JPH05107492A - Light beam scanning optical system - Google Patents

Abstract

PURPOSE:To eliminate compensation for face tilt of a deflection device and provide a light beam scanning optical system high in density of printing. CONSTITUTION:Multiple light beams are radiated from a semi-conductor laser 1 provided with multiple light emitting parts in auxiliary scanning direction. A collimator lens 6 converges these light beams. These converged light beams are deflected by a deflecting device 10 with one reflection surface only, and directed to a spherical mirror 20. Also the light beams reflected on the spherical mirror 20 are deflected on a photo-sensitive body 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an optical beam scanning optical system,
In particular, the present invention relates to a structure of an optical beam scanning optical system incorporated in a laser beam printer, a facsimile or the like, which deflects an optical beam by a rotary deflector.

[0002]

2. Description of the Related Art Generally, an optical beam scanning optical system used in a laser beam printer or a facsimile includes a semiconductor laser as a light emitting portion, a polygon mirror having a plurality of reflecting surfaces, and an fθ lens. Is equipped with. Polygon mirror
Is for deflecting an optical beam emitted from a semiconductor laser at a constant angular velocity. The fθ lens is provided for compensating for the scanning speed difference (distortion aberration) in the main scanning direction that occurs when the light beam is deflected by the polygon mirror.

However, in a polygon mirror having a plurality of reflecting surfaces, if the reflecting surfaces are tilted with respect to each other during processing (surface tilt), the scanning line intervals of the optical beam vary, resulting in defective scanning. Cause to occur. In order to prevent the scanning failure due to the surface tilt, an optical system for correcting the surface tilt may be provided, but if this optical system is provided, the apparatus itself becomes expensive.

Therefore, Japanese Laid-Open Patent Publication No. 63-188112 discloses a rotary deflector having only one reflecting surface. Since the rotary deflector according to this publication has only one surface that reflects the light beam, it is not necessary to provide an optical system for correcting the surface tilt unlike a polygon mirror having a plurality of reflecting surfaces.

[0005]

However, if the number of rotations of the motor for rotating the deflector is the same, a rotary deflector having only one reflecting surface and a polygon mirror having a plurality of reflecting surfaces are provided. In comparison, the print density is lower when the rotary deflector having only one reflecting surface is used than when the polygon mirror having a plurality of reflecting surfaces is used. This is because a rotary deflector having only one reflecting surface has a smaller number of scanning lines formed per revolution of the deflector due to the smaller number of reflecting surfaces. In order to increase the printing density, the motor rotation speed may be increased, but the motor rotation speed is limited.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a light emitting portion for generating a plurality of light beams so as to form a plurality of scanning lines on a scanning medium, and a reflecting surface. 1
And a rotary deflector for deflecting a plurality of optical beams generated from the light emitting section.

[0007]

In the above structure, the plurality of light beams generated from the light emitting portion are deflected by the rotary deflector having only one reflecting surface. The deflected optical beams are
The scan lines are deflected to form a plurality of scan lines on the scan medium.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of the optical beam scanning optical system of this embodiment. The semiconductor laser 1 has three light emitting portions 1a, 1b and 1c as shown in FIG. These light emitting units 1a, 1b, 1c are aligned in the sub-scanning direction, and each is driven by a control circuit described later. These driven light emitting parts generate divergent light beams whose intensity is modulated. Each diverging light beam passes through the collimator lens 6 having the characteristic of converging these light beams, and reaches the deflector 10 as a converging light beam. The deflector 10 is rotationally driven at a constant speed in the direction of arrow a around the support shaft 11 by a motor (not shown). Therefore, the convergent light beam that has passed through the collimator lens 6 is deflected by the deflector 10.
Is continuously reflected by the reflecting surface 10a of the above and is deflected at a constant angular velocity. The light beam reflected by the reflecting surface 10a of the deflector 10 reaches the spherical mirror 20. This spherical mirror-20
The reflecting surface has a concave shape, and the reflecting surface reflects the light beam toward the photoconductor 30. The light beam deflected on the photoconductor 30 is scanned in the direction of arrow b on the photoconductor 30 by the rotation of the deflector 10 (main scanning). On the other hand, the photoconductor 3
0 is rotationally driven at a constant speed in the direction of arrow c. The rotation of the photoconductor 30 determines the scanning line interval formed on the photoconductor 30 (sub-scanning). With the above optical system, three scanning lines lined up in the sub-scanning direction are simultaneously formed, and an image is formed on the photoconductor 30 by the main scanning and the sub-scanning described above.

The deflector 10 has only one reflecting surface 10a, and this reflecting surface 10a forms a convex spherical surface. The deflector 10 is formed by plastic molding, and is formed by vapor-depositing a metal reflection film as a reflection surface 10a on a base body which is colored by mixing a dye so as not to reflect the light beam. Therefore, the non-reflective surface 10b on which the metal reflective film is not deposited does not reflect the light beam.

Since the deflector 10 has a convex reflecting surface 10a and the spherical mirror 20 has a concave reflecting surface, the deflector 10 and the spherical mirror 20 have the same shape. The correction of the distortion aberration of the conventional fθ lens and the correction of the field curvature in the main scanning direction and the sub scanning direction are performed.

An image writing start position detecting light receiving element (SOS sensor) 31 is provided at a position where the deflected light beam can be received before the light beam scans the photosensitive member 30. There is.

Next, the operation of this optical system will be described.

FIG. 5 is a block diagram of the control circuit of the optical system in this embodiment. 6 is a timing chart of the control circuit shown in FIG. 5, and FIG. 7 is a diagram for explaining the image memory 105 in the control circuit. First, when the data 101 from the host computer shown in FIG. 5 is sent to the data analysis section 102, the data analysis section 102 distinguishes the print data 103 from the control command. .. The print data 103 is expanded on the image memory 105 via the memory controller 104. When the expansion of the print data 103 is completed, a print command 107 is output from the data analysis unit 102 to the engine controller 106. When the print command 107 is output, a command 108 for driving a motor (not shown) that rotates the deflector 10 is output. This command 108 causes the deflector 10 to start rotating. On the other hand, the engine controller 106 outputs a drive current 109 for driving the light emitting portion 1a of the semiconductor laser 1. Upon receiving the drive current 109, the light emitting unit 1a emits light. When the SOS sensor 31 detects the light beam of the light emitting section 1a, it sends the SOS signal 112 to the synchronization signal generating circuit 113. In response to the SOS signal 112, the sync signal generation circuit 113 outputs the sync clock 114 to the memory controller 104. After that, all the operation timings are controlled with the synchronous clock 114 as a reference.

Specifically, when the synchronous clock 114 is output a predetermined number of times (the third pulse in FIG. 6), the image memory 10
The image data 115 from the first line to the third line of 5
Engine controller via the memory controller 104
It is read by the printer 106. This image data 115
Based on the above, the engine controller 106 causes the light emitting unit 1 to
Drive a, 1b and 1c. Thereby, the light emitting unit 1a,
The light beams generated from 1b and 1c are image data 115.
Is modulated based on.

Image data 1 from the first line to the third line
When the exposure is completed based on 15, the engine controller 106 then outputs the reference pulse 11 corresponding to the SOS signal.
Determine 2 '. The reference pulse 112 'is one pulse of the synchronous clock 114, and is discriminated by detecting what number of pulse the synchronous clock 114 is.
After the reference pulse 112 'is output and the synchronous clock 114 is output again a predetermined number of times, the image data 115 of the fourth line to the sixth line of the image memory 105 are simultaneously sent to the engine via the memory controller 104. Controller 1
It is read by 06. Engine controller 10
6 is a light emitting unit 1 based on these image data 115.
Drive a, 1b and 1c.

Hereinafter, n + 1 line, n + 2 line, n +
Similarly for the three lines, the engine controller 10
Reference numeral 6 outputs drive currents 109, 110 and 111 for every three lines based on the image data 115 on the image memory 105 to drive the light emitting portions 1a, 1b and 1c.

In this way, printing is performed by exposing the photoconductor 30 on the basis of the image data 115 for three lines in one scan, so that the deflector 10 has only one reflecting surface 10a. It compensates for the decrease in density.

Further, in the present embodiment, since the deflector 10 has only one reflecting surface 10a, it is not necessary to correct the surface tilt necessary for a deflector having a plurality of reflecting surfaces such as a polygon mirror. ..

Further, as shown in the timing chart of FIG. 6, the detection of the image writing start position by the SOS sensor 31 may be carried out only once for recording one page of image.
As a result, the number of times of light emission for detecting the image writing start position can be reduced as compared with the method of detecting the image writing start position for each scan, and the image noise generated by this light emission can be reduced. However, the detection of the image writing start position is not limited to the method of this embodiment, and may be performed for each scanning.

As a modification of the deflector 10, as shown in FIG. 8, the non-reflective surface 10b 'of the deflector 10' may be shaped to diffusely reflect the laser light. 8 (a) and FIG.
8B and 8C are a plan view, a front view, and a side view of the deflector 10 ', respectively. Deflector 1 in FIG.
The 0'non-reflective surface 10b 'has no surface parallel to the reflective surface 10a'. Therefore, even if the light beam hits the non-reflective surface 10b ', it does not reach the spherical mirror 20.

In the embodiment described above, the light emitting portions 1a, 1b, 1c of the semiconductor laser 1 are provided in a straight line in parallel with the sub-scanning direction. However, in order to further increase the printing density, FIG. The semiconductor laser 1 may be inclined as shown in FIG. However, inclining the semiconductor laser 1 causes a shift of the optical beam in the main scanning direction. However, this shift can be corrected by shifting the modulation start timing for each light emitting portion of the semiconductor laser 1. For example, the engine controller 106 outputs the drive current 109 to cause the light emitting unit 1a that scans the (n + 1) th line based on the image data 115 to emit light, and after a delay of a predetermined time, the (n + 2) th line. A drive current 110 for causing the light emitting unit 1b that scans to emit light is output. After a further delay of a predetermined time, the engine controller 106 scans the (n + 3) th line on the basis of the image data 115 to emit a light.
The drive current 111 for causing the light to be emitted is output. Therefore, the engine controller 106 causes the light emitting portion 1a,
The light emitting unit 1b and the light emitting unit 1c are driven in this order with a delay of a predetermined time in between. This delay makes it possible to correct the deviation of the optical beam generated in the main scanning direction.

In the present embodiment, the semiconductor laser 1 has three light emitting portions 1a, 1b and 1c to generate three light beams, but the number is not limited to this. Any number of light emitting units may be provided. Further, other than the semiconductor laser 1, another laser generator or a point light source can be used.

In addition, in this embodiment, the diverging light beam emitted from the semiconductor laser 1 is corrected by the collimator lens 6 into a converging light beam, but a substantially parallel light beam is simply used. You can just modify it.

[0024]

As described above, according to the present invention, by providing only one reflecting surface of the rotary deflector, it becomes unnecessary to perform the surface tilt correction which is necessary for the rotary deflector having a plurality of reflecting surfaces. Further, by generating a plurality of optical beams, the printing density can be increased even if the rotary deflector has only one reflecting surface.

[Brief description of drawings]

FIG. 1 is a perspective view showing the overall configuration of an optical beam scanning optical system according to an embodiment of the present invention.

FIG. 2 is a plan view of an optical beam scanning optical system according to an embodiment of the present invention.

FIG. 3 is a side view of an optical beam scanning optical system according to an embodiment of the present invention.

FIG. 4 is a diagram showing an arrangement of light emitting portions of a semiconductor laser in this embodiment.

FIG. 5 is a block diagram of a control circuit of an optical beam scanning optical system according to an embodiment of the present invention.

FIG. 6 is a timing chart of the control circuit of the optical beam scanning optical system according to the embodiment of the present invention.

FIG. 7 is a diagram illustrating an image memory in a control circuit according to this embodiment.

FIG. 8 is a configuration diagram showing a modified example of the deflector.

FIG. 9 is a diagram showing a modification of the arrangement of the light emitting portions of the semiconductor laser according to the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 6 Collimator lens 10 Deflector 10a Reflecting surface 20 Spherical mirror 30 Photoconductor 31 SOS sensor 1a, 1b, 1c Light emitting part

Claims (1)

[Claims] 1. A light emitting part for generating a plurality of light beams so as to form a plurality of scanning lines on a scanning medium, and a plurality of light emitting parts having only one reflecting surface. And a rotary deflector for deflecting the above-mentioned optical beam.