JP4998378B2 - Laser scanning optical device - Google Patents

Description

  The present invention relates to a laser scanning optical apparatus, and more particularly to a laser scanning optical apparatus that is mounted on an image forming apparatus such as a copying machine or a printer and forms an electrostatic latent image on a photoreceptor.

  In general, this type of laser scanning optical apparatus has a plurality of light emitting points (hereinafter also referred to as multi-beams) that emit light at different positions in the sub-scanning direction in order to cope with higher speed and higher definition of image formation. A light source is used. 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 a laser scanning optical device capable of suppressing image deterioration due to beam misalignment in the main scanning direction without complicating the device and reducing image formation productivity.

In order to achieve the above object, a laser scanning optical device according to an aspect of the present invention is provided.
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;
Control means for controlling a main scanning direction writing position of a beam other than the beam for outputting the main scanning synchronization signal based on a predetermined delay amount;
With
The control means can select which of the plurality of light emitting points emits the synchronizing signal output means with a beam output from the light emitting points, and can change the beam that emits the synchronizing signal output means for each scan. der is,
Further, the control means is an image processing mode in which an image pattern period interferes with the number of beams of the light source, and stripes and unevenness due to interference occur in an image formed when each beam is misaligned in the main scanning direction. Is selected, the beam that irradiates the synchronization signal output means is changed for each scan,
It is characterized by.

In the laser scanning optical device, since the beam irradiating the synchronization signal output means is changed for each scan, the amount of positional deviation in the main scanning direction of each beam is not uniform, and there is an image processing mode that interferes with the number of beams. If selected, it is possible to obtain an image without streaks and unevenness.

  Embodiments of a laser scanning optical apparatus according to the present invention will be described below with reference to the accompanying drawings.

(Schematic configuration of image forming apparatus, see FIG. 1)
First, an image forming apparatus provided with a laser scanning optical apparatus according to 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 (1Y, 1M, 1C, 1K), Developing unit 104 (104Y, 104M, 104C, 104K) and the like are included.

  Beams BY, BM, BC, and BK emitted from each laser scanning optical unit 1 irradiate each photosensitive drum 102 to form an image of each color. 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.

  The image data is transmitted to the storage means 31 (see FIG. 3) as image data for each YMCK from an image reading device (scanner) or a computer (not shown), and each laser scanning optical unit 1 is driven based on these image data. A toner image is formed on each 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.

(Laser scanning optical unit, see FIGS. 2 and 3)
Next, each laser scanning optical unit 1 will be described. Each 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.

(Multi-beam drawing, see FIGS. 4 and 5)
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.

(Pitch deviation in the main scanning direction and its correction, see FIGS. 6 to 8)
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. Then, by changing the delay time, the writing timing in the main scanning direction Y of each beam is changed, and even if each beam is displaced in the main scanning direction Y, the pitch deviation in the main scanning direction Y is changed. It can be corrected.

  6 and 7 show the positions of the beams a to d on the photosensitive drum 102. FIG. FIG. 6 shows the case where the beams a to c are arranged at the designed positions, but only the beam d is shifted by Δ3 in the main scanning direction Y as shown by the dotted line (first example). . FIG. 7 shows a case (second example) in which 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. 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. 8A shows the shift of the image drawn when the beam has the shift shown in FIG. 6 (first example). FIG. 8B shows a deviation of the image drawn when the beam has the deviation shown in FIG. 7 (second example). A dotted line indicates a design drawing position.

  In FIG. 8A, as shown in FIG. 6, only the beam d is shifted by Δ3, and the write timing is set as a design position. Therefore, the shift of Δ3 appears as the image shift as it is. Yes. Similarly, in FIG. 8B, as shown in FIG. 7, image deviation appears as the deviation amounts Δ1, Δ2, and 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, for example, it may be assumed that an oblique line drawn only with the beam a and an oblique line drawn only with the beam d are formed in parallel by image processing. In this case, the deviation of the beam in the main scanning direction Y becomes the deviation of the diagonal line as it is, and it is visually recognized as a streak or unevenness.

(Correction of deviation, see FIGS. 9 to 11)
Therefore, in this embodiment, the beam for obtaining the SOS signal is changed for each scan. 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 for changing the beam for obtaining the SOS signal for each scan is performed (step S3), and an image is drawn (step S5). If there is no interference, an image is drawn (step S5) without performing control to switch the beam for obtaining the SOS signal (step S4).

  The specific control timing is as shown in FIG. That is, the beam for obtaining the SOS signal is switched between the beam a and the beam d every scan. At the same time, the timing of writing image data for the beam a from the SOS signal is switched between time t1 and time t1 '. The difference between the times t1 and t1 'is the time difference from the scanning of the SOS sensor 5 to the image data writing timing based on the pitch shift amount of the beam in the main scanning direction Y. That is, the difference between the times t1 and t1 'is a value obtained by dividing the deviation amount Δ3 of the beam a and the beam d in the main scanning direction Y by the scanning speed.

  FIG. 11A shows the deviation of the image drawn when the correction control is performed when the beam has the deviation shown in FIG. 6 (first example). FIG. 11B shows the deviation of the image drawn when the correction control is performed when the beam has the deviation shown in FIG. 7 (second example). A dotted line indicates a design drawing position.

  As is clear from FIGS. 11A and 11B, when the beam from which the SOS signal is obtained is switched for each scan, the SOS signal is obtained by the beam that is deviated for each scan. Appears in the image. 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.

(LD array angle adjustment, see Figure 12)
In the LD array, the initial beam position may deviate from the designed position due to the temperature change or aging of the optical element. In such a case, the pitch z of each beam a to d in the sub-scanning direction Z can be adjusted by rotating the LD array itself and changing the angle with respect to the sub-scanning direction Z.

  When the above adjustment is performed, the pitch in the main scanning direction Y also shifts. However, assuming that the beam interval is designed, the pitch shift amount in the main scanning direction Y with respect to the rotation angle is calculated, and the image data writing timing is calculated. May be corrected. This correction also causes the image deterioration shown in FIG. 7, but as shown in FIG. 10, the image deterioration can be suppressed by changing the beam for obtaining the SOS signal for each scan.

(Drawing by surface emitting laser, see FIG. 13)
A surface emitting laser can be used as a light source having a plurality of light emitting points. In the surface emitting laser, the light emitting points are two-dimensionally arranged, and for example, scanning with 4 × 4 16 beams is possible as shown in FIG. The pitch z in the sub-scanning direction Z of each beam a to p is an equal pitch determined by the resolution.

  Even in the case of using such a surface emitting laser, for example, the beam for obtaining the SOS signal is changed to a beam a for odd scanning and a beam p for even scanning for every scanning with respect to the pitch deviation in the main scanning direction Y. That's fine.

(Other examples)
The laser scanning optical device according to the present invention is not limited to the above-described embodiments, 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 showing an image forming apparatus equipped with a laser scanning optical device according to the present invention. It is a top view which shows one Example of the laser scanning optical apparatus based on this invention. It is a block diagram which shows the control part of a laser scanning optical apparatus. 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 (1st example) of the main scanning direction of a beam. It is explanatory drawing which shows the shift | offset | difference (2nd example) of the main scanning direction of a beam. (A) is explanatory drawing which shows the image shift by a 1st example, (B) is explanatory drawing which shows the image shift by a 2nd example. It is a flowchart figure which shows the control procedure for correct | amending the shift | offset | difference of an image. It is a chart figure which shows the control timing for correct | amending the shift | offset | difference of an image. (A) is explanatory drawing which shows the image which correct | amended the deviation by a 1st example, (B) is explanatory drawing which shows the image which correct | amended the deviation by a 2nd example. It is explanatory drawing which shows angle adjustment of LD array. It is explanatory drawing which shows the light emission point of a surface emitting laser.

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 (4)

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;
Control means for controlling a main scanning direction writing position of a beam other than the beam for outputting the main scanning synchronization signal based on a predetermined delay amount;
With
The control means can select which of the plurality of light emitting points emits the synchronizing signal output means with a beam output from the light emitting points, and can change the beam that emits the synchronizing signal output means for each scan. der is,
Further, the control means is an image processing mode in which an image pattern period interferes with the number of beams of the light source, and stripes and unevenness due to interference occur in an image formed when each beam is misaligned in the main scanning direction. Is selected, the beam that irradiates the synchronization signal output means is changed for each scan,
A laser scanning optical device. 2. The laser scanning optical apparatus according to claim 1, wherein the control unit corrects the writing position in the main scanning direction of another beam when the beam irradiated to the synchronization signal output unit is changed. 3. 3. The laser scanning optical apparatus according to claim 1, further comprising an adjusting unit that adjusts an angle of the light source having the plurality of light emitting points with respect to a sub-scanning direction. The laser scanning optical device according to any one of claims 1 to 3, characterized by using a surface-emitting laser as a light source having a plurality of light emitting points.

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