Image forming apparatus

Abstract

In an image forming apparatus where two light beam scanning devices are arranged in the scanning direction for each color, the present invention provides an image forming apparatus that can eliminate extra sensors and reduce costs. [Solution] The system includes a correction means that corrects the positional misalignment for each optical writing means by forming correction patterns for each color on a second image carrier and detecting the correction patterns with a plurality of sensors, wherein the divided region and the boundary of the divided region are provided with a region width that is irradiated with a light beam by two adjacent optical writing means, and the region width overlaps by a certain distance only at the edges of the scanning regions of the two adjacent optical writing means, and within the region width, each optical writing means generates the correction pattern, and a common sensor detects the correction pattern of each optical writing means.

Description

Technical Field

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

Background Art

[0002] In an image forming apparatus that forms a latent image by irradiating an image carrier with image light corresponding to image data, develops the latent image with a developing unit, and forms an image by transferring the developed image onto a recording paper, a light beam scanning device that irradiates the image carrier with image light corresponding to image data is installed side by side in two scanning directions per color. A technique has been developed to widen the image width and improve the printing speed by joining images on the image carrier.

[0003] Patent Document 1 discloses a light scanning device that joins scanning lines of a plurality of light scanning units to form one line. For the purpose of making the boundary of the scanning area less conspicuous by preventing the joints of the scanning lines of each color that constitute the same line from overlapping, when dividing the total number of dots L in one line into three parts and assigning and printing 1 to L1, L1 + 1 to L2, and L2 + 1 to L dots from the image start end respectively, an overlap area is provided so that each scanning area overlaps by several millimeters on the photoreceptor, and the pixel numbers L1 and L2 at the division positions are made different for each color instead of being fixed.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, an image forming apparatus using two light beam scanning devices per color has sensors for detecting patterns when performing position deviation correction for each light beam scanning device arranged in the main scanning direction, resulting in an increase in the number of components and a high cost of the apparatus.

[0005] The present invention has been made in view of the above, and an object of the present invention is to provide an image forming apparatus in which two light beam scanning devices per color are arranged in the scanning direction, and an extra sensor can be deleted to reduce the cost. [Means for solving the problem]

[0006] To solve the above-mentioned problems and achieve the objective, the present invention provides an optical writing device having multiple optical writing means arranged in a row in the scanning direction, which divides a scanning area on a first image carrier in the scanning direction and forms a latent image by irradiating each of the divided areas of the scanning area with a light beam using each of the optical writing means; an image forming means which develops each latent image on a plurality of first image carriers with toners of different colors to form images of each color, and transfers them onto a second image carrier to form an image; and each of the latent image on the second image carrier The optical writing means includes a correction means that corrects the positional misalignment for each optical writing means by forming a color correction pattern and detecting the correction pattern with a plurality of sensors, wherein the division region and the boundary of the division region are provided with a region width that is irradiated with a light beam by two adjacent optical writing means, the region width overlaps by a certain distance only at the ends of the scanning regions of the two adjacent optical writing means, the correction pattern is generated by each optical writing means within the region width, and the correction pattern of each optical writing means is detected by a common sensor. [Effects of the Invention]

[0007] According to the present invention, in an image forming apparatus in which two light beam scanning devices per color are arranged in the scanning direction, it is possible to eliminate extra sensors and reduce costs. [Brief explanation of the drawing]

[0008] [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 imaging apparatus included in the image forming apparatus according to the first embodiment. [Figure 3] Figure 3 is a top view of the optical 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 data division 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 of 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 diagram illustrating an example of the image formation correction function of the image forming apparatus according to the first embodiment. [Figure 9] Figure 9 is a diagram illustrating an example of the arrangement of a conventional pattern detection sensor. [Figure 10] Figure 10 is a diagram illustrating an example of the arrangement of pattern detection sensors in an image forming apparatus according to the first embodiment. [Figure 11] Figure 11 is a diagram illustrating an example of the flow of pattern detection processing in an image forming apparatus according to the first embodiment. [Figure 12] Figure 12 is a diagram illustrating an example of a correction pattern for region width in an image forming apparatus according to the first embodiment. [Figure 13] Figure 13 is a diagram illustrating an example of the movement of a pattern detection sensor in an image forming apparatus according to the second embodiment. [Figure 14] Figure 14 is a diagram illustrating an example of the flow of pattern detection processing when the pattern detection sensor is in motion in an image forming apparatus according to the second embodiment. [Modes for carrying out the invention]

[0009] An embodiment of the image forming apparatus will be described in detail below with reference to the attached drawings.

[0010] (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 according to this embodiment 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 which has photoreceptor units 40 of yellow (Y), magenta (M), cyan (C), and black (K), a charging unit 18, a developing unit, and a cleaning unit, and the imaging apparatus 20 is detachably attached to the printer 100 body.

[0011] Above the imaging device 20 is a light beam scanning device 21 that irradiates each photoreceptor drum of each color photoreceptor unit 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 fixes the toner image transferred onto the paper to the paper by melting and pressing it using an endless belt, the fixing belt 26, and a heating and pressurizing roller 27. Below the secondary transfer unit 22 and the fixing unit 25 is a sheet reversal unit 28 that feeds out the paper immediately after an image has been formed on the front surface, inverting it to record an image on the back side as well.

[0012] When the start switch on the operation unit of the image forming apparatus is pressed, if there is a document on the document feed tray 30 of the automatic document feeder (ADF) 400, it is transported onto the contact glass 32. If there is no document in the ADF 400, the scanner of the image reading unit 300 is driven to read a manually placed document on the contact glass 32, and the first carriage 33 and the second carriage 34 are driven to read and scan. 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, where it is reflected by the mirror on the second carriage 34 and formed as an image on the reading sensor 36, such as a CCD, through the imaging lens 35. Based on the image signal obtained by the reading sensor 36, Y, M, C, and K color recording data are generated.

[0013] Furthermore, when the start switch is pressed, or when an image output instruction is received from a PC or other device, or when a fax output instruction is received, the rotation drive of the intermediate transfer belt 10 is started, and the preparation for image formation of each unit of the image formation device 20 is started. Then, the image formation sequence for each color is started, and an exposure laser modulated based on the recorded data of each color is projected onto the photoreceptor drum for each color, and through the image formation process for each color, each color toner image is superimposed and transferred onto the intermediate transfer belt 10 as a single image. The paper is fed into the secondary transfer unit 22 at a timing that coincides with the leading edge of this toner image entering the secondary transfer unit 22, thereby transferring the toner image on the intermediate transfer belt 10 to the paper. In other words, the secondary transfer unit 22 is an example of a transfer means that transfers the image revealed by the developing unit to the secondary transfer belt 24 (an example of a belt). The paper on which the toner image has been transferred is sent to the fixing unit 25, where the toner image is fixed to the paper.

[0014] Note that for the above-mentioned paper, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotationally driven to feed out a sheet from one of the paper feed trays 44 provided in multiple stages in the paper feed unit 43, separate only one sheet with the separation roller 45, put it into the conveyance roller unit 46, convey it with the conveyance roller 47, guide it to the conveyance roller unit 48 in the printer 100, stop it by hitting against the registration roller 49 of the conveyance roller unit 48, and then send it out to the secondary transfer unit 22 at the aforementioned timing. It is also possible to insert and feed the paper on the manual feed tray 51. When the user inserts the paper on the manual feed tray 51, the printer 100 rotationally drives the paper feed roller 50 to separate one sheet of the paper on the manual feed tray 51 and draw it into the manual paper feed path 53, and also stop it by hitting against the registration roller 49.

[0015] The paper discharged after undergoing the fixing process by the fixing unit 25 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 image transfer is removed by the intermediate transfer body cleaning unit 17 in preparation for the next image formation.

[0016] FIG. 2 is a diagram for explaining an example of an image forming device included in the image forming apparatus according to the first embodiment. In the present embodiment, the image forming device 20 includes four sets of image forming units and four sets of optical beam scanning devices 21 in order to form a color image in which four-color (yellow, magenta, cyan, black) images are overlapped.

[0017] The optical beam scanning device 21 (an example of an optical writing device) will be described with reference to FIG. 3. An LD unit is provided that selectively emits an optical beam by being driven and modulated according to image data. The emitted optical beam is deflected by a polygon mirror that rotates by a polygon motor, passes through an fθ lens, is reflected by a folding mirror, and scans on a photoreceptor drum. The optical beam scanning devices 21-1 and 21-2 (see FIG. 3), which are examples of optical writing means for forming a latent image by scanning an optical beam corresponding to image data on a photoreceptor drum (an example of an image carrier) by one LD unit, are arranged in a plurality in the main scanning direction (an example of a scanning direction). Then, in the optical beam scanning device 21, the scanning area on the photoreceptor drum is divided in the main scanning direction, and each optical beam scanning device 21-1 and 21-2 irradiates each of a plurality of areas (divided areas) divided in the scanning area with an optical beam to form a latent image.

[0018] For each color, around the photoreceptor drum, there are provided a charger (charging unit 18), a developing unit (an example of toner developing means) for visualizing the latent image, a transferrer, a cleaning unit, and a discharger. By performing charging, exposure, development, and transfer, which are normal electrophotographic processes, an image of the first color is formed on the intermediate transfer belt 10, and then images of the second, third, and fourth colors are transferred in this order to form a color image in which four-color images are superimposed. Further, by transferring the image formed on the intermediate transfer belt 10 to the recording paper (paper) being conveyed by the secondary transfer unit 22, a color image in which four-color images are superimposed can be formed on the recording paper. Then, the image on the recording paper is fixed by the fixing unit 25. An intermediate transfer body cleaning unit 17 is provided to remove the toner image on the intermediate transfer belt 10. That is, the four sets of image forming units are an example of image forming means for developing each latent image with toner of a different color for a plurality of photoreceptor drums to form images of each color, and superimposing and transferring them onto the intermediate transfer belt 10 (an example of a second image carrier) to form an image.

[0019] A secondary transfer belt cleaning unit is provided to remove the toner image from the secondary transfer belt 24. Additionally, toner bottles containing toner for each color are provided to replenish the developing unit.

[0020] Furthermore, multiple pattern detection sensors 1 (also called detection sensors) are provided on the intermediate transfer belt 10 to detect patterns (for example, a test pattern image for positional misalignment correction, a test pattern image for density correction) for correcting the image formation conditions when forming a color image on the intermediate transfer belt 10. Based on the detection results from each of these pattern detection sensors 1, the image forming apparatus calculates various misalignment amounts, including the skew (slope) of each color relative to the reference color, the main scan resist misalignment amount, the sub scan resist misalignment amount, and the main scan magnification error. Based on these calculation results, it corrects various misalignment amounts related to image quality adjustment, corrects the image formation conditions (for example, positional misalignment correction, density correction) when forming a color image on the intermediate transfer belt 10, and performs various processes related to the generation of test pattern images during image adjustment.

[0021] Figure 3 is a top view of the light beam scanning device of the image forming apparatus according to the first embodiment. The light beam scanning device 21 has the same configuration for each color. For each color, two light beam scanning devices 21, light beam scanning device 21-1 and light beam scanning device 21-2, are installed side by side in the scanning direction. Light beam scanning devices 21-1 and 21-2 have the same configuration, and the light beam emitted from the LD unit passes through a CYL (cylinder lens), enters a polygon mirror, the polygon mirror rotates to deflect the light beam, passes through an fθ lens, and is scanned on the photoreceptor drum by a folding mirror. In this embodiment, the two light beam scanning devices 21-1 and 21-2 scan on the photoreceptor drum in the same scanning direction, but are not limited to this, and the two light beam scanning devices 21-1 and 21-2 may scan on the photoreceptor drum in different directions from the center to the edge of the photoreceptor drum in the scanning direction.

[0022] The main scanning direction write-out end is equipped with a synchronization mirror, a synchronization lens, and a synchronization sensor. The configuration is such that the light beam transmitted through the fθ lens is reflected by the synchronization mirror, focused by the synchronization lens, and incident on the synchronization sensor. The synchronization sensor plays the role of a synchronization sensor for detecting a synchronization detection signal that determines the write timing of the main scan. In this embodiment, the image forming apparatus divides the image data into multiple (for example, two) parts, sends each of the divided image data (divided image data) to the light beam scanning apparatus 21-1 and the light beam scanning apparatus 21-2, and scans (irradiates) the light beam so that the latent image formed by the light beam scanning apparatuses 21-1 and 21-2 are joined together on the photoreceptor drum.

[0023] Furthermore, in this embodiment, the image forming apparatus has an overlapping region A near the center of the photoreceptor drum that can be scanned by both the light beam scanning device 21-1 and the light beam scanning device 21-2. In other words, in this embodiment, the image forming apparatus has an overlapping region (an example of region width) A where the boundary between the two divided regions can be irradiated with light beams by two adjacent light beam scanning devices 21-1 and 21-2. To put it another way, a portion of the divided image data can be irradiated with light beams from both of the two adjacent light beam scanning devices 21-1 and 21-2.

[0024] 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 control unit of the light beam scanning device 21-1, but the configuration is similar for the light beam scanning device 21-2, except for the printer control unit 407, the storage unit 409 (correction data storage unit), the pattern detection sensor 1, the sensor position detection sensor 2, and the sensor movement actuator 3. The light beam scanning devices 21 for each color also have a similar configuration.

[0025] 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 (404). The pixel clock generation unit 1 (401) generates a pixel clock PCLK synchronized with the synchronization detection signal XDETP and sends it to the write start position control unit 1 (404), the synchronization detection lighting control unit 1 (402), and the LD control unit 1 (405).

[0026] 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, and then turns off the LD when the synchronization detection signal XDETP is detected, and sends this signal to the LD control unit 1 (405). In addition, it generates a light intensity control timing signal APC for each LD using the synchronization detection signal XDETP and the pixel clock PCLK, and sends this signal to the LD control unit 1 (405). This signal must be executed outside the image writing area, and the light intensity is controlled to the target light intensity at that timing.

[0027] The LD control unit 1 (405) 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 a polygon mirror, passes through an fθ lens, and scans the photoreceptor drum by a folding mirror.

[0028] The polygon motor control unit 1 (406) controls the rotation of the polygon motor at a specified rotation speed based on a control signal from the printer control unit 407. The write start position control unit 1 (404) generates the main scan control signal XLGATE and the 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, etc.

[0029] 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 write start position control unit 1 (404) and the pixel clock generation unit 1 (401).

[0030] The pattern detection sensor 1, which detects the correction pattern, sends the image pattern information of the detected correction pattern to the printer control unit 407. The printer control unit 407 calculates various deviation amounts, including the skew (slope) of each color relative to the reference color, the main scan resist deviation amount, the sub scan resist deviation amount, and the main scan magnification error. Based on the calculation results, it corrects various deviation amounts related to image quality adjustment and stores the correction data in the storage unit 409. The sensor movement actuator 3 moves the pattern detection sensor 1 in the scanning direction, and the sensor position detection sensor 2 detects the position of the pattern detection sensor 1.

[0031] Figure 5 is a diagram illustrating an example of an image data division unit in an image forming apparatus according to the first embodiment. As shown in Figure 5, the printer control unit 407 of the image forming apparatus according to this embodiment has a division unit 407a, an image writing control unit 1 (407b), and an image writing control unit 2 (407c). Image data from a printer controller, frame memory, scanner, etc. is input to the division unit 407a. The division unit 407a divides the input image data into two parts for each line and sends them to the image writing control unit 1 (407b) and the image writing control unit 2 (407c). In other words, the division unit 407a is an example of a division means that divides image data for each optical beam scanning device 21-1, 21-2. The division unit 407a, the image writing control unit 1 (407b), and the image writing control unit 2 (407c) all function as line memories.

[0032] For example, if the number of image data near the boundary between the area irradiated by the light beam scanning device 21-1 (divided area) and the area irradiated by the light beam scanning device 21-2 (divided area) in the main scanning direction is set to 100, and the number of image data in one line is set to 2000, and the image data is set to D1 to D2000, then the division unit 407a divides the input line of image data D1 to D2000 for each of the light beam scanning devices 21-1 and 21-2. In other words, the division unit 407a functions as an example of a division means that divides image data for each of the light beam scanning devices 21-1 and 21-2. Next, the division unit 407a sends image data D1 to D1050 to the image writing control unit 1 (407b) and divides the image data D950 to D2000 to the image writing control unit 2 (407c).

[0033] As a result, image data D950~D1050 near the boundary of the areas irradiated by the respective light beams of the light beam scanning device 21-1 and light beam scanning device 21-2 is sent to both image writing control units 1,2 (407b,407c). That is, the splitting unit 407a ensures that the amount of data included in both adjacent light beam scanning devices 21-1 and 21-2 from the split image data (split image data) is greater than or equal to the adjustment amount of the image position in the main scanning direction. At this time, the image writing control units 1,2 (407b,407c) may store the split image data in memory and adjust the image data read from that memory. Alternatively, the image forming apparatus ensures that the overlapping area A on the photoreceptor drum that can be irradiated by the light beams of both adjacent light beam scanning devices 21-1 and 21-2 is greater than or equal to the adjustment amount of the image position in the main scanning direction.

[0034] In other words, an overlapping region A is ensured in which light beams can be irradiated to the boundaries of multiple divided regions by both adjacent light beam scanning devices 21-1 and 21-2, and at least one of the data amounts included in both adjacent light beam scanning devices 21-1 and 21-2 of the divided image data is greater than or equal to the adjustment amount of the image position in the main scanning direction.

[0035] Image writing control unit 1 (407b) and image writing control unit 2 (407c) receive divided image data from the printer controller, frame memory, scanner, etc., and send it to LD control unit 1 (405) and LD control unit 2 (405) in synchronization with PCLK at the timings of XFGATE and XLGATE. At that timing, each LD lights up, irradiates the photoreceptor drum with a light beam, and writes the divided image data onto the photoreceptor drum. In this way, by determining the timing and address for reading from the line memory where the image data is stored, the necessary image data can be sent to LD control units 1 and 2 (405) at the required timing.

[0036] Figure 6 is a diagram illustrating an example of a printer control unit of an image forming apparatus according to the first embodiment. The printer control unit 407 is composed of a CPU, RAM, ROM, and I / O ports, and each piece of hardware is connected via a bus. The CPU is a device that executes a program to control the operation of the image forming apparatus and performs predetermined processing. RAM is a volatile memory device that provides the execution space for the program executed by the CPU and is used for storing and retrieving programs and data. ROM is a non-volatile memory device that stores programs and firmware executed by the CPU. I / O ports are devices that process output information to motors controlled by the CPU, input information from various sensors, etc.

[0037] The I / O port is connected to a pattern detection sensor 1 that detects image patterns, a sensor movement actuator 3 that moves the pattern detection sensor 1, and a sensor position detection sensor 2 that detects the position of the moved pattern detection sensor 1.

[0038] The write start position control unit 1,2 (404), LD control unit 1,2 (405), synchronization detection lighting control unit 1,2 (402), pixel clock generation unit 1,2 (401), polygon motor control unit 1,2 (406), 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 the CPU.

[0039] 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 printer control unit 407 first rotates the polygon motor at a specified rotation speed (step S1001). Then, the printer control unit 407 sets correction data (start writing position for the main scanning direction and sub-scanning direction, and magnification setting value) to each control unit (step S1002), lights up the LD to output a synchronization detection signal, and performs APC operation to ensure that each LD is lit at a specified light intensity (step S1003). After that, the printer control unit 407 starts the image forming operation (step S1004), and if there is no next image (step S1005: No), turns off each LD (step S1006), stops the polygon motor (step S1007), and terminates.

[0040] Figure 8 is a diagram illustrating an example of the image formation correction function of an image forming apparatus according to the first embodiment. Specifically, Figure 8 is a functional block diagram of each function realized by the printer control unit 407 executing the image formation correction program stored in ROM. As shown in Figure 8, the printer control unit 407 realizes each function such as 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 formation correction program.

[0041] The correction data setting unit 801 sets the correction data stored in the storage unit 409 to the pixel clock generation unit. The pattern formation control unit 802 generates correction patterns for each color on the intermediate transfer belt 10. The pattern detection unit 803 detects the correction patterns formed on the intermediate transfer belt 10 based on the sensor output. That is, the pattern detection unit 803 detects the correction patterns using multiple pattern detection sensors 1. The displacement amount calculation unit 804 calculates the displacement amount based on the correction patterns detected by the pattern detection unit 803. The decision unit 805 makes a decision on whether or not to perform correction based on the calculated displacement amount. The correction data calculation unit 806 calculates the correction data if correction is to be performed. In other words, the pattern formation control unit 802, pattern detection unit 803, displacement amount calculation unit 804, judgment unit 805, and correction data calculation unit 806 function as an example of correction means for correcting positional displacement (for example, various displacements including the skew (tilt) of each color relative to the reference color, the main scan resist displacement amount, the sub-scan resist displacement amount, and the main scan magnification error) for each optical beam scanning device 21-1, 21-2. The memory control unit 807 updates the correction data stored in the memory unit 409 with the calculated correction data. The image formation control unit 808 performs printing based on the calculated correction data. The correction method is a known method disclosed in Japanese Patent Application Publication No. 2018-066812, etc.

[0042] Figure 9 is a diagram illustrating an example of the arrangement of conventional pattern detection sensors. Conventional pattern detection sensors are placed at the leading edge, trailing edge, and near the center of each optical beam scanning device in the optical beam scanning direction. Therefore, in an optical beam scanning device 21 in which two optical beam scanning devices 21-1 and 21-2 are installed side by side in the scanning direction as in the conventional way, as shown in Figure 9, pattern detection sensor 1a is placed at the leading edge, pattern detection sensor 1c at the trailing edge, and pattern detection sensor 1b at the center of optical beam scanning device 21-1, while pattern detection sensor 1d is placed at the leading edge, pattern detection sensor 1f at the trailing edge, and pattern detection sensor 1e at the center of optical beam scanning device 21-2.

[0043] Figure 10 is a diagram illustrating an example of the arrangement of a pattern detection sensor in an image forming apparatus according to the first embodiment. In this embodiment, as shown in Figure 3, a region width A is secured near the center of the photoreceptor drum where the light beam scanning the photoreceptor drum is scannable (light beam can be irradiated) by both two adjacent light beam scanning devices 21-1 and 21-2. Region width A overlaps by a certain distance only at the edges of the scanning areas of the two adjacent light beam scanning devices 21-1 and 21-2. Furthermore, correction patterns are generated in region width A by the light beam scanning devices 21-1 and 21-2. In addition, a pattern detection sensor 1c is arranged in this region width A and is configured to detect the correction pattern at the rear end position of light beam scanning device 21-1 and the correction pattern at the front end position of light beam scanning device 21-2, respectively. In other words, within region width A, a common pattern detection sensor 1c detects the respective correction patterns of the optical beam scanning devices 21-1 and 21-2.

[0044] By using the same pattern detection sensor 1c positioned in the scannable area width A of both the optical beam scanning devices 21-1 and 21-2, extra sensors can be eliminated, thus reducing costs. For pattern detection sensors 1 outside of area width A, pattern detection sensor 1a is positioned at the front end of optical beam scanning device 21-1, pattern detection sensor 1b is positioned in the center, and pattern detection sensor 1e is positioned at the rear end of optical beam scanning device 21-2, pattern detection sensor 1d is positioned in the center.

[0045] Furthermore, in this embodiment, since the pattern detection sensor 1c, which is positioned in a scannable area width A by both optical beam scanning devices 21-1 and 21-2, is used in common, as shown in Figure 10, the correction pattern is detected by optical beam scanning device 21-1, and then the correction pattern is detected by optical beam scanning device 21-2, with the patterns being generated and detected separately at different timings. In other words, the correction pattern is generated at different timings for each of the two adjacent optical beam scanning devices 21-1 and 21-2, and detected by the pattern detection sensors 1a to 1e. As a result, by detecting the correction pattern by optical beam scanning device 21-1 and then detecting the correction pattern by optical beam scanning device 21-2, the pattern detection sensor 1c, which is positioned in a scannable area width A by both optical beam scanning devices 21-1 and 21-2, can be used in common, reducing the number of components.

[0046] Figure 11 is a diagram illustrating an example of the pattern detection process flow in an image forming apparatus according to the first embodiment. For correction, the printer control unit 407 controls the execution timing and may execute 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 as processing for both light beam scanning devices 21-1 and 21-2 (step S1101). 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 S1102) and lights up the laser (step S1103).

[0048] Next, the printer control unit 407 processes the optical beam scanning device 21-1 by generating a correction pattern in the optical beam scanning device 21-11 (step S1104), detecting it with the pattern detection sensor (step S1105), and calculating the amount of deviation (step S1106). Then, the printer control unit 407 calculates the correction data (step S1107), stores it in the memory control unit 807 (step S1108), and sets the correction data (step S1109).

[0049] Next, the printer control unit 407 processes the optical beam scanning device 21-2 by generating a correction pattern (step S1110), detecting it with the pattern detection sensor 1 (step S1111), and calculating the amount of deviation (step S1112). Then, the printer control unit 407 calculates the correction data (step S1113), stores it in the memory control unit 807 (step S1114), and sets the correction data (step S1115).

[0050] Then, the printer control unit 407 turns off the lasers of both optical beam scanning devices 21-1 and 21-2 (step S1116), stops the polygon motor, and terminates (step S1117). The image forming apparatus may perform the above control during printing. In that case, the image forming apparatus will perform the process from generating the correction pattern for optical beam scanning device 21-1 to setting the correction data for optical beam scanning device 21-2 between printed images. In this embodiment, the image forming apparatus sets the correction data in the order of optical beam scanning device 21-1 to optical beam scanning device 21-2, but if the timings are different, the correction data may be set in the order of optical beam scanning device 21-2 to optical beam scanning device 21-1.

[0051] Figure 12 is a diagram illustrating an example of a correction pattern in a region width in an image forming apparatus according to the first embodiment. For a correction pattern generated in a region width A scannable by two adjacent optical beam scanning devices 21-1 and 21-2, as shown in Figure 12, the width in the scanning direction is made shorter than the width in the scanning direction of region width A, thereby enabling the generation and detection of the correction pattern within region width A. In other words, the width in the scanning direction of region width A is wider than the width in the scanning direction of the correction pattern.

[0052] Thus, according to the image forming apparatus of the first embodiment, both of the two optical beam scanning devices 21-1 and 21-2 are provided with a region width A on which image data can be written. Correction patterns are generated in this region width A by each of the optical beam scanning devices 21-1 and 21-2, and these correction patterns are detected by a common pattern detection sensor 1. In this way, in an image forming apparatus in which two optical beam scanning devices 21-1 and 21-2 are arranged in the scanning direction for each color, an extra sensor can be eliminated, thereby reducing costs.

[0053] (Second Embodiment) In this embodiment, the pattern detection sensor used for detecting the correction pattern is movable, and its detection position can be switched by the light beam scanning device that forms the correction pattern to be detected. In the following description, the same configuration as in the first embodiment will be omitted.

[0054] In this embodiment, the pattern detection sensors 1a to 1c are movable, and their detection positions can be switched by the optical beam scanning devices 21-1 and 21-2 that form the correction patterns to be detected. As a result, the pattern detection sensors 1a to 1c of one optical beam scanning device 21-1 can detect the correction patterns of two optical beam scanning devices 21-1 and 21-2, thereby reducing the number of components.

[0055] Figure 13 is a diagram illustrating an example of the movement of a pattern detection sensor in an image forming apparatus according to the second embodiment. When performing correction of the optical beam scanning device 21-1, a pattern detection sensor 1a is placed at the leading edge of the optical beam scanning device 21-1, a pattern detection sensor 1c is placed at the rear end, and a pattern detection sensor 1b is placed at the center.

[0056] When performing correction of the light beam scanning device 21-2, the movable actuator 1301 moves the pattern detection sensors 1a to 1c toward the light beam scanning device 21-2, positioning pattern detection sensor 1a at the leading edge, pattern detection sensor 1c at the trailing edge, and pattern detection sensor 1b at the center. Note that the pattern detection sensors 1a to 1c are moved simultaneously by a single movable actuator 1301.

[0057] The positions of the pattern detection sensors 1a and 1c are detected by the sensor position detection sensors 2a and 2b located at both ends of the intermediate transfer belt 10. If the sensor position detection sensor 2a can detect the position, it can be confirmed that the pattern detection sensors 1a to 1c are positioned at the location of the light beam scanning device 21-1, and if the sensor position detection sensor 2b can detect the position, it can be confirmed that the pattern detection sensors 1a to 1c are positioned at the location of the light beam scanning device 21-2.

[0058] Figure 14 is a diagram illustrating an example of the flow of the pattern detection process when the pattern detection sensor is in motion in the image forming apparatus according to the second embodiment. The timing of the execution of the pattern detection process is the same as described in Figure 11.

[0059] First, the printer control unit 407 sets the correction data stored in the memory unit 409 as processing for both light beam scanning devices 21-1 and 21-2 (step S1401). 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 S1402) and lights up the LD (step S1403).

[0060] Next, the printer control unit 407 confirms the positions of the pattern detection sensors 1a to 1c using the sensor position detection sensors 2a and 2b (step S1404). If the sensors are not positioned at the location of the light beam scanning device 21-1 (step S1406: No), the printer control unit 407 moves the pattern detection sensors 1a to 1c to the location of the light beam scanning device 21-1 using the movable actuator 1301 (step S1405). As part of the processing of the light beam scanning device 21-1, the printer control unit 407 generates a correction pattern in the light beam scanning device 21-1 (step S1407), detects it with the pattern detection sensors 1a to 1c (step S1408), and calculates the amount of deviation (step S1409). Then, the printer control unit 407 calculates the correction data (step S1410), stores it in the memory control unit 807 (step S1411), and sets the correction data (step S1412).

[0061] Next, the pattern detection sensors 1a to 1c are moved to the position of the light beam scanning device 21-2 by the movable actuator 1301 (step S1413). The printer control unit 407 then checks the position of the pattern detection sensors 1a to 1c using the sensor position detection sensors 2a and 2b (step S1414). If the sensors are not positioned at the location of the light beam scanning device 21-2 (step S1416: No), the pattern detection sensors 1a to 1c are moved to the location of the light beam scanning device 21-2 by the movable actuator 1301 (step S1415).

[0062] As part of the processing for the light beam scanning device 21-2, the printer control unit 407 generates a correction pattern in the light beam scanning device 21-2 (step S1417), detects it with pattern detection sensors 1a to 1c (step S1418), and calculates the amount of deviation (step S1419). Then, the printer control unit 407 calculates the correction data (step S1420), stores it in the memory control unit 807 (step S1421), and sets the correction data (step S1422). Finally, the printer control unit 407 turns off the lasers of both light beam scanning devices 21-1 and 21-2 (step S1423), stops the polygon motor, and terminates the process (step S1424).

[0063] The image forming apparatus may perform the above control during printing. In that case, the image forming apparatus performs the following between printed images: checking the positions of pattern detection sensors 1a to 1c and setting the correction data for the optical beam scanning device 21-2. In this embodiment, the image forming apparatus sets the correction data in the order of optical beam scanning device 21-1 to optical beam scanning device 21-2, but if the timings are different, the correction data may be set in the order of optical beam scanning device 21-2 to optical beam scanning device 21-1.

[0064] Thus, according to the image forming apparatus of the second embodiment, the correction patterns of two optical beam scanning devices 21-1 and 21-2 can be detected by the pattern detection sensors 1a to 1c of one optical beam scanning device 21-1, thereby reducing the number of components.

[0065] 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.

[0066] Examples of the present invention are as follows: <1> An optical writing device having multiple optical writing means arranged in a row in the scanning direction, dividing a scanning area on a first image carrier in the scanning direction, and forming a latent image by irradiating each of the divided areas of the scanning area with an optical writing means, Image forming means for developing each latent image on a plurality of first image carriers with different colored toners to form images of each color, and then transferring them onto a second image carrier to form an image, The system includes a correction means that forms correction patterns for each color on the second image carrier and detects the correction patterns with a plurality of sensors to correct the positional misalignment for each of the optical writing means, The boundary between the divided region and the division region is such that a region width is secured in which light beams are irradiated by two adjacent light writing means. The width of the region overlaps by a certain distance only at the edges of the scanning regions of two adjacent optical writing means. An image forming apparatus that generates the correction pattern in each of the optical writing means within the aforementioned region width, and detects the correction pattern of each of the optical writing means with a common sensor. <2> The correction pattern is generated at different timings for each of the two adjacent optical writing means and detected by the sensor. <1> The image forming apparatus described above. <3> The width of the region in the scanning direction is wider than the width of the correction pattern in the scanning direction. <1> or <2> The image forming apparatus described above. <4> The sensor used for detecting the correction pattern is movable, and its detection position can be switched by the optical writing means that forms the correction pattern to be detected. <1> from <3> An image forming apparatus as described in any one of the following. [Explanation of Symbols]

[0067] 1 Pattern detection sensor 2. Sensor position detection sensor 3 Sensor-driven actuator 21,21-1,21-2 Optical beam scanning device 407 Printer Control Unit 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]

[0068] [Patent Document 1] Japanese Patent Publication No. 2009-3459

Claims

1. An optical writing device having multiple optical writing means arranged in a row in the scanning direction, dividing a scanning area on a first image carrier in the scanning direction, and forming a latent image by irradiating each of the divided areas of the scanning area with a light beam using each of the optical writing means, Image forming means for a plurality of first image carriers, developing each latent image with a different colored toner to form images of each color, and then superimposing and transferring them onto a second image carrier to form an image, The system includes a correction means that forms correction patterns for each color on the second image carrier and detects the correction patterns with a plurality of sensors to correct the positional misalignment for each of the optical writing means, The boundary between the divided region and the division region is such that a region width is secured in which light beams are irradiated by two adjacent light writing means. The width of the region overlaps by a certain distance only at the edges of the scanning regions of two adjacent optical writing means. An image forming apparatus that generates the correction pattern in each of the optical writing means within the aforementioned region width, and detects the correction pattern of each of the optical writing means with a common sensor.

2. The image forming apparatus according to claim 1, wherein the correction pattern is generated at different timings for each of the two adjacent optical writing means and detected by the sensor.

3. The image forming apparatus according to claim 1 or 2, wherein the width of the region in the scanning direction is wider than the width of the correction pattern in the scanning direction.

4. The image forming apparatus according to claim 1 or 2, wherein the sensor used for detecting the correction pattern is movable and its detection position can be switched by the optical writing means that forms the correction pattern to be detected.

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