JP4378787B2 - Optical scanning device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical scanning apparatus that simultaneously scans a surface to be scanned with a plurality of beam spots.
[0002]
[Prior art]
With the development and digitization of information networks in recent years, it has been strongly desired to increase the speed of laser beam printers. One means for increasing the speed of this laser beam printer is to increase the rotation speed of a polygon mirror for scanning. However, at present, when the rotation is close to 50,000 revolutions, the polygonal surface is distorted by the centrifugal force, so that it is considered that there is a limit to further speeding up.
[0003]
Therefore, in order to further increase the drawing speed of the laser beam printer, the surface to be scanned is scanned with a plurality of laser beams.
[0004]
[Problems to be solved by the invention]
However, in the case of using a plurality of laser beams, there are problems in that the control is complicated and costly in various respects in addition to the use of a plurality of light sources as compared with the case of using a single beam. is there. Hereinafter, this problem will be described with an example.
[0005]
In general, a plurality of beam spots are arranged in a direction inclined with respect to the main scanning direction and the direction perpendicular to the main scanning direction on the surface to be scanned. This is because it is possible to form an image with a finer pitch by arranging the members at an inclination. In this case, it is important to adjust the tilt of the laser beam array at the time of manufacture or before the start of scanning, and it is necessary to provide means for adjusting the position and tilt of the light source unit. In the case of a single beam, it is not necessary to adjust the tilt, and the position can be adjusted easily.
[0006]
In view of the above problems, an object of the present invention is to simplify components and reduce costs in an optical scanning apparatus that scans a surface to be scanned with a plurality of beam spots. In particular, the object is to reduce the cost and the means for adjusting the position and inclination of the light source.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a plurality of beams from a light source unit are incident on a surface to be scanned via a deflector and an optical system, and the main scanning direction of the beams and the direction orthogonal to the main scanning direction are related. In an optical scanning device that scans a surface to be scanned with a plurality of beam spots arranged in an inclined direction, each of the beam spots with respect to a direction orthogonal to the main scanning direction except for a region to be scanned on the surface to be scanned A main scanning synchronization signal generating means having a photodetector in which a plurality of photodetectors are arranged so as to be at the same position, and generating a main scanning synchronization signal of each beam spot based on the detection result of the photodetector And means for adjusting the position and inclination of the light source section based on the detection result of the photodetector of the main scanning synchronization signal generating means.
[0008]
In the above configuration, the main scanning synchronization signal generating means is provided for the purpose of knowing the timing for starting scanning of the region or line to be scanned on the surface to be scanned, and a signal for informing the timing is the main scanning synchronization signal. Signal (hereinafter referred to as SOS (start of scanning) signal). The SOS signal synchronizes the modulation signal for recording to be given to the beam spot. In order to generate the SOS signal, it is necessary to know the beam spot position. In the above configuration, this is obtained by detecting the time when the beam spot passes through a predetermined position. A plurality of light detection elements corresponding to each beam spot are arranged at a predetermined position, and the passage time of each beam spot can be known by observing the output of each light detection element. The photodetector composed of the plurality of photodetectors for generating an SOS signal is referred to as an SOS photodetector. The SOS photodetector is for informing each beam spot position. From this detection result, it is also possible to determine whether each beam spot passes through an appropriate position. That is, when the output to be detected is not detected, it does not pass through the appropriate position. By utilizing this, the position and inclination of the light source unit are adjusted in the above configuration.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a plan view showing a schematic configuration of a laser printer as an embodiment to which an optical scanning device of the present invention is applied. In the figure, 3 is a light source unit that simultaneously generates three laser beams, 5 is a collimator lens, 6 is a polygon mirror that simultaneously deflects the laser beam from the light source unit 3, 7 is an imaging lens for scanning, and 8 is photosensitive. The body drum 2 is a photodetector for SOS. FIG. 2 is a plan view showing a detailed configuration of the light source unit 3. A light emitting unit 3a including three semiconductor lasers 31a, 32a, and 33a is fixed to a circular fixed plate 3b, and the position and inclination of the light source unit 3 are adjusted by moving the fixed plate 3b. The light emitting portion 3a is fixed so that the semiconductor laser 31a at the right end in the drawing is positioned at the center of the fixing plate 3b.
[0010]
Returning to FIG. 1, the three laser beams emitted from the light source unit 3 are incident on the polygon mirror 6 through the collimator lens 5, deflected in a time-varying direction by the rotation of the polygon mirror 6, and connected for scanning. The light is condensed on the surface to be scanned including the surface of the photosensitive drum 8 and the light receiving surface of the SOS photodetector 2 through the image lens 7.
[0011]
FIG. 3 is a plan view of a surface to be scanned by a laser beam spot including the light receiving surface 2 a of the photodetector 2. The left side of the figure is the surface to be scanned of the photoconductive drum 8, which is omitted here. In this apparatus, the surface to be scanned is scanned in the main scanning direction A by the three beam spots 31, 32 and 33. The movement of the beam spots 31, 32, 33 in the main scanning direction A is due to the rotation of the polygon mirror 6. The beam spots 31, 32, and 33 are arranged on the straight line j1 at equal intervals on the surface to be scanned.
[0012]
The SOS photodetector 2 has three light detection elements 21, 22, and 23 for detecting light, and the positions of the light detection elements 21, 22, and 23 are equal in the main scanning direction A and in the sub scanning direction. At B, each beam spot 31, 32, 33 is a position to pass. In other words, when the scanning interval is d, the intervals in the sub-scanning direction B of the three photodetecting elements 21, 22, and 23 are also d. When the light source unit 3 is adjusted to an appropriate position and inclination, the distance between the beam spots 31, 32, and 33 in the sub-scanning direction B is also d. The inclination of the straight line j1 with respect to the main scanning direction A is θ.
[0013]
In each of the light detection elements 21, 22, and 23, incident laser beams 31, 32, and 33 are detected. Each of the light detection elements 21, 22, and 23 only needs to be able to detect one laser beam, and therefore a small detection element having a high operating speed is used. Based on the detection results of the light detection elements 21, 22, and 23, SOS signals of the laser beams 31, 32, and 33 are generated by means (not shown).
[0014]
In the present embodiment, data detected by the SOS photodetector 2 is used for adjusting the position and inclination of the light source unit 3, that is, adjusting the inclination of the multi-beam array j1. An embodiment of the adjustment method will be described.
[0015]
FIG. 4 shows a flowchart for adjusting the position and tilt of the light source unit 3 in this embodiment. First, in step # 1, the center position of the fixing plate 3b is fixed. Specifically, the fixed plate 3b is moved in two directions (X direction and Y direction) perpendicular to the optical axis, and the laser beam 31 emitted from the semiconductor laser 31a is incident on the corresponding light detection element 21. Then, the center position of the fixing plate 3b is fixed at a position where the output of the light detection element 21 is maximized. Next, in step # 2, the inclination of the fixed plate 3b is adjusted. Specifically, the fixed plate 3b is rotated, the laser beam 33 emitted from the semiconductor laser 33a is incident on the corresponding light detection element 23, and the inclination of the fixed plate 3b is at a position where the output of the light detection element 23 is maximized. To fix. If the above adjustment is performed using the beams 31 and 33 at both ends, the light source unit 3 is automatically fixed at the optimum position with the optimum inclination. That is, the multi-beam array j1 is tilted by θ with respect to the main scanning direction A, and the pitch of each beam in the sub-scanning direction B is fixed at d.
[0016]
By using the SOS photodetector 2 also for adjusting the position and inclination of the light source unit 3 as in the present embodiment, the number of parts can be reduced. In addition, the position and inclination of the light source unit 3 can be adjusted by a simple method as described above.
[0017]
The configuration of the light source unit 3 is not limited to the above configuration, and may be a multi-light source unit that forms a secondary light source having an arbitrary shape using, for example, an optical fiber or an optical waveguide.
[0018]
【The invention's effect】
As described above, according to the optical scanning device of the present invention, since the SOS photodetector is also used for adjusting the position and tilt of the light source unit, the component is used rather than the case where a separate detector is provided for adjusting the light source unit. There are few points and cost can be reduced. In addition, since the photodetector for SOS is configured to detect a plurality of beams by separate photodetector elements, each photodetector element can be configured to have a small response speed. Thus, high-speed beam control is possible.
[Brief description of the drawings]
FIG. 1 is a plan view showing a schematic configuration of a laser printer as an embodiment to which an optical scanning device of the present invention is applied.
2 is a plan view showing a configuration of a light source unit of the laser printer in FIG. 1. FIG.
3 is a plan view of a surface to be scanned of the laser printer in FIG. 1. FIG.
4 is a flowchart illustrating a position and tilt adjustment of a light source unit of the laser printer in FIG. 1;
[Explanation of symbols]
2 SOS Photodetector 2a SOS Photodetector Light-Receiving Surface 21, 22, 23 Photodetector 3 Light Source 3a Light Emitting Unit 3b Fixing Plates 31a, 32a, 33a Semiconductor Laser 6 Polygon Mirror 7 Imaging Lens 8 for Scanning Photoconductor drum

Claims (1)

A plurality of beams from a light source unit are incident on a surface to be scanned through a deflector and an optical system, and the beams are covered by a plurality of beam spots arranged in a direction inclined with respect to the main scanning direction and the direction orthogonal to the main scanning direction. In an optical scanning device that scans a scanning surface,
A photodetector having a plurality of photodetectors arranged so as to be at the same position as each of the beam spots with respect to a direction orthogonal to a main scanning direction other than a region to be scanned on the surface to be scanned; Main scanning synchronization signal generating means for generating a main scanning synchronization signal of each beam spot based on the detection result of the photodetector;
An optical scanning apparatus comprising: means for adjusting a position and an inclination of the light source unit based on a detection result of a photodetector of the main scanning synchronization signal generating means.

Images