JP4045822B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus that forms an image by scanning an object to be scanned with a light beam whose light intensity is modulated based on image data. In particular, the present invention relates to a technique for controlling an image forming position during image formation, such as color registration correction.
[0002]
[Prior art]
In an image forming apparatus employing an electrophotographic system, a photosensitive member as an image carrier is charged by a charger, and a light (beam light) corresponding to image information is irradiated on the charged photosensitive member to form a latent image. The latent image is developed by a developing device, and the developed toner image is transferred to a sheet material or the like to form an image.
[0003]
On the other hand, with the colorization of an image, an apparatus for forming an image with various kinds of color materials has been proposed. In this case, a good full-color image can be obtained by accurately adjusting the printing amount of each color material. On the other hand, mixing of the color materials before printing leads to a significant decrease in image quality. Accordingly, there is provided a color image forming apparatus of a so-called tandem image forming apparatus in which printing units (image forming units) for performing each image forming process are prepared for the number of color materials and arranged in a line in the sheet conveying direction. Proposed.
[0004]
In this tandem image forming apparatus, for example, three types of yellow (Y), magenta (M), and cyan (C), or four types of color materials with black (K) added thereto are generally used. In order to achieve higher image quality, the above three or four kinds of color materials are used. Then, for example, each color image of a cyan image, a magenta image, a yellow image, and more preferably a black image is formed on each image carrier, and each color image is transferred onto the sheet material in a transfer position of each image carrier. Thus, a full-color image is formed. The tandem color image forming apparatus has an image forming portion corresponding to the number of color materials, which is advantageous for speeding up.
[0005]
However, in a tandem color image forming apparatus, the color material overlap changes when the print position of the color materials changes, so even if the same amount of color material is printed, it is recognized as a different color by human eyes. The That is, a shift in the printing position of each color image appears as a change in color tone. For this reason, the relative positions between the image forming portions for the respective color materials are accurately adjusted, and the adjusted positions are continuously maintained so as not to change with time, so that the print positions between the color materials are always constant. It is necessary to keep. In other words, in the tandem method, how well the registration (registration) of each color image formed by different image forming units is important in terms of image quality.
[0006]
One cause of the displacement of the transferred image is a difference in image width of each color in the main scanning direction and sub-scanning direction. This is due to the replacement of the image forming unit (for example, the difference in image delay amount due to the memory), the change in the installation state of the color image forming apparatus, and the change in the temperature and humidity in the color image forming apparatus. This is mainly caused by the difference in the optical path to the photosensitive drum of each part between the respective colors or the variation in the distance between the image forming parts and the change thereof. When this occurs, the exposure position of each color shifts, thereby shifting the print position of each color, resulting in a color shift in the image and image distortion (bow distortion).
[0007]
For this reason, in the tandem method, a mechanism for aligning (registration) color images formed by different image forming units is essential. Here, in order to correct the print position in the sub-scanning direction, that is, for alignment control, sub-scan magnification correction by image data processing is performed. This sub-scanning magnification correction changes the number of main scanning lines by image data processing, that is, the number of main scanning lines is reduced by thinning out data for the main scanning lines when the image is reduced, while the number of main scanning lines is reduced when the image is enlarged. This is realized by increasing the number of main scanning lines by inserting data.
[0008]
On the other hand, raster scan (ROS) -based image forming apparatuses have been proposed in Japanese Utility Model Laid-Open Nos. 63-170819 and 3-257469, for example. In these methods, the line image request signal (Line-Req) to the image data processing apparatus is used as a reference for scan scanning of a raster scan (ROS) -based image forming unit regardless of whether the laser is a single laser or a multi-laser. Based on the main scanning synchronization signal SOS, the pixel clock (video clock) is counted, and the line synchronization signal LS and the subline synchronization signal which are used as a reference for writing and reading the image memory in synchronization with the period of the main scanning synchronization signal SOS. Line was generated. Here, the line synchronization signal LS has the same cycle as that of one main scanning period, and the subline synchronization signal Line is mainly used for an apparatus using a multi-beam light source. Of the cycle.
[0009]
FIG. 17 is a functional block diagram proposed in Japanese Utility Model Laid-Open No. 63-170819. This configuration is an example of a dual beam laser, but based on the main scanning synchronization signal SOS, the page synchronization signal Page and the subline synchronization signal Line are generated by the signal generator 905 and output to the image data processing device. Thus, image data is received in units of sublines (one unit of subline synchronization signal Line).
[0010]
FIG. 18 is a timing chart of the configuration proposed in Japanese Utility Model Laid-Open No. 63-170819. “Line” in this chart outputs the subline synchronization signal Line twice during one main scanning period based on “SOS”. In this case, the condition is that the number of input lines from the upper level (image data processing apparatus) and the number of output lines to the lower level (ROS-based image forming unit) are transferred on a one-to-one basis.
[0011]
[Problems to be solved by the invention]
However, when sub-scanning magnification correction is performed by image data processing for alignment control, line number control is performed for alignment, and the number of lines in the page increases or decreases. Therefore, as before, when the line synchronization signal LS or the subline synchronization signal Line synchronized with the main scanning synchronization signal SOS is used, data shortage or overflow occurs in the buffer memory, making it impossible to form an appropriate image.
[0012]
For example, line thinning (reduction of the number of lines) at the time of image reduction eliminates the line data that should have been output in synchronization with the SOS signal. If the request is not received early, the number of necessary lines in the main scanning synchronization signal SOS will be insufficient.
[0013]
FIG. 19 is a diagram for explaining line data shortage due to line thinning at the time of reduction. The illustrated example is an example when a buffer memory for three lines is used. As shown in the figure, if the data stored in the buffer memory is thinned out and deleted as shown in the figure, the data that should be output after the next line is output first, and the buffer memory contents are not compensated without compensating for the shortage line. The accumulated number of lines will be exceeded, and the thinned out portion will be lost.
[0014]
In addition, due to line insertion (increase in the number of lines) at the time of image enlargement, data that should have been output in synchronization with the main scanning synchronization signal SOS remains in the buffer memory, and data request / reception for the next line and thereafter cannot be stopped. In this case, the line buffer memory overflows, and the line data that is carried over is overwritten.
[0015]
FIG. 20 is a diagram for explaining line data loss due to line insertion for enlargement. This is also an example in the case of using a buffer memory for three lines. As shown in the figure, if line data loss due to line insertion for enlargement is taken as an example, the data stored in the buffer memory as output is left on the memory as it is, and the data input from the next line onwards is the data Will be overwritten.
[0016]
As a general method, the buffer memory has a sub-scanning magnification correction equivalent to the buffer function that absorbs input / output differences, which is one of the uses of the FIFO memory. This problem can be solved by storing the correction line data first, and when the data is enlarged, the inserted data are sequentially stored in the spare memory of the buffer memory, and finally all the data is output.
[0017]
However, at the present time when the resolution is being increased, having a large amount of buffer memory in the interior goes against cost and downsizing.
[0018]
In any case, when the line synchronization signal LS and the subline synchronization signal Line are synchronized with the main scanning synchronization signal SOS as before, this problem is solved if the number of output lines is not the same as the number of input lines. Incurs an increase in cost.
[0019]
The present invention has been made in view of the above circumstances, and even when correcting the printing position (including magnification) in the sub-scanning direction, an appropriate image can be obtained without causing an underflow or overflow in the memory. An object of the present invention is to provide an image forming apparatus capable of forming images.
[0020]
[Means for Solving the Problems]
  That is, a first image forming apparatus according to the present invention includes an image forming unit that forms an image by scanning a scanned object with a light beam whose light intensity is modulated based on image data, and an image formed by the image forming unit. An image distortion detection unit that detects image distortion in the sub-scanning direction that may occur when forming the image, and a main scanning direction substantially orthogonal to the sub-scanning directionLine ofBased on image distortion detected by image distortion detector, including image memory that can write or read dataLineInsert dataEnterAnd this insertionEnterAnd a sub-scanning magnification correction unit that corrects the image width in the sub-scanning direction by inputting the data after being input to the image forming unit.
[0021]
  Here, in the first image forming apparatus according to the present invention, the sub-scanning magnification correcting unit is detected by the main scanning synchronization signal detecting unit indicating the main scanning reference in the image forming unit and the main scanning synchronization signal detecting unit. A memory access control signal generation unit for generating a memory write control signal and a memory read control signal synchronized with the main scanning synchronization signal is provided. Also, the sub-scanning magnification correction unitBased on the presence or absence ofBased on memory write control signallineThe writing of data to the image memory was controlled, and the data was written to the image memory based on the memory read control signallineWhen controlling the reading of data and performing the process of expanding the image width in the sub-scanning direction in order to reduce the image distortion detected by the image distortion detection unit, when there is no space for writing in the image memory, For image memorylineProhibits data writing and reading, and prepares for enlargementLine ofData is input to the image forming unit.
[0022]
  Further, a second image forming apparatus according to the present invention includes an image forming unit that forms an image by scanning a scanned object with a light beam whose light intensity is modulated based on image data, and the image forming unit includes the image forming unit. An image distortion detector that detects image distortion in the sub-scanning direction that may occur when forming an image, and a main scanning direction that is substantially orthogonal to the sub-scanning directionLine ofBased on image distortion detected by image distortion detector, including image memory that can write or read dataLineA sub-scanning magnification correction unit that corrects the image width in the sub-scanning direction by inputting / removing data and inputting the data after the insertion / removal to the image forming unit;
[0023]
  Here, in the second image forming apparatus according to the present invention, the sub-scanning magnification correction unit includes a main scanning cycle detection unit that detects a main scanning cycle in the image forming unit, and a main scanning reference in the image forming unit. A main scanning synchronization signal detection unit and a memory read control signal synchronized with the main scanning synchronization signal detected by the main scanning synchronization signal detection unit are generated, and the image distortion is detected based on the image distortion detected by the image distortion detection unit. A memory access control signal generation unit that generates a memory write control signal having a period capable of reducing the minutes is provided. Also, the sub-scan magnification correction unit, MeBased on the memory write control signal generated by the memory access control signal generatorlineData was written to the image memory and written to the image memory based on the memory read control signal generated by the memory access control signal generatorlineThe data was read out.
[0026]
  The fourth image forming apparatus according to the present invention includes an image forming unit that forms an image by scanning a scanned object with a beam of light whose intensity is modulated based on image data, and an image formed by the image forming unit. An image distortion detection unit that detects image distortion in the sub-scanning direction that may occur when forming the image, and a main scanning direction substantially orthogonal to the sub-scanning directionLine ofAn image memory capable of writing or reading data, and based on the image distortion detected by the image distortion detectorlineA sub-scanning magnification correction unit that corrects the image width in the sub-scanning direction by inputting / removing data and inputting the data after insertion / removal to the image forming unit;
[0027]
  Here, in the fourth image forming apparatus according to the present invention, the sub-scanning magnification correcting unit includes a main scanning synchronization signal detecting unit indicating a main scanning reference in the image forming unit and a main scanning synchronization signal detecting unit. A memory access control signal generator for generating a memory read control signal synchronized with the scan synchronization signal;, MeAnd a memory read control signal cycle detecting unit for measuring the cycle width of the memory read control signal by counting with a predetermined reference clock.
[0028]
The memory access control signal generation unit has a cycle of m times (m is a positive integer) with respect to the memory read control signal cycle n times (n is a positive integer) detected by the memory read control signal cycle detection unit. A memory write control signal having a predetermined cycle such that
[0029]
[Action]
In the first image forming apparatus having the above-described configuration, first, the memory access control signal generation unit provided in the sub-scanning magnification correction unit performs main scanning synchronization based on the main scanning cycle detected by the main scanning cycle detection unit. A memory write control signal and a memory read control signal synchronized with the signal are generated.
[0030]
  Then, the sub-scanning magnification correction unitBased on the presence or absence ofWhen the image width is increased while controlling the writing and reading to the image memory (for example, the address according to the address counter) based on the memory write control signal and the memory read control signal When there is no free space for writing in the memory,lineData writing and reading are prohibited, and prepared for enlargementLine ofData is input to the image forming unit. That is, at the time of data insertion during the enlargement process, access based on the memory write control signal and the memory read control signal to the image memory is prohibited.
[0031]
On the other hand, in the second image forming apparatus, first, the memory access control signal generation unit provided in the sub-scanning magnification correction unit detects the main scanning synchronization signal based on the main scanning cycle detected by the main scanning cycle detection unit. A synchronous memory read control signal is generated, and a memory write control signal having a period capable of reducing the image distortion detected by the image distortion detection unit is generated. This memory write control signal may be either synchronous or asynchronous with respect to the main scanning synchronization signal.
[0032]
  The sub-scanning magnification correction unit, MeBased on the memory write control signal generated by the memory access control signal generatorlineData was written to the image memory and written to the image memory based on the memory read control signal generated by the memory access control signal generatorlineThe data was read out. At this time, for example, writing and reading are controlled with respect to an address according to an address counter.
[0034]
  The fourth image forming apparatus is a modification of the second image forming apparatus, and includes a memory read control signal cycle detection unit., MeThe period width of the memory read control signal is counted with a predetermined reference clock. The memory access control signal generation unit has a cycle of m times (m is a positive integer) with respect to the cycle of the memory read control signal detected by the memory read control signal cycle detection unit (n is a positive integer). A memory write control signal having a predetermined cycle is generated. For example, the main scanning period in the vicinity of the portion that reduces the image distortion has a period different from the period width of the memory read control signal, and the measured memory reading control is performed in the writing period excluding the vicinity of the portion that reduces the image distortion. A memory write control signal having the same period as the period width of the signal is generated.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0036]
FIG. 1 is a mechanism diagram of an example of a color copying apparatus equipped with an image forming apparatus for recording an image using a surface emitting semiconductor laser (hereinafter referred to as VCSEL) array which is an example of a multi-beam light source.
[0037]
This color copying apparatus 1 records an image on a predetermined recording medium using xerography, and also has functions of an image acquisition unit 10, an image processing unit 20, an image output unit 30, and a platen cover. An ADF (Automatic Document Feeder) device 60 having no circulation function is provided. The image processing unit 20 is provided on a substrate disposed at a boundary portion between the image acquisition unit 10 and the image output unit 30.
[0038]
The color copying apparatus 1 is configured to be able to select and use a fixed reading method and a conveyance reading method depending on whether or not the ADF device 60 provided on the platen glass 11 is used. The ADF device 60 does not have a circulation function, but an automatic document feeder (RDF) having a circulation function can also be used.
[0039]
The image acquisition unit 10 includes a housing 112 and a platen glass (original placement table) 11 made of transparent glass provided on the housing 112. The image acquisition unit 10 emits light from a light source 12 that emits light toward a surface (back surface) opposite to the document placement surface of the platen glass 11 below the inner platen glass 11 of the housing 112. A full rate having a substantially concave reflecting shade 131 and a reflecting mirror 132 for reflecting the reflected light toward the platen glass 11, and a reflecting mirror 134 a for deflecting the reflected light from the platen glass 11 in a direction substantially parallel to the platen glass 11. A carriage (F / R-CRG) 134 is provided.
[0040]
As the light source 12, a fluorescent lamp whose longitudinal direction is the main scanning direction (the direction orthogonal to the paper surface in the figure) is used. The image acquisition unit 10 has two reflection mirrors 136a and 136b arranged so as to form a substantially right angle in the housing 112, and sequentially deflects the reflected light deflected by the full-rate carriage 134 by about 90 °. A half-rate carriage (H / R-CRG) 138 is provided. The full rate carriage 134 and the half rate carriage 138 are configured to reciprocate in the sub-scanning direction (in the direction of arrow X in FIG. 1) and in the opposite direction in conjunction with a stepping motor (not shown).
[0041]
Further, the image acquisition unit 10 receives the reflected light deflected by the reflection mirror 136b in the housing 112 at a predetermined focal position, and the reflected light converged by the lens 140 and receives the reflected light in the sub scanning direction. And a light receiving unit 13 that sequentially reads an image signal (analog electric signal) corresponding to the density.
[0042]
The light receiving unit 13 is arranged on a substrate together with a drive circuit 143 such as a CCD driver for driving a line sensor 142 (not described in detail) composed of a photoelectric conversion element such as a CCD (Charge Coupled Device) (details will be described later), a read signal processing unit 14 and the like. Established.
[0043]
Although not shown, the image acquisition unit 10 also includes a wire, a drive pulley, and the like for moving the reading optical system, the light receiving unit 13, and the like under the platen glass 11 in the housing 112. The driving pulley is reciprocally rotated by the driving force of the driving motor, and the wire is wound around the driving pulley by the rotational driving, thereby moving the reading optical system and the like below the platen glass at a predetermined speed.
[0044]
In the above configuration, the image acquisition unit 10 is normally in the home position (in the vicinity of the fixed read image destination position G indicated by a Δ mark in the figure). In the conveyance reading method, an image is read while the document is conveyed by the ADF device 60 in a state where the reading optical system is fixed (stop-locked) at an arbitrary position below the platen glass 11 on the document conveyance path. On the other hand, at the time of the fixed reading method, a document is manually placed on the platen glass 11 as a document placement table (or the ADF device 60 may be used), and fixed at an arbitrary position on the platen glass 11 (stop lock). In this state, the scanning optical system is moved at a constant speed in the direction of the arrow X with the fixed reading image destination position G as the leading end, and the document is exposed to read the image.
[0045]
Each document image in the conveyance reading method or the fixed reading method is changed in the optical path by the full rate carriage 134 or the half rate carriage 138 and is reduced by the lens 140 and reaches the light receiving unit 13. Then, after being subjected to processing by the read signal processing unit 14, the synchronization processing unit 15, etc., it is sent to the image processing unit 20.
[0046]
In this way, when the reading in the conveyance reading method or the fixed reading method is completed, the image processing unit 20 performs individual printing based on the red, green, and blue image data R, G, and B from the image acquisition unit 10. A binarized signal for color is obtained, and each binarized signal is output to the image output unit 30.
[0047]
In this case, for example, RGB color system image data is converted into YCrCb color system image data, and at least three (preferably four) from the YCrCb color system, for example, the CMY color system or the CMYK color system are used. Raster data that has been color-separated for print output is generated by mapping to the system.
[0048]
In such raster data conversion processing, under color removal (UCR) for reducing the CMY components of the color image or gray component replacement (GCR) for partially replacing the reduced CMY components with the K component is performed. Furthermore, in order to adjust the toner image of the output image created in response to the output data (CMYK or the like), color separation linearization or similar processing is performed.
[0049]
The image processing unit 20 acquires image data from the client terminal via a communication network (not shown), performs predetermined processing based on the image data, and obtains a binarized signal for each print color. You may make it (it is a structure of what is called a network printer).
[0050]
The image output unit 30 according to the present embodiment corresponds to an image forming unit that is an example of an image recording apparatus using an optical scanning device (raster output scan; ROS) according to the present invention for each color of K, Y, M, and C. Thus, it is a thing of what is called a tandem structure provided with four sets. Hereinafter, reference numerals of the respective members are given reference numerals K, Y, M, and C indicating the respective colors, and the reference numerals are omitted when collectively described.
[0051]
The image output unit 30 first includes image forming units 31K, 31Y, 31M, and 31C for each color of K, Y, M, and C, which are sequentially juxtaposed in one direction, and each image from the sheet feeding cassette 41. And a leading edge detector 44 provided close to the conveyance path of the document conveyed to the forming unit 31. The leading edge detector 44 optically detects, for example, the leading edge of the original fed from the paper feed cassette 41 through the registration rollers 42 onto the transfer belt (conveyance belt) 43 to obtain a leading edge detection signal. The data is sent to the processing unit 20. The image processing unit 20 sequentially obtains an on / off binarized signal of each color of K, Y, M, and C at regular intervals in synchronization with the input tip detection signal.
[0052]
A pattern detection unit for detecting a resist pattern (a test pattern for alignment) formed on both sides of the transfer belt 43 above the transfer belt 43 and downstream of the image forming unit 31C in the sheet conveying direction. 614 is provided. In the pattern detection unit 614, for example, three registration correction sensors are arranged in a line in a direction perpendicular to the conveyance direction of the belt 304 (in the main scanning direction).
[0053]
The transfer belt 43 has not only a sheet conveyance but also a function as a recording body on which a resist pattern is directly printed. When a resist pattern is formed on the transfer belt 43, this sensor detects the color misregistration amount in the main and sub scanning directions of the K, Y, M, and C images, and the drawing position control unit 600 (to be described later) corrects the drawing position. By performing image distortion correction, color misregistration of K, Y, M, and C images on a sheet (paper) is prevented.
[0054]
The transfer belt 43 functions as an intermediate transfer belt, and is sequentially transferred to the transfer belt 43 having the function as the intermediate transfer belt by the image forming unit 31 of each color, and then the transfer belt 43 to which the image is transferred. The image on the transfer belt 43 can be transferred to the sheet by passing the sheet between the transfer roller and the transfer roller.
[0055]
The image forming unit 31 includes a semiconductor laser 38 composed of a VCSEL light source group and a polygon mirror (rotation) that reflects laser light (laser beam) emitted from the semiconductor laser 38 toward a photosensitive drum 32 that is an example of a photosensitive member. And an optical scanning device having a (polyhedral mirror) 39.
[0056]
Although not shown in the drawing, in addition to the polygon mirror 39, for example, various lenses constituting an optical system such as a collimator lens and a scanning lens, or a half for allowing laser light emitted from the VCSEL 380a to enter the light amount sensor. A mirror or the like is arranged on the optical axis of the laser beam.
[0057]
Further, the image output unit 30 includes a manual document cassette 41 and a conveyance path 42 for conveying printing paper to the image forming unit 31. A leading edge detector 44 is provided in proximity to a conveyance path 42 for printing paper conveyed from the document cassette 41 to each image forming unit 31. The leading edge detector 44 optically detects, for example, the leading edge of the printing paper sent onto the transfer belt 43 through the registration roller 42 a to obtain a leading edge detection signal, and sends the leading edge detection signal to the image processing unit 20. The image processing unit 20 sequentially inputs image forming data of each color of K, Y, M, and C to the image output unit 30 at regular intervals in synchronization with the input leading edge detection signal.
[0058]
A reversing mechanism unit 50 is disposed below the image output unit 30. The reversing mechanism unit 50 includes a built-in paper feed tray 52, a paper reversing mechanism 54 for duplex copying, and a duplex copying path 56. The paper feed tray 52 has a structure in which a plurality of stages are arranged. Each paper feed tray 52 has a print paper size detection unit 58 for detecting the size of the print paper as a recording medium. The print paper size detection unit 58 optically detects, for example, the front end of the print paper at a position corresponding to the size of the print paper to obtain a size detection signal, and sends the size detection signal to the image processing unit 20.
[0059]
Information indicating which side of the front / back side of the printing paper should be arranged is input from the image processing unit 20 to the image output unit 30. When the image output unit 30 obtains information to be arranged on the back side, the image output unit 30 sends the printing paper to the reversing mechanism unit 50 side without discharging the printing paper to the outside of the apparatus.
[0060]
In the image output unit 30 and the reversing mechanism unit 50 configured as described above, first, for example, in the black (K) image forming unit 31K, the semiconductor laser 38K first receives the black on / off binary signal from the image processing unit 20. The black on / off binarized signal is converted into an optical signal, and the converted laser beam is emitted toward the polygon mirror 39. The laser light further scans the photosensitive drum 32K charged by the primary charger 33K via the reflection mirrors 47K, 48K, and 49K, thereby forming an electrostatic latent image on the photosensitive drum 32K.
[0061]
The electrostatic latent image is converted into a toner image by a developing device 34K to which black toner is supplied. The toner image is converted by the transfer charger 35K while the document on the transfer belt 43 passes through the photosensitive drum 32K. Transcribed above. After the transfer, excess toner is removed from the photosensitive drum 32K by the cleaner 36K.
[0062]
Similarly, the semiconductor lasers 38Y, 38M, and 38C respectively turn on / off binarized signals of corresponding Y, M, and C colors that are sequentially obtained from the image processing unit 20 with respect to the black on / off binarized signals at regular intervals. , The on / off binarized signal of each color is converted into an optical signal, and the converted laser beam is emitted toward the polygon mirror 39.
[0063]
The laser light is further scanned on the corresponding photosensitive drums 32Y, 32M, and 32C charged by the primary chargers 33Y, 33M, and 33C via the reflection mirrors 47Y to 49Y, 47M to 49M, and 47C to 49C. Then, electrostatic latent images are sequentially formed on the photosensitive drums 32Y, 32M, and 32C.
[0064]
Each electrostatic latent image is sequentially converted into a toner image by developing units 34Y, 34M, and 34C to which each color toner is supplied. Each toner image is a photosensitive drum 32Y, 32M, and 32C corresponding to the original on the transfer belt 43. Are sequentially transferred onto the original by the corresponding transfer chargers 35Y, 35M, and 35C.
[0065]
The original on which the toner images of each color of K, Y, M, and C are sequentially transferred in this manner is peeled off from the transfer belt 43, the toner is fixed by the fixing roller 45, and is discharged outside the copying machine. .
[0066]
When the double-sided printing mode is set, the printing paper on which the image is fixed on the surface by the fixing roller 45 as described above is guided to the paper reversing mechanism 54 without being discharged out of the apparatus, and the printing paper. Is then fed to the duplex copying path 56. The sheet reversing mechanism 54 and the double-sided copying path 56 are units for making double-sided copying, and when the printing paper is discharged from the fixing roller 45, the printing paper is lowered by a claw (not shown) through the roller 54a of the paper reversing mechanism 54. Then, the roller 54b pushes up the printing paper and guides it onto the double-sided copying path 56 on the right to reverse the printing paper. Thereafter, the toner image for the back surface formed on the photosensitive drum 32 is transferred to the back surface of the printing paper through the conveyance path 42 so that the back surface faces the photosensitive drum 32 side.
[0067]
The image output unit 30 sequentially forms an electrostatic latent image of each color of K, Y, M, and C on one photosensitive drum by one laser light scanner, and the electrostatic latent image is formed on the photosensitive drum. Are sequentially formed into toner images by a developing device provided with toners of respective colors K, Y, M, and C, and the toner images are sequentially transferred onto a document adsorbed on a transfer drum. It may be configured.
[0068]
FIG. 2 is a diagram illustrating a configuration example of the image forming unit 31. Here, the description will be made with the reflection mirrors 47 to 49 omitted. A plurality of laser beams L emitted from the VCSEL light source group 380 constituting the semiconductor laser 38 shown in FIG. 1, that is, the VCSEL 380a, are collimated (collimated) into laser beams having a predetermined beam diameter by the collimator lens 382. Is done. This laser light is incident on the polygon mirror 39 via the cylindrical lens 387, and is reflected by its reflection surface (six surfaces in the figure) as the polygon mirror 39 rotates, and is deflected respectively.
[0069]
The laser beam L reflected and deflected by the polygon mirror 39 passes through a toroidal lens 388 having a tilt correction function and a scanning lens group 384 having an fθ function, and is a photosensitive drum 32 as an image carrier placed on the surface to be scanned. An image is formed on the spot 386 on the surface to be scanned.
[0070]
The reflection mirror 391 and the photodetector 392 are incident on the photodetector 392 at a position within the deflection range of the laser beam L and not involved in scanning of the surface to be scanned. Is arranged. In order to detect the laser beam L1 with the photodetector 392, the laser is turned on immediately before the laser beam L1 is deflected to the photodetector 392 during the scanning period, and is turned off before the scanning range necessary for the original scanning. Control is performed. The start of modulation of the laser light according to the image data is controlled by the main scanning synchronization signal output from the photodetector 392.
[0071]
As the VCSEL light source group 380, a VCSEL 380a serving as a light source is arranged on the surface of the semiconductor substrate 381 in a two-dimensional matrix, or a plurality of VCSELs 380a arranged in one line (in-line).
[0072]
FIG. 3 is a diagram showing the relationship between the scanning line and the imaging spot on the surface to be scanned by the laser beam emitted from the VCSEL light source group 380. In the illustrated VCSEL light source group 380, VCSELs 380a are two-dimensionally arranged on the surface of a semiconductor substrate so as to be 8 × 4. Here, the vertical arrangement (eight in this example) of the VCSEL light source group 380 is in the vertical direction with respect to the polygon mirror 39, that is, in the sub-scanning direction and the optical direction on the photoconductor as the scanning surface. So that it is parallel to This arrangement form is hereinafter referred to as vertical arrangement. Note that the vertical arrangement of the VCSEL light source group 380 is arranged so as to be in the horizontal direction with respect to the polygon mirror 39, that is, arranged so as to be optically parallel to the sub-scanning direction on the photoconductor as the scanning surface. The form is hereinafter referred to as horizontal arrangement.
[0073]
As shown in the figure, the VCSEL light source group 380 has a base line (one point in the figure) having an angle φ with respect to the main scanning direction and an arbitrary line (main scanning line) in the main scanning direction and passing over the VCSEL 380a on the main scanning line. An arrangement pattern is defined by an inclination line indicated by a chain line. Each VCSEL 380a is formed on a single semiconductor substrate, and is 8 at regular intervals along an arbitrary line (sub-scanning line) in the sub-scanning direction, and 4 at regular intervals along the main scanning line, for a total of 8 × 4 VCSELs 380a are arranged in a two-dimensional matrix. Reference numerals L1 to L32 indicate sub-scanning lines.
[0074]
In the VCSEL light source group 380, each VCSEL 380a (that is, the light emitting point) is positioned at each vertex of the parallelogram, and a scanning line having a predetermined resolution (for example, 2400 dpi) is formed on the photosensitive member by being inclined at an appropriate angle. To do. For example, when the interval in the main scanning direction of the VCSEL 380a is SL, the sub-scanning line interval Δ is set to SL × tanφ.
[0075]
That is, the imaging spot of the laser beam periodically moves at a substantially constant speed in the main scanning direction (from left to right in the figure), the scanning lines are scanned at equal intervals with a pitch Δ, and each main scanning is performed each time. On the other hand, the surface to be scanned moves by a predetermined interval in the sub-scanning direction in the figure. Regardless of the positional relationship of the spot to be scanned, the movement of the surface to be scanned in the sub-scanning direction is 32 scanning lines per main scanning period. In the figure, two main scans are shown, and the positions of the first and second VCSEL light source groups 380 are shown shifted in the main scan direction, but this is for convenience of illustration. Actually, scanning starts from the same position.
[0076]
During scanning, the laser is turned on / off or the intensity is modulated according to the image density according to the image data. The modulation or lighting control is started based on the main scanning synchronization signal output from the photodetector 392. At this time, a total of 32 laser beams of 8 × 4 operate simultaneously. Then, by repeating this operation, the entire surface to be scanned is filled with the scanning lines at equal intervals, and two-dimensional scanning is realized. Such a scanning form is called adjacent exposure. Of course, it is not limited to the adjacent exposure, but can be used in a multiple exposure mode in which a part is overlapped (overlapped) for exposure.
[0077]
Note that if the distance measured in the sub-scanning direction from one spot to another spot is divided by the scanning line pitch Δ, and the remainder divided by the number of scanning lines simultaneously scanned is a natural number different from each other, they always overlap. Therefore, the surface to be scanned can be filled with the scanning lines at regular intervals. Note that the spot SL in the main scanning direction can be arbitrarily set as long as the sub-scanning line interval Δ = SL × tan φ is satisfied.
[0078]
Here, since the image formation position in the main scanning direction of the VCSEL 380a is shifted by SL, each light beam corresponding to one column on the image data emitted from the VCSEL 380a which is a light emitting point is sub-scanning direction. By performing delay control on the modulation signal of each VCSEL 380a by a delay control unit (for example, 4-bit FIFO or 8-bit FIFO) so that an image is formed substantially in a single line, 32 (4 × 8) on the signal Are simultaneously scanned adjacent to each other.
[0079]
FIG. 4 is a diagram showing an outline of a processing circuit (image recording control unit) for forming an image in the image forming unit 31 including the VCSEL light source group 380 having the above configuration.
[0080]
The image recording control unit is configured to acquire image data from the client terminal 8 such as a personal computer via the image acquisition unit 10 or the network 9, and based on the image data from the image data generation unit 200. The write signal generation unit 220 generates a laser modulation signal for the VCSEL 380a, and the delay adjuster 240 adjusts the write timing for the laser modulation signal from the write signal generation unit 220. A color misregistration correction unit 613 (see FIG. 6 described later) in the drawing position control unit 600 includes an image data generation unit 200, a write signal generation unit 220, a machine controller 270, and the like.
[0081]
The image data generation unit 200 includes a page memory 202 and a CPU 204. The image data generation unit 200 converts RGB color system image data input from the image acquisition unit 10 or the like into YCrCb color system image data, and further performs mapping from the YCrCb color system to the CMYK color system. Then, raster data (halftone data) representing a halftone image or character image with a resolution of 600 dpi / multi-gradation (for example, 8 bits) separated for print output is generated and received via the I / F unit 222 Based on the subline synchronization signal Line, the image data is transferred to the write signal generation unit 220 in units of sublines.
[0082]
At this time, under color removal (UCR) for reducing the CMY components of the color image and gray component exchange (GCR) for partially replacing the reduced CMY components with the K component are performed. Further, in order to adjust the toner image of the output image created in response to the output data (CMYK or the like), processing such as linearization of color separation is performed.
[0083]
The write signal generation unit 220 includes an I / F (interface) unit 222 that functions as an interface with the image data generation unit 200, a modulation signal generation unit 224 that generates a laser modulation signal (light beam modulation signal), and a plurality of signals A line buffer memory group 226 having a line buffer memory 226 a and having a function of coarsely adjusting the write timing for the laser modulation signal from the modulation signal generation unit 224. The line buffer memory group 226 and the delay adjuster 240 connected to the subsequent stage function as a data delay unit.
[0084]
Further, the write signal generation unit 220 includes an additional line buffer memory 229 that holds data for an insertion line in order to insert a line during the enlargement process. The data for the insertion line may be, for example, data of a line in the vicinity (preferably immediately before) of the input image data, or obtained based on data of several lines in the vicinity of the additional part. There may be.
[0085]
The additional line buffer memory 229 is necessary to use a FIFO memory as each memory of the line buffer memory group 226 (because no data remains after reading), and can hold data even after data reading. When using the type of memory, for example, when the line data itself in the vicinity of the additional portion is used as insertion line data, this is not always necessary.
[0086]
The write signal generation unit 220 includes a memory controller 228 that controls the I / F unit 222, the modulation signal generation unit 224, and the line buffer memory group 226, the I / F unit 222, the modulation signal generation unit 224, and the line buffer memory. A timing signal generator 230 that controls the group 226 and the memory controller 228, and a sub-scanning magnification correction unit 700 that corrects a magnification error in the sub-scanning direction (details of its operation will be described later).
[0087]
Further, the image recording control unit generates a main scanning synchronization synchronizing signal SOS that is a reference signal for controlling writing timing (that is, scanning scanning) based on a detection signal obtained from the photodetector 392 of the image forming unit 31. A signal generator 260 and a machine controller 270 which is a functional part for controlling the entire color copying apparatus 1 are provided. The synchronization signal generator 260 functions as a main scanning synchronization signal detector according to the present invention.
[0088]
The timing signal generator 230 performs various operations based on the main scanning synchronization signal SOS indicating that the scanning beam has reached the position immediately before entering the photosensitive drum 32 and the print request signal PRQ instructing the start of image recording output from the machine controller 270. Control signals are generated and supplied to each unit. For example, the write reference signal ROS_PS, the write valid signal ROS_LS, the page synchronization signal Page, the line synchronization signal LS (Line Sync), the subline synchronization signal Line corresponding to the number of FIFO memories, or the pixel clock PCK.
[0089]
The timing signal generator 230 determines the phase difference between the page synchronization signal Page instructing the start of image recording in the sub-scanning direction and the main scanning synchronization signal SOS, and controls the memory controller 228. The memory controller 228 adds margin data to the writing to each line buffer memory 226a according to this phase difference, and adjusts the image recording position in the sub-scanning direction on the photosensitive drum 32.
[0090]
The delay adjuster 240 performs a bit shift corresponding to a fine phase difference when reading data from the line buffer memory 226 with respect to a fine phase difference that cannot be adjusted by writing margin data to the line buffer memory 226a. A modulation signal corresponding to N laser beams for the multi-beam scanning device is supplied to the image forming unit 31.
[0091]
Further, the image forming unit 31 includes a laser driving circuit (multi-LDD) 300 that drives each VCSEL 380a of the VCSEL light source group 380 based on the laser modulation signal whose output timing is adjusted by the delay adjuster 240, And a drive control unit 310 that controls various control signals for controlling the drive current of the VCSEL 380a and the rotation amount (rotation amount in the sub-scanning direction) of the photosensitive drum 32.
[0092]
Based on a temperature sensor (not shown), the number of used mirrors of the polygon mirror 39 (used number counter; 6 in this example), for example, a print mode indicating a screen type, an external input, or the like, A light amount setting condition selection unit 304 that generates a light amount control level change signal for setting the amount of light. The drive control unit 310 also detects the light amount of each VCSEL 380 a acquired by the light amount sensor 302, the light amount control level change signal generated by the light amount setting condition selection unit 304, and the light amount setting from the machine controller 270. A level change unit 306 that changes the light amount level based on the signal, and a drive amount setting signal (1 to n corresponding to each) for controlling the drive current of each VCSEL 380a under the control of the level change unit 306 And a drive amount control unit 308 that generates a light amount control drive signal. Further, the drive control unit 310 includes a rotation control unit 309 that controls the amount of rotation of the photosensitive drum 32 in the sub-scanning direction and the surface skip of the polygon mirror 39 based on the timing signal from the timing signal generator 230.
[0093]
Here, if the light quantity of the beam is not constant, the density of the formed image is not constant, and the image quality is not stable. Further, when an image is formed with a plurality of light beams, if the amount of light of each light beam is not constant, density unevenness occurs in the formed image, and the image quality is deteriorated. This is why the light amount sensor 302 detects the light amount of each VCSEL 380a and provides a mechanism for controlling the laser drive amount (APC: Auto Power Control) so that the light amount becomes constant.
[0094]
In the present embodiment, in order to make the functional part of the optical scanning device in the image forming unit 31 a multi-beam scanning device that simultaneously scans N light beams that can be modulated independently, the write signal generation unit 220 first starts. , N light beams are grouped by k, and image data for k lines is scanned while the multi-beam scanning device scans the N light beams once on the photosensitive drum 32 as a recording medium. The process of taking one scan in pixel order is repeated N / k times. Then, after data for N lines in the sub-scanning direction substantially orthogonal to the optical scanning is aligned, recording is performed by N multi-beam scanning devices.
[0095]
Specifically, when the scanning density of N beams in the sub-scanning direction is nndpi (dots / inch) and the resolution of image data to be recorded is mmdpi, k = nn / mm and a divisor of N, Each time the scanning device scans the photosensitive drum 32 with N beams once, N / k sub-line synchronization signals Line are generated during one period of the main scanning synchronization signal. Then, the modulation signal generation unit 224 receives mmdpi image data in accordance with the subline synchronization signal Line from the higher-level image data generation unit 200 that stores the image data to be recorded, via the I / F unit 222.
[0096]
Next, the modulation signal generation unit 224 generates laser modulation signals for k lines in the sub-scanning direction for each mmdpi / 1 pixel, and sequentially writes the laser modulation signals in the line buffer memory 226. Finally, the delay adjuster 240 aligns the data for N lines in the sub-scanning direction, and then the individual VCSELs 380a of the VCSEL light source group 380 are driven by the laser driving circuit 300, so that images (in this example, static An electrostatic latent image) is recorded on the photosensitive drum 32. At this time, the delay amount (corresponding to SL shown in FIG. 3) of the VCSEL 380a in the main scanning direction is controlled using a 4-bit FIFO.
[0097]
The modulation signal generation unit 224 generates 2400 dpi bitmap halftone image data (16 bits) for each pixel of 600 dpi multi-value data received from the image data generation unit 200 via the I / F unit 222. Then, the modulation signal generation unit 224 writes the halftone image data in the line buffer memory 226a (FIFO memory) in units of k (4) bits.
[0098]
In order to process image data in this way, data for 4 lines of 2400 dpi must be stored. If the scanning width is 300 mm,
(300 / 25.4) × 2400≈28,300
Therefore, a FIFO memory having a capacity of about 30k words × 4 bits is required. There are many methods for generating halftone dot image data, such as a dither matrix method and an error diffusion method, and any technique may be used here.
[0099]
Under the control of the memory controller 228, the line buffer memory 226a outputs modulation signals simultaneously at a predetermined timing. That is, the modulation signals for 32 laser beams used in the VCSEL light source group 380 are simultaneously output, and the output timing of the image data to the light source (VCSEL 380a) is simultaneous. The VCSEL light source group 380 having eight light sources (VCSEL 380a) in the vertical direction (process direction) and having an 8 × 4 matrix structure can function as a light source for 32-line beam simultaneous scanning.
[0100]
Therefore, by having eight light sources in the vertical direction (process direction), the read timing from the 4-bit FIFO memory can be set to be the same, so that the output timing can be adjusted without waste using the 4-bit FIFO memory. it can. In addition, the number of beams can be expanded without waste by having a FIFO memory in the main scanning direction in accordance with a matrix of light sources.
[0101]
FIG. 5 is a diagram illustrating a correspondence relationship between halftone data generated by the image data generation unit 200 and a laser modulation signal generated by the write signal generation unit 220 (particularly, the modulation signal generation unit 224). Here, as shown in FIG. 4, the line buffer memory group 226 is configured by using eight 4-bit FIFO memories (numbers 1 to 8) as the individual line buffer memories 226a.
[0102]
Here, when image data is output at high speed, a memory (line buffer memory in FIG. 4) is used as a mechanism for handling image data at a frequency (pixel clock; pixel clock) as low as possible before the output side. A group 226) is prepared, and the preceding stage is configured to handle a plurality of pixels in one clock. In this example, the modulation signal generation unit 224 generates 2400 dpi bitmap halftone image data (16 bits) for each pixel of 600 dpi multi-value data received from the sub-scanning magnification correction unit 700. Then, the modulation signal generation unit 224 writes the halftone image data in the line buffer memory 226a (FIFO memory) in units of k (= 4) bits. Hereinafter, a method of writing data in the line buffer memory 226a (FIFO memory) in units of k (= 4) bits is referred to as k pixel packing. In this example, since k = 4, four pixel packing is performed.
[0103]
In the figure, the case where multi-value data of 600 dpi / 8 bit / 40 MHz is converted using a FIFO, resolution is converted to binary data of 2400 dpi / 1 bit, and after packing four pixels, it is output to the subsequent stage at 2400 dpi / 200 MHz. Illustrated. Since the output (area B) is 200 MHz and the preceding stage (area A) is a 4-pixel packing, the area A can be handled at a frequency of 200 MHz / 4 = 50 MHz (Min).
[0104]
FIG. 6 is a diagram for explaining a mechanism for detecting a shift of the drawing position in order to make the image width of each color constant during color position formation (color registration correction) during the drawing position control. Here, FIG. 6A is a schematic diagram focusing on the drawing position shift detection mechanism of the drawing position control unit 600. Further, FIG. 6B (each figure is referred to as B1 to B5) is a diagram for explaining the shift of the drawing position of each color.
[0105]
As shown in FIG. 6A, the color copying apparatus 1 is a copying machine for simultaneous color output of one scan and four colors. In the image output unit 30 having a tandem configuration, black (K), yellow (Y), magenta ( The four color image forming units 31K, 31Y, 31M, and 31C of M) and cyan (C) are arranged in a line vertically in the paper transport direction (see also FIG. 1). In the tandem configuration, the K, Y, M, and C toner components need to be transferred onto the paper fed on the transfer belt 43 without color misregistration.
[0106]
However, as schematically shown in each drawing of FIG. 6B, color misregistration occurs due to various factors. For example, the development timing of each toner of K, Y, M, and C is the time corresponding to the interval between the photosensitive drums 32 because the photosensitive drums 32 of the respective colors are arranged at substantially equal intervals with respect to the transfer belt 43. It is done out of place. Therefore, the sub-scan delay module is used to control the delay for each of K, Y, M, and C in the sub-scan direction by an amount corresponding to the interval between the photosensitive drums 32.
[0107]
  However, as shown in (B1), when the C drawing position (including the magnification in the sub-scanning direction) is shifted in the sub-scanning direction, for example, color shift occurs. In addition to this, the printing start position deviation (B5) in the main scanning direction by the beam scanning of each color, the main scanning partial magnification distortion (B4), the baud distortion in the sub scanning direction (B3), the arrangement of the photosensitive drum 32 and the beam scanning. Skew distortion (B2) due to the parallelism shift occurs, which causes a color shift. The drawing position control unit 600 prevents these color shifts by performing position correction and image correction on the K, Y, M, and C data..
[0108]
The drawing position control unit 600 corrects the drawing position of each color and forms a predetermined resist detection test pattern (hereinafter referred to as a resist pattern), which serves as a reference for the drawing position, at a predetermined position of the transfer belt 43 for each color. A resist pattern generator 621 that generates a signal is included. A pattern detection unit 614 for detecting a resist pattern formed on both sides of the transfer belt 43 is disposed downstream of the image forming unit 31C in the sheet conveyance direction.
[0109]
In order to correct the input image data Vy, Vm, Vc, Vk of each color based on the detection result obtained by the pattern detection unit 614, the color misregistration correction units 613Y, 613M, 613C, 613K are input image data Vy, Vm, Vc, It is provided corresponding to each of Vk. A clock is input from the clock generator 622 to the color misregistration correction units 613Y, 613M, 613C, and 613K (also collectively referred to as the color misregistration correction unit 613). The K, Y, M, and C image data transferred from the image processing unit 20 are input to the color misregistration correction units 613Y, 613M, 613C, and 613K.
[0110]
With the configuration described above, first, transfer is performed based on predetermined resist pattern data Ry, Rm, Rc, Rk (see, for example, Japanese Patent Laid-Open Nos. 2000-15870, 2001-5245, etc.) generated in the resist pattern generation unit 621. The pattern detection unit 614 arranged on the downstream side of the most downstream image forming unit 31C sequentially detects the resist patterns corresponding to the respective colors, and sequentially detects the detection results. The color misregistration correction units 613Y, 613M, 613C, and 613K are provided.
[0111]
The color misregistration correction units 613Y, 613M, 613C, and 613K detect the color misregistration amount based on the detection result detected by the pattern detection unit 614, and based on the detected color misregistration amount, the input image data Vy, Vm, Vc and Vk are respectively corrected and the corrected image data Qy, Qm, Qc, and Qk are output to the corresponding image forming unit 31. In other words, in order to correct the deviation in the development timing according to the interval between the photosensitive drums 32, the K component position is corrected based on the drawing position in the image forming unit 31K (K developing unit) arranged at the most upstream. For the other color components, position correction on the sub-scanning side is performed for the K component.
[0112]
At this time, the color misregistration correction unit 613 performs processing for inserting and removing image data in units of sublines (corresponding to the subline synchronization signal Line) in order to correct a magnification error in the sub-scanning direction, and is sent to the image forming unit 31. Increase or decrease the number of data lines. Next, a detailed description will be given of processing for dealing with an increase / decrease in the number of lines in the sub-scanning magnification correction.
[0113]
FIG. 7 is a block diagram showing the configuration of the peripheral portion of the memory controller 228 by paying attention to the increase / decrease of the number of lines by the sub-scanning magnification correction in the configuration shown in FIG. The correspondence according to this configuration is the first embodiment.
[0114]
The line buffer memory group 226 of this example has two sets (each A and B) of FIFO groups each having eight 4-bit FIFO memories 227 as line buffer memories. The timing signal generator 230 generates various control signals (ROS_PS, ROS_LS, Line, Page, PCK, etc.) from the main scanning synchronization signal SOS and the print request signal (PRQ), and supplies them to each unit.
[0115]
The memory controller 228 has a clock generator 228a and a 1/4 frequency divider 228b, and generates a write clock FIFO_WCK of eight 4-bit FIFO memories 227 (A1 to A8) constituting the FIFO group A as a clock generator. The transfer clock generated by dividing the write clock FIFO_WCK by 4 is generated by the quarter frequency divider 228b. Then, this transfer clock is sent to the image data generation unit 200 via the I / F unit 222.
[0116]
When the page synchronization signal Page and the subline synchronization signal Line become active, the image data generation unit 200 sends 8-bit image data to the modulation signal generation unit 224 via the I / F unit 222 in synchronization with the transfer clock.
[0117]
The modulation signal generation unit 224 generates 16-bit bitmap data from halftone data of 8 bits per pixel, and writes this into one FIFO memory 227 in units of 8 bits. Also, FIFO_WCK having a frequency four times that of the transfer clock is used as the write clock.
[0118]
At this time, the output of the modulation signal generator 224 is connected to the inputs of all the FIFO memories 227 of the FIFO memories 227 groups A and B, and is realized by the memory controller 228 sequentially controlling the write enable terminals.
[0119]
From the FIFO memory 227, image data is read in synchronization with the pixel clock PCK using the write valid signal ROS_LS generated from the main scanning synchronization signal SOS as a read reference. At this time, switching between the A group and the B group of the FIFO memory 227 is realized by the memory controller 228 controlling the read enable terminal and the output enable terminal of each FIFO memory 227.
[0120]
Hereinafter, in order to simplify the explanation, the line synchronization signal LS having the same cycle as one main scanning period is used instead of the multi-beam light source used for the memory write and read control signals. A description will be given of the case where it is used as a memory write / read control signal. In this case, as indicated by Line (LS) in the figure, the memory access may be considered as a form in which the line synchronization signal LS is used instead of the subline synchronization signal Line.
[0121]
In a configuration in which the line synchronization signal LS is used as a memory write / read control signal, the image data generation unit 200 uses the page synchronization signal Page from the I / F unit 222 as the image data acquired from the image acquisition unit 10 or the like. And output in synchronization with the line synchronization signal LS.
[0122]
The machine controller 270 functions as a main part of the image distortion detection unit according to the present invention, and detects a color misregistration amount based on the detection result detected by the pattern detection unit 614 (see FIG. 6). A correction value (specifically, an address position at which line data should be inserted / removed) relating to the magnification in the sub-scanning direction necessary for canceling the color deviation in the sub-scanning direction of the deviation amount is sub-scanning correction magnification correction register 650. Set to.
[0123]
In the drawing position control unit 600 (particularly the functional part of the color misregistration correction unit 613), the timing signal generator 230, which forms the main part of the memory access control signal generation unit according to the present invention, receives the print request signal PRQ from the machine controller 270. Upon receipt, a line synchronization signal LS synchronized with the main scanning synchronization signal SOS is generated based on the main scanning synchronization signal SOS from the synchronization signal generator 260, and a page synchronization signal Page which is a page-by-page writing control signal. Is generated. The line synchronization signal LS functions as a memory write control signal for writing image data to the line buffer memory group 226 and a memory read control signal for reading.
[0124]
The timing signal generator 230 inputs the line synchronization signal LS and the page synchronization signal Page to the memory controller 228 and the I / F unit 222. In response to the print request signal PRQ from the machine controller 270, the I / F unit 222 generates a page synchronization signal Page or line synchronization generated by the timing signal generator 230 based on the main scanning synchronization signal SOS from the synchronization signal generator 260. The signal LS is output to the image data generation unit 200 to request image data in line units (one main scanning unit).
[0125]
The memory controller 228 monitors the vacant address of the line buffer memory group 226 based on the line synchronization signal LS input from the timing signal generator 230, and performs image processing based on the line synchronization signal LS as a memory write control signal. The writing of data to the line buffer memory group 226 is controlled, and the reading of image data written to the line buffer memory group 226 is controlled based on the line synchronization signal LS as a memory reading control signal. At this time, the memory controller 228 controls the line address depending on which FIFO memory 227 the R / W (Read / Write) control signal is activated. That is, an R / W (Read / Write) control signal functions as a line address control signal.
[0126]
Further, the memory controller 228 uses the line buffer memory group 226 to insert line data based on correction values stored in advance in the sub-scan correction magnification correction register 650 in order to perform sub-scan magnification correction. Control the line address to be removed (Line-Address-Control). Under this control, the line buffer memory group 226 delivers the image data in units of lines to the delay adjustment unit 240, the laser drive circuit 300, or the VCSEL light source group 380 that function as the next connected output stage.
[0127]
At this time, the drawing position control unit 600 switches various signals generated from the timing signal generator 230 and the memory controller 228 so as to be surely output from the line buffer memory group 226 without missing image data. . Alternatively, the memory controller 228 controls the I / F unit 222 to prohibit data writing to the line buffer memory group 226 and the memory controller 228 prohibits data reading from the line buffer memory group 226.
[0128]
For example, the memory controller 228 determines the free capacity of the line buffer memory group 226 and passes the determination result to the I / F unit 222 as pre-full (0 Pre-Full) / pre-empty (Pre-Empty) information. The I / F unit 222 refers to this information, that is, determines whether or not line image data is requested, and sends the line synchronization signal LS acquired from the timing signal generator 230 to the image data generation unit 200 as necessary. The delivery of is prohibited.
[0129]
FIG. 8 is a timing chart for explaining an embodiment corresponding to an increase in the number of lines by correcting the sub-scanning magnification while taking the configuration shown in FIG. Hereinafter, this embodiment is referred to as a corresponding method of the first example of the first embodiment. In the figure, for ease of explanation, an example in which three lines are provided as a buffer portion is shown. In the following description, it is assumed that data writing to and reading from the buffer memory (line buffer memory group 226) can be performed simultaneously. That is, it is assumed that the written pixel data can be read immediately (the same applies hereinafter).
[0130]
As shown in FIG. 8, the first example is characterized in that the sub-scanning magnification correction is limited to the enlargement direction only, the line image data is only inserted, and the original image is output faithfully without being discarded. It is said.
[0131]
For example, when the line buffer memory group 226 runs out of space for writing, that is, when data is inserted during the enlargement process, which is the period indicated by a in FIG. In order to prohibit the writing of image data to the line buffer memory group 226, the transmission of the line synchronization signal LS to the image data generation unit 200 is stopped.
[0132]
At this time, the memory controller 228 prohibits reading of the image data from the line buffer memory group 226 and reads out the data for the insertion line from the additional line buffer memory 229 and passes it to the delay adjuster 240. Further, when the processing for the insertion line is completed, the drawing position control unit 600 controls writing and reading to the line buffer memory group 226 based on the line synchronization signal LS as usual.
[0133]
  As described above, according to the control method of the first example of the first embodiment, the page synchronization signal Page and the line synchronization signal LS for the image data generation unit 200 are synchronized with the main scanning synchronization signal SOS from the synchronization signal generator 260. In addition, the line synchronization signal LS of the insertion line portion generated by the magnification correction is used as the FIFO free space in the line buffer memory group 226.Based on the presence or absence ofStoppedOrThe suspension was released.
[0134]
Accordingly, it is possible to reliably output appropriate data from the line buffer memory group 226 without causing an overflow in the line buffer memory group 226 and without missing image data from the image data generation unit 200. Accordingly, an appropriate enlarged image is formed by the image forming unit 31. Basically, since access (writing and reading) to the line buffer memory group 226 is controlled by the line synchronization signal LS synchronized with the main scanning synchronization signal SOS, the circuit is simplified and the circuit scale is increased. Small configuration can be achieved.
[0135]
FIG. 9 is a diagram for explaining another embodiment that takes the configuration shown in FIG. 7 and copes with an increase in the number of lines due to sub-scanning magnification correction. Hereinafter, this embodiment is referred to as a corresponding method of the second example of the first embodiment. The second example mainly deals with the mechanical tolerance of the image forming unit, and FIG. 9 is a diagram showing the concept of the mechanical tolerance of the image forming unit (IOT; image output terminal).
[0136]
In this second example, “rotational speed error of each motor”, “positional accuracy to the photosensitive drum 32”, “mechanical accuracy”, “assembly accuracy”, etc., which are factors that deviate the sub-scanning magnification on the image forming unit 31 side. The various design tolerances that determine them are always in the direction of enlarging the image in order to correct this tolerance.
[0137]
In FIG. 9, for the sake of easy understanding, only the photoconductor outer circumference error of each color is given, and the others are shown in a simplified manner with a tolerance of ± 0. The photoreceptor outer periphery “a” shown here is the sub-scanning dimension of the paper, and the respective colors are on the minus side (the direction in which they are printed smaller). That is, the image forming unit 31 is installed with a mechanical tolerance so that the image distortion in the sub-scanning direction based on the resist pattern detected by the pattern detection unit 614 is detected as a reduction distortion.
[0138]
Here, if 2400 dpi,
Yellow (Y): 0.9 mm / (25.4 inches / 2400 dots) = 85.03 ≈ 85 Line,
Magenta (M): 0.6 mm / (25.4 inches / 2400 dots) = 56.69≈57 Line,
Cyan (C): 0.1 mm / (25.4 inches / 2400 dots) = 9.44≈9 Line,
Black (K): 0.8 mm / (25.4 inches / 2400 dots) = 75.59≈76 Line
It is.
[0139]
Therefore, by inserting the number of lines into each color, the absolute magnification (in the sub-scanning direction) of the image printed by the image forming unit 31 can be adjusted.
[0140]
As usual, if the design tolerance of each part is designed on the basis of “0”, reduction processing by image processing may be performed, but in the case of reduction, the signal processing is synchronized with the main scanning synchronization signal SOS cycle. Is not. In this regard, as described above, by providing a mechanical tolerance in one direction in advance so that the correction is only in the enlargement direction, processing using the line synchronization signal LS synchronized with the main scanning synchronization signal SOS can be performed. You can enjoy the merit of the configuration with the integrated circuit.
[0141]
FIG. 10 is a diagram for explaining another embodiment that takes the configuration shown in FIG. 7 and copes with an increase in the number of lines by sub-scanning magnification correction. Hereinafter, this embodiment is referred to as a corresponding method of the third example of the first embodiment. This third example is intended for the tandem apparatus shown in FIG.
[0142]
The machine controller 270 detects the color misregistration amount based on the detection result detected by the pattern detection unit 614, and the sub-scanning direction necessary to cancel out the color misregistration with respect to the sub-scanning direction of the color misregistration amount. A correction value relating to magnification (specifically, an address position where line data should be inserted / removed) is obtained for each color of K, Y, M, and C, and is set in the sub-scan correction magnification correction register 650.
[0143]
The drawing position control unit 600 (particularly a functional part related to sub-scanning magnification correction) matches the image widths of the K, Y, M, and C images based on the detection result of the shift amount by the image distortion detection unit. As described above, pixel data is inserted / removed in units of lines for each color image data of K, Y, M, and C, and the data after the insertion / removal is input to the corresponding color image forming unit 31.
[0144]
At this time, as shown in FIG. 10, for each color having a magnification error component, such as a tandem color machine, each color is given a sub-scanning magnification correction value, and other colors are always enlarged from all colors. The direction color is determined, and the difference from each color is set as a new sub-scanning magnification correction value based on that color. Thereafter, similarly to the first example, the drawing position control unit 600 outputs image data necessary for the image forming unit 31 for each color while correcting the magnification using the line buffer memory group 226. The example illustrated in FIG. 10 is a conceptual diagram in which the enlargement magnification is corrected according to each parameter for the remaining colors on the basis of black (K).
[0145]
FIG. 11 is a diagram for explaining another embodiment that takes the configuration shown in FIG. 7 and copes with an increase in the number of lines due to sub-scanning magnification correction. Hereinafter, this embodiment is referred to as a corresponding method of the fourth example of the first embodiment. This fourth example solves a problem peculiar to double-sided printing.
[0146]
For example, although it is not a mechanical tolerance, there is a front / back image position shift during double-sided printing as a similar element. In the fourth example, in order to correct the front / back image positional deviation, first, the color copying apparatus 1 relates to the image width in the sub-scanning direction on one and the other sides of the sheet as shown in FIG. A double-sided image width information acquisition unit 660 that acquires information is provided.
[0147]
The detection of the double-sided magnification error in the double-sided image width information acquisition unit 660 does not require real-time detection, and separately measures the double-sided magnification difference that may occur depending on the type of paper and the environment, and obtains a correction value based on the result Anything can be used. For example, the front and back of a sample printed out by the apparatus is read by a scanner or the like, and the image size is obtained for each front and back. The result is input to the double-sided image width information acquisition unit 660. Based on the result, sub-scan magnification correction values are obtained (each distortion is measured), and individual parameters under various conditions are measured in advance, so that information on the double-side magnification error is When apply. The double-sided image width information acquisition unit 660 sets the input information in the machine controller 270.
[0148]
The machine controller 270 determines based on the sub-scan magnification correction values 1 and 2 for each of the front and back surfaces, which front / back sub-scan magnification correction value is used so that one side is always in the enlargement direction. Then, as shown in FIG. 11B, the difference is set as an enlargement magnification correction value, and this enlargement magnification correction value is stored in the sub-scanning correction magnification correction register 650. That is, out of the image widths for each surface acquired by the double-sided image width information acquisition unit 660, the surface having the larger image width in the sub-scanning direction is used as a reference, and the surface opposite to the larger surface is used. An enlargement magnification correction value that absorbs the difference in image width from the larger surface is set in the sub-scan correction magnification correction register 650.
[0149]
For example, in a transfer method using an intermediate transfer body, the conditions do not change on the front and back of the paper up to the intermediate transfer body, but the paper on the front and back is due to shrinkage due to moisture evaporation due to heat during fixing and expansion / contraction due to roll pressure. Changes appear in dimensions. Match this with the type of paper (material / size / thickness, etc.) and the characteristics of the device (fixing conditions such as temperature and passage time), and reference the opposite side so that one side is enlarged (sub-scanning) By setting the difference to the enlargement magnification correction value, the front and back image sizes can be matched.
[0150]
As mentioned above, although an example of the control method in the structure of 1st Embodiment was demonstrated, it will become a more excellent structure if the 1st-4th example of the said 1st Embodiment is each combined and taken correspondingly.
[0151]
FIG. 12 is a block diagram showing a modification of the configuration shown in FIG. The correspondence according to this configuration is the second embodiment. The difference from the first embodiment is that the provision of the pseudo-synchronization signal generator 262 not only corrects the magnification in the “enlargement direction only” shown in the first embodiment, but also corrects the magnification in the reduction direction. In order to make this possible, we have taken action.
[0152]
In this configuration, first, the memory access control signal generation unit according to the present invention includes a pseudo synchronization signal generator 262 in addition to the timing signal generator 230. As in the first embodiment, when the timing signal generator 230 receives the print request signal PRQ from the machine controller 270, the timing signal generator 230 generates the main scanning synchronization signal SOS based on the main scanning synchronization signal SOS from the synchronization signal generator 260. A synchronized line synchronization signal LS is generated, and a page synchronization signal Page that is a page-by-page write control signal is generated. The timing signal generator 230 inputs a line synchronization signal LS synchronized with the main scanning synchronization signal SOS to the memory controller 228 and inputs a page synchronization signal Page to the I / F unit 222. As in the first embodiment, the line synchronization signal LS functions as a memory read control signal for reading image data from the line buffer memory group 226.
[0153]
On the other hand, the newly provided pseudo synchronization signal generator 262 reduces the amount of image distortion detected by the machine controller 270 under the control signal CNT from the machine controller 270 functioning as an image distortion detection unit according to the present invention. A pseudo main scanning synchronization signal SOS1 having a possible period and different from the main scanning synchronization signal SOS generated by the synchronization signal generator 260 is generated.
[0154]
Specifically, the pseudo synchronization signal generator 262 sets the magnification correction value obtained by the machine controller 270 separately from the main scanning synchronization signal SOS detected by the photodetector 392 from the polygon mirror 39 that scans the light beam. Accordingly, a counter (not shown) for generating the pseudo main scanning synchronization signal SOS1 is provided. The pseudo synchronization signal generator 262 sets, for example, a standard main scanning cycle known in advance as a design value to 100% of the cycle of the pseudo main scanning synchronization signal SOS1. Then, the pseudo synchronization signal generator 262 has a pseudo main signal so as to have a period capable of canceling the image distortion based on the image distortion correction value (sub scanning magnification correction ratio) obtained in advance by the machine controller 270. Set the scan synchronization signal SOS1. That is, the period of the pseudo main scanning synchronization signal SOS1 is adjusted according to the correction value for correcting the image distortion.
[0155]
Based on the pseudo main scanning synchronization signal SOS1 from the pseudo synchronization signal generator 262, the pseudo line synchronization signal generation unit 232 in the timing signal generator 230 generates a pseudo line synchronization signal LS1 synchronized with the pseudo main scanning synchronization signal SOS1. Generate. That is, the pseudo line synchronization signal generation unit 232 corrects a standard main scanning period (a pseudo main scanning synchronization signal SOS1 having a period of 100%) that is known in advance as a design value and image distortion that is obtained in advance by the machine controller 270. Based on the value (sub-scanning magnification correction ratio), the pseudo line synchronization signal LS1 having a period capable of canceling the image distortion is generated as the memory write control signal.
[0156]
This pseudo line synchronization signal LS1 functions as a memory write control signal, and it does not matter whether it is synchronous or asynchronous with respect to the main scanning synchronization signal SOS. The pseudo line synchronization signal generation unit 232 in the timing signal generator 230 inputs the generated pseudo line synchronization signal LS 1 to the memory controller 228 and the I / F unit 222.
[0157]
In response to a control start signal from the machine controller 270, the I / F unit 222 is based on a signal from the synchronization signal generator 260 and generates a page synchronization signal Page and pseudo line synchronization signal generation unit 232 generated by the timing signal generator 230. Is output to the image data generation unit 200, and image data in units of lines (one main scanning unit) is requested.
[0158]
The color copying apparatus 1 is controlled based on the pseudo main scanning synchronization signal SOS1 from the pseudo synchronization signal generator 262, thereby correcting the enlargement / reduction sub-scanning magnification. In other words, the memory access is different from the first embodiment in that the memory write control signal is generated separately from the main scanning synchronization signal SOS, not the line synchronization signal LS having the same period as the main scanning synchronization signal SOS. The pseudo line synchronization signal LS1 is used that is synchronized with the pseudo main scanning synchronization signal SOS1 and has the same period.
[0159]
When the memory is controlled based on the line synchronization signal LS based on the main scanning synchronization signal SOS, which is a conventional technique, as described in the section of the prior art, it is originally output by deleting the line data by image data processing. In order to compensate for the thinned lines of power data, the line synchronization signal LS must be output (requested) to the image data processing device at a timing other than the original main scanning synchronization signal SOS cycle. However, it is very difficult on the circuit to generate the line synchronization signal LS at a timing other than the reference main scanning synchronization signal SOS cycle, and even if it is realized, an increase in circuit scale cannot be avoided. Further, the time required for verifying the function of such a circuit becomes enormous.
[0160]
On the other hand, when data writing to the line buffer memory group 226 is controlled using the pseudo line synchronization signal LS1 that is synchronized with the pseudo main scanning synchronization signal SOS1 generated separately from the main scanning synchronization signal SOS and has the same cycle. In either case of enlargement correction and reduction correction, appropriate data can be reliably output from the line buffer memory group 226 without causing overflow or underflow in the line buffer memory group 226. In addition, the image data from the image data generation unit 200 is not lost during enlargement. As a result, an appropriate enlarged image is formed by the image forming unit 31. Hereinafter, this point will be described with reference to the drawings.
[0161]
FIG. 13 is a diagram for explaining an embodiment in which the configuration shown in FIG. 12 is taken and the increase / decrease in the number of lines due to sub-scanning magnification correction is taken. FIG. 13 shows the concept of the pseudo main scanning synchronization signal SOS1 based on the sub-scanning magnification correction value. In the figure, for ease of explanation, an example in which three lines are provided as a buffer portion is shown.
[0162]
The color copying apparatus 1 uses the pseudo line synchronization signal generation unit 232 based on the pseudo main scanning synchronization signal SOS1 ± set by the pseudo synchronization signal generator 262 under the control of the machine controller 270 before starting the printing operation. A pseudo line synchronization signal LS1 is generated. Then, for example, the pseudo line synchronization signal LS1 is made to move completely asynchronous with the main scanning synchronization signal SOS cycle that is originally detected based on the photodetector 392, and the output to the VCSEL light source group 380 and the image data generation unit 200 , More specifically, the ratio of line image data request to the image data generation unit 200 is changed.
[0163]
Explaining based on the conceptual diagram shown in FIG. 13, the main scanning synchronization signal SOS cycle, which is determined in advance as the specification of the apparatus or the driving mode, is set to 100%, and the pseudo main scanning corresponding to the ratio of magnification correction with respect to this. Synchronization signal SOS1 is set. Here, as an example, a 99% period is set for reduction, and a 101% period is set for enlargement. The pseudo main scanning synchronization signal SOS1 and the main scanning synchronization signal SOS at the time of 100% are assumed to have substantially the same cycle.
[0164]
In the case of 99% reduction, the cycle of the pseudo line synchronization signal LS1 is shortened by the amount corresponding to the shortening of the cycle of the pseudo main scanning synchronization signal SOS1, and the data writing to the line buffer memory group 226 is accelerated. Then, the 100th line of writing based on the pseudo line synchronization signal LS1 and the reading of the 99th line based on the line synchronization signal LS are substantially at the same time, and the pseudo line before the completion of reading of the 99th line is completed. Writing of the 101st line based on the synchronization signal LS1 has started.
[0165]
Therefore, the next reading based on the line synchronization signal LS is not the data on the 100th line but the data on the 101st line, so the data on the 100th line is thinned out. Further, the same thing occurs after 100 lines have elapsed, and data on the 200th line is thinned out. As a result, line data is thinned out every 100 lines, and reduction correction is realized.
[0166]
On the other hand, in the case of 101% enlargement, the cycle of the pseudo line synchronization signal LS1 is increased by the amount of the cycle of the pseudo main scanning synchronization signal SOS1, and the data writing to the line buffer memory group 226 is delayed. Then, the write completion of the 100th line based on the pseudo line synchronization signal LS1 and the read completion of the 100th line based on the line synchronization signal LS are substantially the same time, and at the time of reading the next 101st line, Writing has not started yet. For this reason, reading from the line buffer memory group 226 is impossible.
[0167]
Therefore, during this period, the memory controller 228 reads data from the additional line buffer memory 229 based on the line synchronization signal LS and passes it to the image forming unit 31 side. Then, when the reading from the additional line buffer memory 229 is completed, the writing of the data on the 101st line has already started, so the memory controller 228 returns to the original state and reads out from the line buffer memory group 226. Switch.
[0168]
That is, in the reading process based on the line synchronization signal LS, when the line data becomes insufficient in the line buffer memory group 226, the data for one line is simply switched to reading from the additional line buffer memory 229 (in the previous example, the first data (Between the 100th line and the 101st line). Further, the same thing occurs after 100 lines have elapsed, and line data is inserted between the 200th line and the 201st line. As a result, line data is inserted every 100 lines, and enlargement correction is realized.
[0169]
As described above, the writing system and the reading system shown in the prior art are controlled based on the main scanning synchronization signal SOS cycle, and the writing system is changed to the pseudo main scanning synchronization signal as in the configuration of the second embodiment. By switching to the control based on SOS1, it is possible to reliably output appropriate data from the line buffer memory group 226 without causing overflow or underflow in the line buffer memory group 226 in both cases of enlargement correction and reduction correction. Can be made. Further, since the basic concept of the circuit configuration is the same between the conventional configuration and the configuration of the second embodiment, the circuit can be easily changed.
[0170]
In the second embodiment, in setting the pseudo line synchronization signal LS1 having a period necessary for correcting image distortion, the pseudo main scanning synchronization signal SOS1 is once set separately from the main scanning synchronization signal SOS. However, this is because the circuit configuration in which the line signal LS is generated based on the conventional main scanning synchronization SOS signal is used as it is, and thus there is a great advantage that the circuit scale does not have to be increased so much. Based on the reason. In other words, since the synchronization signal generator 260 is a circuit that creates a line signal based on a signal of a certain period, this circuit is used as it is, and the basic concept of a conventional circuit is simply changed by changing the periodic signal input thereto. Same and easy to change.
[0171]
As can be inferred from this, if attention is paid only to setting the pseudo line synchronization signal LS1 having a period necessary for correcting image distortion, it is set separately from the main scanning synchronization signal SOS. It is not essential to generate the pseudo line synchronization signal LS1 using the pseudo main scanning synchronization signal SOS1. However, due to the circumstances as described above, in the second embodiment, first, the pseudo main scanning synchronization signal SOS1 is generated, and the pseudo line synchronization signal LS1 is set with reference to the pseudo main scanning synchronization signal SOS1. . The same applies to modified embodiments described later.
[0172]
If the conventional basic circuit concept (conventional circuit) is not inherited, it is not essential to first generate the pseudo main scanning synchronization signal SOS1. For example, the synchronization signal generator 260 is provided with a period counter register, and the pseudo line The synchronization signal LS1 may be directly generated. That is, it is sufficient if the period width of the pseudo line synchronization signal LS1 is substantially counted by a predetermined reference clock. Therefore, in this specification, “the main scanning period detection unit that measures the main scanning period width by counting with a predetermined reference clock” means “substantially counts the periodic width of the pseudo-line synchronization signal with a predetermined reference clock”. "To do".
[0173]
FIG. 14 is a diagram showing a modification of the configuration shown in FIG. Hereinafter, this modification is referred to as a corresponding method of the second example of the second embodiment. On the other hand, the above-described embodiment (including its micro deformation) is referred to as a corresponding method of the first example of the second embodiment.
[0174]
In the first example (basic configuration) of the second embodiment shown in FIG. 12, a standard main scanning cycle that is known in advance as a design value is set as an example of a method for setting the pseudo main scanning synchronization signal SOS1. . On the other hand, in the second example (modified example), the period width of the actual main scanning synchronization signal SOS detected based on the photodetector 392 is measured by counting with a predetermined reference clock. The period width of the pseudo main scanning synchronization signal SOS1 is set based on the measurement result.
[0175]
For example, as shown in FIG. 14, the pseudo synchronization signal generator 262 receives the main scanning synchronization signal SOS output from the synchronization signal generator 260 and converts the period width of the main scanning synchronization signal SOS to the timing signal generator 230. Is provided with a counter 263 that counts with a pixel clock PCK (for example, 50 to 100 MHz) input from. The counter 263 functions as a memory read control signal cycle detector according to the present invention.
[0176]
The counter 263 may be any counter as long as it effectively counts the period width of the line synchronization signal LS for reading synchronized with the main scanning synchronization signal SOS, and is not limited to the main scanning period itself. You may count the period width of the other signal corresponding to the period width of LS. Naturally, the counter 263 may count the period width of the read line synchronization signal LS itself with the pixel clock PCK instead of the main scanning synchronization signal SOS. In this specification, “substantially count the cycle width of the memory read control signal with a predetermined reference clock” means that the cycle width of the read line synchronization signal LS synchronized with the main scanning synchronization signal SOS is a predetermined reference. This means that it is actually counted by the clock, and as long as it is not limited to counting the period width of the line synchronization signal LS for reading.
[0177]
The pseudo synchronization signal generator 262 sets the number of clocks indicating the period width of the main scanning counted by the counter 263 functioning as the main scanning period detection unit to 100% of the period of the pseudo main scanning synchronization signal SOS1. In this case, it is preferable to increase the accuracy of the counted value by taking an average value of those counted a plurality of times. Next, the pseudo synchronization signal generator 262 is based on the image distortion correction value (sub-scan magnification correction ratio) obtained by the machine controller 270 under the control signal CNT from the timing signal generator 230. The pseudo main scanning synchronization signal SOS1 is set so as to have a period capable of canceling the image distortion.
[0178]
The pseudo line synchronization signal generation unit 232 generates a pseudo line synchronization signal LS1 synchronized with the pseudo main scanning synchronization signal SOS1 based on the pseudo main scanning synchronization signal SOS1 from the pseudo synchronization signal generator 262. That is, the pseudo line synchronization signal generation unit 232 corrects the actual main scanning period (the pseudo main scanning synchronization signal SOS1 having a 100% period) counted by the pixel clock PCK and the image distortion obtained in advance by the machine controller 270. Based on the value (sub-scanning magnification correction ratio), the pseudo line synchronization signal LS1 having a period capable of canceling the image distortion is generated as the memory write control signal.
[0179]
As a result, the machine difference of the pseudo main scanning synchronization signal SOS1 generated by the pseudo synchronization signal generator 262 is corrected, and the pseudo main scanning synchronization signal based on the ratio of magnification correction with respect to a more accurate main scanning period. SOS1 can be set. As a result, the pseudo-line synchronization signal LS1 is also corrected for machine differences, and a more accurate scaling process can be realized. For example, in the example shown in FIG. 13, in the case of 99% reduction, the line data is naturally thinned out every 100 lines to realize reduction correction, and in the case of 101% enlargement, the line data is naturally drawn every 100 lines. It has been explained that enlargement correction is realized by inserting data. However, if the main scanning period of the design value is different from the actual main scanning period, it is not accurately connected, and overflow or underflow may occur in a long span. On the other hand, as in this modification, the frequency of occurrence of overflow or underflow can be reduced by generating the pseudo main scanning synchronization signal SOS1 adapted to the actual machine.
[0180]
Even when the main scanning cycle is counted with a predetermined reference clock and the pseudo main scanning synchronization signal SOS1 corresponding to the actual machine is generated, it cannot be said that overflow and underflow can be completely prevented. In particular, in the case of a configuration with a small number of line buffer memories, the possibility increases.
[0181]
Therefore, regardless of whether or not the main scanning period is counted with a predetermined reference clock, when control with a smaller capacity of the line buffer memory is considered, the configuration of the second embodiment also differs from that of the first embodiment. Similarly, as a more detailed control of the so-called line buffer that cannot be compensated only by changing the ratio, it is better to monitor the free capacity of the line buffer and use it together with the stop and release of the pseudo line synchronization signal LS1. become.
[0182]
Actually, such control has an effect only in the case of reduction correction. As estimated from FIG. 13, at the time of enlargement correction, data for the next line is written in the memory (line buffer memory group 226) while the line is inserted using the additional line buffer memory 229. This is because if the pseudo-line synchronization signal LS1 is stopped, the next line data after the line insertion is insufficient, so that it is practically impossible to apply it during enlargement correction. That is, the effect of stopping the pseudo line synchronization signal LS1 is limited to suppressing excessive writing and excessive thinning of image data to the memory.
[0183]
In addition, as an active usage mode (referred to as a modified example of the third example) in which the pseudo line synchronization signal LS1 is stopped or released together, the pseudo synchronization signal generator 262 performs the main scanning measured by the counter 263. The pseudo main scanning synchronization signal SOS1 having a cycle shorter than the cycle width may be set. That is, the pseudo main scanning cycle is shorter than the detected main scanning synchronization signal SOS cycle. As a result, the subsequent line data is accumulated in the buffer memory earlier than the output line data, and the pseudo line synchronization signal LS1 is stopped and released in combination with the free capacity of the line buffer, thereby further improving the system. become.
[0184]
That is, in this control, a pseudo main scanning period shorter than the detected main scanning period is set, so that the input line data is always sent at a short interval with respect to the output line data. For this reason, the buffer memory (in this example, the FIFO memory group 226) is always kept in a pre-full state by stopping or canceling the pseudo-line synchronization signal LS1, and when the line data has been output, the data is stored with a margin. Can be replenished.
[0185]
The reading system is the same as the conventional apparatus in that data is always sent to the image forming unit side in synchronization with the main scanning synchronization signal SOS. At this time, whether to read data from the FIFO memory group 226 or the additional line buffer memory 229 is realized by switching a read address (including a read line) according to a circuit configuration, a place to be enlarged, and the like. . This is also the same as the conventional device.
[0186]
FIG. 15 is a diagram for explaining another embodiment that takes the configuration shown in FIG. 12 and copes with increase / decrease in the number of lines by sub-scanning magnification correction. Hereinafter, this embodiment is referred to as a corresponding method of the third example of the second embodiment. FIG. 15 is a diagram showing the concept of the pseudo main scanning synchronization signal SOS1 in the third example.
[0187]
The third example of the second embodiment is not the pseudo main scanning synchronization signal SOS1 that is asynchronous with respect to the main scanning synchronization signal SOS period detected as in the first example, but a plurality of main scanning periods (n The pseudo main scanning synchronization signal SOS1 is synchronized m times every time. As a result, the pseudo line synchronization signal generation unit 232 generates the pseudo line synchronization signal LS1 such that m times of the pseudo line synchronization signal LS1 is synchronized with n times of the main scanning period.
[0188]
Referring to FIG. 15, the pseudo main scanning synchronization signal SOS1 is determined by register setting of how many times the pseudo main scanning synchronization signal SOS1 is set for 100 main scanning periods of the image forming unit 31. In this case, if the pseudo main scanning synchronization signal SOS1 is 101 times during the main scanning period of 100 times, the setting is made to quickly compensate for the shortage of input line data when lines are thinned out, and is effective at the time of reduction. It becomes. Further, when the pseudo main scanning synchronization signal SOS1 is 99 times, the setting is made when a line is inserted and the buffer memory cannot be emptied, and becomes effective at the time of enlargement.
[0189]
FIG. 16 is a diagram for explaining another embodiment that takes the configuration shown in FIG. 12 and copes with increase / decrease in the number of lines by sub-scanning magnification correction. Hereinafter, this embodiment is referred to as a corresponding method of the fourth example of the second embodiment. FIG. 16A shows the concept of the pseudo main scanning synchronization signal SOS1 based on the sub-scanning magnification correction value.
[0190]
In this fourth example, the pseudo synchronization signal generator 262 is based on a magnification correction value for correcting image distortion obtained in advance by the machine controller 270, and a main scanning period in the vicinity of a portion where image distortion is reduced. The main scanning period except for the vicinity of the portion having a period different from the main scanning period width measured by the counter 263 functioning as the main scanning period detection unit and reducing the image distortion is measured by the counter 263. A line synchronization signal LS having the same cycle as the scanning cycle width is generated as a memory write control signal. As in the modification of the third example, the pseudo synchronization signal generator 262 uses the main scan measured by the counter 263 as an active usage mode in combination with the stop and release of the pseudo line synchronization signal LS1. Is set to a pseudo main scanning synchronization signal SOS1 having a period shorter than the period width (not related to the enlargement / reduction ratio).
[0191]
For example, as shown in FIG. 16B, the pseudo synchronization signal generator 262 generates the pseudo main scanning synchronization signal SOS1 in the pseudo main scanning synchronization signal generation unit 262a, and the generated pseudo main scanning synchronization signal SOS1. The main scanning synchronization signal SOS may be switched and output according to whether or not it is in the vicinity of the line increase / decrease point by the switching SW 262b, and this output may be used as the pseudo main scanning synchronization signal SOS1 that is actually used. Of course, it may be configured without providing such a switch SW262b.
[0192]
This fourth example is a pseudo line synchronization signal in which the number of lines after correction (after insertion or thinning) is set in the pseudo SOS synchronization counter in the vicinity of the line inserted or thinned by actual sub-scan magnification correction. The other portions that are not used for insertion or thinning are made pseudo-line synchronization signals having the same period as the detected main scanning synchronization SOS signal.
[0193]
According to this configuration / method, only the portion that requires line increase / decrease changes the number of pseudo line synchronization signals LS1 functioning as a write control signal, so that one page is read by the main scanning synchronization signal SOS. The required number of line data per hour will match.
[0194]
Since the location where distortion is corrected differs depending on the apparatus, even if there is no insertion or thinning point evenly (at a fixed interval) with respect to the paper size, the line increase / decrease point recognized by the machine controller 270 itself (its set value is a secondary value). It is meaningful to change the pseudo SOS synchronization counter value in accordance with (registered in the scanning correction magnification correction register 650).
[0195]
For example, as shown in the conceptual diagram of FIG. 16A, the pseudo main scanning synchronization signal SOS1 is set to 10 cycles other than the line increase / decrease point, which is the same as 10 detected main scanning cycles. It shall have a cycle of ± 1 time for 10 times. Alternatively, the same relationship as shown in FIG. 15, that is, the cycle other than the line increase / decrease point is set to 100 times the same as the detected main scanning cycle 100 times, and the line increase / decrease point has a cycle of ± 1 for this 100 times. It may be included. Here, at the line increase / decrease point, the period is set to ± 1 time with respect to 10 times of the main scanning period in order to realize magnification correction with small image distortion by performing magnification correction for each line. When correcting a plurality of (= n) lines at once, it is assumed that there are ± n cycles for 10 main scanning cycles.
[0196]
As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various modifications or improvements can be added to the above-described embodiment, and forms obtained by adding such modifications or improvements are also included in the technical scope of the present invention. Moreover, said embodiment does not limit the invention concerning a claim, and all the combinations of the characteristics demonstrated in embodiment are not necessarily essential for the solution means of invention.
[0197]
For example, in the above embodiment, the memory controller 228 and the I / F unit 222 cooperate with each other based on the line synchronization signal LS and the pseudo line synchronization signal LS1 while monitoring the free address of the line buffer memory group 226. The configuration is such that data writing to and reading from the line buffer memory group 226 is controlled. However, the configuration is not limited to this configuration, and any member that manages access (write / read) to the memory may be used.
[0198]
In the above-described embodiment, correction of magnification error in the sub-scanning direction in a mechanism for preventing a phenomenon that appears as color misregistration in a color image forming apparatus having a tandem configuration has been described. However, the embodiment can be applied to a configuration other than a tandem configuration. . For example, in the case of providing a mechanism for correcting the image position in the sub-scanning direction in order to correct the shift of the drawing position in the sub-scanning direction with respect to the absolute reference, if the above embodiment is applied, the same effective image range / position is always used. An image can be formed. Of course, the present invention can be applied not only to a color device but also to a monochrome (single color printing) device.
[0199]
In the above embodiment, as a multi-beam light source, an example in which a VCSEL arranged in a two-dimensional matrix of 8 × 4 is vertically arranged with respect to a polygon mirror (in the sub-scanning direction) is used. However, the present invention is not limited to this. For example, a VCSEL semiconductor such as a vertical arrangement of 4 × 4 horizontal, 8 × 8 horizontal, 2 × 8 × 2 horizontal, or 8 × 4 horizontal, etc. The arrangement form on the substrate and the arrangement form in the sub-scanning direction are free.
[0200]
In the above embodiment, a polygon mirror (rotating polygonal mirror) is used as the deflecting device. However, any other device that can periodically deflect the direction of light, such as a galvano mirror or a hologram disk, is equivalent to the above example. Has an effect. Further, in the configuration of the optical system, the collimator lens, the scanning lens, and the tilt correction optical system are not essential, and the presence or absence thereof does not affect the above-described effect.
[0201]
Further, the present invention is not limited to a case where VCSELs are arranged in a two-dimensional matrix, and can be applied to a case where a large number of VCSELs are arranged in one line (in-line). In this case, since the required number of VCSELs are arranged and driven simultaneously in the main scanning direction, it is needless to say that a polygon mirror (rotating polygonal mirror which is a functional part that scans the beam light in the main scanning direction is not required.
[0202]
In the above-described embodiment, the VCSEL is disposed at the light emitting point. However, the present invention is not limited to the VCSEL, and the effect of the above-described embodiment is not limited to the arrangement of an edge-emitting laser array or LED. When an LED is used as a light source, it is preferable to change a control signal for memory access or the like based on a recording start signal related to LED scanning instead of the main scanning synchronization signal SOS as necessary.
[0203]
In the case of a two-dimensional array of light sources arranged with a VCSEL, a monolithic structure in which light emitting units are arranged two-dimensionally on one semiconductor chip can be used. Further, in the VCSEL, since the cross-sectional area of the laser beam emitting portion can be made larger than that of a conventional edge-emitting semiconductor laser, the spread angle of the laser beam is reduced.
[0204]
Furthermore, the present invention can be applied not only to printing apparatuses such as printers and copiers, but also to facsimiles and displays, for example.
[0205]
【The invention's effect】
As described above, according to the present invention, as a first method, the writing and reading to the image memory are controlled based on the memory writing control signal and the memory reading control signal while monitoring the empty address of the image memory. On the other hand, if there is no space for writing in the image memory when processing for expanding the image width is performed, writing and reading of image data to the image memory is prohibited, and a predetermined amount of pixel data for enlargement prepared in advance is prohibited. Input to the image forming unit.
[0206]
As a result, when data is inserted during enlargement processing, access based on the memory write control signal and memory read control signal for the image memory can be prohibited, and image data can be transferred to the output stage at a constant transfer speed during enlargement processing. Can prevent the loss of line data due to lack of line data or overwriting to the line buffer memory, and overflow or underflow does not occur in the image memory.
[0207]
In the second method, the readout system is controlled by a memory readout control signal synchronized with the main scanning synchronization signal, while the writing system is controlled based on a pseudo main scanning synchronization signal generated separately from the main scanning synchronization signal. A memory write control signal (pseudo line synchronization signal LS1 in the embodiment) is generated, and write access is controlled under the pseudo memory write control signal.
[0208]
Thus, by setting the period of the pseudo main scanning synchronization signal so that the image distortion can be corrected, the pseudo memory write control signal also has a period capable of correcting the image distortion. In both processing and enlargement processing, even if image data is output to the output stage at a constant transfer speed, overflow and underflow do not occur in the image memory.
[Brief description of the drawings]
FIG. 1 is a mechanism diagram of an example of a color copying apparatus equipped with an image recording apparatus that records an image using a surface emitting semiconductor laser array.
FIG. 2 is a diagram illustrating a configuration example of an image forming unit.
FIG. 3 is a diagram illustrating a relationship between a scanning line and an imaging spot on a surface to be scanned by a laser beam emitted from an 8 × 4 array / vertical VCSEL light source group;
FIG. 4 is a diagram illustrating an outline of a first example of a signal processing circuit for forming an image in an image forming unit including a VCSEL light source group.
FIG. 5 is a diagram illustrating a correspondence relationship between halftone data generated by an image data generation unit and a laser modulation signal generated by a modulation signal generation unit;
FIG. 6 is a diagram illustrating a mechanism for detecting a drawing position shift.
FIG. 7 is a block diagram showing a first embodiment of the configuration of the periphery of the memory controller.
FIG. 8 is a timing chart for explaining an embodiment corresponding to an increase in the number of lines by sub-scanning magnification correction while adopting the configuration of the first embodiment.
FIG. 9 is a diagram for explaining another embodiment (mechanical tolerance) that takes a configuration corresponding to an increase in the number of lines by sub-scanning magnification correction while adopting the configuration of the first embodiment.
FIG. 10 is a diagram for explaining another embodiment (tandem method) that takes a configuration corresponding to an increase in the number of lines by sub-scanning magnification correction while adopting the configuration of the first embodiment.
FIG. 11 is a diagram for explaining another embodiment (double-side magnification difference) that takes the configuration of the first embodiment and copes with an increase in the number of lines by sub-scan magnification correction.
FIG. 12 is a block diagram showing a modification (second embodiment) of the configuration of the first embodiment.
FIG. 13 is a diagram for explaining an embodiment that takes the configuration of the second embodiment and copes with increase / decrease in the number of lines by sub-scanning magnification correction.
FIG. 14 is a diagram showing a modification of the configuration of the second embodiment.
FIG. 15 is a diagram for explaining another embodiment that takes the configuration of the second embodiment and copes with the increase / decrease in the number of lines by sub-scanning magnification correction.
FIG. 16 is a diagram for explaining another embodiment that takes the configuration of the second embodiment and copes with increase / decrease of the number of lines by sub-scanning magnification correction.
FIG. 17 is a functional block diagram of the configuration proposed in Japanese Utility Model Laid-Open No. 63-170819.
FIG. 18 is a timing chart of the configuration proposed in Japanese Utility Model Laid-Open No. 63-170819.
FIG. 19 is a diagram for explaining a shortage of line data due to line thinning during reduction.
FIG. 20 is a diagram for explaining line data loss due to line insertion at the time of enlargement;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Color copying apparatus, 10 ... Image acquisition part, 11 ... Platen glass, 12 ... Light source, 13 ... Light-receiving part, 20 ... Image processing part, 30 ... Image output part, 31 ... Image formation part, 32 ... Photosensitive drum, 38 ... Semiconductor laser, 39 ... Polygon mirror, 200 ... Image data generation unit, 220 ... Write signal generation unit, 222 ... I / F unit, 224 ... Modulation signal generation unit, 226 ... Line buffer memory group, 228 ... Memory controller , 230 ... Timing signal generator, 232 ... Pseudo line synchronization signal generator, 240 ... Delay adjuster, 260 ... Synchronization signal generator, 262 ... Pseudo synchronization signal generator, 270 ... Machine controller, 300 ... Laser drive circuit, 304 ... light quantity setting condition selection unit, 306 ... level change unit, 308 ... drive amount control unit, 310 ... drive control unit, 380 ... VCSEL light source group, 380 ... VCSEL, 392 ... photodetector, 600 ... drawing position controller, 613 ... color shift correction unit, 614 ... pattern detection unit, 621 ... resist pattern generation unit, 650 ... subscanning correction magnification correction register

Claims (10)

An image forming unit that forms an image by scanning a scanned object with a light beam whose light intensity is modulated based on image data, and an image in the sub-scanning direction that can be generated when the image forming unit forms the image an image distortion detection unit, wherein the includes a sub-scanning direction substantially perpendicular to the main scanning direction of the line data writing or readable image memory, based on the image distortion detected by the image distortion detection unit line for detecting the strain data insertion City, an image forming apparatus and a subscanning magnification correction unit for correcting the sub scanning direction of the image width by inputting the data after entering this interpolation to the image forming section,
The sub-scanning magnification correction unit
A main scanning synchronization signal detecting unit indicating a main scanning reference in the image forming unit, and a memory writing control signal and a memory reading control signal synchronized with the main scanning synchronizing signal detected by the main scanning synchronization signal detecting unit are generated. And a memory access control signal generation unit
Based on the presence or absence of free of said image memory, said memory write control signals to control the writing to the image memory line data based on, and the memory read control signal line data written in the image memory based on Control the reading of
When performing processing for enlarging the image width in the sub-scanning direction to reduce the amount of image distortion detected by the image distortion detection unit, when there is no space for writing in the image memory, a line for the image memory is used. An image forming apparatus characterized in that writing of data is prohibited and line data for enlargement prepared in advance is input to the image forming unit.   The image forming apparatus according to claim 1, wherein the image memory includes a FIFO memory that handles pixel data in a first-in first-out manner. A double-sided printing mechanism that reverses the recording sheet on which the image is transferred and fixed on one surface via the scanned body so that the image forming surface becomes the other surface and then carries the recording sheet into the image forming unit When,
A double-sided image width information acquisition unit that acquires information about the image width in the sub-scanning direction of each of the one side and the other side;
The sub-scanning magnification correction unit uses the larger one of the image widths of the surfaces acquired by the double-sided image width information acquisition unit as a reference and the larger image width in the sub-scanning direction. 2. The process according to claim 1, wherein a process of enlarging the image width in the sub-scanning direction is performed on a surface opposite to the surface so as to absorb a difference in image width with the larger surface. The image forming apparatus described. The image forming unit includes a plurality of color printing units arranged in a line, which forms a plurality of color images based on a plurality of image data divided for each color,
The image distortion detection unit detects a shift amount of an image width in the sub-scanning direction of the images of the plurality of colors.
The sub-scanning magnification correction unit performs line data for each of the plurality of color image data so that the image widths of the plurality of color images match based on the detection result of the shift amount by the image distortion detection unit. the insert city, the image forming apparatus according to claim 1, characterized in that inputting the data after entering this inserted into the printing unit of the corresponding color. The image distortion detection unit detects the image distortion in the sub-scanning direction, which may occur when the image of each color is formed by the print unit for each of the plurality of colors, to thereby detect the plurality of the plurality of colors. It detects the amount of deviation of the image width in the sub-scanning direction of the color image,
The sub-scanning magnification correction unit is based on one color having a large image width in the sub-scanning direction among the image distortions for the colors detected by the image distortion detection unit, and for the other color, The image forming apparatus according to claim 4 , wherein a process of enlarging the image width in the sub-scanning direction is performed so as to absorb a difference in image width from the one color. An image forming unit that forms an image by scanning a scanned object with a light beam whose light intensity is modulated based on image data, and an image in the sub-scanning direction that can be generated when the image forming unit forms the image An image distortion detection unit for detecting distortion; and an image memory capable of writing or reading line data in the main scanning direction substantially orthogonal to the sub-scanning direction, and based on the image distortion detected by the image distortion detection unit An image forming apparatus comprising a sub-scanning magnification correction unit that corrects an image width in the sub-scanning direction by inserting and removing line data and inputting the data after the insertion and removal to the image forming unit,
The sub-scanning magnification correction unit
A main scanning synchronization signal detection unit indicating a main scanning reference in the image forming unit; and a memory read control signal synchronized with the main scanning synchronization signal detected by the main scanning synchronization signal detection unit; A memory access control signal generation unit that generates a memory write control signal having a period capable of reducing the image distortion based on the image distortion detected by the detection unit, and
Before SL based on the memory write control signal generated by the memory access control signal generating unit, writes the input line data in the image memory, and the memory read control generated by the memory access control signal generating unit An image forming apparatus that reads line data written in the image memory based on a signal. The memory access control signal generation unit generates the memory write control signal based on a predetermined cycle width of the memory read control signal and the image distortion detected by the image distortion detection unit. The image forming apparatus according to claim 6 . Comprising a memory read control signal period detector for measuring by counting the period width before Symbol memory read control signal at a predetermined reference clock,
The memory access control signal generation unit is based on the number of clocks indicating the cycle width of the memory read control signal counted by the memory read control signal cycle detection unit and the image distortion detected by the image distortion detection unit. The image forming apparatus according to claim 6 , wherein the memory write control signal is generated. An image forming unit that forms an image by scanning a scanned object with a light beam whose light intensity is modulated based on image data, and an image in the sub-scanning direction that can be generated when the image forming unit forms the image An image distortion detection unit for detecting distortion; and an image memory capable of writing or reading line data in the main scanning direction substantially orthogonal to the sub-scanning direction, and based on the image distortion detected by the image distortion detection unit An image forming apparatus comprising a sub-scanning magnification correction unit that corrects an image width in the sub-scanning direction by inserting and removing line data and inputting the data after the insertion and removal to the image forming unit,
The sub-scanning magnification correction unit
A main scanning synchronization signal detecting unit indicating a main scanning reference in the image forming unit;
A memory access control signal generator for generating a memory read control signal synchronized with the main scan synchronization signal detected by the main scan synchronization signal detector;
; And a memory read control signal period detector for measuring by counting the period width before Symbol memory read control signal at a predetermined reference clock,
The memory access control signal generation unit has a cycle of m times (m is a positive number) with respect to a cycle of n times (n is a positive integer) of the memory read control signal detected by the memory read control signal cycle detection unit. An image forming apparatus that generates a memory write control signal having a predetermined cycle such that an integer). The memory access control signal generation unit has a period different from a period width of the memory read control signal measured by the memory read control signal period detection unit for a main scanning period of a portion where line increase / decrease is required , Generating the memory write control signal having the same period as the period width of the memory read control signal measured by the memory read control signal period detection unit for a write period excluding the vicinity of a portion that reduces image distortion; The image forming apparatus according to claim 9 .

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