JPH1062701A - Laser beam scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a laser beam scanning optical device permitting to precisely detect a deviation of the laser beam scanning position at low cost by a simple signal processing. SOLUTION: This laser beam scanning device is mainly composed of a laser diode 2, polygon mirror 6, and fθ lens 7, and prints a picture on a photoreceptor drum 101. A scanning position detector 10 is arranged in the neighborhood of an almost optically equivalent position on a surface of the photoreceptor 101. This detector 10 is composed of a first filter 11 having a space grating parallel to the laser beam scanning direction b, a second filter 12 having a space grating tilted at a small angle to the laser beam scanning direction b, cylindrical lens 13, 14 composing a small optical system 14, and a photoelectric converter element 15 receiving the laser beam transmitted through the filters 11, 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam scanning optical device, and more particularly to a laser beam scanning optical device incorporated as an image printing means in a laser printer or a digital copying machine.

[0002]

2. Description of the Related Art In recent years, laser beam scanning optical apparatuses incorporated as image printing means in laser printers and digital copiers are required to print at high density in order to improve image quality. Printing dot misalignment and color misalignment during multiple transfer of a machine that sequentially superimposes and transfers toner images (for example, a full-color laser printer or digital copying machine) have become an important problem.

On the other hand, in order to meet the demands of users to reduce the price of laser printers and digital copiers, inexpensive resin materials are often used as component materials.
However, resin materials have a large coefficient of thermal expansion, and heavy use of resin materials causes mechanical expansion and changes in the refractive index of the lens due to changes in the surrounding environment (temperature), causing the laser beam scanning position to shift in the sub-scanning direction. It is easy to cause print dot shift and color shift at the time of multiple transfer.

In order to solve this problem, Japanese Patent Laid-Open No.
The image forming apparatus described in Japanese Patent No. 7116 has a temperature control unit for controlling the temperature of the laser beam scanning optical device within a certain range. Further, an optical writing device described in Japanese Patent Application Laid-Open No. 4-16967 discloses a light source position detecting means for detecting the position of each of a plurality of light sources in the sub-scanning direction, and a photosensitive member based on a detection signal from the light source position detecting means. And a writing position correcting means for correcting a light writing position to the optical disk.

[0005]

However, in the former (Japanese Patent Laid-Open No. 4-127116), in order to keep the temperature of the laser beam scanning optical device constant, a Peltier element which performs heating and cooling operations in accordance with the detected temperature. And the like, and the laser beam scanning optical device must have a closed structure or a heat insulating structure so as not to generate a temperature gradient.

Further, the latter (Japanese Patent Laid-Open No. 4-16967) has a disadvantage that an expensive CCD having complicated signal processing is used as a light source position detecting means. Accordingly, an object of the present invention is to be able to accurately detect a laser beam scanning position shift by simple signal processing, and
An object is to provide an inexpensive laser beam scanning optical device.

[0007]

In order to achieve the above object, a laser beam scanning optical apparatus according to the present invention comprises:
Moiré fringe generating means for disposing a moiré fringe pattern by disposing a laser beam emitted from a laser light source to generate a moiré fringe pattern, which is arranged near an optically equivalent position to the surface to be scanned, And (b) scanning position shift detecting means for detecting a scanning position shift based on an output of the light receiving element.

[0008] For example, the moiré fringe generating means has, in order from the laser light source side, a first spatial grid having a stripe shape parallel to one of the main scanning direction and the sub-scanning direction of the laser beam. The filter comprises a filter and a second filter having a striped spatial grid inclined at a small angle with respect to the direction of the spatial grid of the first filter.

[0009]

With the above arrangement, the laser beam emitted from the laser light source forms moire fringes on the light receiving surface of the light receiving element via the moire fringe generating means. When the scanning position of the laser beam is shifted in the sub-scanning direction, the position of the moiré fringes is enlarged in accordance with the shift amount of the scanning position of the laser beam and is shifted in the sub-scanning direction. In addition, the moire fringes also shift in the same direction as the direction of the shift of the scanning position of the laser beam. Therefore, the shift amount and the shift direction of the scanning position of the laser beam can be accurately measured by detecting the change in the position of the moire fringes by the light receiving element.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a laser beam scanning optical device according to the present invention will be described below with reference to the accompanying drawings. (Overall Configuration of Laser Beam Scanning Optical Device) In FIG. 1, a laser beam scanning optical device 1 includes a laser diode 2, a collimator lens 3, and a cylindrical lens 4.
A plane mirror 5, a polygon mirror 6, an fθ lens 7 (constituted of lenses 7a, 7b, 7c), a plane mirror 8, an SOS cylindrical lens 16,
It comprises an SOS optical sensor 17 and a scanning position detector 10.

The laser diode 2 is modulated (on / off) based on print data input to a drive circuit (not shown).
It is controlled and emits a laser beam L when turned on. This laser beam L is converged substantially parallel by the collimator lens 3 and reaches the polygon mirror 6 from the cylindrical lens 4 via the plane mirror 5. The polygon mirror 6 is driven to rotate at a constant speed in the direction of arrow a around the rotation axis 6a. The laser beam L is deflected at a constant angular velocity on each deflecting surface based on the rotation of the polygon mirror 6 and enters the fθ lens 7. The laser beam L transmitted through the fθ lens 7 is reflected by the plane mirror 8 and then condensed on the photosensitive drum 101, and scans the photosensitive drum 101 in the direction of arrow b.
lens 7 mainly emits the laser beam L deflected at a constant angular velocity by the polygon mirror 6 onto the surface to be scanned (photosensitive drum 1).
01) has a function of correcting the main scanning speed at a constant speed, that is, correcting distortion.

The photosensitive drum 101 is driven to rotate at a constant speed in the direction of arrow c, and an image (electrostatic image) is formed on the drum 101 by the main scanning in the direction of arrow b by the polygon mirror 6 and the sub-scanning of the drum 101 in the direction of arrow c. Latent image) is formed.
Further, the laser beam L at the front end in the main scanning direction is
And is transmitted through the SOS cylindrical lens 16 and enters the SOS optical sensor 17. The beam detection signal output from the SOS optical sensor 17 generates a vertical synchronization signal for determining a printing start position for each scanning line.

(Description of Scanning Position Detector) The scanning position detector 10 is installed outside the image area near the optically substantially equivalent position to the surface to be scanned, and the scanning position of the laser beam L on the surface to be scanned. Is detected. Specifically, as shown in FIG. 1 and FIG. 2, it is composed of grating filters 11 and 12, cylindrical lenses 13 and 14, and a photoelectric conversion element 15 arranged in the optical axis direction. The grating filters 11 and 12 have striped spatial gratings A and B, respectively. The spatial grating A is parallel to the main scanning direction b of the laser beam L, and the spatial grating B
Is inclined by a small angle. The laser beam L transmitted through the grating filters 11 and 12 is modulated, and forms moire fringes 35 (see FIG. 3) on the photoelectric conversion element 15.

The photoelectric conversion element 15 is a two-division photodiode having left and right divided light receiving surfaces 15a and 15b for receiving a laser beam.
a and 15b output a current proportional to the amount of received light. Incidentally, the light receiving surfaces 15a and 15b of the photoelectric conversion element 15 may be too small as compared with the size of the moire fringes generated by the two lattice filters 11 and 12. In order to solve this problem and the like, there are provided cylindrical lenses 13 and 14 forming a reduction optical system for reducing moire fringes.

In the cylindrical lenses 13 and 14, the cylindrical lens 13 has a light condensing action only in the main scanning direction b, and the cylindrical lens 14 has a light condensing action only in the sub-scanning direction c. Therefore, the laser beam L transmitted through the grating filters 11 and 12 is applied to the cylindrical lenses 13 and 1.
4, the light-receiving surface 1 of the photoelectric conversion element 15
Moire fringes are formed on 5a and 15b. Therefore, the small-sized photoelectric conversion element 15 can detect the scanning position shift without losing the light amount of the moire fringes.

As described above, by forming the reduction optical system with the two cylindrical lenses 13 and 14, the reduction magnification of the moire fringes in the main scanning direction and the sub-scanning direction can be easily changed. If the reduction magnifications in the main scanning direction and the sub-scanning direction can be made different, the appropriate number of the light-receiving surfaces 15a and 15b of the photoelectric conversion element 15
Moire fringes of a size can be projected, which is desirable. The same effect can be obtained even if such a reduction optical system is configured by an anamorphic lens having different magnifications in the main scanning direction and the sub-scanning direction. In this case, however, the main scanning direction and the sub-scanning direction are simultaneously performed. Since adjustment must be performed, positioning with respect to the light receiving surfaces 15a and 15b becomes more difficult than when two cylindrical lenses are used. Note that the reduction optical system may be composed of one lens having a positive refractive power as long as appropriate moire fringes can be projected on the light receiving surfaces 15a and 15b of the photoelectric conversion element 15.

Next, the procedure for detecting the deviation of the scanning position will be described. The current values Ia and Ib output from the light receiving surfaces 15a and 15b in proportion to the amount of received light are converted into voltage values Va and Vb, respectively, and then the values of Va and Vb are processed by a difference circuit to obtain (Va-Vb). ) Is calculated. Normally, in the initial state, as shown in FIG. 3, the light receiving surface 15a, the center of 15b is set to match the center of the spot Lb of the laser beam L (the position in the drawing Lb _1). Further, the bright portions of the moiré fringes 35 are formed at the portions indicated by oblique lines in FIG. 3, and are set so that the amounts of light incident on the light receiving surfaces 15a and 15b are equal. Thus, output currents Ia and Ib having the same value are obtained from the light receiving surfaces 15a and 15b. Therefore, (V
The value of a-Vb) becomes 0.

However, changes in the ambient environment (temperature)
Therefore, the housing or part of the laser beam scanning optical device 1
Products 2 to 8 etc. cause mechanical expansion and change in the refractive index of the lens.
However, the scanning position of the laser beam L is not below the sub-scanning direction.
(Lb in the figure_TwoIs the bright part of the moiré fringe 35
Also shifts downward in the sub-scanning direction, and (Va−Vb) becomes positive.
You. Conversely, the scanning position of the laser beam L is
Side (Lb in the figure) _ThreeIs the moiré fringe 35
Is also shifted upward in the sub-scanning direction, and (Va-Vb) is negative.
Becomes At this time, the scanning position of the laser beam L is
In the direction, the position of the moire fringes 35 is also changed to the laser beam L.
Is enlarged in accordance with the deviation of the scanning position
It is. Therefore, the amount of displacement of the moiré fringes 35 is detected.
This enables accurate detection of laser beam scanning position deviation.
Can be

Based on the result, the scanning position shift may be corrected by simple electric processing or image processing. That is, when (Va−Vb) is positive, it is determined that the scanning position of the laser beam L is shifted downward in the sub-scanning direction,
When (Va-Vb) is 0, it is determined that no shift has occurred, and when (Va-Vb) is negative, it is determined that the shift is upward. Then, the shift amount is calculated by | Va−Vb |.

Further, the procedure for adjusting the scanning position deviation (print dot deviation) of the laser beam in the sub-scanning direction will be described in detail with reference to the electric circuit diagram of the scanning position deviation detection control unit shown in FIG. Outputs from the light receiving surfaces 15a and 15b of the photoelectric conversion element 15 are photoelectrically converted and output as a current corresponding to the amount of incident light. Therefore, when the laser beam L is applied to each of the light receiving surfaces 15a and 15b, the output current Ia from the light receiving surface 15a is converted into a voltage by an IV (current-voltage) conversion circuit 21, and the voltage is output as a voltage output Va. Input to the circuit 23. Similarly, the output current Ib from the light receiving surface 15b is I-
It is converted into a voltage by a V (current-voltage) conversion circuit 22,
The voltage output Vb is input to the difference circuit 23.

After calculating the difference (Va−Vb), the difference circuit 23 calculates the result as a voltage output Vc and outputs the result to the arithmetic circuit 24.
To enter. The arithmetic circuit 24 outputs a correction signal to the bitmap correction circuit 25 based on the result of the voltage output Vc. The bitmap correction circuit 25 corrects the image data stored in the bitmap memory, and adjusts the print start time of the LD driver 26. That is, as shown in FIG.
When the value of (Va−Vb) becomes 0, the arithmetic circuit 2
4, it is determined that the scanning position of the laser beam L is not shifted, and the bitmap correction circuit 25 does not correct the image data stored in the bitmap memory.
Therefore, there is no change in the print start timing of the LD driver 26.

On the other hand, as shown in FIG. 6, (Va-Vb)
Is positive, the arithmetic circuit 24 determines that the scanning position of the laser beam L is shifted downward in the sub-scanning direction, and based on the value of | Va−Vb | A shift amount is calculated. Then, the bitmap correction circuit 25
Accordingly, the image data stored in the bitmap memory is shifted upward by the calculated number of dots. Therefore, the printing start timing of the LD driver 26 is advanced by the number of dots.

As shown in FIG. 7, (Va-Vb)
Is negative, the arithmetic circuit 24 determines that the scanning position of the laser beam L is shifted upward in the sub-scanning direction, and based on the value of | Va-Vb | The amount is calculated. Then, the bitmap correction circuit 25
Accordingly, the image data stored in the bitmap memory is shifted downward by the calculated number of dots. Therefore, the printing start timing of the LD driver 26 is delayed by the number of dots. With these adjustments, it is possible to prevent a print dot shift due to a scan position shift of the laser beam L in the sub-scanning direction.

(Application to Full-Color Copying Machine) FIG. 8 shows the overall configuration of a tandem-type full-color copying machine 100 provided with the laser beam scanning optical device. This copier 100 is generally used for cyan arranged in a line.
Photoconductor drums 101C, 101M, 101Y, 101Bk for magenta, yellow and black
And laser beam scanning optical devices 1 for cyan, magenta, yellow, and black disposed corresponding to these photosensitive drums 101C to 101Bk.
C, 1M, 1Y, 1Bk and a transfer belt 110.

The photosensitive drums 101C to 101Bk rotate in the direction of arrow c in FIG. Although not shown, around the photosensitive drums 101C to 101Bk, a charger for uniformly charging the surfaces of the photosensitive drums 101C to 101Bk, a photosensitive drum 101C, respectively.
The electrostatic latent images of each color formed on 101 Bk are cyan,
A developing device for visualizing with magenta, yellow, and black toners, a cleaner for residual toner, and an eraser lamp for residual charge are provided.

Laser beam scanning optical device 1C-1Bk
Modulates the laser diode 2 based on the image data stored in the bitmap memory, respectively, and
The electrostatic latent images of cyan, magenta, yellow, and black are formed on the photosensitive drums 101C to 101Bk rotating in the directions. A transfer material such as a sheet is supported by the transfer belt 110 and is conveyed in the direction of arrow d in the figure, on which cyan, magenta, yellow, and black images are sequentially transferred to form a color image.

That is, the laser beam scanning optical device 1C
By the modulated light emission of the laser diode 2, a cyan electrostatic latent image is formed on the photosensitive drum 101C. This electrostatic latent image is developed by a cyan developing device. The cyan toner image is transferred onto a transfer material supported by the transfer belt 110. The transfer material to which the cyan image has been transferred is sent to the transfer drum 101M by the transfer belt 110 in order to transfer the magenta image next. On the other hand, a magenta electrostatic latent image is formed on the photosensitive drum 101M by the modulated light emission of the laser diode 2 of the laser beam scanning optical device 1M, and this electrostatic latent image is developed by a magenta developing device. The magenta toner image is transferred onto the transfer material supported by the transfer belt 110 so as to match the cyan image already transferred on the transfer material. Similarly, when the transfer material is the photosensitive drum 101Y, 101Bk
And the yellow and black toner images are sequentially transferred onto the transfer material. When the four color images are matched on the transfer material, the images are sent to a fixing device by a conveying roller or the like, where the toner is fixed, and then conveyed to a paper discharge tray.

In the full-color copying machine 100 having the above-described configuration, a frame of the copying machine that holds the laser beam scanning optical devices 1C to 1Bk due to a change in the surrounding environment (temperature).
Alternatively, the housings of the laser beam scanning optical devices 1C to 1Bk, or the laser beam scanning optical devices 1C to 1Bk
Even if the components 2 to 8 of 1Bk cause mechanical expansion or a change in the refractive index of the lens, and the scanning position of the laser beam shifts in the sub-scanning direction, the laser beam scanning optical devices 1C to 1C
Since each of Bk has the scanning position detector 10, the scanning position deviation can be detected based on the output from the scanning position detector 10. Therefore, the image data stored in the bitmap memory can be corrected by the bitmap correction circuit 25 from the shift amount and the shift direction of the scanning position of the laser beam in the sub-scanning direction.

For example, if it is detected that the scanning position of the laser beam of the cyan laser beam scanning optical device 1C is shifted by one dot in the sub-scanning direction from the initial state, the bit map memory is used. The stored cyan image data is shifted upward by one dot, so that the cyan image printing start timing is advanced by one scanning line. In this way, it is possible to prevent a color shift due to a shift in the beam position of the laser beam in the sub-scanning direction, and to obtain a full-color image without a color shift.

(Other Embodiments) The laser beam scanning optical device according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention. In the above-described embodiment, an example of application to a full-color copying machine has been described. However, the application of the present invention is not limited to this, and is effectively applied to all cases where two or more toner images are sequentially overlaid and transferred on the same transfer material. Is done. In this case, the colors of the toner images need not necessarily be different.

Further, the moiré fringe generating means is not limited to a combination of two filters having a striped spatial grating. For example, a spatial grating may be formed on each of the reflection surfaces of two folding mirrors without using a filter. Pattern A, B
And Moire fringes can also be generated by combining these folding mirrors. Further, the spatial grating of the filter arranged on the light source side may be arranged so as to be parallel to the sub-scanning direction of the laser beam. Also, the spatial grid of the filter arranged on the light source side need not necessarily be parallel to the main scanning direction or parallel to the sub-scanning direction. Or in the sub-scanning direction. However, in this case, the amount of received light is slightly reduced.

[0032]

As is apparent from the above description, according to the present invention, the scanning position shift caused by the change of the surrounding environment and the like is replaced with the movement of the moire fringes, so that the amount of the scan position shift is enlarged, and the scanning position is increased. A laser beam scanning optical device capable of accurately detecting the displacement with simple processing is obtained.

The laser beam scanning optical device is incorporated as a printing means into a machine for sequentially superimposing and transferring two or more toner images on the same transfer material, for example, a full-color laser printer or a digital copying machine. The printing dot deviation at the time can be easily suppressed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a laser beam scanning optical device according to the present invention.

FIG. 2 is an exploded perspective view of a scanning position detector.

FIG. 3 is an explanatory diagram showing a relationship between moiré fringes and a light receiving surface of a light receiving element.

FIG. 4 is an electric circuit diagram showing a scanning position shift detection control unit.

FIG. 5 is a timing chart of a scanning position shift detection control unit in an initial state.

FIG. 6 is a timing chart of a scanning position shift detection control unit in a state where the scanning position is shifted.

FIG. 7 is a timing chart of a scanning position shift detection control unit in a state where the scanning position is shifted.

FIG. 8 is a perspective view showing a full-color copying machine provided with the laser beam scanning optical device shown in FIG.

[Explanation of symbols]

1 (1C, 1M, 1Y, 1Bk) laser beam scanning optical device 2 laser diode 6 polygon mirror 7 fθ lens 10 scanning position detector 11 grating filter (first filter) 12 grating filter ( 13, 14 ... cylindrical lens 15 ... photoelectric conversion element 101 (101C, 101M, 101Y, 101Bk)
... Photoreceptor drums A, B ... Spatial grid

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasushi Nagasaka 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Inventor Hiroshi Hiraguchi Azuchi-cho, Chuo-ku, Osaka-shi, Osaka 2-3-13 Osaka International Building Minolta Co., Ltd.

Claims (2)

[Claims] 1. A laser beam scanning optical system which focuses a laser beam emitted from a laser light source via a deflector and an optical element to a minute point and scans a surface to be scanned in a line at a substantially constant speed. In the apparatus, a moiré fringe generating means for disposing a moiré fringe pattern which is arranged near an optically equivalent position to a scanned surface and modulates a laser beam emitted from the laser light source to generate a moiré fringe pattern is generated. A laser beam comprising: a scanning position detecting unit configured to receive a moiré fringe pattern; and a scanning position deviation detecting unit that detects a scanning position deviation based on an output of the light receiving element. Scanning optics. 2. The method according to claim 1, wherein the moiré fringe generating means has a first spatial grating parallel to one of the main scanning direction and the sub-scanning direction of the laser beam in order from the laser light source side. And a second filter having a striped spatial grating inclined at a small angle with respect to the direction of the spatial grating of the first filter. The laser beam scanning optical device according to claim 1.