Image forming apparatus

Abstract

The present invention provides an image forming apparatus in which two optical scanning devices are arranged in the scanning direction for each color, and which can prevent misalignment of the main scanning magnification of each device within the same color, and also prevent misalignment of the main scanning magnification of the entire combined image. [Solution] The image magnification correction pattern includes at least a first pattern for correcting the main scan magnification generated by each adjacent optical writing means in the scanning direction, and a second pattern for correcting the main scan magnification of the entire image including the adjacent optical writing means. The correction means corrects the main scan magnification of each of the adjacent optical writing means based on the detection result of the first pattern, and then corrects the main scan magnification of the entire image including the adjacent optical writing means based on the detection result of the second pattern.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] In a color image forming apparatus that forms a latent image by irradiating an image carrier with image light corresponding to image data, develops the latent image by a developing means, and forms an image by transferring the developed image onto a recording paper, a pattern for correcting image misregistration for each color is formed on a belt, the pattern for correcting image misregistration is detected, the amount of image misregistration for each color with respect to a reference color is calculated based on the detection result, and the image position is corrected according to the calculation result. Also, in an image forming apparatus in which two light scanning devices corresponding to each color are arranged side by side in the scanning direction for irradiating an image carrier with image light corresponding to image data, a technique has been developed to widen the image width by joining images on the image carrier.

[0003] Patent Document 1 discloses a configuration in which a plurality of writing optical systems are arranged in parallel in the main scanning direction, the writing width is divided and scanned, and a configuration for correcting the full-width magnification error is disclosed for the purpose of increasing the full writing width.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the correction of image position deviation, it was effective to correct the deviation between colors for an image forming apparatus using one light scanning device per color, but for an image forming apparatus in which two light scanning devices per color are arranged side by side in the scanning direction, there are problems that the main scanning magnification within the same color deviates, and furthermore, the main scanning magnification of the entire combined two images deviates.

[0005] Furthermore, in the configuration described in Patent Document 1, in order to eliminate the shift in the main scanning magnification without distortion across the entire area, it is necessary to correct the main scanning magnification of each of the multiple writing optical systems before correcting the magnification error across the entire width. This results in a shift in the main scanning magnification of each system within the same color, and furthermore, a shift in the combined main scanning magnification of the two systems.

[0006] The present invention has been made in view of the above, and aims to provide an image forming apparatus in which two optical scanning devices are arranged in the scanning direction for each color, which can prevent a shift in the main scanning magnification of each device within the same color, and also prevent a shift in the main scanning magnification of the entire combined image. [Means for solving the problem]

[0007] To solve the above-mentioned problems and achieve the objective, the present invention comprises: an optical writing means for forming a latent image by irradiating an image carrier with a light beam corresponding to image data; a toner developing means for making the latent image visible; a forming means for forming the latent image of an image magnification correction pattern; a transfer means for transferring the visible image magnification correction pattern onto a belt; a detection means for detecting the image magnification correction pattern on the belt; and a correction means for correcting the image magnification based on the detection result of the image magnification correction pattern, wherein the optical writing means are arranged in a plurality in the scanning direction, dividing the scanning area on the image carrier in the main scanning direction, and each The optical writing means forms the latent image by irradiating each of the divided regions obtained by dividing the scanning region with an optical beam, and the image magnification correction pattern includes at least a first pattern that corrects the main scan magnification generated by each of the adjacent optical writing means in the scanning direction, and a second pattern that corrects the main scan magnification of the entire image including the adjacent optical writing means, and the correction means corrects the main scan magnification of each of the adjacent optical writing means based on the detection result of the first pattern, and then corrects the main scan magnification of the entire image including the adjacent optical writing means based on the detection result of the second pattern. [Effects of the Invention]

[0008] According to the present invention, in an image forming apparatus in which two optical scanning devices are arranged in the scanning direction for each color, it is possible to prevent a shift in the main scanning magnification of each device within the same color, and also to prevent a shift in the main scanning magnification of the entire combined image. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a diagram illustrating an example of an image forming apparatus according to the first embodiment. [Figure 2] Figure 2 is a diagram illustrating an example of an image forming unit in an image forming apparatus according to the first embodiment. [Figure 3] Figure 3 is a diagram illustrating an example of a light beam scanning device included in the image forming apparatus according to the first embodiment. [Figure 4] Figure 4 is a diagram illustrating an example of an image forming control unit and an optical beam scanning device included in an image forming apparatus according to the first embodiment. [Figure 5] Figure 5 is a diagram illustrating an example of an image clock generation unit in an image forming apparatus according to the first embodiment. [Figure 6] Figure 6 is a diagram illustrating an example of a printer control unit in an image forming apparatus according to the first embodiment. [Figure 7] Figure 7 is a diagram illustrating an example of the control process flow during printing of an image forming apparatus according to the first embodiment. [Figure 8] Figure 8 is a functional block diagram of each function realized by the printer control unit of the image forming apparatus according to the first embodiment executing the image magnification correction program stored in ROM. [Figure 9] Figure 9 is a diagram illustrating an example of an image magnification correction pattern in an image forming apparatus according to the first embodiment. [Figure 10]Figure 10 is a diagram illustrating an example of the detection process for an image magnification correction pattern in an image forming apparatus according to the first embodiment. [Figure 11] Figure 11 is a diagram illustrating an example of an image magnification correction pattern in an image forming apparatus according to the first embodiment. [Figure 12] Figure 12 is a diagram illustrating an example of the detection process for an image magnification correction pattern in an image forming apparatus according to the first embodiment. [Figure 13] Figure 13 is a diagram illustrating an example of an image magnification correction pattern in an image forming apparatus according to the first embodiment. [Figure 14] Figure 14 is a diagram illustrating an example of the detection process for an image magnification correction pattern in an image forming apparatus according to the first embodiment. [Figure 15] Figure 15 is a flowchart showing an example of the image magnification correction process in an image forming apparatus according to the first embodiment. [Figure 16] Figure 16 shows an example of the configuration of an image forming apparatus in the image forming apparatus according to the second embodiment. [Modes for carrying out the invention]

[0010] An embodiment of the image forming apparatus will be described in detail below with reference to the attached drawings.

[0011] (First Embodiment) Figure 1 is a diagram illustrating an example of an image forming apparatus according to the first embodiment. The printer 100 of the image forming apparatus has an intermediate transfer unit in the center, and the intermediate transfer unit has an endless belt, the intermediate transfer belt 10. The intermediate transfer belt 10 is wrapped around three support rollers 14 to 16 and is driven to rotate clockwise. To the right of the second support roller 15 is an intermediate transfer body cleaning unit 17 that removes residual toner remaining on the intermediate transfer belt 10 after image transfer. Along the direction of movement of the intermediate transfer belt 10 between the first support roller 14 and the second support roller 15 is an imaging apparatus 20 consisting of yellow (Y), magenta (M), cyan (C), and black (K) photoreceptor units 40, a charging unit 18, a developing unit, and a cleaning unit, and the imaging apparatus 20 is detachably mounted to the printer 100 body.

[0012] Above the imaging device 20 is a light beam scanning device 21 that irradiates each photoreceptor drum of each color photoreceptor unit 40 with laser light for image formation. Below the intermediate transfer belt 10 is a secondary transfer unit 22. The secondary transfer unit 22 is positioned so as to push up the intermediate transfer belt 10 and press it against the third support roller 16 by stretching an endless belt, the secondary transfer belt 24, between two rollers 23. This secondary transfer belt 24 transfers the image on the intermediate transfer belt 10 onto the paper. Next to the secondary transfer unit 22 is a fixing unit 25 that fixes the transferred image on the paper, and the paper with the toner image transferred onto it is fed into it. The fixing unit 25 has a heating and pressure roller 27 pressed against an endless belt, the fixing belt 26. Below the secondary transfer unit 22 and the fixing unit 25 is a sheet reversal unit 28 that feeds out the paper immediately after the image has been formed on the front side, inverting it to record an image on the back side as well.

[0013] When the start switch of the operation unit is pressed, if there is a document on the document feeder 30 of the automatic document feeder (ADF) 400, it is conveyed onto the contact glass 32. When there is no document in the ADF 400, in order to read the document placed by hand on the contact glass 32, the scanner of the image reading unit 300 is driven, and the first carriage 33 and the second carriage 34 are driven for reading and scanning. Then, light is emitted from the light source on the first carriage 33 onto the contact glass, and the reflected light from the document surface is reflected by the first mirror on the first carriage 33 and directed towards the second carriage 34. It is reflected by the mirror on the second carriage 34 and forms an image on the CCD (Charge Coupled Device) image sensor 36, which is a reading sensor, through the imaging lens 35. Based on the image signal obtained by the CCD 36, Y, M, C, and K color recording data are generated.

[0014] Also, when the start switch is pressed, or when an image output instruction is received from a personal computer or the like, or when a FAX output instruction is received, the rotational drive of the intermediate transfer belt 10 is started, the image formation preparation of each unit of the image forming device 20 is started, and the image formation sequence of each color is started. An exposure laser modulated based on the color recording data is projected onto the photosensitive drum for each color, and by the image formation process of each color, the toner images of each color are superposed and transferred as a single image onto the intermediate transfer belt 10. When the leading edge of this toner image enters the secondary transfer unit 22, the paper is fed into the secondary transfer unit 22 at a timing such that the leading edge also enters the secondary transfer unit 22 simultaneously. Thus, the toner image on the intermediate transfer belt 10 is transferred onto the paper. The paper with the transferred toner image is fed into the fixing unit 25, where the toner image is fixed onto the paper.

[0015] Note that the above-mentioned paper is fed as follows: one of the paper feed rollers 42 of the paper feed table 200 is selectively rotationally driven, a sheet is fed out from one of the paper feed trays 44 provided in multiple stages in the paper feed unit 43, separated by only one sheet by the separation roller 45, put into the conveyance roller unit 46, conveyed by the conveyance roller 47, guided to the conveyance roller unit 48 in the printer 100, abutted against the registration roller 49 of the conveyance roller unit 48 and stopped, and then sent out to the secondary transfer unit 22 at the aforementioned timing. It is also possible to insert the paper into the manual feed tray 51 for paper feeding. When the user inserts the paper into the manual feed tray 51, the printer 100 rotationally drives the paper feed roller 50 to separate one sheet of the sheet on the manual feed tray 51 and draw it into the manual paper feed path 53. Similarly, it is abutted against the registration roller 49 and stopped.

[0016] The paper that has undergone the fixing process by the fixing unit 25 and is discharged is guided to the discharge roller 56 by the switching claw 55 and stacked on the paper discharge tray 57. Or, it is guided to the sheet reversing unit 28 by the switching claw 55, reversed there, and guided back to the transfer position again. After recording an image on the back side as well, it is discharged onto the paper discharge tray 57 by the discharge roller 56. On the other hand, the residual toner remaining on the intermediate transfer belt 10 after the image transfer is removed by the intermediate transfer body cleaning unit 17 in preparation for the next image formation.

[0017] FIG. 2 is a diagram for explaining an example of an image forming section included in the image forming apparatus according to the first embodiment. The image forming apparatus includes four sets of image forming sections (image forming apparatus 20) and four sets of optical beam scanning devices 21 for forming a color image by overlapping four-color (yellow, magenta, cyan, black) images. The optical beam scanning device 21 will be described in FIG. 3. An LD unit that selectively emits an optical beam by being driven and modulated according to image data is provided. The emitted optical beam is deflected by a polygon mirror rotated by a polygon motor, passes through an fθ lens, is reflected by a folding mirror, and scans the photosensitive drum.

[0018] Each color image-forming unit (image-forming device 20) is equipped with a charging unit 18, a developing unit (an example of a toner developing means) that reveals the latent image formed on the photoreceptor drum, a transfer unit, a cleaning unit, and a static eliminator around the photoreceptor drum. The first color image is formed on the intermediate transfer belt 10 by the normal electrophotographic process of charging, exposure, development, and transfer. Then, the second, third, and fourth colors are transferred in that order to form a color image in which the four colors are superimposed. Furthermore, the image formed on the intermediate transfer belt 10 is transferred to the transported recording paper by the secondary transfer unit 22, thereby forming a color image in which the four colors are superimposed on the recording paper. The image on the recording paper is then fixed by the fixing unit 25. An intermediate transfer belt cleaning unit is provided to remove the toner image on the intermediate transfer belt 10.

[0019] The secondary transfer unit 22 is equipped with a sensor 1 for detecting the image magnification correction pattern formed on the secondary transfer belt 24. Sensor 1 is an image reading sensor such as a CCD or CIS. The secondary transfer unit 22 is also an example of a transfer means for transferring the visualized image magnification correction pattern onto the secondary transfer belt 24. The image forming apparatus then corrects the deviation in the image magnification in the main scanning direction (hereinafter also referred to as the main scanning magnification) for each color based on the detection result of the image magnification correction pattern after it has been transferred onto the secondary transfer belt 24. A secondary transfer belt cleaning unit is provided to remove the toner image on the secondary transfer belt 24. In addition, a toner bottle containing toner to be replenished to the developing unit is provided for each color.

[0020] Figure 3 is a diagram illustrating an example of a light beam scanning device in an image forming apparatus according to the first embodiment. Figure 3 is a top view of the light beam scanning devices 21-1 and 21-2 in Figure 2. The light beam scanning devices 21 of each color have the same configuration. The light beam scanning devices 21-1 and 21-2 are examples of optical writing means that form a latent image by irradiating a photoreceptor drum with a light beam corresponding to the image data. In addition, multiple light beam scanning devices 21-1 and 21-2 are installed side by side in the main scanning direction. Furthermore, the light beam scanning devices 21-1 and 21-2 divide the scanning area on the photoreceptor drum in the main scanning direction, and each light beam scanning device forms a latent image by irradiating the divided area with a light beam.

[0021] The optical beam scanning devices 21-1 and 21-2 have the same configuration. The optical beam emitted from the LD passes through a cylinder lens (CYL), enters a polygon mirror, and the polygon mirror rotates to deflect the optical beam. The beam then passes through an fθ lens and is scanned on the photoreceptor drum by a folding mirror. The main scanning direction write-side end is equipped with a synchronization mirror, a synchronization lens, and a synchronization sensor. The optical beam that passes through the fθ lens is reflected by the synchronization mirror, focused by the synchronization lens, and enters the synchronization sensor. The synchronization sensor acts as a synchronization detection sensor to detect a synchronization detection signal that determines the write timing in the main scanning direction. For the optical beam scanning on the photoreceptor drum, the entire area of ​​the image in the main scanning direction can be formed by two scanning beams for each color.

[0022] Figure 4 is a diagram illustrating an example of an image forming control unit and a light beam scanning device in an image forming apparatus according to the first embodiment. Figure 4 shows the image forming control unit of the light beam scanning device 21-1, but the configuration is the same for the light beam scanning device 21-2, except for the printer control unit 407, the storage unit 409 (correction data storage unit), and the sensor 1. Also, the configuration is the same for each color.

[0023] The optical beam scanning device 21-1 is equipped with a synchronization sensor on the image writing side at the end of the main scanning direction to detect the optical beam. The optical beam that has passed through the fθ lens is reflected by the synchronization mirror, focused by the synchronization lens, and incident on the synchronization sensor. As the optical beam passes over the synchronization sensor, the synchronization sensor outputs a synchronization detection signal XDETP, which is sent to the pixel clock generation unit 1 (401), the synchronization detection lighting control unit 1 (402), and the write start position control unit 1 (403).

[0024] The pixel clock generation unit 1 (401) generates a pixel clock PCLK synchronized with the synchronization detection signal XDETP and sends it to the LD control unit 1 (404), the write start position control unit 1 (403), and the synchronization detection lighting control unit 1 (402). The synchronization detection lighting control unit 1 (402) first turns on the LD forced lighting signal BD to forcibly light up the LD in order to detect the synchronization detection signal XDETP. After detecting the synchronization detection signal XDETP, it uses the synchronization detection signal XDETP and the pixel clock PCLK to generate an LD forced lighting signal BD that lights up the LD at a timing that ensures the synchronization detection signal XDETP is reliably detected without generating flare light, and then turns off the LD when the synchronization detection signal XDETP is detected, and sends this signal to the LD control unit 1 (404). In addition, it generates the light intensity control timing signal APC for each LD using the synchronization detection signal XDETP and the pixel clock PCLK and sends it to the LD control unit 1 (404). This signal must be executed outside the image writing area, and at that time, the light intensity is controlled to the desired level.

[0025] The LD control unit 1 (404) controls the illumination of the LD according to the synchronization detection forced illumination signal BD, the light intensity control timing signal APC, and image data synchronized with the pixel clock PCLK. Then, a laser beam is emitted from the LD, deflected by the polygon mirror, passes through the fθ lens, and scans the photoreceptor drum by the folding mirror. The polygon motor control unit 1 (405) controls the rotation of the polygon motor at a specified rotation speed based on the control signal from the printer control unit 407.

[0026] The write start position control unit 1 (403) generates a main scan control signal XLGATE and a sub-scan control signal XFGATE, which determine the image write start timing and image width, based on the synchronization detection signal XDETP, the pixel clock PCLK, and control signals from the printer control unit 407. The sensor 1 that detects the image magnification correction pattern sends the detected image pattern information to the printer control unit 407, which calculates the magnification shift amount, calculates correction data, sets it in the pixel clock generation unit 1 (401), and stores the correction data in the storage unit 409. When performing an image forming operation, the storage unit 409 reads the stored correction data at the instruction of the printer control unit 407, and the correction data is set in the pixel clock generation unit 1 (401).

[0027] Figure 5 is a diagram illustrating an example of an image clock generation unit in an image forming apparatus according to the first embodiment. The image clock generation unit 1 (401) according to this embodiment includes a reference clock generation unit 501, a VCO clock generation unit 502, a phase-synchronous clock generation unit 503, and the like.

[0028] The reference clock signal FREF from the reference clock generator 501 and the signal obtained by dividing VCLK by N using the 1 / N frequency divider 502d are input to the phase comparator 502a. The phase comparator 502a performs a phase comparison of the falling edges of both signals and outputs a constant current to remove the error component. Unwanted high-frequency components and noise are then removed by the LPF (low-pass filter) 502b and sent to the VCO 502c. The VCO 502c outputs an oscillation frequency VCLK that depends on the output of the LPF 502b and sends it to the phase-synchronous clock generator 503. The phase-synchronous clock generator 503 generates a pixel clock PCLK synchronized with the synchronization detection signal XDETP. Therefore, the frequency of VCLK can be varied by changing the frequency of FREF and the division ratio N from the printer control unit 407, and the frequency of the pixel clock PCLK also changes as the frequency of VCLK changes.

[0029] Figure 6 is a diagram illustrating an example of a printer control unit in an image forming apparatus according to the first embodiment. The printer control unit 407 is composed of a CPU (Central Processing Unit) 601, RAM (Random Access Memory) 602, ROM (Read Only Memory) 603, and I / O ports 604, and each piece of hardware is connected via a bus.

[0030] The CPU 601 is a device that executes a program to control the operation of the image forming apparatus and performs predetermined processing. The RAM 602 is a volatile memory device that provides the execution space for the program executed by the CPU 601 and is used for storing and retrieving programs and data. The ROM 603 is a non-volatile memory device that stores programs and firmware executed by the CPU 601. The I / O port 604 is a device that processes output information to motors controlled by the CPU 601, input information from various sensors, etc.

[0031] Sensor 1, which detects image patterns, is connected to I / O port 604. In addition, write start position control units 1,2 (403), LD control units 1,2 (404), synchronization detection lighting control units 1,2 (402), pixel clock generation units 1,2 (401), polygon motor control units 1,2 (405), and HDD (storage unit 409) are also connected via the bus, and various data settings, ON / OFF control, data saving and reading, etc. are performed by instructions from CPU 601.

[0032] Figure 7 is a diagram illustrating an example of the control process flow during printing of an image forming apparatus according to the first embodiment. When the start key on the operation panel is pressed, the image forming apparatus first rotates the polygon motor at a specified rotation speed according to instructions from the printer control unit 407 (step S701). Then, the image forming apparatus sets correction data (start positions for writing main scan and sub scan, and magnification settings) to each control unit (step S702), lights up the LD to output a synchronization detection signal (step S703), and performs APC operation to ensure that each LD is lit at a specified light intensity. After that, the image forming apparatus starts the image forming operation (step S704), and if there is no next image (step S705: No), turns off each LD (step S706), stops the polygon motor, and finishes (step S707).

[0033] Figure 8 is a functional block diagram of each function realized by the printer control unit of the image forming apparatus according to the first embodiment executing an image magnification correction program stored in ROM. As shown in Figure 8, the printer control unit 407 realizes the functions of the correction data setting unit 801, pattern formation control unit 802, pattern detection unit 803, displacement amount calculation unit 804, judgment unit 805, correction data calculation unit 806, storage control unit 807, and image formation control unit 808 by executing the image magnification correction program.

[0034] The correction data setting unit 801 sets the correction data stored in the storage unit 409 to the pixel clock generation unit 401. The pattern formation control unit 802, which is an example of a forming means, forms a latent image of the image magnification correction pattern. The pattern detection unit 803, which is an example of a detection unit, detects the image magnification correction pattern formed on the secondary transfer belt (an example of a belt) 24 based on the output of the sensor 1. The displacement amount calculation unit 804 calculates the displacement amount based on the detection result of the image magnification correction pattern detected by the pattern detection unit 803. The decision unit 805 makes a decision on whether or not to perform image magnification correction based on the calculated displacement amount. The correction data calculation unit 806 calculates correction data when image magnification correction is performed. In other words, the displacement amount calculation unit 804, the decision unit 805, and the correction data calculation unit 806 are an example of a correction means that corrects the image magnification based on the detection result of the image magnification correction pattern. The storage control unit 807 updates the correction data stored in the storage unit 409 with the calculated correction data. The image forming control unit 808 performs printing based on the calculated correction data.

[0035] Figure 9 is a diagram illustrating an example of an image magnification correction pattern in an image forming apparatus according to the first embodiment. As shown in Figure 9, the pattern forming control unit 802 forms an image magnification correction pattern on the secondary transfer belt 24 in order to correct the image magnification in the main scanning direction. Patterns K11a and K11b of the image magnification correction pattern are patterns formed by the optical beam scanning device 21-1. Patterns K21a and K21b of the image magnification correction pattern are patterns formed by the optical beam scanning device 21-2. An image is formed on the secondary transfer belt 24, and each pattern is detected by the sensor 1 as the secondary transfer belt 24 moves in the direction of the arrow.

[0036] Here, patterns K11a and K11b are examples of first patterns for correcting the main scanning magnification generated by the optical beam scanning device 21-1 in the main scanning direction (an example of a scanning direction). Also, patterns K21a and K21b are examples of first patterns for correcting the main scanning magnification generated by the optical beam scanning device 21-2 in the main scanning direction (an example of a scanning direction).

[0037] Figure 10 is a diagram illustrating an example of the detection process for image magnification correction patterns in an image forming apparatus according to the first embodiment. Specifically, the displacement amount calculation unit 804 determines the interval (number of dots) calculated from the pattern data used to form patterns K11a and K11b as DK11ab, and the interval (number of dots) calculated from the pattern data used to form patterns K21a and K21b as DK21ab. Then, DK11ab and DK21ab become the ideal distance (number of dots).

[0038] The displacement calculation unit 804 calculates the distances of patterns K11a, K11b, K21a, and K21b, using the area near the edge of sensor 1 as the reference position, outside the image magnification correction pattern. The displacement calculation unit 804 then calculates the difference ΔK11ab between the distance of pattern K11a (DK11a) and the distance of pattern K11b (DK11b), compares this to the ideal distance (DK11ab), and determines the magnification shift amount. The pixel clock frequency of the optical beam scanning device 21-1 is then changed by an amount corresponding to this magnification shift amount. Similarly, the displacement calculation unit 804 calculates the difference ΔK21ab between the distance of pattern K21a (DK21a) and the distance of pattern K21b (DK21b), compares this to the ideal distance (DK21ab), and determines the magnification shift amount. The pixel clock frequency of the optical beam scanning device 21-2 is then changed by an amount corresponding to this shift amount. As a result, the displacement calculation unit 804, the judgment unit 805, and the correction data calculation unit 806 correct the respective main scanning magnifications of adjacent optical beam scanning devices 21-1 and 21-2 based on the detection results of patterns K11a, K11b, K21a, and K21b.

[0039] Regarding the detection of the position of the image magnification correction pattern, in this embodiment, since the image magnification correction pattern has a width, its median is calculated as the position of the image magnification correction pattern, but this is not the only method. The edges of the image magnification correction pattern may also be detected as the position of the image magnification correction pattern. In this embodiment, there is one set of image magnification correction patterns, but it is possible to improve the correction accuracy by generating multiple sets, calculating the magnification shift amount for each set, and averaging them. The same applies to each color in the case of a color image forming apparatus. The shape of the image magnification correction pattern is just an example and is not limited to this.

[0040] As a method for correcting image magnification, instead of matching the ideal distance, it is also possible to correct the image magnification of the optical beam scanning device 21-2 based on the image magnification of the optical beam scanning device 21-1, for example. The difference between the distance of pattern K11a (DK11a) and the distance of pattern K11b (DK11b), ΔK11ab, and the difference between the distance of pattern K21a (DK21a) and the distance of pattern K21b (DK21b), ΔK21ab, becomes the amount of magnification shift, and the pixel clock frequency of the optical beam scanning device 21-2 is changed by an amount equivalent to this. In this case, it is not necessary to calculate the ideal distance in advance, and correction can be performed using only the detection results, simplifying control. Since the purpose is to match the magnification of the optical beam scanning device 21-1 and the optical beam scanning device 21-2, there is no impact on image quality and it is not a problem. In other words, the deviation amount calculation unit 804 may correct the main scanning magnification generated between adjacent optical beam scanning devices 21-1 and 21-2 using patterns K11a, K11b, K21a, and K21b by matching the main scanning magnification of one optical beam scanning device (e.g., optical beam scanning device 21-1) with the main scanning magnification of the adjacent optical beam scanning device (e.g., optical beam scanning device 21-2). Alternatively, the deviation amount calculation unit 804 may correct the main scanning magnification generated between adjacent optical beam scanning devices 21-1 and 21-2 using patterns K11a, K11b, K21a, and K21b to predetermined magnifications. This reduces the overall magnification error in the main scanning direction.

[0041] Figure 11 is a diagram illustrating an example of an image magnification correction pattern in an image forming apparatus according to the first embodiment. The image magnification correction pattern shown in Figure 11 differs from the image magnification correction pattern shown in Figure 9 in that the patterns of the optical beam scanning device 21-1 and the optical beam scanning device 21-2 are formed with a timing difference in the transport direction of the secondary transfer belt 24. That is, the pattern formation control unit 802 may change the generation timing in the transport direction of the secondary transfer belt 24 for each image magnification correction pattern (patterns K11a, K11b, K21a, K21b) generated by adjacent optical beam scanning devices 21-1 and 21-2. For example, this is effective when patterns K11b and K21a near the center are close together and the image magnification correction pattern cannot be detected. Sometimes, when the image magnification is high, the image magnification correction patterns may become close together.

[0042] Figure 12 is a diagram illustrating an example of the detection process for the image magnification correction pattern in an image forming apparatus according to the first embodiment. In the image forming apparatus according to this embodiment, as shown in Figure 12, the timing of detection of the image magnification correction pattern changes, but the image magnification correction pattern is detected in the same way as when detecting the image magnification correction pattern shown in Figure 11.

[0043] Figure 13 is a diagram illustrating an example of an image magnification correction pattern in an image forming apparatus according to the first embodiment. In this embodiment, an image forming apparatus forms an image magnification correction pattern on a secondary transfer belt 24 in order to correct the image magnification of the entire area in the main scanning direction. Pattern K12a of the image magnification correction pattern is a pattern formed by the optical beam scanning device 21-1. Also, pattern K22b of the image magnification correction pattern is a pattern formed by the optical beam scanning device 21-2. An image is formed on the secondary transfer belt 24, and each pattern is detected by the sensor 1 as the secondary transfer belt 24 moves in the direction of movement (transport direction) indicated by the arrow. Here, patterns K12a and K22b are examples of second patterns that correct the main scanning magnification of the entire image, which is a combination of adjacent optical beam scanning devices 21-1 and 21-2.

[0044] Figure 14 is a diagram illustrating an example of the detection process for the image magnification correction pattern in the image forming apparatus according to the first embodiment. The displacement amount calculation unit 804 sets the interval (number of dots) calculated from the pattern data used when forming patterns K12a and K22b as DK12ab. DK12ab becomes the ideal distance (number of dots). The displacement amount calculation unit 804 uses the vicinity of the edge of sensor 1, outside the image magnification correction pattern, as the reference position and calculates the distance DK12a for pattern K12a and the distance DK22b for pattern K22b. Then, the displacement amount calculation unit 804 calculates the difference ΔK12ab between the distance DK12a for pattern K12a and the distance DK22b for pattern K22b, compares it with the ideal distance DK12ab, calculates the difference as the magnification displacement amount, and changes the pixel clock frequencies of optical beam scanning devices 21-1 and 21-2 by an amount corresponding to that difference. Specifically, the displacement calculation unit 804, the judgment unit 805, and the correction data calculation unit 806 correct the main scan magnification of adjacent optical beam scanning devices 21-1 and 21-2 based on the detection results of patterns K11a, K11b, K21a, and K21b, and then correct the main scan magnification of the entire image combining adjacent optical beam scanning devices 21-1 and 21-2 based on the detection results of patterns K12a and K22b.

[0045] The image magnification correction pattern consists of a single set of patterns K12a and K22b. However, it is possible to improve the correction accuracy by generating multiple sets of patterns, calculating the magnification shift of each set, and averaging them. The same applies to each color in the case of a color image forming apparatus. The pattern shape shown is just an example and is not limited to this.

[0046] Figure 15 is a flowchart showing an example of the image magnification correction process in an image forming apparatus according to the first embodiment. The printer control unit 407 controls the timing of the image magnification correction process, which is executed when the power of the image forming apparatus is turned ON, when printing starts, after a specified number of printed pages, or when the temperature is monitored and a temperature change exceeding a specified level is detected.

[0047] First, the printer control unit 407 sets the correction data stored in the memory unit 409 (step S1501). The correction data set here is the correction data set in the previous correction operation and is stored in the memory unit 409. Then, the printer control unit 407 rotates the polygon motor (step S1502), lights up the LD (step S1503), generates patterns K11a, K11b, K21a, and K21b (the patterns shown in Figure 9 or Figure 11) from the image magnification correction patterns (step S1504), detects them with sensor 1 (step S1505), and calculates the amount of image magnification shift (step S1506).

[0048] The printer control unit 407 then determines whether to perform correction (step S1507). This determination is made so that correction is performed if the magnification deviation is 1 / 2 or more of the correction resolution. If correction is performed (step S1507: Yes), the printer control unit 407 calculates correction data (step S1508), stores it (step S1509), and sets the correction data (step S1510). The correction data here is a setting value that determines the pixel clock frequency. If correction is not performed (step S1507: No), the printer control unit 407 does not update the correction data.

[0049] Next, the printer control unit 407 generates patterns K12a and K22b (the patterns shown in Figure 13) from the image magnification correction patterns (step S1511), detects them with sensor 1 (step S1512), and calculates the magnification shift amount (step S1513). Then, the printer control unit 407 decides whether to perform the correction (step S1514). This decision is made to perform the correction if the magnification shift amount is 1 / 2 or more of the correction resolution. If correction is performed (step S1514: Yes), the printer control unit 407 calculates the correction data (step S1515), stores it (step S1516), and sets the correction data (step S1517). The correction data here is a setting value that determines the pixel clock frequency. If correction is not performed (step S1514: No), the printer control unit 407 does not update the correction data.

[0050] Then, the printer control unit 407 turns off the LD (step S1518) and stops the polygon motor to terminate (step S1519). In the case of a color image forming apparatus, the same procedure is followed for each color. The above control can be performed during printing without any problems. During the time between printed images, the process from generating the first pattern of image magnification correction patterns to setting the correction data using the second pattern of image magnification correction patterns will be carried out.

[0051] Thus, according to the image forming apparatus of the first embodiment, in an image forming apparatus in which two optical scanning devices are arranged in the scanning direction for each color, it is possible to prevent a shift in the main scanning magnification of each device within the same color, and also to prevent a shift in the main scanning magnification of the entire image when the two are combined.

[0052] (Second Embodiment) This embodiment is an example of correcting the main scanning magnification of adjacent optical beam scanning devices, and the main scanning magnification of the entire image combining adjacent optical beam scanning devices, based on the detection result of an image magnification correction pattern on the recording paper. In the following description, the same configuration as in the first embodiment will be omitted from the explanation.

[0053] Figure 16 shows an example of the configuration of an image forming apparatus in the image forming apparatus according to the second embodiment. The image forming apparatus shown in Figure 16 is the same as the image forming apparatus shown in Figure 2, except that the position of sensor 1 is different. In this embodiment, sensor 1 detects an image magnification correction pattern on the recording paper. This makes it possible to correct for the effects of fixing to the recording paper. The image magnification correction pattern is the same as in Figures 9, 11, and 13, and the image magnification correction pattern on the intermediate transfer belt 10 is transferred to the recording paper instead of the secondary transfer belt 24. The flow of the image magnification correction process is the same as in Figure 15, and the generation of patterns K11a, K11b, K21a, and K21b, and the generation of patterns K12a and K22b, are performed on the recording paper instead of the secondary transfer belt 24.

[0054] Thus, according to the image forming apparatus of the second embodiment, the shift in image magnification can be corrected even with respect to the influence on the image after transfer to the secondary transfer belt 24, thereby reducing the magnification error of the printed image.

[0055] In the above embodiment, the image forming apparatus of the present invention is described using an example in which it is applied to a multifunction device having at least two functions from among a copy function, a printer function, a scanner function, and a facsimile function. However, it can be applied to any image forming apparatus such as a copier, printer, scanner, or facsimile device. [Explanation of Symbols]

[0056] 1 sensor 21,21-1,21-2 Optical beam scanning device 407 Printer Control Unit 601 CPU 602 RAM 603 ROM 604 I / O ports 801 Correction Data Setting Unit 802 Pattern Forming Control Unit 803 Pattern detection unit 804 Calculation unit for displacement 805 Judgment Department 806 Correction Data Calculation Unit 807 Memory Control Unit 808 Image Forming Control Unit [Prior art documents] [Patent Documents]

[0057] [Patent Document 1] Japanese Patent Publication No. 2003-315708

Claims

1. A light writing means that forms a latent image by irradiating an image carrier with a light beam corresponding to the image data, Toner developing means for making the latent image visible, A forming means for forming the latent image of the image magnification correction pattern, A transfer means for transferring the visualized image magnification correction pattern onto a belt, A detection means for detecting the image magnification correction pattern on the belt, The system includes a correction means for correcting the image magnification based on the detection result of the image magnification correction pattern, Multiple optical writing means are arranged in a row in the scanning direction, and divide the scanning area on the image carrier in the main scanning direction. Each of the optical writing means irradiates a light beam onto the divided areas of the scanning area to form the latent image. The image magnification correction pattern includes at least a first pattern for correcting the main scan magnification generated by each of the adjacent optical writing means in the scanning direction, and a second pattern for correcting the main scan magnification of the entire image, combining the adjacent optical writing means. The correction means corrects the main scan magnification of each of the adjacent optical writing means based on the detection result of the first pattern, and then corrects the main scan magnification of the entire image combining the adjacent optical writing means based on the detection result of the second pattern.

2. The image forming apparatus according to claim 1, wherein the correction means corrects the correction of the main scan magnification occurring between adjacent optical writing means according to the first pattern so as to match the main scan magnification of one optical writing means to the main scan magnification of an adjacent optical writing means.

3. The image forming apparatus according to claim 1, wherein the correction means corrects the main scanning magnification that occurs between adjacent optical writing means in the first pattern to a predetermined magnification.

4. The image forming apparatus according to any one of claims 1 to 3, wherein the generation timing in the conveying direction of the belt is changed for each of the first patterns generated by the adjacent optical writing means.

5. A light writing means that forms a latent image by irradiating an image carrier with a light beam corresponding to the image data, Toner developing means for making the latent image visible, A generation means for generating the image data of the image magnification correction pattern, A transfer means for transferring the visualized image magnification correction pattern onto recording paper, A detection means for detecting the image magnification correction pattern on the recording paper, The system includes a correction means for correcting the image magnification based on the detection result of the image magnification correction pattern, Multiple optical writing means are arranged in a row in the scanning direction, and divide the scanning area on the image carrier in the main scanning direction. Each of the optical writing means irradiates a light beam onto the divided areas of the scanning area to form the latent image. The image magnification correction pattern includes at least a first pattern for correcting the main scan magnification generated by each of the adjacent optical writing means in the scanning direction, and a second pattern for correcting the main scan magnification of the entire image, combining the adjacent optical writing means. The correction means corrects the main scan magnification of each of the adjacent optical writing means based on the detection result of the first pattern, and then corrects the main scan magnification of the entire image combining the adjacent optical writing means based on the detection result of the second pattern.

Images