Image forming apparatus and method for controlling the same, and program

Abstract

To prevent a reduction in the accuracy of positional deviation correction depending on the timing to perform positional deviation correction in an image forming apparatus.SOLUTION: An image forming apparatus acquires wave form data indicating a wave form approximating the amount of positional deviation in a sub scanning direction on the basis of a result of detection of the amount of positional deviation for a toner pattern. The image forming apparatus generates, on the basis of the wave form data, first correction data for correcting periodic positional deviation in the sub scanning direction of a toner image formed on an intermediate transfer belt, and on the basis of a wave form value of the wave form data at the timing to start correction based on the first correction data in forming an image, second correction data for correcting a certain amount of positional deviation in the sub scanning direction of the entire image to be formed. The image forming apparatus corrects an image forming condition for forming a toner image on an image carrier on the basis of the first and second correction data to perform positional deviation correction of the image.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that forms images by an electrophotographic method, a control method thereof, and a program. [Background technology]

[0002] In electrophotographic image forming devices that form images using a developer (toner), such as printers, copiers, and facsimile machines, the toner image transferred from the photosensitive drum to the intermediate transfer belt or recording material can deviate from its ideal position (misalignment). Furthermore, in image forming devices that form color images, misalignment of the toner images of each color can cause the toner images of each color to not be transferred to the same position on the intermediate transfer belt, resulting in color shift, which reduces image quality.

[0003] As a technique for preventing such misalignment (color misalignment), Patent Document 1 describes a technique for eliminating periodic misalignment in the sub-scanning direction that occurs in images formed in an image forming apparatus. Patent Document 2 describes a technique for suppressing the phase difference of relative misalignment (color misalignment) by matching the phase of periodic misalignment of an image of a reference color with the phase of periodic misalignment of images of other colors. In Patent Document 2, an encoder is used to detect the rotation speed of the photosensitive drum. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 8,526,867 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-75257 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, when correcting periodic positional deviations in the sub-scanning direction that occur in the formed image, positional deviations in the sub-scanning direction may occur in the formed image depending on the timing of the correction. However, if the correction timing is adjusted using an encoder, for example, this may result in an increase in parts costs and may limit the start timing of image formation.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide a technique for preventing a decrease in the accuracy of misregistration correction depending on the timing of misregistration correction in an image forming apparatus. [Means for solving the problem]

[0007] An image forming apparatus according to one aspect of the present invention includes an image carrier that is rotated, a transfer unit that transfers a toner image formed on the image carrier to a transferee, a detection unit that detects the amount of positional deviation of a pattern image formed on the transferee from an ideal position when the pattern image is formed on the transferee as a toner image, an acquisition unit that acquires waveform data that indicates a waveform that approximates the amount of positional deviation in a sub-scanning direction, which is the transport direction of the toner image on the transferee, based on the detection result by the detection unit, a generation unit that generates first correction data based on the waveform data to correct periodic positional deviation in the sub-scanning direction of the toner image formed on the transferee, and generates second correction data based on the waveform value of the waveform data at the start timing of correction based on the first correction data when forming an image to correct a certain amount of positional deviation in the sub-scanning direction of the entire image to be formed, and a control unit that corrects the positional deviation in the sub-scanning direction of the toner image transferred from the image carrier to the transferee by correcting image formation conditions for forming the toner image on the image carrier based on the first correction data and the second correction data. [Effects of the Invention]

[0008] According to the present invention, it is possible to prevent the accuracy of positional deviation correction from being reduced depending on the timing of performing positional deviation correction in an image forming apparatus. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view showing an example of the hardware configuration of the image forming apparatus. [Figure 2] FIG. 2 is a block diagram showing an example of the hardware configuration of an image forming unit 20. [Figure 3] 6A and 6B are diagrams showing an example of detection of the amount of positional deviation of an image using an image detector 61. [Figure 4] 6A and 6B are diagrams showing an example of detection of a toner pattern 5 by an image detector 61. [Figure 5] FIG. 2 is a block diagram showing an example of the configuration of a control system 80 of the image forming apparatus 1. [Figure 6] 10A and 10B are diagrams showing an example of acquiring the amount of misalignment of an image in the sub-scanning direction. [Figure 7] 10A and 10B are diagrams showing an example of a process for generating predicted data of the amount of positional deviation of an image in the sub-scanning direction. [Figure 8] FIG. 10 is a diagram showing an example of predicted data expressed using a sine function. [Figure 9] 10A and 10B are diagrams showing examples of various data derived from prediction data 91. [Figure 10] FIG. 2 is a diagram showing an example of the configuration of a detection device used to detect the rotation of a photosensitive drum 23. [Figure 11] 10 is a flowchart showing an example of a procedure for image forming processing. [Figure 12] 6 is a timing chart showing the timing of control for correcting positional deviation. [Figure 13] 6 is a timing chart showing the timing of control for correcting positional deviation. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe multiple features, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0011] <Image forming device> 1 is a cross-sectional view showing an example of the hardware configuration of an image forming apparatus according to an embodiment of the present disclosure. The image forming apparatus 1 of this embodiment may be a printer, a copier, a multifunction peripheral, a facsimile, a multifunction peripheral (MFP), or the like that is capable of forming color images.

[0012] The image forming apparatus 1 includes multiple image forming units for forming images of different colors. In this embodiment, the image forming apparatus 1 includes four image forming units 20Y, 20M, 20C, and 20K. The image forming units 20Y, 20M, 20C, and 20K constitute image forming units for forming images (toner images) of yellow (Y), magenta (M), cyan (C), and black (K), respectively. The image forming units 20Y, 20M, 20C, and 20K have similar configurations and perform similar operations. Note that the subscripts Y, M, C, and K added to the reference numbers indicate the toner colors of yellow, magenta (M), cyan (C), and black (K). In the following, when matters common to each color are described, these subscripts will be omitted.

[0013] The image forming apparatus 1 further includes an intermediate transfer belt 3 disposed above the image forming units 20Y, 20M, 20C, and 20K. The intermediate transfer belt 3 is an intermediate transfer body in the form of an endless belt. As shown in FIG. 1, the image forming apparatus 1 of this embodiment employs a tandem system in which multiple image forming units 20Y, 20M, 20C, and 20K are arranged along the intermediate transfer belt 3.

[0014] The image forming units 20Y, 20M, 20C, and 20K are equipped with photosensitive drums 23Y, 23M, 23C, and 23K, respectively, and each photosensitive drum is a drum-shaped photosensitive member. The image forming unit 20Y forms a yellow toner image on the photosensitive drum 23Y. The image forming unit 20M forms a magenta toner image on the photosensitive drum 23C. The image forming unit 20C forms a cyan toner image on the photosensitive drum 23M. The image forming unit 20K forms a black toner image on the photosensitive drum 23K. The photosensitive drums 23Y, 23M, 23C, and 23K are arranged at predetermined intervals along the intermediate transfer belt 3.

[0015] The intermediate transfer belt 3 is stretched over multiple rollers and driven to rotate counterclockwise in Fig. 1. While the intermediate transfer belt 3 is rotating, toner images of each color are transferred from the photosensitive drums 23Y, 23M, 23C, 23K, and 23K to the intermediate transfer belt 3 in succession, superimposed on one another, to form a toner image (multicolor image) made up of toners of four colors on the intermediate transfer belt 3. The toner image carried on the intermediate transfer belt 3 is transported to a secondary transfer unit 4 between the intermediate transfer belt 3 and a secondary transfer roller 41 as the intermediate transfer belt 3 rotates.

[0016] A sheet-shaped recording material is transported to the secondary transfer unit 4 in accordance with the timing at which the toner image is transported to the secondary transfer unit 4 by the intermediate transfer belt 3. At the secondary transfer unit 4, the toner image is transferred from the intermediate transfer belt 3 to the recording material while the recording material is transported between the intermediate transfer belt 3 and the secondary transfer roller 41. The secondary transfer roller 41 transports the recording material onto which the toner image has been transferred to the fixing unit 30. The fixing unit 30 performs a fixing process in which the toner image is fixed to the recording material by heating and pressurizing the recording material transported from the secondary transfer unit 4. The recording material after the fixing process is discharged outside the image forming apparatus 1 (to an output tray).

[0017] 2 is a block diagram showing an example of the hardware configuration of the image forming unit 20. The image forming unit 20 includes a charger 21, an exposure unit 24, and a development unit 22, which are arranged around a photosensitive drum 23. The image forming unit 20 further includes a primary transfer unit 25, which is arranged at a position facing the photosensitive drum 23 with the intermediate transfer belt 3 interposed therebetween.

[0018] A photosensitive layer is formed on the surface of the photosensitive drum 23. During image formation, the photosensitive drum 23 is driven to rotate clockwise in FIG. 2 around a drum axis (rotation axis). In this embodiment, the photosensitive drum 23 is an example of an image carrier that is driven to rotate. The charger 21 is configured to uniformly charge the surface of the rotating photosensitive drum 23 with a predetermined polarity and a predetermined potential. The exposure unit 24 outputs a light beam modulated based on input image data representing an image to be formed, thereby exposing the charged surface of the photosensitive drum 23 to the light beam. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 23.

[0019] As an example, the exposure unit 24 of this embodiment employs a bottom exposure method in which the photosensitive drum 23 is exposed by irradiating it with light from below. The exposure unit 24 includes LED heads arranged in a line along the drum axis direction (main scanning direction) of the photosensitive drum 23. An electrostatic latent image is formed on the surface of the photosensitive drum 23 line by line by the light output from the LED heads. The exposure units 24 are arranged in a line along the drum axis direction of the photosensitive drum 23, and by irradiating them all at once, the surface of the photosensitive drum 23 is exposed linearly in the main scanning direction, thereby forming a linear electrostatic latent image. The drum axis direction of the photosensitive drum 23 corresponds to the main scanning direction, and the rotation direction of the photosensitive drum 23 (the direction in which the toner image is transported), which is perpendicular to the drum axis direction, corresponds to the sub-scanning direction.

[0020] The developing unit 22 contains toner of a corresponding color as a developer for developing the electrostatic latent image. The developing unit 22 develops the electrostatic latent image by attaching toner (developer) to the electrostatic latent image formed on the surface of the photosensitive drum 23. By developing the electrostatic latent image, a toner image (developer image) is formed on the surface of the photosensitive drum 23. The primary transfer unit 25 transfers the toner image formed on the surface of the photosensitive drum 23 to the intermediate transfer belt 3. In this embodiment, the primary transfer unit 25 is an example of a transfer means that transfers the toner image formed on the image carrier to a transfer recipient, and the intermediate transfer belt 3 is an example of a transfer recipient to which the toner image formed on the photosensitive drum 23 (image carrier) is transferred.

[0021] <Image detector> With reference to FIG. 3, an example of detection of the amount of image misalignment performed using the image detector 61 in the image forming apparatus 1 will be described. In an image forming apparatus, the position of a formed image may deviate from the ideal position (misalignment). As described above, such misalignment includes a fixed amount of misalignment of the entire image in the sub-scanning direction and periodic misalignment in the sub-scanning direction. The image forming apparatus 1 of this embodiment is configured to detect the amount of periodic misalignment of the image in the sub-scanning direction using the image detector 61 and prevent the occurrence of such misalignment based on the detection result. The amount of misalignment is detected using the image detector 61 by detecting the position of the toner image formed on the intermediate transfer belt 3.

[0022] In the image forming apparatus 1 of this embodiment, a detection image is formed on the intermediate transfer belt 3 to detect the amount of misalignment in the sub-scanning direction of a toner image transferred from the photosensitive drum 23 to the intermediate transfer belt 3. FIG. 3 shows an example in which a toner pattern 5 (pattern image) is formed on the intermediate transfer belt 3 as the detection image. The toner pattern 5 is generated by the image forming units 20Y, 20M, 20C, and 20K and transferred to the intermediate transfer belt 3. The toner pattern 5 is made up of a plurality of rectangular images (patch images). Ideally, the plurality of rectangular images making up the toner pattern 5 are formed on the intermediate transfer belt 3 at known intervals in the sub-scanning direction. As shown in FIG. 3, the toner pattern 5 is made up of multiple rows of patterns (three rows of patterns in this example) arranged in different regions in the main scanning direction.

[0023] The image forming apparatus 1 includes an image detector 61 for detecting the toner pattern 5 (pattern image) formed on the intermediate transfer belt 3. In the example of FIG. 3, the image detector 61 is provided below the intermediate transfer belt 3 and downstream of the imaging unit 20K in the rotation direction (sub-scanning direction) of the intermediate transfer belt 3. The image detector 61 has a plurality of optical sensors 62 (in this example, three optical sensors 62 corresponding to three rows of patterns) respectively corresponding to the multiple rows of patterns included in the toner pattern 5. The optical sensors 62 are arranged in a line in the main scanning direction and are configured to detect the toner pattern 5 passing through different positions (detection positions) in the main scanning direction. Each rectangular image included in the toner pattern 5, arranged in the sub-scanning direction, moves in accordance with the rotation of the intermediate transfer belt 3 and sequentially passes the detection position of the optical sensor 62. Image misalignment can be detected based on the detection result of the toner pattern 5 on the intermediate transfer belt 3 by the image detector 61 (optical sensor 62).

[0024] Each optical sensor 62 is configured to irradiate light toward the intermediate transfer belt 3 and receive the reflected light. Each optical sensor 62 outputs a detection signal (analog detection signal) having a voltage value corresponding to the amount of reflected light received. The amount of reflected light received by the optical sensor 62 varies depending on whether or not a toner image is present at the irradiation position on the intermediate transfer belt 3 where the light is irradiated. As a result, the voltage value of the analog detection signal output from the optical sensor 62 varies depending on whether or not a toner image is present at the irradiation position on the intermediate transfer belt 3. The reflectance of the surface of the intermediate transfer belt 3 onto which the toner image is transferred is higher than the reflectance of the toner pattern 5 (toner image). Therefore, when no toner image is present at the irradiation position on the intermediate transfer belt 3, the amount of reflected light received by the optical sensor 62 is greater than the amount of light when a toner image is present at that irradiation position.

[0025] An example of detection of the toner pattern 5 by the image detector 61 will be described with reference to FIG. 4. FIG. 4(A) shows an example of the relationship between the toner pattern 5 and light irradiation positions (spots) 63 and 64 by one optical sensor 62. Spot 63 shows the case where light is irradiated onto the surface of the intermediate transfer belt 3 (a position where the toner pattern 5 is not formed). Spot 64 shows the case where light is irradiated onto the toner pattern 5 formed on the intermediate transfer belt 3. Spots 63 and 64 correspond to the detection positions of the optical sensor 62. Note that in reality, spots 63 and 64 do not move, and the toner pattern 5 moves in the sub-scanning direction in accordance with the rotation of the intermediate transfer belt 3 (movement of the circumferential surface of the intermediate transfer belt 3).

[0026] 4(B) shows an example of an analog detection signal output from optical sensor 62 when detecting toner pattern 5 shown in FIG. 4(A). Analog detection signal B output from optical sensor 62 becomes a high (H) level voltage value when optical sensor 62 receives reflected light from spot 63 (i.e., when not detecting a toner image). On the other hand, analog detection signal B becomes a low (L) level voltage value when optical sensor 62 receives reflected light from spot 64 (i.e., when detecting a toner image). In this way, optical sensor 62 outputs a lower voltage value when detecting a toner image than when not detecting a toner image, depending on the amount of light reflected from spot 63 or 64.

[0027] The analog detection signal B output from the optical sensor 62 is converted into a digital detection signal. This allows processing by the CPU 82 (shown in FIG. 5). FIG. 4C shows an example of a digital detection signal obtained by converting the analog detection signal B into a digital signal. In the example of FIG. 4C, the L level of the analog detection signal B is converted into the H level of the digital detection signal S, and the H level of the analog detection signal B is converted into the L level of the digital detection signal S. In this way, when the optical sensor 62 detects a toner image (each rectangular image included in the toner pattern 5), the digital detection signal S becomes the H level, and when the optical sensor 62 does not detect a toner image, the digital detection signal S becomes the L level.

[0028] The correspondence between the logic of the analog detection signal B and the logic of the digital detection signal S may be reversed from the correspondence described above. That is, the L level of the analog detection signal B may be converted to the L level of the digital detection signal S, and the H level of the analog detection signal B may be converted to the H level of the digital detection signal S. In this case, when a toner image is detected by the optical sensor 62, the digital detection signal S becomes the L level, and when a toner image is not detected by the optical sensor 62, the digital detection signal S becomes the H level.

[0029] The spacing of the toner patterns 5 in the sub-scanning direction (the spacing of each rectangular image included in the toner patterns 5 in the sub-scanning direction) can be measured using at least one of the rising edge U and the falling edge D of the digital detection signal S. For example, the spacing of the rising edges U or the falling edges D in the digital detection signal S can be measured as the spacing of the toner patterns 5 in the sub-scanning direction. Alternatively, the spacing of the centers of gravity (the center between the rising edge U and the falling edge D) in the digital detection signal S can be measured as the spacing of the toner patterns 5 in the sub-scanning direction.

[0030] <Control System> 5 is a block diagram showing an example of the configuration of a control system 80 that controls the operation of the image forming apparatus 1, and shows an example of the configuration related to positional misalignment correction (color misalignment correction) of the formed image. The control system 80 is built into the image forming apparatus 1. The control system 80 controls various processes related to image formation, such as the image formation process by the image forming apparatus 1, the conveyance process of the recording material, and the fixing process of the image.

[0031] The control system 80 includes a conversion unit 81, a CPU 82, a storage unit 83, an image processing control unit 84, and an exposure unit control unit 85. The storage unit 83 can be configured as a rewritable nonvolatile memory (for example, an EPROM).

[0032] The conversion unit 81 performs a conversion process to convert the analog detection signal B output from the image detector 61 (optical sensor 62) into a digital detection signal S. In the conversion process, binarization is performed by comparing with a predetermined threshold value. The conversion unit 81 outputs the digital detection signal S obtained by the conversion process to the CPU 82.

[0033] The CPU 82 reads and executes a control program (computer program) stored in the storage unit 83, thereby controlling the overall operation of the image forming apparatus 1. By executing the control program, the CPU 82 functions as a pattern reading unit 821, a misalignment amount obtaining unit 822, and a pattern generating unit 823.

[0034] The pattern reading unit 821 performs processing to read (measure) the toner pattern 5 on the intermediate transfer belt 3 based on the digital detection signal S output from the conversion unit 81. Specifically, the pattern reading unit 821 detects the timing (rising edge U) at which the digital detection signal S changes from L level to H level and the timing (falling edge D) at which the digital detection signal S changes from H level to L level.

[0035] The deviation amount acquisition unit 822 calculates the amount of positional deviation in the sub-scanning direction of the formed image (using a calculation method described later) based on at least one of the rising edge U and the falling edge D detected by the pattern reading unit 821. The deviation amount acquisition unit 822 stores the calculated amount of positional deviation in the storage unit 83.

[0036] The pattern generation unit 823 generates image data of the above-mentioned toner pattern 5 (pattern image) and transmits it to the exposure unit control unit 85. The exposure unit control unit 85 controls the operation of the exposure unit 24 based on the received image data. The pattern generation unit 823 also generates correction data (first correction data) for correcting periodic positional deviation in the sub-scanning direction of the toner image formed on the intermediate transfer belt 3, and second correction data (second correction data) for correcting a certain amount of positional deviation in the sub-scanning direction of the entire image to be formed. The pattern generation unit 823 transmits the generated correction data to the exposure unit control unit 85.

[0037] The image processing control unit 84 performs predetermined image processing on the image data. For example, the image processing control unit 84 can correct misalignment by executing image processing on image data representing the image to be formed. For example, the image processing control unit 84 can perform image processing on the image data so as to correct the write start position of the image to be formed on the recording material. For example, the image processing control unit 84 can perform image processing on the image data so as to correct the magnification of the image to be formed on the recording material. Furthermore, the image misalignment correction may be performed by correcting the light emission (exposure timing) of the exposure device 24 by the exposure unit control unit 85.

[0038] Furthermore, the correction of the positional deviation of the image may be performed by a drive unit control unit (not shown) that controls a drive unit that drives the image forming unit (imaging unit 20). In this case, the drive unit control unit corrects the periodic positional deviation of the image in the sub-scanning direction, for example, by correcting the rotation speed of the photosensitive drum 23 based on the amount of positional deviation stored in the storage unit 83.

[0039] The exposure unit control unit 85 corrects the positional deviation of the image in the sub-scanning direction by correcting the exposure timing of the photosensitive drum 23 by the exposure unit 24 based on the correction data (first and second correction data) received or stored in the memory unit 83.

[0040] <Image position deviation amount> 6 shows an example of the amount of positional deviation of an image in the sub-scanning direction obtained by the deviation amount obtaining unit 822. In this example, the center of gravity C of the digital detection signal S (the center between the rising edge U and the falling edge D) is used as the position of each rectangular image of the toner pattern 5.

[0041] 6(A) shows an example of the digital detection signal S when the toner pattern 5 on the intermediate transfer belt 3 is formed in an ideal position. FIG. 6(B) shows an example of the digital detection signal S when the formation position of the toner pattern 5 on the intermediate transfer belt 3 is deviated from the ideal position due to some kind of disturbance. The disturbance may be, for example, a fluctuation in the transport speed of the intermediate transfer belt 3 or a fluctuation in the rotation speed of the photosensitive drum 23. In the example of FIG. 6(B), the rising edge U', falling edge D', and center of gravity C' detected for the digital detection signal S are deviated from the rising edge U, falling edge D, and center of gravity C shown in FIG. 6(A) due to such a disturbance.

[0042] FIG. 6C shows an example of detecting the amount of misalignment of the toner pattern 5 at each position on the intermediate transfer belt 3 in the sub-scanning direction (the direction of transport of the intermediate transfer belt 3) when misalignment occurs due to an external disturbance. In FIG. 6C, the horizontal axis represents the position (phase) on the intermediate transfer belt 3 in the sub-scanning direction. The vertical axis represents the amount of misalignment 90 of the toner pattern 5 at each position on the intermediate transfer belt 3 in the sub-scanning direction. The amount of misalignment 90 is obtained by the misalignment amount obtaining unit 822 as the difference between the center of gravity C' of each rectangular image of the toner pattern 5 that is actually detected and the center of gravity C that would be obtained if the toner pattern 5 were formed in the ideal position. Note that in the graph of FIG. 6C, the amount of misalignment 90 is plotted at the ideal position (center of gravity C) of each rectangular image of the toner pattern 5.

[0043] As shown in FIG. 6C, the misalignment amount 90 is acquired (detected) as an intermittent, discrete value. This is because rectangular images of the toner pattern 5 are formed at predetermined intervals. Based on the discrete misalignment amount 90 detected in this manner, predicted data 91 of the misalignment amount is acquired. The predicted data 91 is acquired by approximating the misalignment amount 90 to a sine function, and indicates the predicted result of the temporal fluctuation of the misalignment amount.

[0044] <Predicted data for misalignment amount> FIG. 7 shows an example of a process for generating predicted data for the amount of misalignment of an image in the sub-scanning direction based on detected data for the amount of misalignment of the image in the sub-scanning direction. Using this example, a process for generating predicted data 91 based on detected data including an actual amount of misalignment 92 detected using a toner pattern 5 will be described. As shown in FIG. 7, the actual amount of misalignment 92 detected using a toner pattern 5 has variations (errors) with respect to an approximate curve (sine function) expressed by a sine wave. The predicted data 91 can be obtained by fitting a sine function to the detected data (amount of misalignment 92) with such variations, as will be described below.

[0045] The amount of misalignment of the formed image in the sub-scanning direction generally fluctuates with the same period as the rotation period of the rotating body (such as the photosensitive drum 23) that constitutes the image forming unit. This is because the toner pattern 5 formed on the intermediate transfer belt 3 periodically expands and contracts in the conveying direction (sub-scanning direction) of the intermediate transfer belt 3 with the same period as the rotation period of the rotating body due to variations in the shape of the rotating body and / or variations in the rotation speed of the rotating body. Therefore, the period of the sine wave representing the predicted data 91 is the same as the rotation period of the rotating body (mainly assumed to be the photosensitive drum 23 in this embodiment) that is causing the misalignment of the formed image in the sub-scanning direction.

[0046] In this way, the amount of misalignment of the formed image in the sub-scanning direction has a variation similar to that of a sine function with the position (phase) in the sub-scanning direction as a variable. Therefore, by fitting a sine function to approximate the misalignment amount 92 included in the detection data, the amount of misalignment can be expressed by two parameters, the amplitude and phase of the sine function. Note that since the diameter of the rotating body that constitutes the photosensitive drum 23 is known in advance, the period of the sine function, which corresponds to the rotation period of the rotating body, is also known in advance.

[0047] 7, the differences between predicted data 91 and detected data (amount of positional deviation 92) are represented as differences e1 to e7. In this case, the predicted data 91 is derived as a sine function that minimizes the value of the following equation (1), which is expressed using the differences e1 to e7. That is, the predicted data 91 is found by fitting a predetermined sine wave (a sine wave having a predetermined wavelength) using the least squares method. (e1) 2 +(e2) 2 +(e3) 2 +(e4) 2 +(e5) 2 +(e6) 2 +(e7) 2 (1)

[0048] 8 shows an example of predicted data expressed using a sine function. As shown in the figure, when predicted data 91 (positional deviation amount Y(t)) is expressed using a sine function, it is expressed as the sum of a time-constant DC component and a time-varying AC component. In this embodiment, the AC component of the positional deviation amount Y(t) corresponds to the AC component caused by rotational fluctuations of the photosensitive drum 23, one of the rotating bodies that make up the image forming unit in the image forming apparatus 1, and this AC component is the target of positional deviation correction. This is because, in general, the rotational fluctuations of the photosensitive drum 23 have the greatest effect as a factor that causes periodic deviations in the image formation position in the sub-scanning direction.

[0049] The positional deviation amount Y(t) can be expressed as an AC component (a component expressed as a sine function) and a DC component, which are expressed as dependent variables of time t, using the frequency F, which is known from the circumferential length of the rotating body (photosensitive drum 23), and the amplitude A and phase Φ, which are to be derived, as shown in the following equation. Y(t) = A sin(2π / F(t-Φ))+DC (2) As described above, the actual positional deviation amount 92 in the sub-scanning direction (detected data) detected using the toner pattern 5 has differences e1 to e7 (FIG. 7) with respect to the predicted data 91. Therefore, the actual positional deviation amount in the sub-scanning direction can be expressed by the following equation. Y(t) = A sin(2π / F(t-Φ))+DC+e(t) (3)

[0050] <Fitting process using least squares method> In this embodiment, as described above, fitting processing by the least squares method is performed as fitting processing for acquiring predicted data 91 based on the actual positional deviation amount 92 (detection data) in the sub-scanning direction detected using the toner pattern 5. Generally, a sine function Y(t) is expressed as Y(t) = A a sin(t) + A bcos(t) + DC. Y(t) represents the amount of misalignment of the formed image in the sub-scanning direction at time t. DC represents the DC component of the misalignment amount. Furthermore, if the rotation frequency of the rotating body (photosensitive drum 23 in this embodiment) that causes the periodic misalignment that is the target of misalignment correction is F, Y(t) is ideally represented by the following equation. TIFF2025134543000002.tif15114

[0051] Here, the total number of data items regarding the actual positional deviation amount in the sub-scanning direction detected using the toner pattern 5 is set to N. In this case, the error e(A a ,A b ,DC) to minimize the sum of (A a ,A b ,DC) is required. TIFF2025134543000003.tif13128

[0052] As shown in the following equation, when the partial differential value of equation (5) becomes 0, the error e(A a ,A b ,DC) to minimize the sum of (A a ,A b ,DC) is derived. TIFF2025134543000004.tif45158

[0053] The least squares method is used to obtain the forecast data 91 based on the simultaneous equations in Eq. (6), A a and A b Finally, by deriving the matrix (A a ,A b , DC) are derived. Furthermore, by transforming Y(t) shown in equation (4) into the form of equation (3), the amplitude A and phase Φ to be derived are obtained.

[0054] <Correction data generation> In the image forming apparatus 1, in order to correct (reduce or suppress) periodic misalignment in the sub-scanning direction that occurs in the formed image, it is necessary to correct the image formation conditions (for example, correct the exposure timing) so as to cancel out the periodic fluctuation of the misalignment. In this embodiment, correction data for correcting the image formation conditions so as to cancel out such periodic fluctuation of the misalignment is generated as correction data for misalignment correction, and the image formation conditions are corrected in accordance with the generated correction data.

[0055] FIG. 9 shows examples of various data derived from the predicted data 91. The correction data for correcting misalignment is generated using the predicted data 91 (Y(t)) of the misalignment amount obtained based on the detection results of the toner pattern 5 as described above. Specifically, inverse phase data 94 is generated, which represents a sine function (sine wave) of opposite phase to the sine function (sine wave) corresponding to the predicted data 91. The inverse phase data 94 represents a fluctuation pattern of opposite phase to the phase of the fluctuation in the misalignment amount indicated by the predicted data 91, in order to cancel out the periodic fluctuation pattern of the misalignment amount indicated by the predicted data 91. By correcting the magnification (partial magnification) in each region in the sub-scanning direction of the image to be formed in accordance with the inverse phase data 94, it is possible to correct the periodic misalignment in the sub-scanning direction.

[0056] 9, partial magnification data 95 for correcting the partial magnification in each region in the sub-scanning direction of the image is generated based on the reverse phase data 94 as correction data for correcting misalignment. The partial magnification data 95 includes, for example, a correction value (magnification correction value) for correcting the partial magnification of each region when one circumferential region on the photosensitive drum 23 (on the image carrier) is divided into multiple regions (n ​​divided regions x1 to xn from the first to nth). That is, the partial magnification data 95 is configured as a table including correction values ​​y1 to yn corresponding to the divided regions x1 to xn. The divided regions x1 to xn are obtained by, for example, dividing one circumferential region on the photosensitive drum 23 into n equal parts.

[0057] The partial magnification data 95 (each correction value included therein) can be calculated, for example, as the first derivative of the antiphase data 94. When the predicted data 91 is expressed as Y(t) as described above, the antiphase data 94 is calculated as Y(t) with the polarity inverted (-Y(t)). The partial magnification data 95 is calculated as the first derivative (-Y'(t)) of the antiphase data 94. This differentiation operation may be replaced with a difference operation. That is, the difference between Y(t) at time t and temporally adjacent data (e.g., Y(t)-Y(t-1)) may be calculated as the correction value. Note that by making the length of the toner pattern 5 in the sub-scanning direction equal to or greater than the circumferential length of the photosensitive drum 23, it may be possible to perform the differentiation operation or difference operation using the predicted data (Y(t)) and temporally adjacent data.

[0058] The partial magnification data 95 is used as correction data for correcting periodic misalignment in the sub-scanning direction (misalignment of the AC component) that occurs in the formed image. However, when misalignment in the sub-scanning direction is corrected using the partial magnification data 95, misalignment in the sub-scanning direction may occur in the formed image depending on the start timing of the correction. As a result of the accumulation of misalignment due to correction based on the partial magnification data 95, a state may arise in which misalignment correction is performed based on data in which a certain amount of offset 97 (misalignment) occurs with respect to the antiphase data 94, as shown in accumulated data 96 in FIG. 9. In this case, a certain amount of misalignment in the sub-scanning direction (misalignment of the DC component) may occur in the formed image as a whole.

[0059] In the image forming apparatus 1 of this embodiment, among the misalignments that occur in the formed image, not only the misalignment of the AC component but also the misalignment of the DC component described above can be addressed, thereby enabling misalignment correction to be started at any timing. For this reason, in this embodiment, correction data (correction values) for the misalignment of the AC component in the sub-scanning direction and correction data (correction values) for the misalignment of the DC component are generated based on the prediction data 91, and are stored in the storage unit 83 as correction data for misalignment correction.

[0060] Specifically, the partial magnification data 95 described above is generated as correction data for the AC component misalignment. Furthermore, a correction value is generated as correction data for the DC component misalignment to correct the image write timing (formation start timing) in the sub-scanning direction so as to cancel out the misalignment of the entire image in the sub-scanning direction, which corresponds to a certain offset 97. FIG. 9 shows an example in which misalignment correction using the partial magnification data 95 is started at time t=0. In this case, the waveform value of the antiphase data 94 at time t=0 (-Y(0), i.e., the waveform value of the antiphase data 94 corresponding to the first divided area x1) is acquired as the correction value for the DC component misalignment. The correction value for the DC component misalignment corresponds to the delay amount (adjustment amount) of the image write timing in the sub-scanning direction. In the correction for the DC component misalignment, the image write timing (formation start timing) is changed (advanced or delayed) by the delay amount set as the correction value.

[0061] The image forming apparatus 1 of this embodiment performs positional deviation correction based on the correction data generated in this manner, thereby forming an image in which the positional deviation of the AC component and the DC component is corrected. The generated correction data is stored in the storage unit 83 and is used repeatedly until it is updated using the toner pattern 5.

[0062] <Correction of positional deviation in the sub-scanning direction> Based on the correction data obtained as described above, it is possible to correct image misalignment in the sub-scanning direction. The image forming apparatus 1 (CPU 82) of this embodiment corrects image misalignment by correcting image formation conditions based on the acquired correction data. Below, a case will be described in which image misalignment in the sub-scanning direction is corrected by correcting the timing of exposure of the photosensitive drum 23 by the exposure unit 24 as the correction of image formation conditions. Note that, in addition to correcting the exposure timing, the correction of image formation conditions may also include correcting the rotational speed (driving speed) of a rotating body constituting the image forming unit. In this case, for example, by correcting the rotational speed (driving speed) of the photosensitive drum 23, more efficient misalignment correction can be achieved.

[0063] In this embodiment, the home position (HP) of the photosensitive drum 23 is detected as a reference for image positional deviation in the sub-scanning direction. The HP of the photosensitive drum 23 corresponds to a reference position that serves as a reference for the rotation of the photosensitive drum 23. The HP of the photosensitive drum 23 can be detected, for example, by a detection method using a sensor or a detection method using a signal output from a drive source of the photosensitive drum 23. The detection method using a sensor uses, for example, a flag provided in a drive mechanism of the photosensitive drum 23, such as a drive shaft (drum shaft) that drives the photosensitive drum 23 or a drive gear that transmits drive force to the photosensitive drum 23, and a sensor such as a photointerrupter.

[0064] FIG. 10 shows a configuration example of a detection device used to detect the rotation of the photosensitive drum 23. In this example, a detection device 233 is provided on the photosensitive drum 23 and a drive gear 231 that drives the photosensitive drum. The detection device 233 includes a photointerrupter and a flag. While the drive mechanism of the photosensitive drum 23 is rotating, the HP of the photosensitive drum 23 is determined (detected) based on the timing at which the flag is detected by the photointerrupter. Specifically, the phase of the photosensitive drum 23 at the timing at which the flag is detected is determined as the HP of the photosensitive drum 23. Note that in a detection method that uses a signal output from a drive source, the HP of the photosensitive drum 23 is determined (detected) based on, for example, a count value of a signal output from a drive motor.

[0065] <Processing Procedure> 11 is a flowchart showing an example of the procedure for image formation processing, including misalignment correction (color misalignment correction) of an image in the sub-scanning direction, in the image forming apparatus 1. This procedure includes a first phase (Phase 1) of processing to generate correction data for misalignment correction, and a second phase (Phase 2) of processing to perform image formation processing, including misalignment correction (color misalignment correction) based on the generated correction data. In this example, misalignment correction is performed based on the detection timing of the HP of the photosensitive drum 23.

[0066] In S100, the CPU 82 starts processing to detect the HP of the photosensitive drum 23 and stores the timing at which the HP is detected in the memory unit 83. Detecting the HP of the photosensitive drum 23 makes it possible to recognize the rotation period of the photosensitive drum 23. In parallel with the HP detection processing in S100, the CPU 82 performs processing to form a toner pattern 5 (pattern image) by the image creating unit 20 in S110. In this processing, the CPU 82 transmits image data of the toner pattern 5 generated by the pattern generating unit 823 to the exposure unit control unit 85. The exposure unit control unit 85 controls the operation of the exposure unit 24 based on the received image data. As a result, the image creating unit 20 forms the toner pattern 5 on the photosensitive drum 23 based on the image data of the toner pattern 5. The toner pattern 5 formed on each photosensitive drum 23 is transferred to the intermediate transfer belt 3 in the primary transfer unit 25.

[0067] Thereafter, in S120, the CPU 82 uses the image detector 61 to perform a measurement process on the toner pattern 5 formed on the intermediate transfer belt 3. Specifically, the CPU 82 uses the image detector 61 to detect the toner pattern 5 formed on the intermediate transfer belt 3. The CPU 82 further measures the spacing of the toner pattern 5 in the sub-scanning direction based on the detection result of the toner pattern 5 output from the image detector 61, thereby detecting the amount of misalignment regarding the formation position of the toner pattern 5 (image).

[0068] In S130, the CPU 82 performs the above-described fitting process using the detection timing of the HP of the photosensitive drum 23 as a reference (time t=0) to obtain predicted data 91 of the amount of misalignment of the image. Specifically, the CPU 82 obtains (calculates) the amount of misalignment of the toner pattern 5 in the sub-scanning direction based on the measurement results of the toner pattern 5, and approximates the change in the obtained amount of misalignment over time with a sine wave Y(t). As a result, the CPU 82 obtains, as predicted data 91, parameters (amplitude and phase) related to the sine wave Y(t), which represents the amount of misalignment due to rotational fluctuations of the photosensitive drum 23 and is to be corrected.

[0069] In this embodiment, the target of correction is image positional deviation caused by rotational fluctuations of the photosensitive drum 23. To achieve this correction, as described above, the phase Φ of the sine wave Y(t) is defined based on the detection timing of the HP of the photosensitive drum 23. The CPU 82 stores the amplitude A and phase Φ of the sine wave Y(t) in the storage unit 83 as predicted data 91.

[0070] In S140, the CPU 82 generates inverse phase data 94 representing a sine function with an inverse phase to the sine function Y(t) represented by the predicted data 91 (amplitude A and phase Φ) stored in the storage unit 83. The CPU 82 stores the generated inverse phase data 94 in the storage unit 83. Upon completion of generation of the inverse phase data 94, in S150 the CPU 82 generates the above-mentioned partial magnification data 95 based on the inverse phase data 94. The CPU 82 stores the generated partial magnification data 95 in the storage unit 83 as correction data (first correction data) for periodic positional deviation (positional deviation of AC components) in the sub-scanning direction of the image to be formed. Each correction value included in the partial magnification data 95 corresponds to each of the divided areas x1 to xn on the photosensitive drum 23, and is a correction value for the partial magnification (amount of expansion / contraction) in each divided area.

[0071] Further, in S160, the CPU 82 generates a correction value for the timing of writing the image in the sub-scanning direction based on the reverse phase data 94, in order to correct a certain amount of positional deviation of the entire image. For example, the waveform value (-Y(0)) of the reverse phase data 94 corresponding to the first divided area x1 of the divided areas x1 to xn on the photosensitive drum 23 is set as the correction value. The CPU 82 stores the generated correction value in the storage unit 83 as correction data (second correction data) for the certain amount of positional deviation of the entire image (positional deviation of the DC component).

[0072] The above-described processes from S100 to S160 correspond to the first phase process. Through the first phase process, correction data based on the measurement results for the toner pattern 5 is generated and stored in the storage unit 83. When the above-described first phase process is completed, the CPU 82 starts the second phase process. In the second phase process, positional deviation of the image in the sub-scanning direction is corrected based on the correction data generated in the first phase process, and a corrected image is formed.

[0073] In the second phase of processing, first, in S210, when the CPU 82 accepts a print job, it starts processing to detect the HP of the photosensitive drum 23 and waits until the HP of the photosensitive drum 23 is detected. When the HP of the photosensitive drum 23 is detected by the sensor, the CPU 82 proceeds to S220.

[0074] In S220, the CPU 82 causes the exposure unit control unit 85 to correct the timing of exposure by the exposure unit 24 based on the correction data for the positional deviation of the AC component acquired in the processing of the first phase. The exposure unit control unit 85 corrects the timing of exposure by the exposure unit 24 by generating (correcting) a line synchronization signal based on the correction data (partial magnification data 95) so that the partial magnification of the image formed in each divided area on the photosensitive drum 23 is corrected. The line synchronization signal is a signal that represents the division of each line in the main scanning direction of the image, and is an analog signal whose level switches at regular intervals regardless of the image. Note that the exposure unit 24 exposes the photosensitive drum 23 in accordance with input signals such as an image data signal and a clock signal in addition to the line synchronization signal.

[0075] Furthermore, in S230, the CPU 230 causes the exposure unit control unit 85 to correct the timing of writing the image in the sub-scanning direction based on the correction data for the DC component misalignment acquired in the first phase processing. This corrects a certain amount of misalignment of the entire image in the sub-scanning direction (DC component misalignment) that occurs due to the correction for the AC component misalignment described above.

[0076] The misregistration correction in S230 may be performed independently for each toner color. Alternatively, the misregistration correction may be performed for color misregistration between specific toner colors (for example, between toner colors that are easily recognized visually). In this case, a correction value for correcting the misregistration of the DC component for the formed images of the other colors may be set so as to correct the relative misregistration from the formed image of the first color (for example, Y color).

[0077] In S240, the CPU 82 controls the image processing control unit 84 and the exposure unit control unit 85 to form an image on a recording material based on the print job. Specifically, the CPU 82 forms a toner image on the photosensitive drum 23 based on the print job. At this time, the positional deviation correction (exposure timing correction) in the above-mentioned S220 and S230 is performed, thereby reducing or suppressing positional deviation (color deviation) of the image formed on the photosensitive drum 23. The CPU 82 further controls the exposure unit control unit 85 to transfer the toner image formed on the photosensitive drum 23 to the intermediate transfer belt 3 and then to the recording material. Thereafter, the CPU 82 controls the fixing device 30 to fix the toner image transferred to the recording material.

[0078] The above processing from S210 to S250 corresponds to the second phase processing. By the second phase processing, an image based on the print job is formed (printed) on a recording material. In the second phase processing, misregistration correction is performed based on the correction data acquired in the first phase processing, so that the image is formed at an appropriate position in the sub-scanning direction on the intermediate transfer belt 3. In other words, misregistration in the sub-scanning direction (misregistration of AC components and DC components) that may occur in the formed image is reduced or suppressed.

[0079] <Processing example 1> 12 is a timing chart showing the timing of control for misregistration correction in the image forming apparatus 1 according to this embodiment. This timing chart shows an example of the timing of each process included in the first phase process and the second phase process described above.

[0080] In this example, the image forming apparatus 1 (CPU 82) performs the following processing as the first phase of processing. First, the image forming unit starts forming a toner pattern 82, which is an image for detecting the amount of misregistration of an image formed by the image forming unit. After the toner pattern 5 is formed on the intermediate transfer belt 3, the toner pattern 5 is measured using the image detector 61. This measurement acquires detection data of the amount of misregistration of the image in the sub-scanning direction, and based on the detection data, an amplitude A and a phase Φ indicating the amount of misregistration of the image in the sub-scanning direction are acquired. The amplitude A and the phase Φ correspond to the predicted data 91 described above. The phase Φ is a phase based on the detection timing of the HP of the photosensitive drum 23 and can be acquired based on the phase θ based on the formation start timing of the toner pattern 82. As described above, the inverse phase data 94 is generated based on the amplitude A and the phase Φ (predicted data 91), and correction data for the misregistration of the AC component is generated based on the inverse phase data 94. Furthermore, the value (waveform value) D1 of the inverse phase data 94 at the correction start timing (image formation start timing) is set as correction data (correction value) for the misregistration of the DC component. These correction data are stored in the storage unit 83.

[0081] Thereafter, the image forming apparatus 1 (CPU 82) performs the following processing as the second phase processing. As shown in Fig. 12, when job 1 is input as a print job, the image forming apparatus 1 starts image creation processing based on job 1, using the detection timing of the HP as a reference. The image forming apparatus 1 also starts image misalignment correction based on the correction data acquired in the first phase processing, using the detection timing of the HP as a reference.

[0082] In this example, in image misalignment correction, the line synchronization signal is corrected in accordance with the correction data as described above in order to correct misalignment of AC components occurring in the image to be formed. Specifically, the line synchronization signal is corrected so that the partial magnification corresponding to each division position on the photosensitive drum 23 is corrected in accordance with partial magnification data 95 generated based on reverse phase data 94 representing a waveform that is reverse phase to the sine wave represented by the predicted data 91. Furthermore, in order to correct misalignment of DC components occurring in the image to be formed, the image write start timing in the sub-scanning direction is corrected in accordance with the correction data as described above.

[0083] By applying such misregistration correction, it becomes possible to correct (reduce or suppress) misregistration that may occur in the image formed on the intermediate transfer belt 3, as shown as the misregistration amount 93 of the corrected image in Fig. 12. That is, it is possible to correct periodic misregistration of the image in the sub-scanning direction, and also to correct a certain amount of misregistration of the entire image that occurs due to the correction of the periodic misregistration.

[0084] In this example, after job 1 is completed, the image forming apparatus 1 is restarted by operating the power switch (OFF / ON operation). At this time, the correction data acquired in the above-mentioned first phase processing is not deleted from the storage unit 83. After that, job 3 is input to the image forming apparatus 1 as a print job. In this case, the image forming apparatus 1 starts image formation processing based on job 3, based on the detection timing of the HP of the photosensitive drum 23, without performing the first phase processing again. In this image formation processing, the correction data stored in the storage unit 83 is used to correct positional deviation of the image.

[0085] <Processing example 2> 11, correction data for misregistration correction is generated (set) and misregistration correction is started based on the detection timing of the HP of the photosensitive drum 23. That is, the detection timing of the HP of the photosensitive drum 23 corresponds to the first divided area x1 of the divided positions x1 to xn on the photosensitive drum 23. Also, image formation (image creation) is started based on the detection timing of the HP. In this embodiment, the start timing of image formation and the start timing of misregistration correction can also be set to a timing other than the detection timing of the HP of the photosensitive drum 23.

[0086] 13 is a timing chart showing the timing of control for correcting misalignment in the image forming apparatus 1 when image formation is started at any timing (t1 to t3). Similar to FIG. 12, this timing chart shows an example of the timing of each process included in the first phase process and the second phase process described above.

[0087] 12, the toner pattern 5 is measured in the first phase of processing, and the amplitude A and phase Φ (predicted data 91) are obtained based on the measurement results, and correction data for the positional deviation of the AC component is generated and saved. However, the correction value for the positional deviation of the DC component (correction value D1 in the example of FIG. 12) changes depending on the start timing of actual image formation and positional deviation correction, so the correction value is not set at this stage.

[0088] The start timings t1 to t3 of image formation are set for each print job (jobs 1 to 3) based on the detection timing of the HP of the photosensitive drum 23. In the processing of the second phase, the image forming apparatus 1 delays the start of image formation from the detection timing of the HP of the photosensitive drum 23 to the timings t1 to t3 in accordance with the settings of the print job, for example, by using counting by a timer of the drive motor of the photosensitive drum 23. In this case, it is possible to obtain a phase shift amount α' with respect to (the phase represented by) predicted data 91 at the start timing of image formation based on one rotation period of the photosensitive drum 23. Correction data for the positional deviation of the AC component is derived based on the predicted data 91 (amplitude A and phase Φ) and the phase shift amount α'.

[0089] Furthermore, the correction value D1' for the DC component positional deviation is determined by the waveform value of the anti-phase data 94 at the start of the positional deviation correction. Therefore, the correction value D1' is derived based on the anti-phase data 94 and the phase deviation amount α'. As shown in FIG. 13, when the start timing of image formation is changed to t2, it is possible to obtain the phase deviation amount α'' and obtain the correction data for the AC component positional deviation and the correction data for the DC component positional deviation (correction value D1'') in the same manner as in the above-described process.

[0090] In the process of FIG. 11 , the timing at which the exposure unit 24 starts writing an image in the sub-scanning direction is determined by the process of S230. In this process, the timing at which the image starts writing is determined based on the detection timing of the HP of the photosensitive drum 23 or the count value of a timer. Because the phase of the rotating body (photosensitive drum 23) at the timing at which the image starts writing is known and the function (sine function) for acquiring the correction data is also known, it is possible to calculate (acquire) correction data for correcting misalignment at the timing at which the image starts writing. In other words, it is possible to acquire and apply correction data in real time during image formation processing. However, due to processing delays associated with the calculation of the correction data, there may be limitations to the image forming apparatus 1 in acquiring and applying correction data for correcting misalignment in real time.

[0091] A case will now be described in which misalignment in the sub-scanning direction is corrected by correcting the timing at which an image starts to be written in the sub-scanning direction. If the exposure unit 24 is configured to scan the photosensitive drum 23 with laser light in the main scanning direction (drum axis direction), correction of the image start position in the main scanning direction can be easily achieved. On the other hand, in order to correct the image start position in the sub-scanning direction, it is necessary to more precisely adjust the rotation period of the photosensitive drum 23 and the timing at which the exposure unit 24 emits the laser light. For example, the exposure timing of the laser light by the exposure unit 24 is corrected while accurately monitoring the rotation phase in accordance with the rotation speed of the photosensitive drum 23.

[0092] In contrast, the exposure unit 24 may be configured to include multiple light-emitting elements (light-emitting element array) linearly arranged in the main scanning direction (drum axis direction) of the photosensitive drum 23. In this case, the number of pixels in the main scanning direction depends on the number of light-emitting elements constituting the light-emitting element array. Each light-emitting element may be, for example, a light-emitting diode (LED). When the exposure unit 24 has such a configuration, laser light scanning in the main scanning direction (drum axis direction) on the photosensitive drum 24 is not required. The light-emitting element array can output laser light at predetermined time intervals. The image formation position in the sub-scanning direction is controlled by controlling the exposure timing of the light-emitting element array. A light-emitting element array is provided for each of the photosensitive drums 23Y, 23M, 23C, and 23K. Therefore, the light-emitting timing of the light-emitting element array is controlled for each photosensitive drum 23.

[0093] In this way, when correcting misregistration (color misregistration) in the sub-scanning direction by correcting the timing of writing an image in the sub-scanning direction, the misregistration (color misregistration) can be corrected by detecting the HP of at least one of the photosensitive drums 23. In this case, for example, even in a configuration in which all of the photosensitive drums 23Y, 23M, 23C, and 23K are driven by a single drive source, the misregistration can be corrected for each of the photosensitive drums 23.

[0094] As described above, in the image forming apparatus 1 of this embodiment, the CPU 82 uses the image detector 61 to detect the amount of misalignment of a pattern image (toner pattern 5) from an ideal position when the pattern image is formed on the intermediate transfer belt 3 (on a transfer recipient). Based on the result of the detection of the amount of misalignment, the CPU 82 acquires waveform data (predicted data 91) that indicates a waveform approximating the amount of misalignment in the sub-scanning direction, which is the direction in which the toner image is transported on the intermediate transfer belt 3. Based on the waveform data, the CPU 82 generates first correction data for correcting periodic misalignment in the sub-scanning direction of the toner image formed on the intermediate transfer belt 3. The CPU 82 further generates second correction data for correcting a certain amount of misalignment in the sub-scanning direction of the entire image to be formed, based on the waveform value of the waveform data (predicted data 91) at the start timing of correction based on the first correction data when forming the image. The CPU 82 corrects the positional deviation in the sub-scanning direction of the toner image transferred from the photosensitive drum 23 to the intermediate transfer belt 3 by correcting the image forming conditions for forming a toner image on the photosensitive drum 23 based on the first correction data and the second correction data.

[0095] In this embodiment, the first correction data may include a correction value for correcting the partial magnification of each region when one circular region on the photosensitive drum 23 is divided into multiple divided regions. The second correction data may include a correction value for correcting the timing of writing an image in the sub-scanning direction. The CPU 82 may control the timing of exposure by the exposure unit 24 in accordance with the first correction data so that the partial magnification of the image formed in the multiple divided regions in the sub-scanning direction is corrected. Furthermore, the CPU 82 may control the timing of exposure by the exposure unit 24 in accordance with the second correction data so that the timing of writing an image in the sub-scanning direction is corrected.

[0096] According to this embodiment, it is possible to prevent the accuracy of positional deviation correction from decreasing depending on the timing of performing positional deviation correction in the image forming apparatus 1. Also, since positional deviation correction can be achieved without the need for components such as an encoder, there is no increase in component costs. Furthermore, it is possible to perform positional deviation correction by setting the start timing of image formation at any timing.

[0097] Although the image forming apparatus 1 of this embodiment is configured to form multi-color images (color images), it may also be configured to form monochromatic images (monochrome images) using a monochromatic toner (developer). In this case, the image forming apparatus 1 has only one image forming unit 20 that forms a monochromatic toner image, such as black (K), and does not have an intermediate transfer belt 3. The toner image is directly transferred from the photosensitive drum 23 to the recording material. The image forming apparatus 1 is also configured to correct misalignment in the sub-scanning direction that may occur in the toner image (monochromatic image) formed on the recording material through the above-described process. The image detector 61 may be positioned at a position where it can detect the toner image formed on the photosensitive drum 23. In the above-described configuration for forming a multi-color image, the intermediate transfer belt 3 corresponds to the transfer medium, whereas in this configuration for forming a monochromatic image, the recording material corresponds to the transfer medium.

[0098] The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0099] The disclosure of this specification includes the following image forming apparatus, a control method thereof, and a program. (Item 1) An image forming apparatus, an image carrier that is driven to rotate; a transfer means for transferring the toner image formed on the image carrier to a transfer receiving member; a detecting means for detecting a positional deviation of a forming position of the pattern image from an ideal position when the pattern image is formed as a toner image on the transfer body; an acquiring means for acquiring waveform data representing a waveform approximating the amount of positional deviation in a sub-scanning direction, which is a transport direction of the toner image on the transfer medium, based on the detection result by the detecting means; a generating means for generating first correction data based on the waveform data for correcting periodic positional deviation in the sub-scanning direction of a toner image formed on the transfer medium, and generating second correction data based on a waveform value of the waveform data at a start timing of correction based on the first correction data when forming an image for correcting a fixed amount of positional deviation in the sub-scanning direction of the entire image to be formed; a control unit that corrects a positional deviation in the sub-scanning direction of a toner image transferred from the image carrier to the transferee by correcting an image forming condition for forming a toner image on the image carrier based on the first correction data and the second correction data; and An image forming apparatus comprising: (Item 2) the first correction data includes a correction value for correcting a partial magnification of each region when a region of one circumference on the image carrier is divided into a plurality of divided regions, the second correction data includes a correction value for correcting the timing of starting to write an image in the sub-scanning direction. Item 2. The image forming apparatus according to item 1. (Item 3) an exposure unit that exposes the image carrier based on input image data to form an electrostatic latent image on the image carrier; The control means controlling the timing of exposure by the exposure unit so that the partial magnifications of the images formed in the plurality of divided regions in the sub-scanning direction are corrected in accordance with the first correction data; controlling the timing of exposure by the exposure means so that the timing of starting to write an image in the sub-scanning direction is corrected in accordance with the second correction data; Item 3. The image forming apparatus according to item 2. (Item 4) a rotation detecting means for detecting a reference position that serves as a reference for the rotation of the image carrier; a first area among the plurality of divided areas corresponds to the reference position; the generating means generates the second correction data based on a waveform value of the waveform data at a timing corresponding to the first region. Item 4. The image forming apparatus according to item 2 or 3. (Item 5) the acquiring means acquires waveform data representing a sine wave by fitting a sine wave to the positional deviation amount at each position in the sub-scanning direction on the transfer object detected by the detecting means; the generating means generates the first correction data and the second correction data based on antiphase data representing a sine wave having an antiphase to the sine wave represented by the waveform data. 5. The image forming apparatus according to any one of items 2 to 4. (Item 6) a rotation detecting means for detecting a reference position that serves as a reference for the rotation of the image carrier; a first area among the plurality of divided areas corresponds to the reference position; the generating means generates the second correction data by setting a waveform value of the opposite phase data at a timing corresponding to the first region as a correction value for correcting an image writing timing in the sub-scanning direction. Item 6. The image forming apparatus according to item 5. (Item 7) When the formation of the toner image on the image carrier is started at a timing different from the detection timing of the reference position of the image carrier, the generation unit acquires the waveform value of the waveform data at the start timing of the correction based on a delay in the timing at which the formation of the toner image is started relative to the detection timing. Item 7. The image forming apparatus according to item 4 or 6. (Item 8) a sensor for detecting the pattern image formed on the transfer object; the pattern image includes a plurality of patch images formed at predetermined intervals in the sub-scanning direction, the detection means detects the amount of misalignment by measuring intervals between the plurality of patch images in the sub-scanning direction. 8. The image forming apparatus according to any one of items 1 to 7. (Item 9) the transfer medium is a recording material, 9. The image forming apparatus according to any one of items 1 to 8. (Item 10) the transfer medium is an intermediate transfer medium, the image forming apparatus, a plurality of image carriers on which toner images of different colors are formed; a secondary transfer unit that transfers a multicolor image formed by transferring toner images from the plurality of image carriers onto an intermediate transfer body in a superimposed manner onto a recording material, 9. The image forming apparatus according to any one of items 1 to 8. (Item 11) A control method for an image forming apparatus including an image carrier that is rotationally driven and a transfer unit that transfers a toner image formed on the image carrier to a transfer target, the method comprising: a detection step of detecting a positional deviation amount of a formation position of the pattern image from an ideal position when the pattern image is formed as a toner image on the transfer object; an acquiring step of acquiring waveform data representing a waveform approximating the amount of misalignment in a sub-scanning direction, which is a transport direction of the toner image on the transfer medium, based on the detection result in the detecting step; a generation step of generating, based on the waveform data, first correction data for correcting periodic positional deviation in the sub-scanning direction of a toner image formed on the transfer medium, and generating, based on a waveform value of the waveform data at a start timing of correction based on the first correction data when forming an image, second correction data for correcting a certain amount of positional deviation in the sub-scanning direction of the entire image to be formed; a control process for correcting a positional deviation in the sub-scanning direction of the toner image transferred from the image carrier to the transferee by correcting image forming conditions for forming a toner image on the image carrier based on the first correction data and the second correction data; A control method for an image forming apparatus, comprising: (Item 12) Item 12. A program for causing a computer to execute the control method for an image forming apparatus according to Item 11.

[0100] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0101] 1: image forming device, 3: intermediate transfer belt, 20: image forming unit (image forming unit), 23: photosensitive drum, 24: exposure unit, 25: primary transfer unit, 61: image detector, 82: CPU, 83: storage unit

Claims

1. An image forming apparatus, an image carrier that is driven to rotate; a transfer means for transferring the toner image formed on the image carrier to a transfer receiving member; a detecting means for detecting a positional deviation of a forming position of the pattern image from an ideal position when the pattern image is formed as a toner image on the transfer body; an acquiring means for acquiring waveform data representing a waveform approximating the amount of positional deviation in a sub-scanning direction, which is a transport direction of the toner image on the transfer medium, based on the detection result by the detecting means; a generating means for generating, based on the waveform data, first correction data for correcting periodic positional deviation in the sub-scanning direction of a toner image formed on the transfer medium, and generating, based on a waveform value of the waveform data at a start timing of correction based on the first correction data when forming an image, second correction data for correcting a fixed amount of positional deviation in the sub-scanning direction of the entire image to be formed; a control unit that corrects a positional deviation in the sub-scanning direction of a toner image transferred from the image carrier to the transfer object by correcting an image forming condition for forming a toner image on the image carrier based on the first correction data and the second correction data; and An image forming apparatus comprising:

2. the first correction data includes a correction value for correcting a partial magnification of each region when one circumferential region on the image carrier is divided into a plurality of divided regions, the second correction data includes a correction value for correcting the timing of starting to write an image in the sub-scanning direction; The image forming apparatus according to claim 1 .

3. an exposure unit that exposes the image carrier based on input image data to form an electrostatic latent image on the image carrier; The control means controlling the timing of exposure by the exposure unit so that the partial magnifications of the images formed in the plurality of divided regions in the sub-scanning direction are corrected in accordance with the first correction data; controlling the timing of exposure by the exposure means so that the timing of starting to write an image in the sub-scanning direction is corrected in accordance with the second correction data; The image forming apparatus according to claim 2 .

4. a rotation detecting means for detecting a reference position that serves as a reference for the rotation of the image carrier; a first area among the plurality of divided areas corresponds to the reference position; the generating means generates the second correction data based on a waveform value of the waveform data at a timing corresponding to the first region. The image forming apparatus according to claim 2 .

5. the acquiring means acquires waveform data representing a sine wave by fitting a sine wave to the positional deviation amount at each position in the sub-scanning direction on the transfer object detected by the detecting means; the generating means generates the first correction data and the second correction data based on antiphase data representing a sine wave having an antiphase to the sine wave represented by the waveform data. The image forming apparatus according to claim 2 .

6. a rotation detecting means for detecting a reference position that serves as a reference for the rotation of the image carrier; a first area among the plurality of divided areas corresponds to the reference position; the generating means generates the second correction data by setting a waveform value of the opposite phase data at a timing corresponding to the first region as a correction value for correcting an image writing timing in the sub-scanning direction. The image forming apparatus according to claim 5 .

7. When the formation of the toner image on the image carrier is started at a timing different from the detection timing of the reference position of the image carrier, the generation unit acquires the waveform value of the waveform data at the start timing of the correction based on a delay in the timing at which the formation of the toner image is started relative to the detection timing. The image forming apparatus according to claim 4 .

8. a sensor for detecting the pattern image formed on the transfer object; the pattern image includes a plurality of patch images formed at predetermined intervals in the sub-scanning direction, the detection means detects the amount of misalignment by measuring intervals between the plurality of patch images in the sub-scanning direction. The image forming apparatus according to claim 1 .

9. the transfer medium is a recording material, The image forming apparatus according to claim 1 .

10. the transfer medium is an intermediate transfer medium, the image forming apparatus, a plurality of image carriers on which toner images of different colors are formed; a secondary transfer unit that transfers a multicolor image formed by transferring toner images from the plurality of image carriers onto an intermediate transfer body in a superimposed manner onto a recording material, The image forming apparatus according to claim 1 .

11. A control method for an image forming apparatus including an image carrier that is rotationally driven and a transfer unit that transfers a toner image formed on the image carrier to a transfer target, the method comprising: a detection step of detecting a positional deviation amount of a formation position of the pattern image from an ideal position when the pattern image is formed as a toner image on the transfer object; an acquiring step of acquiring waveform data representing a waveform approximating the amount of misalignment in a sub-scanning direction, which is a transport direction of the toner image on the transfer medium, based on the detection result in the detecting step; a generation step of generating, based on the waveform data, first correction data for correcting periodic positional deviation in the sub-scanning direction of a toner image formed on the transfer medium, and generating, based on a waveform value of the waveform data at a start timing of correction based on the first correction data when forming an image, second correction data for correcting a certain amount of positional deviation in the sub-scanning direction of the entire image to be formed; a control process for correcting a positional deviation in the sub-scanning direction of the toner image transferred from the image carrier to the transfer object by correcting an image forming condition for forming a toner image on the image carrier based on the first correction data and the second correction data; A control method for an image forming apparatus, comprising:

12. A program for causing a computer to execute the method for controlling an image forming apparatus according to claim 11.

Images