JPS6314327B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotation control device for a rotary scanner in an optical scanner.

2. Description of the Related Art Conventionally, various types of electronic printers, copying machines, facsimile machines, etc. that play a part in information transmission equipment using lasers have been proposed and are being put into practical use.

In devices using these lasers, an information image is converted into a signal, the intensity of a laser beam from a laser light source is modulated by an optical modulator according to this signal, and this intensity-modulated laser beam is transmitted at a predetermined angular velocity. The reflected light from the rotating scanner is focused onto the scanned surface of the recording medium by making the light incident on a rotating scanner having n deflection surfaces, such as a rotating polygon mirror that rotates at high speed, and keeping the reflected light constant. An optical scanner is provided which scans the surface to be scanned on the recording medium and performs writing scanning by deflecting the recording medium at a period of .

Usually, the above-mentioned rotary scanner of this optical scanner is
It is designed to be rotationally driven by a driving means such as a synchronous motor, and in this case, the driving means must have a high-speed rotation function or must not cause uneven rotation. In particular, if rotational unevenness occurs in the drive motor, this is one of the causes of a decrease in writing scanning accuracy.

When a synchronous motor is used as the drive means, rotation has conventionally been stabilized by frequency-dividing a stable frequency output signal from a crystal oscillator and inputting this to the drive power source. However, when driving a load with constant torque using this method, a steady rotation speed can be obtained, but when the load torque fluctuates for some reason, the synchronization as a synchronous motor is lost and the rotation speed is reduced. It has the disadvantage of causing unevenness. In addition, the synchronous SMOSE itself is expensive and requires a mechanical speed increasing mechanism, which makes the entire device expensive. On the other hand, in addition to such drive means, there are methods using servo motors, DC motors, etc. that can rotate at high speed, but these have the drawback of lacking rotational stability.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide an inexpensive rotation control device for a rotary scanner that is capable of high-speed rotation and provides a stable rotational speed.

The present invention will be explained below with reference to illustrated embodiments.

FIG. 1 shows a schematic configuration diagram of an optical scanner, in which reference numeral 1 is a laser light source, numerals 2 and 3 are reflecting mirrors, numeral 4 is a convergence lens, numeral 5 is an optical modulator, 6 is an image control system, 7 is a lens, 8 is a beam expander 8, 9 and 14 are cylindrical lenses, 11 is a rotating scanner having n deflection surfaces, and 12 is a rotating scanner. Reference numeral 13 indicates an fθ lens system, and reference numeral 15 indicates a recording medium. In the figure, a laser beam emitted from a laser light source 1 is reflected by reflecting mirrors 2 and 3, then transmitted through a lens 4, focused, and incident on an optical modulator 5.

On the other hand, the image control system 6 is configured to receive an image signal obtained by converting the image of the document into a signal, and the signal, which is made into a high frequency and amplified by the image control system 6, is sent to the optical modulator 5. applied. The laser light incident on the optical modulator 5 is intensity-modulated in accordance with this applied signal. This laser beam is transmitted through lens 7,
It passes through the beam expander 8 and the cylindrical lens 9, enters the rotating polygon mirror 11 as a rotating scanner, is reflected, and then enters the fθ lens system 13.
The light passes through the cylindrical lens 14 and is focused on a single point on the scanned surface of the drum-shaped recording medium 15.

The rotating polygon mirror 11 is a regular polygon with a mirror surface on its peripheral surface, and is fixed to the shaft 12a of a DC motor 12 having high-speed rotation characteristics. The rotating polygon mirror 11 is rotated at high speed at a predetermined angular velocity in the direction of the arrow by the driving action of the DC motor 12 .

The rotating polygon mirror 11 and the DC motor 12 constitute a means for deflecting the laser beam, and as the rotating polygon mirror 11 rotates, the angle of incidence of the laser beam at the incident part changes continuously, so that the reflected laser beam is deflected continuously in one plane. Moreover, since the above-mentioned deflection is repeated every time the mirror surface in the incident section is switched, the laser beam is periodically deflected within one plane. In other words, if the rotating polygon mirror 11 has eight mirror surfaces, the beam light is transmitted through the rotating polygon mirror 1.
1 is periodically deflected eight times for one rotation. And, due to this deflection,
A drawing scan is performed on the recording medium 15 rotating in the direction of the arrow.

By the way, it has already been mentioned that a DC motor is used as a driving means for the rotating polygon mirror 11, but in this case, by using such a DC motor, high-speed rotation that can cope with the above-mentioned deflection effect can be achieved. Moreover, since it does not require a speed increasing device etc. when using a synchronous motor,
The entire device can be made inexpensive.
However, due to the characteristics of the DC motor, there is a problem of lack of stability in rotation, such as uneven rotation.

Such factors or factors such as variations in the parallelism of the individual plane mirror surfaces of the rotating polygon mirror 11 with respect to the rotation axis cause errors in scanning. For example, as shown in FIG. 2, the polarized laser beams reflected in order from the individual flat mirror surfaces 11a, 11b, and 11c are projected onto the scanned surface of the recording medium 15 in a state in which variations occur.

Therefore, in FIG. 1, a beam position detection element 16 such as a photodetector is provided in the optical scanner shown in the vicinity of one end of the recording medium 15 and on the deflection plane of the laser beam. The beam position detection element 16 plays the role of starting reading of the information image of the document. That is, when a laser beam is incident on the detection element 16, a synchronization signal is output from the detection element 16, and after this signal is input to the image control system 6 and amplified, it is used as a drive pulse to generate an image for reading the document image. applied to a sensor (not shown).

Then, reading by the image sensor is started by this application, and this read image signal is input to the image control system 6, and the intensity-modulated laser light is polarized through the above-mentioned process to record the image. A writing scan on the body 15 is performed. In other words, reading and writing are performed in synchronization.

By the way, if the rotating polygon mirror 11 has n mirror surfaces, the detection element 16 will detect the laser beam n times for each rotation of the polygon mirror 11. In other words, the detection element 16 outputs n pulses for each rotation of the rotating polygon mirror 11. This output signal is input to the frequency divider 17, and if the frequency division characteristic of this frequency divider 17 is set to 1/n, the output signal from the frequency divider 17 is as shown in FIG. One pulse is output for each rotation of the rotating polygon mirror 11. This repetition has periodicity.

Therefore, if the rotating polygon mirror 11 rotates N times per second, the frequency of the output signal from the frequency divider 17 will be NHz. This signal is input to the phase detector 18. Here, reference numeral 19 indicates a crystal oscillator, and reference numeral 2 indicates a crystal oscillator.
0 indicates a frequency divider, and these and the phase detector 18 and the like constitute a so-called phase lock loop.

Now, if the oscillation frequency of the crystal oscillator 19 is fHz, when this fHz output signal is passed through the frequency divider 20 having a frequency division characteristic of 1/M, the output frequency will be f/
It becomes M. The output signal of this frequency becomes a reference signal for normalizing the rotation speed of the DC motor 12 to a steady value, and is input to the phase detector 18.

Here, as shown in FIG. 2, the rotating polygon mirror 11
If scanning errors are caused by factors such as uneven rotation of the rotating polygon mirror and variations in the parallelism of the individual plane mirror surfaces of the rotating polygon mirror to the rotation axis 12a, then the output signal from the frequency divider 17 is as follows. This results in a delay or lead with respect to the reference signal from the other frequency divider 20. That is, a phase difference will occur between these two signals. This phase difference is detected by the phase detector 18.

Now, assuming that an error occurs in the output signal from the frequency divider 17, the phase lock loop operates so that the relationship between this error signal N and the reference signal f/M becomes N=f/M. This point will be described in more detail below.
2 have characteristics as shown in FIG. 4, for example, if the rotational speed of the DC motor 12 changes for some reason, a phase difference will naturally occur. Here, in FIG. 4a, the phase detector 1 when no phase difference is generated.
Let the output voltage of 8 be V ₀ . Now, if the rotational speed of the motor 12 slows down and a phase lag occurs, the output voltage will increase in proportion to the amount of lag relative to the reference voltage V ₀ when no phase difference occurs. do. This signal is input to the motor drive control system 21 shown in FIG. 1 to increase the rotational speed of the motor.

When the rotation of the motor is accelerated and reaches a steady rotation speed, the reference signal from the crystal oscillator 19 and the signal from the frequency divider 17 match each other in frequency and phase, and therefore the signal is detected by the phase detector 18. The detected phase difference becomes 0. Then, the motor 12 is maintained at a constant rotation speed using the reference voltage V ₀ . Note that when the rotation of the motor becomes faster and the phase advances, the output voltage of the phase detector 18 becomes equal to the reference voltage V ₀
Therefore, the rotational speed of the motor is correspondingly slowed down, and when the steady rotational speed is reached, the phase difference becomes 0. In this way, the rotation speed of the motor is constantly detected, and if a phase difference occurs,
By feeding this back to the motor drive control system 21, the operating system is controlled so that the frequency phase maintains a constant relationship, so that the rotation of the motor, so to speak, the rotation of the rotating polygon mirror can be kept stable.

In addition, in the embodiment of the present invention, the rotating polygon mirror 1
The frequency divider 17 outputs n signals per rotation of the beam position detection element 16.
It has the advantage that one pulse is outputted from the circuit, and this pulse is supplied to the phase detection control system at a precise period. On the other hand, if the signals from the detection element 16 are used as they are, there is a drawback that the pitch intervals of each signal will be uneven due to accuracy errors of each plane mirror surface of the rotating polygon mirror 11, which will impede the phase detection control function. There is a risk.

As described above, according to the present invention, it is possible to provide an inexpensive rotation control device for a rotary scanner that is capable of high-speed rotation, provides a stable rotation speed, and does not require a speed increasing mechanism as in the conventional example. can.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of an optical scanner to which the present invention is applied, Fig. 2 is a plan view showing the relative relationship between a rotating polygon mirror and a recording medium to explain scanning errors, and Fig. 3 is a plan view of the present invention. Signal waveform diagrams of the signal system used in the embodiment, FIGS. 4a and 4b are characteristic diagrams showing the characteristics of the phase detector and the drive motor, respectively. 11... Rotating scanner, 12... Drive motor, 1
5...Recording body, 16...Beam position detection element, 1
7... Frequency divider, 18... Phase detector.

Claims (1)

[Claims] 1. Read an information image, convert it into an image signal, intensity-modulate a laser beam from a laser light source using an optical modulator according to the image signal, and transmit the intensity-modulated laser beam to a drive motor. The reflected light from this rotating scanner is focused onto the scanned surface of the recording medium, and the reflected light is An optical scanner that scans a surface to be scanned on a recording medium and performs write scanning by deflecting the laser beam at a constant cycle, and detects the laser beam deflected by the rotary scanner every cycle, In a rotation control device for the rotary scanner in an optical scanner including a beam position detecting element that starts reading the information image, the beam position detecting element outputs one pulse every time the rotary scanner rotates once. a frequency divider having a frequency division characteristic of 1/n for dividing an output signal from the rotary scanner; a motor drive control system for rotating a drive motor that rotates the rotary scanner at a predetermined angular velocity at a predetermined angular velocity; Directly detects the phase difference between the output signal from the frequency divider and the reference signal for determining the rotation speed of the drive motor at a steady value, and outputs a signal corresponding to the phase difference, A rotation control device for a rotary scanner comprising a phase detector for bringing the rotation speed of the drive motor to a steady value based on this phase difference.