JPH11237578A - Optical diaphragm device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily control the diameter of a light beam projected from a light source. SOLUTION: A light beam B1 is projected from a laser diode 11 based on an output signal from a laser diode driving circuit 12. The beam B1 is led into a Digital micromirror device (DMD)(R) 20 to be a light reflecting means by a collimator lens 30 as a parallel beam. Respective micromirrors formed like a matrix on the DMD 20 are ON/OFF controlled and properly tilted to a 1st or 2nd tilting direction to control the diameter of a light beam B2 and switch the resolution of an electrostatic latent image formed on a photoreceptor drum D.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a resolution control mechanism in an optical scanning device such as a laser printer.

[0002]

2. Description of the Related Art Conventionally, in a laser printer, a light beam output from a laser light source is guided to a polygon mirror through an optical system such as a collimator lens and a slit.
Scanning is performed on the photosensitive drum by a polygon mirror. The photosensitive member on the photosensitive drum is exposed by scanning the light beam, and an electrostatic latent image is formed on the photosensitive drum. One of the factors that determine the resolution of the electrostatic latent image, that is, the image printed on the recording paper, is the diameter of the light beam scanned on the photosensitive drum. That is, the resolution of the electrostatic latent image is controlled by changing the diameter of the light beam. The diameter of the light beam scanned on the photosensitive drum is defined by a slit provided between the collimator lens and the polygon mirror. Therefore, changing the diameter of the light beam requires replacement of the slit.

[0003]

However, the slit is built in the laser printer manufacturing process, and it is impossible to change the slit at any time according to the required resolution. Therefore, it has been difficult to control the resolution of the electrostatic latent image by changing the diameter of the light beam.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide an optical diaphragm device that can easily control the diameter of a light beam emitted from a light source in a laser printer or the like.

[0005]

An optical diaphragm device according to the present invention is an optical scanning device for writing predetermined information on a photosensitive member by deflecting and scanning a light beam emitted from a light source by an optical deflector. A plurality of light reflections on an optical path of a light beam between a light source and an optical deflector, which can selectively set an ON state for deflecting incident light in a first direction and an OFF state for deflecting incident light in a second direction. The configuration of the light beam guided to the optical deflector is defined by arranging the light reflecting means having the element.

In the light reflecting means, the shape of the light beam is defined by changing the number of light reflecting elements in the ON state and the number of light reflecting elements in the OFF state.

The light reflecting element is a mirror element which is set to an on state or an off state by changing an inclination angle by an electrostatic force.

The light reflecting element is a diffractive light modulation element which is set to an on state or an off state by the diffraction of light.

The first direction is a direction guided to the optical deflector, and the light shielding member is provided in the second direction.

The light deflector is a polygon mirror of a laser printer, and the light source is a laser diode or a gas laser.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing an apparatus configuration of a laser printer to which the first embodiment of the present invention is applied, and FIG. 2 is a block diagram of the first embodiment. The system control circuit 100 is, for example, a microcomputer that controls the entire laser printer. The laser diode drive circuit 12, the DMD drive circuit 26, the scanner motor 51, the sensor control circuit 91, and the photosensitive drum drive circuit 110 are connected to the system control circuit 100, respectively. Each circuit outputs a drive signal based on a control signal output from the system control circuit 100.

The light source unit 10 includes a laser diode 11 and a laser diode drive circuit 12. A light beam B1 is emitted from the laser diode 11 based on an output signal from the laser diode drive circuit 12. The light beam B1 is converted into parallel light by the collimator lens 30, and is guided to the DMD 20, which is a light reflection unit. A light shielding plate 42 is provided near the DMD 20. A part of the light beam B1 incident on the DMD 20 is reflected toward the cylindrical lens 40 (reference B2), and a part is reflected toward the light shielding plate 42 (reference B5).

Here, DMD is a trade name, which is an abbreviation for a digital micromirror device. The DMD is configured by arranging a large number of micromirrors each having a side of about 16 μm in a lattice shape. Each micromirror can be tilted in two directions, and the tilt direction is changed by an electrostatic field effect of a memory element provided immediately below each micromirror. That is, assuming that the micromirror receiving the electrostatic force is tilted in the first tilt direction, the micromirror not receiving the electrostatic force tilts in the second tilt direction. Therefore, for example, each micromirror is tilted in the first or second tilt direction, and the traveling direction of light incident on the DMD differs depending on the tilt direction of the micromirror.

The entire area of the DMD 20 has a size that includes the sectional area of the light beam B1. In this embodiment, as shown in FIG. 3, m × n-bit micromirrors (light reflecting elements) 21 are provided on the surface of the DMD 20, and these micromirrors 21 are arranged in a matrix of m rows × n columns. ing. By appropriately tilting each micro mirror 21 in the DMD 20 in the first or second tilt direction, a part of the light beam B1 is reflected to the cylindrical lens 40 as described above.

The light beam B2 reflected by the DMD 20 is
After passing through a cylindrical lens 40 as shown in FIG.
The light is incident on the reflection surface of the polygon mirror 50 that rotates counterclockwise at a constant speed by the scanner motor 51. The light beam B2 scans in the direction of arrow A with the rotation of the polygon mirror 50, and the scanning speed of the light beam B2 is corrected to a fixed position by the fθ lens 60, and the light beam B2 is focused on the scanning surface of the photosensitive drum D.

The light beam B3 emitted from the fθ lens 60
Arrives at the position of the reflection mirror 70,
And is incident on the horizontal synchronization detection sensor 90 via the correction cylinder lens 80. When the light beam B3 enters the horizontal synchronization detection sensor 90, a horizontal synchronization signal is output from the sensor control circuit 91 to the system control circuit 100. As a result, the system control 100 detects that the light beam scanned on the scanning surface of the photosensitive drum D has reached a predetermined position, that is, a position on the scanning surface of the photosensitive drum D upstream of the writing start position. The drive start timing of the laser diode 11 is determined in units of one horizontal scanning period based on the detection time. At this timing, the system control circuit 100
A drive signal is output from the laser diode drive circuit 12 to the laser diode 11 based on the control signal output from the, and drive control such as turning on and off the laser diode 11 is performed.

FIG. 4 is a diagram conceptually showing a configuration for driving the micro mirror 21. As shown in FIG. The micromirror 21 is a substantially rectangular plate-shaped member, and a thin film of aluminum is formed on the surface (that is, the mirror surface). One side of the micromirror 21 is, for example, about 16 μm. Two corners 21a and 21b on the diagonal line of the micro mirror 21
Is connected via a torsion hinge 24 to a pair of support columns 23 provided on the silicon substrate 22. That is, the micro mirror 21 is rotatable around the torsion hinge 24, and stably stops at a position where one of the two corners 21 c and 21 d different from the corners 21 a and 21 b is in contact with the silicon substrate 22.

A plurality of electrodes 25 (memory elements) are formed on the surface of the silicon substrate 22 on the side of the micro mirror 21. By applying a voltage to a predetermined one of these electrodes 25, an electrostatic force acts on the micromirror 21, and the micromirror 21 is tilted in the first tilt direction when the corner 21c comes into contact with the silicon substrate 22. (ON state). On the other hand, when no electrostatic force is applied, the micromirror 21 is inclined in the second inclination direction with the corner 21d abutting on the silicon substrate 22 (OFF state).

FIG. 5 is a diagram showing a state of reflection of light incident on the micro mirror 21. In this figure, when the micro mirror 21 is in the ON state, as shown by the solid line L1, -1
It is rotationally displaced in the counterclockwise direction by 0 °, and when it is in the off state, it is rotationally displaced in the clockwise direction by + 10 ° as shown by the broken line L2. In the ON state, light (reference numeral B1) emitted from the laser diode 11 (see FIG.
1 and is guided to the cylindrical lens 40 (reference B2). On the other hand, in the off state, the light emitted from the laser diode 11 and reflected by the micromirror 21 does not enter the reflection surface of the polygon mirror (reference B5). That is, the micromirror 21 is turned on to reflect the incident light toward the polygon mirror 50,
It can be selectively set between the off state where the light is not reflected to the polygon mirror 50 side.

In this embodiment, the optical axis of the collimating lens 30 and the optical axis of the cylindrical lens 40 are DM
The collimating lens 30 and the cylindrical lens 40 are arranged such that the micromirror 21 at the center of D20 is symmetric with respect to the normal of the mirror surface when the micromirror 21 is in the first direction (on state). Thus, when the micromirror 21 is in the first direction (on state), incident light is reflected most efficiently and guided to the cylindrical lens 40.

FIG. 6 is a diagram schematically showing the range of incident light and reflected light on the DMD 20. The region 20a is a range where the light beam B1 is irradiated. The micromirror 2 in the elliptical region 20b in the state where the light beam B1 is irradiated
1 is driven to the on state, and the micromirrors 21 outside the area 20b are driven to the off state. as a result,
Only the part of the light beam B1 that is irradiated on the region 20b passes through the cylindrical lens 40 and the polygon mirror 50
Led to. That is, the light beam B1 emitted from the laser diode 11 and converted into parallel light by the collimator lens 30 is incident on the DMD 20, whereby the light beam B2 whose sectional shape corresponds to the region 20b is guided to the polygon mirror 50. As described above, since the resolution of the image is determined by the diameter of the scanning beam scanned on the photosensitive drum D, each micro-electrode of the DMD 20 is adjusted so that the size and shape of the area 20b correspond to the resolution specified by the operator. The mirror 21 is driven.

The driving of the micro mirror 21 is performed as follows. In a built-in memory (not shown) of the system control circuit 100, data of a slit dimension corresponding to a resolution of an image drawn on the scanning surface of the photosensitive drum D is stored in advance. When the resolution is selected by the operator, the number and position of the micromirrors 21 to be turned on by the system control circuit 100 are determined based on the data stored in the internal memory, and the control signal is sent to the DMD drive circuit 26. Is output. Each micro mirror 21 of the DMD 20 is driven according to a drive signal output from the DMD drive circuit 26 based on a control signal of the system control circuit 100. As a result, a light beam B2 having a beam diameter corresponding to the selected resolution is guided to the polygon mirror 50. The data stored in the built-in memory is obtained in advance by an experiment in consideration of optical characteristics such as diffraction and variations in the amount of light.

As described above, according to the present embodiment, by controlling the number and position of the micromirrors 21 driven in the ON state, the diameter of the light beam scanned on the scanning surface of the photosensitive drum D is controlled. Therefore, the resolution of the electrostatic latent image formed on the scanning surface can be freely switched.

In addition, it is possible to prevent a decrease in resolution accuracy due to abrasion of a notch portion of a slit plate such as a conventional slit or a processing defect.

Further, each micro mirror 2 of the DMD 20
1 are individually driven in an on / off state, so that not only the beam diameter but also the shape of the light beam B2 guided to the polygon mirror 50 can be freely controlled.

FIGS. 7 to 10 show a second embodiment of the present invention.
May be used. FIG.
FIG. 10 shows a diffractive light modulation element 200 provided in the second embodiment. In this embodiment, light used for optical communication scanned on the photosensitive drum D is monochromatic light, for example, infrared light. Diffractive light modulation element 20
0 is provided in place of the DMD 20 (see FIG. 1), and the other configuration is the same as that of FIG.

The diffraction type light modulation element 200 has a large number of beam members 2.
01. The beam member 201 is made of, for example, silicon nitride and has a width of 1.0 to 1.5 μm and a length of 15 to 120 μm.
It is a thin plate-shaped member of μm. The surface of the beam member 201 is coated with a thin film 202 of, for example, aluminum to form a mirror surface. Both ends of each beam member 201 are supported by spacers 204 fixed on a substrate 203. The spacer 204 is made of, for example, silicon dioxide. Each beam member 201 is arranged in parallel with each other, and the interval between adjacent beam members 201 is substantially equal to the width of the beam member 201.

The surface of the beam member 201 (ie, the thin film 202)
Is smaller than 1 / of the wavelength (λ) of the light applied to the diffractive light modulation element 200.
2. Further, the plate thickness of the beam member 201 is 1 / the wavelength thereof.
4.

When no voltage is applied between the beam member 201 and the substrate 203, the beam member 201 is parallel to the substrate 203, as shown in FIGS. Are separated by λ / 2. In this state, the monochromatic light having the wavelength λ applied to the substrate 203 is reflected by the diffraction action (on state). On the other hand, when a voltage is applied between the beam member 201 and the substrate 203, as shown in FIGS. 16 and 17, the beam member 201 bends so that its back surface is in close contact with the substrate 203, and The distance between the surface of the substrate 201 and the substrate 203 is λ / 4. In this state, the incident light and the reflected light on the substrate 203 cancel each other, and there is no reflected light (OFF state).

As described above, in the second embodiment, since the diffractive light modulating element 200 which is set to the on state or the off state by the diffraction of light is used, the first embodiment is used except that monochromatic light is used as a light source. The operation is the same as that of the first embodiment, and an equivalent effect is obtained.

[0031]

As described above, according to the present invention, the diameter of a light beam emitted from a light source in a laser printer or the like can be easily controlled, and the resolution of an image can be switched.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a configuration of a laser printer to which a first embodiment of the present invention is applied.

FIG. 2 is a block diagram of the first embodiment.

FIG. 3 is a diagram schematically showing a DMD.

FIG. 4 is a diagram conceptually showing a configuration for driving a micromirror.

FIG. 5 is a diagram illustrating a reflection state of light incident on a micro mirror.

FIG. 6 is a diagram schematically showing ranges of incident light and reflected light in a DMD.

FIG. 7 is a cross-sectional view of a diffractive light modulation element provided in a second embodiment of the present invention and in an ON state, cut along a plane perpendicular to a beam member.

8 is a side view of the diffractive light modulation device shown in FIG.

FIG. 9 is a cross-sectional view showing the diffractive light modulation element in an off state by cutting along a plane perpendicular to a beam member.

FIG. 10 is a side view of the diffractive light modulation element shown in FIG.

[Explanation of symbols]

 Reference Signs List 11 laser diode 20 DMD 21 micro mirror 30 collimating lens 40 cylindrical lens 42 light shielding plate 50 polygon mirror 60 fθ lens 200 diffractive light modulating element D photosensitive drum

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Takaaki Yoshinari 2-36-9 Maenocho, Itabashi-ku, Tokyo Asahi Gaku Kogyo Co., Ltd. (72) Inventor Kiyoshi Negishi 2-36-9 Maenocho, Itabashi-ku, Tokyo No. Asahi Gaku Kogyo Co., Ltd.

Claims (9)

[Claims] 1. An optical scanning device for writing predetermined information on a photosensitive member by deflecting a light beam emitted from a light source by an optical deflector and scanning the light beam, the light beam between the light source and the optical deflector. Light reflecting means having a plurality of light reflecting elements capable of selectively setting an ON state in which incident light is deflected in a first direction and an OFF state in which the incident light is deflected in a second direction is disposed on an optical path of the beam. An optical diaphragm device, which defines the shape of the light beam guided to the optical deflector. 2. The light reflecting means defines the shape of the light beam by changing the number of the light reflecting elements in an on state and the number of the light reflecting elements in an off state. 6. The optical diaphragm device according to 5. 3. The optical diaphragm device according to claim 1, wherein the light reflecting element is a mirror element that is set to an on state or an off state by changing an inclination angle by an electrostatic force. 4. The optical diaphragm device according to claim 1, wherein said light reflecting element is a diffractive light modulation element which is set to an on state or an off state by a diffraction effect of light. 5. The optical stop device according to claim 1, wherein the first direction is a direction guided to the optical deflector. 6. The optical stop device according to claim 5, wherein a light blocking member is provided in the second direction. 7. The optical stop device according to claim 1, wherein the optical deflector is a polygon mirror of a laser printer. 8. The optical stop device according to claim 7, wherein the light source is a laser diode. 9. The optical stop device according to claim 7, wherein the light source is a gas laser.