JP2013218040A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress toner consumption in a position correction (a color shift correction), and shorten time taken for the color shift correction.SOLUTION: A control part 39 draws print position confirmation patterns in such a manner that print position confirmation patterns of respective photoreceptors are transferred on an intermediate transfer belt 31 within a movement range thereof with respect to one speed unevenness period of the photoreceptors 33 (hereinafter just referred to as "Movement range"), and the total of speed variation amounts caused by speed unevenness, of the respective photoreceptors is zero at the time of transferring the respective print position confirmation patterns. Further, the control part 39 determines a color shift correction amount H so as to make zero the total of differences between position variation amounts of the respective colors corresponding to the determined color shift correction amount in a correction amount determination table 60, and position variation amounts of the respective colors calculated in a position variation amount calculation part 53.

Description

  The present invention relates to an image forming apparatus that includes a plurality of photoconductors, sequentially transfers images from a plurality of photoconductors to an intermediate transfer member, and superimposes, and retransfers the superimposed image to a final medium. More specifically, the present invention relates to an image forming apparatus that forms an image while preventing a shift of an image overlapping position in the sub-scanning direction.

  Conventionally, a so-called tandem type color image forming apparatus having a plurality of photoconductors has been used. In such a tandem type color image forming apparatus, the alignment accuracy between the images of the respective colors is important. This is because if the transfer position to the intermediate transfer member is shifted between the images of the respective colors, the image quality is significantly deteriorated. For this reason, it is common to perform alignment correction (hereinafter also referred to as “color shift correction”).

  An example of such alignment correction is as follows. The image forming apparatus first transfers the print position confirmation pattern for each color to the intermediate transfer member. The transferred print position confirmation pattern for each color is sequentially detected by the toner image sensor. The image forming apparatus calculates a color misregistration amount (position change amount) of each color based on the detection result by the toner image sensor. This color misregistration amount is the color misregistration amount to be corrected (hereinafter also referred to as “color misregistration correction amount”). The image forming apparatus changes the drawing timing of the photosensitive member so that the transfer position to the intermediate transfer member is corrected by the amount of color misregistration correction. In this way, alignment correction (color misregistration correction) is performed.

  Here, the rotation speed of the photosensitive member has unevenness (speed unevenness). The speed unevenness changes at the same cycle as the rotation cycle of the photoconductor. That is, while the photosensitive member makes one revolution, the change in speed unevenness is also cycled. The transfer position of the image from the photosensitive member to the intermediate transfer member is affected by this speed unevenness. Therefore, in order to perform color misregistration correction with high accuracy, it is necessary to obtain a color misregistration correction amount that eliminates the influence of the transfer position change caused by speed unevenness. As a technique for obtaining a color misregistration correction amount from which the influence of a transfer position change caused by speed unevenness is removed, for example, there is a technique described in Patent Document 1 below.

  The image forming apparatus described in Patent Document 1 repeatedly draws a printing position confirmation pattern for each color in the order of each color during one turn of the intermediate transfer member. A collection of print position confirmation patterns for each color is referred to as a “unit pattern”. Then, one of the plurality of colors is determined as a reference color, and the amount of color misregistration of other colors from the reference color is detected for each unit pattern. Then, the detected color misregistration amount is averaged for each color. In this way, it is said that the influence of the speed unevenness included in the color misregistration amount can be removed by averaging the detected color misregistration amount for each color. In this image forming apparatus, the color misregistration amount averaged for each color is the color misregistration correction amount for each photoconductor. The image forming apparatus changes the drawing timing of each photoconductor based on these color misregistration correction amounts. As a result, the drawing position of each photoconductor changes so that printing without color misregistration is possible.

JP 2003-263002 A

  However, the technique described in Patent Document 1 has the following problems. That is, in the technique described in Patent Document 1, it is necessary to repeatedly transfer the print position confirmation pattern for each color over the circumference of the intermediate transfer member. Therefore, there has been a problem that a large amount of toner is consumed for alignment correction (color misregistration correction). In addition, it is necessary to detect a plurality of printing position confirmation patterns for each color. Therefore, there is a problem that it takes time to calculate the color misregistration correction amount.

  The present invention has been made in order to solve the problems of the conventional techniques described above. That is, the problem is to suppress toner consumption in alignment correction (color misregistration correction). Another object is to reduce the time required for color misregistration correction.

  In order to solve this problem, an image forming apparatus of the present invention includes a plurality of photoconductors having the same diameter carrying toner images of different colors, and a plurality of drawing devices for drawing latent images on the plurality of photoconductors, respectively. And an intermediate transfer body that sequentially transfers toner images from a plurality of photoconductors and re-transfers the superimposed toner images to the final medium. The peripheral speed of the plurality of photoconductors at the transfer position to the intermediate transfer body is , The phase and amplitude of unevenness (hereinafter referred to as “speed unevenness”) in a period that coincides with the rotation period are aligned. Further, the image forming apparatus includes a pattern drawing control unit for drawing a print position confirmation pattern on each of a plurality of photoconductors by a plurality of drawing devices, and a detection unit for detecting each print position check pattern transferred to the intermediate transfer member. Based on the elapsed time measured from the drawing of the print position confirmation pattern by the pattern drawing control unit to the detection of the print position confirmation pattern by the detection unit, and A position change amount calculation unit for calculating a position change amount from a reference position in the sub-scanning direction of the toner image transferred from the body to the intermediate transfer member, a position change amount calculated by the position change amount calculation unit, and a correction amount to be corrected Refer to a storage unit that stores a correction amount determination table that indicates a correspondence with a color misregistration amount (hereinafter referred to as “color misregistration correction amount”), and a correction amount determination table that is stored in the storage unit. A color misregistration correction amount calculation unit that calculates one color misregistration correction amount from the amount of change in position of each photoconductor, and a color misregistration correction amount calculated by the color misregistration correction amount calculation unit. A drawing timing adjustment unit that changes the drawing position on the photosensitive member by adjusting the drawing timing of each of the drawing units. The pattern drawing control unit transfers the print position confirmation pattern of each photoconductor one by one within a range in which the intermediate transfer body moves in one cycle of speed unevenness of the photoconductor (hereinafter referred to as “movement range”), and The print position confirmation pattern is drawn so that the sum of the speed fluctuations due to the speed unevenness of each photoconductor during transfer of each print position confirmation pattern becomes zero. The color misregistration correction amount calculation unit sums the difference between the position change amount of each color corresponding to the determined color misregistration correction amount in the correction amount determination table and the position change amount of each color calculated by the position change amount calculation unit. The color misregistration correction amount is determined so that becomes zero.

  According to the present invention, the transfer position of the print position confirmation pattern for each color onto the intermediate transfer member is devised as described above. Therefore, the sum of the differences between the position change amount of each color corresponding to the determined color misregistration correction amount in the correction amount determination table and the position change amount of each color calculated by the position change amount calculation unit becomes zero. By determining the color misregistration correction amount, it is possible to cancel the position change amount caused by the speed unevenness included in the position change amount of each photoconductor between the colors. Therefore, it is possible to perform color misregistration correction that eliminates the influence of speed unevenness by only transferring one print position check pattern for each color without transferring a plurality of print position check patterns for each color. Therefore, it is possible to suppress toner consumption as compared with the case of transferring a plurality of printing position confirmation patterns for each color. Further, since the number of print position confirmation patterns detected by the detection unit is small, the color misregistration correction amount can be calculated in a short time. Therefore, the time required for color misregistration correction can be shortened.

In the image forming apparatus of the present invention, the pattern drawing control unit is configured to detect unevenness in speed within the moving range of the print position confirmation patterns of the plurality of photoreceptors that are located at the same position from the upstream side and the downstream side. It is desirable that the printing position confirmation pattern be drawn so that it is transferred to a position that is equidistantly spaced in the opposite direction from the point at which the speed fluctuation amount due to is zero.
With this configuration, a position change amount due to speed unevenness included in the position change amount calculated by detecting the print position confirmation pattern (hereinafter simply referred to as “position change amount due to speed unevenness”) is obtained. , Those located at equal positions from the upstream side and the downstream side have the same size and cancel each other. Therefore, it is possible to perform color misregistration correction by removing the influence of speed unevenness by simply transferring one print position confirmation pattern for each color.

In the image forming apparatus of the present invention, the pattern drawing control unit is separated by a phase angle of 180 ° within the movement range with respect to the position where one printing position confirmation pattern among the plurality of photosensitive members is transferred within the movement range. The print position confirmation pattern can be drawn so that another print position confirmation pattern of the plurality of photoconductors is transferred to the position.
If configured in this way, the amount of position change caused by the speed unevenness becomes the same in the movement range and located at a phase angle of 180 °, and cancels each other. Therefore, it is possible to perform color misregistration correction by removing the influence of speed unevenness by simply transferring one print position confirmation pattern for each color.

  According to the image forming apparatus of the present invention, it is possible to suppress toner consumption in the alignment correction (color misregistration correction). In addition, the time required for color misregistration correction can be shortened.

It is sectional drawing which shows the structure of the image forming apparatus which concerns on a 1st form. FIG. 2 is a front view showing a part of an exposure device, a photoreceptor, and an intermediate transfer belt extracted from the image forming apparatus of FIG. 1. FIG. 5 is a diagram illustrating a printing position confirmation pattern transferred to an intermediate transfer belt. It is a figure which shows the content of the position change amount-elongation amount table which shows the correspondence of the printing position change amount of a subscanning direction, and the elongation amount of exposure apparatus. It is a figure which shows a response | compatibility with the periodic nonuniformity (speed nonuniformity) of the rotational speed of a photoreceptor, and the printing position confirmation pattern. It is a figure which shows a mode that a color shift correction amount is calculated from the printing position change amount of each color. FIG. 7 is a diagram illustrating a state in which a color misregistration correction amount is calculated from the print position change amount of each color together with FIG. FIG. 2 is a schematic block diagram illustrating a configuration of a control unit included in the image forming apparatus in FIG. 1. It is a flowchart of a color misregistration correction process. 10 is a flowchart of color misregistration correction amount calculation processing. It is a figure which shows a response | compatibility with the speed irregularity of the photoconductor in a 2nd form, and the printing position confirmation pattern.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an image forming apparatus which is a tandem type full-color copying machine. The configuration of the full-color copying machine of this embodiment is shown in FIG.

[First embodiment]
The full-color copying machine 1 shown in FIG. 1 has a paper feeding unit 2, a printing unit 3, and a reading unit 4. The paper feeding unit 2 is a part that supplies printing paper, which is a final medium carrying an image, for image formation in the printing unit 3. For this reason, the paper feed unit 2 is provided with a paper feed cassette 20 and a manual feed tray 21. The reading unit 4 is a part that reads an image of a document and supplies it to the printing unit 3 as image data. The full-color copying machine 1 may be capable of forming an image based on a print job received from an external device or an external line in addition to copying an image of a document read by the reading unit 4. In that case, the reader 4 may not be provided.

  The print unit 3 includes four image forming units 30Y, 30M, 30C, and 30K, an intermediate transfer belt (corresponding to an intermediate transfer member) 31, and an exposure device 32. The image forming units 30Y, 30M, 30C, and 30K have the same mechanical configuration, although the colors of images to be formed are different. For this reason, in the following description, unless otherwise distinguished, the color symbols Y (indicating yellow), M (indicating magenta), C (indicating cyan), and K (indicating black) are omitted. To do. The image forming unit 30 includes a photoconductor 33 and a developing device 45, respectively. The photosensitive member 33 has a toner image of a corresponding color formed on the surface thereof and transfers the toner image to the intermediate transfer belt 31. The radii of the photoconductors 33Y, 33M, 33C, and 33K are the same. The developing unit 45 applies toner of a corresponding color to the electrostatic latent image on the surface of the photoconductor 33 and develops it. In addition to the photosensitive member 33 and the developing unit 45, the image forming unit 30 is publicly known, and thus detailed illustration is omitted, but a charging device, a cleaning device after transfer, and the like are incorporated.

  The intermediate transfer belt 31 is an endless belt that is stretched between rollers 34 and 35, and moves in a counterclockwise direction in FIG. That is, of the four image forming units 30 described above, the image forming unit 30Y is the most upstream and the image forming unit 30K is the most downstream with respect to the moving direction of the intermediate transfer belt 31. The intermediate transfer belt 31 sequentially receives toner images from the respective photoreceptors 33 and re-transfers the superimposed image onto the printing paper. For this reason, the intermediate transfer belt 31 is provided with a secondary transfer roller 36.

  The exposure device 32 is a device that draws an electrostatic latent image on each photoconductor 33. Therefore, the exposure device 32 irradiates the photoconductors 33Y, 33M, 33C, and 33K with laser beams LY, LM, LC, and LK corresponding to the image data, respectively. The position where each photoconductor 33 is irradiated with laser light is a position after charging and before development. The photosensitive member 33K corresponds to the first photosensitive member, the photosensitive member 33C corresponds to the second photosensitive member, the photosensitive member 33M corresponds to the third photosensitive member, and the photosensitive member 33Y corresponds to the fourth photosensitive member. It corresponds to.

  In addition to the above, the print unit 3 is provided with a fixing device 37, a toner image sensor (IDC sensor) 38, and a control unit 39. The fixing device 37 is a device that fixes the toner image transferred onto the printing paper by the secondary transfer roller 36 onto the printing paper. The printing paper that has passed through the fixing device 37 is discharged to the paper discharge tray 40 on the upper surface of the printing unit 3. A toner image sensor (corresponding to a detection unit) 38 detects the presence and density of a toner image on the intermediate transfer belt 31. The position is a position further downstream than the most downstream photoconductor 33 </ b> K and upstream of the secondary transfer roller 36 with respect to the moving direction of the intermediate transfer belt 31. The controller 39 controls each part of the full-color copying machine 1 and performs data processing. The toner image sensor 38 is connected to the control unit 39. A detection signal from the toner image sensor 38 is input to a CPU included in the control unit 39.

  The exposure device 32 will be further described. As shown in FIG. 2, the exposure device 32 is provided with emission heads 41Y, 41M, 41C, and 41K corresponding to the photoreceptors 33Y, 33M, 33C, and 33K, respectively. Laser beams LY, LM, LC, and LK are emitted from the emission heads 41Y, 41M, 41C, and 41K toward the photoconductors 33Y, 33M, 33C, and 33K, respectively. Note that the emission heads 41Y, 41M, 41C, and 41K correspond to a drawing device.

  The exposure device 32 is attached to the main body chassis of the full-color copying machine 1 at two points, a fixed point 42 and a free point 43. The fixed point 42 is a reference position, and this point in the exposure apparatus 32 is immovable with respect to the main body chassis. On the other hand, the free point 43 is slightly movable with respect to the main body chassis. This is because the thermal expansion due to the temperature of the exposure device 32 is absorbed. Due to the thermal expansion of the exposure device 32, the positions of the emission heads 41Y, 41M, 41C, and 41K also shift slightly. Accordingly, the drawing positions on the photoconductors 33Y, 33M, 33C, and 33K are also shifted.

  In the exposure apparatus 32 described above, the exit head 41Y is the closest to the fixed point 42 among the exit heads 41Y, 41M, 41C, and 41K. As described above, the emission head 41Y performs drawing on the photosensitive member 33Y whose transfer order to the intermediate transfer belt 31 is the head. Further, the emission head 41 farthest from the fixed point 42 is the emission head 41K. As described above, the emission head 41K performs drawing on the photoconductor 33K whose transfer order is final.

  The basic operation of the full-color copying machine 1 in FIG. 1 is to form an image in the image forming unit 30 based on the image data acquired from the original by the reading unit 4 and transfer the image to the printing paper. As a result, the image of the original is copied. For this reason, the exposure device 32 draws on the photosensitive member 33 by emitting laser light from the emission head 41 based on the image data. The toner images of each color thus obtained are superimposed on the intermediate transfer belt 31 by transfer. The superimposed toner image is retransferred onto the printing paper supplied from the paper supply unit 2 by the secondary transfer roller 36 and is discharged onto the paper discharge tray 40 through the fixing device 37.

  Here, regarding the superposition of the toner images of the respective colors on the intermediate transfer belt 31, accurate alignment (color misregistration correction) is necessary to prevent color misregistration. Therefore, the control unit 39 of the full-color copying machine 1 performs alignment control (color misregistration correction control). The alignment includes alignment in the main scanning direction (width direction of the intermediate transfer belt 31) and alignment in the sub-scanning direction (movement direction of the intermediate transfer belt 31). The subject of the present invention is alignment in the sub-scanning direction.

  The main cause of color misregistration in the sub-scanning direction is that the internal temperature rises due to the use of the full-color copying machine 1, the exposure device 32 expands and contracts due to thermal expansion, and the exposure position of the photoconductor 33 changes. The body of the exposure apparatus 32 is often made of resin, and the degree of thermal expansion is larger than that of a metal member such as a main body chassis of the full-color copying machine 1. Therefore, expansion / contraction of the exposure apparatus due to thermal expansion affects the exposure position of the photoreceptor. Note that the color misregistration amount of each photoconductor in the sub-scanning direction is uniquely determined with respect to the degree of thermal expansion of the exposure device 32.

  In order to correct the color misregistration in the sub-scanning direction of each photoconductor as described above, the full-color copying machine 1 performs the following color misregistration correction control other than during image formation. First, the control unit 39 outputs an image printing permission signal (hereinafter referred to as “TOD”) for instructing the start of drawing to the exposure device 32. Receiving the TOD, the exposure device 32 draws a print position confirmation pattern on each photoconductor 33 in accordance with the emission time for each photoconductor 33. The printing position confirmation pattern is a pattern for confirming the position where the toner image is formed on the intermediate transfer belt 31. Here, the position in the sub-scanning direction is a problem. For this reason, a line-shaped pattern parallel to the main scanning direction as shown in FIG. 3 is formed as the print position confirmation pattern. Image data of the print position confirmation pattern is stored in a ROM (storage unit 58) described later. As shown in FIG. 3, the print position confirmation pattern drawn on each photoconductor 33 is from the upstream side (right side in FIG. 3) to the downstream side (in FIG. 3) with respect to the moving direction (conveying direction) of the intermediate transfer belt 31. Toward the left) side, the toner images are transferred to the intermediate transfer belt 31 in the order of Y (yellow), M (magenta), C (cyan), and K (black).

  The print position confirmation patterns for all colors transferred to the intermediate transfer belt 31 are sequentially detected from the downstream side by the toner image sensor 38, that is, in the order of K, C, M, and Y. At this time, the control unit 39 determines the elapsed time from the output of the image print permission signal (TOD) to the detection of the print position confirmation pattern by the toner image sensor 38 (in other words, the drawn print position confirmation pattern is the toner image sensor 38). The time to reach (hereinafter referred to as “pattern arrival time”) is measured for each color. Then, the control unit 39 calculates the printing position change amount for each color from the measured pattern arrival time. In other words, the control unit 39 is based on the length of the required time (pattern arrival time) from the time when the printing position confirmation pattern is drawn by the exposure device 32 to the time when the pattern is detected by the toner image sensor 38. Then, the shift amount of the pattern formation position (print position change amount) is measured for each color. The calculation of the print position change amount is measured, for example, by how much the pattern arrival time of each color is deviated from the standard value of each color. The standard value for each color is the pattern arrival time when the printing position confirmation pattern for each color is at a reference position without positional deviation.

  Subsequently, the control unit 39 calculates a color misregistration correction amount from the print position change amount of each color. A ROM (storage unit 58), which will be described later, stores a position change amount-elongation amount table (corresponding to a correction amount determination table) indicating the correspondence between the print position change amount and the color misregistration correction amount. The control unit 39 refers to the position change amount-elongation amount table and calculates a color misregistration correction amount from the print position change amount of each color.

  The contents of the position change amount-elongation amount table are shown in FIG. FIG. 4 is a graph showing the relationship between the printing position change amount (vertical axis) and the color misregistration amount to be corrected (color misregistration correction amount, horizontal axis). In FIG. 4, the amount of color misregistration correction is expressed as the amount of elongation of the exposure apparatus. This is because the cause of color misregistration is related to the growth of the exposure apparatus as described above. As shown in FIG. 4, for each color, the amount of change in the printing position in the sub-scanning direction increases as the extension amount of the exposure device 32 increases. In other words, for each color, the amount of color misregistration to be corrected increases as the printing position change amount in the sub-scanning direction increases. In FIG. 4, when the amount of extension of the exposure device 32 for each color is the same, the amount of change in the printing position in the sub-scanning direction increases in the order of K color, C color, M color, and Y color. This is because as the distance from the fixed point 42 of the exposure apparatus 32 to the emission head 41 is larger, the shift amount of the drawing position when the extension amount of the exposure apparatus 32 is increased.

  In the embodiment, in order to calculate the color misregistration correction amount from which the influence of the periodic unevenness of the rotation speed of the photoconductor 33 (hereinafter referred to as “speed unevenness”) is calculated, the color misregistration correction amount is calculated as follows. In describing the calculation of the color misregistration correction amount, the speed unevenness will be described first. FIG. 5 shows speed unevenness that periodically varies as the photosensitive member 33 rotates. Since the speed unevenness is accompanied by the rotation of the photosensitive member 33, the length of one cycle of the speed unevenness is the same as the length of one rotation of the photosensitive member 33. The cause of the uneven speed is the eccentricity of the photoreceptor. The rotational speed of the photoconductor 33 increases at a location where the amount of eccentricity is large, and the speed of the photoconductor 33 decreases at a location where the amount of eccentricity is small. The degree of eccentricity of each photoconductor 33 is the same. Thereby, the amplitude of the speed unevenness of each photoconductor 33 is matched. Further, the phases of the photoconductors 33 are matched with each other. As a result, the phase of the speed unevenness of each photoconductor 33 is matched. Matching the phase of the speed irregularity means that the photosensitive drums 33Y, 33M, 33C, and 33K are transferred to the same position on the intermediate transfer belt 31 at the same phase position. The same phase position means the same position on the waveform indicating the speed unevenness in FIG.

  The printing position confirmation pattern transferred to the intermediate transfer belt 31 is assumed to be equally spaced one by one for each color during the distance that the intermediate transfer belt 31 moves in one cycle of speed unevenness, assuming that no positional deviation has occurred. It is drawn as follows. That is, the separation distance in the sub-scanning direction of the printing position confirmation pattern for K and C colors, the separation distance in the sub-scanning direction of the printing position confirmation pattern for C and M colors, and the printing position confirmation for M and Y colors All the separation distances in the sub-scanning direction of the pattern are equal. In addition, in the waveform of the speed unevenness shown as a point a in FIG. 5, the print position of the C color is confirmed in the half cycle of one speed unevenness period starting from the zero point (position where the speed fluctuation amount due to the speed unevenness becomes zero). Each print position confirmation pattern is drawn so that the center position along the sub-scanning direction of the transfer position of the pattern for printing and the transfer position of the print position confirmation pattern for the M color is located. In other words, the print position confirmation pattern for K color (first from the downstream side) and the print position confirmation pattern for Y color (first from the upstream side) are center positions (one point b in FIG. The print position confirmation pattern for C (second from the downstream side) and the print position confirmation pattern for M (second from the upstream side) are separated from each other by the same distance L1 from the position shown in the opposite direction. They are separated by the same distance L2 in the opposite direction from the center position of the unevenness 1 period (position shown as point b in FIG. 5). This means that “the print position confirmation patterns of the plurality of photoreceptors 33Y, 33M, 33C, and 33K that are located at the same position from the upstream side and the downstream side have the intermediate transfer belt 31 in one cycle of speed unevenness. A pattern for confirming the printing position is drawn so that it is transferred to a position equidistant in the opposite direction from the point where the speed fluctuation amount due to speed unevenness is zero (point b in FIG. 5) within the range in which the "That's what it means. It should be noted that the actual indispensable condition is that the separation distances of the K and C color print position confirmation patterns in FIG. 5 are the same as the separation distances of the M and Y color print position confirmation patterns. 5, the positions of the K and C color print position confirmation patterns and the positions of the M and Y color print position confirmation patterns are symmetrical about the point b in FIG. The separation distance between the C and M printing position confirmation patterns does not have to be the same as the separation distance between the K and C printing position confirmation patterns.

  The print position change amount described above is calculated by detecting the print position confirmation pattern drawn in this way. For this reason, the printing position change amount includes speed unevenness components indicated as Q, R, S, and T in FIG. That is, the speed unevenness component indicated by Q in FIG. 5 for the K color print position confirmation pattern, and the speed unevenness component indicated by R in FIG. 5 for the C color print position confirmation pattern, A speed unevenness component indicated by S in FIG. 5 enters the M color print position confirmation pattern, and a speed unevenness component indicated by T in FIG. 5 enters the Y color print position confirmation pattern. . If the color misregistration correction amount is obtained without considering such speed unevenness components, accurate color misregistration correction cannot be performed.

  Therefore, the control unit 39 calculates the color misregistration correction amount by the method shown in FIG. 6 in order to calculate the color misregistration correction amount by removing the influence of these speed unevenness components. FIG. 6 is a graph in which the print position change amounts of the respective colors calculated by the control unit 39 are plotted with circles on the graph showing the contents of the position change amount-elongation amount table shown in FIG. As shown in this graph, the K color printing position change amount calculated by the control unit 39 includes a position change amount Q caused by the speed unevenness of the photosensitive member 33K. Also, the C color printing position change amount calculated by the control unit 39 includes a position change amount R caused by the speed unevenness of the photoconductor 33C. Further, the M color print position change amount calculated by the control unit 39 includes a position change amount S caused by the speed unevenness of the photosensitive member 33M. Further, the Y color printing position change amount calculated by the control unit 39 includes a position change amount T caused by the speed unevenness of the photoconductor 33Y. Here, the values of the position change amounts Q, R, S, and T due to the speed unevenness of each color are unknown. This is because the amplitude of the speed unevenness is unknown. Therefore, the control unit 39 obtains the color misregistration correction amount H from which the influence of the speed unevenness shown in FIG. 6 is removed by performing the processing described below with reference to FIG.

  As shown in FIG. 7, the control unit 39 provisionally determines a reference color misregistration correction amount (hereinafter referred to as “provisional color misregistration correction amount G”), and this temporary color misregistration correction amount on the position change amount-elongation amount table. Differences U, V, W, and X between the printing position change amount of each color corresponding to G (see the square plot in the figure) and the calculated position change amount of each color (see the circle plot in the figure) are obtained. This difference is obtained as a value considering the sign of positive and negative. In FIG. 7, U and V indicated by upward arrows are positive values, and W and X indicated by downward arrows are negative values. The same calculation is repeated while changing the provisional color misregistration correction amount G (see the right-pointing arrow in FIG. 7) until the sum of these differences (U + V + W + X) becomes substantially zero. Under the provisional color misregistration correction amount G shown in FIG. 7, since the magnitudes of U and V are larger than the magnitudes of W and X, the sum of the differences (U + V + W + X) does not become substantially zero, but the provisional color misregistration correction amount. When the value of G is changed to be as shown in FIG. 6, the sum of differences (Q + R + S + T) becomes substantially zero. The control unit 39 determines the temporary color misregistration correction amount G when the sum of the differences becomes substantially zero as the color misregistration correction amount H (see FIG. 6). If the color misregistration correction amount is obtained in this way, the calculated color misregistration correction amount H is one in which the influence of speed unevenness is removed. This is because the position change amount Q caused by the speed unevenness and the magnitude of T are the same, so they cancel each other, and the magnitudes of R and S are the same, so they cancel each other. This is because the transfer position of the print position confirmation pattern for C color and the print position confirmation pattern for M color are detected in the half cycle of one cycle of speed unevenness starting from the zero point (see point a in FIG. 5). This is because the print position confirmation pattern of each color is drawn uniformly within one cycle of speed unevenness so that the center position of the transfer position along the sub-scanning direction comes.

  The control unit 39 having calculated the color misregistration correction amount H adjusts the drawing position by adjusting the drawing timing of each emitting head 41 on each photoconductor 33 based on the color misregistration correction amount H. Here, the relationship between the drawing timing and the drawing position will be described. For a certain color, it is assumed that the position of the image is shifted to the downstream side in the moving direction of the intermediate transfer belt 31 from the original position if the alignment control is not performed. In that case, the drawing position of that color must be shifted upstream by that amount. In this case, the drawing position is shifted upstream by delaying the drawing timing. On the other hand, if the position of the image is shifted to the upstream side without performing alignment control, the drawing position is shifted to the downstream side by advancing the drawing timing.

  More specifically, for example, when the temperature of the exposure device 32 rises, the position of each emission head 41 shifts to the right in FIG. 2 due to thermal expansion. Thereby, the irradiation position of the laser beam on each photoconductor 33, that is, the drawing position is also shifted rightward in FIG. This means that the drawing position is shifted to the upstream side, so that the drawing timing must be advanced to correct the drawing position to shift toward the downstream side. Conversely, when the temperature falls, the drawing position shifts to the downstream side, so correction must be made to delay the drawing timing and shift the drawing position toward the upstream side.

  Next, based on the schematic block diagram shown in FIG. 8, the structure and function of the control part 39 are demonstrated collectively. The control unit 39 includes a CPU that is an arithmetic processing unit, a ROM (storage unit 58) that stores various control programs and fixed value data executed by the CPU, and various types of control programs stored in the ROM. The RAM is a working memory for temporarily storing the data. The ROM (storage unit 58) stores the program shown in the flowchart in FIG. 9 as a part of the control program. The ROM (storage unit 58) stores a position change-elongation table 60 whose contents are shown in FIG. Each value such as the pattern arrival time, the printing position change amount, and the color misregistration correction amount is stored in the RAM.

  The control unit 39 configured as described above functions as a pattern drawing control unit 51, a timing unit 52, a print position change amount calculation unit 53, a color misregistration correction amount calculation unit 54, and a drawing timing adjustment unit 55. The pattern drawing control unit 51 outputs an image printing permission signal (TOD) for instructing the start of drawing to the exposure device 32. The timer 52 measures the elapsed time (pattern arrival time) from the output of the image print permission signal (TOD) to the detection of the print position confirmation pattern by the toner image sensor 38.

  The print position change amount calculation unit 53 calculates the print position change amount for each color from the measured pattern arrival time. The color misregistration correction amount calculation unit 54 calculates one color misregistration correction amount from the print position change amount of each color with reference to the print position change amount-elongation amount table. The drawing timing adjustment unit 55 adjusts the drawing timing on the photosensitive member 33 based on the calculated color misregistration correction amount.

  Next, the color misregistration correction process executed by the full-color copying machine 1 will be described based on the flowcharts shown in FIGS. This color misregistration correction process is executed when the full-color copying machine 1 is turned on or restarted from the sleep mode.

  In the color misregistration correction process, the control unit 39 first outputs an image print permission signal (TOD) (step S001). As a result, drawing of the printing position confirmation pattern on the photosensitive member 33 is started. Accordingly, the control unit 39 starts measuring the time (pattern arrival time) from the output of TOD to the detection of the print position confirmation pattern by the toner image sensor 38 (S002). Subsequently, the control unit 39 determines whether or not the printing position confirmation pattern is detected by the toner image sensor 38 (S003). If the print position confirmation pattern is detected by the toner image sensor 38 (S003: Yes), the pattern arrival time is stored in the RAM, and the process proceeds to step S005. On the other hand, if the print position confirmation pattern is not detected by the toner image sensor 38 (S003: No), step S003 is repeated until it is detected. In step S005, it is determined whether a print position confirmation pattern has been detected for all colors. If all the colors have not been detected (S005: No), the process returns to step S003. By repeating the processing from step S003 to step S005 in this way, the print position confirmation patterns for all colors are detected by the toner image sensor 38 in the order of K, C, M, and Y, and the patterns for the respective colors are detected. The arrival time is stored in the RAM. If all colors have been detected (S005: Yes), the process proceeds to step S006.

  In step S006, the control unit 39 calculates the printing position change amount (color misregistration amount) for each color based on the pattern arrival time. When the print position change amount is calculated, as described above with reference to FIGS. 6 and 7, the process of calculating the color misregistration correction amount H is performed with reference to the print position change amount-elongation amount table (S007). In the color misregistration correction amount calculation process, as shown in FIG. 10, the control unit 39 first determines a temporary color misregistration correction amount G (see FIG. 7) to a certain value (S101). Then, the difference between the print position change amount of each color corresponding to the provisional color misregistration correction amount and the print position change amount of each color calculated in step S006 is obtained on the position change amount-elongation amount table (S102). Subsequently, the control unit 39 determines whether the sum of the differences obtained in step S102 is zero (S103). If the sum of the differences is zero (S103: Yes), the provisional color misregistration correction amount is determined as the color misregistration correction amount H (see FIG. 6) (S104), and the process ends. If the sum of the differences is not zero (S103: No), the value of the provisional color misregistration correction amount is changed so that the sum of the differences determined in step S103 is zero (S105), and steps S102 and S103 are performed again. Process. Even if the sum of the differences calculated in step S103 is not zero, the temporary color misregistration correction amount at that time may be determined as the color misregistration correction amount as long as it is a value close to zero.

  After calculating the color misregistration correction amount H in this way, the control unit 39 adjusts the drawing timing from the emission head 41 to the photoconductor 33 so that the color misregistration of each color is corrected based on the color misregistration correction amount H. (S008 in FIG. 9). As a result, each color toner image is transferred to the intermediate transfer belt 31 without color misregistration.

  As described above in detail, in the full-color copying machine 1 according to the present embodiment, each photosensitive member is within a range in which the intermediate transfer belt 31 moves in one cycle of speed unevenness of the photosensitive member 33 (hereinafter simply referred to as “moving range”). The printing position confirmation pattern of the body 33 is transferred one by one, and the printing position confirmation is performed so that the sum of the speed fluctuation amounts due to the speed unevenness of each photosensitive member 33 at the time of transferring each printing position confirmation pattern becomes zero. A pattern is drawn. More specifically, as shown in FIG. 5, the K-color print position confirmation pattern and the Y-color print position confirmation pattern correspond to the center position of one period of speed unevenness of the photosensitive member 33 (see point b in FIG. 5). ) From the center position of one period of speed unevenness of the photosensitive member 33 (see point b in FIG. 5), the C color printing position confirmation pattern and the M color printing position confirmation pattern are separated by the same distance in the opposite direction. A print position confirmation pattern for each color is drawn so as to be separated by the same distance in opposite directions.

  Therefore, the sum of the difference between the position change amount of each color corresponding to the determined color misregistration correction amount in the correction amount determination table 60 and the position change amount of each color calculated by the print position change amount calculation unit 53 is zero. By determining the color misregistration correction amount H (see FIG. 6) in such a manner, the position change amount caused by the speed unevenness included in the position change amount of each photoconductor 33 can be canceled between the respective colors. Therefore, it is possible to perform color misregistration correction that eliminates the influence of speed unevenness by only transferring one print position check pattern for each color without transferring a plurality of print position check patterns for each color. Therefore, it is possible to suppress toner consumption as compared with the case of transferring a plurality of printing position confirmation patterns for each color. Further, since the number of printing position confirmation patterns detected by the toner image sensor 38 is small, the color misregistration correction amount H (see FIG. 6) can be calculated in a short time. Therefore, the time required for color misregistration correction can be shortened. The ability to shorten the time required for color misregistration correction shortens the recovery time from sleep until printing is possible and the rise time from when the power is turned on until printing is possible. Therefore, the user's feeling of use for the full-color copying machine 1 can be improved.

  In the first embodiment, the number of the photoreceptors 33 provided in the full-color copying machine 1 is an even number (four, Y, M, C, and K), but the number of the photoreceptors 33 provided in the full-color copying machine 1 is the same. In the case of an odd number (for example, three of Y, M, and C), the following configuration may be used. That is, one printing position confirmation pattern is transferred to a point (point a or b in FIG. 5) where the amount of speed fluctuation due to speed unevenness is zero, and the remaining two printing position confirmation patterns have already been described. Similarly to the above, it may be configured such that the image is transferred to a position equidistant in the opposite direction from the point where the amount of speed fluctuation due to speed unevenness is zero.

[Second form]
Next, the second embodiment will be described. In the second embodiment, the configuration other than the transfer position of the printing position confirmation pattern is the same as that of the first embodiment. The description of the same configuration as that of the first embodiment is omitted. In the second embodiment, as shown in FIG. 11, the printing position confirmation pattern is transferred. That is, two colors are transferred with a half cycle shift. More specifically, in the printing position confirmation pattern, two of the four colors (K color and C color) are transferred within the distance of the first half cycle in one cycle of speed unevenness, and the second half cycle in one cycle of speed unevenness. The remaining two colors (M color and Y color) are transferred within the distance. The M color print position confirmation pattern is transferred to a position that is 180 degrees out of phase with the K color print position confirmation pattern. The Y color print position confirmation pattern is transferred to a position that is 180 degrees out of phase with the C color print position confirmation pattern. This means that “the plurality of photoconductors 33 are located at positions that are 180 ° apart from each other in the movement range with respect to the position at which one printing position confirmation pattern is transferred within the movement range. Another one of the print position confirmation patterns is transferred.

  When the printing position confirmation pattern is transferred in this manner, the speed unevenness component E of the photoconductor 33K and the speed unevenness component G of the photoconductor 33M have the same magnitude as absolute values. Further, the speed unevenness component F of the photoconductor 33C and the speed unevenness component H of the photoconductor 33Y have the same magnitude in absolute value. Therefore, the speed unevenness components E and G, F and H cancel each other. Therefore, similarly to the case shown in FIG. 6 in the description of the first embodiment, the color misregistration correction amount from which the influence of the speed unevenness is removed is calculated.

  Therefore, according to the second embodiment, similarly to the first embodiment, the speed of the rotation cycle of the photoconductor 33 is simply formed by forming a print position confirmation pattern for each color during one rotation cycle of the photoconductor 33. It is possible to calculate a color misregistration correction amount that eliminates the influence of unevenness. That is, the color misregistration correction can be performed with high accuracy by removing the influence of the speed irregularity of the rotation cycle of the photoconductor 33 only by forming the print position confirmation pattern for each color in one rotation cycle of the photoconductor 33. be able to. Further, since it is only necessary to form a printing position confirmation pattern for each color during one rotation period of the photoconductor 33, the amount of toner consumed for color misregistration correction can be suppressed. In addition, since it is only necessary to detect a print position confirmation pattern for each color, the time required for color misregistration correction can be shortened. The ability to shorten the time required for color misregistration correction shortens the recovery time from sleep until printing is possible and the rise time from when the power is turned on until printing is possible. Therefore, the user's feeling of use for the full-color copying machine 1 can be improved.

  In the second embodiment, the number of the photoreceptors 33 provided in the full-color copying machine 1 is an even number (four, Y, M, C, and K), but the number of the photoreceptors 33 provided in the full-color copying machine 1 is the same. In the case of an odd number (for example, three of Y, M, and C), the following configuration may be used. That is, one printing position confirmation pattern is transferred to a point (point a or b in FIG. 5) where the amount of speed fluctuation due to speed unevenness is zero, and the remaining two printing position confirmation patterns have already been described. Similarly to the above, the image may be transferred to a position separated by 180 ° in the movement range.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the toner used in the developing unit 45 may be either a one-component system or a two-component system. Further, the arrangement of the four image forming units 30Y, 30M, 30C, and 30K is not limited to the horizontal direction illustrated in FIG.

  Moreover, you may mix a 1st form and a 2nd form. That is, a plurality of photoconductors (excluding one in the case of an odd number) is a set of two pairs. In each pair, with respect to the position where one print position confirmation pattern is transferred within the movement range of one rotation of the photoreceptor on the intermediate transfer belt 31, the other print position confirmation pattern is the following two. It suffices to be located at either one of the two positions. The two positions are a symmetrical position centering on point b in FIG. 5 (corresponding to the first embodiment) and a position separated by 180 ° in phase angle (corresponding to the second embodiment) in FIG.

  In the present specification, a difference of about 15% in amplitude is included in “the amplitude is matched”. The difference in amplitude is preferably within 10% rather than within 15%, and more preferably within 5% than within 10%. Further, in this specification, a shift of about 30 ° in phase angle is included in “the phase is matched”. The phase shift is preferably within 20 ° rather than within 30 °, and more preferably within 10 ° than within 20 °.

1. Full-color copier (image forming device)
31. Intermediate transfer belt (intermediate transfer member)
33 ... Photoconductor 38 ... Toner image sensor (detector)
39: Control unit (pattern drawing control unit, timing unit, position change amount calculation unit, color misregistration correction amount calculation unit, drawing timing adjustment unit)
41 ... Output head (drawer)
58... Storage unit 60... Position change-elongation amount table (correction amount determination table)

Claims (3)

A plurality of photoconductors having the same diameter carrying toner images of different colors, a plurality of imagers for drawing latent images on the plurality of photoconductors, and sequentially transferring toner images from the plurality of photoconductors. An intermediate transfer member that re-transfers the superimposed toner image to the final medium,
In the image forming apparatus in which the phase and amplitude of unevenness (hereinafter referred to as “speed unevenness”) of the peripheral speed at the transfer position to the intermediate transfer member in the plurality of photosensitive members are equal to each other in a cycle that coincides with the rotation cycle ,
A pattern drawing control unit for drawing a print position confirmation pattern on each of the plurality of photosensitive members by the plurality of drawing units;
A detection unit for detecting each printing position confirmation pattern transferred to the intermediate transfer member;
A time measuring unit for measuring an elapsed time from the drawing of the printing position confirmation pattern by the pattern drawing control unit to the detection of the printing position confirmation pattern by the detection unit;
A position change amount calculation unit that calculates a position change amount from a reference position in the sub-scanning direction of the toner image transferred from each of the photoconductors to the intermediate transfer body based on the elapsed time measured by the time measuring unit;
A storage unit for storing a correction amount determination table indicating a correspondence relationship between the position change amount calculated by the position change amount calculation unit and a color shift amount to be corrected (hereinafter referred to as “color shift correction amount”);
A color misregistration correction amount calculation unit that calculates one color misregistration correction amount from a position change amount of each photoconductor with reference to a correction amount determination table stored in the storage unit;
A drawing timing adjustment unit that changes the drawing position on the photoconductor by adjusting the drawing timing of each drawing unit during normal image formation based on the color misregistration correction amount calculated by the color misregistration correction amount calculation unit. And comprising
The pattern drawing control unit transfers the print position confirmation pattern for each photoconductor one by one within a range in which the intermediate transfer body moves in one cycle of speed unevenness of the photoconductor (hereinafter referred to as “movement range”). And the printing position confirmation pattern is drawn so that the sum of the speed fluctuation amounts due to the speed unevenness of each photosensitive member at the time of transfer of each printing position confirmation pattern becomes zero.
The color misregistration correction amount calculation unit
A positional change amount of each color corresponding to the determined color misregistration correction amount in the correction amount determination table;
A position change amount of each color calculated by the position change amount calculation unit;
An image forming apparatus, wherein a color misregistration correction amount is determined so that a sum of differences between the two becomes zero. The image forming apparatus according to claim 1,
The pattern drawing control unit
Among the plurality of photoconductors, a pattern for confirming the printing position of the ones located at the same position from the upstream side and the downstream side is,
To be transferred to a position equidistantly spaced in the opposite direction from the point where the speed fluctuation amount due to speed unevenness is zero within the moving range,
An image forming apparatus for drawing a print position confirmation pattern. The image forming apparatus according to claim 1,
The pattern drawing control unit
At a position separated by a phase angle of 180 ° within the movement range with respect to a position at which one printing position confirmation pattern of the plurality of photosensitive members is transferred within the movement range,
In order to transfer another print position confirmation pattern of the plurality of photoconductors,
An image forming apparatus for drawing a print position confirmation pattern.

Images