JPH01154018A - Light beam deflector driving device - Google Patents

Abstract

PURPOSE:To suppress the shift of displacement of a piezoelectric actuator element to the minimum by matching forcibly a voltage of the piezoelectric actuator with a specified voltage the instant an inputted AC signal voltage takes a prescribed value, controlling the charge quantity of a monitor capacitor and controlling the charge quantity of the piezoelectric actuator element. CONSTITUTION:A leakage resistance 62 of a piezoelectric actuator element 13 has such a quality as it is varied against an applied voltage, and a leakage current has an hourly variation although it is a little. That is, a small leakage current which cannot be obviated by a constant-current is generated. In order to eliminate a shift of the charge quantity of a monitor capacitor 14 and the piezoelectric element 13, which is generated by such a minute leakage current, a charge/discharge circuit 64 is provided, and it is controlled by charging or discharging periodically the piezoelectric actuator element 13. In such a way, a shift of an input signal and displacement caused by a hysteresis of displacement against a voltage of the piezoelectric actuator element 13 can be suppressed to the minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a device for driving a deflection mirror of a light beam deflector used in an optical scanning device or the like using a piezoelectric actuator element.

[Prior art and its problems] Optical scanning to record high-precision images @Stomach light beam reflects and scans the light beam due to differences in surface tilt w4 of the rotating polygon mirror, precession of the rotation axis, or photosensitive material feeding speed Due to fluctuations in the projection angle, etc., a shake occurs in the sub-scanning direction with respect to the desired projection position on the photosensitive material.

Incidentally, even in such a light beam scanning device, there is a growing demand for a high-precision device that can not only output characters but also output halftone dots of wJm images in photographs and the like. In order to meet this request, for example, 64 lines (is, eμm/1 line) to 128 lines (7,8μm/1 line) per 11II.
Therefore, it is necessary to perform rask scans of the order of m/1 scan. Moreover, in order to obtain an image free from unevenness such as so-called moire, it is necessary to maintain the pitch of each scanning line with high precision. In general, pitch accuracy of 1/4 to 115 of a scanning line pip or less is required for uniform, high-quality output, so in the above case, pitch accuracy of 1 to 3 μ or less is required. It won't happen.

Moreover, it is required to correct the blur in accordance with the detected shake amount within a short period of time from when the light beam passes over the shake amount detector until the light beam reaches the photosensitive material. Since piezoelectric actuator elements can produce displacement with high precision in a short response time, the angle of the deflection mirror of the light beam deflector is changed using the piezoelectric actuator element as a driving source.
It is desired to correct the deflection of the light beam by controlling the traveling direction of the light beam reflected on the deflection mirror.

However, the displacement of the piezoelectric actuator element has hysteresis with respect to the applied voltage. (1) in FIG. 4 is a graph representing the relationship between the voltage (2) and the displacement (X) of the piezoelectric actuator element. The relationship between displacement and voltage when the applied voltage is gradually increased from O is the curve A of (υ) in Figure 4. The curve B is when a certain voltage is reached and the voltage is gradually lowered. .

Curve C shows that the voltage is increased again. In this way, even if the applied voltage is the same, the displacement of the piezoelectric actuator element will differ depending on the difference in the voltage history.

On the other hand, since the light beam deflection correction signal is given in the form of alternating current, it is desired that the control circuit characteristic is a displacement that depends only on the current command value, regardless of past command values. Therefore, in order to use a piezoelectric actuator element as a drive source for a light beam deflector, it is necessary to solve the problem of hysteresis in voltage-displacement characteristics.

[Means for solving the problem] By the way, it is known that the displacement of a piezoelectric actuator element is proportional to the amount of charge accumulated at both ends of the piezoelectric actuator element, and that the displacement does not have hysteresis with respect to changes in the amount of charge. There is. 4 in FIG. 4 is a graph showing the relationship between the amount of charge Q and the displacement X. That is, by measuring the amount of charge of the piezoelectric actuator element, the current accurate displacement can be estimated, and the displacement can be I-controlled by adjusting the amount of charge.

In order to achieve this, the present invention provides a light beam deflector control circuit that uses a piezoelectric actuator element as a drive source to minutely change the angle of a deflection mirror to change the traveling direction of a light beam. a load circuit coupled in series, and a negative feedback circuit that drives the load circuit using the input AC correction signal VA as a command signal and using the capacitor applied voltage taken out from the connection point of the load circuit as a negative feedback signal. , a charging/discharging circuit that brings the voltage applied to the piezoelectric actuator element close to a preset voltage value at the moment when the voltage value of the correction signal VA takes a predetermined value; and a leakage current of the piezoelectric actuator element and the monitor capacitor. and a constant current circuit that generates a current that cancels out the correction signal VA.
The present invention is characterized in that the displacement of the piezoelectric actuator element is controlled based on the following.

[Embodiment 1] First, an embodiment of a light beam scanning device using a light beam deflector driving device according to the present invention will be described with reference to FIG.

51 is a light beam oscillator, and 52 is a light beam emitted from the light beam oscillator 51. The traveling direction of the light beam 52 is changed by a light beam deflector 53. Furthermore, light beam 5
2 is reflected by a rotating polygon mirror 54 and scans on a photosensitive material 56.

The main scanning direction of the light beam 52 is indicated by an arrow 57. An f-theta lens 55 is provided between the rotating polygon mirror 54 and the photosensitive material 56 to correct the scanning of the light beam over the photosensitive material at a constant speed. A shake amount detector 59 is provided to detect the shake amount in the sub-scanning direction 58 caused by a surface tilt error of the rotating polygon mirror 54.

In accordance with signals from the shake amount detector 59 and the encoder 511, the control unit 510 sends a correction signal to the light beam deflector 53 to slightly change the traveling direction of the light beam 52 to correct shake in the sub-scanning direction. The encoder 511 detects fluctuations in the feeding speed of the photosensitive material. Light beam deflector 5
3 consists of a deflection mirror, piezoelectric actuator elements for changing the tilt of the deflection mirror, and their supports. Then, the angle of the mirror is changed using the displacement of the piezoelectric actuator element to control the traveling direction of the light beam. The device of the present invention is a drive device for a light beam deflector, which includes a piezoelectric actuator element which is a drive source for the light beam deflector, and a circuit for controlling the piezoelectric actuator element. Note that FIG. 5 is an example of implementation, and it is obvious that the various optical systems 54 and 55 and the sensitive material 56 can be replaced with other ones, and the present invention is not limited to these.

The present invention will be explained in detail with reference to FIGS. 1 and 2.

FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows signal waveforms at each point (1) to (8) of the circuit shown in FIG.

The circuit shown in FIG. 1 can be divided into four parts in terms of function. - The portion 1 surrounded by the dotted chain line is a circuit that amplifies the input signal and applies a driving voltage to the piezoelectric actuator element 13 in accordance with the signal. Portion 2 is a constant current circuit that supplies a current that cancels out leakage current that slightly leaks from each element. Portion 3 is configured to bring the voltage of piezoelectric actuator element 13 closer to a preset voltage.
This is a circuit that charges or discharges the piezoelectric actuator element 13. Part 4 is a circuit that emits a sine wave signal when no signal is input.

Now, in part 1 of FIG. 1, the input signal VA (see υ in FIG. 2) is combined with the bias voltage Vo and amplified by the amplifier 11. According to the signal, the amplifier 12 applies the drive voltage P⊂ to one input terminal of the piezoelectric actuator element 13 . Charge is accumulated in the piezoelectric actuator element 13 according to the drive voltage P■. At the same time, the same amount of charge is stored in the monitor capacitor 14 connected in series to the other input terminal of the piezoelectric actuator element 13. The voltage on the monitor capacitor 14 is input to the amplifier 12 as a negative feedback signal so that the voltage waveform on the monitor capacitor 14 follows the input signal VA. Further, it is considered that the voltage of the monitor capacitor 14 is approximately proportional to the amount of charge thereof. Therefore, said part 1
The basic operation of the circuit shown in FIG. 1 is to apply a change in the charge layer to the piezoelectric actuator element 13 in accordance with a change in the input signal VA. In other words, the amount of charge of the piezoelectric actuator element maintains a linear relationship with respect to the input signal VA. Therefore, the displacement of the piezoelectric actuator element maintains a linear relationship with respect to the input signal VA without having hysteresis.

However, the voltage across the piezoelectric actuator element 13 differs in the amount of charge between the piezoelectric actuator element 13 and the monitor capacitor 14 due to accumulation of charge due to leakage current. The constant current circuit in the portion 2 surrounded by the dashed-dotted line cancels this leakage current.

However, in a constant current circuit, it is not possible to completely cancel out a very small leakage current that changes over time.The circuit in part 3 cancels out the t1 charge that accumulates in the piezoelectric actuator element 13 due to such a small leakage current. be.

The drive voltage PV of the piezoelectric actuator element 13 and the voltage of the monitor capacitor 14 are input to the differential amplifier 15,
The differential amplifier 15 detects the voltage applied to the piezoelectric actuator element 13. The voltage output from the differential amplifier 15 is input to the comparator 16. The voltage input to the comparator is compared with a preset voltage Vs, and when the input voltage>Vs, a HIGH signal is output and data is input to the flip 70 knob 17. Flip-flop 17, in the illustrated embodiment, is a D-type flip-flop (DFF) having two inputs: a data signal and a clock signal for timing its latching.

On the other hand, an input signal of 9 VA is input to the amplifier 18, and the amplifier 1
8 outputs a signal (ω (see figure 2)).

The output signal (3) is converted into a monostable multivibrator-19.
input as a trigger. The signal (4) output from this monostable multivibrator 19 and the signal (
3), a pulse-like signal (0) is obtained.In other words, the monostable multivibrator 19 has been returned to a stable state after a predetermined time has elapsed since the previous operation, and the input signal VA is When it passes through O and indicates a positive value, one pulse signal of the signal (2) is output.Then, this pulse-like signal (0 is input as the clock signal of the flip 70 knob 17. is input to the monostable multivibrator 110 as a trigger.

The flip-flop 17 latches and outputs the state of the data signal at the moment when the pulse of the clock signal is input. The output signal of the flip 70 knob 17 is ANDed with the output signal (6) of the monostable multivibrator 110, and the switch 111 on the high potential side and the switch 112 on the low potential side are turned ON-OFF, and the piezoelectric actuator 13
bring the voltage closer to the set value. That is, when the voltage across the piezoelectric actuator element is higher than the voltage Vs, the switch 112 on the low potential side is turned on to lower the voltage. When the voltage across the piezoelectric actuator element is lower than the voltage Vs, the switch 111 on the high potential side is turned on to increase the voltage. In this way, the voltage of the piezoelectric actuator element 13 is brought closer to the set value intermittently with a period longer than the operating time of the monostable multivibrator 19.

The part 4 surrounded by the one-dot chain line is a circuit that always supplies a sine wave signal in place of the signal qvA when it is not input. is output. The enable signal input from the ENB is ANDed with the signal from the switch (SW3) to control SWl. When the VA double signal is not input, the enable signal turns ON and SWl
is turned off, and conversely, SW2 is turned on to supply a sine wave.

In other words, when the input signal VA is interrupted, the signal voltage frequently passes through 0■, and a signal is created by inputting a signal that is not far from around 0■, and the amount of charge of the piezoelectric actuator element due to part 3 frequently increases. so that it is corrected to
A voltage near half the maximum displacement is always applied to the piezoelectric actuator element. This is to prevent the voltage across the piezoelectric actuator element from changing suddenly when the input signal is turned off and the input is restarted again.

SW3 is one point! This switch is used to set the current of the constant current circuit in the portion 3 surrounded by the line II. SW3
When turned on, both SWI and SW2 are turned off, the operation of the monostable multivibrator 110 is prohibited, and the switches 111 and 112 are disconnected. In such a state, after applying an appropriate drive voltage PV to the piezoelectric actuator element, the current of the constant current circuit is set so that the amount of charge of the piezoelectric actuator element 13 remains equal to the charge of the monitor capacitor 14. do.

The function of the circuit of the present invention will be explained using FIGS. 3 and 6. FIG. 6 is a simplified circuit of the circuit shown in FIG. The signal voltage input to the amplifier 12 is obtained by negative feedback of the input (signal voltage (voltage at point A) obtained by applying a bias voltage to the nth VA) and the voltage at point D. , outputs a voltage that equalizes the voltage at point D.

Reference numeral 61 indicates a component functioning as a capacitor of the piezoelectric actuator element, and reference numeral 62 indicates a component functioning as a leakage resistance R of the piezoelectric actuator element. Reference numeral 63 indicates a constant current circuit in section 2 of FIG. 1, and 64 indicates a charging/discharging circuit in section 3.

Immediately after inputting the signal voltage (time 1-0>), no charge is accumulated due to leakage current.Since the capacitor component 61 of the piezoelectric actuator element and the monitor capacitor 14 are connected in series, the amount of charge of each is equal. The charge amount of the capacitor component 61 of the piezoelectric actuator element and the monitor capacitor 14 at time 1=0
Then, Qo=CMV.

becomes. CM is the capacitance of the monitor capacitor 14, and Vo is the capacitance of the monitor capacitor 14 at time 1-0.
voltage.

However, as time passes, the piezoelectric actuator element 61 is discharged due to leakage current due to the leakage resistance 62 of the piezoelectric actuator element, and the voltage across the piezoelectric actuator element 61 decreases. On the other hand, since the voltage of the monitor capacitor 14, that is, the potential at point D, is maintained the same as the voltage at point A, the monitor capacitor 14 and the capacitor component 61 of the piezoelectric actuator element
There will be a difference in the voltage. The difference increases over time until it reaches the limit of what the amplifier 12 can supply, making it impossible to control the charge on the piezoelectric actuator element. Therefore, it is necessary to provide a constant current circuit 63 that supplies a current that cancels out the leakage current caused by the leakage resistor 62.

However, the leakage resistance 62 of the piezoelectric actuator element has a property of changing depending on the applied voltage. Therefore, the leakage current has a slight change over time.

In other words, a slight leakage current occurs that cannot be eliminated with a constant current. In order to eliminate the difference between the charges of the monitor capacitor 14 and the piezoelectric actuator element caused by such a minute leakage current, a charging/discharging circuit 64 is provided to periodically charge or discharge the piezoelectric actuator element 13 for adjustment. .

The graph in Figure 3 (1) shows that if the leakage current is not canceled out,
3 shows a temporal change in the amount of charge discharged in the piezoelectric actuator cord 13. The charge of the piezoelectric 7cutuator element 13 decreases by the amount of discharge.

Direct mA in the graph indicates the total discharge charge amount. Since straight line A shows a straight line macroscopically, it can be canceled out by constant current.

Straight line B is the amount of charge due to the leakage current component which varies from time to time out of the total amount of discharged charge shown by the straight line.

It is extremely difficult to completely cancel out such a minute leakage current that changes over time with a constant current. Therefore, by charging or discharging the piezoelectric actuator element 13 in a pulsed manner at certain intervals as shown in part 3 of FIG. Keep the amount of charge the same.

It is also possible to omit the constant current circuit of part 2 and correct the charge difference of the piezoelectric actuator element 13 using only the charging/discharging circuit of part 3. However, if the 71 load of the piezoelectric actuator element is corrected only by the circuit of this part 3, charging and discharging with large swings will frequently occur as shown in (■) in FIG. Since there is a linear relationship between the amount of charge and the displacement of the piezoelectric actuator element, a sudden change in charge is the result of a sudden swing of a light beam in an optical scanning device or the like. A sudden deflection of the light beam causes uneven scanning, which is undesirable. Therefore, the circuit of part 2 cancels out most of the leakage current, and then charges or discharges the amount of charge in the piezoelectric actuator element 13, which changes due to the leakage current that cannot be canceled out and adjusts by charging or discharging. Then, (
As shown in (2), the time constant of the change in the amount of charge due to the leakage current accumulated in the piezoelectric actuator element 13 becomes extremely long, and the cycle of charging and discharging can also be improved, making it possible to maintain light beam scanning with less deflection. .

Incidentally, if the leakage current from each element is very small and the electric charge m of the piezoelectric actuator element 13 can be sufficiently corrected by the circuit of part 3, the constant current circuit of part 2 may be omitted.

[Effects of the Invention] As described above, according to the present invention, the voltage of the piezoelectric actuator element is forcibly adjusted to the specified voltage at the moment when the input AC signal voltage takes a predetermined value, and the voltage of the monitor capacitor 14 is ffi? By controlling the charge of the piezoelectric actuator element by controlling 7ffi, it is possible to minimize the deviation between the input signal and the displacement due to the hysteresis of the displacement with respect to the voltage of the piezoelectric actuator element.

[Brief explanation of the drawing]

FIG. 1 is an embodiment of the present invention, FIG. 2 is a signal waveform explaining the embodiment, FIG. 3 is a diagram explaining the function of the circuit in FIG. 1, and FIG. 4 is a diagram showing the characteristics of the piezoelectric actuator element. , FIG. 5 is a diagram showing an outline of the implementation of the present invention, and FIG. 6 is a simplified diagram of the circuit of FIG. 1. 1: Drive voltage application circuit 2: Constant current circuit 3: Charging/discharging circuit 4: Sine wave signal circuit 11: Amplifier 13: Piezoelectric actuator element 14: Continuous contact 16: Comparator 17: Flip flop 19: Monostable multivibrator 51: Optical Beam oscillator 53: Light beam deflector 54: Rotating polygon mirror 56: Sensitive material 59: Deflection detector

Claims (1)

[Claims] (1) In a drive device for a light beam deflector that uses a piezoelectric actuator element as a drive source to minutely change the angle of a deflection mirror to change the traveling direction of a light beam, the piezoelectric actuator element and a monitor capacitor are coupled in series. a load circuit; a negative feedback circuit that drives the load circuit by using the input AC correction signal VA as a command signal and using the capacitor applied voltage extracted from the connection point of the load circuit as a negative feedback signal; and the correction signal VA. a charging/discharging circuit that brings the voltage applied to the piezoelectric actuator element close to a preset voltage value at the moment when the voltage value of the piezoelectric actuator element takes a predetermined value; a constant current that generates a current that cancels the leakage current of the piezoelectric actuator element and the capacitor; A light beam deflector driving device comprising: a circuit; and controlling displacement of a piezoelectric actuator element based on the correction signal VA.