JP3548319B2 - Scanning optical device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION
The present invention relates to a scanning optical device used for a laser printer or the like, and more particularly, to a device using a polygon mirror having a plurality of reflection surfaces as a deflector.
[0001]
[Prior art]
The scanning optical device reflects and deflects a light beam emitted from a light source such as a semiconductor laser with a polygon mirror, and converges the light beam with an fθ lens to form a spot to be scanned in a main scanning direction on a scanning target surface such as a photosensitive drum.
[0002]
The polygon mirror is generally manufactured by processing metal, and a plurality of reflection surfaces are individually polished. For this reason, an error occurs in which the reflection surface, which should be originally parallel to the rotation axis, is inclined with respect to the rotation axis, that is, a so-called surface tilt error, and the amount of the error is different for each reflection surface.
[0003]
The conventional scanning optical device arranges a cylindrical lens between the light source and the polygon mirror in order to correct the deviation of the spot position in the sub-scanning direction due to a surface tilt error, and uses an anamorphic fθ lens to reflect the polygon mirror. The surface and the photosensitive drum surface are set to be optically conjugate in the sub-scanning direction.
[0004]
[Problems to be solved by the invention]
However, if the conjugate relationship is broken due to a lens processing error or the like, or the conjugate position of the photosensitive drum surface is deliberately set before and after the reflection surface to avoid the influence of dust and scratches on the reflection surface of the polygon mirror. In the case of shifting, there is a problem that the positional deviation of the spot due to the surface tilt error remains without being completely corrected.
[0005]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a scanning optical device that can correct a position shift of a spot due to a surface tilt error that occurs when a conjugate relationship is not maintained.
[0006]
[Means for Solving the Problems]
A scanning optical apparatus according to the present invention includes a light source, a polygon mirror that reflects and deflects a light beam emitted from the light source, and a beam spot on a photosensitive drum surface, which is disposed in an optical path between the light source and the polygon mirror. A scanning prism that forms a beam spot on the photosensitive drum surface by converging a light beam reflected by the polygon mirror, and a plurality of polygon mirrors. Detecting means for outputting an index signal each time a specific reflection surface among the reflection surfaces passes a specific rotation position, and sub-scanning of a beam spot on the photosensitive drum surface based on a surface tilt error for each of the plurality of reflection surfaces Based on the index signal and a predetermined synchronizing signal, the memory for storing the surface tilt shift amount, which is a deviation in the direction, and the reflection surface corresponding to the current scan are determined. Surface tilt shift amount determining means for reading the shift amount corresponding to the specified reflection surface from the memory, rotation unevenness detecting means for detecting rotation unevenness of the photosensitive drum, and rotation unevenness detected by the rotation unevenness detecting means. Rotation unevenness shift amount calculating means for performing a predetermined calculation based on predetermined reference writing position information and calculating a rotation unevenness shift amount which is a deviation of the beam spot in the sub-scanning direction due to the rotation unevenness, and a surface tilt shift amount determining means Adding means for calculating the total shift amount by adding the surface tilt shift amount determined by the above and the rotation unevenness shift amount calculated by the rotation unevenness shift amount calculating means, and canceling the total shift amount calculated by the adding means. Control means for controlling the rotation of the dynamic prism and angle detecting means for detecting the rotation angle of the dynamic prism. Control means, based on the rotation angle and overall shift amount detected by the angle detection means, and controlling rotation by closed-loop dynamic prism. Thereby, the position deviation of the beam spot on the photosensitive drum surface in the sub-scanning direction due to the surface inclination of the polygon mirror, and the deviation of the beam spot on the photosensitive drum surface in the sub-scanning direction due to uneven rotation of the photosensitive drum itself. By correcting both of the positional deviations, it is possible to prevent the degradation of the drawing performance.
[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 scanning optical apparatus will be described with reference to FIG. 1 which is a perspective view of the entire scanning optical apparatus, FIG. 2 which shows an arrangement of the optical system, FIG. 3 which is a sectional view, and FIG. In this specification, the “main scanning direction” is a direction corresponding to the scanning direction of the light beam in a plane perpendicular to the optical axis, and the “sub-scanning direction” is orthogonal to the main scanning direction in a plane perpendicular to the optical axis. Direction.
[0008]
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]
As shown in FIGS. 1 and 2, the light source unit 100 of the scanning optical system includes eight laser blocks 310a to 310h attached to a support substrate 300, and semiconductor lasers attached to these laser blocks one by one. 101 to 108, eight optical fibers 121 to 128 made of quartz glass for transmitting a light beam emitted from a semiconductor laser, and end portions on the emission side of these optical fibers arranged in a straight line and arranged in a straight line. And a fiber alignment block 130 forming two point light sources. The ends of the optical fibers 121 to 128 on the incident side are held by fiber supports 319a to 319h fixed to the laser blocks 310a to 310h.
[0010]
The divergent light beam emitted from the fiber alignment block 130 of the light source unit 100 is converted into a parallel light beam by the collimating lens 140 held by the cylindrical collimating lens holder 340, passes through the diaphragm 142, and enters the half mirror 144. The transmittance of the half mirror 144 is 5 to 10%.
[0011]
The monitor light beam transmitted through the half mirror 144 enters an APC (auto power control) signal detection unit 150. The APC signal detection unit 150 includes a condenser lens 151 that converges the transmitted light beam, a polarization beam splitter 153 as a polarization separation element that separates the light beam into two orthogonal polarization components, and an APC light receiving device that receives the respective polarization components. It comprises one light receiving element 155 and an APC second light receiving element 157, and its output signal is used for feedback control so that the output of each semiconductor laser with respect to the same drive signal becomes substantially the same.
[0012]
On the other hand, the main light beam reflected by the half mirror 144 is angle-controlled by a dynamic prism 160 that sequentially controls the angle in the sub-scanning direction, and is then transmitted to the polygon mirror 180 by a cylindrical lens 170 having positive power only in the sub-scanning direction. A linear image is formed near the mirror surface. The dynamic prism 160 is provided so as to be rotatable around an axis parallel to the bottom surface of the casing 1, and the rotation causes the deflection effect to change so that the position of the beam spot on the photosensitive drum 210 is shifted in the sub-scanning direction. Shift. The dynamic prism 160 is used to correct a positional deviation of a spot on the surface to be scanned in the sub-scanning direction due to a surface tilt error of a polygon mirror, which will be described later, and uneven rotation of the photosensitive drum. The cylindrical lens 170 is held by a cylindrical cylindrical lens holder 361, and includes two lenses 171 and 173 having positive and negative powers in the sub-scanning direction, as shown in FIG.
[0013]
The polygon mirror 180 is driven by a polygon motor 371 fixed to the casing 1 as shown in FIG. 3, and rotates clockwise as indicated by an arrow in FIG. The polygon mirror 180 is shielded from the outside air by a cup-shaped polygon mirror cover 373 as shown in FIG. 1 in order to avoid generation of wind noise due to rotation and damage to the mirror surface due to collision with dust in the air. Is arranged.
[0014]
An optical path hole 373e is formed in the side wall of the polygon mirror cover 373, and a cover glass 375 is fitted in the optical path hole 373e. The light beam transmitted through the cylindrical lens 170 enters the cover through the cover glass 375, is reflected and deflected by the polygon mirror 180, and is emitted again through the cover glass 375. A sensor block 376 including a polygon sensor (not shown) for detecting a mark M attached to the upper surface of the polygon mirror 180 and outputting an index signal is provided on the upper surface of the polygon mirror cover 373. .
[0015]
The reflection surface of the polygon mirror 180 has a surface tilt error even when processed with high precision, and the error amount generally differs for each reflection surface. Therefore, the error amount of each surface is measured and stored in advance, and by identifying which reflecting surface is used in accordance with the index signal output from the polygon sensor at the time of use, the unique amount of each reflecting surface is determined. The turning angle of the dynamic prism 160 is adjusted in accordance with the amount of the surface tilt error to correct the beam position.
[0016]
The light beam reflected by the polygon mirror 180 passes through the fθ lens 190 which is an image forming optical system, is reflected by the folding mirror 200 as shown in FIG. 3, reaches the photosensitive drum 210, and has eight beam spots. To form These beam spots are scanned simultaneously with the rotation of the polygon mirror 180, and eight scanning lines are formed on the photosensitive drum 210 by one scan.
[0017]
The photosensitive drum 210 is driven to rotate in the direction of arrow R shown in FIG. 3 in synchronization with the scanning of the beam spot, whereby an electrostatic latent image is formed on the photosensitive drum 210. This latent image is transferred to a sheet (not shown) by a known electrophotographic process.
[0018]
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. Fourth lenses 191, 193, 195, and 197 are arranged, and a light beam linearly formed near the mirror surface of polygon mirror 180 in the sub-scanning direction is re-imaged on photosensitive drum 210 in an elliptical shape. It has the power to make it.
[0019]
The four lenses of the fθ lens 190 are fixed on a single lens mount 380 as shown in FIGS. Since the fθ lens 190 is assumed to be used at a single wavelength, chromatic aberration is not corrected.
[0020]
1 to 4, the x axis is an axis parallel to the optical axis of the fθ lens 190, and the y axis and the z axis are axes orthogonal to each other in a plane perpendicular to the x axis. The y axis coincides with the main scanning direction, and the z axis coincides with the sub scanning direction in the optical path between the polygon mirror 180 and the return mirror 200.
[0021]
The light beam transmitted through the fθ lens 190 is detected by the synchronization signal detecting optical system 220 before entering the drawing range for each scan, that is, for each scan by one reflection surface of the polygon mirror. The synchronization signal detecting optical system 220 includes a first mirror 221 that is disposed in an optical path between the fourth lens 197 of the fθ lens 190 and the return mirror 200 and reflects a light beam before the drawing range, and the first mirror 221. The second mirror 223 and the second mirror 225 sequentially reflect the light beam reflected by the light receiving device 221 and the light receiving element 230 that receives the light beam guided by these mirrors. The light receiving element 230 is arranged at a position optically equivalent to the photosensitive drum 210. The eight beams are sequentially incident on the light receiving element 230 one by one with the scanning, and the light receiving element 230 outputs eight pulses for each scanning. When a pulse is detected, one line of image data is transferred to a laser driving unit that drives a semiconductor laser corresponding to the pulse, and writing is started after a certain period of time has elapsed from the detection of the pulse.
[0022]
In addition, the casing 1 is formed with a drawing opening 11 for transmitting the light beam reflected by the folding mirror 200, and an optical adjustment opening 12 behind the folding mirror 200. A cover glass 201 is attached to the drawing opening 11. The optical adjustment opening 12 is used for adjusting these optical elements after assembling the optical elements except for the folding mirror 200, and is closed by the cover plate 13 as shown in FIG. Is done.
[0023]
Next, the configuration of a system for controlling the dynamic prism 160 of the above-described scanning optical device and its operation will be described.
FIG. 5 is a block diagram illustrating a portion related to the control of the dynamic prism 160 in the control system of the scanning optical device according to the embodiment. This control circuit controls the dynamic prism 160 so as to correct the deviation of the beam spot on the photosensitive drum surface in the sub-scanning direction caused by the surface tilt error of the polygon mirror 180 and the uneven rotation of the photosensitive drum 210. I do.
[0024]
The surface tilt shift amount calculating device 461 determines whether the current scanning is performed by any of the reflecting surfaces of the polygon mirror based on the index signal output from the polygon sensor 374 and the synchronization signal output from the synchronization signal detecting light receiving element 230. The shift amount of the beam spot due to the surface tilt error of the corresponding reflection surface is read from the memory 401 and output.
[0025]
The polygon sensor 374 includes, for example, a light emitting diode that projects light toward the polygon mirror 180 and a light receiving element that receives light emitted from the light emitting diode and reflected by the polygon mirror 180. In this example, the mark M is attached with black oil-based ink and has a lower reflectance than other portions made of metal. Therefore, every time the mark M passes under the polygon sensor 374, the output of the light receiving element is temporarily stopped. Decline. The polygon sensor 374 outputs this change in output as an index signal.
[0026]
When a single mark M is attached to the polygon mirror 180 as in the apparatus of the embodiment, an index signal is output each time the polygon mirror 180 makes one rotation. When the index signal is output, it is possible to identify the reflection surface that is scanning the light beam at that time, and since the switching of the surface can be determined from the synchronization signal, the light beam is always reflected on any of the reflection surfaces. Is deflected.
[0027]
In the memory 401, the shift amount of the spot on the photosensitive drum 210 due to the inclination of each surface of the polygon mirror 180 is input in advance. The data relating to the shift amount may be obtained by calculation by measuring the surface tilt angle of each reflecting surface, or may be obtained by calculating the beam spot at a predetermined image height when one semiconductor laser emits light. The difference may be obtained by actually measuring the difference on the photosensitive drum 210 or on a surface optically equivalent to the difference. The obtained data of the shift amount is input from the shift amount input device 460 connected to the tilting shift amount calculating circuit 461. The shift amount input device 460 only needs to be connected at least in the adjustment stage, and may be removed after the adjustment.
Since the spot shift due to the surface tilt has a constant value for each reflection surface, the output of the surface tilt shift amount calculation circuit 461 determines the reference angle of the dynamic prism 160 on the reflection surface.
[0028]
On the other hand, the rotation unevenness of the photoconductor drum 210 is not a known error such as surface tilt but an error generated at random. The rotation unevenness shift amount calculation unit 463 performs sub-scanning of the spot due to the detected rotation unevenness based on the original writing position input from the printer controller 465 and the rotation unevenness of the photosensitive drum 210 output from the drum sensor 213. Calculate the shift amount in the direction.
[0029]
The shift amount of the beam spot in the sub-scanning direction due to the surface tilt error output from the surface tilt shift amount calculation unit 461 and the spot shift amount due to the rotation unevenness output from the rotation unevenness shift amount calculation unit 463 are added to the addition circuit 467. The sum is added and input to the dynamic prism position controller 469. The dynamic prism position control device 469 determines the adjustment angle of the dynamic prism 160 for canceling the total shift amount output from the adding circuit, and controls the rotation of the dynamic prism 161. The set angle of the dynamic prism 160 is detected by the prism sensor 163, and the dynamic prism position control device 469 controls the dynamic prism in a closed loop based on the sensor output. The prism sensor 163 includes, for example, a light-emitting element that causes a light beam to enter a mirror portion formed on one surface of the dynamic mirror 160 and a light-receiving element that detects the position of the light beam emitted from the light-emitting device and reflected by the mirror portion. Be composed.
[0030]
The above control corrects the surface tilt of the polygon mirror 180, which cannot be completely corrected by the combination of the cylindrical lens and the fθ lens, and the shift of the spot in the sub-scanning direction due to the uneven rotation of the photosensitive drum 210, and corrects the scanning line. The position in the sub-scanning direction can be accurately controlled.
[0031]
The position control of the dynamic prism 160 for correcting the shift of the beam spot due to the surface tilt error is performed at a timing from the end of the previous scan to the start of the drawing. In order to secure this position control time, the scanning efficiency, that is, the ratio of the drawing time to the switching interval of the reflection surface is set relatively small.
[0032]
【The invention's effect】
As described above, according to the present invention, even when the conjugate position of the drawing target surface is deviated from the reflection surface of the polygon mirror, the beam on the scanning target surface is different for each reflection surface due to the surface tilt error. The displacement of the spot in the sub-scanning direction can be corrected. Therefore, even when the conjugate point in the sub-scanning direction of the scanning target surface is separated from the reflection surface of the polygon mirror in order to avoid the influence of dust and scratches on the polygon mirror surface, it cannot be corrected by the static characteristics of the optical system. It is possible to correct the positional deviation of the spot in the sub-scanning direction and prevent the drawing performance from deteriorating.
[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 sectional view of the apparatus in FIG. 1 in the sub-scanning direction.
FIG. 3 is a plan view of the apparatus of FIG. 1 in the main scanning direction.
FIG. 4 is an explanatory view in the main scanning direction showing only the optical system of the apparatus in FIG. 1;
FIG. 5 is a block diagram illustrating a control system of the scanning optical device according to the embodiment.
[Explanation of symbols]
Reference Signs List 100 light source units 101 to 108 semiconductor lasers 121 to 128 optical fiber 130 fiber alignment block 160 dynamic prism 180 polygon mirror 190 fθ lens 210 photosensitive drum 213 drum sensor 230 synchronous signal detecting light receiving element 374 polygon sensor M mark 401 memory 461 surface tilt shift Amount calculation device 463 Rotation unevenness shift amount calculation device 469 Dynamic prism position control device

Claims (1)

A light source,
A polygon mirror for reflecting and deflecting a light beam emitted from the light source,
A dynamic prism that is arranged in an optical path between the light source and the polygon mirror and that rotates to shift the position of the beam spot on the photosensitive drum surface that is rotationally driven in the sub-scanning direction;
A scanning lens for converging the light beam reflected by the polygon mirror to form a beam spot on the photosensitive drum surface;
Detecting means for outputting an index signal each time a specific reflection surface among a plurality of reflection surfaces of the polygon mirror passes a specific rotation position;
A memory for storing a surface tilt shift amount, which is a shift in a sub-scanning direction of a beam spot on the photosensitive drum surface based on a surface tilt error for each of the plurality of reflection surfaces;
Based on the index signal and the predetermined synchronization signal, a reflection surface corresponding to the current scan is specified, and a surface tilt shift amount determination unit that reads a shift amount corresponding to the specified reflection surface from the memory,
Rotation unevenness detecting means for detecting rotation unevenness of the photosensitive drum,
A predetermined calculation is performed based on the rotation unevenness detected by the rotation unevenness detection means and predetermined reference writing position information, and a rotation unevenness shift amount, which is a shift of the beam spot in the sub-scanning direction due to the rotation unevenness, is calculated. A rotation unevenness shift amount calculating means for calculating;
An adding unit that calculates the total shift amount by adding the surface tilt shift amount determined by the surface tilt shift amount determining unit and the rotation unevenness shift amount calculated by the rotation unevenness shift amount calculating unit;
Control means for controlling the rotation of the dynamic prism so as to cancel the total shift amount calculated by the adding means,
An angle detecting means for detecting a rotation angle of the dynamic prism,
The scanning optical apparatus according to claim 1, wherein the control means controls the rotation of the dynamic prism in a closed loop based on the rotation angle detected by the angle detection means and the total shift amount.

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