JP5849467B2 - Image forming apparatus and image forming method - Google Patents

Description

The present invention relates to an image forming apparatus and an image forming method .

  As an exposure apparatus used when forming an electrostatic latent image on a photoreceptor, an exposure apparatus using an exposure apparatus in which a plurality of light emitting chips in which a plurality of light emitting elements are arranged is arranged in the main scanning direction is known (for example, a patent) Reference 1).

  Patent Document 1 discloses an image forming apparatus including a recording element array in which a plurality of recording chips in which a plurality of recording elements are arranged are arranged in the main scanning direction. Further, in Patent Document 1, a line image in the main scanning direction of image data is divided into a plurality of pixel columns, and an image of the divided pixel columns is formed by shifting in the sub-scanning direction. It is disclosed that a skew which is a deviation between the arrangement direction and the rotation axis direction (main scanning direction) of the photosensitive member is corrected.

  In an electrophotographic image forming apparatus, dither processing is performed using a dither matrix on image data of a multi-tone image received from an external device or the like, and binarized. An image is formed by adjusting lighting and non-lighting of the light emitting elements according to the dithered image data.

  Here, when skew correction processing is performed on image data that has been dithered using a dither matrix, streaks may occur. This is because the shape of the pattern obtained by the dither matrix changes at a position where the image is shifted in the sub-scanning direction.

  As a technique for suppressing such streaks formed on an image, Patent Document 1 discloses shifting a boundary position between recording chips and a division position of image data for one line at the time of skew correction. Has been. Further, Patent Document 2 discloses that the image shift position in the sub-scanning direction at the time of skew correction is matched with a position that is a multiple of the size of the dither matrix in the main scanning direction.

  However, in Patent Document 1 and Patent Document 2, it is difficult to suppress the streaks that occur when the application position of the dither matrix matches the boundary position between the recording chips. For this reason, in the image forming apparatus, the density correction image formed at the time of correcting the density of the image to be formed is streaked, and the density correction accuracy may be deteriorated.

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 and an image forming method capable of suppressing streaking in a density correction image.

In order to solve the above-described problems and achieve the object, the present invention provides a photosensitive member and an exposure unit in which a plurality of light emitting chips in which a plurality of light emitting elements are arranged in the main scanning direction are arranged in the main scanning direction, A developing unit that develops an electrostatic latent image formed on the photosensitive member by an exposure unit to form a toner image, and an image is formed on the transferred body by transferring the toner image to the transferred body. a transfer unit, a detecting means for detecting a skew amount indicating an amount of deviation between the previous SL-emitting chips, in the case of forming the density correction image used for the density correction as the image, when forming the printing image as the image A resolution changing means for generating image data of the density correction image having a higher resolution by dithering as the skew amount is higher than that of the image, and main scanning the image of the dithered image data And correcting means for skew correction by shifting in the sub-scanning direction according to the skew amount for each division unit set in advance in the direction, which is an image forming apparatus having a.

  According to the present invention, there is an effect that it is possible to suppress a streak from entering the density correction image.

FIG. 1 is a schematic diagram illustrating an example of the configuration of the image forming apparatus according to the present embodiment. FIG. 2 is a schematic diagram showing an example of the configuration of the exposure apparatus. FIG. 3 is a functional block diagram in which the main control unit is divided for each function realizing means determined based on hardware and software. FIG. 4 is a functional block diagram showing the write control unit. FIG. 5 is a flowchart showing the flow of the image forming process. FIG. 6 is a schematic diagram showing the correspondence between the image data of the density correction image and the density correction image formed by the image forming apparatus using the image data of the density correction image for each resolution. is there. FIG. 7 is a schematic diagram illustrating an example of the skew correction image when the skew correction is performed and when each of the two types of skew correction is performed. FIG. 8 is a block diagram illustrating a hardware configuration of the image forming apparatus according to the present embodiment.

Exemplary embodiments of an image forming apparatus and an image forming method will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus 10 according to the present embodiment.

  The image forming apparatus 10 includes a paper feed tray 12, an image forming unit 18, a fixing unit 40, a main control unit 42, and a sensor 46.

  The paper feed tray 12 accommodates a plurality of recording media P. The recording medium P is conveyed to the image forming unit 18 by the paper feed roller 14 and a conveyance unit (not shown).

  The image forming unit 18 includes an image forming unit 32 that forms an image of each color, and a conveyance belt 34. The image forming unit 18 forms an image on the recording medium P and a conveyance belt 34 described later.

  The conveyor belt 34 is supported from the inside by a driving roller 36 and a roller 38, and is conveyed along the rotation of the driving roller 36 and the roller 38.

  The image forming unit 32 forms an image forming unit 32K that forms a black toner image, an image forming unit 32M that forms a magenta toner image, an image forming unit 32C that forms a cyan toner image, and a yellow toner image. An image forming unit 32Y is provided. Each of these image forming units 32 is arranged along the conveyance direction of the conveyance belt 32.

  The image forming unit 32K is a photosensitive member 22K that rotates with the main scanning direction as the rotation axis direction, a charging device 24K that charges the photosensitive member 22K, an exposure device 20K that forms an electrostatic latent image, and develops the electrostatic latent image with toner. A developing device 26K, a transfer device 28K that transfers the toner image to the conveyance belt 34 or the recording medium P, and a cleaning member 30K that removes deposits on the photoreceptor 22K are provided. Similarly, for the image forming units 32M, 32C, and 32Y, the photosensitive members (22M, 22C, and 22Y), the charging devices (24M, 24C, and 22Y), the exposure units (20M, 20C, and 20Y), and the developing devices (26M, 26C, and 26Y), transfer devices (28M, 28C, 28Y), and cleaning members (30M, 30C, 30Y).

  These image forming units 32 have the same configuration except that the color of toner used for development in the developing device 26K is different. These image forming units 32 are well-known electrophotographic systems except that the exposure apparatus 20 has a configuration to be described later, and thus detailed description thereof is omitted.

  Further, in the following description, when the parts provided in the image forming parts 32 are collectively described, the reference numerals C, M, Y, and K are omitted.

  The recording medium P supplied to the image forming unit 18 is conveyed by the conveying belt 34, and the toner images are sequentially transferred by the image forming unit 32. The fixing device 40 fixes the toner image transferred to the recording medium P to the recording medium P.

  In the image forming apparatus 10 of the present embodiment, the exposure apparatus 20 has a configuration in which a plurality of optical elements are arranged along the main scanning direction that is the rotation axis direction of the photosensitive member 22.

  As described above, the main scanning direction indicates a direction that coincides with the rotational axis direction of the photosensitive member 22 (see the arrow X direction in FIG. 2). Further, a sub-scanning direction to be described later indicates a direction orthogonal to the main scanning direction.

  FIG. 2 shows an example of the exposure apparatus 20.

  As shown in FIG. 2, the exposure apparatus 20 has a configuration in which a plurality of light emitting chips 44 are arranged along the main scanning direction. Each light emitting chip 44 has a configuration in which a plurality of light emitting elements 44A are arranged along the main scanning direction. Examples of the light emitting element 44A include an LED (Light Emitting Diode).

  The sensor 46 reads a density correction image, a skew correction image, and a light amount correction image formed on the conveyance belt 34 and the recording medium P.

  The density correction image is an image used for density correction, for example, an image having a plurality of regions having different gradation values (density). The light amount correction image is an image used for correcting the light amount of light emitted from each light emitting element 44 </ b> A of the exposure apparatus 20. Examples of the light quantity correction image include an image having a predetermined reference density.

  The skew correction image is an image used for skew correction. In the present embodiment, the skew indicates a deviation in the arrangement direction of the light emitting elements 44 </ b> A with respect to the main scanning direction, which is a direction coinciding with the rotation axis direction of the photoconductor 22. The skew correction image is formed, for example, on a long image extending from one end to the other end of the photoconductor 22 in the main scanning direction, or on one end and the other end of the photoconductor 22 in the main scanning direction. A pair of images.

  As the sensor 46, a known sensor that detects the density correction image, skew correction image, and light amount correction image may be used. For example, the sensor 46 detects various images (density correction image, skew correction image, light amount correction image) formed on the recording medium P or the conveyor belt 34, and the presence or absence of these images. A known sensor for detecting the image density may be used.

  These density correction image, skew correction image, and light amount correction image are formed on the conveyance belt 34 at a position detected by the sensor 46.

  The main control unit 42 controls each unit provided in the image forming apparatus 10. The main control unit 42 includes a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores an image forming program that executes an image forming process described later, a RAM (Random Access Memory) that stores data, and the like. It includes a bus to be connected. The main control unit 42 is electrically connected to each unit provided in the image forming apparatus 10.

  FIG. 3 shows a functional block diagram in which the main control unit 42 is divided for each function realizing means determined based on hardware and software. The main control unit 42 includes an image processing unit 54, a detection unit 50, and a writing control unit 52. A sensor 46 is electrically connected to the detection unit 50. The sensor 46 outputs a detection signal to the detection unit 50.

  The detection signal includes detection timing of various images formed on the conveyor belt 34 and density information indicating the density of various images. The detection unit 50 outputs the detection signal received from the sensor 46 to the image processing unit 54 and the writing control unit 52.

  Specifically, when the detection signal received from the sensor 46 is a detection signal for a density correction image or a light amount correction image, the detection unit 50 outputs the detection signal to the image processing unit 54. In addition, when the detection signal received from the sensor 46 is a detection signal for a skew correction image, the detection unit 50 outputs the detection signal to the image processing unit 54 and the writing control unit 52.

  The determination as to which detection signal received from the sensor 46 is a skew correction image, a density correction image, or a light amount correction image may be made as follows. For example, when an operation unit (not shown) is operated by a user, a signal indicating a density correction instruction is input, and the detection unit 50 receives a detection signal after the image forming unit 18 forms a density correction image. The detecting unit 50 may determine that the detection signal is a density correction image. Similarly, when a signal indicating a skew correction instruction is input and the detection unit 50 receives a detection signal after the image forming unit 18 forms a skew correction image, the detection unit 50 detects the skew correction image. What is necessary is just to judge it as a signal. Similarly, when a signal indicating a skew correction instruction is input and the detection unit 50 receives a detection signal after the image forming unit 18 forms a light amount correction image, the detection unit 50 detects the light amount correction image. What is necessary is just to judge it as a signal.

  The image processing unit 54 receives image data of a printing image from an external device such as a personal computer, and converts RGB multi-gradation image data into CMYK multi-gradation image data. Further, the image processing unit 54 includes a dither processing unit 54A, and performs dithering by performing dither processing on the multi-tone image data using a predetermined dither pattern. Then, the image data of the dithered printing image is output to the writing control unit 52.

  The write control unit 52 outputs the detection signal received from the detection unit 50 and the image data of the dithered print image received from the image processing unit 54 to the exposure device 20 for each color when a print image is formed.

  The write control unit 52 outputs the image data of the density correction image, which has a higher resolution than the print image, to the exposure apparatus 20 for each color, as will be described in detail later, when the density correction image is formed.

  The write control unit 52 includes a plurality of write control units 56 (56K, 56M, 56C, 56Y) corresponding to the image forming units 32 of the respective colors.

  FIG. 4 shows the configuration of each write control unit 56. Note that the write control unit 56K, the write control unit 56Y, the write control unit 56M, and the write control unit 56C have the same configuration, and therefore will be collectively referred to as the write control unit 56.

  The writing control unit 56 includes an input image control unit 60, a skew correction processing unit 61, an LD data output unit 64, a resolution adjustment unit 68, a transfer rate control unit 70, and a photoconductor drive speed control unit 72.

  The skew correction processing unit 61 performs skew correction processing. Specifically, the skew correction processing unit 61 shifts (moves) the image of the dithered image data in the sub-scanning direction according to the skew amount for each of a plurality of blocks set in advance in the main scanning direction. . Accordingly, the skew correction processing unit 61 performs a skew correction process.

  Specifically, the skew correction processing unit 61 includes a line memory 62 and a correction value calculation unit 66.

  The line memory 62 includes a plurality of line memories 62A to 62D. Each of the line memories 62A to 62D stores line image data for one line in the main scanning direction. The line image data stored in each of the line memories 62A to 62D is sequentially stored and updated by the input image control unit 60.

  The input image control unit 60 receives the image data of the printing image input from the image processing unit 54, the image data of the density correction image received from the resolution adjustment unit 68 described later, and the like. The image data is output to the line memory 62.

  The input image control unit 60 includes an oscillator 60A, a counter 60B, a clear signal generation unit 60C, and a line memory update signal output unit 60D.

  The oscillator 60A oscillates a high frequency clock. The clock of the oscillator 60A is configured to be switchable to a frequency that is 1 / P (P is an integer) times the oscillator intrinsic value by frequency division. The write controller 56 operates based on the clock generated by the oscillator 60A.

  Further, as described above, the input image control unit 60 accepts image data of the density correction image and information indicating the resolution of the density correction image from the resolution adjustment unit 68 described later when the density correction image is formed. The input image control unit 60 causes the oscillator 60 </ b> A to generate N times as many clocks when forming the density correction image as when forming the printing image. “N” represents the ratio (N times) of the resolution of the density correction image to the resolution of the printing image (N is an integer). The information indicating “N” is received from the resolution adjustment unit 68 described later as a clock change signal of the oscillator 60A. In the present embodiment, it is assumed that the resolution of the printing image is set in advance.

  The counter 60B counts the time required for the image forming unit 18 to form an image for one dot in the main scanning direction. The clear signal generator 60C generates a line clear signal when the counter 60B reaches a specified value. Then, the clear signal generating unit 60C outputs the generated line clear signal to the counter 60B, the line memory update signal output unit 60D, and the exposure apparatus 20. When receiving the line clear signal, the counter 60B resets the counter value to “0”.

  When the line memory update signal output unit 60D receives the image data of the printing image from the image processing unit 54, that is, when the printing image is formed, the line memory update signal output unit 60D To 62. On the other hand, when the input image control unit 60 receives the image data of the density correction image, that is, when the density correction image is formed, the input image control unit 60 changes the update cycle of the line memory 62 and generates the line clear signal N times. In addition, a line memory update signal is output to the line memory 62. That is, when the density correction image is formed, the input image control unit 60D changes the update cycle of the line memory 62 to 1 / N. Note that “N” is the same numerical value as “N”, which is the ratio of the resolution of the density correction image to the resolution of the print image described above (hereinafter the same). Information indicating the update cycle of the line memory 62 (that is, information indicating 1 / N) is received from the resolution adjustment unit 68.

  The line memory 62 stores line image data for four lines in the main scanning direction continuous in the sub-scanning direction in separate line memories 62A to 62D for each line image data. Specifically, the line memory 62 stores the line image data for four lines in the main scanning direction in the line memories 62A to 62D for the image data of the printing image at the time of forming the printing image. Further, when forming the density correction image, the line memory 62 stores the line image data for four lines in the main scanning direction in the line memories 62 </ b> A to 62 </ b> D one by one for the image data of the density correction image.

  In this embodiment, the case where the line memory 62 includes four line memories 62A to 62D will be described. However, the configuration includes line memories corresponding to the number of lines corresponding to the maximum amount of skew that may occur. What is necessary is not limited to four line memories.

  Then, each time the line memory 62 receives the line memory update signal, the line memory 62 stores the line image data stored in the line memories 62A to 62D in order from the oldest (most recently stored) line image data. Update to new (next line) line image data. As described above, the line memory 62 repeats the update process of holding the line image data for four lines in the line memories 62A to 62D and overwriting and erasing the old data in order.

  The timing for reading the line image data stored in the line memories 62 </ b> A to 62 </ b> D of the line memory 62 is controlled by the correction value calculation unit 66.

  The correction value calculation unit 66 calculates a correction value for correcting the skew.

  Specifically, the correction value calculation unit 66 includes a skew correction area calculation unit 66A, a skew amount storage unit 66B, a read control unit 66C, a skew amount calculation unit 66D, and a skew correction value calculation unit 66E.

  The skew correction area calculation unit 66 </ b> A and the skew amount calculation unit 66 </ b> D receive a detection signal that is a detection result of the skew correction image from the detection unit 50.

  The skew correction area calculation unit 66A calculates a skew occurrence location from the detection signal received from the detection unit 50, and calculates a skew correction area. The skew correction area indicates the position in the main scanning direction of the division unit to be skew corrected when the image of the image data is divided into a plurality of division units in the main scanning direction. The skew correction area calculation unit 66A calculates a skew correction area from the detection signal using a known calculation method. The skew correction area calculation unit 66A outputs information indicating the calculated skew correction area to the read control unit 66C.

  Note that a skew correction area may be determined in advance and stored in the skew correction area calculation unit 66A. In this case, the skew correction area calculation unit 66A may output information indicating the stored skew correction area to the read control unit 66C.

  The skew amount calculation unit 66D calculates the skew amount from the detection signal received from the detection unit 50. A known method may be used for the calculation of the skew amount. The skew amount storage unit 66B stores the skew amount calculated by the skew amount calculation unit 66D.

  The skew correction value calculation unit 66E calculates a skew correction value for correcting the skew from a skew amount calculated by the skew amount calculation unit 66D using a known method. Then, the obtained skew correction value is output to the read control unit 66C.

  The read controller 66C uses the information indicating the skew correction area received from the skew correction area calculator 66A and the skew correction value received from the skew correction value calculator 66E to store the lines stored in the line memories 62A to 62D. Controls reading of image data. Specifically, the read control unit 66C reads the pixel data group for each division unit from the line image data stored in each of the line memories 62A to 62D from the information indicating the skew correction area and the skew correction value.

  Specifically, the read control unit 66C sequentially sets a pixel data group for each predetermined division unit in the main scanning direction in order from the pixel side at one end in the main scanning direction of the image of the image data to the pixel side at the other end. Read and sequentially output to the LD data output unit 64. At the time of reading this pixel data group, the read control unit 66C stores the line image data of the line shifted in the sub-scanning direction according to the skew correction value in the line memories 62A to 62D at the position corresponding to the skew correction area. The pixel data group is read from any of the line memories 62A to 62D. For this reason, the pixel data groups of the divided pixel columns at positions shifted in the sub-scanning direction according to the skew amount are sequentially read from the line memories 62A to 62D by the read control by the read control unit 66C, and sent to the LD data output unit 64. Is output.

  In the present embodiment, it is assumed that information indicating a division unit when image data is divided in the main scanning direction is determined in advance. Information indicating the division unit is stored in advance in the write control unit 56.

  The division unit in the main scanning direction of the image data, which is a unit for shifting in the sub-scanning direction according to the skew amount, may be set to an arbitrary value. The division unit is preferably determined so that the image of the dithered image data is divided at a position corresponding to the boundary between the adjacent light emitting chips 44. By setting the division unit of the image data in the main scanning direction in this way, it is possible to further suppress streaks that occur in the density correction image.

  The resolution adjustment unit 68, when forming the density correction image, has higher resolution and higher skew as compared with the case of forming the printing image, and the density correction image data and the density correction image. Is output to the skew correction processing unit 61 via the input image control unit 60. The input image control unit 60 outputs the received image data of the density correction image to the line memory 62 for each line image data of one line in the main scanning direction as described above.

  Specifically, the resolution adjustment unit 68 includes a resolution enhancement processing unit 74, an output unit 75, a dither processing unit 76, a basic density correction image storage unit 77, and an output unit 78.

  The basic density correction image storage unit 77 stores in advance image data of a basic density correction image that is a density correction image having a predetermined resolution. Note that the basic density correction image storage unit 77 stores in advance the multi-tone image data that has not been dithered. The predetermined resolution may be any resolution that is equal to or higher than the resolution of the print image. In the present embodiment, the basic density correction image storage unit 77 stores in advance a basic density correction image that is a density correction image having the same resolution as the resolution of the print image.

  Based on the skew amount calculated by the correction value calculation unit 66, the high resolution processing unit 74 forms a density correction image having a higher resolution than the print image and a higher resolution as the skew amount is larger. Set various conditions.

  Specifically, the resolution enhancement processing unit 74 includes a skew amount reading unit 74A, a dither matrix setting unit 74B, and a drive condition setting unit 74C.

  The skew amount reading unit 74A reads the skew amount calculated by the skew amount calculation unit 66D from the skew amount storage unit 66B and outputs it to the dither matrix setting unit 74B. The dither matrix setting unit 74B stores in advance a plurality of types of dither matrices having different resolutions than the resolution of the print image. This dither matrix is a pattern used when binarizing a multi-tone image and is also referred to as a dither pattern. In the dither processing, an image of multi-gradation image data is divided into blocks corresponding to a dither matrix having a threshold value of M × M pixels (M is an integer), and is compared with the threshold value of the dither matrix for each block. Then, binarization is performed for each block.

  When a plurality of types of dither matrices having different resolutions are used, the resolutions of images of binarized image data obtained by performing dither processing using each dither matrix are different. Specifically, examples of the dither matrices of different types having different resolutions include dither matrices having different dither pattern sizes (that is, different values of M in dither patterns corresponding to M × M pixels). . The dither matrix having a larger value of M has a smaller image resolution of the binarized image data obtained by performing the dither process (the dot size is larger). On the other hand, as the dither matrix having a larger value of M, the image resolution of the binarized image data obtained by performing the dither process increases (the size of the dot is smaller).

  The dither matrix setting unit 74B stores in advance a plurality of types of dither matrices that are larger than the resolution of the print image and have different resolutions so that an image having a resolution larger than that of the print image can be obtained by dither processing. . The dither matrix setting unit 74B stores information indicating the resolution and information indicating the dither matrix used for realizing the resolution in advance in association with each other.

  The dither matrix setting unit 74B reads the information indicating the dither matrix corresponding to the higher resolution information as the skew amount read from the skew amount calculation unit 66D is larger, so that the image data of the multi-tone basic density correction image is read. Sets the dither matrix used for the dither processing.

  Accordingly, the dither matrix setting unit 74B sets the dither matrix having a higher resolution than the print image and having a higher resolution as the skew amount is larger as a dither matrix used for dither processing of the image data of the basic density correction image. . The dither matrix setting unit 74B determines the resolution of the density correction image according to the setting of the dither matrix.

  Then, the dither matrix setting unit 74B outputs information indicating the set dither matrix to the dither processing unit 76. Further, the dither matrix setting unit 74B outputs information indicating the resolution corresponding to the set dither matrix, that is, information indicating the resolution of the density correction image, to the output unit 75 and the drive condition setting unit 74C.

  The drive condition setting unit 74C sets the drive condition of the image forming apparatus 10 based on information indicating the resolution of the density correction image received from the dither matrix setting unit 74B.

  The driving conditions are the rotation speed of the photosensitive member 22, the transfer rate when the image data of the density correction image is output from the output unit 75 to the input image control unit 60, the update cycle of the line memory 62, and one line in the main scanning direction. At least one of the ratio of the light emission time of the light emitting element 44A during the image formation and the drive current for driving the light emitting element 44A.

  The drive condition setting unit 74C sets the drive condition based on the resolution of the density correction image and the predetermined resolution of the print image.

  Specifically, it is assumed that the ratio of the resolution of the density correction image received from the dither matrix setting unit 74B to the resolution of the print image stored in advance is N times.

  In this case, the drive condition setting unit 74C sets the drive current of the exposure apparatus 20 to 1 / N at the time of print image formation at the time of density correction image formation, or prints the light emission time of the light emitting element 44A in the image formation of one line. Set to 1 / N during image formation.

  In addition, the drive condition setting unit 74C sets the line memory update period to 1 / N when forming the print image when forming the density correction image.

  In addition, the drive condition setting unit 74C adjusts the drive speed of the photosensitive member 22 in accordance with the period scaling (1 / N) of the line memory update signal by the line memory update signal output unit 60D during density correction image formation. Set to 1 / N at the time of printing image formation.

  Further, the drive condition setting unit 74C determines the transfer rate of the image data of the density correction image output from the output unit 75 of the resolution adjustment unit 68 to the input image control unit 60 when the density correction image is formed. Is set to 1 / N of the transfer rate of the image data of the printing image to the input image control unit 60.

  Then, the drive condition setting unit 74C outputs the set drive conditions to the output unit 78. The output unit 78 outputs each drive condition received from the drive condition setting unit 74C to the transfer rate control unit 70, the photosensitive member drive speed control unit 72, the input image control unit 60, and the LED control unit 64A.

  The transfer rate control unit 70 receives information indicating the transfer rate of the image data of the density correction image as a drive condition from the drive condition setting unit 74C. Then, the output unit 75 is controlled to transfer the image data of the density correction image at the received transfer rate.

  The photoconductor drive speed control unit 72 receives information indicating the rotation speed of the photoconductor 22 as a drive condition from the drive condition setting unit 74C. The photoconductor drive speed control unit 72 controls a drive unit (not shown) of the image forming unit 18 so as to rotate the photoconductor 22 at the received rotation speed at the time of density correction image formation.

  The LD data output unit 64 receives, from the drive condition setting unit 74C, information indicating the drive current of the exposure apparatus 20 or information indicating the ratio of the light emission time of the light emitting element 44A in the one-line image formation as the drive condition. The LED control unit 64A of the LD data output unit 64 outputs an LED control signal corresponding to the drive current or the ratio of the light emission time to the exposure device 20 at the time of density correction image formation. In the exposure apparatus 20, a driving current corresponding to the LED control signal installed on the house is applied to each light emitting element 44A, or a driving signal corresponding to the ratio of the light emission time is output to each light emitting element 44A.

  The dither processing unit 76 performs dither processing on the multi-tone image data of the basic density correction image stored in the basic density correction image storage unit 77 using the dither matrix set by the dither matrix setting unit 74B. Do. By this dither processing, the dither processing unit 76 generates image data of a density correction image having a higher resolution than the printing image and having a higher skew amount as the skew amount is larger. The dither processing unit 76 outputs the obtained image data of the density correction image to the output unit 75.

  The output unit 75 outputs the image data of the density correction image received from the dither processing unit 76 to the input image control unit 60 at the transfer rate set by the transfer rate control unit 70. The output unit 75 outputs information indicating the resolution of the density correction image received from the dither matrix setting unit 74B to the input image control unit 60.

  Next, the flow of image forming processing in the image forming apparatus 10 will be described. FIG. 5 is a flowchart showing the flow of image forming processing in the image forming apparatus 10 according to the present embodiment.

  In the main control unit 42 of the image forming apparatus 10, when the main control unit 42 receives a print job from an external device such as a personal computer, the image forming program for performing the image forming process is read from the ROM, and the process shown in FIG. Execute.

  First, the main control unit 42 determines whether or not to execute skew correction (step S100). In the main control unit 42, for example, when an operation unit (not shown) is instructed by the user and a signal indicating a skew correction instruction is received from the operation unit, execution of skew correction is determined (step S100: Yes). When a signal indicating a skew correction instruction is input as a result of a user operating an operation unit (not shown), the main control unit 42 may store the signal in a memory (not shown). Good. The main control unit 42 may make an affirmative determination in step S100 when a signal indicating a skew correction instruction is stored in the memory. The signal indicating the skew correction instruction stored in the memory is cleared (erased) every time a power switch (not shown) of the image forming apparatus 10 is operated to supply power to each part of the image forming apparatus 10. ).

  If the main control unit 42 determines not to perform skew correction (step S100: No), the process proceeds to step S114 described later.

  Next, the image processing unit 54 forms an image for skew correction (step S102). Specifically, the image processing unit 54 stores image data of a multi-gradation skew correction image in advance. The dither processing unit 54A of the image processing unit 54 performs dither processing on the image data of the skew correction image by using the same dither matrix as that used in the dither processing of the image data of the printing image, and performs write control. To the unit 52. When the writing control unit 52 receives the image data of the skew correction image, the input image control unit 60, the line memory 62, and the LD data output unit 64 in the writing control unit 56 for each color use the image data of the printing image described above. The same processing is performed during the processing. As a result, the image forming unit 18 forms an image for skew correction on the transport belt 34.

  Next, the detection unit 50 detects an image for skew correction (step S104). The detection unit 50 outputs a detection signal indicating the detection result of the detected skew correction image to the correction value calculation unit 66.

  The skew amount calculation unit 66D calculates a skew amount based on the detection signal of the skew correction image received from the detection unit 50, and stores it in the skew amount storage unit 66B (steps S106 and S108). Then, the skew correction value calculation unit 66E calculates a skew correction value using the skew amount stored in the skew amount storage unit 66B, and outputs it to the read control unit 66C (step S110).

  The skew correction area calculation unit 66A calculates a skew correction area based on the detection signal of the skew correction image received from the detection unit 50, and outputs the skew correction area to the read control unit 66C (step S112).

  Next, the main control unit 42 determines whether or not to execute density correction (step S114). In the main control unit 42, for example, when a signal indicating a density correction instruction is received from the operation unit when an operation unit (not shown) is instructed by the user, execution of density correction is determined (step S114: Yes). In addition, when a signal indicating a density correction instruction is input when an operation unit (not shown) is instructed by the user, the main control unit 42 may store the signal in a memory (not shown). Good. The main control unit 42 may make an affirmative determination in step S114 when a signal indicating a density correction instruction is stored in the memory. The signal indicating the density correction instruction stored in the memory is cleared (erased) every time a power switch (not shown) of the image forming apparatus 10 is operated to supply power to each part of the image forming apparatus 10. ).

  On the other hand, when the main control unit 42 determines not to execute density correction (step S114: No), the process proceeds to step S134.

  The skew amount reading unit 74A reads the skew amount from the skew amount storage unit 66B (step S116). Next, the dither matrix setting unit 74B sets a dither matrix having a resolution corresponding to the skew amount read by the skew amount storage unit 66B (step S118).

  Next, the drive condition setting unit 74C sets the drive condition based on the information indicating the resolution of the density correction image received from the dither matrix setting unit 74B (step S120). Next, the dither processing unit 76 performs dither processing on the image data of the basic density correction image stored in the basic density correction image storage unit 77 using the dither matrix set by the dither matrix setting unit 74B ( Step S122).

  Next, the output unit 78 outputs the drive condition set by the drive condition setting unit 74C to the output unit 75, the LED control unit 64A, and the photosensitive member drive speed control unit 72 via the transfer rate control unit 70 ( Step S124).

  Next, the output unit 75 outputs the image data of the density correction image received from the dither processing unit 76 to the input image control unit 60 at the transfer rate set by the transfer rate control unit 70. The output unit 75 outputs information indicating the resolution of the density correction image received from the dither matrix setting unit 74B to the input image control unit 60 (step S126).

  Next, the image forming unit 18 forms a density correction image (step S128).

  Next, the detection unit 50 detects a detection signal that is a detection result of the density correction image sensor 46 formed on the conveyance belt 34 (step S130).

  Next, the image processing unit 54 performs a known density correction process on the image data of the print image based on the detection signal detected by the detection unit 50 in step S130 (step S132).

  Next, the main control unit 42 executes print image forming processing for forming a print image using the image data of the print image whose density has been corrected in step S134 (step S134), and then ends this routine.

  By executing the image forming process, when the density correction image is formed, the higher the density and the larger the skew amount, the higher the density correction image can be formed.

  FIG. 6 shows the correspondence between the image data of the density correction image and the density correction image formed by the image forming apparatus 10 using the image data of the density correction image for each resolution.

  Using the image data of the density correction image that has been dithered using the dither pattern having the same resolution as the print image (see image data 80A in FIG. 6A), the density correction image is obtained under the same drive conditions as the print image. Form. In this case, the formed density correction image is an image shown as an image 82A in FIG. In FIG. 6, the length Q corresponds to the length of the image for one line in the main scanning direction.

  On the other hand, as shown in FIG. 6B, image data of a density correction image that has been dithered using a dither pattern having a resolution twice that of a print image (N = 2) (in FIG. 6B, the image Using the data 80B), the density correction image is formed by setting the value of N to “2” in the driving condition described above. In this case, as shown in an image 82B in FIG. 6B, the density correction image to be formed has the same density as the printing image and the density correction image (see the image 82A in FIG. 6A). ) And higher resolution.

  Further, as shown in FIG. 6C, image data of the density correction image that is dithered using a dither pattern having a resolution four times that of the print image (N = 4) (in FIG. 6C, the image data Using the data 80C), the density correction image is formed by setting the value of N in the above driving condition to “4”. In this case, as shown in the image 82C in FIG. 6C, the density correction image to be formed is the density image for printing and the density correction image having the resolution (see the image 82A in FIG. 6A). ) And higher resolution.

  As described above, in the image forming apparatus 10 according to the present embodiment, when the density correction image is formed, the resolution is higher and the skew amount is larger than when the image for printing is formed by executing the image forming process. The higher the density correction image is formed.

  In the image forming apparatus 10 according to the present embodiment, as the skew amount increases, a higher-resolution density correction image is formed as compared to when the printing image is formed. Therefore, generation of streaks in the density correction image is suppressed. can do.

  Further, in the image forming apparatus 10 of the present embodiment, at the time of density correction, density correction is performed based on the detection result obtained by detecting the density correction image, so that highly accurate density correction can be performed.

  Further, in the image forming apparatus 10 of the present embodiment, the higher the skew amount, the higher the density correction image is formed. For this reason, on the contrary, in the image forming apparatus 10, the smaller the skew amount, the higher the resolution and the lower resolution the density correction image than the print image. For this reason, in the image forming apparatus 10, the driving time can be shortened by reducing the value of “N” described above, and the time required for forming the density correction image can be shortened.

  Further, as described above, the drive condition setting unit 74C assumes that the ratio of the resolution of the density correction image received from the dither matrix setting unit 74B to the resolution of the print image stored in advance is N times. In this case, at the time of density correction image formation, the drive condition setting unit 74C sets the drive current of the exposure apparatus 20 to 1 / N at the time of print image formation, or prints the light emission time of the light emitting element 44A in image formation of one line. Set to 1 / N during image formation.

  For this reason, it is possible to shorten the time required for forming the density correction image.

  In the image forming apparatus 10 according to the present embodiment, the drive condition setting unit 74C is configured to periodically change the line memory update signal (set to 1 / N) by the line memory update signal output unit 60D during density correction image formation. At the same time, the driving speed of the photosensitive member 22 is set to 1 / N when the printing image is formed.

  For this reason, it is possible to shorten the time required for forming the density correction image.

  In the image forming apparatus 10 of the present embodiment, the drive condition setting unit 74C outputs the density correction image output from the output unit 75 of the resolution adjustment unit 68 to the input image control unit 60 when the density correction image is formed. The image data transfer rate is set to 1 / N of the image data transfer rate of the print image from the image processing unit 54 to the input image control unit 60.

  For this reason, it is possible to shorten the time required for forming the density correction image.

  Further, in the image forming apparatus 10 according to the present embodiment, the image of the dithered image data is determined to be divided at a position corresponding to the boundary between the adjacent light emitting chips 44, thereby generating a density correction image. Muscles can be further suppressed.

  In the present embodiment, the case where the skew amount calculation unit 66D calculates the skew amount from the detection signal received from the detection unit 50 using a known method has been described. However, the skew amount calculation unit 66D divides the skew correction image into a plurality of division units for each number of pixels corresponding to the number of light emitting elements 44A arranged in the light emitting chip 44, and for each divided unit. A skew amount may be calculated. Then, the skew correction value calculation unit 66E may calculate a skew correction value for each adjacent skew correction area in accordance with the skew amount for each division unit and output it to the read control unit 66C. In this case, the skew correction value calculation unit 66E may calculate a skew correction value for each skew correction area so that a step between adjacent skew correction areas is minimized.

  In this way, it is possible to suppress the occurrence of a shift (step) corresponding to a region corresponding to a plurality of light emitting chips 44 arranged along the main scanning direction in the formed image.

  FIG. 7 shows an example of the skew correction image when the skew correction is performed and when each of the two types of skew correction is performed.

  As shown in FIG. 7, when the skew correction is not performed, an image 90 having a step at the boundary between the skew correction areas P <b> 1 to P <b> 3 corresponding to each light emitting chip 44 is formed on the photoconductor 22. Then, when a known skew amount calculation is performed to calculate a shift amount with respect to the main scanning direction of the entire arrangement direction of the plurality of light emitting chips 44 instead of each skew correction area, the skew correction is performed as compared with the image 90. However, an image 92 having a step at the boundary between the skew correction areas P1 to P3 is formed. In FIG. 7, a dotted line 92A indicates an image forming position without skew correction, and a solid line 92B indicates an image forming position with skew correction.

  When the skew correction value is calculated for each skew correction area so that the level difference between the adjacent skew correction areas is minimized and the skew correction is performed for each skew correction area, the skew correction areas P1 to P3 are calculated. An image 94 in which the level difference at the boundary is suppressed is formed. In FIG. 7, a dotted line 94A indicates an image forming position without skew correction, and a solid line 94B indicates an image forming position with skew correction.

  That is, as shown in FIG. 7, when the skew correction value is calculated for each skew correction area so that the step between adjacent skew correction areas is minimized by the skew correction value calculation unit 66E, the skew correction value is calculated along the main scanning direction. A shift (step) generated in a region corresponding to the plurality of light emitting chips 44 arranged can be suppressed. For this reason, in the image forming apparatus 10 of the present embodiment, it is preferable to calculate a skew correction value for each skew correction area so that a step between adjacent skew correction areas is minimized.

  Although not shown in FIG. 5, other correction processes may be performed before the print image forming process (step S134). For example, a known color misregistration correction process for correcting the color misregistration of each color image, a known light quantity correction process for correcting the light quantity of the exposure apparatus 20, and the like may be performed. However, these other correction processes are preferably performed before the print image formation process (step S134) and the density correction process (steps S114 to S132).

  As described above, by executing the light amount correction process before the density correction process, it is possible to form the density correction image formed at the time of the density correction process with an appropriate light amount.

  In the present embodiment, the case where the image forming apparatus 10 is a so-called tandem type image forming apparatus 10 having a plurality of image forming units 32 (32K, 32M, 32C, and 32Y) has been described. The structure provided with the two image creation parts 32 may be sufficient. In the present embodiment, the image forming apparatus 10 is configured to transfer an image from the photoconductor 22 to the recording medium P. However, the image forming apparatus 10 is configured to transfer an image to the recording medium P via an intermediate transfer body. It may be.

  The image forming program executed by the image forming apparatus 10 according to the present embodiment is provided by being incorporated in advance in a ROM or the like. The image forming program executed by the image forming apparatus 10 according to the present embodiment is a file in an installable format or an executable format, and is a CD-ROM, a flexible disk (FD), a CD-R, a DVD (Digital Versatile). It may be configured to be recorded on a computer-readable recording medium such as Disk).

  Further, the image forming program executed by the image forming apparatus 10 according to the present embodiment may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network. . Further, the image forming program executed by the image forming apparatus 10 of the present embodiment may be provided or distributed via a network such as the Internet.

  The image forming program executed by the image forming apparatus 10 according to the present embodiment has a module configuration including the above-described units (the detection unit 50, the writing control unit 52, and the image processing unit 54). As the wear, a CPU (processor) reads out and executes an image forming program from the ROM, and the above-described units are loaded onto the main storage device. The detection unit 50, the write control unit 52, and the image processing unit 54 are included in the main storage device. It is supposed to be generated above.

  In the above embodiment, an example in which the image forming apparatus 10 according to the present embodiment is applied to an image forming apparatus having a printer function will be described. However, at least of a printer function, a copy function, a scanner function, and a facsimile function. You may apply to the multifunctional machine which has one function.

  FIG. 8 is a block diagram illustrating a hardware configuration example of the image forming apparatus 10 according to the present embodiment. As shown in the figure, the image forming apparatus 10 has a configuration in which a controller 270 and an engine unit (Engine) 260 are connected by a PCI (Peripheral Component Interface) bus. The controller 270 is a controller that controls the entire image forming apparatus and controls drawing, communication, and input from an operation unit (not shown). The engine unit 260 is a printer engine that can be connected to a PCI bus, and is, for example, a monochrome plotter, a 1-drum color plotter, a 4-drum color plotter, a scanner, or a fax unit. The engine unit 260 includes an image processing unit such as error diffusion and gamma conversion in addition to a so-called engine unit such as a plotter.

  The controller 270 includes a CPU 271, a north bridge (NB) 273, a system memory (MEM-P) 272, a south bridge (SB) 274, a local memory (MEM-C) 277, and an ASIC (Application Specific Integrated Circuit). 276 and a hard disk drive (HDD) 278, and the North Bridge (NB) 273 and the ASIC 276 are connected by an AGP (Accelerated Graphics Port) bus 275. The MEM-P 272 further includes a ROM (Read Only Memory) 272a and a RAM (Random Access Memory) 272b.

  The CPU 271 performs overall control of the image forming apparatus 100, has a chip set including the NB 273, the MEM-P 272, and the SB 274, and is connected to other devices via the chip set.

  The NB 273 is a bridge for connecting the CPU 271 to the MEM-P 272, SB 274, and AGP 275, and includes a memory controller that controls reading and writing to the MEM-P 272, a PCI master, and an AGP target.

  The MEM-P 272 is a system memory used as a memory for storing programs and data, a memory for developing programs and data, a memory for drawing printers, and the like, and includes a ROM 272a and a RAM 272b. The ROM 272a is a read-only memory used as a memory for storing programs and data, and the RAM 272b is a writable and readable memory used as a program and data development memory, a printer drawing memory, and the like.

  The SB 274 is a bridge for connecting the NB 273 to a PCI device and peripheral devices. The SB 274 is connected to the NB 273 via a PCI bus, and a network interface (I / F) unit and the like are also connected to the PCI bus.

  The ASIC 276 is an IC (Integrated Circuit) for image processing having hardware elements for image processing, and has a role of a bridge for connecting the AGP 275, the PCI bus, the HDD 278, and the MEM-C 277, respectively. The ASIC 276 includes a PCI target and an AGP master, an arbiter (ARB) that forms the core of the ASIC 276, a memory controller that controls the MEM-C 277, and a plurality of DMACs (Direct Memory) that rotate image data using hardware logic. (Access Controller) and a PCI unit that performs data transfer between the engine unit 260 via the PCI bus. The ASIC 276 is connected to an FCU (Facsimile Control Unit) 230, a USB (Universal Serial Bus) 240, and an IEEE 1394 (the Institute of Electrical and Electronics 13 interface) via a PCI bus. The operation display unit 220 is directly connected to the ASIC 276.

  The MEM-C277 is a local memory used as an image buffer for copying and a code buffer, and an HDD (Hard Disk Drive) 278 is a storage for storing image data, programs, font data, and forms. It is.

  The AGP 275 is a bus interface for a graphics accelerator card that has been proposed to speed up graphics processing. The AGP 275 speeds up the graphics accelerator card by directly accessing the MEM-P 272 with high throughput.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 18 Image forming part 20 Exposure part 22 Photoconductor 24 Charging apparatus 26 Developing apparatus 28 Transfer apparatus 34 Conveying belt 42 Main control part 44 Light emitting chip 44A Light emitting element 50 Detection part 52, 56 Write control part 54 Image processing part 60 Input image control unit 61 Skew correction processing unit 62, 62A to 62D Line memory 64 LD data output unit 66 Correction value calculation unit 66D Skew amount calculation unit 66C Read control unit 68 Resolution adjustment unit 74 High resolution processing unit 74B Dither matrix setting unit 78, 75 Output section

JP 2007-14001 A JP 2009-27683 A

Claims (6)

A photoreceptor,
Exposure means in which a plurality of light emitting chips in which a plurality of light emitting elements are arranged in the main scanning direction are arranged in the main scanning direction;
Developing means for developing an electrostatic latent image formed on the photoreceptor by the exposure means to form a toner image;
Transfer means for forming an image on the transfer object by transferring the toner image to the transfer object;
Detection means for detecting a skew amount indicating an amount of deviation between the previous SL-emitting chip,
When forming a density correction image used for density correction as the image, the higher the resolution and the larger the skew amount, the higher the image of the density correction image compared to when forming a printing image as the image. Resolution changing means for generating data by dithering;
Correction means for correcting skew by shifting the dither-processed image data image in the sub-scanning direction in accordance with the skew amount for each predetermined division unit in the main scanning direction;
An image forming apparatus. The correction means includes
The image of the dithered image data is divided into a plurality of division units in the main scanning direction at a position corresponding to a boundary between the adjacent light emitting chips, and the image of the dithered image data is The image forming apparatus according to claim 1, wherein the image forming apparatus is shifted in a sub-scanning direction according to the skew amount for each division unit. The resolution changing means includes
First setting means for setting a high-resolution dither matrix as the skew amount increases;
Dither processing means for dithering image data of a multi-gradation basic image used for density correction using the set dither matrix;
Second output means for outputting the dithered image data of the basic image to the correction means as image data of the density correction image;
A second setting means for setting a drive condition of the image forming apparatus main body according to the resolution of the density correction image;
The image forming apparatus according to claim 1, further comprising: The correction means includes
A plurality of line memories storing each of line image data for one line in the main scanning direction in the dithered image data;
Read control means for reading a pixel data group for each of the division units from line image data stored in any of the plurality of line memories in accordance with the skew amount, and outputting it to a first output means;
The image forming apparatus according to any one of claims 1 to 3, further comprising:   The driving conditions include the rotational speed of the photoconductor, the transfer rate when the image data of the density correction image is output to the correction unit, the update cycle of the plurality of line memories, and the image for one line in the main scanning direction. The image forming apparatus according to claim 4, wherein the image forming apparatus is at least one of a ratio of a light emission time of the light emitting element at the time of formation and a driving current for driving the light emitting element.   An electrostatic latent image formed on the photosensitive member is developed by the photosensitive member, an exposure unit in which a plurality of light emitting chips having a plurality of light emitting elements arranged in the main scanning direction are arranged in the main scanning direction, and the exposure unit. An image forming method executed by an image forming apparatus including: a developing unit that forms a toner image; and a transfer unit that forms an image on the transfer target by transferring the toner image to the transfer target. And
  Detecting a skew amount indicating a shift amount between the light emitting chips;
  When forming a density correction image used for density correction as the image, the higher the resolution and the larger the skew amount, the higher the image of the density correction image compared to when forming a printing image as the image. Generating data by dithering; and
  Skew correcting the dither-processed image data image by shifting in the sub-scanning direction in accordance with the skew amount for each preset division unit in the main scanning direction;
  An image forming method comprising:

Images