JP3579530B2 - Scanning optical device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a scanning optical device for scanning a light beam in a laser printer or the like, and more particularly, to a multi-beam scanning optical device for simultaneously scanning a plurality of light beams.
[0002]
[Prior art]
Here, the scanning optical device includes a detector for detecting the amount of light for controlling the light source of each semiconductor laser or the like, and controls the amount of light output from the light source by feedback from the detector. Therefore, conventionally, a half mirror is provided in the optical path from the light source of the scanning optical device to the polygon mirror, the light beam reflected by the half mirror is guided to the polygon mirror, and the light beam transmitted through the half mirror is guided to the detector.
[0003]
[Problems to be solved by the invention]
However, the surface of the half mirror is coated with a dielectric material for reflecting a part of the incident light and transmitting a part thereof, and the dielectric material has a polarization property. On the other hand, each point light source using an optical fiber has a different polarization characteristic due to an individual difference of the optical fiber or the like. Therefore, there is a problem that a difference in polarization dependency occurs for each point light source, and it is extremely difficult to correct such a difference in polarization dependency.
In addition, even if such a multi-beam scanning optical device is used, if a polarization-dependent member is used as a light source, the problem that polarization dependence differs due to individual differences between products still occurs. I do.
[0004]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a scanning optical device capable of accurately detecting the amount of light.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, a scanning optical device according to the present invention includes a light source, a deflecting unit that scans a light beam from the light source in a predetermined direction, and a detecting unit that detects a light amount from the light source to control the light source. , Provided between the light source and the deflecting means, the light beam separating means for guiding the light beam from the light source to the deflecting means and the detecting means, respectively, and the light beam separating means is incident on the reflecting mirror and the reflecting mirror. An opening penetrating the reflecting mirror in the optical axis direction of the light beam, wherein the light beam reflected by the reflecting mirror is guided to the deflecting means, and the light beam passing through the opening is guided to the detecting means. It is. With this configuration, the light beam transmitted through the aperture enters the detector, and is not affected by polarization.
[0006]
The above-mentioned opening can be formed in a circular shape or a slit shape. Then, the slit may be configured to have a shape extending in a direction corresponding to the sub-scanning direction on the scanning target surface. Further, the slit may be formed in a shape extending in a direction corresponding to the main scanning direction on the surface to be scanned by the deflecting unit. Here, the main scanning direction is the direction of scanning by the above-mentioned deflecting means, and the sub-scanning direction is the direction orthogonal to the main scanning direction on the surface to be scanned by the above-mentioned deflecting means.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a scanning optical device according to the present invention will be described. The scanning optical device shown as the embodiment is a multi-beam scanning optical device that simultaneously forms eight scanning lines by one scanning by simultaneously scanning eight laser beams. First, a schematic configuration of the entire apparatus will be described.
[0008]
FIG. 1 is a perspective view showing an optical scanning device, and FIG. 2 is a side view showing the optical scanning device together with a photosensitive drum. As shown in FIG. 1, the scanning optical device is configured by disposing a scanning optical system in a substantially rectangular parallelepiped flat casing 1. The upper opening of the casing 1 is closed by the upper lid 2 during use.
[0009]
In the upper part of the casing 1 in the figure, a connector section 102 for receiving a signal relating to image information is provided. A laser block support substrate 300 is provided adjacent to the connector 102. The support substrate 300 includes a laser block 310 that holds the eight semiconductor lasers 101 that emit light beams based on the signals and the input ends of the optical fibers 120 facing each other. Fixed. Thereby, a light beam is guided to the eight optical fibers 120.
[0010]
The end face 120b on the emission side of the optical fiber 120 is held by a fiber alignment block 130. The light beam from the exit end face 120b enters the polygon mirror 180 via the collimator lens 140, a mirror 146 described later, the dynamic prism 160, and the cylindrical lens 170. The polygon mirror 180 is rotationally driven by a polygon motor 371 (see FIG. 2) fixed to the casing 1, and reflects and deflects a light beam incident on the mirror surface. The light beam deflected by the polygon mirror 180 enters an fθ lens 190 which is an imaging lens. The light beam from the fθ lens 190 is reflected by the folding mirror 200 downward in the figure, and forms an image on the photosensitive drum 210 which is a scanning target surface as shown in FIG.
[0011]
Here, in order to define the operation of the optical element, the scanning direction of the light beam on the fθ lens 190 and the photosensitive drum 210 (FIG. 2) in a plane perpendicular to the optical axis is a main scanning direction, and a plane perpendicular to the optical axis. The direction perpendicular to the main scanning direction is defined as the sub-scanning direction. In the drawing, an X axis parallel to the optical axis of the fθ lens 190, and a Y axis and a Z axis orthogonal to each other in a plane perpendicular to the X axis are defined. The Y axis and the Z axis correspond to the main scanning direction and the sub scanning direction, respectively.
[0012]
Next, each component of the optical system will be described with reference to FIG.
The light source unit 100 includes eight semiconductor lasers 101, eight optical fibers 120 for transmitting divergent light beams emitted from these semiconductor lasers, and a fiber alignment block 130 for aligning these optical fibers 120 in a straight line. . The optical fiber 120 is a quartz glass fiber having a core diameter of 6 μm and an overall diameter including the cladding of 125 μm.
[0013]
The end of the optical fiber 120 including the incident end face 120a is held by a fiber support 319 which is a support tube. The fiber support 319 is held by the laser block 310 with the incident end 120a and the semiconductor laser 101 facing each other. Then, the light beam emitted from the semiconductor laser 101 enters the incident end face 120 a of the optical fiber 120.
[0014]
As shown in FIG. 3, in the optical path between the light source unit 100 and the polygon mirror 180, a collimating lens 140 that converts a divergent light beam emitted from the emission end face of the optical fiber into a parallel light beam, and a main light beam emitted from the collimator lens 140. A slit 142 for controlling a beam shape by a rectangular opening having sides in the scanning direction and the sub-scanning direction, a mirror 146 for separating a light beam transmitted through the slit 142 into two, and a light beam reflected by the mirror 146 in the sub-scanning direction. A dynamic prism 160 that sequentially controls by rotating the angle, and a cylindrical lens 170 that converges a light beam whose angle is controlled by the dynamic prism 160 in the sub-scanning direction are provided.
[0015]
The exit end face 120b of the fiber 120 is arranged at predetermined intervals on a straight line inclined at a predetermined angle with respect to the main scanning direction by the fiber alignment block 130 and the like, and forms a point light source row shown in FIG. In FIG. 3, the light beam from the point light source array including the eight point light sources passes through the collimator lens 140, the cylindrical lens 170, and the like, and forms an image near the mirror surface of the polygon mirror 180 in the sub-scanning direction. The light beam incident on the polygon mirror 180 is scanned in the Y direction by the rotation of the polygon mirror 180, and is incident on the fθ lens 190.
[0016]
lens 190 includes first, second, third, and third powers having negative, positive, positive, and negative powers in the main scanning direction and the sub-scanning direction, respectively, from the polygon mirror 180 side toward the return mirror 200 side. It comprises fourth lenses 191, 193, 195 and 197.
[0017]
The light beam transmitted through the fθ lens 190 forms an image on the surface of the photosensitive drum 210 (FIG. 2) via the folding mirror 200, and the scanning speed in the main scanning direction becomes constant. The photosensitive drum 210 is driven to rotate in the direction of arrow R in synchronization with the scanning, whereby an electrostatic latent image is formed on the surface of the photosensitive drum 210.
[0018]
Next, the mirror 146 will be described.
FIG. 5 shows the mirror 146. As shown in FIG. 5, the mirror 146 includes a reflecting portion 146a, which is a rectangular reflecting mirror, and a transmitting portion 146b, which is a hole penetrating the center of the reflecting mirror 146a from front to back. In FIG. 5, the vertical direction corresponds to the sub-scanning direction (Z direction), and the horizontal direction corresponds to the main scanning direction on the scanning target surface (here, the Y 'direction).
[0019]
The mirror 146 receives a light beam in which light beams emitted from eight point light sources (FIG. 4) composed of the light emitting end surfaces 120b of the fibers 120 overlap and become almost one. The luminous flux is shaped into a substantially rectangular shape by passing through the slit 142 (FIG. 3). The incident range of the light beam on the mirror 142 is indicated by L.
[0020]
Of the light beams incident on the incident range L, the light beams incident on the reflecting portion 146a are reflected toward the polygon mirror 180. On the other hand, the light beam that has entered the transmission unit 146b passes through the transmission unit 146b, and enters an APC (automatic power control) signal detection unit 150 that detects a light amount and obtains a signal for controlling the output of the semiconductor laser. The area of the transmission section 146b is 1/20 of the incident range L, and 5% of the entire incident light is guided to the APC signal detection section 150.
[0021]
As shown in FIG. 3, the light beam incident on the APC signal detection unit 150 is converged by the condenser lens 151 and is incident on the APC light receiving element 155.
Each semiconductor laser 101 emits light separately and sequentially at a timing before the beam spot on the photosensitive drum 210 enters the drawing range for each scan, and the light beam from each semiconductor laser 101 is supplied to the APC light receiving element 155. Are temporally separated and enter.
[0022]
The output of each semiconductor laser 101 detected from the APC light receiving element 155 is input to an APC signal generation circuit (not shown), and a semiconductor laser drive for driving each semiconductor laser as a signal (APC signal) corresponding to each output. Input to the circuit. For example, an APC signal output from the APC signal generation circuit during a certain period within a period during which the first semiconductor laser 101 emits light is input to a first semiconductor laser driving circuit that drives the first semiconductor laser 101. You. Each semiconductor laser drive circuit sets a gain based on the input APC signal so that the output of the semiconductor laser becomes a reference level.
[0023]
When the beam spot on the photosensitive drum 210 enters the drawing range, the semiconductor laser driving circuit controls the semiconductor laser 101 on and off based on the input drawing signal. The driving voltage at this time is set based on the APC signal. It is adjusted by the gain. With this configuration, the output of the semiconductor laser 101 is controlled so that the intensity of the beam spot on the surface of the photosensitive drum becomes the reference level.
[0024]
As described above, the APC signal detection unit 150 receives the light beam that has passed through the transmission unit 146b and is not affected by polarization. Therefore, the APC signal detection section 150 can detect an accurate light amount.
[0025]
Note that the formation of the transmission portion 146b causes a diffraction phenomenon to occur in the light beam reflected by the reflection portion 146a, and changes the light amount distribution formed on the image plane.
FIG. 6 shows an example of the light amount distribution in the main scanning direction (Y direction) on the image forming plane when the transmission unit 146b is provided and when it is not provided. FIG. 7 shows a beam spot shape corresponding to FIG. In FIG. 6, the minimum light amount E required to form an electrostatic latent image on the surface of the photosensitive drum 210 is indicated by a broken line.
[0026]
As shown in FIG. 6, when the transmitting portion 146b is provided, diffracted light is generated in the periphery, and the light amount is distributed in a narrower range than when the transmitting portion 146b is not provided. That is, the beam spot diameter (W1) in the main scanning direction when the transmission section 146b is provided is smaller than that when the transmission section 146b is not provided (W0). The beam spot is formed in an elliptical shape long in the sub-scanning direction as shown in FIG. 7 by setting various dimensions of the optical system. However, the beam spot diameter in the sub-scanning direction becomes small as in the main scanning direction. In addition, as shown in FIG. 6, the diffracted light is equal to or less than the minimum light amount E for forming an electrostatic latent image on the surface of the photosensitive drum 210, so that the photosensitive drum 210 is not exposed to the diffracted light.
[0027]
In this case, if the dimensions of the optical system are the same (the F number is the same), the beam spot diameter can be reduced by diffraction. However, in the first embodiment, various dimensions of the optical system are set so as to reduce the divergence angle of the light beam with respect to the imaging plane (increase the F number) only by offsetting the decrease in the beam spot diameter due to diffraction. As described above, as a result of reducing the divergence angle of the beam, there is obtained an effect that the change of the beam spot diameter on the imaging plane in the optical axis direction is reduced, that is, the depth is increased.
[0028]
In this manner, each of the light beams from the eight point light sources (FIG. 4) forms an image on the image forming surface of the photosensitive drum 210, and forms eight beam spots shown in FIG. Note that the diffracted light is omitted in FIG. As shown in FIG. 8, eight scanning lines having no gap in the sub-scanning direction are formed by the eight aligned beam spots.
[0029]
Next, a scanning optical device according to a second embodiment of the present invention will be described.
The mirror 246 shown in FIG. 9 is mounted in the scanning optical device at the same position as the mirror 146 of the first embodiment. The mirror 246 includes a reflecting portion 246a, which is a rectangular mirror, and a slit 246b extending in the Y ′ direction (a direction corresponding to the main scanning direction on the scanning target surface) at the center of the reflecting portion 246a. As in the first embodiment, the area of the slit 246b is set to 1/20 of the incident range L.
[0030]
FIG. 10 shows the shape of a beam spot formed on the image plane when the mirror 246 is used. As shown in FIG. 10, the diffraction phenomenon occurs only in the sub-scanning direction. Here, if the dimensions of the optical system are the same, the beam spot diameter decreases in the sub-scanning direction due to diffraction. However, in the second embodiment, various dimensions of the optical system are set so as to reduce the divergence angle in the sub-scanning direction with respect to the image plane (increase the F number) only by offsetting the decrease in the beam spot diameter due to diffraction. I do. As described above, as a result of reducing the divergence angle of the beam, there is obtained an effect that the change in the beam spot diameter in the sub-scanning direction in the optical axis direction becomes smaller, that is, the depth increases in the sub-scanning direction.
[0031]
Generally, in such a scanning optical device, since the power in the sub-scanning direction is higher than the power in the main scanning direction, the curvature of the image plane in the sub-scanning direction is more problematic than in the main scanning direction. Therefore, the effect of increasing the depth in the sub-scanning direction as in the second embodiment is significant.
[0032]
Further, in the mirror 246 of the second embodiment, since the transmission portion 246b is configured as a slit, processing is easier than in the first embodiment. Further, if the two mirrors are arranged separated by the slit width instead of forming the slit 246b in the reflection portion 246a, the processing becomes easier.
[0033]
Next, a scanning optical device according to a third embodiment of the present invention will be described.
The mirror 346 shown in FIG. 11 is mounted at the same position as the mirrors 146 and 246 of the first and second embodiments, and includes a reflecting portion 346a and a slit extending the reflecting portion 346a in the vertical direction, that is, the sub-scanning direction. 346b.
[0034]
FIG. 12 shows the shape of a beam spot formed on the image plane when the mirror 346 is used. As shown in FIG. 12, the diffraction phenomenon occurs in the sub-scanning direction in the second embodiment, whereas the diffraction phenomenon occurs in the main scanning direction in the third embodiment. Therefore, a beam spot smaller in the main scanning direction due to the influence of diffraction is maintained in the optical axis direction, and the allowable range for the positional deviation of the imaging plane in the main scanning direction becomes larger. That is, in the third embodiment, the beam can be narrowed in the main scanning direction while maintaining the depth in the main scanning direction.
[0035]
Further, since the mirror 346 of the third embodiment uses the slit 346b as a transmission part, it is easier to process than the first embodiment. If two mirrors are arranged separated by the slit width instead of forming the slit 346b in the reflecting portion 346a, the processing becomes easier.
[0036]
【The invention's effect】
As described above, according to the scanning optical device according to the first aspect of the present invention, the light transmitted through the aperture provided in the mirror enters the detector, so that the incident light is not affected by the polarization. That is, an accurate light amount is detected, and erroneous control is prevented.
Further, according to the scanning optical device according to the second aspect of the present invention, by forming the transmitting portion in a circular shape, it is possible to increase the depth of focus on the image plane by utilizing the occurrence of a diffraction phenomenon. Further, according to the scanning optical device according to the fourth aspect of the present invention, it is possible to narrow the beam in the main scanning direction. According to the scanning optical device of the fifth aspect, the depth of focus in the sub-scanning direction can be increased.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a scanning optical device according to the present invention.
FIG. 2 is a side view of the scanning optical device of FIG.
FIG. 3 is a diagram illustrating an optical system of the scanning optical device in FIG. 1;
FIG. 4 is a front view showing a point light source of the scanning optical device of FIG. 1;
FIG. 5 is a front view showing a mirror according to the first embodiment.
FIG. 6 is a diagram showing a light amount distribution by the mirror of FIG. 5;
FIG. 7 is a diagram showing a beam spot shape by the mirror of FIG. 5;
FIG. 8 is a diagram showing an array of beam spots formed on an image plane.
FIG. 9 is a front view showing a mirror according to the second embodiment.
FIG. 10 is a diagram showing a beam spot shape by the mirror of FIG. 9;
FIG. 11 is a front view illustrating a mirror according to a third embodiment.
12 is a diagram showing a beam spot shape by the mirror of FIG.
[Explanation of symbols]
100 light source unit 120 fiber 146 mirror 146a reflecting unit 146b transmitting unit 180 polygon mirror 190 fθ lens 210 photosensitive drum 246, 346 mirror 246a, 346a reflecting unit 246b, 346b slit

Claims (5)

A light source,
Deflecting means for scanning a light beam from the light source in a predetermined direction,
Detecting means for detecting the amount of light from the light source to control the light source,
A light beam separating unit is provided between the light source and the deflecting unit, and guides the light beam from the light source to the deflecting unit and the detecting unit, respectively.
The light beam separating means has a reflecting mirror, and an opening penetrating the reflecting mirror in the optical axis direction of the light beam incident on the reflecting mirror,
The light beam reflected by the reflecting mirror is guided to the deflecting means, and the light beam passing through the opening is guided to the detecting means. The scanning optical device according to claim 1, wherein the opening has a circular shape. The scanning optical device according to claim 1, wherein the opening has a slit shape. The predetermined direction is a main scanning direction, and a direction orthogonal to the main scanning direction on a surface to be scanned by the deflection unit is a sub-scanning direction.
The scanning optical device according to claim 3, wherein the slit extends in a direction corresponding to the sub-scanning direction on the surface to be scanned in a plane of the reflecting mirror. The predetermined direction as a main scanning direction,
The scanning optical device according to claim 3, wherein the slit extends in a direction corresponding to the main scanning direction on a surface to be scanned by the deflecting unit in a plane of the reflecting mirror.

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