JPH09211353A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent incident light from being affected by polarized light, to detect exact light quantity and to prevent erroneous control by constituting a device so that a luminous flux transmitted through an aperture formed on a mirror may be made incident on a detector. SOLUTION: The mirror 146 separating the luminous flux transmitted through a slit into two is constituted of a reflection part 146a being a rectangular reflection mirror and a transmission part 146b being a hole piercing the center part of the mirror 146a from a front surface to a back surface. The vertical direction of the mirror 146 is aligned with a subscanning direction (direction Z) and the horizontal direction thereof corresponds to a main scanning direction (direction Y' in this case) on a scanning object plane. The luminous flux made incident on the reflection part 146b out of the luminous flux made incident on an incident range L is reflected toward a polygon mirror. Meanwhile, the luminous flux made incident on the transmission part 146b passes through the transmission part 146b and is made incident on an APC(automatic power control) signal detection part detecting light quantity and obtaining a signal for controlling output from a semiconductor laser.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. 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]

2. Description of the Related Art Here, a scanning optical device is provided with a detector for detecting a light amount for controlling a light source such as each semiconductor laser, and the output light amount of the light source is controlled by feedback from the detector. There is. 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 flux reflected by the half mirror is guided to the polygon mirror, and the light flux transmitted through the half mirror is guided to the detector.

[0003]

However, the surface of the half mirror is coated with a dielectric material for reflecting a part of incident light and transmitting a part thereof, and the dielectric material has a polarization property. have. On the other hand, each point light source using an optical fiber has different polarization characteristics due to individual differences of the optical fiber. Therefore, there is a problem in that the polarization dependence differs for each point light source, and it is extremely difficult to correct such a polarization dependence difference.
Further, even if not limited to such a multi-beam scanning optical device, if a member having a polarization dependency is used as a light source, the problem that the polarization dependency is different due to the individual difference between products still occurs. To do.

An object of the present invention is to provide a scanning optical device which enables accurate detection of the amount of light.

[0005]

In order to solve the above-mentioned problems, a scanning optical device according to the present invention comprises a light source, a deflection means for scanning a light beam from the light source in a predetermined direction, and a light source for controlling the light source. The light beam separating means is provided between the light source and the deflecting means, and the light beam separating means is provided between the light source and the deflecting means for guiding the light beam from the light source to the deflecting means and the detecting means respectively. A mirror and an opening penetrating the reflecting mirror in the optical axis direction of the light entering the reflecting mirror, the light reflected by the reflecting mirror is guided to the deflecting means, and the light passing through the opening is detected by the detecting means. It is characterized by being guided. With this configuration, the light flux that has passed through the aperture is incident on the detector, and thus is not affected by the polarization.

The above-mentioned opening can be formed in a circular shape or a slit shape. Then, the slit may be formed in a shape extending in a direction corresponding to the sub-scanning direction on the surface to be scanned. 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 means. Here, the main scanning direction is the scanning direction of the deflecting means, and the sub-scanning direction is the direction orthogonal to the main scanning direction on the surface to be scanned by the deflecting means.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a scanning optical device according to the present invention will be described below. The scanning optical device shown as the embodiment is a multi-beam scanning optical device that simultaneously scans eight laser beams to simultaneously form eight scanning lines in one scan. First, the schematic configuration of the entire apparatus will be described.

FIG. 1 is a perspective view showing a scanning optical device, and FIG. 2 is a side view showing the scanning optical device together with a photosensitive drum.
As shown in FIG. 1, the scanning optical device is configured by arranging a scanning optical system in a flat casing 1 having a substantially rectangular parallelepiped shape. The upper opening of the casing 1 is closed by the upper lid 2 when in use.

At the upper part of the casing 1 in the figure, a connector section 102 for receiving signals relating to image information is provided. A laser block support substrate 300 is provided adjacent to the connector 102, and a laser block 310 that holds the eight semiconductor lasers 101 that emit a light beam based on the above signals and the input ends of the optical fibers 120 face each other is provided on the support substrate 300. It is fixed. As a result, 8
The light flux is guided to one optical fiber 120.

The end face 120 of the optical fiber 120 on the exit side
b is held by the fiber alignment block 130. The light flux from the exit end face 120b enters a polygon mirror 180 via a collimator lens 140, a mirror 146 described later, a dynamic prism 160, and a 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 / deflects the light beam incident on the mirror surface. The light beam deflected by the polygon mirror 180 is fθ which is an imaging lens.
It enters the lens 190. The light flux from the fθ lens 190 is reflected downward by the folding mirror 200 in the figure and forms an image on the photosensitive drum 210, which is the surface to be scanned, as shown in FIG.

Here, in order to define the operation of the optical element,
In the plane perpendicular to the optical axis, the scanning direction of the light flux on the fθ lens 190 and the photosensitive drum 210 (FIG. 2) is the main scanning direction, and in the plane perpendicular to the optical axis, the direction orthogonal to the main scanning direction is the sub-scanning direction. Define as direction. Further, in the figure, 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.

Next, each component of the optical system will be described with reference to FIG. 3 showing the outline of the optical system of the above-mentioned apparatus. The light source unit 100 includes eight semiconductor lasers 101, eight optical fibers 120 that transmit divergent light beams emitted from these semiconductor lasers, and a fiber alignment block 1 that aligns these optical fibers 120 in a straight line.
30. The optical fiber 120 is a silica glass fiber having a core diameter of 6 μm and an overall diameter including the cladding of 125 μm.

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 has an entrance end 1
The semiconductor laser 101 is held by the laser block 310 while the semiconductor laser 101 and the semiconductor laser 101 face each other. Then, the light flux emitted from the semiconductor laser 101 is reflected by the optical fiber 120.
Is incident on the incident end face 120a.

As shown in FIG. 3, in the optical path between the light source section 100 and the polygon mirror 180, the collimating lens 140 and the collimating lens 140 which make the divergent light beam emitted from the exit end face of the optical fiber into a parallel light beam are emitted. A slit 142 for controlling the beam shape by a rectangular opening having sides in the main scanning direction and the sub-scanning direction of the light beam, and a mirror 14 for separating the light beam transmitted through the slit 142 into two.
6, a dynamic prism 160 that sequentially controls the angle of the light beam reflected by the mirror 146 in the sub-scanning direction, and a cylindrical lens 170 that converges the light beam whose angle is controlled by the dynamic prism 160 in the sub-scanning direction. Has been.

The exit end face 120b of the fiber 120 is
By the fiber alignment block 130 and the like, they are arranged at a predetermined interval on a straight line inclined at a predetermined angle with respect to the main scanning direction to form the point light source array shown in FIG. The light flux 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 in FIG. 3, and forms an image in the sub-scanning direction near the mirror surface of the polygon mirror 180. The incident light flux 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.

The fθ lens 190 is a polygon mirror 18
From the 0 side to the folding mirror 200 side, negative, positive, and positive in the main scanning direction and the sub scanning direction, respectively.
The first, second, third, and fourth lenses 191, 193, 195, and 197 having positive and negative powers are used.

The light flux 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 photoconductor drum 210 is rotationally driven in the direction of arrow R in synchronization with scanning, whereby an electrostatic latent image is formed on the surface of the photoconductor drum 210.

Next, the mirror 146 will be described. The mirror 146 is shown in FIG. As shown in FIG. 5, the mirror 1
Reference numeral 46 denotes a reflecting portion 146a which is a rectangular reflecting mirror, and a transmitting portion 1 which is a hole which penetrates the center of the reflecting mirror 146a to the front and back.
It consists of 46b. 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 surface to be scanned (here, the Y'direction).

The mirror 146 receives a bundle of light beams, which are formed by overlapping the light beams emitted from the eight point light sources (FIG. 4) composed of the light emitting end face 120b of the fiber 120. The light flux is shaped into a substantially rectangular shape by passing through the slit 142 (FIG. 3). The incident range of the light flux on the mirror 142 is indicated by L.

Of the light fluxes incident on the incident range L, the light fluxes incident on the reflecting portion 146a are reflected toward the polygon mirror 180. On the other hand, the light flux incident on the transmission part 146b passes through the transmission part 146b, detects the light amount, and obtains a signal for controlling the output of the semiconductor laser.
PC (Automatic Power Control) signal detector 1
It is incident on 50. The area of the transmission part 146b is 1/20 of the incident range L, and 5% of the entire incident light is guided to the APC signal detection part 150.

As shown in FIG. 3, the APC signal detecting section 15
The light flux incident on 0 is converged by the condenser lens 151 and is incident on the APC light receiving element 155. Each semiconductor laser 101 sequentially emits light separately for each scan at a timing before the beam spot on the photosensitive drum 210 enters the drawing range, and the light receiving element 155 for APC emits a light beam from each semiconductor laser 101. Are temporally separated and are incident.

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 signals (AP) corresponding to the respective outputs are output.
It is input to the semiconductor laser drive circuit that drives each semiconductor laser as C signal). For example, when the first semiconductor laser 101 emits light, A
The APC signal output from the PC signal generation circuit is input to the first semiconductor laser drive circuit that drives the first semiconductor laser 101. Each semiconductor laser drive circuit,
The gain is set so that the output of the semiconductor laser becomes the reference level based on the input APC signal.

When the beam spot on the photoconductor drum 210 enters the drawing range, the semiconductor laser driving circuit controls the semiconductor laser 101 on / off based on the inputted drawing signal. The driving voltage at this time is the APC signal. It is adjusted by the gain set based on the above. 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 photoconductor drum becomes the reference level.

As described above, the light beam that has passed through the transmission part 146b and is not affected by the polarization enters the APC signal detection part 150. Therefore, the APC signal detector 150
Can detect the exact amount of light.

By the formation of the transmissive portion 146b, a diffraction phenomenon occurs in the light beam reflected by the reflective portion 146a, and the light amount distribution imaged on the image plane changes. In FIG.
An example of the light amount distribution in the main scanning direction (Y direction) on the image plane with and without the transmission part 146b is shown. Further, FIG. 7 shows the shape of the beam spot corresponding to FIG. In FIG. 6, the minimum amount of light E required to form an electrostatic latent image on the surface of the photoconductor drum 210 is indicated by a broken line.

As shown in FIG. 6, when the transmissive portion 146b is provided, diffracted light is generated in the periphery, and the light amount is distributed in a narrower range than when the transmissive portion 146b is not provided. That is, the beam spot diameter (W1) in the main scanning direction when the transmissive portion 146b is provided is smaller than when the transmissive portion 146b is not provided (W0). Although the beam spot is formed in an elliptical shape that is long in the sub-scanning direction as shown in FIG. 7 by setting various dimensions of the optical system, the beam spot diameter in the sub-scanning direction also becomes small as in the main scanning direction. The diffracted light is shown in FIG.
As shown in (1), since the light amount E is the minimum amount or less for forming an electrostatic latent image on the surface of the photoconductor drum 210, the photoconductor drum 210 is not exposed to the diffracted light.

In this case, if the dimensions of the optical system are the same (the F numbers are the same), the beam spot diameter can be reduced by diffraction. However, in the first embodiment, the divergence angle of the light beam with respect to the image plane is reduced by just offsetting the decrease in the beam spot diameter due to diffraction (F
Increase the number) and set the various dimensions of the optical system. As described above, as a result of reducing the divergence angle of the beam, there is an effect that the change in the beam spot diameter on the imaging plane in the optical axis direction is reduced, that is, the depth is increased.

In this way, each of the light beams from the eight point light sources (FIG. 4) is imaged on the image forming surface of the photosensitive drum 210 to form eight beam spots shown in FIG. Diffracted light is omitted in FIG. As shown in FIG. 8, eight aligned beam spots form eight scan lines with no gap in the sub-scanning direction.

Next explained is a scanning optical device according to the second embodiment of the invention. Mirror 246 shown in FIG.
Is the mirror 1 of the first embodiment in the scanning optical device.
It is attached at the same position as 46. 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 scan target surface) at the center of the reflecting portion 246a.
Is made up of Similar to the first embodiment, the slit 246
The area of b is 1/20 of the incident range L.

FIG. 10 shows the shape of the beam spot formed on the image plane when the mirror 246 is used. FIG.
As shown in, 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, the dimensions of the optical system are set so that the divergence angle in the sub-scanning direction with respect to the image plane is reduced (the F number is increased) by offsetting the decrease in the beam spot diameter due to diffraction. To do. As described above, as a result of reducing the divergence angle of the beam, there is an effect that the change in the beam spot diameter in the sub-scanning direction in the optical axis direction is smaller, that is, the depth is increased in the sub-scanning direction.

Generally, in such a scanning optical device, since the power in the sub-scanning direction is stronger than the power in the main-scanning direction, the curvature of the image plane in the sub-scanning direction rather than the main scanning direction becomes a problem. Therefore, the effect of increasing the depth in the sub-scanning direction as in the second embodiment is great.

Further, in the mirror 246 of the second embodiment,
Since the transmissive portion 246b is configured as a slit, processing is easier than in the first embodiment. In addition, the reflector 24
Instead of forming the slit 246b on the 6a, if the two mirrors are arranged with a gap corresponding to the slit width, the processing becomes easier.

Next explained is a scanning optical device according to the third embodiment of the invention. Mirror 346 shown in FIG.
Is attached at a position similar to that of the mirrors 146 and 246 of the first and second embodiments.
The reflecting portion 346a is formed of a slit 346b extending in the vertical direction, that is, the sub-scanning direction.

FIG. 12 shows the shape of the beam spot formed on the image plane when the mirror 346 is used. FIG.
As shown in FIG. 5, 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 smaller beam spot is maintained in the optical axis direction due to the influence of diffraction in the main scanning direction, and the permissible range regarding the positional deviation of the image forming surface in the main scanning direction is correspondingly increased. That is, in the third embodiment, the beam can be focused in the main scanning direction while maintaining the depth in the main scanning direction.

Further, since the mirror 346 of the third embodiment uses the slit 346b as the transmitting portion, it is easier to process than the first embodiment. Further, instead of forming the slit 346b in the reflecting portion 346a, if the two mirrors are arranged so as to be separated by the slit width, processing becomes easier.

[0036]

As described above, according to the scanning optical device of the first aspect of the present invention, since the light beam transmitted through the opening provided in the mirror enters the detector, the incident light is affected by the polarization. Absent. That is, an accurate light amount is detected and erroneous control is prevented. Further, according to the scanning optical device of the invention described in claim 2, by making the transmitting portion circular,
It is possible to increase the depth of focus on the image plane by utilizing the occurrence of the diffraction phenomenon. Furthermore, according to the scanning optical device of the fourth aspect, the beam can be focused 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 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.

3 is a diagram showing an optical system of the scanning optical device of FIG.

FIG. 4 is a front view showing a point light source of the scanning optical device of FIG.

FIG. 5 is a front view showing the mirror of the first embodiment.

FIG. 6 is a diagram showing a light amount distribution by the mirror of FIG.

FIG. 7 is a diagram showing a beam spot shape by the mirror of FIG.

FIG. 8 is a diagram showing a row of beam spots formed on an image plane.

FIG. 9 is a front view showing a mirror of a second embodiment.

10 is a diagram showing a beam spot shape by the mirror of FIG.

FIG. 11 is a front view showing a mirror of a third embodiment.

12 is a diagram showing a beam spot shape by the mirror of FIG.

[Explanation of symbols]

 100 light source section 120 fiber 146 mirror 146a reflection section 146b transmission section 180 polygon mirror 190 fθ lens 210 photoconductor drum 246, 346 mirror 246a, 346a reflection section 246b, 346b slit

Front page continued (72) Inventor Hiroshi Kanazawa 2-36-9 Maenocho, Itabashi-ku, Tokyo Asahi Kogaku Kogyo Co., Ltd.

Claims (5)

[Claims] 1. A light source, a deflection means for scanning a light beam from the light source in a predetermined direction, a detection means for detecting a light amount from the light source to control the light source, the light source and the deflection means. And a light beam separating means for guiding the light beam from the light source to the deflecting means and the detecting means, respectively, the light beam separating means includes a reflecting mirror, and the reflecting mirror is incident on the reflecting mirror. And an opening penetrating in the direction of the optical axis of the luminous flux, wherein the luminous flux reflected by the reflecting mirror is guided to the deflecting means,
The light flux passing through the opening is guided to the detection means,
A scanning optical device. 2. The scanning optical device according to claim 1, wherein the opening has a circular shape. 3. The scanning optical device according to claim 1, wherein the opening has a slit shape. 4. The predetermined direction is a main scanning direction, a direction orthogonal to the main scanning direction on a surface to be scanned by the deflecting device is a sub-scanning direction, and the slit is in the plane of the reflecting mirror. The scanning optical device according to claim 3, wherein the scanning optical surface extends in a direction corresponding to the sub-scanning direction. 5. The predetermined direction is defined as a main scanning direction, and the slit extends in the plane of the reflecting mirror in a direction corresponding to the main scanning direction on a surface to be scanned by the deflecting means. The scanning optical apparatus according to claim 3, wherein the scanning optical apparatus is a scanning optical apparatus.