JPS5952451B2 - optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical scanning device, and particularly to an optical scanning device that performs scanning by driving an optical system with a vibrator that generates torsional vibration.

An infrared imaging device optically scans an object with a narrow instantaneous field of view, and obtains a video signal by inputting the infrared rays that have passed through the scanning system into an infrared detector and photoelectrically converting them.

This optical scanning is performed by the rotational movement of a scanning mirror, which is usually of the flat type. Conventionally, in the optical scanning line of an infrared imaging device, a plane mirror is driven using electric-mechanical energy from a drive source having an oscillation circuit that oscillates at a period close to an integer ratio with the natural vibration period of a torsional oscillator. For example, by driving the vibrator with a solenoid, a natural vibration is applied, and the object is scanned with this vibration period.

In this method, the mechanical resonance frequency of the vibrator changes due to factors such as changes in air resistance due to ambient temperature, external noise, and atmospheric pressure fluctuations, and the vibration period and vibration amplitude (torsion angle) of the scanning mirror change accordingly. There was a problem in that the infrared image on the display screen was disturbed due to changes in the amount of light.

In addition, as a measure to deal with the fluctuation of the mechanical resonance frequency of the vibrator due to the environmental change as described above, for example, as shown in Japanese Patent Laid-Open No. 47-28937, the scanning mirror is driven by detecting its vibration phase. It has also been proposed to maintain the vibration amplitude of the scanning mirror constant by providing a feedback loop in the circuit and controlling the phase of the drive signal to follow changes in the resonance frequency. Because there was a lack of consideration to prevent this, the imaging system of an infrared imaging device for the purpose of displaying images still had the drawback of causing blurring in the displayed image. The present invention has been made in view of the above points, and includes driving an optical system by a vibration system that performs torsional vibration, and supplying the vibration energy from a signal generation circuit that forcibly cycles the vibration energy to its own oscillation period. Furthermore, the present invention provides an optical scanning device that uses automatic phase control to correct phase shifts in electrical circuits and mechanical systems, detects the amplitude of the vibrator, and returns it to the drive source, and has little variation in scanning angle. .

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

FIG. 1 shows a system diagram of an embodiment of an optical scanning device according to the present invention. Reference numeral 1 denotes a metal rod having one end fixed to perform torsional vibration, and is referred to as a vibrator.

The vibrator 1 is driven by an electromagnetic system consisting of a solenoid coil 2 and an iron piece 3 attached to the vibrator 1. That is, the iron piece 3 receives torsional stress due to the current applied to the solenoid coil 2, and when the current is cut off, it returns to its original state due to its elasticity. Therefore, the vibrator is driven by the voltage cycle supplied to the solenoid coil 2 to perform torsional vibration, and the scanning mirror 4 attached to the vibrator performs optical scanning. The period of the voltage supplied to the solenoid coil 2 is determined by a reference synchronization signal source 9. In this embodiment, the reference synchronization signal source 9 is a rectangular wave signal generator with a constant duty ratio, which is well known. A gate signal is generated by the gate signal generating circuit 5 which detects the vibration of the vibrator 1, and the swing angle and phase of the vibrator 1 are controlled by this gate signal as described later. After the power is turned on, when the vibrator 1 is not performing the desired vibration, the gate signal generation circuit 5 does not generate a gate signal, so the phase comparator circuit 11 outputs a constant DC voltage determined by the reference synchronization signal. Output.

When the DC voltage that has passed through the low-pass filter 12 is input to the voltage controlled oscillator 13, a rectangular wave voltage synchronized with the reference synchronization signal is generated. Note that the phase comparator circuit 11. The low-pass filter 12 and the voltage controlled oscillator] 3 are commonly used in PLLs and are well known. The rectangular wave voltage generated by the voltage controlled oscillator 13 is transferred to the waveform conversion circuit 14.
After being converted into a sine wave voltage, the voltage is applied to the multiplier 15.
The amplitude control signal, which is another input to the multiplier 15, is applied to the gate circuit 10, the counter circuit 17, and the D/A converter 18 by the reference synchronization signal and the clock signal from the clock signal source 8.
is created and maximizes the multiplier output signal. As a result, the vibrator quickly shifts from a stationary state to a steady vibration state. The multiplier output signal is amplified to a required amplitude by the amplifier circuit 16, and when applied to the drive solenoid 2, the vibrator 1 and the scanning mirror 4 begin to vibrate. The gate signal generation circuit 5 detects the movement of the scanning mirror due to the vibration of the vibrator.
generate a gate signal with a repetition period equal to the motion of . In this way, the gate signal generation circuit 5 constitutes a vibration detection system that detects vibrations in the vibration system and converts them into electrical signals. To detect motion, it is sufficient to use a transducer that generates a voltage or current that is approximately proportional to the displacement of the moving body, and many types of such transducers are already well known, such as electromagnetic, piezoelectric, and photoelectric conversion methods. Any suitable one may be selected and used among these. The gate signal generated by the gate signal generation circuit 5 is sent to the gate circuit 7 and the gate circuit 10 to control the phase and vibration angle of the vibration of the vibrator 1. In other words, when the vibrator 1 begins to vibrate, the gate signal generated by the gate signal generation circuit 5 is transmitted to the gate circuit 7 and the gate circuit 1.
0, and the motion of the vibrator, hitherto controlled only by the reference synchronization signal, is now subject to phase control and swing angle control.

That is, the phase of the vibrator is controlled by the gate signal sent to the gate circuit 7, and the swing angle of the vibrator is controlled by the gate signal sent to the gate circuit 10. The gate circuit 7 feeds back a part of the output signal of the voltage controlled oscillator 13 to the phase comparator circuit 11 under the control of the pulse extinction detection circuit 6 during a period when no gate signal is generated, and sends it to the vibrator driving solenoid 2. The phase of the drive signal is made to match the phase of the reference synchronization signal.

Next, when a gate signal is output from the gate signal generation circuit 5 as the vibrator 1 vibrates, the gate circuit 7 sends only the gate signal to the phase comparator circuit 11 by the action of the pulse extinction detection circuit 6. The phase comparison circuit 11 generates a difference signal voltage according to the phase difference between the reference synchronization signal and the gate signal. The low-pass filter 12 has a function of attenuating high frequency components included in the difference signal voltage and improving interference signal removal characteristics. The difference signal voltage that has passed through the low-pass filter 12 has a control function that matches the oscillation frequency of the voltage controlled oscillator 13 with the frequency of the reference synchronization signal, so even if there is a phase difference between the gate signal and the reference synchronization signal, this A PLL that eliminates this will be constructed. Voltage controlled oscillator 13
The rectangular wave output signal is converted into a sine wave by the waveform shaping circuit 14.

Such a waveform shaping circuit 14 can be constituted by an active feeder consisting of a low frequency filter and a notch filter. In the multiplier 15, the amplitude of the sinusoidal signal is D/
Based on the swing angle control signal sent from the A converter 18. The amplitude of the output signal from the multiplier 15 decreases as the vibration angle of the vibrator increases, and the amplitude of the output signal from the multiplier 15 increases as the vibration angle decreases. Become.

This point will be discussed in detail later. Therefore, amplifier circuit 1
The solenoid drive signal amplified in step 6 is always in phase with the reference synchronization signal, and is controlled so that the vibration angle of the vibrator is constant. Here, the above-mentioned swing angle control signal will be described.

When the vibrator 1 has not started to vibrate, that is, during the period when the gate signal generation circuit 5 is not generating the gate signal,
Under the control of the pulse extinction detection circuit 6, the gate circuit 10
The number of pulses of the clock signal during one period of the reference synchronization signal is sent to the counter circuit 17. In this case, the periods of the reference synchronization signal and clock signal are always held constant, so
Since the count in the counter circuit is always constant, the magnitude of the swing angle control signal, which is the output signal of the D/A converter 18, is also constant.

Since the amplitude of the output signal of the multiplier 15 at this time is set to be maximum, the vibrator 1 obtains a large amount of energy and promptly starts a predetermined vibration. As a result, when a gate signal is generated in the gate signal generation circuit 5 due to the vibration of the vibrator 1, the gate circuit 10 generates a clock signal during a period corresponding to the vibration angle of the vibrator 1 under the control of the pulse extinction detection circuit 6. The number of pulses is sent to a counter circuit 17 and counted. If the vibration angle of the vibrator increases for some reason, the number of pulses of the clock signal counted by the counter circuit 17 will increase, and the vibration angle control signal output from the D/A converter 18 will decrease accordingly. and the output signal of the multiplier 15,
That is, the amplitude of the solenoid drive signal becomes smaller, and the solenoid drive signal becomes smaller, so that the vibration angle of the vibrator 1 is controlled to become smaller. Conversely, when the vibration angle of the vibrator 1 becomes smaller, contrary to the above case, the amplitude of the output signal of the multiplier 15 increases, so the vibrator 1 is energized with large energy and vibrates with a large vibration angle. be controlled. As is clear from the above description, the present invention detects the vibration of the scanning mirror to obtain an electrical signal, and compares this with the phase of the reference synchronization signal to constantly maintain the vibration frequency of the scanning mirror constant. This phase control results in the scanning mirror's actual vibration frequency being detuned from the mechanical resonance frequency of the torsional oscillator, which changes with environmental changes. It is characterized by the provision of an oscillation angle control loop that compensates for changes in the vibration amplitude of the scanning mirror, and these control loops keep the vibration frequency and vibration amplitude of the scanning mirror constant regardless of changes in the surrounding environmental conditions. Therefore, a high quality display image can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram showing an embodiment of an optical scanning device using a torsional oscillator according to the present invention. 1: Torsional vibrator, 2: Solenoid coil, 3: Iron piece,
4: Scanning mirror, 5: Gate pulse generation circuit, 6: Pulse extinction detection circuit, 7 Regate circuit (1), 8: Tarock signal source, 9: Reference synchronization signal source, 10: Gate circuit (2), 1
1: Phase comparison circuit, 12° low-pass filter, 13 Voltage controlled oscillator, 14: Waveform shaping circuit, 15: Multiplier, 16: Amplifier, 17: Counter circuit, 18: D/A converter.

Claims (1)

[Claims] 1. A drive circuit having a torsional oscillator, a scanning mirror fixed to the torsional oscillator, a reference synchronous signal source that oscillates at a frequency that is approximately an integer ratio to the natural frequency of the torsional oscillator, and the drive circuit. an electromagnetic system for energizing the torsional vibrator with a drive signal from the scanning mirror; a vibration detection system for detecting vibration of the scanning mirror and converting it into an electric signal; and an output signal of the detection system and the reference synchronization signal source. a phase control system that controls the phase of the drive signal applied to the electromagnetic system by comparing the phase with a synchronization signal from the detection system; and an oscillation angle control system that controls a drive signal applied to the electromagnetic system, and the phase control system synchronizes the vibration of the scanning mirror with respect to the reference synchronization signal, and the oscillation angle control system synchronizes the vibration of the scanning mirror with the reference synchronization signal. An optical scanning device characterized in that the swing angle is controlled.