JPH0998268A - Synchronizing signal generating circuit for optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a synchronizing signal of the optical scanner able to detect a synchronizing signal with high accuracy. SOLUTION: An optical scanner is made up of a light source section provided with a laser light source, a rotary polygon mirror, an fθ lens, a photosensing drum and a synchronizing signal generating circuit or the like. The synchronizing signal generating circuit is made up of a photo diode 6 and a signal processing circuit processing an output signal from the photo diode 6. Then a width L of an effective light receiving area of the photo diode 6 in the main scanning direction is selected to satisfy an equation of L<=2W, where W is a diameter of a laser beam 21 in the main scanning direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronizing signal generation circuit for an optical scanning device used for a laser beam printer or the like.

[0002]

2. Description of the Related Art In an optical scanning device used for a laser beam printer or the like, a laser beam emitted from a light source section having a laser diode is rotated by a polygon mirror.
Deflects and scans in a predetermined direction within a predetermined angle range, focuses the laser beam light thus deflected and scanned on a photosensitive surface of a photosensitive drum through an fθ lens, and thereby, a scanning beam that moves at a constant speed in the rotation axis direction of the photosensitive drum. It is configured to obtain light.

In a laser beam printer, a laser beam light is modulated in a light source section of an optical scanning device based on drawing data, and a photosensitive drum is rotated based on a timing of a scanning operation of the optical scanning device, so that the photosensitive drum is rotated. An electrostatic latent image corresponding to the drawing data is formed on the outer peripheral surface (light receiving surface), toner is adsorbed on the outer peripheral surface of the photosensitive drum in accordance with the electrostatic latent image, and the toner image is transferred (recorded) on recording paper. I do.

In such an optical scanning device of a laser beam printer, a synchronizing signal (horizontal synchronizing signal) _HSYNC is generated in order to know the scanning start position on the light receiving surface of the photosensitive drum, that is, the drawing start position of the recording paper. Detecting this, the drawing is started after a lapse of a fixed time from the synchronization signal _HSYNC .

The synchronizing signal H _SYNC is provided by setting a photodiode (light receiving element) at a position apart from the drawing start position in the main scanning direction outside the drawing area, and receiving a laser beam at the light receiving surface of the photodiode. Is generated and detected based on a signal output by photoelectrically converting the signal.

However, conventionally, there is no particular limitation on the relationship between the beam diameter of the laser beam and the size of the light receiving element, so that the synchronization signal H _SYNC may not be accurately detected.

For example, if the length of the light receiving surface of the light receiving element in the main scanning direction is longer than the beam diameter of the laser beam, the time during which the spot of the laser beam is included in the light receiving surface of the light receiving element becomes longer, Enables high-precision synchronization signal H
_SYNC is difficult to detect or sensitivity is significantly reduced,
As a result, the drawing start position is disturbed and the quality of drawing (printing) is degraded.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sync signal generation circuit for an optical scanning device capable of detecting a sync signal with high accuracy.

[0009]

This and other objects are achieved by the present invention which is defined below as (1) to (4).

(1) The scanning light beam is provided in an optical scanning device that deflects the light beam incident from a light source and emits it as scanning light beam that moves at a constant speed in a predetermined direction, and the scanning light beam reaches a predetermined position within the scanning region. And a signal processing circuit for generating a synchronization signal for specifying a scanning start position by the scanning beam light based on a signal from the light receiving element, and scanning the scanning beam. The width L of the effective light receiving region of the light receiving element in the direction and the diameter W of the scanning beam in the scanning direction of the scanning beam light are set so as to satisfy L ≦ 2W. Synchronous signal generation circuit of scanning device.

(2) The scanning light beam is provided in an optical scanning device that deflects the light beam incident from the light source and emits it as scanning light beam that moves at a constant speed in a predetermined direction, and the scanning light beam reaches a predetermined position within the scanning region. And a signal processing circuit for generating a synchronization signal for specifying a scanning start position by the scanning beam light based on a signal from the light receiving element, and scanning the scanning beam. The width L of the effective light receiving area of the light receiving element in the direction and the diameter W of the scanning beam in the scanning direction of the scanning beam light are set so as to satisfy L ≦ W. Synchronous signal generation circuit of scanning device.

(3) The signal processing circuit generates the synchronization signal by detecting a peak point of the signal from the light receiving element, and the synchronization signal generation of the optical scanning device according to (1) or (2). circuit.

(4) The detection of the peak point is performed by detecting a zero-cross point of the differential value of the signal based on the signal from the light receiving element, and the synchronization signal of the optical scanning device according to the above (3). Generation circuit.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a synchronizing signal generating circuit of an optical scanning device according to the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings.

FIG. 1 is a plan view showing an embodiment in which a synchronizing signal generating circuit of an optical scanning device of the present invention is applied to a synchronizing signal generating circuit of an optical scanning device of a laser beam printer.
FIG. 6 is a circuit diagram showing a circuit configuration example of a synchronization signal generation circuit of the optical scanning device of the present invention.

As shown in these figures, an optical scanning device (laser scanning unit) 1 includes a light source section 2 and a rotary polygon mirror 5 for reflecting a laser beam 21 from the light source section 2.
And a motor (not shown) for rotating the rotating polygon mirror 5, and fθ
It has a lens 7, a photosensitive drum 8, and a synchronization signal generation circuit 10 including a photodiode 6 which is a light receiving element (photoelectric conversion element) and a signal processing circuit 9.

The light source unit 2 comprises a laser light source 3 composed of a semiconductor laser and a front optical system 4 comprising a collimating lens and a condenser lens provided on the light emitting side of the laser light source 3. The laser beam 21 from the unit 2 is focused on the reflecting surface 51 of the rotary polygon mirror 5.
The timing of turning on / off the laser light source 3 is controlled by the control means 15 including a microcomputer.

The rotary polygon mirror (polygon mirror) 5 has a regular polygonal shape and is rotated at a constant speed by a motor (not shown). The illustrated rotating polygon mirror 5 has six reflecting surfaces 51 formed on the outer periphery thereof, each reflecting surface 51 is a flat surface, and the adjacent reflecting surfaces 51 are equiangular (1).
20 °). Each reflection surface 51 is formed of, for example, an aluminum vapor deposition layer.

As shown in FIG. 1, the laser beam 21 from the light source unit 2 is reflected by the reflecting surface 51 of the rotary polygon mirror 5. At this time, the laser beam 21 of the rotary polygon mirror 5 rotates as the rotary polygon mirror 5 rotates. The incident point on the reflecting surface 51 moves from one corner portion 52 to the other corner portion 52 via the central portion of the reflecting surface 51, and the reflection direction of the reflected light can be changed within a predetermined angle range. Hereinafter, the angle range of the reflected light is referred to as a deflection angle. In the configuration shown, the rotary polygon mirror 5 is rotated counterclockwise in FIG. 1 at a constant speed by a motor. The rotation control of the motor is performed by the control unit 15.

The fθ lens 7 is installed in a range that covers the deflection angle. Since the direction of the laser beam 21 reflected by the rotary polygon mirror 5 changes at a constant angular velocity, the laser beam 21 is corrected by the fθ lens 7 to have a constant speed on a light receiving surface 81 described later. Also, this fθ lens 7
As a result, the tilt of each reflecting surface 51 of the rotary polygon mirror 5 is also corrected.

Laser beam 21 passing through the fθ lens 7
Is focused on a light receiving surface (imaging surface) 81 formed on the outer peripheral surface of the photosensitive drum 8. When the rotary polygon mirror 5 rotates by 60 °, the laser beam 21 is swung once within the range of the swing angle,
One direction of the rotation axis 82 of the photosensitive drum 8 is
Scan twice (main scan).

Sub-scanning is performed by rotating the photosensitive drum 8 in a predetermined direction, for example. Each time the rotary polygon mirror 5 is rotated by 60 °, that is, each time the main scanning is performed on the light receiving surface 81, the photosensitive drum 8 is rotated by one dot, and the main scanning in the next row is performed. Therefore, when the rotary polygon mirror 5 makes one rotation, main scanning is performed six times, that is, scanning corresponding to drawing of six dots in the sub-scanning direction is performed.

The rotation of the photosensitive drum 8 is performed by the driving means 16 including a motor, a transmission gear and the like. The driving unit 16 controls the rotation amount and the rotation timing of the photosensitive drum 8 by the control unit 15.

By performing the main scanning and the sub scanning as described above, an electrostatic latent image corresponding to the irradiation point (dot) of the laser beam 21 is formed on the outer peripheral surface of the photosensitive drum 8. Then, the toner supplied from the toner supply unit (not shown) to the outer peripheral surface of the photosensitive drum 8 is attracted corresponding to the electrostatic latent image, and the toner image is recorded on a recording paper (not shown).
The image is transferred onto the recording paper and fixed, whereby drawing on a recording sheet is performed.

A photodiode 6 is installed at a predetermined position on the main scanning line by the laser beam 21. As will be described later, a signal processing circuit 9 is connected to the photodiode 6, and the photodiode 6 and the signal processing circuit 9 constitute a synchronization signal generation circuit 10 of the present invention.

Here, on the light receiving surface 81 of the photosensitive drum 8, a scanning area in the main scanning, that is, a drawing area 11 on the recording paper is set, and one end thereof becomes a scanning start position, that is, a drawing start position 12, and this position is set. Then, the light modulation operation of the laser light source 3 is started based on the drawing data.
The other end is a scanning end position (drawing end position) 14.

When drawing on a recording sheet (not shown), it is necessary to specify the drawing start position 12 and make this position constant in the sub-scanning direction. Therefore, by irradiating the photodiode 6 with the laser beam 21, the signal obtained from the signal processing circuit 9 is used as a synchronization signal (horizontal synchronization signal) H _SYNC, and the position when a certain time has elapsed from this synchronization signal H _SYNC is drawn. The starting position is 12. That is, the synchronization signal generation circuit 10 is provided to obtain a synchronization signal H _SYNC for detecting the drawing start position 12.

Therefore, the photodiode 6 is installed on the optical path of the laser beam 21 and at the light receiving position 13 for synchronizing signal generation, which is separated from the drawing start position 12 by a predetermined distance S in the main scanning direction outside the drawing area 11. There is. Hereinafter, the synchronization signal generation circuit 10 will be described.

As shown in FIG. 2, a resistor (resistor) 31 is connected to the photodiode 6 as its load circuit, and the output side of the resistor 31, that is, the photodiode 6 and the resistor 31 is connected. The amplifier 32 is connected to the connection point.

A differential circuit 35 and a positive side input terminal of a comparator (comparator) 34 are connected in parallel to the output side of the amplifier 32. In this case, a reference voltage generator 33 having a variable reference voltage is connected to the negative input terminal of the comparator 34, and the reference voltage generator 33
Therefore, the reference voltage (threshold voltage) is applied. As shown in FIG. 4, the reference voltage is preset to a predetermined value that is sufficiently smaller than the maximum value (peak value) of the voltage after the signal from the photodiode 6 is amplified by the amplifier 32 and is sufficiently larger than the minimum value. Has been done.

The differentiating circuit 35 includes a capacitor 3
6, a resistor (resistor) 37 and a differential amplifier 38. In this case, the capacitor 36 is connected to the output side of the amplifier 32, and the negative side input terminal of the differential amplifier 38 is connected to the output side of the capacitor 36.
One end of the resistor 37 is connected between the capacitor 36 and the negative input terminal of the differential amplifier 38, and the other end of the resistor 37 is connected to the output side of the differential amplifier 38. The positive side input terminal of the differential amplifier 38 is grounded.

The negative side input terminal of a comparator 39 is connected to the output side of the differentiating circuit 35. The positive input terminal of the comparator 39 is grounded.

The output side of the comparator 39 is connected to one input terminal of an AND circuit (logical AND circuit) 40, and the output side of the comparator 34 is connected to the other input terminal of the AND circuit 40. .

The resistor 31, the amplifier 32, the differentiating circuit 35, the reference voltage generator 33, the comparators 34 and 3 as described above.
5 and the AND circuit 40 configure a signal processing circuit 9 that processes an output signal from the photodiode 6.

FIG. 3 is a schematic view showing the vicinity of the photodiode 6 in this embodiment. As shown in FIG. 3, the synchronization signal generating light receiving position 13 and its vicinity, that is,
In the light receiving surface of the photodiode 6 and its vicinity,
The relationship between the diameter (diameter) W of the laser beam 21 (spot 22) in the main scanning direction and the width L of the effective light receiving area of the photodiode 6 in the main scanning direction is set so that the maximum output from the photodiode 6 does not continue. It is set.

As a specific example, the laser beam 21
The diameter W in the main scanning direction and the width L in the main scanning direction of the effective light receiving area of the photodiode 6 are set so as to satisfy the following expression (1), particularly the following expression (2). L ≦ 2W (1) L ≦ W (2)

Here, the "diameter W" means the width in the main scanning direction of the point where the laser beam intensity is at the level of 1 / e ² when the peak (spot center) of the laser beam intensity is 1. .

The "effective light receiving area" means that the laser beam 21 is received and the received laser beam 2 is received.
1 means a region on the light receiving surface where 1 can be photoelectrically converted. The width of the effective light-receiving area of the photodiode 6 in the sub-scanning direction is set to be large enough to receive the laser beam 21.

As shown in FIG. 3, in this embodiment, L = W
3 is set to the effective light receiving area of the photodiode 6 from the time when the laser beam 21 is irradiated to the right end in FIG. 3 of the effective light receiving area of the photodiode 6 with the main scanning of the laser beam 21. The output from the photodiode 6 until the left end in FIG. 3 is irradiated is as shown in FIG.

FIG. 6 is a schematic diagram showing the vicinity of the photodiode 6 in the comparative example. As shown in FIG. 6, as a comparative example, the width L of the effective light receiving region of the photodiode 6 in the main scanning direction is set to L> 2W. In this case, the laser beam 21 in the effective light receiving area of the photodiode 6 shown in FIG.
The output from the photodiode 6 from when the laser beam 21 is emitted to the left end in FIG. 6 of the effective light receiving region of the photodiode 6 is shown in FIG.
It is as shown in.

As shown in these figures, the maximum output from the photodiode 6 is maintained by setting the width L of the effective light receiving area of the photodiode 6 in the main scanning direction so as to satisfy the above equation (1). Instead, a steep waveform 25 is obtained. That is, from the photodiode 6 to the peak point 43
An output signal capable of properly and reliably detecting is obtained. As will be described later, the peak point 43 (zero cross point 44)
Since consistent with the timing of the fall of the synchronizing signal H _SYNC, a synchronization signal H _SYNC, in particular, can be detected in the timing of fall of the synchronizing signal H _SYNC properly and securely.

On the other hand, when the above expression (1) is not satisfied, the time during which the spot 22 is included in the effective light receiving area of the photodiode 6 becomes long, the maximum output continues and the peak of the waveform 26 is maintained. Since the vicinity of the point 43 becomes a straight line, its peak point 43 (zero cross point 44)
Becomes difficult to detect.

Next, the operation of the synchronization signal generation circuit 10 will be described. FIG. 4 is a timing chart showing the operation of the synchronization signal generation circuit 10 of this embodiment, and FIG. 5 is a timing showing the relationship between the lighting timing of the laser light source 3 and the synchronization signal H _SYNC for detecting the drawing start position 12. Chart, Figure 7
FIG. 6 is a timing chart showing the operation of the synchronization signal generation circuit of the comparative example.

As shown in FIG. 5, the laser light source 3 is turned on for a predetermined time before and after the light receiving position 13 for generating the synchronization signal, and the auxiliary scanning by the laser beam 21 is performed. Thus, the laser beam 21 is received by the photodiode 6, as described later, and outputs the synchronizing signal H _SYNC from the signal processing circuit 9, the synchronization signal H _SYNC control unit 1
5 is input. The lighting timing of the laser light source 3 before and after the light receiving position 13 for generating the synchronization signal is determined, for example, based on the detection of a scan end position 14 described later in the previous main scan.

As shown in FIG. 4A, when the spot 22 of the laser beam 21 passes through the effective light receiving area of the photodiode 6, the photodiode 6 supplies a current having a magnitude corresponding to the amount of received light. (Voltage), that is, a signal is output.

The signal output from the photodiode 6 is input to the amplifier 32 and is amplified by the amplifier 32. The signal output from the amplifier 32 is output to the comparator 3
4 is input to the plus side input terminal.

On the other hand, the reference voltage is applied from the reference voltage generator 33 to the negative input terminal of the comparator 34. In the comparator 34, the voltage of the signal input to the plus side input terminal is compared with the reference voltage, and the high level signal is output from the comparator 34 in the section where the signal voltage is higher. That is, as shown in FIG. 4B, in the comparator 34, a rectangular signal (pulse) that rises at the cross point 41 and falls at the cross point 42 is generated, and this signal is output from the comparator 34 and the AND circuit. 40 is input.

The signal output from the amplifier 32 is also input to the differentiating circuit 35. In the differentiating circuit 35,
The signal is differentiated and inverted, and a signal having a waveform as shown in FIG. The zero-cross point 44 of the signal output from the differentiating circuit 35 coincides with the peak point 43 of the signal output from the photodiode 6 (the signal output from the amplifier 32).

The signal output from the differentiating circuit 35 is input to the negative side input terminal of the comparator 39. In the comparator 39, the high-level signal is output from the comparator 39 while the voltage of the signal input to the negative side input terminal is negative (<0). That is, as shown in FIG. 4D, in the comparator 39, the zero cross point 44
A rectangular signal (pulse) falling at is generated, and this signal is output from the comparator 39 to the AND circuit 40.
Is input to Note that, in FIG. 4D, the signal in the shaded area can be either a high level or a low level due to a subtle change in the signal from the differentiating circuit 35 (one-time differential value). Then, this area is the synchronization signal H _{SY NC}
Since it is a region outside the detection section of, there is no influence on the detection of the synchronization signal H _SYNC .

As shown in FIG. 4E, the AND circuit 40.
Then, a rectangular synchronization signal H _SYNC rising at the cross point 41 and falling at the zero cross point 44 is generated. The synchronization signal H _SYNC generated by the auxiliary scanning by the laser beam 21 a is output from the AND circuit 40 and input to the control means 15.

In the control means 15, the falling timing of the synchronizing signal H _SYNC is used to identify the scanning start position on the light receiving surface of the photosensitive drum 8, that is, the drawing start position 12.

Specifically, as shown in FIG. 5, the irradiation point of the laser beam 21 on the light receiving surface 81 is set to a distance S in the main scanning direction by a timer (not shown) incorporated in the control means 15. The time to move (timer setting time) is set in advance. Then, when the sync signal H _SYNC is detected, that is, the timing of the fall of the sync signal H _SYNC , the timer is started, and the time when the timer set time has elapsed is set as the drawing start position 12.

After that, in the drawing area 11, while the main scanning by the laser beam 21 is performed, the laser light source 3 is turned on / off according to the drawing data (not shown) sent from the outside to the control means 15, and desired. Forming dots.

When the scanning end position 14 is reached, the laser light source 3 is turned off, the photosensitive drum 8 is rotated by one dot, and auxiliary scanning and main scanning are performed in the same procedure as described above. Here, in the comparative example, in detecting the synchronization signal H _SYNC , as shown in FIG.
As shown in FIG. 7A, the vicinity of the peak point 43 of the waveform 26 becomes linear, and the signal having the waveform as shown in FIG. 7C is output from the differentiating circuit 35. In this case, the signal from the differentiating circuit 35 (one-time differential value) is near the zero-cross point 44,
It slightly changes to positive or negative (or 0) due to the influence of noise or the like. Therefore, as shown in FIG. 7D, an unstable signal that can be both high level and low level at the zero cross point 44 and its vicinity is output from the comparator 39, and as shown in FIG. In addition, variations occur in the falling timing of the synchronization signal H _SYNC . As described above, in the comparative example, it is difficult to match the falling timing of the synchronization signal H _SYNC with the zero-cross point 44.

On the other hand, in the synchronizing signal generating circuit 10 of the present embodiment, a steep waveform 25 is obtained as shown in FIG. 4, so that the falling timing of the synchronizing signal H _SYNC almost coincides with the zero cross point 44. Therefore, it is possible to accurately detect the synchronization signal H _SYNC , particularly the zero-cross point 44 (falling timing of the synchronization signal H _SYNC ).

Further, since the sync signal generating circuit 10 detects the peak point 43, that is, the zero-cross point 44, as long as the zero-cross point 44 does not change,
Detecting the synchronization signal H _SYNC with high accuracy regardless of fluctuations in the output from the photodiode 6, for example, fluctuations in the laser beam output and fluctuations in the DC component output from the photodiode 6 due to tilting of the rotary polygon mirror 5 and the like. It can be performed.

Further, in the synchronizing signal generating circuit 10, since the signal processing circuit 9 is only configured to detect the zero cross point 44, the circuit configuration is simple. Further, when the synchronization signal generation circuit 10 is manufactured, the photodiode 6
Since the upper limit of the width L of the effective light receiving area in the main scanning direction is known, the width L can be made relatively large within the range not exceeding the upper limit (for example, 0.5 W ≦ L ≦ 2).
W) As a result, for example, an existing photodiode (light receiving element) can be used, and the accuracy of detecting the synchronization signal H _SYNC can be improved.

The sync signal generation circuit of the present invention is not limited to the sync signal generation circuit of an optical scanning device used for various recording (writing) such as a laser beam printer or a laser photoplotter, and may be, for example, a bar code reader or an image. It can also be applied to a synchronizing signal generating circuit of an optical scanning device used for various readings such as a reader.

The sync signal generating circuit of the present invention has been described above based on the illustrated configuration example, but the present invention is not limited to this. For example, in the present invention, in order to regulate the width L of the effective light receiving region of the photodiode (light receiving element) in the main scanning direction to a predetermined size, a mask for light shielding is provided on the light receiving surface of the photodiode (light receiving element). Etc. may be provided.

[0060]

As described above, according to the synchronizing signal generating circuit of the optical scanning device of the present invention, it is possible to detect the synchronizing signal with high accuracy, and in particular, the irradiation of the beam light to the light receiving element is performed. , And the timing of the synchronization signal can be matched.

As a result, it is possible to prevent the variation of the scanning position of the beam light, especially the variation of the scanning start position of the beam light. When the present invention is applied to the synchronizing signal generating circuit of the optical scanning device of the laser beam printer. In addition, it is possible to effectively prevent the disorder of the drawing start position and obtain good drawing (printing) quality.

Further, when the synchronization signal is generated by detecting the peak point based on the signal from the light receiving element, especially, the differential value of the signal from the light receiving element (one-time differential value)
When the synchronization signal is generated by detecting the zero-cross point of, the zero-cross point (the timing of the falling edge of the synchronization signal) can be accurately detected, and moreover,
As long as the zero-cross point does not change, it is possible to detect the synchronization signal with high accuracy regardless of the change in the output from the light receiving element (for example, the change in the DC component output from the light receiving element).

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment in which a synchronization signal generation circuit of an optical scanning device of the present invention is applied to a synchronization signal generation circuit of an optical scanning device of a laser beam printer.

FIG. 2 is a circuit diagram showing a circuit configuration example of a synchronization signal generation circuit of the optical scanning device of the present invention.

FIG. 3 is a schematic view showing the vicinity of a photodiode according to the present invention.

FIG. 4 is a timing chart showing the operation of the synchronization signal generation circuit of the optical scanning device of the present invention.

FIG. 5 is a timing chart showing a relationship between a lighting timing of a laser light source and a synchronization signal in the present invention.

FIG. 6 is a schematic diagram showing the vicinity of a photodiode in a comparative example.

FIG. 7 is a timing chart showing the operation of the synchronization signal generation circuit of the comparative example.

[Explanation of symbols]

1 Optical Scanning Device (Laser Scanning Unit) 2 Light Source Section 3 Laser Light Source 4 Front Optical System 5 Rotating Polygonal Mirror (Polygon Mirror) 51 Reflecting Surface 52 Corner 6 Photodiode 7 fθ Lens 8 Photosensitive Drum 81 Light-Receiving Surface 82 Rotation Axis 9 Signal processing circuit 10 Synchronization signal generation circuit 11 Drawing area 12 Drawing start position 13 Sync signal generation light receiving position 14 Scanning end position 15 Control means 16 Driving means 21 Laser beam 22 Spot 25, 26 Waveform 31 Resistance (resistor) 32 Amplifier 33 Reference voltage generator 34 Comparator (comparator) 35 Differentiation circuit 36 Capacitor 37 Resistance (resistor) 38 Differential amplifier 39 Comparator (comparator) 40 AND circuit (logical product circuit) 41, 42 Cross point 43 Peak point 44 Zero cross point

Claims (4)

[Claims] 1. A light scanning device provided in a light scanning device for deflecting a light beam incident from a light source and emitting the light beam as a scanning light beam that moves at a constant speed in a predetermined direction, and the scanning light beam reaches a predetermined position within the scanning region. And a signal processing circuit for generating a synchronization signal for specifying a scanning start position by the scanning beam light based on a signal from the light receiving element, and a scanning direction of the scanning beam In the optical scanning, the relationship between the width L of the effective light receiving area of the light receiving element and the diameter W of the scanning beam in the scanning direction is set so as to satisfy L ≦ 2W. Synchronous signal generation circuit of device. 2. A light scanning device provided in an optical scanning device for deflecting a light beam incident from a light source and emitting the light beam as a scanning light beam that moves at a constant speed in a predetermined direction, and the scanning light beam reaches a predetermined position within the scanning region. And a signal processing circuit for generating a synchronization signal for specifying a scanning start position by the scanning beam light based on a signal from the light receiving element, and a scanning direction of the scanning beam In the optical scanning, the relationship between the width L of the effective light receiving area of the light receiving element and the diameter W of the scanning beam in the scanning direction is set so as to satisfy L ≦ W. Synchronous signal generation circuit of device. 3. The synchronization signal generation circuit of the optical scanning device according to claim 1, wherein the signal processing circuit generates the synchronization signal by detecting a peak point of a signal from the light receiving element. 4. The synchronization signal generating circuit of the optical scanning device according to claim 3, wherein the peak point is detected by detecting a zero-cross point of a differential value of the signal based on the signal from the light receiving element. .