JP5622817B2 - Image forming apparatus - Google Patents

Description

  Embodiments described herein relate generally to an image forming apparatus.

  In an image forming apparatus using an electrophotographic process using a laser optical system, Y (yellow / yellow), M (magenta / bright red), and C (cyan / blue purple) are applied by an LSU (Laser Scanning Unit / Laser Scan Unit / Exposure Device). ), Image light corresponding to four color image data of K (black / black) is scanned by a polygon, and scanning of a plurality of lines is repeated in a direction orthogonal to the scanning direction to form an image of a predetermined size. To do.

  In order to reduce the size of the LSU, an LSU (double swing LSU) using two lens systems divided into two colors is used at a point-symmetrical position with respect to the polygon.

JP-A-5-83485

  The number of pixels per line scanned by the above-mentioned LSU is, for example, about 7500 pixels in the long side direction of A4 size, and 7500 bytes / line × 3 times per color when having 8 bit density data per pixel Memory capacity is required.

  On the other hand, in recent years, cost reduction and low power consumption have become increasingly important, and it is indispensable to reduce the memory capacity mounted on an ASIC (Application Specific IC).

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of reducing costs and reducing power consumption.

  In the embodiment, an image forming apparatus including a laser exposure apparatus in which a laser scanning system for two colors is positioned on both sides around a polygon includes a beam detection unit and an exposure unit. The beam detecting means detects the incidence of laser light in each of the laser scanning systems for two colors. The exposure means uses the second beam detection signal that precedes the first beam detection signal as the main scanning reference signal of the image processing circuit as a reference for the beam detection signal detected by the beam detection means. Light is intensity-modulated with an image signal.

1 illustrates an example of an image forming apparatus according to an embodiment. 1 shows an example of an exposure apparatus included in an image forming apparatus according to an embodiment. 2 shows an example of exposure order and memory use in the image forming apparatus of the embodiment. 2 shows an example of exposure order and memory use in the image forming apparatus of the embodiment. 1 illustrates an example of an image exposure apparatus (laser exposure circuit) in an image forming apparatus according to an embodiment. 2 shows an example of image exposure (exposure timing) in the image forming apparatus of the embodiment. 2 shows an example of image exposure timing (control signal) in the image forming apparatus of the embodiment. 2 shows an example of image exposure timing (control signal) in the image forming apparatus of the embodiment. 2 shows an example of image exposure timing (control signal) in the image forming apparatus of the embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

  An image forming apparatus (MFP, Multi-Functional Peripheral) 101 shown in FIG. 1 outputs an image forming unit corresponding to image information to be output, for example, called “printout”. A main body 1 is included.

  An MFP 101 shown in FIG. 1 includes a sheet supply unit 3 that supplies a sheet of an arbitrary size used for image output to the image forming unit main body 1, and image information that is a target of image formation in the image forming unit main unit 1. An image reading unit (scanner) 5 that captures image data from a reading object (hereinafter referred to as a document) that holds information is included. Note that an automatic document feeder (ADF) 7 may be attached to the image reading unit 5. The image reading unit 5 may be directly connected to the image forming apparatus 101 or may be connected via a communication network such as a LAN (Local Area Network). Note that a control panel 9 that gives an instruction to start image formation to the image forming unit main body 1 and an instruction to start reading an original image by the image reading unit 5 is provided by a column and a swing arm fixed to the image forming unit main body 1. It is located behind the left side or the right side of the image reading unit 5. The paper supply unit 3 includes two or more sheet holding mechanisms, that is, cassettes 31.

  The image forming unit main body 1 includes first to fourth photosensitive drums 11a to 11d that hold latent images, and a developing device that supplies a developer, that is, toner, to the latent images held by the photosensitive drums 11a to 11d to develop the latent images. 13a to 13d, a transfer belt 15 for sequentially holding toner images held by the photosensitive drums 11a to 11d, and first to fourth toners that remove toner remaining on the photosensitive drums 11a to 11d from the individual photosensitive drums 11a to 11d. The transfer roller 19 for transferring the toner image held by the cleaners 17a to 17d and the transfer belt 15 to a sheet that is a transparent resin sheet such as plain paper or an OHP sheet, and fixing the toner image transferred to the sheet by the transfer roller 19 to the sheet A fixing device 21 that performs image forming, and an exposure device 23 that forms latent images on the photosensitive drums 11a to 11d.

  The image forming apparatus 101 also includes a control block 111 that is responsible for operations such as operation of the image forming unit main body 1 and image processing for image output at each station, or reception of operation input from the operation panel 9.

  The control block 111 integrates a CPU (Central Processing Unit) or MPU (Main Processing Unit) and a main storage device (main memory or work memory, storage section), which are main control devices (firmware). As) or as an external unit. In addition, for example, the main storage device performs RIP processing (develops image data for each page according to the Raster Image Process) to print output image data, and outputs it to each station of the image forming unit main body 1 as an image signal for each color component. Output.

  The control block 111 is also connected to the operation unit 9, receives an operation input from the user, outputs a control command corresponding to the input (to the control block), and guides the user to the display unit included in the operation unit 9. Display error messages.

  In the image forming apparatus 101 shown in FIG. 1, the first to fourth developing devices 13a to 13d are Y (yellow / yellow), M (magenta / bright red), C used for obtaining a color image by subtractive color mixing. A latent image stored in each of the photosensitive drums 11a to 11d is stored in any color of Y, M, C, and K, containing toner of any color of (cyan / blue purple) and K (black / black K). Visualize with. The order of the colors is determined in a predetermined order according to the image forming process and the characteristics of the toner.

  The transfer belt 15 holds the toner images of the respective colors formed by the first to fourth photosensitive drums 11a to 11d and the corresponding developing devices 13a to 13d in the order of toner image formation.

  The paper supply unit 3 supplies a sheet for moving the toner image to the transfer roller 19 at a predetermined timing.

  A cassette 31 located in each cassette slot accommodates a sheet of an arbitrary size, and the pickup roller 33 takes out the sheet from the corresponding cassette according to an image forming operation in the image forming unit main body 1. The sheet size corresponds to the magnification required for image formation and the size of the toner image formed by the image forming unit main body 1.

  The separation mechanism 35 prevents the pickup roller 33 from taking out two or more sheets from the cassette.

  The plurality of transport rollers 37 send the sheet separated by the separation mechanism 35 into one sheet toward the aligning roller 39.

  The aligning roller 39 sends the sheet to a transfer position where the transfer roller 19 and the transfer belt 15 are in contact with each other at the timing when the transfer roller 19 transfers the toner image from the transfer belt 15.

  The fixing device 21 receives heat from the first roller 121 and the first roller 121 that generate heat due to heat from the heater 129, and is passed between the second roller 123 and the first roller 121, and the heat of the first roller 121 is transferred to the first roller 121. A belt 127 moving toward the two-roller 123 side, and a third roller 125 that provides a predetermined pressure to the sheet that moves in contact with the belt 127 in contact with the belt 127 are included.

  An arbitrary part of the belt 127 and the outer periphery of the third roller 125 form a nip by the pressure applied to the second roller 123 and the third roller 125. Thus, a predetermined pressure and a temperature at which the toner can be melted (fixing temperature) are applied to the sheet passing through the nip so that the toner (toner image) held by the sheet can be fixed.

  The fixing device 21 fixes the toner image on a sheet and sends it as an image output (hard copy or printout) to a stock unit 47 located in a space between the image reading unit 5 and the image forming unit main body 1.

  The fixing device 21 reverses a reversing path 43 of an automatic duplex unit (ADU) 41 that reverses the front and back of a sheet holding a toner image corresponding to image information independently of the operation of moving the image output to the stock unit 47. The reversing roller 49 is moved to

  In the image forming unit main body 1, the ADU 41 is located between the final conveying roller 37 (near the transfer roller 19) and the aligning roller 39, or between the aligning roller 39 and the fixing device 21, or between the transfer roller 19 and the fixing device 21. If the sheet is jammed (when jammed), move to the side (right side). The ADU 41 integrally includes a cleaner 43 that cleans the transfer roller 19.

  Although the exposure device 23 is shown in a plan view in FIG. 2, the intensity is modulated corresponding to the image data of one polygon 23-1, Y, M, C, and K, and each of the corresponding photosensitive drums 11a to 11d. In addition, the first to fourth laser elements 23Y, 23M, 23C and 23K that output laser beams for forming the respective images of Y, M, C, and K, and the polygon 23-1, are positioned point-symmetrically. Relative to the rotation direction of the first and second fθ lenses 23-2 and 23-3, the first and second mirrors 23-4 and 23-5, and the polygon 23-1 BD (Beam Detect) sensors 23-7L, 23-7R located at the same position and a mirror 23-6 that reflects laser light scanned by the polygon 23-1 toward the BD sensors 23-7L, 23-7R Including. As is apparent from FIG. 2, for example, L-side BD detection is detected by the BD sensor 23-7L with M-color laser light, and R-side BD detection is detected by the BD sensor 23-7R with C-color laser light. Shall.

  As shown in FIG. 2, when the polygon 23-1 rotates in the direction of, for example, CCW (Counter Clock Wise), the image light (laser light) output from the laser elements 23Y and 23M in the laser element arrangement shown in FIG. ) Moves in the direction of arrow L. The image light (laser light) output from the laser elements 23C and 23K moves in the direction of the arrow R. That is, the two groups (two) of laser beams move in opposite directions (the two groups (two) of laser beams are scanned in the opposite directions due to the rotation of the polygon 23-1).

  In the example shown in FIG. 2, the two BD sensors 23-7L and 23-7R are positioned on the movement start position side when the two groups (two) of laser beams move. At this time, as shown in FIG. 6 as an example, the timing at which the laser light (LY / LM) from the laser elements 23Y and 23M enters the BD sensor 23-7L, the output timing of the main scanning counter, and the laser elements 23C and 23K The timing at which the laser beam (LC / LK) is incident on the BD sensor 23-7R and the output timing of the main scanning counter do not match even when the direction in which each laser beam moves (laser scanning direction) is considered.

  For example, the timing at which the laser beam LY (LM) is incident on the BD sensor 23-7L and the timing at which the laser beam LC (LK) is incident on the BD sensor 23-7R are only the time indicated by [A] in FIG. Shift.

  In FIG. 6, the time indicated by [B] indicates the time between the time point (time) when the laser beam LC (LK) is incident on the BD sensor 23-7R and the image area (sheet width). Further, the time indicated by [D] in FIG. 6 is a time point (time) when the laser beam LC (LK) is incident on the BD sensor 23-7R and a time point when the laser beam LY (LM) is incident on the BD sensor 23-7L ( Time).

  Here, the respective times [A], [B], and [D] coincide with the time elements [A], [B], and [D] described in the present embodiment according to FIGS. To do.

  FIG. 5 shows an example of an image processing circuit to which this embodiment can be applied.

  An image processing circuit (ASIC (Application Specific IC / Application Specific IC)) 131 illustrated in FIG. 5 includes a CPU 133 connected to the CPU 119 on the image forming apparatus 101 side included in the control block 111.

  The ASIC 131 has registers for each circuit (for example, the image processing A circuit block 139A, the image processing B circuit block 139B, the image processing C circuit block 139C, and the image processing D circuit block 139D), and these registers are read and written by the CPU 133. it can.

The ASIC 131 is, for example,
1) Receive image data from the CPU I / F block, the image generation image processing circuit 121 on the image forming apparatus 101 side, the image processing ASIC for preprocessing, and the like, and perform various necessary image processing.
2) Clock CLK (MCLK) used for operations of image processing (A, B, C, D) circuit block 139 (AD), image processing (A, B, C, D) circuit block 139 (AD), etc. )
3) In order to receive image data from the PLL unit 137 and the image processing (A, B, C, D) circuit block 139 (AD) and output it to the laser driver 151 (AD), the clock CLK. Frequency conversion function for changing M to the clock PCLK from the laser driver 151 (AD) side, launching of image data (modulation start when intensity modulation is performed on laser light output from laser element according to image information) A function for adjusting a position, a margin amount, and the like, and a function for generating a BD (Beam Detect) signal generation signal that is a main scanning reference signal and a calibration signal for the laser driver 151 (AD).
4) Laser control processing unit (A, B, C, D) 141 (AD), PLL function for generating PCLK for laser control, and multivalued image data received from the laser control processing unit, pulse width A function for converting to modulated serial data, a function for outputting serial image data in synchronization with a BD signal reference, and a laser for emitting laser light during the active period of the BD signal generation signal in order to emit laser light. H) has a function, etc.
5) PLL / PWM section (A, B, C, D) 147 (AD), PLL / PWM section 147 (AD) as a reference, and the PLL / PWM as the main scanning reference timing Selects one of the HSYNC signals (A, B, C, D) output from the unit and switches to the MCLK signal timing
6) Control signal selector 145
including.

  In the ASIC 131, the control signal selection circuit 145 and the laser control processing unit (A, B, C, D) 141 (AD) include a frequency conversion unit / line memory switching signal selection circuit (A, B, C, D) 143 (AD) has a memory for two lines of <A> and <B> per color as shown in FIG. That is, the image processing circuit (ASIC) 131 shown in FIG. 5 has a line memory necessary for each color for only two lines <A> and <B>, and is related to standard image data as shown in FIG. Compared with the memory for three lines used for the control, the memory capacity can be reduced so that the power consumption can be reduced.

  FIG. 7 shows an outline of signals related to control related to image data in the present embodiment.

  In FIG. 7, 23-7L (BD-1 (L)) indicates a main scanning reference signal based on the laser beam LY (LM) input to the L-side BD sensor 23-7L, and image processing described in FIG. This signal is a source of the main scanning reference signal (MHSYNC) output to the circuit. Similarly, 23-7R (BD-1 (R)) indicates a main scanning reference signal based on the laser beam LC (LK) input to the R-side BD sensor 23-7R.

  The memory switching (L / R) signal corresponds to the memory switching signal shown in FIG. 3, and the L side two colors (Y, M) and the R side two colors (C, K), that is, the frequency conversion circuit unit for all colors. These memory switching signals are common signals.

  HDEN-0 (L / R) is an image valid signal in the main scanning direction from the image processing circuit shown in FIG. Note that VDEN-0 (L / R) is actually output at a different timing for each color. However, the outline of the operation of the frequency conversion circuit unit may be explained here, and the explanation is omitted.

  DATA “7: 0” (L) indicates image data of the L side color, and DATA “7: 0” (R) indicates image data of the R side color.

  OHDEN-0 (L) is an L-side main scan image data valid signal read from the frequency conversion circuit unit, and ODATA “7: 0” (L) indicates image data.

  OHDEN-0 (R) is an R-side main scan image data valid signal read from the frequency conversion circuit unit, and ODATA “7: 0” (R) indicates image data.

  OVDEN-0 (L) indicates an L side color sub-scan image data valid signal, and OVDEN-0 (R) indicates an R side color sub-scan image data valid signal.

  In FIG. 7, since the required memory is for two lines, the numerical value indicating the memory switching state is either <1> or <2>, and the read completion timing of the image data on the R side is the memory switching. Optical design to come before the timing. By designing the double swing LSU at such a timing, as shown in FIG. 3, it is possible to use the control (mode) of this embodiment that can use two lines of memory for the double swing LSU.

  That is, the LSU is designed so that the control shown in FIG. 7 can be applied (mainly the laser beam incident timing to the L-side BD sensor 23-7L and the laser beam incident timing to the R-side BD sensor 23-7R). 3), the line memory necessary for each color as shown in FIG. 3 is set to <A> and <B> for two lines, and writing and reading are performed alternately (low power consumption) Reduction of memory capacity that can be realized).

  FIG. 8 shows an overview of signals related to the proposed image data-related control when the mode shown in FIG. 7 is used.

  The difference between the example shown in FIG. 8 and the example shown in FIG. 7 is that the main scanning reference signal passed to the image processing board circuit side shown in FIG. 5 is the first (first color laser beam) from the R-side BD sensor 23-7R. ) Output signal (preceding) followed by the output signal of the second (second color laser beam) and the memory switching signal on the L side and the R side are different, and the L side BD sensor 23 for the L side. The laser beam input to -7L is used as a reference, and the R side is switched based on the laser beam input to the R side BD sensor 23-7R.

  The image data transferred from the image processing board circuit is output between the output of the succeeding BD sensor 23-7R and the output of the preceding BD sensor 23-7R (corresponding to the image data). The image signal is output after the input of the laser beam for the second color is detected until the input of the laser beam for the first color is detected (next). By providing such a circuit configuration that can be used, frequency conversion can be realized with a memory for two lines.

  That is, the LSU is designed so that the control shown in FIG. 7 can be applied (mainly the laser beam incident timing to the L-side BD sensor 23-7L and the laser beam incident timing to the R-side BD sensor 23-7R). 3), the line memory necessary for each color as shown in FIG. 3 is set to <A> and <B> for two lines, and writing and reading are performed alternately (low power consumption) (Reduction of memory capacity that can be realized) paper, and further frequency conversion can be realized.

  FIG. 9 shows an outline of signals related to standard image data related control in the double swing LSU for comparison with the present embodiment described with reference to FIG. 7 (FIG. 8). As described with reference to FIG. 7, 23-7L (BD-1 (L)) indicates a main scanning reference signal based on the laser beam LY (LM) input to the L-side BD sensor 23-7L. This is a signal that is a source of the main scanning reference signal (MHSYNC) output to the image processing circuit described in FIG. Similarly, 23-7R (BD-1 (R)) indicates a main scanning reference signal based on the laser beam LC (LK) input to the R-side BD sensor 23-7R.

  The memory switching (L / R) signal corresponds to the memory switching signal shown in FIG. 4, and the L side two colors (Y, M) and the R side two colors (C, K), that is, the frequency conversion circuit unit for all colors. These memory switching signals are common signals.

  HDEN-0 (L / R) is an image valid signal in the main scanning direction from the image processing circuit board shown in FIG. Note that VDEN-0 (L / R) is actually output at a different timing for each color. However, the outline of the operation of the frequency conversion circuit unit may be explained here, and the explanation is omitted.

  DATA “7: 0” (L) indicates image data of the L side color, and DATA “7: 0” (R) indicates image data of the R side color.

  OHDEN-0 (L) is an L-side main scan image data valid signal read from the frequency conversion circuit unit, and ODATA “7: 0” (L) indicates image data.

  OHDEN-0 (R) is an R-side main scan image data valid signal read from the frequency conversion circuit unit, and ODATA “7: 0” (R) indicates image data.

  OVDEN-0 (L) indicates an L side color sub-scan image data valid signal, and OVDEN-0 (R) indicates an R side color sub-scan image data valid signal.

  In the outline of signals related to standard image data-related control shown in FIG. 9, the line memory necessary for each color is <a>, by not applying this embodiment shown in FIG. 7 or FIG. <B> and <c> are for 3 lines. That is, in the example shown in FIG. 9, the image data on the image processing circuit side operates on the basis of the preceding L side 23-7L (BD-1 (L)) signal, and the memory switching timing of the frequency conversion circuit unit is It is synchronized with this signal. Therefore, the L side image data can be read regardless of the memory switching timing, but the R side reading which operates based on the subsequent 23-7R (BD-1 (R)) signal has a special optical design. If this is not applied, memory switching timing will be required. Therefore, as described above, a memory for three lines is required.

  As described above, in the image processing circuit 131 shown in FIG. 5, the frequency conversion unit / line memory included in the control signal selection circuit 145 and the laser control processing unit (A, B, C, D) 141 (AD). The switching signal selection circuit (A, B, C, D) 143 (AD) is configured to have a memory for two lines of <A> and <B> per color as shown in FIG. Accordingly, it is possible to realize a reduction in memory capacity that can realize low power consumption as compared with a memory for three lines used for standard image data-related control.

  That is, in a color image forming apparatus having Y, M, C, and K using a standard laser optical system as shown in FIG. 9, two polygons differ for each two colors in order to reduce the size of the LSU unit. When an LSU having one lens system is used, an image of image data is compared with an optical design in which main scanning optical coordinate positions such as L-side and R-side BD signal detection timings and image areas with respect to each BD signal reference are different. Since the processing needs to be performed at the same timing of Y, M, C, and K, the image is usually processed when processing is performed based on one main scanning reference signal (BD reference preceding in timing). Since the CLK on the processing side and the CLK on the laser control side are usually not the same CLK, a conversion circuit (hereinafter referred to as a frequency conversion circuit) from the image processing side CLK to the laser control side CLK is required. That.

  In this case, as the CLK conversion circuit, there is a circuit that has a line memory for one line for a plurality of lines, writes the line memory by image processing CLK, and reads the written image data from another line memory by laser control CLK. Since the line memory capacity required here is the same, the writing timing in the image processing CLK is the same for the four colors, while the reading needs to be read with two BD reference signals having different timings. Therefore, in order to satisfy any timing, a memory capacity of 3 lines per color is required. However, according to the present embodiment, the memory capacity is increased to the memory capacity of 2 lines per color. Can be reduced.

That is, in an exposure apparatus in which a four-color laser beam scanning system is positioned on both sides of a polygon in a point-symmetric manner around one polygon.
A) It has a circuit that can select which of the two or more BD signals is generated as the main scanning reference signal (MHSYNC) of the image processing side circuit.
A) A circuit that can independently select the BD reference signal for each color or the MHSYNC signal common to the four colors as the switching timing of the frequency conversion circuit / line memory.
With configuration,
According to the coordinate information in the optical design of the LSU (laser exposure apparatus), the main scanning reference signal (MHSYNC (above)) and the line memory switching signal of the image processing side circuit can be switched according to the above a), A frequency conversion operation is also possible and can be used in combination.

  As a result, it is possible to realize an image forming apparatus and an exposure apparatus control method capable of reducing cost and reducing power consumption.

Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.
The invention described in the scope of the claims at the beginning of the present application is added below.
[1]
In an image forming apparatus including a laser exposure apparatus in which a laser scanning system for two colors is positioned on both sides around a polygon,
Beam detection means for detecting the incidence of laser light in each of the two color laser scanning systems;
The beam detection signal detected by the beam detecting means is used as a reference for the second beam detection signal that precedes the first beam detection signal, which is the main scanning reference signal of the image processing circuit, as an image signal. An image forming apparatus comprising: an exposure unit that modulates the intensity of the image with an exposure unit.
[2]
In an image forming apparatus including a laser exposure apparatus in which a laser scanning system for two colors is positioned on both sides around a polygon,
Beam detection means for detecting the incidence of laser light in each of the two color laser scanning systems;
The frequency difference between the operation clock (CLK.M) on the image processing apparatus side and the operation clock (PCLK) on the exposure means side that modulates the intensity of the laser beam with the image signal is converted in a memory for two lines, An image forming apparatus comprising: a laser processing circuit that absorbs.
[3]
The image of [1] or [2], wherein a laser scanning system for two colors that outputs a reference beam detection signal out of the beam detection signals output by the beam detection means can be selected with the polygon as a center. Forming equipment.
[4]
The switching timing of the memory included in the exposure means or the laser processing circuit is selected from a reference signal based on the beam detection signal by an arbitrary laser beam, or a main scanning synchronization signal common to each laser beam, for each color. The image forming apparatus according to any one of [1] to [3], which can be independently selected.
[5]
The image forming apparatus according to [1] or [2], wherein the exposure unit finishes the image reading operation by the subsequent main scanning reference signal within the range of one cycle of the preceding main scanning reference signal.

  DESCRIPTION OF SYMBOLS 1 ... Image forming part main body, 23 ... Exposure apparatus, 23-7L, 23-7R ... Beam detection apparatus, 101 ... Image forming apparatus, 111 ... Control block, 131 ... Image processing circuit (ASIC), 133 ... Control apparatus (CPU) 139: Image processing (A, B, C, D) circuit, 141: Laser control processing (A, B, C, D) circuit, 143: Frequency conversion / line memory (A, B, C, D), 145 ... Control signal selection, 151 ... Laser driver.

Claims (4)

In an image forming apparatus including a laser exposure apparatus in which a laser scanning system for two colors is positioned symmetrically with respect to a polygon as a center,
Beam detection means for detecting the incidence of laser light in each of the two color laser scanning systems;
A second beam detection signal that operates at an operation clock (PCLK) and precedes the beam detection signal detected by the beam detection means in timing with respect to the first beam detection signal that becomes the main scanning reference signal of the image processing circuit. With reference to the exposure means for modulating the intensity of the laser beam with the image signal,
The difference in frequency between the operation clock (CLK.M) of the image processing apparatus and the operation clock (PCLK) of the exposure means that modulates the intensity of laser light with an image signal is converted in a memory for two lines, Or with a laser processing circuit to absorb,
An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein a laser scanning system for two colors that outputs a reference beam detection signal out of the beam detection signals output by the beam detection unit can be selected with the polygon as a center. . The switching timing of the memory included in the exposure means or the laser processing circuit is selected from a reference signal based on the beam detection signal by an arbitrary laser beam, or a main scanning synchronization signal common to each laser beam, for each color. The image forming apparatus according to claim 1, wherein the image forming apparatus can be independently selected. 4. The image forming apparatus according to claim 1, wherein the exposure unit finishes an image reading operation by a subsequent main inspection reference signal within a range of one period of the preceding main scanning reference signal. 5.

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