JP2002169121A - Optical scanning device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To set an optimum delay time from the initial lock of a PLL signal to the permission of optical scanning of a surface to be scanned by a polygon mirror, thereby suppressing a defective image output and extending a process life. An optical scanning device is provided. At the start of copying, the polygon motor is increased in rotation speed from a stopped state (or ready rotation state) to a target speed, and by referring to a PLL signal output from a PLL circuit, the polygon motor is rotated. It is detected that the rotation speed of the motor has reached a specific range with respect to the target speed.After that, it is checked whether or not the state has been continuously detected for a predetermined predetermined time, and the state can be continuously detected for a predetermined time. Then, it is considered that the rotation speed of the polygon motor 1 has converged to the target speed, and light scanning of the photoconductor 5 by the polygon mirror 2 is permitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a digital copying machine or a laser printer using an electrophotographic process. The present invention relates to an optical scanning device for forming an electrostatic latent image on a photosensitive member by performing scanning exposure.

[0002]

2. Description of the Related Art In a digital copying machine equipped with this type of optical scanning device, a motor for rotating a polygon mirror at the start of copying (hereinafter, this motor is referred to as a polygon motor).
The number of rotations is changed to the ready rotation state (or the stop state:
The number of rotations is increased from the number of rotations to the number of rotations that can be copied (the second number of rotations), and by referring to a PLL (phase loop lock) signal output from the polygon motor, the number of rotations is increased to a predetermined speed (target speed). Has reached that point.

However, even if the rotation speed of the polygon motor reaches the target speed, it may deviate from the target speed several times immediately after overshoot or undershoot. After a predetermined fixed time elapses from the detection, optical scanning of the surface to be scanned (photoconductor) by the polygon mirror is permitted, that is, a copy permission signal is output.

[0004]

However, in the above-described conventional control method, a defective image is output as a copy permission before the rotation speed of the polygon motor deviates from the target speed due to overshoot or undershoot, or the target speed is reduced. After the convergence, the time is wastedly delayed, and it takes time to start up the machine, which adversely affects the process life.

Accordingly, the present invention sets an optimum delay time from the initial lock of the PLL signal to the permission of light scanning of the surface to be scanned by the polygon mirror, thereby suppressing the output of a defective image and extending the process life. It is an object to provide an optical scanning device.

[0006]

An optical scanning device according to the present invention comprises:
A light source for outputting light, a mirror surface around the light source, a rotating mirror that deflects light output from the light source by the mirror surface by rotating, and optically scans the surface to be scanned, A motor that rotates at a speed of?, And when changing the rotation speed of the motor from the first rotation speed to the second rotation speed, the rotation speed of the motor reaches a specific range with respect to the second rotation speed. Detecting means for detecting that the rotation speed of the motor has reached a specific range with respect to the second rotation speed, and then detecting the state continuously for a predetermined period of time. Control is performed to determine whether or not the rotation speed of the motor has converged to the target speed, and permit light scanning of the surface to be scanned by the rotating mirror. Means .

Further, the optical scanning device of the present invention comprises a laser light source for outputting a laser light, a polygon mirror for optically scanning a surface to be scanned by deflecting the laser light output from the laser light source, A motor for rotating a mirror at a predetermined speed, rotation detection means for detecting rotation of the motor and outputting a rotation detection signal, and operating based on a rotation detection signal output from the rotation detection means;
The motor has a lower threshold and an upper threshold indicating a specific range with respect to the target speed of the motor, and when changing the rotation speed of the motor from a first rotation speed to a second rotation speed which is the target speed, Until the rotation speed of the motor reaches the lower limit threshold, it changes at the first level, when it reaches the lower limit threshold, it changes to the second level, and when it reaches the upper limit threshold, it changes again to the first level, and then again. When the upper threshold value is reached, the level changes to the second level.
PLL, and the level similarly changes thereafter.
(Phase loop lock) signal output means for outputting a signal, detection means for detecting a point in time when the PLL signal output from the signal output means first reaches the second level, and detection means for detecting the PLL signal First detects the time point when the signal reaches the second level, and then samples the PLL signal at predetermined time intervals. When the signal is at the second level continuously for a predetermined number of times, A control unit that considers that the rotation speed of the motor has converged to the target speed and permits optical scanning of the surface to be scanned by the polygon mirror.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the present embodiment, for example,
1 schematically shows a configuration of an optical scanning device used in a digital copying machine using an electrophotographic process. In FIG. 1, a polygon motor 1 is a DC motor, which is driven by a motor driver 9 described later, and rotates a polygon mirror 2 as a rotating mirror. The laser diode 3 as a laser light source is driven to emit light by an LD driver 11 described later. Laser light output from the laser diode 3 is reflected by the rotating polygon mirror 2, and the reflected laser light Is guided to the photoreceptor 5 as a surface to be scanned via the fθ lens 4 and optically scans the photoreceptor 5.

In the polygon motor 1, an encoder (for example, FG: frequency generator) 6 serving as rotation detecting means for detecting rotation of the motor and outputting a rotation detection signal is provided.
Is provided. Note that the encoder 6 is shown outside the polygon motor 1 for easy understanding.

The frequency signal (rotation detection signal) output from the encoder 6 is a PLL (phase loop lock)
The signal is input to a PLL circuit 7 as signal output means for outputting a signal. Further, a reference clock signal generated from a clock generation circuit 8 is input to the PLL circuit 7.

The PLL circuit 7 controls the rotation of the polygon motor 1 by controlling the motor drive current of the motor driver 9 so that the frequency signal from the encoder 6 and the reference clock signal from the clock generation circuit 8 have the same phase. The number is controlled to a desired rotation speed (target speed).

When the difference between the frequency signal from the encoder 6 and the reference clock signal from the clock generation circuit 8 falls within a predetermined range, the PLL circuit 7 sends a signal to the main control unit 10 as control means. To output a PLL signal (convergence signal).

Here, the PLL signal will be described in detail with reference to FIG. The PLL signal is normally off level (first
), The rotation speed of the polygon motor 1 is equal to the target speed 2
When the value approaches 1 and falls between a lower threshold 22 and an upper threshold 23 indicating a specific range with respect to the target speed 21, the target speed 21 changes to an on level (second level).

That is, when the rotation speed of the polygon motor 1 reaches the lower threshold value 22, it is off level, when it reaches the lower threshold value 22, it changes to on level, and when it reaches the upper threshold value 23, it changes to off level again. Again upper threshold 2
When it reaches 3, it changes to the on level, and when it again reaches the lower threshold value 22, it changes to the off level, and thereafter the level similarly changes.

Normally, the lower threshold 22 and the upper threshold 23 are set to, for example, about 10% of the target speed 21.

The main control section 10 controls the overall control, and modulates and drives the laser diode 3 via the LD driver 11 according to the image data transmitted from the recording control section 12 of the copying machine.

The motor driver 9 and the PLL circuit 7 may be installed in the vicinity of the polygon motor 1 or integrally with the polygon motor 1 due to noise or the like. Similarly, the LD driver 11 may be installed near the laser diode 3 or integrated with the laser diode 3.

A control method according to the present invention in such a configuration will be described. Now, in order to start copying, it is assumed that the rotation speed of the polygon motor 1 is increased from, for example, a stopped state (or a ready rotation state) to a rotation speed at which copying is possible. It is assumed that the main control unit 10 first detects that the PLL signal has been first locked at the time t1 in FIG.

In the main control unit 10, at time t1, the PLL
Upon detecting the first lock on the signal, the minimum sampling period allowed by the system from that point on, eg, 5
By sampling the PLL signal every 0 msec, four consecutive times are at the on level, ie, 1
When the ON level of the PLL signal is detected for 50 msec continuously, it is determined that the rotation speed of the polygon motor 1 has converged to the target speed.

The value of 150 msec is usually determined appropriately from the time constant of the system and the like. For example, for example, the times t1 to t2, t3 to t4, and t4 in FIG.
As in the case of 5 to t6, a plurality of times during which the PLL signal is turned on may be measured and determined from the maximum value.

For example, a specific example will be described with reference to FIG.
As shown in (a), the first on-level is detected at time t11, and if the second to fourth detections (time t12 to t14) are all on-level, it is deemed to have converged.

If the off level is detected even once in the four detections, it is determined that convergence has not occurred, and the detection is continued. For example, a specific example will be described. As shown in FIG. 3B, the first on-level is detected at time t21 and the time t21 is detected.
The on level is detected continuously at 22 and t23, but at time t24.
To return to the off level, and if the fourth detection is performed at time t25, it is not regarded as having converged.

For example, at times t1 to t2, t3 to t3 in FIG.
It is assumed that the on level cannot be detected four times consecutively at t4 and t5 to t6. However, after time t7, 150
If the PLL signal is at the off level continuously for msec or more, it is regarded as having converged. And, just in case, wait for another 400 msec from there,
Further stabilization as copying permission. Where 400
The numerical value of msec sets a minimum value that absorbs an error that can be expected to occur, such as a variation between aircrafts.

If the off-level of the PLL signal is detected after 400 msec, it is determined that an abnormal situation has occurred and error processing is performed.

The delay time of 400 msec is not always required, but may be provided as needed.

Next, a specific example of the above control method will be described with reference to a flowchart shown in FIG. Now, in order to start copying, it is assumed that the rotation speed of the polygon motor 1 is increased from the stopped state to the rotation speed at which copying is possible.
First, the main controller 10 drives the polygon motor 1 by sending a motor-on signal to the motor driver 9,
The rotation is started (S1). Next, the main controller 10 clears a built-in counter (not shown) (S2),
It waits until the L signal goes to the on level (S3).

When the PLL signal is turned on (at time t).
1) The main control unit 10 delays by a predetermined time T1 (50 msec in this example) from that time (S4), and thereafter, the PL
It is checked whether the L signal is on level (S
5). As a result of the check, if the main control unit 10 is not at the on-level, the main control unit 10 returns to step S2 and repeats the above operation.

If the result of the check in step S5 indicates that the counter is on level, the main control unit 10 sets the counter to "+".
1 "(S6), and then the value of the counter becomes a predetermined value N
It is checked whether (3 in this example) or not (S7). If the result of this check is that the counter value is not "3", the main control unit 10 returns to step S4 and repeats the above operation.

If the value of the counter is "3" as a result of the check in step S7, the main control unit 10 considers that the rotation speed of the polygon motor 1 has converged to the target speed, and a predetermined time T2 ( (400 msec in this example)
After a delay (S8), a copy permission signal is sent to the LD driver 11 (S9).

When the LD driver 11 receives the copy permission signal, it modulates and drives the laser diode 3 in accordance with the image data sent from the main controller 10 at this time.
Optical scanning of the photoconductor 5 by the modulated laser light is started.

According to such a control method, it is possible to set an optimum delay time from the initial lock of the PLL signal to permission of copying (permission of light scanning of the photosensitive member by the polygon mirror).
Therefore, unlike the related art, the copy permission signal is not output before the rotation speed of the polygon motor converges, so that the output of a defective image can be prevented and the process life can be extended.

By setting the predetermined time T1 in step S4 to, for example, 1 msec, and setting the predetermined value N in step S7 to, for example, "150", the PLL is set every 1 msec.
The signal is sampled and turned on for 150 consecutive times, that is, as a result, 150
It can be determined whether or not the on level of the PLL signal has been detected continuously for msec.

[0034]

As described in detail above, according to the present invention, P
It is possible to provide an optical scanning device that sets an optimum delay time from the initial lock of the LL signal to the permission of optical scanning of the surface to be scanned by the polygon mirror, thereby suppressing a defective image output and extending the process life.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a configuration of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a timing chart illustrating a PLL signal with respect to a rotation speed of a polygon motor.

FIG. 3 is a timing chart illustrating an example in which convergence of a PLL signal is considered and an example in which convergence is not considered.

FIG. 4 is a flowchart illustrating a specific example of a control method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Polygon motor, 2 ... Polygon mirror (rotating mirror), 3 ... Laser diode (laser light source), 5 ... Photoconductor (scanning surface), 6 ... Encoder (rotation detecting means), 7
... PLL circuit (signal output means), 8 ... clock generation circuit, 9 ... motor driver, 10 ... main control unit (control means), 11 ... LD driver.

Claims (5)

[Claims] A light source that outputs light; a rotating mirror that has a mirror surface around it, deflects light output from the light source by the mirror surface by rotating, and optically scans a surface to be scanned. A motor for rotating the rotating mirror at a predetermined speed; and when changing the rotation speed of the motor from the first rotation speed to the second rotation speed, the rotation speed of the motor is higher than the second rotation speed. Detecting means for detecting that the motor has reached a specific range; and after detecting that the rotational speed of the motor has reached a specific range with respect to the second rotational speed, the state is determined in advance. It is checked whether or not the detection can be continuously performed for a predetermined period of time, and when the detection can be continuously performed for a predetermined period of time, it is considered that the rotation speed of the motor has converged to the target speed, and the light on the surface to be scanned by the rotating mirror is detected. Control hand to allow scanning When the optical scanning apparatus characterized by comprising a. 2. The method according to claim 1, wherein the control unit determines that the rotation speed of the motor has converged to a target speed, and further delays the motor for a predetermined time before permitting the rotating mirror to scan the surface to be scanned. The optical scanning device according to claim 1. 3. A laser light source for outputting a laser light, a polygon mirror for optically scanning a surface to be scanned by deflecting the laser light output from the laser light source, and rotating the polygon mirror at a predetermined speed. A motor, rotation detection means for detecting rotation of the motor and outputting a rotation detection signal, and operating based on a rotation detection signal output from the rotation detection means, wherein a specific speed with respect to a target speed of the motor is specified. It has a lower threshold value and an upper threshold value indicating a range, and when changing the rotation speed of the motor from the first rotation speed to the second rotation speed that is the target speed, the rotation speed of the motor becomes the lower threshold value. Up to the first level, when the lower threshold is reached, the level changes to the second level, and when the upper threshold is reached, the level changes again to the first level, and then the upper threshold again A signal output means for outputting a PLL (Phase Loop Lock) signal which changes to a second level, then changes to the first level when the lower threshold value is reached again, and changes in the same manner thereafter; Detecting means for detecting the time when the output PLL signal first reaches the second level; and detecting means for detecting the time when the PLL signal first reaches the second level. The PLL signal is sampled at predetermined time intervals. When the PLL signal is at the second level continuously for a predetermined number of predetermined times, it is considered that the rotation speed of the motor has converged to the target speed, and the rotation of the motor is controlled by the polygon mirror. Control means for permitting optical scanning on the scanning surface; and an optical scanning device comprising: 4. The control means according to claim 1, further comprising, after assuming that the rotation speed of said motor has converged to the target speed, further delaying the motor by a certain time before permitting the polygon mirror to scan the surface to be scanned. The optical scanning device according to claim 3, wherein 5. The image forming apparatus according to claim 1, wherein the surface to be scanned is a surface of a photoconductor on which an electrostatic latent image is formed in an image forming apparatus such as a digital copying machine or a laser printer. Optical scanning device.