JP5315804B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an electrophotographic image forming apparatus such as a copying machine or a printer.

  In general, a laser scanning optical device mounted on this type of image forming apparatus includes a plurality of light emitting points (hereinafter referred to as “light emitting points”) that emit light at different positions in the sub-scanning direction in order to cope with high speed and high definition of image formation. A light source having a multi-beam). As a method for detecting a synchronization signal in the main scanning direction, one of the multi-beams irradiates the SOS sensor to output a synchronization signal, and the other beams correct the beam interval in the main scanning direction from the synchronization signal. There has been proposed a method for controlling the beam position in the main scanning direction by using the delayed synchronization signal.

  Further, Patent Document 1 describes a positional deviation in the main scanning direction of a beam due to an optical element processing error, a position and shape error of a reflecting surface of a deflector, and a video detector of each beam of a multi-beam by a beam detector. For a beam that has been detected and the amount of video skew has been detected, it is described that a video controller corrects the video skew by generating a synchronization signal whose phase is shifted in the opposite direction by the amount of video skew.

However, the image forming apparatus described in Patent Document 1 requires a detector for detecting the scanning position of the multi-beam or the video skew amount, and the configuration of the apparatus is complicated. Further, depending on the image processing mode, the above-described misalignment in the main scanning direction may be allowed, but even in such a case, since the video skew amount is detected and corrected, the processing takes time and the productivity of image formation is reduced. It has the problem of being lowered.
JP 2003-266770 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing image degradation due to beam misalignment in the main scanning direction without complicating the apparatus and reducing image forming productivity.

In order to achieve the above object, an image forming apparatus according to the first embodiment of the present invention includes:
A light source having a plurality of light emitting points that emit light at different positions in the sub-scanning direction;
Scanning means for scanning the photosensitive member with a plurality of beams output from the light source;
Synchronization signal output means arranged outside the image area and outputting a main scanning synchronization signal by irradiation of any one of the light sources;
Driving means for modulating the light source based on image data;
A laser scanning optical device having
The plurality of beams draw the same color;
Control means for controlling the laser scanning optical device, when the cycle of the image pattern by the screen ruling and angle in the selected image processing mode interferes with beam number of the light source to reduce the number of beams to use when drawing ,
It is characterized by.

An image forming apparatus according to a second aspect of the present invention is
A plurality of light sources having a plurality of light emitting points that emit light at different positions in the sub-scanning direction;
Scanning means for deflecting a plurality of beams respectively output from the plurality of light sources by a single deflector, and scanning each of a plurality of photosensitive members corresponding to each light source;
Synchronization signal output means arranged outside the image region and outputting a main scanning synchronization signal by irradiation of one beam output from any one of the plurality of light sources;
Driving means for modulating the plurality of light sources based on image data;
A laser scanning optical device having
The plurality of beams respectively output from the plurality of light sources draw the same color,
Control means for controlling the laser scanning optical device, when the cycle of the image pattern by the screen ruling and angle in the selected image processing mode interferes with beam number of the light source to reduce the number of beams to use when drawing ,
It is characterized by.

An image forming apparatus according to a third aspect of the present invention is:
A light source having a plurality of light emitting points that emit light at different positions in the sub-scanning direction;
Scanning means for scanning the photosensitive member with a plurality of beams output from the light source;
Synchronization signal output means arranged outside the image area and outputting a main scanning synchronization signal by irradiation of any one of the light sources;
Driving means for modulating the light source based on image data;
A plurality of laser scanning optical devices having
The plurality of beams of each laser scanning device draw the same color,
Control means for controlling the laser scanning optical device, when the cycle of the image pattern by the screen ruling and angle in the selected image processing mode interferes with beam number of the light source to reduce the number of beams to use when drawing ,
It is characterized by.

In each of the image forming apparatuses, the control unit reduces the number of beams to be used based on the selected image processing mode . The selected image processing mode means that the period of the image pattern depending on the number of screen lines and angles interferes with the number of beams of the light source, and the image formed when each beam is misaligned in the main scanning direction It means something that causes unevenness.

In the image forming apparatus, when an image processing mode that interferes with the number of beams is selected, the number of beams used for drawing is reduced , so that the cycle of the image pattern and the cycle of the beam used for drawing are reduced. In other words, the amount of displacement in the main scanning direction is not uniform, and an image having no streaks or unevenness can be obtained.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. In each figure, the reference numerals are used in common.

(Refer 1st Example and FIGS. 1-15)
First, a schematic configuration of an image forming apparatus according to a first embodiment of the present invention will be described with reference to FIG. This image forming apparatus is an electrophotographic monochrome printer, and includes an image forming station 101, a photosensitive drum 102, a laser scanning optical unit 1, a charger 103, a developing device 104, and the like.

  The beam B emitted from the laser scanning optical unit 1 irradiates the photosensitive drum 102 to form an image. In addition, an automatic paper feeding unit 130 that feeds the stacked transfer materials one by one is installed in the lower part of the image forming apparatus.

  The image data is transmitted as image data from an image reading device (scanner) or a computer (not shown) to the storage means 31 (see FIG. 3). Based on these image data, the laser scanning optical unit 1 is driven and the photosensitive drum 102 is driven. A toner image is formed thereon. Such an electrophotographic process is well known and will not be described.

  The toner image formed on the photoconductive drum 102 is transferred from the paper supply unit 130 to a transfer material fed one by one, and the fixing device 135 heats and fixes the toner. Thereafter, the transfer material is discharged from the image forming apparatus.

  Next, the laser scanning optical unit 1 will be described. As shown in FIG. 2, the laser scanning optical unit 1 includes a light source unit and a scanning unit including a polygon mirror 4. The light source unit includes a semiconductor laser array 2 (hereinafter also referred to as an LD array), a collimator lens 3, and a slit plate 8. The scanning unit includes an optical sensor 5 (hereinafter also referred to as an SOS sensor) for outputting a main scanning synchronization signal (hereinafter also referred to as an SOS signal), scanning lenses 6a and 6b, and a folding mirror 7. . The polygon mirror 4 is rotationally driven at a predetermined speed based on a drive signal input to the drive unit 11 (see FIG. 3).

  The LD array 2 has four light emitting points that emit light at different positions in the sub-scanning direction Z, and the beam emitted from each light emitting point is made substantially parallel light by the collimator lens 3 and reflected by the polygon mirror 4. The light is deflected in the main scanning direction Y at a constant angular velocity on the surface, transmitted through the scanning lenses 6 a and 6 b, reflected by the folding mirror 7, imaged on the photosensitive drum 102, and scanned in the main scanning direction Y. A two-dimensional electrostatic latent image is formed on the photosensitive drum 102 by the main scanning and the sub scanning by the rotation of the photosensitive drum 102.

  Scanning lens 6a. 6 b has an fθ characteristic for correcting the beam deflected at a constant angular velocity by the polygon mirror 4 to a constant velocity in the main scanning direction Y, and an imaging characteristic for forming an image of the beam on the photosensitive drum 102.

  The SOS sensor 5 is disposed outside the image area, and a beam that has passed through the scanning lenses 6a and 6b and reflected by the folding mirror 7 is incident thereon. The SOS sensor 5 is used for detecting the scanning speed of the polygon mirror 4 and synchronizing the main scanning direction Y of each beam.

  The laser scanning optical unit 1 is controlled by a control unit shown in FIG. Image data Da to Dd corresponding to each of the four beams is supplied to the modulation circuits 35a to 35d. In the modulation circuits 35a to 35d, signals based on the image data Da to Dd and the data clocks DCKa to DCKd are generated. Signals from the modulation circuits 35a to 35d are supplied to the respective light emitting points of the LD array 2 via the laser driving circuits 10a to 10d, and beams are emitted.

  The laser drive circuits 10a to 10d are individually driven by a control signal from the CPU 32 so as to be driven only in the horizontal and vertical effective periods. A signal indicating the amount of light from the LD array 2 is fed back to each of the laser drive circuits 10a to 10d, and driving of each light emitting point of the LD array 2 is controlled so that the amount of light is constant.

  As described above, the laser beam output from the LD array 2 is deflected by the polygon mirror 4 and scans on the photosensitive drum 102. Drawing by scanning on one surface of the polygon mirror 4 is referred to as one scanning. The writing position of the deflected beam in the main scanning direction Y is controlled based on the SOS signal detected by the SOS sensor 5 disposed on the tip side of the scanning region. That is, the beam detection signal of the SOS sensor 5 is supplied to the pixel clock generation circuit 34 via the CPU 32, and the image writing timing by each light emitting point of the LD array 2 is controlled.

  The LD array 2 is a multi-beam laser that simultaneously emits four beams. As shown in FIG. 4, the light emitting points a to d are arranged obliquely so as to be in different positions with respect to the sub-scanning direction Z. . The pitch z in the sub-scanning direction Z is determined by the resolution of the image. In the main scanning direction Y, the light emitting points b, c, d have the pitches L1, L2, L3 with respect to the light emitting point a. .

  The light emission timings of the beams a to d output from each light emitting point are as shown in FIG. That is, first, the beam a is emitted to scan the SOS sensor 5 to generate an SOS signal. Thereafter, the beam “a” is delayed from the SOS signal by a time t 1, modulated based on the image data, and scanned on the photosensitive drum 102. The beams b, c, and d are modulated based on the image data after being delayed from the beam a by times t2, t3, and t4, respectively, and scan on the photosensitive drum 102.

  The delay times t2, t3, and t4 are values obtained by dividing the pitches L1, L2, and L3 in the main scanning direction Y of the beam shown in FIG. 4 by the main scanning speed. By changing this delay time, the write timing in the main scanning direction Y for each beam can be changed.

  FIG. 6 shows the positions of the beams a to d on the photosensitive drum 102, and the beams b to d are shifted in the main scanning direction Y by Δ1, Δ2, and Δ3 from the designed positions, as indicated by dotted lines. Shows the case. Here, the design position is a position in the main scanning direction Y calculated by design when the pitch z in the sub-scanning direction Z is arranged at a desired value. The reason why the beam deviates from the design position is that the interval between the light emitting points is shifted in the manufacturing process in the LD array 2, or the magnification of the optical system or the error in arrangement.

  FIG. 7 shows a deviation of the drawn image when the beam has the deviation shown in FIG. A dotted line indicates a design drawing position. Since the writing timing is set as a design position, in FIG. 7, it appears as an image shift with the shift amounts Δ1, Δ2, Δ3 of the beams b to d.

  These image shifts occur at a cycle of the number of beams. In this case, since scanning is performed with four beams, the shift period is every four lines. These shifts do not pose a problem as quality degradation in a normal image, but depending on the image processing mode, the image pattern period and the number of beams interfere to cause streaking and unevenness in the image, resulting in degradation of quality. There is a case.

  Specifically, as shown in FIG. 8, it may be assumed that, for example, a line 1 drawn only with the beam a and a line 4 drawn only with the beam d are formed in parallel by image processing. In this case, the deviation in the main scanning direction Y of the beam becomes the gap deviation between the line 1 and the line 4 as it is and is visually recognized as a streak or unevenness.

  Therefore, in the first embodiment, the number of beams used for drawing is changed. Such control is executed when the period of the image pattern in the selected image processing mode interferes with the number of beams and streaks or unevenness due to interference occurs in the image. This will be described in detail below.

  The control procedure is as shown in FIG. First, an image processing mode is selected (step S1), and it is determined whether or not the selected image processing mode interferes with the number of beams (step S2). If it is determined that interference occurs, a process of changing the number of beams to be used (for example, 3 beams) is performed (step S3), and an image is drawn (step S6). If there is no interference, the image is drawn (step S6) without changing the number of beams used (step S4).

  FIG. 10 shows the positions in the sub-scanning direction Z and the number of scans of each of the beams a to d using the normal four beams. FIG. 11 shows the positions of the beams a to c in the sub-scanning direction Z and the number of scans when the number of beams is changed to 3 without using the beam d according to the first embodiment.

  As for the position in the sub-scanning direction Z of each beam at the time of normal drawing shown in FIG. 10, the scanning n + 1-th beam a is arranged on the line in the sub-scanning direction Z next to the n-th scanning beam d. In the first embodiment shown in FIG. 11, drawing is performed with three beams a to c in one scan without using the beam d. Therefore, the positions of the n-th scanning beam d and the scanning n + 1-th beam a in the sub-scanning direction Z are matched.

  FIG. 12 shows the shift of the image drawn when the control of the first embodiment is performed when the beam has the shift shown in FIG. A dotted line indicates a design drawing position. Since scanning is performed with three beams while reducing the number of beams to be used, the shift period on the image is also every three lines.

  FIG. 13 shows an example of an image drawn in the first embodiment. Line 1 and line 4 correspond to line 1 and line 4 in FIG. By reducing the number of used beams to 3, line 1 is drawn with beam a for the nth scan, drawn with beam b for scan n + 1, drawn with beam c for scan n + 2, and beam n for scan n + 3. Rendered with a. In this way, the line 1 is sequentially drawn with the beams a to c. Similarly to the line 1, the line 4 is sequentially drawn with the beams a to c. Since the beams a to c are displaced in the main scanning direction Y (see FIG. 6), the line 1 and the line 4 are not strictly straight lines. However, since the shift is every scan, the shift amount on the image is not uniform, interference with the image pattern is suppressed, and streaks and unevenness are not noticeable.

  In this type of image forming apparatus, the rotational speed of the polygon mirror 4 is the main scanning speed, and the rotational speed of the photosensitive drum 102 is the sub-scanning speed (system speed). The sub-scanning speed in the normal state is a speed at which the distance of the beams a to d in the sub-scanning direction Z moves in the sub-scanning direction Z in one main scanning time.

  Therefore, when the number of beams used is changed to 3, if the main scanning speed is not changed, the sub-scanning speed (system speed) is changed to the sub-scanning direction Z in the sub-scanning direction Z in one main scanning time. It is necessary to change the distance in the scanning direction Z to the moving speed (see the first example of the control procedure, step S5 in FIG. 14). Specifically, changing the system speed means changing the rotation speed of the photosensitive drum 102 and the rotation speeds of various rollers that convey the transfer material.

  In addition, when the number of beams used is changed to 3, if the system speed is not changed, the time required to move the distance in the sub-scanning direction Z with 4 beams in the sub-scanning direction Z is equivalent to 4 beams with 3 beams. The rotation speed of the polygon mirror 4 is changed so that the scanning time during which the main scanning line can be drawn is changed (see the second example of the control procedure, step S5 in FIG. 15). At the same time, the image data frequency, the image writing timing, and the laser light emission amount corresponding to the changed rotation speed of the polygon mirror 4 are changed.

(Refer 2nd Example and FIGS. 16-19)
A schematic configuration of an image forming apparatus according to a second embodiment of the present invention will be described with reference to FIG. This image forming apparatus is an electrophotographic color printer and is configured to form an image of four colors (Y: yellow, M: magenta, C: cyan, K: black) by a so-called tandem method. is there. An image is formed at each image forming station 101 and is combined on the intermediate transfer belt 112. In each figure, the letters Y, M, C, and K attached to the reference numerals mean members for yellow, magenta, cyan, and black, respectively.

  The outline of the image forming station 101 (101Y, 101M, 101C, 101K) will be described. The photosensitive drum 102 (102Y, 102M, 102C, 102K), the laser scanning optical unit 1, and the developing device 104 (104Y, 104M, 104C). , 104K).

  Beams BY, BM, BC, and BK emitted from the laser scanning optical unit 1 irradiate the photosensitive drums 102 to form images of the respective colors. On the other hand, an intermediate transfer belt 112 is stretched endlessly by rollers 113, 114, and 115 immediately below the image forming station 101, is driven to rotate in the direction of arrow A, and is a portion where the driving roller 113 is installed. A secondary transfer roller 116 is disposed in a portion (secondary transfer portion) facing the belt 112. In addition, an automatic paper feeding unit 130 that feeds the stacked transfer materials one by one is installed in the lower part of the image forming apparatus.

  Image data is transmitted to the storage means 31 (see FIG. 17) as image data for each YMCK from an image reading device (scanner) or a computer (not shown), and the laser scanning optical unit 1 is driven based on these image data. A toner image is formed on the photosensitive drum 102. Such an electrophotographic process is well known and will not be described.

  The toner images formed on the respective photosensitive drums 102 are sequentially primary-transferred onto the intermediate transfer belt 112 that is rotationally driven in the direction of arrow A, and four color images are combined. On the other hand, the transfer material is fed one sheet at a time from the sheet feeding unit 130, and the composite image is secondarily transferred from the intermediate transfer belt 112 by the electric field applied from the transfer roller 116 in the secondary transfer unit. Thereafter, the transfer material is conveyed to a fixing device (not shown), and the toner is heated and fixed, and is discharged to the upper surface of the image forming apparatus.

  A TOD sensor 106 for detecting the fed paper is installed immediately before the secondary transfer unit, and the transfer material and the image on the intermediate transfer belt 112 are synchronized. In addition, a registration sensor 105 for detecting a registration correction image formed on the intermediate transfer belt 112 is provided. A registration correction image is formed on the belt 112 for each image forming station 101, and the correction image is detected by the sensor 105, thereby adjusting the light emission timing of each laser beam BY, BM, BC, BK, and YMCK. These images are accurately synthesized on the belt 112.

  The laser scanning optical unit 1 includes an LD array 2 and its driving circuit for each color of YMCK, and simultaneously deflects / scans 4 × 4 = 16 beams by a single polygon mirror 4. The configuration of the laser scanning optical unit 1 is basically the same as that shown in FIG. The drive circuit is as shown in FIG. 17, and drives the LD arrays 2Y, 2M, 2C, and 2K by the respective image data modulators 36Y, 36M, 36C, and 36K. In FIG. 17, the reference numerals are used in common with FIG.

  The SOS signal output from the SOS sensor 5 is obtained by any one of a total of 16 beams, for example, any beam of the LD array 2K that draws black.

  The problem described in the first embodiment also occurs in the laser scanning optical unit 1 including the four LD arrays 2 corresponding to the respective colors of YMCK, the respective modulators 36, and the single polygon mirror 4. That is, when the image pattern is different for each color of YMCK and the period of the image pattern interferes with the number of beams in drawing of any color, main scanning is performed on the corresponding four beams of the LD arrays 2Y, 2M, 2C, and 2K. If the positional deviation in the direction Y occurs, streaks and unevenness occur in the image and the quality deteriorates.

  In order to avoid such deterioration in image quality, in the second embodiment, the number of beams used in each LD array 2 at the time of drawing is changed. Such control is executed when the period of the selected image pattern interferes with the number of beams for each color of YMCK and when lines or unevenness due to interference occurs in the image. This will be described in detail below.

  A first example of the control procedure is as shown in FIG. First, an image processing mode for each color of YMCK is selected (step S11), and it is determined for each color of YMCK whether the selected image processing mode and the number of beams interfere (step S12). If it is determined that interference occurs, a process of changing the number of beams used in the LD array 2 for each color of YMCK (for example, 3 beams) is performed (step S13). Then, the system speed is changed in the same manner as in step S5 in FIG. 14 (step S15), and an image is drawn (step S16). If there is no interference, the image is drawn (step S16) without changing the number of beams used (step S14).

  A second example of the control procedure is as shown in FIG. 19 and is different from the first example in that it is used in the LD array 2 of each color of YMCK when the selected image processing mode and the number of beams interfere. The number of beams is changed (step S13), and the rotation speed of the polygon mirror 4, the image data frequency, the image writing start timing, and the laser light emission amount are changed (step S15), and the system speed is not changed. The change control in step S15 is as described in FIG.

(Refer 3rd Example and FIGS. 20-23)
A schematic configuration of a third embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. This image forming apparatus is an electrophotographic color printer as in the second embodiment, and is an image of four colors (Y: yellow, M: magenta, C: cyan, K: black) by a so-called tandem method. It is comprised so that may be formed. The difference from the second embodiment is that laser scanning optical units 1Y, 1M, 1C, and 1K are provided for each color of YMCK.

  The laser scanning optical unit 1 includes an LD array 2, a driving circuit thereof, and a polygon mirror 4 for each color of YMCK, and simultaneously deflects / scans four beams. The configuration of the laser scanning optical unit 1 is basically the same as that shown in FIG. The drive circuit is as shown in FIG. 21, and drives the LD arrays 2Y, 2M, 2C, and 2K by the respective image data modulators 36Y, 36M, 36C, and 36K. In FIG. 21, the reference numerals are used in common with FIG.

  The four laser scanning optical units 1 driven independently corresponding to each color of YMCK also have the problem described in the first embodiment. That is, when the image pattern is different for each color of YMCK and the period of the image pattern interferes with the number of beams in drawing of any color, main scanning is performed on the corresponding four beams of the LD arrays 2Y, 2M, 2C, and 2K. If the positional deviation in the direction Y occurs, streaks and unevenness occur in the image and the quality deteriorates.

  In order to avoid such deterioration in image quality, in the third embodiment, the number of beams used in each LD array 2 at the time of drawing is changed. Such control is executed when the period of the selected image pattern interferes with the number of beams for each color of YMCK and when lines or unevenness due to interference occurs in the image. This will be described in detail below.

  A first example of the control procedure is as shown in FIG. First, an image processing mode for each color of YMCK is selected (step S21), and it is determined for each color of YMCK whether the selected image processing mode and the number of beams interfere (step S22). If it is determined that interference occurs, a process of changing the number of beams used in the LD array 2 for each color of YMCK (for example, 3 beams) is performed (step S23). Then, the system speed is changed in the same manner as in step S5 in FIG. 14 (step S25), and an image is drawn (step S26). If there is no interference, the image is drawn (step S26) without changing the number of beams used (step S24).

  A second example of the control procedure is as shown in FIG. 23. The difference from the first example is that when the selected image processing mode and the number of beams interfere, the color determined to interfere is drawn. The number of beams used in the LD array 2 is changed (step S23), the rotational speed of the polygon mirror 4 of the laser scanning optical unit 1 that draws the color determined to interfere, the image data frequency, the image writing start timing, and the laser emission. Only the amount of light is changed (step S25), and the system speed is not changed. The change control in step S25 is as described in FIG.

(Other examples)
Note that the image forming apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  In particular, the number of light emitting points incorporated in the light source is not limited to four. Further, the type and arrangement of optical elements for scanning the beam are arbitrary.

1 is a schematic configuration diagram illustrating a first embodiment of an image forming apparatus according to the present invention. It is a top view which shows a laser scanning optical unit. It is a block diagram which shows the control part of a laser scanning optical unit. It is explanatory drawing which shows the light emission point of LD array. It is a chart figure which shows the light emission timing of a beam. It is explanatory drawing which shows the shift | offset | difference of the main scanning direction of a beam. It is explanatory drawing which shows the image shift by the said shift | offset | difference of a beam. It is explanatory drawing which shows the shift | offset | difference of the image by interference in two dimensions. It is a flowchart figure which shows the control procedure used as the basis for correct | amending the shift | offset | difference of an image. It is explanatory drawing which shows the drawing by normal four beams. It is explanatory drawing which shows drawing at the time of changing the number of used beams. It is explanatory drawing which shows the image which correct | amended deviation. It is explanatory drawing which shows in two dimensions the image which correct | amended deviation. It is a flowchart figure which shows the 1st example of the control procedure in 1st Example for correct | amending the shift | offset | difference of an image. It is a flowchart figure which shows the 2nd example of the control procedure in 1st Example for correct | amending the shift | offset | difference of an image. It is a schematic block diagram which shows 2nd Example of the image forming apparatus which concerns on this invention. It is a block diagram which shows the control part of a laser scanning optical unit. It is a flowchart figure which shows the 1st example of the control procedure in 2nd Example for correct | amending the shift | offset | difference of an image. It is a flowchart figure which shows the 2nd example of the control procedure in 2nd Example for correct | amending the shift | offset | difference of an image. It is a schematic block diagram which shows 3rd Example of the image forming apparatus which concerns on this invention. It is a block diagram which shows the control part of a laser scanning optical unit. It is a flowchart figure which shows the 1st example of the control procedure in 3rd Example for correct | amending the shift | offset | difference of an image. It is a flowchart figure which shows the 2nd example of the control procedure in 3rd Example for correct | amending the shift | offset | difference of an image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser scanning optical unit 2 ... LD array 4 ... Polygon mirror 5 ... SOS sensor 6a, 6b ... Scan lens 10a-10d ... Laser drive circuit 32 ... CPU
102: Photosensitive drums a to d: Light emitting points (beams)
Z ... Sub-scanning direction

Claims (9)

A light source having a plurality of light emitting points that emit light at different positions in the sub-scanning direction;
Scanning means for scanning the photosensitive member with a plurality of beams output from the light source;
Synchronization signal output means arranged outside the image area and outputting a main scanning synchronization signal by irradiation of any one of the light sources;
Driving means for modulating the light source based on image data;
A laser scanning optical device having
The plurality of beams draw the same color;
Control means for controlling the laser scanning optical device, when the cycle of the image pattern by the screen ruling and angle in the selected image processing mode interferes with beam number of the light source to reduce the number of beams to use when drawing ,
An image forming apparatus. The image forming apparatus according to claim 1, wherein when the number of beams to be used is reduced, the control unit changes the system speed to correspond to the reduced number of beams. Wherein, when reducing the number of beams to be used, the rotational speed of the deflector corresponding to the reduced number of beams, the image data frequency, the image writing timing, claim 1, characterized in that to change the light emission amount or The image forming apparatus according to claim 2 . A plurality of light sources having a plurality of light emitting points that emit light at different positions in the sub-scanning direction;
Scanning means for deflecting a plurality of beams respectively output from the plurality of light sources by a single deflector, and scanning each of a plurality of photosensitive members corresponding to each light source;
Synchronization signal output means arranged outside the image region and outputting a main scanning synchronization signal by irradiation of one beam output from any one of the plurality of light sources;
Driving means for modulating the plurality of light sources based on image data;
A laser scanning optical device having
The plurality of beams respectively output from the plurality of light sources draw the same color,
Control means for controlling the laser scanning optical device, when the cycle of the image pattern by the screen ruling and angle in the selected image processing mode interferes with beam number of the light source to reduce the number of beams to use when drawing ,
An image forming apparatus. The image forming apparatus according to claim 4, wherein when the number of beams to be used is decreased, the control unit changes the system speed to correspond to the decreased number of beams. Wherein, when reducing the number of beams to be used, the rotational speed of the deflector corresponding to the reduced number of beams, the image data frequency, the image writing timing, claim 4 or and changes the light emission amount The image forming apparatus according to claim 5 . A light source having a plurality of light emitting points that emit light at different positions in the sub-scanning direction;
Scanning means for scanning the photosensitive member with a plurality of beams output from the light source;
Synchronization signal output means arranged outside the image area and outputting a main scanning synchronization signal by irradiation of any one of the light sources;
Driving means for modulating the light source based on image data;
A plurality of laser scanning optical devices having
The plurality of beams of each laser scanning device draw the same color,
Control means for controlling the laser scanning optical device, when the cycle of the image pattern by the screen ruling and angle in the selected image processing mode interferes with beam number of the light source to reduce the number of beams to use when drawing ,
An image forming apparatus. The image forming apparatus according to claim 7, wherein when the number of beams to be used is decreased, the control unit changes the system speed to correspond to the decreased number of beams. Wherein, when reducing the number of beams to be used, the rotational speed of the deflector corresponding to the reduced number of beams, the image data frequency, the image writing timing, claim 7, characterized in that to change the light emission amount or The image forming apparatus according to claim 8 .

Images