JP3225749B2 - Laser light scanning device - Google Patents

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 device which scans an object to be scanned by a laser beam emitted from a laser light source and reflected and deflected by a polygon mirror, and more particularly to a laser beam scanning device which emits light from a plurality of laser light sources. The present invention relates to a laser beam scanning device that scans a scanned object in directions parallel to each other with a plurality of laser beams reflected and deflected by a plurality of polygon mirrors.

[0002]

2. Description of the Related Art In a laser printer, a digital copying machine, or the like that forms an image by an electrophotographic process, a laser beam that repeatedly scans the surface of a photoconductor with a laser beam in order to form an electrostatic latent image on the surface of the photoconductor. A scanning device is incorporated. This laser light scanning device is provided with a laser light source and a polygon mirror for repeatedly reflecting and deflecting the laser light emitted from the laser light source. The laser light reflected and deflected by the polygon mirror repeatedly scans the photosensitive member surface. Is done. Normally, the laser beam repeatedly scans the surface of the photoconductor in a predetermined main scanning direction, during which the photoconductor rotates or moves at a constant speed in a sub-scanning direction that intersects the main scanning direction. , Photoconductor surface is 2
Scanning is performed two-dimensionally, and a two-dimensional electrostatic latent image is formed on the surface of the photoconductor.

In such an image forming apparatus such as a laser printer or a digital copier incorporating the laser beam scanning device, the laser beam scanning device is formed on the surface of the photoreceptor by repeated scanning with the laser beam emitted from the laser beam scanning device.
It is known that if the pitch in the sub-scanning direction of the electrostatic latent image row for each main scan is not uniform, the quality of an output image obtained by developing the electrostatic latent image and transferring it to paper is deteriorated. ing. In particular, in a full-color copying machine, even if this irregularity is slight, color unevenness and color tone change occur in the output image, and in order to prevent this, it is important that the image latent image sequence is formed with high precision at regular intervals. is there.

[0004]

In the case of a laser beam scanning device having a single polygon mirror, the main cause of the irregularity of the image latent image row is the division accuracy and inclination of a plurality of reflection surfaces constituting the polygon mirror. However, these are usually sufficiently accurate, and it is not necessary to particularly consider irregularities in the image latent image sequence.

However, for the purpose of, for example, improving the speed of forming an electrostatic latent image, a plurality of laser beams emitted from a plurality of laser light sources and reflected and deflected by a plurality of polygon mirrors respectively cause the surface of the photoconductor to be parallel to each other. It has been considered to form a plurality of rows of electrostatic latent images simultaneously along a plurality of main scanning lines. In this case, in order to form an electrostatic latent image row having a uniform pitch, first, the rotation speeds of all the polygon mirrors must be equal, and second, the scanning start timings of all the polygon mirrors need to be respectively set. It is required that the timing is determined. The second requirement is that, in other words, the direction of the reflection surface of each polygon mirror that is currently reflecting the laser beam is completely uniform, for example, for all polygon mirrors, that is, the rotation phase of the polygon mirror. The angles are required to be equal for all polygon mirrors.

As a technique for controlling the rotation speed and rotation phase angle of a polygon mirror, conventionally, a PLL (Pha) has been used to control the rotation speed of a polygon motor that rotates the polygon mirror.
An SOS (Start Of Scan) sensor is provided at a position for receiving the laser light reflected in a predetermined direction by the polygon mirror, and the laser light output from the SOS sensor is applied to the polygon mirror. Feeding back the SOS signal indicating the timing reflected in a predetermined direction, and controlling the phase difference between the phase of the speed reference signal generated by the reference signal source and the phase of the SOS signal to be a predetermined phase difference. Thus, a technique has been proposed in which the start timing of optical scanning by laser light is made coincident for all laser lights, and the rotational speeds of all polygon motors are kept at a constant constant speed.

However, since the proposed technique uses the above-mentioned SOS signal as a feedback signal for controlling the rotation speed of the polygon motor, the laser light output from the laser light source during the rotation operation of the polygon motor is required. If the rotation is interrupted, the rotation speed cannot be controlled, and not only can the constant speed not be maintained, but also the polygon motor may be in the maximum acceleration state and the large current may continue to flow.In the worst case, the polygon motor may be damaged. There is a risk that it will. If the control circuit is designed to prevent this and rotate at a substantially constant speed even when the SOS signal is not input, the cost will increase accordingly, and control performance will usually increase if such an additional circuit is added. Inferior results. Therefore, when trying to adopt this proposed technique, it is necessary to always output the laser light at least at the timing when the laser light irradiates the SOS sensor, even when the image output is not performed. Is significantly reduced.

Further, the PLL control system is a system for controlling an object, for example, a polygon motor, based on a signal phase difference between a reference signal and a feedback signal. There is variation in the conversion efficiency and the like for converting electric power into mechanical force for rotational driving.To rotate a plurality of polygon motors having this variation at the same speed,
It is necessary to generate a phase difference between the reference signal and the feedback signal according to the variation. On the other hand, the SOS signal detects whether or not the polygon motor is at a predetermined rotation phase angle. Therefore, in order to make the scanning timing uniform, the phase difference between the speed reference signal and the SOS signal is constant for all polygon motors. Needs to be Therefore, when the SOS signal is used as a feedback signal, it is required that the phase between the speed reference signal and the SOS signal needs to be constant for all polygon motors in order to equalize the rotational phase angles of all polygon motors, In order to rotate the motor at a constant constant speed, it is necessary to satisfy two contradictory requirements, that is, a requirement that a variation in the phase difference corresponding to the variation in the conversion efficiency and the like for each polygon motor is required. Will happen. It is conceivable to adjust the phase so as to satisfy these two requirements simultaneously. However, since this phase difference has a strong effect on the stability of the rotation speed control of the polygon motor, this phase difference is constant for all polygon motors. If it is attempted to adjust the phase, the rotation speed control of the polygon motor may not be successful.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a laser beam scanning apparatus having a plurality of polygon mirrors, in which the rotation phase angle is adjusted and all polygon motors are stably rotated at the same speed. It is an object of the present invention to provide a laser beam scanning device having a control method that can be used.

[0010]

FIG. 1 is a block diagram showing the configuration of a laser beam scanning device according to the present invention. The laser beam scanning apparatus includes a plurality of scanning units 10A, 10B,.
0N is provided. Each of the scanning units 10A, 10B,.
10N scans a predetermined object to be scanned in a direction parallel to each other by a laser beam, and each of the scanning units 10A, 10B,
, 10N are not shown in FIG. 1; (a) a laser light source; (b) a polygon mirror having a plurality of reflecting surfaces in the circumferential direction and reflecting and deflecting the laser light emitted from the laser light source on the reflecting surface. c) a polygon motor for rotating the polygon mirror; and (d) an optical sensor for receiving a laser beam reflected by the polygon mirror and outputting a timing signal indicating a timing at which the laser beam is reflected in a predetermined direction by the polygon mirror. .

Further, the present laser light scanning device is provided with a motor drive unit 20. This motor drive unit 20
, 10N. Each of the scanning units 10A, 10B,..., 10N is driven to rotate. The motor driving unit 20 includes (e) a plurality of scanning units 10A, 10B,. , A predetermined rotation speed reference signal provided thereto, and controls the corresponding polygon motor to a rotation speed corresponding to the frequency of the reference signal of the rotation speed, 21A, 21B,..., 21N ( f) Original signal generating means 22 commonly provided for the plurality of scanning units 10A, 10B,..., 10N for generating a predetermined original reference signal. (g) Corresponding to the plurality of scanning units 10A, 10B,. A timing signal obtained by a corresponding optical sensor and an original signal generated by the original signal generating means 22 are inputted, and a constant drive signal having a predetermined reference frequency is generated based on the original signal. At least one adjustment drive signal having a frequency changed from the reference frequency is switchably generated in accordance with the input timing of the timing signal, and is supplied to the corresponding rotation speed control means 21A, 21B,. Reference signal adjusting means 23A, 2
, 23N are provided. Here, the reference signal adjusting units 23A, 23B,..., 23N perform the above-described operations during the period from the start of the adjustment of the rotation of the corresponding polygon motor to the end of the adjustment when the timing signal is input at a predetermined timing. An adjustment drive signal is output as the rotation speed reference signal, and after the end of the adjustment, the constant drive signal is output as the rotation speed reference signal.

In the laser beam scanning device of the present invention configured as described above, the motor drive section 20 generates a phase reference signal representing the phase reference of the rotation of the polygon motor as shown by a broken line in FIG. Reference signal adjusting means 23A, 23
, 23N to be inputted to the reference signal adjusting means 23A, 23B,.
, The reference signal adjusting means 23A, 23B,.
It is preferable that the constant drive signal or the adjustment drive signal is output as the rotation speed reference signal in accordance with the comparison result between the phase reference signal and the timing signal input to the controller.

The reference signal adjusting means 23A, 23
B,..., 23N are, as the adjustment driving signals, at least two adjustment driving signals of a signal whose frequency has changed to a frequency higher than the reference frequency and a signal whose frequency has changed to a frequency lower than the reference frequency. Generate freely switchable,
During the period from the start of the adjustment to the end of the adjustment, of the at least two adjustment drive signals, the adjustment drive signal for rotating the polygon motor so that the input timing of the timing signal sequentially approaches a predetermined timing is changed to the rotation speed. It is preferable that the signal is output as a reference signal.

Further, in the laser beam scanning device of the present invention, the rotational speed control means 21A, 21B,.
It is also a preferable embodiment that 1N controls the rotation speed of the corresponding polygon motor by a PLL control method.

[0015]

According to the laser beam scanning apparatus of the present invention constructed as described above, the polygon motors provided in the plurality of main scanning units 10A, 10B,..., 10N use the corresponding rotation speed control means 21A, 21B,. 21N. Each of these rotation speed control means 21A, 21B,.
The corresponding polygon motor is controlled to a rotation speed corresponding to the frequency of the rotation speed reference signal sent from the corresponding reference signal adjusting means 23A, 23B,..., 23N. Therefore, each of the rotation speed control means 21A, 21B,.
When a rotation speed reference signal having a reference frequency is input to
All polygon motors correspond to their reference frequency,
They rotate at the same rotational speed. However, in this state, the rotational phases of the polygon motors are not always aligned (or have a phase adjusted in advance).
The reference signal adjusting means 23A, 23B,..., 23N can generate not only a constant drive signal of the reference frequency but also a drive signal for adjustment of a frequency changed from the reference frequency. When adjusting the rotation of the polygon motor, first, The adjustment drive signal is input to the corresponding rotation speed control means 21A, 21B,..., 21N as the rotation speed reference signal. Then, the rotation speed control means 21A, 21B,..., 21N rotates the corresponding polygon motor at the 'changed' rotation speed corresponding to the frequency changed from the reference frequency. The rotation speed adjusting means 23A, 23B,..., 23N monitor timing signals from the optical sensors provided in the corresponding scanning units 10A, 10B,. Since the polygon motor is rotating at the 'changed' rotation speed, the input timing of the timing signal is sequentially shifted and coincides with a predetermined timing.

The phase reference signal representing this predetermined timing may be generated inside each of the reference signal adjusting means 23A, 23B,..., 23N, but as shown by a broken line in FIG. A phase reference signal is generated, and the generated phase reference signal is used as each of the reference signal adjusting units 23A and 23A.
3B,..., 23N. The reference signal adjusting means 23A, 23B,..., 23N converts the output rotational speed reference signal from the adjusting drive signal (the signal having the 'changed' frequency) to the constant drive signal (the signal of the reference frequency) at the coincident timing. Switch to). Then, the corresponding polygon motor then has its phase adjusted,
The rotation will continue at the rotation speed corresponding to the reference frequency. By performing the above adjustment for all the polygon motors at the time of the predetermined adjustment, all the polygon motors rotate at the same rotation speed and in the same phase. Therefore, in the laser beam scanning device of the present invention, for the purpose of the adjustment, it is sufficient that the optical sensor is irradiated with the laser beam only at the time of the adjustment, and it is possible to prevent the life of the laser light source from being significantly reduced.

In the motor drive unit 20, since the output of the optical sensor is monitored only at the time of adjustment, for example, by performing adjustment at a timing other than the time of scanning for performing the above-described scanning for forming an electrostatic latent image or the like, Even if the amount of laser light output from the laser light source during scanning varies, it is possible to avoid a situation in which the rotation phase angle of the polygon motor varies during scanning and affects the output image.

In the laser beam scanning device of the present invention,
When there is only one type of adjustment drive signal having a frequency changed from the reference frequency, even if the input timing of the timing signal from the optical sensor is earlier or later than the predetermined timing, the one type of adjustment drive signal is used. The phase adjustment is performed by using, for example, when the one type of the adjustment drive signal is a signal that advances the phase of the polygon motor little by little as compared with the signal of the constant drive, the signal is slightly advanced. If the adjustment drive signal is used to adjust the phase of the polygon motor, the phase will further advance and the phase will match after one rotation, and it will take time to adjust the phase. Therefore, in the laser light scanning device of the present invention, as the adjustment driving signal, at least two adjustment driving signals of a signal whose frequency has changed to a higher frequency and a signal whose frequency has changed to a lower frequency than the reference frequency are generated, The phase adjustment time is shortened by selectively using the phase of the polygon motor in accordance with the advance / delay of the phase.

In the laser beam scanning device of the present invention,
The rotation speed control means 21A, 21B,.
When the rotation speed of the polygon motor is controlled by the PLL control method, the rotation speed of the polygon motor is controlled with high accuracy. However, this PLL control does not use the timing signal output from the optical sensor as a feedback signal, but directly measures the rotation phase angle of the polygon motor as the feedback signal.
For example, an output signal of an encoder or the like is used.

[0020]

Embodiments of the present invention will be described below. FIG. 2 is a schematic diagram of a scanning optical unit as an example of a scanning unit of the laser beam scanning device of the present invention. However, the scanning optical unit 100 is also equipped with a PLL control circuit which is an example of a rotation speed control unit in the motor control unit according to the present invention.

A laser light source 12, a polygon mirror 13, a polygon motor 14, an fθ lens 15, a reflection mirror 16, a SOS are provided in a housing 11 of the scanning optical unit 100.
A sensor 17 and a PLL control circuit 18 are provided, and an opening 11 a for emitting laser light from the housing 11 is formed at the bottom of the housing 11. The laser light emitted from the laser light source 12 is repeatedly reflected and deflected by the polygon mirror 13 rotated by the polygon motor 14, and fθ
After the spot diameter is adjusted by the lens, the reflection mirror 1
The light is reflected at 6 and is emitted through the opening 11a.

An SOS sensor 17 is provided at the scanning start position of the laser beam reflected and polarized by the polygon mirror 13, and outputs a SOS signal indicating the timing of the start of each scan. Also,
The rotation of the polygon motor 14 is controlled by a PLL control circuit 18 which is an example of a rotation speed control means according to the present invention.

FIG. 3 is a schematic diagram showing a state where an electrostatic latent image is formed on the surface of a belt-shaped photosensitive member by a plurality of (here, four) optical scanning units 100A to 100D.
FIG. 3 is a schematic diagram showing a part of an electrostatic latent image formed on the surface of a photoconductor. An endless photoreceptor belt 31 is stretched around a driving roll 32 and a driven roll 33,
2 rotates at a constant speed in the direction of arrow C, so that the latent image forming area of the photoreceptor belt 31 moves at a constant speed in the direction of arrow Y (sub-scanning direction).

On the upper part of the photosensitive belt 31, four optical scanning units 100A and 100A each having the structure shown in FIG.
00B, 100C, and 100D are provided. Each optical scanning unit 100A, 100B, 100C, 100D
The rotation speed reference signal, which is generated on the control circuit 34 shown in FIG. 3 and determines the rotation speed of the polygon motor 14 (see FIG. 2), is input to the PLL control circuit 18 (see FIG. 2) provided in Further, each optical scanning unit 100A, 100
Image signals for forming a desired electrostatic latent image on the photoreceptor belt 31 generated by the image signal generation circuit 35 are input to the laser light sources 12 provided for the laser beams B, 100C, and 100D. The light source 12 repeats on / off based on the input image signal.

Each optical scanning unit 100A, 100B,
From 100C and 100D, each laser beam 19A, 19B,
19C and 19D are ejected.
1 is scanned in the arrow X direction (main scanning direction). When the electrostatic latent image sequence A0 by the laser beam 19A emitted from the optical scanning unit 100A is conveyed in the direction of arrow Y and reaches the position of the electrostatic latent image sequence A1, the laser emitted from the optical scanning unit 10B. By the light 19B, the electrostatic latent image sequence A
An electrostatic latent image row B0 adjacent to No. 1 is formed. Similarly, when the electrostatic latent image sequence B0 reaches the illustrated electrostatic latent image sequence B1, the laser beam 19C emitted from the optical scanning unit 100C causes the electrostatic latent image sequence B1 The latent image row CO is formed, and when the electrostatic latent image row CO reaches the illustrated electrostatic latent image row C1, the optical scanning unit 100
D, the electrostatic latent image train C
An electrostatic latent image row D0 adjacent to No. 1 is formed. As described above, on the photoreceptor belt 31, as shown in FIG.
Each optical unit 100A, 100B, 100C, 100
Laser light 19A, 19B, 19C, 1 emitted from D
A two-dimensional electrostatic latent image is formed in which the electrostatic latent image rows A, B, C, and D formed by 9D are arranged cyclically.

At this time, in order to obtain an output image having good image quality, it is required that the intervals d _AB , d _BC , d _CD , and d _DA between the adjacent electrostatic latent image rows shown in FIG. 4 are all equal. Is done. Hereinafter, a description will be given of adjusting means for making all of the intervals d _AB , d _BC , d _CD , and d _DA equal. FIG. 5 is a block diagram of one embodiment of the laser beam scanning device of the present invention.

Here, four optical scanning units 100A, 100B, 100C and 100D having the same structure are provided. Each optical scanning unit 100A, 100
B, 100C, and 100D include laser light source 12, polygon mirror 13, and polygon motor 1 as main components.
4, an SOS sensor 17 and a PLL control circuit 18 are provided (see FIG. 2).

As described with reference to FIG. 3, each of the optical scanning units 100A, 1
An image signal is transmitted to each of the laser light sources 12 provided in 00B, 100C, and 100D. The SOS signal is input to the image signal generation circuit 35, and the image signal generation circuit 35 determines the timing of outputting the image signal to the laser light source 12 based on the SOS signal. Also,
Signals are exchanged between the image signal generation circuit 35 and a phase adjustment control circuit 41, which will be described later, constituting the control circuit 34 (see FIG. 3). The main signal transmitted between these components is to adjust the rotation phase of the polygon motor 14 which is output from the image signal generation circuit 35 to the control circuit 34 at a predetermined timing at which no image is generated. A phase adjustment instruction signal to be instructed, an image output enable signal indicating that the rotation phase adjustment of the polygon motor 14 is completed from the control circuit 34 to the image signal generation circuit 35, and an image output is possible, and any of them When an error occurs in one of them, there is an error signal or the like that notifies the other to that effect.

On the control circuit 34, a crystal oscillator 42 for generating a high-precision high-frequency pulse signal is provided. In the crystal oscillator 42, for example, the frequency f ₀ = 10 MHz
Is generated. This crystal oscillator 42
The high-frequency pulse signal generated by the
Is input to the phase reference signal generation circuit 44. The original signal generation circuit 43 divides the frequency of the input high-frequency pulse signal of, for example, f ₀ = 10 MHz and, for example, frequency f ₁ = 1M
An original signal in Hz is generated. The original signal output from the original signal generation circuit 43 is transmitted to each of the optical scanning units 100A and 100A.
Reference signal adjustment circuits 45A, 45B, 45C, 45D provided corresponding to OB, 100C, and 100D, respectively.
Is input to

In the phase reference signal generation circuit 44, based on the input high frequency pulse signal, each phase reference signal φ _A , which is a reference of the rotation phase angle of each polygon motor 14, is used.
φ _B , φ _C , and φ _D are generated, and each reference signal adjustment circuit 45 is generated.
A, 45B, 45C, 45D. Each of the reference signal adjustment circuits 45A, 45B, 45C, and 45D has a corresponding optical scanning unit 100A, 100B, 100C,
SOD obtained by the SOS sensor 17 provided in the 100D
The S signal is also input.

Each of the reference signal adjusting circuits 45A, 45B, 45
Reference numerals C and 45D denote the original signals input from the original signal generation circuit 43 as they are (corresponding to the constant drive signals in the present invention), and the corresponding optical scanning units 100A, 100B,
The frequency is output to the PLL control circuit 18 provided in each of 100C and 100D, or the frequency is slightly shifted to a higher frequency side than the original signal by adding one pulse for each predetermined number of pulses of the signal. By generating a signal (one of the adjustment drive signals according to the present invention) and outputting it to the PLL control circuit 18, or removing one pulse every predetermined number of pulses of the original signal, Also, a signal whose frequency is slightly changed to a lower frequency side (another drive signal for adjustment according to the present invention) is generated and output to the PLL control circuit 18. The signal output to the PLL control circuit 18 (a constant drive signal or one of two adjustment drive signals) corresponds to the rotation speed reference signal according to the present invention. The PLL control circuit inputs the rotation speed reference signals output from the corresponding reference signal adjustment circuits 45A, 45B, 45C, and 45D, and the corresponding polygon motor 14 outputs a signal at a rotation speed corresponding to the input rotation reference signal. The polygon motor 14 is controlled to rotate. Reference signal adjustment circuits 45A, 45B, 45C, 45D
The rotation speed reference signal output from the
If the adjustment drive signal has a frequency different from the frequency of the original signal generated in step 3, the polygon motor 14 rotates slightly faster or slightly slower than the reference rotation speed,
The phase reference signal φ generated by the phase reference signal generation circuit 44
_A, φ _B, φ _C, will change timing slightly between phi _D and SOS signals, and supplies the timing coincide at some point. Reference signal adjustment circuits 45A, 45B, 45C,
In 45D, the phase adjustment of the polygon motor 14 is performed in this manner, and when the timing of the phase reference signal and the timing of the SOS signal match, the reference signal adjustment circuits 45A and 45D.
B, 45C and 45D output the speed reference signal generation circuit 43
Is switched to a rotation speed reference signal (a signal of constant drive) generated as described above. Therefore, after the switching, the corresponding polygon motor 14 rotates at a predetermined reference rotational speed while the phase adjustment is completed (the state at the time of the switching).

The above-described phase adjustment sequence is controlled by the phase adjustment control circuit 41. In the phase adjustment control circuit 41, when the phase adjustment instruction signal is transmitted from the image signal generation circuit 35, each of the reference signal adjustment circuits 45
A, 45B, 45C, 45D for polygon motor 14
An adjustment start signal is sent to start the adjustment of the rotation phase angle. Each reference signal adjustment circuit 45A, 45B, 45C, 45
In D, the phase adjustment is performed as described above, and when the phase adjustment is completed, an adjustment completion signal is sent to the phase adjustment control circuit 41. The phase adjustment control circuit 41 sends an image output enable signal to the image signal generation circuit 35 in response to the adjustment completion signals sent from all the reference signal adjustment circuits 45A, 45B, 45C, and 45D.

FIG. 6 shows each reference signal adjusting circuit 4 shown in FIG.
It is a flowchart of the above-mentioned phase adjustment sequence in 5A, 45B, 45C, and 45D. Each of the reference signal adjustment circuits 45A, 45B, 45C, and 45D waits at step S1 until an active (in this example, an “H” level) adjustment start signal is transmitted from the phase adjustment control circuit 41. Signal is active ('H' level)
Then, the process proceeds to step S2. In step S2, the phase reference signal generated by the phase reference signal generation circuit 44 and SO
The phase of the S signal is compared with the phase of the S signal, and it is determined whether or not the phase difference exists, and if the phase difference exists, whether the phase of the SOS signal is delayed or advanced (step S3).
If the phase of the SOS signal is delayed, the process branches to step S4. If the phase of the SOS signal is advanced, the process proceeds to step S4.
5 and if the phase difference is "0", the flow branches to step S7.

In step S4, the original signal generation circuit 43
One pulse per predetermined number of pulses is added to the original signal generated in (see FIG. 5). In the present embodiment, the addition of one pulse is realized by a logic circuit. When a pulse is added to the original signal in this manner, the rotation speed of the corresponding polygon motor 14 increases, and the phase delay of the SOS signal is gradually reduced. Thereafter, the predetermined time elapses in step S6, and the process returns to step S1, proceeds to steps S1, S2, and S3, and the next branch destination is determined depending on whether or not there is still a phase delay.

In step S5, one pulse per predetermined number of pulses is removed from the original signal generated by the original signal generation circuit 43. In the present embodiment, the erasing of one pulse is also realized by a logic circuit. When the pulse is erased in this manner, the rotation speed of the corresponding polygon motor 14 decreases,
The advance of the phase of the SOS signal is gradually eliminated. If it is determined in step S3 that the phase difference is "0", the process proceeds to step S7. If a pulse has been added to the original signal or the pulse has been deleted from the original signal, the original signal is returned. The state of the original signal itself is restored, and the phase adjustment control circuit 4
Toward 1, a completion signal ('H' level) indicating that the adjustment of the rotation phase angle of the polygon motor 14 is completed is transmitted. Thereafter, in step S8, the transmission of the adjustment start signal sent from the phase adjustment control circuit 41 stops ('L').
Level), and when the transmission of the adjustment start signal is stopped (becomes “L” level), the completion signal is stopped (changed to “L” level).

Each of the reference signal adjusting circuits 45A, 45B, 45
In C and 45D, each time the adjustment start signal is sent from the phase adjustment control circuit 41, the phase adjustment according to the above sequence is performed. The timing for performing the phase adjustment is not particularly limited, but a timing when the power of the apparatus is turned on, or a timing when the image is not output after e.g. 30 minutes has elapsed is selected.

FIG. 7 is a block diagram showing a polygon motor control circuit comprising a PLL control circuit and its peripheral circuits. P constituting the PLL control circuit 18 (see FIG. 2)
The LL control unit 18a includes a rotation speed reference signal sent from a corresponding reference signal adjustment circuit (see FIG. 5) and a polygon motor generated by a field generator (FG) 14b that picks up the rotation of the polygon motor 14. The FG signal representing the rotation speed of the fourteen signals is input, and the PLL control unit 18a generates a control signal according to the PLL control method so that the phase difference between the two input signals is always constant. The control signal is input to the phase compensating unit 18b, and after the phase of the control signal is compensated, is input to the motor driving amplifying unit 18c. In the motor drive amplifying section 18c, the transmission of power to each winding of the polygon motor 14 is switched according to the rotating magnetic field of the polygon motor 14 detected by the magnetic detection element 14a. The polygon motor 14 rotates at a rotation speed according to the rotation speed reference signal by, for example, such a PLL control method.

[0038]

As described above, the laser beam scanning apparatus according to the present invention changes the rotation speed of the polygon motor by changing the frequency of the reference signal at the time of adjustment. The rotation speed of the polygon motor is controlled to be constant at a constant speed. Therefore, when image output is not performed, the emission of laser light from the laser light source and the operation of the SOS sensor are unnecessary except during adjustment, and the laser Shortening of the life of the light source is avoided, stable and accurate phase adjustment is performed, and a plurality of polygon motors can be rotated at the same rotation speed and at a predetermined phase.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image scanning device according to the present invention.

FIG. 2 is a diagram illustrating an optical scanning unit as an example of a scanning unit of the laser light scanning device of the present invention.

FIG. 3 is a schematic diagram illustrating a state in which an electrostatic latent image is formed on a belt-shaped photosensitive member surface by a plurality of optical scanning units.

FIG. 4 is a schematic view showing a part of an electrostatic latent image formed on a photoconductor surface.

FIG. 5 is a block diagram showing one embodiment of a laser beam scanning device of the present invention.

6 is a flowchart of a phase adjustment sequence in each reference signal adjustment circuit shown in FIG.

FIG. 7 includes a PLL control circuit and its peripheral circuits.
FIG. 3 is a block diagram illustrating a polygon motor control circuit.

[Explanation of symbols]

100A, 100B, 100C, 100D Scanning unit 12 Laser light source 13 Polygon mirror 14 Polygon motor 20 Motor driving unit 21A, 21B,..., 21N Rotation speed control unit 22 Reference signal generation unit 23A, 23B,. Photoconductor belt 34 Control circuit 35 Image signal generation circuit 41 Phase adjustment control circuit 42 Crystal oscillator 43 Speed reference signal generation circuit 44 Phase reference signal generation circuit 45A, 45B, 45C, 45D Reference signal adjustment circuit 100, 100A, 100B,. 100N optical scanning unit

Claims (4)

(57) [Claims] A polygon mirror having a plurality of reflecting surfaces in a circumferential direction for reflecting and deflecting laser light emitted from the laser light source on the reflecting surface; a polygon motor for rotating the polygon mirror; An optical sensor for receiving the laser beam reflected by the polygon mirror and outputting a timing signal indicating a timing at which the laser beam is reflected by the polygon mirror in a predetermined direction. A plurality of scanning units that scan in directions parallel to each other by light, and provided corresponding to each of the plurality of scanning units, input a predetermined rotation speed reference signal,
Rotation speed control means for controlling the corresponding polygon motor to a rotation speed corresponding to the frequency of the rotation speed reference signal; and an original signal for generating a predetermined original signal, which is provided in common for the plurality of scanning units. Generating means for inputting the timing signal obtained by the corresponding optical sensor provided for each of the plurality of scanning units and the original signal generated by the original signal generating means; A drive signal for generating a constant drive signal having a predetermined reference frequency and at least one adjustment drive signal having a frequency changed from the reference frequency in accordance with an input timing of the timing signal, based on the input signal; And a reference signal adjusting means for outputting the rotation speed reference signal to a control means. During the period from the start of adjustment for starting the adjustment of the rotation of the Rigon motor to the end of adjustment at which the timing signal is input at a predetermined timing, the drive signal for adjustment is output as the rotation speed reference signal. A laser beam scanning device for outputting the constant drive signal as the rotation speed reference signal. 2. The system according to claim 1, wherein the motor driving unit includes a phase reference signal generating unit that generates a phase reference signal representing a reference of a rotation phase of the polygon motor and inputs the signal to the reference signal adjusting unit. Outputting the constant drive signal or the adjustment drive signal as the rotation speed reference signal in accordance with a comparison result between the phase reference signal and the timing signal input to the reference signal adjustment means. The laser beam scanning device according to claim 1, wherein: 3. The reference signal generating means, as the adjustment drive signal, includes at least a signal whose frequency has changed to a frequency higher than the reference frequency and a signal whose frequency has changed to a frequency lower than the reference frequency. The two drive signals for adjustment are switchably generated, and the input timing of the timing signal of the at least two drive signals for adjustment is sequentially changed to the predetermined timing from the start time of the adjustment to the end time of the adjustment. 2. The laser beam scanning device according to claim 1, wherein an adjustment drive signal for rotating the polygon motor so as to approach is output as the rotation speed reference signal. 4. The laser beam scanning apparatus according to claim 1, wherein said rotation speed control means controls the rotation speed of said polygon motor by a PLL control method. apparatus.