JP6659159B2 - Image forming device - Google Patents

Description

  The present invention relates to an image forming apparatus having a line buffer.

  2. Description of the Related Art In recent years, in an image forming apparatus such as a copying machine or a printer that forms an image using a laser beam, an image forming apparatus that forms an image using a plurality of laser beams in order to achieve high printing speed and high image quality. It has been known. Such an image forming apparatus emits laser light from a plurality of light emitting points based on image data, deflects the laser light using a deflecting means such as a polygon mirror, and the deflected laser light travels on the photoconductor. Scanning is performed simultaneously.

  This image forming apparatus includes an image control unit that generates binary image data (one-bit bit data) for ON / OFF-controlling each light emitting point, and a laser driver. The image control unit performs image processing on image data input from an image reading device or image data input from a personal computer (PC). As a result, image data (multi-valued gradation data larger than binary indicating density) is generated, and the image data is converted into a bit pattern including a plurality of the binary bit data. Further, the image control unit outputs bit data included in the bit pattern to the laser driver one bit at a time according to the scanning position of the laser light. The laser driver drives each light emitting point based on the bit data output for each light emitting point.

Normally, the image control unit includes a circuit board, and an image processing unit, which is an IC for executing image processing, is mounted on the circuit board. The number of light emitting points provided in the image forming apparatus varies depending on the specifications of the product. Generally, many image forming apparatuses have 2 n light emitting points (n is 0 and a natural number). The image processing unit is designed to have versatility so that it can be mounted on many of such various image forming apparatuses.
Patent Literature 1 discloses an image forming apparatus that forms an image using two laser beams, a first laser beam and a second laser beam, includes an image processing circuit (image processing unit) that generates image data; An image forming apparatus including a buffer for storing data output by a unit is disclosed. The buffer A stores image data (raster data) for the first laser light output from the image processing unit, and the buffer B stores image data for the second laser light output from the image processing unit. The buffer stores image data (line data) for each scanning line of the laser light. The line data is data in which a plurality of the bit patterns are arranged, that is, the binary bit data string.

  The input timing of the image data from the image processing unit to the buffers A and B and the output timing of the image data from the buffers A and B to the control circuit (laser driver) for controlling a plurality of light emitting points depend on the specifications of the apparatus. Is designed. For example, in an image forming apparatus that outputs two laser beams, a configuration in which line data is simultaneously output to the buffer A and the buffer B from the image processing unit may be considered. In this configuration, image data is output to the laser driver in units of 1 bit from the line data stored in the buffers A and B. In designing such an image forming apparatus, it is necessary to supply image data from the image processing unit to the laser driver without delay. For this purpose, an image control unit is designed in accordance with an image forming apparatus that outputs two laser beams, that is, transmission timing of image data using a buffer is designed. As described above, the design of the image control unit is often appropriately designed in accordance with the specifications of each image forming apparatus.

JP 2010-208032 A

  Since designing an image control unit for each image forming apparatus having different specifications leads to an increase in cost in designing a plurality of products, it is preferable to design a general-purpose image control unit. However, the timing of supplying image data from the image control unit to the laser driver depends on the specifications of the image forming apparatus, particularly, the number of laser beams used for image formation. Therefore, if the image control unit for two lasers designed for an image forming apparatus using two laser beams is directly converted to an image forming apparatus using three laser beams, an image control unit that does not conform to the specifications of the apparatus can be obtained. And the production cost of the product increases.

  SUMMARY An advantage of some aspects of the invention is to provide an image forming apparatus in which cost is suppressed by suppressing the number of line buffers provided between an image control unit and a laser driver. And

An image forming apparatus according to the present invention is an image forming apparatus that forms an image on a recording medium, and includes a photoconductor that is driven to rotate, a first light emitting point that emits a first laser light, and a second laser light. A laser light source including a second light emitting point for emitting light, and a third light emitting point for emitting third laser light; a first driving unit for driving the first light emitting point; A driving unit including: a second driving unit for driving a light emitting point; and a third driving unit for driving the third light emitting point; the first laser beam; Deflecting means for deflecting each laser light so that the laser light and the third laser light scan on the photoconductor in a direction intersecting the rotation direction of the photoconductor. The order of the scanning position from the downstream side in the direction is the first laser light, Scanning means in which the first light emitting point, the second light emitting point, and the third light emitting point are arranged so as to be a second laser light and the third laser light; Detecting means for receiving the laser light and generating a detection signal based on the timing of receiving the laser light, and synchronizing with the detection signal, generating a synchronization signal having a frequency which is 3/2 times the frequency of the detection signal. Signal generating means for generating, based on input image data, a plurality of line data corresponding to each scanning line of the laser light, which is line data for forming an image on a recording medium; Processing means for outputting line data generated two lines at a time in synchronism with the processing means; and nine line buffers for holding the line data output from the processing means. Nine line buffers respectively holding the line data corresponding to the scan lines, and the input destinations of the two line data output by the processing means are switched among the nine line buffers in synchronization with the synchronization signal. A first selector, a first driver, a second driver, and a third driver in which input destinations of line data stored in the nine line buffers are synchronized with the detection signal; And a second selector for switching among them.
Output start timing of line data corresponding to the one recording medium from the buffer unit to the driving unit with respect to output start timing of line data corresponding to one recording medium from the processing unit to the buffer unit Is delayed by at least two cycles of the detection signal, and the first selector performs synchronization with the line data of the first line and the line data of the second line in the plurality of line data corresponding to the one recording medium. The connection between the processing means and the nine line buffers is switched so as to be sequentially input to the nine line buffers in synchronization with a signal, and the second selector includes a plurality of lines corresponding to the one recording medium. The line data of the first line in the line data of No. is not output to the first drive unit, and the line data of the second line is The first driver, the third line data is input to the second driver, the fourth line data is input to the third driver, the fifth and subsequent line data Are output to the first drive unit, the second drive unit, and the third drive unit in the order in which they are input to the line buffer, so that the nine line buffers and the first drive unit, The connection between the second drive unit and the third drive unit is switched.

  According to the present invention, a processing unit for generating line data used in an image forming apparatus that forms an image using two laser lights can be employed in an image forming apparatus that forms an image using three laser lights. it can. Further, the number of line buffers in the image forming apparatus can be reduced.

FIG. 1 is an overall configuration diagram of an image forming apparatus. The block diagram of a laser scanner unit. FIG. 6 is a functional block diagram illustrating image control in a comparative example. FIG. 4 is an explanatory diagram of a synchronization signal and a buffer. FIG. 4 is an explanatory diagram of a circuit including a buffer. FIG. FIG. 2 is a functional block diagram illustrating image control according to the embodiment. 5 is a flowchart illustrating processing by an image processing unit. FIG. 4 is an explanatory diagram of a synchronization signal and a buffer. FIG. 4 is an explanatory diagram of a circuit including a buffer.

<Comparative example>
Hereinafter, a comparative example of the present invention will be described using a four-drum color copying apparatus in which four photosensitive members are arranged in tandem as an example of an image forming apparatus.

FIG. 1 is an overall configuration diagram of a color copying apparatus 7 according to a comparative example. The color copying apparatus 7 includes a color image reading device (hereinafter, referred to as “color scanner”) 700 and a color image recording device (hereinafter, referred to as “color printer”) 701.
The color scanner 700 includes an illumination lamp 703, mirror groups 704A, 704B, 704C, a lens 705, and a color sensor 706. The illumination lamp 703 irradiates the original 702 with light, and the mirror group 704A, 704B, 704C and the lens 705 guide the reflected light from the original to the color sensor 706. The color sensor 706 separates and reads components of each color of blue (B), green (G), and red (R), and generates a read signal corresponding to each color component.

  Based on the intensity levels of the B, G, and R read signals output from the color scanner 700, a color conversion process is performed by an image processing unit 1151 shown in FIG. 3, which will be described later, and black (BK), cyan (C), and magenta (M) and yellow (Y) color input image data are obtained.

  The color printer 701 includes photosensitive drums 708Y, 708M, 708C, and 708K, which are photosensitive members. The photosensitive drums 708Y, 708M, 708C, and 708K rotate counterclockwise as shown in FIG. Around the photosensitive drums 708Y, 708M, 708C, and 708K, chargers 709Y, 709M, 709C, and 709K are arranged. The chargers 709Y, 709M, 709C, and 709K charge the surfaces of the photosensitive drums 708Y, 708M, 708C, and 708K, respectively. The laser scanner units 707Y, 707M, 707C and 707K provided one for each color toner emit laser light based on the corresponding image data. On the charged photosensitive drums 708Y, 708M, 708C, and 708K, an electrostatic latent image is formed by laser beams emitted from the corresponding laser scanner units 707M, 707Y, 707C, and 707K.

  Around the photosensitive drums 708Y, 708M, 708C, and 708K, developing units 710Y, 710M, 710C, and 710K are arranged. The electrostatic latent images formed on the photosensitive drums 708Y, 708M, 708C, and 708K are developed with toner held by the respective developing devices. The toner image developed on each photosensitive drum is transferred onto an intermediate transfer belt 711 as an intermediate transfer body. The intermediate transfer belt is stretched around a drive roller 713 for driving the intermediate transfer belt 711 and driven rollers 714 and 715. First transfer bias blades 712Y, 712M, 712C, and 712K as first transfer units for each color transfer the toner images on the corresponding photosensitive drums 708Y, 708M, 708C, and 708K to the intermediate transfer belt 711.

  The toner image transferred onto the intermediate transfer belt 711 is transferred to a recording medium at a transfer nip formed by a second transfer bias roller 716 and a driven roller 714. The recording medium set in the cassette 718 is conveyed to the transfer nip portion in synchronization with the toner image on the intermediate transfer belt 711 by the paper feed roller 719 and the conveyance rollers 720, 721, 722, and 723.

  The recording medium onto which the toner image has been transferred as described above is conveyed to the fixing device 724. The fixing device 724 heats and fixes the toner image on the recording medium by a pair of fixing rollers. The toner remaining on the intermediate transfer belt 711 after the transfer of the toner image to the recording medium is cleaned by the cleaning unit 717.

  Next, with reference to the front view of the laser scanner unit shown in FIG. 2A, the plan view shown in FIG. 2B, and the control block diagram of the image forming apparatus shown in FIG. Will be described in detail. In the following description, since the same processing is performed in any of the laser scanner units 707Y, 707M, 707C, and 707K, these are simply described as a laser scanner unit 707.

  As shown in FIGS. 2A and 2B, the laser scanner unit 707 includes a semiconductor laser 7071, which is a light emitting element that emits laser light, a lens 7072, and a rotating polygon mirror (polygon mirror) 7073. In addition, the laser scanner unit 707 further includes an fθ lens 7074, a Beam Detector 7075 (BD), and a reflection mirror 7076. Laser light emitted from the semiconductor laser 7071 based on the image data passes through the lens 7072 and is incident on the reflection surface of the polygon mirror 7073 driven to rotate by the motor 7077.

  The polygon mirror 7073 deflects the laser light so that the incident laser light scans the photoconductor, that is, scans the photosensitive drums 708Y, 708M, 708C, and 708K. The laser light deflected by the polygon mirror 7073 is guided onto the photosensitive drums 708Y, 708M, 708C, and 708K by the fθ lens 7074 and the reflection mirror 7076. The BD 7075 is provided on the scanning path of the laser light deflected by the polygon mirror 7073. The BD 7075 generates a BD signal (detection signal) based on a light receiving timing at which the laser light deflected by the polygon mirror 7073 is received. The BD signal is used as a reference for controlling the timing at which each unit described below transmits image data to a subsequent unit. That is, by transmitting the image data based on the BD signal, the emission timing of the laser light based on the image data in each scanning cycle of the laser light is controlled as a result.

  FIG. 3 is a functional block diagram illustrating image control in the comparative example. As illustrated, the CPU 1100 is connected to the image processing unit 1151 and the buffer unit 2000, and controls image processing in the image processing unit 1151. The image processing unit 1151 is connected to the color scanner 700, the image processing unit 1151, the buffer unit 2000, and an I / O unit 730 that inputs and outputs data to and from an external information device such as a PC. The synchronization control unit 2005 as a signal generation unit receives a BD signal from the laser scanner unit 707 and inputs an image synchronization signal to the image processing unit 1151. The buffer unit 2000 includes a write selector 2001, a line buffer 2002, and a read selector 2003.

  Note that the line buffer 2002 has a plurality of line buffers, and image data is sequentially and cyclically written in numerical order from the first line buffer. For example, when the line buffer 2002 includes line buffers 1 to n as n line buffers, the image data 1, 2, 3,... Are sequentially written to the line buffers 1, 2, 3,. After the image data n is written to the line buffer n, the next image data n + 1 is written to the line buffer 1. At this time, the image data 1 previously written in the line buffer 1 is overwritten by the image data n + 1.

  The units and the like shown in FIG. 3 are attached to the color printer 701 except for the color scanner 700 and the laser scanner unit 707. In this comparative example, the image processing unit 1151 is configured by an IC. The buffer unit 2000 is configured by an IC, a discrete component, or a combination thereof, and the image processing unit 1151 and the buffer unit 2000 are mounted on the same board. The buffer unit 2000 and the laser driver 2006 are connected by flexible wiring, and image data is serially transmitted in units of 1 bit by the flexible wiring.

  The laser scanner unit 707 includes a laser driver 2006 and a semiconductor laser 7071. A semiconductor laser 7071 as a laser light source is a one-chip semiconductor laser including three light emitting points. The laser driver 2006 includes a laser driving circuit 2004 as a driving unit corresponding to each light emitting point. The laser driving circuit 2004 controls on / off of each light emitting point by image data (bit data) output one bit at a time from the buffer unit 2000. The three light emitting points are a first light emitting point for emitting the first laser light, a second light emitting point for emitting the second laser light, and a third light emitting point for emitting the third laser light. And The first light emitting point, the second light emitting point, and the third light emitting point are arranged such that the order of the scanning positions from the downstream side in the rotation direction of the photosensitive drums 708Y, 708M, 708C, and 708K is the first laser light, The laser beams are arranged so as to be a second laser beam and a third laser beam.

  An image reading signal output from the color scanner 700 is input to the image processing unit 1151. The image processing unit 1151 performs color separation processing for YMCK, gradation correction processing (γ correction processing), and screen processing. For example, the image processing unit 1151 generates 10-bit multivalued image data by performing color separation processing on YMCK. Next, the image processing unit 1151 executes a gradation correction process (γ correction process) on the 10-bit image data. Then, the image processing unit 1151 sets 4-bit image data indicating a density value by performing screen processing on the 10-bit image data using a dither matrix in which four different threshold values are set. The 4-bit image data is data decomposed for each light emitting point by screen processing. Further, the image processing unit 1151 converts the 4-bit image data into a sequence of binary bit data, that is, a bit pattern using a conversion table. Each bit data included in the bit pattern is binary data for turning the light emitting point on (ON) or off (OFF). Hereinafter, a bit data string corresponding to one scan line is referred to as line data. The BD signal from the laser scanner unit 707 is input to the synchronization control unit 2005 as described above, and is also sent to the read selector 2003 of the buffer unit 2000. The synchronization control unit 2005 generates an image synchronization signal that is a multiple of the detection signal for the image processing unit 1151 based on the number of laser beams specified in advance by the CPU 1100. In this example, three laser beams are provided in the laser scanner unit 707, and the CPU 1100 specifies that the number of laser beams used for the buffer unit 2000 and the synchronization control unit 2005 is three. The synchronization control unit 2005 generates an image synchronization signal having a frequency of 3/2 times the detection signal based on the designation.

Under the control of the CPU 1100, the image processing unit 1151 transmits two lines of line data to be written to the line buffer 2002 per one cycle of the image synchronization signal to the write selector 2001 in synchronization with the image synchronization signal.
Similarly, when the image processing unit 1151 supports three laser beams, two lines of line data are written in the line buffer 2002 with two lines per one cycle of the image synchronization signal in synchronization with the image synchronization signal. The data is transmitted to the selector 2001.

  However, in the comparative example and the embodiment described later, the image processing unit 1151 corresponding to two laser beams is diverted to a laser scanner unit using three laser beams. Accordingly, the write selector 2001 writes line data to the line buffer 2002 for each of two input line buffers. On the other hand, since the number of laser beams is specified to be three by the CPU 1100, the line data stored in the line buffer 2002 is sequentially read out every three lines by the read selector 2003 based on the detection signal. Note that a clock signal higher in frequency than the detection signal is input to the line buffer 2002, and the detection signal functions as a trigger for outputting line data stored in the line buffer 2002. The line buffer 2002 outputs bit data included in the line data one bit at a time in synchronization with the clock signal to the laser driving circuit 2004 at the subsequent stage.

  The laser drive circuit 2004 drives each light emitting point of the semiconductor laser 7071 in each of the laser scanner units 707M, 707Y, 707C, and 707K based on bit data sequentially output from the read selector 2003. Hereinafter, the laser scanner unit 707M will be described as an example with reference to FIG. 2 again. The laser light emitted from the semiconductor laser 7071 is applied to the surfaces of six polygon mirrors 7073 that rotate while being coupled to a motor 7077 via a lens 7072.

The laser light deflected by the polygon mirror 7073 is deflected so as to scan in a direction intersecting the rotation direction of the photosensitive drum 708M. The laser light is corrected by the fθ lens 7074 so that the scanning speed on the surface of the photosensitive drum is substantially constant, and is deflected by the reflection mirror 7076.
Thereafter, the deflected laser light is applied to a photosensitive drum 708M disposed below the laser scanner unit 707M to form a latent image. Thereafter, development is performed by the developing device 710M, and transfer to the intermediate transfer belt 711 is performed. While the laser scanner unit 707M has been described above, the same processing is performed for the laser scanner units 707Y, 707C, and 707K.

  FIG. 4 shows details of reading and writing of line data in the line buffer 2002 including the ten line buffers 1 to 10 in the above-described processing. FIG. 5 shows details of a circuit including the write selector 2001, the line buffer 2002, and the read selector 2003.

  As shown in FIG. 4, the image processing unit 1151 outputs line data every two lines in accordance with the image synchronization signal. The write selector 2001 writes the two output image data sequentially from the first line buffer 1 of the line buffer 2002.

As shown in FIG. 5, line data (write_odd) of odd lines and line data (write_even) of even lines are input to the line buffers 1 to 10, respectively. The write selector 2001 separately selects a line buffer in which writing is performed for each of the line data of the even-numbered line and the line data of the odd-numbered line in accordance with the write selection signal (write_sel). As a result, the line data of the odd line and the line data of the line line are stored in separate buffers.
Also, as shown in FIG. 5, read signals (read_0 to read_3) are input to the line buffers 1 to 10, respectively. The read selector 2003 selects three line buffers from which reading is to be performed, based on a read selection signal (read_sel).

  In the example of FIG. 4, as shown in the data read / write state of the line buffer 2002, the line data 1 which is the first (first line) line data is stored in the line buffer 1, and the line data of the second line is stored in the line buffer 2 Is stored in The line data of the third line is stored in the line buffer 3, and the line data of the fourth line is stored in the line buffer 4.

The line data stored in the line buffer 2002 is read from the three (read_sel) line buffers selected from the line buffers 2002 by the read selector 2003 in synchronization with the detection signal. In the example of FIG. 4, the image data stored in the line buffers 1 to 3 is read out at a time, and the line data stored in the line buffers 4 to 6 is selected and output by the next detection signal.
FIG. 4 shows an output start timing at which the image processing unit 1151 outputs a plurality of line data to the buffer unit 2000 for forming an image on one recording medium. An output start timing at which the buffer unit 2000 outputs line data for forming an image on one recording medium from the line buffer 2002 to the laser drive circuit 2004 is also shown. Compared with the former output timing, the latter output timing is delayed by at least three periods of the image synchronization signal (two or more periods of the detection signal).

To write and read line data to and from the line buffer 2002 normally, it is necessary to avoid simultaneous writing and reading of line data to the same line buffer.
As shown in FIG. 4, the line data (write_odd) of the odd lines and the line data (write_even) of the even lines are sequentially written to the line buffers 1 to 10. In such a configuration, a line buffer for at least 10 lines is required for normal writing and reading.

  Hereinafter, the reason will be described. FIG. 6 shows an example in which nine line buffers 2002 are used in the data read / write state of FIG. As illustrated, when the number of line buffers 2002 is nine, if writing is performed sequentially from the line buffer 1, the image data of the tenth line is written to the line buffer 1. The reading of the line data 1 as the first line data is performed after the data of the fifth and sixth lines are written in the line buffers 5 and 6. For this reason, as shown in the figure, in the line buffer 1, the writing of the line data of the tenth line occurs while the line data 1 is being read. As a result, normal reading and writing of the line data of the tenth line becomes impossible.

Therefore, in the comparative example, it is necessary to use ten line buffers in order to avoid simultaneous writing and reading to the same line buffer.
Specifically, as shown in FIG. 4, by providing the line buffer 10, at the time of writing the line data of the ninth and tenth lines, the line data of the tenth line is written to the line buffer 10. At this time, line data 1 to line data 3 are read from the line buffers 1 to 3, respectively. Therefore, the writing of the line data 10 and the reading of the line data 1 are performed on separate line buffers, and the reading and writing are performed normally. Further, writing and reading of line data to and from the same line buffer as shown in FIG. 6 are not performed.

<Embodiment>
Next, an embodiment of the present invention will be described. Since the configuration of the entire color copying apparatus and the configuration of the laser scanner unit are the same as those of the comparative example, description thereof will be omitted, and only the control part of the image will be described.
FIG. 7 is a functional block diagram illustrating image control according to the present embodiment. In this embodiment, similarly to the above-described comparative example, the image processing unit 1151 transmits image data to the write selector 2001 of the buffer unit 2000 every two lines in accordance with the image synchronization signal.

  Unlike the comparative example described above, in the present embodiment, a TOP signal representing the head line of image data is input from the image processing unit 1151 to the buffer unit 2000 at the same time as the image synchronization signal and the image data. In the comparative example, the beam detection signal is directly input to the readout selector 2003. However, in the present embodiment, the beam detection signal is input to the synchronization control unit 2005. The synchronization control unit 2005 inputs a detection signal to the write selector 2001 and the read selector 2003.

  FIG. 8 is a flowchart showing this control. 9 shows details of reading and writing of image data in the line buffer 2002, and FIG. 10 shows an explanatory diagram of the line buffer 2002. Note that the processing illustrated in the flowchart of FIG. 8 is executed by the CPU 1100 through the image processing unit 1151, the write selector 2001, and the read selector 2003.

  As shown in FIG. 8, the CPU 1100 determines whether or not the line data 1 of the first line in the rotation direction of the photosensitive drums 708Y, 708M, 708C, and 708K has been input through the image processing unit 1151 (S101). If not input (S101: N), S101 is executed again. If input (S101: Y), a TOP signal indicating the leading end of the image in the rotation direction of the photosensitive drums 708Y, 708M, 708C, and 708K is input to the synchronization control unit 2005. Thereafter, the CPU 1100 determines whether or not to output the line data 1 obtained by reading the document 702 through the write selector 2001 of the buffer unit 2000 (S102).

  This determination is made based on the number of laser beams specified in advance and the setting of whether or not to discard the line data 1. In the present embodiment, the CPU 1100 detects whether the image processing unit 1151 supports two laser beams or three laser beams, and determines the detection result as the number of laser beams “3”. ".

  When the number of laser beams supported by the image processing unit 1151 is “2”, the image processing unit 1151 does not support the number “3” of laser beams used in image processing. In this case, if the output is performed as it is, as in the comparative example, ten line buffers are required for normal reading and writing of the line data. Therefore, in the present embodiment, the CPU 1100 determines that the image data 1 is not to be output (S102: N), and controls the write selector 2001 so that the line data 1 is not output to the line buffers 1, 2, 3,. Is written (S103). This is because it is possible to reduce the number of line buffers to nine.

  Note that the number of laser beams used for image formation is not always fixed, and the number of laser beams used may change due to a change in process speed or designation by a user. For example, although three laser beams are provided in the examples of FIGS. 3 and 7, only two of them may be used in image formation. In this case, in step S102, the CPU 1100 detects the number of laser beams to be used, and compares the detection result with the number of corresponding laser beams by the image processing unit 1151 to determine whether to output image data 1. I do.

  In the example of FIG. 9, the line buffer 9 is selected as the write destination of the line data 1, and the line data 2 and subsequent lines are sequentially written from the line buffer 1. Before the line data 1 written in the line buffer 9 is read out, the line data 1 is overwritten with the line data 10 of the tenth line as shown in FIG. Therefore, the line data 1 is not read and output.

  If the written line data 1 is not read, the write destination may be another line buffer. For example, when the line data 1 is written in the line buffer 8, the ninth line data is written before the line buffer 8 is read. Therefore, the line data 1 may be written into the line buffer 8 and the line data 2 may be written into the line buffer 1. In any case, at the time of the first reading, by starting reading from the line buffer 1 which is the line buffer on which the line data 2 is recorded, the line data 1 is overwritten with another image data. As a result, the line data 1 is discarded. As a method of discarding the line data 1, a method of overwriting with the dummy data or not writing the line data 1 may be adopted.

After finishing writing the line data 1, the CPU 1100 receives the image synchronization signal and writes the line data 2 to the line buffer 1 through the synchronization control unit 2005 and the write selector 2001. Thereafter, the line data 3 and the line data 4 are written into the line buffer 2 and the line buffer 3, respectively, and the line data 5 and the line data 6 are written into the line buffer 4 and the line buffer 5, respectively.
Further, the CPU 1100 receives the detection signal input from the laser scanner unit 707 to the synchronization control unit 2005, and reads out the line data of the line buffers 1, 2, and 3 by the read selector 2003 (S104). As a result, the line data 2, 3, and 4 are read from the line buffers 1, 2, and 3.

  In the example of FIG. 9, the line data 1 is not output. However, many image forming apparatuses, including an image forming apparatus using a laser beam, have a margin at the head of line data. Therefore, even if the line data 1 is deleted, important image information is not deleted, and there is substantially no problem.

After executing the processing of S104, the CPU 1100 repeats the writing and reading processing (S105), and executes the processing by determining whether or not the line data of the last line has been read. When the reading of the line data of the last line is completed (S106: Y), the copy processing is completed. If the reading of the line data of the last line has not been completed (S106: N), S105 is executed again.
As described above, the writing of the line data 1 is performed to the line buffer of the line buffers 1 to 9 in which the written line data 1 is overwritten by another line data before the reading. As a result, the line buffer for one line per color can be reduced as compared with the comparative example.

  As shown in FIG. 9, the reading of the line data 1 is performed after the data of the fifth line and the sixth line are written into the line buffers 5 and 6. Then, while the line data 1 is being read from the line buffer 1, the line data 9 and 10 are written into the line buffers 8 and 9. Here, when the number of line buffers is 8, the line data 10 is written into the line buffer 1. On the other hand, when the line data 10 is written, the line data 1 is read from the line buffer 1, so that reading and writing to the line buffer 1 occur simultaneously. Therefore, in this embodiment, it is understood that a line buffer for at least 9 lines is required.

  On the other hand, if it is determined in S102 that the number of laser beams supported by the image processing unit 1151 matches the number of laser beams used in the image forming process, it is determined that the line data 1 is output as usual. (S102: Y). Since the number of laser beams supported by the image processing unit 1151 matches the number of laser beams used in the image forming process, writing and reading are performed normally even if the line data 1 is written to the line buffer 1 as usual. This is because that. Thereafter, the CPU 1100 controls the write selector 2001 to sequentially write data from the line data 1 to the buffer lines 1, 2, 3,... (S107), and executes the above-described processing from S104.

  FIG. 9 shows details of reading and writing of line data in the line buffer 2002 in the flowchart shown in FIG. FIG. 10 shows details of the circuits of the write selector 2001, the line buffer 2002, and the read selector 2003.

  As shown in FIG. 10, in this example, nine line buffers are prepared, and one of the odd-numbered line data (write_odd) and the even-numbered line data (write_even) is stored in each of the line buffers 1 to 9. Is written to. Other configurations are the same as the details of the circuit including the line buffer 2002 shown in FIG.

  On the other hand, as shown in FIG. 9, in this example, the image processing unit 1151 inputs a TOP signal indicating that the head of the image of the document 702 has been read out to the synchronization control unit 2005. In response, the write selector 2001 writes the line data 1 of the first line in the rotation direction of the photosensitive drums 708Y, 708M, 708C, and 708K to the line buffer 9, and writes the second line data to the line buffer 1. . Thereafter, the write selector 2001 writes the line data of the third line and the line data of the fourth line to the line buffers 2 and 3 so as to be sequentially input.

  The written line data is selected from the line buffer selected by the read selector 2003 in synchronization with the detection signal (read_sel). The bit data included in the line data stored in the selected line buffer is output to the laser drive circuit 2004 via the high frequency clock read selector 2003. In this example, reading is performed from the line data 2 of the second line from the head. Accordingly, first, the line data 2 to 4 stored in the line buffers 1 to 3 are simultaneously read, and the line data 5 to 7 stored in the line buffers 4 to 6 are selected and read by the next detection signal.

  The line buffer 9 storing the line data of the first line is overwritten with the line data of the tenth line before the line data of the first line is read. Thereafter, the line data 8 to 10 stored in the line buffers 6 to 9 are selected and read. Therefore, although the line data of the first line is not output, the image data of the second and subsequent lines are normally read and written.

The laser drive circuit 2004 drives the semiconductor laser 7071 based on the line data read in this way, and couples the laser light to the surface of the six polygon mirrors 7073 that rotate by being coupled to the motor 7077 via the lens 7072. Irradiate.
The laser beam deflected by the polygon mirror 7073 is corrected in scanning speed by the fθ lens 7074, is deflected by the reflection mirror 7076, and is irradiated on the photosensitive drums 708Y, 708M, 708C, and 708K arranged below. In this manner, after forming the latent images on the photosensitive drums 708Y, 708M, 708C, and 708K, image formation can be performed by performing development and transfer in the same manner as in the comparative example.

  As described above, in the present embodiment, when the image processing unit 1151 supports two laser beams and three laser beams are used in the image forming process, the image processing unit 1151 outputs the image data 1 Writing and reading are performed so as not to be performed. As a result, the number of line buffers required for normal writing and reading can be reduced from ten lines in the comparative example to nine lines.

  As described above, according to the present embodiment, it is possible to form an image using three laser beams by using the image processing unit 1151 corresponding to two laser beams. At this time, in the comparative example, ten line buffers are required, but in the present embodiment, the number of line buffers can be reduced to nine. Therefore, the same image forming unit is used for any of the image forming apparatus having nine line buffers and two laser beams and the image forming apparatus having nine line buffers and three laser beams. The line data can be read and written normally by using this.

The same image processing unit is used regardless of whether the number of laser beams used in an image forming apparatus having nine line buffers and three laser beams is three or two. Reading and writing of image data can be performed normally using the 1151.
Therefore, it is not necessary to exchange the image processing units 1151 depending on whether the number of laser beams to be used is three or two, or to prepare two image processing units 1151 corresponding to the respective laser beams. Manufacturing cost can be suppressed. In particular, when the image processing unit 1151 and the buffer unit 2000 are mounted on the same board, it is virtually impossible to replace the image processing unit 1151. Therefore, the manufacturing cost can be reduced by using a single image processing unit 1151 that can cope with both the case of using two laser beams and the case of using three laser beams as in the present embodiment.

  In the present embodiment, when the determination result in S102 is Y, the CPU 1100 controls the read selector 2003 to read image data from the line buffer 1 when reading the first data from the line buffer 2002. ing. However, the reading of the image data does not necessarily have to be started from the line buffer 1.

  For example, the first data read from the line buffer may be performed from the line buffer in which the line data 2 is written. In this case, in the first writing of the line data, the line buffer to which the line data 2 is written can be arbitrarily determined. The line data 1 is written to a line buffer different from the line buffer to which the line data 2 is written so that another line data is written before the line data 1 is read.

  For example, in the first write, the line data 1 is written into the line buffer 8 and the line data 2 is written into the line buffer 9, and in the second write, the line data 3 is written into the line buffer 1 and the line data 4 is written into the line buffer 2. Thereafter, the line data 5, 6,... Are sequentially written into the line buffers 3, 4,. In the first reading, line data 2, line data 3, and line data 4 are read from the line buffer 9, line buffer 1, and line buffer 2. Note that, in this example, when the line data 1 is written into the line buffer 9 in the first writing, the operation becomes the same as that shown in FIG. As described above, even if the number of line buffers is 9, line data can be written and read normally.

  Alternatively, the line data 2 may be written to the line buffer 1 and the line data 1 may be written to a line buffer other than the line buffer 1. In this case, the reading of the first data from the line buffer is started from the line buffer 1. The line buffer into which the line data 1 is written is a line buffer into which another line data is written before the line data 1 is read. For example, in the first write, the line data 1 is written in the line buffer 5 and in the second write, the line data 3 is written in the line buffer 1 and in the second write, the line data 4 is written in the line buffer 2. Thereafter, the line data 5, 6,... Are sequentially written into the line buffers 3, 4,.

  In the first reading, line data 2, line data 3, and line data 4 are read from the line buffer 1, the line buffer 2, and the line buffer 3. Note that, in this example, when the line data 1 is written into the line buffer 9 in the first writing, the operation becomes the same as the example shown in FIG. As described above, even if the number of line buffers is 9, line data can be written and read normally.

  As another mode, at the time of the first writing, the line data 1 of the P image data may be deleted and only the P-1 line data may be written to the line buffer 1. In this case, the line data 1 is not recorded in the line buffer. For example, in this embodiment, the line data 1 is written in the line buffer 9 as shown in FIG. 9, but the line data 1 is not written in any line buffer. In the subsequent writing, writing to the line buffer 2002 is performed for every P image data. Even in this case, the use of the nine line buffers 1 to 9 allows normal writing and reading of line data.

Claims (3)

An image forming apparatus that forms an image on a recording medium,
A rotating photoreceptor,
A laser light source comprising a first light emitting point for emitting a first laser light, a second light emitting point for emitting a second laser light, and a third light emitting point for emitting a third laser light; A first driver for driving one light emitting point, a second driver for driving the second light emitting point, and a third drive for driving the third light emitting point A scanning unit that scans the photoconductor in a direction in which the first laser beam, the second laser beam, and the third laser beam intersect with the rotation direction of the photoconductor. Deflecting means for deflecting each laser light so that the order of scanning positions from the downstream side in the rotation direction of the photoconductor is the first laser light, the second laser light, and the third laser. The first light emitting point, the second light emitting point, and the Scanning means third light-emitting points are arranged,
Detecting means for receiving the laser light deflected by the deflecting means and generating a detection signal based on the light receiving timing of the laser light;
Signal generation means for synchronizing with the detection signal and generating a synchronization signal having a frequency that is 3/2 times the frequency of the detection signal;
On the basis of the input image data, a plurality of line data corresponding to each scanning line of the laser light, which are line data for forming an image on a recording medium, are generated, and are generated in synchronization with the synchronization signal. Processing means for outputting line data every two lines;
Nine line buffers for holding line data output from the processing means, nine line buffers for holding line data corresponding to nine scanning lines on the photoconductor, respectively, and the processing means outputs A first selector for switching an input destination of the line data of the two lines in the nine line buffers in synchronization with the synchronization signal, and detecting the input destination of each of the line data stored in the nine line buffers; Buffer means comprising: a second selector that switches among the first driving unit, the second driving unit, and the third driving unit in synchronization with a signal;
Output start timing of line data corresponding to the one recording medium from the buffer unit to the driving unit with respect to output start timing of line data corresponding to one recording medium from the processing unit to the buffer unit Is delayed by at least two periods of the detection signal,
The first selector sequentially inputs a plurality of line data corresponding to the one recording medium from the first line data and the second line data to the nine line buffers in synchronization with the synchronization signal. Switch the connection between the processing means and the nine line buffers,
The second selector does not output the line data of the first line among the plurality of line data corresponding to the one recording medium to the first drive unit, and outputs the line data of the second line to the first drive unit. The first drive unit, the third line data is input to the second drive unit, the fourth line data is input to the third drive unit, and the fifth and subsequent line data are input to the third drive unit. The nine line buffers, the first driving unit, and the first driving unit are output so as to be output to the first driving unit, the second driving unit, and the third driving unit in the order of input to the line buffer. An image forming apparatus for switching connection between the second drive unit and the third drive unit.   The image forming apparatus according to claim 1, wherein the line data is a sequence of a plurality of bit data, and the bit data is used to turn on or off the laser light source.   The image forming apparatus according to claim 1, wherein the nine line buffers are overwritten with line data input from the processing unit.