JPH1026731A - Light beam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely correct the fluctuation of an irradiation position in a subscanning direction by providing a light receiving surface whose width in a main scanning direction is changed in accordance with the position in the subscanning direction on a main scanning line and outputting a signal in accordance with the irradiation position in the subscanning direction on an image carrier with a light beam. SOLUTION: A triangle type photodetector 13 is constituted of a photodetector having a triangular light receiving surface 13A whose width in the main scanning direction is changed in accordance with the position on the subscanning direction, and its light receiving area is changed in accordance with the position of the passing light beam LB in the subscanning direction. Namely, when the light beam LB is used for scanning in the main scanning direction at positions P1 , P2 and P3 in the subscanning direction, the light beam LB is detected at the light receiving areas R1 , R2 and R3 . Thus, the position in the subscanning direction so detected by the photodetector 13 outputting a detection signal whose output time differs according to the position of the light beam in the subscanning direction. Therefore, the restriction of the position of the photodetector on the main scanning line is eliminated and the fluctuation of the scanning position is surely detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device for scanning a light beam in a main scanning direction of an image carrier, and more particularly, to easily and surely correct the fluctuation of the scanning position of the light beam in the sub-scanning direction. The present invention relates to a light beam scanning device with improved image quality.

[0002]

2. Description of the Related Art As a light beam scanning device applied to a digital copying machine, a laser printer, or the like, a light beam modulated in accordance with image information is reflected and deflected by an optical deflector, for example, a polygon mirror, and is used for a photosensitive member or the like. A device that scans a scanning surface to record image information is generally known.

By the way, in such a light beam scanning device, the scanning line of the light beam on the scanning surface is discretized at the period of the main scanning, so that the resolution in the sub-scanning direction is low and jaggies of oblique lines are caused. There is a problem in that the accuracy of drawing in the sub-scanning direction is reduced, such as the occurrence of fine lines and the reproducibility of fine lines.
For this reason, it has been difficult to provide high-accuracy character and line drawing images required in the printing and desktop publishing fields.

On the other hand, the resolution in the sub-scanning direction can be increased by rotating the polygon mirror at high speed to perform main scanning at high speed. However, high-speed rotation of the polygon mirror has a limitation in mechanical driving. It was difficult to achieve both high speed and high resolution.

Therefore, in order to solve such a problem,
A method of scanning a light beam zigzag has been proposed, for example, in Japanese Patent Application Laid-Open No. 3-131818.

In this light beam scanning method, when a light beam is scanned in a main scanning direction, the light beam is minutely moved in a sub-scanning direction (for example, by using a light beam deflecting element such as an acousto-optic element or an electro-optical element). The displacement is repeated by a distance equal to the sub-scanning pitch or １ ／ of the pitch. FIG. 12 shows the scanning trajectory of the light beam at this time,
A scanning locus of a zigzag light beam is formed on a main scanning line (N, N + 1,...) On the scanning surface.

In this light beam scanning method, when a light beam is scanned in the main scanning direction, the area between adjacent main scanning lines can also be scanned, so that the resolution in the sub scanning direction can be increased. The drawing accuracy in the direction can be improved.

However, when an acousto-optical element is used as the light beam deflecting element, the diffraction grating changes due to modulation frequency fluctuation. When an electro-optical element is used, the refractive index changes due to temperature. Is the wavelength fluctuation of the light source, the surface of the polygon mirror is changed over time, the rotation axis is tilted,
Since the relationship between the drive signal of the light beam deflecting element and the scanning position of the light beam is not always constant due to factors such as temporary disturbance, there is a problem that image quality is deteriorated. For example, the deflection angle of an acousto-optic device is proportional to the wavelength of a semiconductor laser, but a 780-nm wavelength GaAs semiconductor laser generally used in a printer has a wavelength drift of about 15% in a temperature range of about 0 to 60 ° C. Occur. For this reason,
The irradiation position of the light beam in the sub-scanning direction fluctuates with respect to the ambient temperature, and an image defect occurs.

On the other hand, as a conventional light beam scanning device for correcting a change in the irradiation position of the light beam in the sub-scanning direction, there is one disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 4-240814.

This light beam scanning device comprises a light source for emitting a light beam modulated based on an image signal, a polygon mirror for reflecting and deflecting the light beam, and an electrostatic device by exposing the reflected and deflected light beam to light. A photoconductor on which a latent image is formed, an irradiation position sensor that detects an irradiation position of the light beam in the sub-scanning direction on the main scanning line, and a light beam deflecting element that displaces the light beam in the sub-scanning direction, A control unit is provided for driving the light beam deflecting element so as to apply a displacement to the light beam according to the variation of the irradiation position of the light beam.

FIG. 13 shows an irradiation position sensor 1 used in this light beam scanning device. The irradiation position sensor 1 has light receiving surfaces 1A and 1B divided into upper and lower parts by a main scanning line of the light beam LB. The detection signal corresponding to the irradiation position in the direction is output.

The control unit includes a light receiving surface 1 of the irradiation position sensor 1.
A change in the irradiation position of the light beam in the sub-scanning direction is calculated by comparing the detection signals A and 1B, and the deflection angle of the light beam deflecting element is adjusted according to the comparison result to irradiate the light beam in the sub-scanning direction. Correct the position fluctuation.

[0013]

However, according to the conventional light beam scanning device, unless the divided area of the light receiving surface of the irradiation position sensor is attached near the center of the scanning beam, the irradiation position of the light beam in the sub-scanning direction is not determined. Fluctuations cannot be detected accurately. Generally, the beam diameter of the light beam in the sub-scanning direction is as small as 40 to 60 μm, which is equal to the scanning pitch. For this reason, there is a problem that high accuracy is required for mounting the sensor.

Accordingly, it is an object of the present invention to improve the image quality by easily and surely compensating for the fluctuation of the irradiation position of the light beam on the image carrier in the sub-scanning direction. It is to provide.

[0015]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention makes it easy to set the light beam in the sub-scanning direction on the image carrier, and
A displacement signal generating means for generating a displacement signal for displacing the light beam in the sub-scanning direction, and a light beam displacement for displacing the light beam in the sub-scanning direction according to the displacement signal in order to improve the image quality by reliably correcting the light beam. And a light receiving surface that is arranged on the main scanning line of the light beam and has a width in the main scanning direction that changes in accordance with the position in the sub scanning direction, and performs detection in accordance with the irradiation position of the light beam in the sub scanning direction. An object of the present invention is to provide a light beam scanning apparatus comprising: a light beam irradiation position detecting means for outputting a signal; and a control means for outputting a calibration signal for calibrating a displacement signal to the displacement signal generating means in accordance with the detection signal.

The light beam irradiation position detecting means may be a triangular photodetector having a triangular light receiving surface whose width in the main scanning direction changes in accordance with the position in the sub-scanning direction, or a triangular photodetector in accordance with the position in the sub-scanning direction. It is preferable that the light receiving surface whose width in the scanning direction changes is a trapezoidal trapezoidal photodetector. The triangular photodetector or trapezoidal photodetector is preferably configured by applying a triangular mask to a square light receiving surface.

Further, the light beam irradiation position detecting means includes:
It is preferable that the photodetector is constituted by a rectangular photodetector having a rectangular light receiving surface and having one side arranged at a predetermined angle with respect to the main scanning line of the light beam.

The light beam displacing means comprises an acousto-optic element for displacing the light beam in accordance with the frequency of the drive signal, and the displacement signal generating means generates a displacement signal having a frequency corresponding to the displacement of the light beam. It is preferable that the configuration be generated. Preferably, the displacement signal generating means generates a displacement signal whose frequency changes in a sawtooth manner during an image forming cycle.

The light beam displacing means comprises an electro-optical element for displacing the light beam in accordance with the voltage of the drive signal, and the displacement signal generating means generates a displacement signal of a voltage corresponding to the displacement of the light beam. It is preferable that the configuration is such that: Preferably, the displacement signal generating means generates a displacement signal in which the voltage changes in a sawtooth manner during an image forming cycle.

Before the image forming cycle, the control means
By outputting a predetermined displacement signal from the displacement signal generating means to the light beam displacing means, displacing the light beam in the sub-scanning direction, and causing the light beam irradiation position detecting means to detect the irradiation position of the light beam on the image carrier. Preferably, a predetermined displacement signal and a displacement amount of the light beam in the sub-scanning direction are calculated, and a calibration signal is output to the displacement signal generating means based on the result.

Further, it is preferable that the light beam scanning device is provided with a stabilizing means for stabilizing an output value of a detection signal outputted from the light beam irradiation position detecting means. The stabilizing means includes an integrating circuit for integrating a detection signal output from the light beam irradiation position detecting means, and a reset circuit for discharging the electric charge stored in the integrating circuit. It is preferable that the reset circuit discharge the electric charge every time the scanning is completed.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a light beam scanning device according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a light beam scanning device according to a first embodiment of the present invention. This light beam scanning device includes a semiconductor laser 2 that emits a light beam modulated according to image data, a collimator lens 3 that converts a diffused light beam emitted from the semiconductor laser 2 into a parallel beam, and a collimator lens 3. An acousto-optic element 4 for displacing the passed parallel beam in the sub-scanning direction, a cylindrical lens 5 for converging the parallel beam passing through the acousto-optic element 4 in the sub-scanning direction, and a light beam passing through the cylindrical lens 5 in a predetermined direction. A reflecting mirror 6 for reflecting light to the polygon mirror 7, a polygon mirror 7 for reflecting and deflecting the light beam reflected from the reflecting mirror 6,
An fθ lens 8 for converging the deflection beam reflected and deflected by the polygon mirror 7 in the main scanning direction to scan a predetermined main scanning line at a constant speed, and converging the deflection beam of the polygon mirror 7 in the sub-scanning direction to a predetermined direction. A cylindrical lens 9 for focusing on the main scanning line, a photosensitive drum 10 on which an electrostatic latent image is formed by scanning with a light beam, and a non-image forming of the photosensitive drum 10 which is disposed in front of the photosensitive drum 10 A reflection mirror 11 for reflecting a light beam for scanning an area in a predetermined direction; and a reflection mirror 11 disposed at a position optically equivalent to a predetermined main scanning line, receiving the light beam reflected by the reflection mirror 11 and generating a scanning start signal. The scanning start photodetector 12 to be output is disposed at a position optically equivalent to a predetermined main scanning line, and receives a light beam reflected by the reflection mirror 11 to perform beam position detection. Triangular photodetector 13 which outputs a signal
And a predetermined control signal from the CPU 16 described later,
An image recording control unit 15 that receives the 16-bit image data from an external host or the like and controls the semiconductor laser 2 and the acousto-optic device 4, and outputs a beam position detection signal output from the triangular photodetector 13. A stabilization circuit 15 for stabilizing a value, an image recording control unit 11 based on a beam position detection signal output from the stabilization circuit 15 and a scanning start signal output from the scanning start photodetector 12, and various devices. Is configured to include a CPU 16 for controlling

FIG. 2 shows a triangular photodetector 13. The triangular photodetector 13 is constituted by a photodiode having a triangular light receiving surface 13A whose width in the main scanning direction changes according to the position in the sub-scanning direction.
The light receiving area changes according to the position in the sub-scanning direction. That is, for example, when the light beam LB is scanned in the main scanning direction at the positions P ₁ , P ₂ , and P ₃ in the sub-scanning direction, the light beam LB is received in the light receiving regions R ₁ , R ₂ , and R ₃ .
B are respectively detected.

FIG. 3 shows beam position detection signals at positions P ₁ , P ₂ and P ₃ in the sub-scanning direction of the light beam LB output from the triangular photodetector. Based on the current ip, the light receiving areas R ₁ , R ₂ , R
Each is output for a time corresponding to ₃ .

FIG. 4 shows the image recording control unit 14. The image recording control unit 14 receives the main scanning synchronization signal Line Sync and the sweep range setting signals Vh and Vl from the CPU 16 during the image forming process, and outputs a pixel clock P-CLK for accessing image data and a quadruple thereof. And a D / A converter 18 for D / A converting a displacement signal output from the CPU 16 in the inspection mode before the image forming cycle.
Is switched by a control signal output from the CPU 16 so that the sweep signal output from the sweep signal control unit 17 is passed during the image forming cycle, and the D / A is output during the inspection mode.
An analog switch 19 for passing the displacement signal output from the converter 18 and a synchronization signal Line S for main scanning;
Each time yn is input, 16-bit image data corresponding to each pixel is input in synchronization with the pixel clock P-CLK in order from the top pixel of each line, and the pixel clock P-CLK is input.
A laser control unit 20 that outputs a laser modulation signal according to an image pattern by performing parallel / serial conversion of image data in order from the most significant bit based on a dot clock D-CLK having a frequency 16 times higher than that of the laser modulation signal. Drive circuit 21 for driving semiconductor laser 2 based on
And an acousto-optic element drive circuit 22 that outputs a drive signal frequency-modulated in accordance with the voltage of the sweep signal and the displacement signal to drive the acousto-optic element 4.

FIG. 5 shows the sweep signal control unit 17. The sweep signal control unit 17 performs D / A conversion on the sweep range setting signals Vh and Vl output from the CPU 16.
The clocks output from the converters 23A and 23B and the high frequency oscillation circuit 24 are used as the main scanning synchronization signal Line Sy.
frequency divider circuit 25 that divides the frequency in synchronization with nc to generate a pixel clock P-CLK and a sweep clock S-CLK having a cycle that is four times that of the pixel clock P-CLK, and a D / A with a cycle of the sweep clock S-CLK.
It has a sweep signal generation unit 26 that generates a sawtooth sweep signal with the sweep range setting signals Vh and Vl output from the converters 23A and 23B as the maximum voltage value and the minimum voltage value.

FIG. 6 shows the scanning trajectory of the light beam during the image forming process. When the sweep signal is output from the sweep signal control unit 17, the irradiation position (spot position) of the light beam on the photosensitive drum 10 is displaced in the sub-scanning direction during scanning of the light beam in the main scanning direction, and one pixel is scanned. The scanning lines of the light beam on the photosensitive drum 10 are parallel inclined straight lines AB, CD, E- having a predetermined angle with respect to the main scanning direction.
F, GH, and vertical lines BC, D- extending in the sub-scanning direction.
E, FG, and HA are alternately repeated to form a sawtooth locus.

FIG. 7 shows the stabilizing circuit 15. Stabilization circuit 15 is adapted to integrate the current i _p based on the beam position detection signal output from the triangular-type optical detector 13, an integration circuit 27 for storing the charge for a predetermined time, the integrating circuit 2
, A reset circuit 28 for discharging the electric charge stored in the memory 7 at a predetermined timing, a data bus 30, and a control bus 31.
A / D which is connected to the CPU 16 through the A / D converter and A / D converts the voltage output _Vf based on the electric charge stored in the integration circuit 27
It has a converter 29.

The integration circuit 27 is constituted by a capacitance C _f has a capacitor 32 for feedback of the operational amplifier 33 the output signal to generate a voltage equal output V _f to the integration time of the sum of weighted input signal Have been. Integrated voltage V _f output from the operational amplifier 33 is given by the current i _p.

(Equation 1) Therefore, the operational amplifier 33 detects that the light beam is a triangular photodetector 1
After passing through 3, the value of _Vf is maintained.

The reset circuit 28 is inserted between the input side of the operational amplifier 27 and the ground, and receives a control signal from an I / O port 35 connected to the CPU 16 via the data bus 30 and the control bus 31 to open and close. Switch 34
It is composed of

The CPU 16 executes a test mode control program when the power switch is turned on or before an image forming cycle such as between print jobs. That is, as shown in FIG. 4, a control signal is output to the analog switch 19 so that the D / A converter 18 and the acousto-optical element driving circuit 22 are connected.
Switch. Then, the polygon mirror 7 is driven,
When the steady rotation is reached, a predetermined control signal is output to the laser control unit 20 to cause the semiconductor laser 2 to emit a test light beam, thereby causing the light beam to scan in the main scanning direction. At the same time, a displacement signal of a predetermined voltage is output to the D / A converter 18, and the acousto-optical element driving circuit 22 outputs a driving signal of a predetermined frequency to the acousto-optical element 4.
The acousto-optic element 4 is displaced in the sub-scanning direction of the test light beam. At this time, the irradiation position of the light beam on the photosensitive drum 10 in the sub-scanning direction is determined by the triangular photodetector 13.
The beam position detection signal output from the triangular photodetector 13 is input through the integration circuit 27. next,
Scan the light beam in the main scanning direction again according to the procedure described above,
At this time, a displacement signal having a voltage different from that at the time of the previous scanning of the light beam in the main scanning direction is output to the D / A converter 18, and the acousto-optic device driving circuit 22 sends the acousto-optic device 4 a predetermined frequency. The drive signal is output and the acousto-optic element 4
In this case, the inspection light beam is displaced in the sub-scanning direction. Then, the irradiation position of the light beam on the photosensitive drum 10 in the sub-scanning direction at this time is detected by the triangular photodetector 13, and the beam position detection signal output from the triangular photodetector 13 is integrated by the integration circuit 27. To enter through. In this manner, scanning of the light beam in the circumferential scanning direction is performed a plurality of times, and the voltage of the displacement signal is changed for each main scan, and the irradiation position of the light beam on the photosensitive drum 10 in the sub-scanning direction at this time. Is detected. Then, based on these detection results, the relationship between the voltage value of the displacement signal and the position of the light beam in the sub-scanning direction as shown in FIG. 8 is calculated. Voltage value V of the sweep range in the amount
h and the minimum voltage value Vl are calculated and output to the sweep signal control unit 17 as Vh and Vl as sweep range setting signals. On the other hand, in the image forming cycle, a control signal is output to the analog switch 19, and the analog switch 19 is switched so that the sweep signal control unit 17 and the acousto-optic element driving circuit 22 are connected. When a scan start signal is input from the scan start photodetector 11, a main scan synchronization signal Line Sync is output to the sweep signal control unit 17 and the laser control unit 20, and normal image formation control is performed. ing.

The operation of the light beam scanning device according to the present invention will be described below with reference to FIGS. 9 and 10.

When the power switch is turned on, the CPU 16
Executes the control program in the inspection mode. That is, CP
U16 outputs a control signal to the analog switch 19,
The analog switch 19 is switched so that the D / A converter 18 and the acousto-optical element drive circuit 22 are connected. Then, the polygon mirror 7 is driven, and when the rotation reaches a steady state, a predetermined control signal is output to the laser control unit 20 to cause the semiconductor laser 2 to emit a test light beam.

The light beam emitted from the semiconductor laser 2 is reflected and deflected by a polygon mirror 7 through a collimator lens 3, an acousto-optic device 4, a cylindrical lens 5, and a reflection mirror 6, and thereafter, is fθ lens 8 and a cylindrical lens Through 9, the main scanning line on the photosensitive drum 10 is scanned. At the same time, a displacement signal of a predetermined voltage is output from the CPU 16 to the D / A converter 18, and a driving signal of a predetermined frequency is output from the acousto-optic device driving circuit 22 to the acousto-optic device 4, and the acousto-optic device 4 The beam is displaced in the sub-scanning direction.

At this time, a light beam is incident on the triangular photodetector 13 via the reflection mirror 11, and the triangular photodetector 13
From the photosensitive drum 10 of the light beam in the sub-scanning direction output time corresponding to the irradiation position of the current i _p (in to FIG. 9 (a)) is outputted to the integration circuit 27 as a beam position detection signal. Integration circuit 27 integrates the current i _p based on the beam position detection signal, the output values to stabilize. The integrated voltage V _f ((b) in FIG. 9) integrated by the integration circuit 27 is converted from the value at time t ₁ by the A / D converter 29 to the CPU 1.
Read at 6.

The CPU 16 outputs a control signal to the reset circuit 28 via the I / O port 35 at time t ₂ , and closes the switch 34 to bring the electric charge accumulated in the capacitor 32 of the integration circuit 27 to ground. Let go. Thus, the integrated voltage V output from the integrating circuit 27
_f becomes 0V. At time t ₃ , the CPU 16 outputs a control signal to the reset circuit 28 via the I / O port 35, and opens the switch 34.

When the irradiation position of the light beam in the sub-scanning direction on the photosensitive drum 10 is detected by scanning the light beam in the main scanning direction in this manner, the scanning of the light beam in the main scanning direction is again performed in the previous main scanning direction. Scanning is performed in the same manner as in the scanning direction, and the triangular photodetector 13 detects the irradiation position of the light beam on the photosensitive drum 10 in the sub-scanning direction at this time. At that time, a displacement signal having a displacement amount different from that at the time of the previous scan in the main scanning direction is output to the D / A converter 18 of the image recording control unit 14, and the signal is transmitted from the acousto-optic device drive circuit 22 to the acousto-optic device 4. A drive signal having a predetermined frequency is output to cause the acousto-optic element 4 to perform displacement of the light beam in the sub-scanning direction. The beam position detection signal output from the triangular photodetector 13 is integrated by the integration circuit 27 in the same manner as in the previous scanning in the main scanning direction, and then read by the CPU 16.

In this manner, the scanning of the light beam in the main scanning direction is performed a plurality of times, and the voltage of the displacement signal is changed for each main scanning. The irradiation position of is detected. When the predetermined number of samplings are completed, the CPU 16 calculates the relationship between the voltage value of the displacement signal and the position of the light beam in the sub-scanning direction as shown in FIG. The sweep range of the displacement signal in the displacement amount, that is, the maximum voltage value Vh and the minimum voltage value Vl are calculated.

Here, the value to be set as the amount of displacement for displacing the spot position of the light beam in the sub-scanning direction when the light beam is scanned in the main scanning direction during the image forming process is ± 20 μm, and the measurement result is a solid line. In the case of (Environment B), the maximum voltage value Vh of the modulation signal is 0.4 V and the minimum voltage value is 1.7 V.

The CPU 16 determines the maximum voltage value Vh of the modulation signal,
Once the minimum voltage value Vl has been calculated, it is
The sweep signal controller 1 of the image recording controller 14 as h and Vl
7 is output. The voltage setting signals Vh and Vl input to the sweep signal control unit 17 are D / A converted by the D / A converters 23A and 23B and are kept constant until they are set again.

Next, when the CPU 16 receives an image forming command, it executes an image forming mode program. First, C
PU 16 is an analog switch 19 of the image recording control unit 14.
And switches the analog switch 19 so that the sweep signal control unit 17 and the acousto-optic element drive circuit 22 are connected. Next, the polygon mirror 7 is driven, and when it reaches a steady rotation, a predetermined drive signal is output to the laser control unit 20 of the image recording unit 14 so that the semiconductor laser 2
To emit a light beam.

When the light beam emitted from the semiconductor laser 2 is reflected and deflected by the polygon mirror 7 and the scanning start photodetector 11 detects the light beam, the scanning start signal is sent to the CP.
Output to U16. The CPU 16 sends the main scanning synchronization signal Line Sync to the sweep signal control unit 17 of the image recording control unit 15 and the laser control unit 2 based on the input of the scan start signal.
Output to 0.

The sweep signal controller 17 of the image recording controller 14
, The frequency dividing circuit 25 outputs the main scanning synchronization signal Line
When Sync is input, the main scanning synchronization signal Line S
The pixel clock P-CLK synchronized with the sync signal is output to the laser control unit 20, and the pixel clock P-CLK and the sweep clock S-CLK having a cycle four times as long as the pixel clock P-CLK are output to the sweep signal generation unit 26. The sweep signal generation unit 26 outputs to the acousto-optical element drive circuit 22 a sawtooth sweep signal in which the voltage setting signals Vh and Vl stored in the memory at maximum and minimum values are stored in the memory with the cycle of the sweep clock S-CLK. .

The laser control unit 20 outputs the main scanning synchronization signal Li
Each time ne Sync is input, 16-bit image data corresponding to each pixel is sequentially input in synchronization with the pixel clock P-CLK from the top pixel of each line. Then, based on a dot clock D-CLK having a frequency 16 times as high as the pixel clock P-CLK, the image data is parallel / serial converted in order from the most significant bit to generate a laser modulation signal corresponding to the image pattern, Output to the drive circuit 21.

The laser drive circuit 21 makes the semiconductor laser 2 emit a light beam based on the laser modulation signal. The light beam emitted from the semiconductor laser 2 is reflected and deflected by a polygon mirror 7 through a collimating lens 3, an acousto-optic element 4, a cylindrical lens 5, and a reflecting mirror 6, and is passed through an fθ lens 8 and a cylindrical lens 9 to a photoconductor. The main scanning line on the drum 10 is scanned.

On the other hand, the acousto-optic device drive circuit 22 outputs a drive signal having a carrier frequency corresponding to the sawtooth sweep signal to the acousto-optic device 4, and displaces the light beam passing through the acousto-optic device 4 in the sub-scanning direction. .

When the light beam is displaced in the sub-scanning direction in accordance with the light beam sawtooth sweep signal during scanning in the main scanning direction, each vertical line B- of the scanning lines in FIG.
Since the C, DE, FG, and HA portions are instantaneously scanned, the photosensitive drum 10 is not exposed and each of the inclined straight lines AB, CD, EF,
An exposure image of a dot pattern corresponding to each of the 4 bits from the most significant bit of the 16-bit image data is formed on GH. At this time, since the displacement amount of the light beam in the sub-scanning direction is calibrated based on the detection result of the inspection mode,
The connection between the inclined straight lines of the N line and the (N + 1) th line is maintained, and it is possible to prevent the image quality from deteriorating. If the above-described inspection mode is executed between print jobs, the temperature around the device changes, and the displacement signal changes as shown by a broken line (environment A) or a dotted line (environment C) shown in FIG. Even if the relationship between the position and the position of the light beam in the sub-scanning direction changes, the sweep range of the displacement signal with respect to the sub-scanning displacement to be set can be obtained.

As described above, in the present embodiment, the light receiving surface 13A whose width in the main scanning direction changes according to the position in the sub scanning direction.
Since the triangular photodetector 13 outputs detection signals having different output times according to the position of the light beam in the sub-scanning direction, the position of the light beam in the sub-scanning direction is detected. There is no restriction on the position of the photodetector with respect to the main scanning line of the beam, and a change in the scanning position of the light beam in the sub-scanning direction can be detected easily and reliably. Usually, the photodiode has a side length of about 1 mm to several mm, so the accuracy of the mounting position of the photodetector can be very loose for the scanning line traversed by a beam of several tens of microns. it can.

In the above embodiment, the position of the light beam in the sub-scanning direction is detected by the triangular photodetector 13, but may be detected by a trapezoidal photodetector having a trapezoidal light-receiving surface. Further, as shown in FIGS. 11A and 11B, these photodetectors have a triangular mask 37 on the light receiving surface 36A of the rectangular photodetector 36.
May be applied. Further, FIG.
As shown in (c), the rectangular photodetector 36 has a predetermined angle with the main scanning line of the light beam, and is arranged so that the light beam passage area is effectively in the range of the triangle. It may be detected. Further, the light beam may be displaced in the sub-scanning direction using an electro-optic element instead of the acousto-optic element 4.

[0051]

As described above, according to the light beam scanning device of the present invention, a light receiving surface whose width in the main scanning direction changes on the main scanning line of the light beam in accordance with the position in the sub scanning direction is provided. Light beam irradiation position detecting means for outputting a detection signal corresponding to the irradiation position of the light beam on the image carrier in the sub-scanning direction is provided, so that the irradiation position of the light beam on the image carrier in the sub-scanning direction can be easily changed. In addition, the correction can be reliably performed, and as a result, the image quality can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a triangular photodetector according to the first embodiment.

FIG. 3 is an explanatory diagram showing a beam position detection signal according to the first embodiment.

FIG. 4 is an explanatory diagram illustrating an image recording control unit according to the first embodiment.

FIG. 5 is an explanatory diagram illustrating a sweep signal control unit according to the first embodiment.

FIG. 6 is an explanatory diagram illustrating a scanning locus of a light beam during an image forming process according to the first embodiment.

FIG. 7 is an explanatory diagram showing a stabilizing circuit according to the first embodiment.

FIG. 8 is a graph showing the relationship between the displacement signal and the position of the light beam in the sub-scanning direction in the first embodiment.

FIG. 9 is an explanatory diagram showing waveforms of a beam position detection signal before and after input of the integration circuit according to the first embodiment.

FIG. 10 is a timing chart illustrating an operation during an image forming process according to the first embodiment.

FIG. 11 is an explanatory view showing another embodiment of the present invention.

FIG. 12 is an explanatory diagram showing a light beam scanning method having a high resolution in the sub-scanning direction.

FIG. 13 is an explanatory view showing a conventional light beam scanning device.

[Description of Signs] 1 Irradiation position sensor 1A, 1B Light receiving surface 2 Semiconductor laser 3 Collimator lens 4 Acousto-optic element 5 Cylindrical lens 6 Reflection mirror 7 Polygon mirror 8 fθ lens 9 Cylindrical lens 10 Photoconductor drum 11 Reflection mirror 12 Scanning start Photodetector 13 Triangular photodetector 13A Light receiving surface 14 Image recording control unit 15 Stabilization circuit 16 CPU 17 Sweep signal control unit 18 D / A converter 19 Analog switch 20 Laser control unit 21 Laser drive circuit 22 Acousto-optic element drive circuit 23A, 23B D / A converter 24 High frequency oscillation circuit 25 Divider circuit 26 Sweep signal generator 27 Integration circuit 28 Reset circuit 29 A / D converter 30 Data bus 31 Control bus 32 Capacitor 33 Operational amplifier 34 Switch 35 I / O Port 36 Rectangular photodetector 36A Light receiving surface 37 Mask

Claims (23)

[Claims] 1. An image carrier that moves at a predetermined speed in a sub-scanning direction is scanned in a main scanning direction with a light beam modulated by an image signal via an optical system including a polygon mirror, and the image carrier is statically moved on the image carrier. In a light beam scanning device for forming an electrostatic latent image, a displacement signal generating means for generating a displacement signal for displacing the light beam in the sub-scanning direction, and a light for displacing the light beam in the sub-scanning direction in response to the displacement signal A beam displacing unit, having a light receiving surface that is arranged on the main scanning line of the light beam and has a width in the main scanning direction that changes in accordance with a position in the sub scanning direction, and an irradiation position of the light beam in the sub scanning direction Light beam irradiation position detecting means for outputting a detection signal according to the following, and control means for outputting a calibration signal for calibrating the displacement signal to the displacement signal generating means according to the detection signal. Light beam scanning device. 2. The light beam irradiation position detecting means is constituted by a triangular photodetector having a triangular light receiving surface whose width in the main scanning direction changes in accordance with a position in the sub-scanning direction. Light beam scanning device. 3. The trapezoidal photodetector having a trapezoidal light-receiving surface whose width in the main scanning direction changes according to the position in the sub-scanning direction. Light beam scanning device. 4. The light beam scanning device according to claim 2, wherein the triangular photodetector is configured by applying a triangular mask to a square light receiving surface. 5. The light beam scanning device according to claim 3, wherein the trapezoidal photodetector is configured by applying a triangular mask to a square light receiving surface. 6. The light beam irradiation position detecting means includes a rectangular light detector having a rectangular light receiving surface, one side of which is arranged at a predetermined angle with respect to a main scanning line of the light beam. The light beam scanning device according to claim 1. 7. The light beam displacing means is constituted by an acousto-optical element for displacing the light beam in accordance with the frequency of a drive signal, and the displacement signal generating means is provided with a frequency having a frequency corresponding to the displacement amount of the light beam. 2. The light beam scanning device according to claim 1, wherein the light beam scanning device is configured to generate the displacement signal. 8. The light beam scanning device according to claim 7, wherein said displacement signal generating means generates said displacement signal in which said frequency changes in a sawtooth manner during an image forming cycle. 9. The light beam displacing means is constituted by an electro-optical element for displacing the light beam according to a voltage of a drive signal, and the displacement signal generating means is configured to generate a voltage corresponding to a displacement amount of the light beam. 2. The light beam scanning device according to claim 1, wherein the light beam scanning device is configured to generate the displacement signal. 10. The light beam scanning device according to claim 9, wherein said displacement signal generating means generates said displacement signal in which said voltage changes in a sawtooth manner during an image forming cycle. 11. The control unit outputs a predetermined displacement signal from the displacement signal generation unit to the light beam displacement unit before the image forming cycle to displace the light beam in the sub-scanning direction. The beam irradiation position detection means detects the irradiation position of the light beam on the image carrier, calculates the predetermined displacement signal and the amount of displacement of the light beam in the sub-scanning direction, and based on the result, the displacement signal 2. The light beam scanning device according to claim 1, wherein the calibration signal is output to a generation unit. 12. An image carrier that moves at a predetermined speed in a sub-scanning direction is scanned in a main scanning direction with a light beam modulated by an image signal via an optical system including a polygon mirror, and is statically moved on the image carrier. In a light beam scanning device for forming an electrostatic latent image, a displacement signal generating means for generating a displacement signal for displacing the light beam in the sub-scanning direction, and a light for displacing the light beam in the sub-scanning direction in response to the displacement signal A beam displacing unit, having a light receiving surface that is arranged on the main scanning line of the light beam and has a width in the main scanning direction that changes in accordance with a position in the sub scanning direction, and an irradiation position of the light beam in the sub scanning direction A light beam irradiation position detecting means for outputting a detection signal according to the following; a stabilizing means for stabilizing an output value of the detection signal outputted from the light beam irradiating position detecting means; Light beam scanning apparatus characterized by comprising a control means for outputting a calibration signal for calibrating the displacement signal in accordance with a stability detection signal to said displacement signal generating means. 13. The light beam irradiation position detecting means is constituted by a triangular photodetector having a triangular light receiving surface whose width in the main scanning direction changes according to a position in the sub-scanning direction. Light beam scanning device. 14. The trapezoidal photodetector having a trapezoidal light-receiving surface whose width in the main scanning direction changes in accordance with a position in the sub-scanning direction. Light beam scanning device. 15. The light beam scanning device according to claim 13, wherein the triangular photodetector is configured by applying a triangular mask to a square light receiving surface. 16. The light beam scanning device according to claim 14, wherein the trapezoidal photodetector is configured by applying a triangular mask to a square light receiving surface. 17. The light beam irradiation position detecting means is constituted by a rectangular photodetector having a rectangular light receiving surface, one side of which is arranged at a predetermined angle with respect to the main scanning line of the light beam. The light beam scanning device according to claim 12. 18. The stabilizing means includes an integrating circuit for integrating the detection signal output from the light beam irradiation position detecting means, and a reset circuit for discharging electric charges stored in the integrating circuit. 13. The control unit causes the reset circuit to discharge the charge each time one main scan of the light beam is completed.
The light beam scanning device according to claim 1. 19. The light beam displacing means is constituted by an acousto-optic element for displacing the light beam in accordance with the frequency of a drive signal, and the displacement signal generating means is provided with a frequency signal corresponding to the displacement amount of the light beam. 13. The light beam scanning device according to claim 12, wherein the displacement signal is generated. 20. The light beam scanning device according to claim 18, wherein said displacement signal generating means generates said displacement signal in which said frequency changes in a sawtooth manner during an image forming cycle. 21. The light beam displacing means is constituted by an electro-optical element for displacing the light beam according to a voltage of a drive signal, and the displacement signal generating means is configured to generate a voltage corresponding to a displacement amount of the light beam. 13. The light beam scanning device according to claim 12, wherein the displacement signal is generated. 22. The light beam scanning apparatus according to claim 20, wherein said displacement signal generating means generates said displacement signal in which said voltage changes in a sawtooth manner during an image forming cycle. 23. The control unit outputs a predetermined displacement signal from the displacement signal generating unit to the light beam displacing unit before the image forming cycle to displace the light beam in the sub-scanning direction. The beam irradiation position detection means detects the irradiation position of the light beam on the image carrier, calculates the predetermined displacement signal and the amount of displacement of the light beam in the sub-scanning direction, and based on the result, the displacement signal 13. The light beam scanning device according to claim 12, wherein the calibration signal is output to a generation unit.