration adjustment sequence, and a prediction formula for predicting from the amount of color misregistration between Y-K is prepared separately. deep. By taking such a method, it is possible to prevent the predicted value from significantly deviating by periodically grasping the state of the image forming station that is sensitive to temperature rise.

  In the present embodiment, the case of an intermediate transfer type image forming apparatus has been described, but it goes without saying that the present invention can also be suitably used for an image forming apparatus using a conveyance transfer belt. 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.

<Effect of this embodiment>
As described above, the small-scale color misregistration adjustment sequence and the large-scale color misregistration adjustment sequence are provided, and the color misregistration amount is corrected by either of them. Accordingly, it is possible to provide an image forming apparatus that suppresses color misregistration while reducing downtime of the image forming apparatus and maintaining productivity. In addition, by predicting and correcting the color misregistration amount of colors not measured from the actual color misregistration amounts measured in the small-scale color misregistration adjustment sequence, downtime of the image forming apparatus is reduced and productivity is maintained. However, an image forming apparatus that suppresses color misregistration can be provided. Further, the color measured in the small-scale color misregistration adjustment sequence is changed in the next small-scale color misregistration adjustment sequence. As a result, one large-scale color misregistration adjustment sequence can be divided into three small-scale color misregistration adjustment sequences, and after the three small-scale color misregistration sequences are completed, There is no accuracy. Furthermore, by predicting the color misregistration of other colors that are not measured during each small color misregistration sequence, the color misregistration was suppressed while maintaining the productivity by distributing the downtime of the image forming apparatus over a long period of time. An image forming apparatus can be provided. Further, the average print interval is measured, and the prediction formula used in the small-scale calibration is made different between continuous printing and intermittent printing. Accordingly, it is possible to provide an image forming apparatus in which color misregistration is further suppressed by correcting color misregistration with higher accuracy while maintaining productivity while suppressing downtime of the image forming apparatus.

Claims (9)

Based on the detection result of detecting the toner marks of the respective colors, a measuring means for measuring a relative color misregistration amount of the toner image of each color, the relative of the respective color toner images on the basis of the measured amount of color shift an image forming apparatus having a color shift correcting means for correcting the color shift, and
At the timing of color misregistration correction, toner marks of all the colors are formed, and a relative color misregistration amount of each color toner image is measured to determine whether or not a condition for correcting color misregistration is satisfied. Have a judgment means,
When it is determined by the determination means that the condition is not satisfied,
The measuring unit measures a relative color shift amount between a reference color and another one color,
The color misregistration correction means includes
Based on the relative color shift amount between the measured reference color and the other one color, the relative color shift between the reference color and the color other than the one other color. Predicting means for predicting the amount, correcting the color misregistration of the other one color based on the color misregistration amount measured by the measuring means, and based on the color misregistration amount predicted by the predicting means one correct the color of the color shift other than the color of
The image forming apparatus further includes a storage unit that stores the other one color when the color misregistration correction unit performs color misregistration correction at a first timing;
When the color misregistration correction unit performs the color misregistration correction at a second timing after the first timing, the measurement unit compares the color different from the stored color with the reference color. A color misregistration amount is measured, and the predicting unit determines a color other than the reference color and the different color based on a relative color misregistration amount between the measured reference color and the different color. An image forming apparatus that predicts a relative color misregistration amount . When it is determined by the determination means that the condition is satisfied,
The measuring means measures the amount of relative color misregistration between the reference color and all other colors with the formation of the toner mark,
The color misregistration correction unit corrects each color misregistration of all the other colors based on a relative color misregistration amount between the measured reference color and all other colors. The image forming apparatus according to claim 1.   The condition includes a condition that an elapsed time from the previous print is a predetermined time or more and a difference between a fixing temperature of the fixing device and an environmental temperature in the apparatus is within a predetermined temperature. The image forming apparatus according to 1 or 2. The measuring means forms a first patch pattern for measuring the color misregistration amount in the main scanning direction and the sub scanning direction and the color misregistration amount due to the eccentricity of the drum, and measures the color misregistration amount due to the eccentricity of the driving roller. Further has a patch forming means for forming a second patch pattern,
An image is formed between the first patch pattern and the second patch pattern shortened in the sub-scanning direction when the determination unit determines that the condition is not satisfied. The image forming apparatus according to 1. A determination means for determining whether the image formation by the image forming apparatus is continuous printing or intermittent printing with a print interval;
The image forming apparatus according to claim 1, wherein the prediction unit predicts a different color misregistration amount corresponding to the continuous printing or the intermittent printing. The image forming apparatus is a tandem color image forming apparatus having a plurality of image forming stations for forming toner images of respective colors.
Each color of the plurality of toner images is yellow, magenta, cyan, and black,
It said reference to become color is black, the image forming apparatus according to any one of claims 1 to 5, wherein the other one color is magenta. Based on the detection result of detecting the toner marks of the respective colors, a measuring means for measuring a relative color misregistration amount of the toner image of each color, the relative of the respective color toner images on the basis of the measured amount of color shift a method of controlling an image forming apparatus having a color shift correcting means for correcting the color shift, and
Whether the determination unit satisfies the condition for correcting the color misregistration by forming the toner marks of all the colors of the respective colors at the timing of color misregistration correction and measuring the relative color misregistration amounts of the toner images of the respective colors. A determination process for determining whether or not
When it is determined that the condition is not satisfied in the determination step,
A measuring step in which the measuring unit measures a relative color shift amount between a reference color and another one color;
A predicting unit configured to determine a relative value between the reference color and the color other than the other one color based on a relative color shift amount between the measured reference color and the other one color; A prediction process for predicting the amount of color misregistration,
The color misregistration correction unit corrects the color misregistration of the other one color based on the color misregistration amount measured in the measurement step, and the other one based on the color misregistration amount predicted in the prediction step. A color misregistration correction process for correcting color misregistration of colors other than one color ,
A storage step of storing the other one color when the storage unit performs the color shift correction at the first timing;
When the color misregistration correction unit performs color misregistration correction at a second timing subsequent to the first timing, the measurement unit compares the color different from the stored color with the reference color. A color misregistration amount is measured, and the prediction unit determines a color other than the reference color and the different color based on a relative color misregistration amount between the measured reference color and the different color. Predicting the relative color misregistration amount with
A control method for an image forming apparatus, comprising:   An image forming apparatus,
  Forming means for forming a toner mark of a reference color and a toner mark of one other color;
  Measuring means for measuring a relative color misregistration amount between the reference color and another one color based on a detection result of detecting the formed toner mark;
  Based on the relative color shift amount between the measured reference color and the other one color, the relative color shift between the reference color and the color other than the one other color. Predicting the amount, correcting the color misregistration of the other one color based on the measured color misregistration amount, and color other than the one other color based on the predicted color misregistration amount Color misregistration correction means for correcting the misregistration;
  Storage means for storing the other one color when the color misregistration correction unit performs color misregistration correction,
  When the color misregistration correction unit performs color misregistration correction at a first timing, the forming unit forms a toner mark of the reference color and the toner mark of the other one color, and the measuring unit Measures the amount of relative color shift between the reference color and the other one color,
  When the color misregistration correction unit performs color misregistration correction at a second timing after the first timing, the forming unit stores the toner mark of the reference color and the color stored at the first timing. And a toner mark of a different color from the first color, and the measuring unit measures a relative color shift amount between the reference color and the different color.
An image forming apparatus.   An image forming apparatus control method comprising:
  A forming step of forming a toner mark of a reference color and a toner mark of another one color by a forming unit;
  A measuring step in which a measuring unit measures a relative color shift amount between the reference color and another one color based on a detection result of detecting the formed toner mark;
  And a color misregistration correction unit, based on a relative color misregistration amount between the measured reference color and the other one color, and a color other than the reference color and the other one color A relative color shift amount is predicted, the color shift of the other one color is corrected based on the measured color shift amount, and the other one color is corrected based on the predicted color shift amount. A color misregistration correction process for correcting color misregistration of colors other than colors;
  A storage unit that stores the other one color when the color misregistration correction unit performs color misregistration correction; and
  When the color misregistration correction unit performs color misregistration correction at a first timing, the forming unit forms a toner mark of the reference color and the toner mark of the other one color, and the measuring unit Measures the amount of relative color shift between the reference color and the other one color,
  When the color misregistration correction unit performs color misregistration correction at a second timing after the first timing, the forming unit stores the toner mark of the reference color and the color stored at the first timing. And a toner mark of a different color from the first color, and the measuring unit measures a relative color shift amount between the reference color and the different color.
A control method for an image forming apparatus.

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