JPS6023544B2 - optical scanning device - Google Patents

Description

Detailed Description of the Invention 'a} Technical Field of the Invention The present invention relates to an improvement in an optical scanning device, and in particular to a method for stabilizing the vibration of a scanning mirror by detecting changes in the amplitude of a vibrating scanning mirror as changes in pulse width. The present invention relates to an optical scanning device.

[bl Prior Art and Problems As is well known, infrared imaging devices optically scan objects with a narrow instantaneous field of view, and generate video signals by inputting the infrared rays that have passed through the scanning system into an infrared detector and photoelectrically converting them. It has gained.

This optical scanning is normally performed by vibrating a plane mirror on a rotation axis as a scanning mirror. Therefore, the amplitude accompanying the vibration of the scanning mirror must always be a constant value. However, it is difficult to maintain the amplitude of the scanning mirror at a constant value as described above due to disturbances to the vibration system or errors in input signals to the driving means of the plane scanning mirror. In so-called open-loop control, it is nearly impossible to maintain the amplitude of the plane mirror at a constant value. Therefore, conventionally, the amplitude of the scanning mirror has been maintained at a constant value by so-called closed-loop control, which detects the vibration of the scanning mirror and changes the signal to the driving means based on the detection result. FIG. 1 shows a system diagram of a conventional optical scanning device that employs such closed-loop control. A vibrator 1 serving as a rotating shaft is fixed at one end and performs torsional vibration, and along with this vibration, a plane scanning mirror 2 fixed to the vibrator 1 vibrates to perform optical scanning.
An iron piece 3 is further fixed to the vibrator 1, and by applying a periodic pulse voltage to a solenoid coil 4 serving as a driving means to attract the iron piece, the vibrator 1 is driven at a period equal to the period of the voltage. The period of this pulse is controlled by the drive signal generator 11. On the other hand, the amplitude of the scanning mirror 2 is detected by an amplitude detector 5 as a voltage value corresponding to the amplitude, and the detection signal is half-wave or full-wave rectified by a detection circuit 6, smoothed by a low-pass filter 7, and then sent to a comparator 8. is input. The comparator 8 compares the value of this detection signal with the value of the reference voltage from the reference signal generating circuit 9, and the difference value is applied to the control circuit 10'. Control circuit 10
Then, the value of the signal from the drive signal generator 11 is changed based on this value. A drive signal reflecting the amplitude of the plane mirror 2 in this manner is supplied to the coil 4 via the amplifier 12. Incidentally, when the amplitude of the scanning mirror 2 becomes smaller than the specified value, the output value of the comparator 8 becomes small and the control circuit 10 increases the value of the drive signal, and conversely, when the amplitude becomes larger than the specified value, the output value of the comparator 8 Since the output value becomes large, the control circuit 10 controls the amplitude of the scanning mirror to be constant in order to decrease the value of the drive signal. However, in such a conventional control system, since the amplitude of the scanning mirror is detected as a voltage value, circuits such as a detection circuit 6 and a low-pass filter 7 are required, making the circuit configuration complicated.

In addition, the response speed cannot be improved due to the time delay associated with the charging and discharging of the low-pass filter 7, and the circuit structure is complicated, so that deterioration over time is greatly affected by temperature changes. 'c-Object of the Invention The present invention has been devised to eliminate the above-mentioned drawbacks, and aims to simplify the circuit configuration, improve response speed, and stabilize control operation in an optical scanning device using a torsional oscillator. The purpose is to

Structure of 'd' Invention Briefly stated, the gist of the present invention is to obtain the vibration amplitude of a scanning mirror not as a voltage value of a detection signal but as a pulse width of a pulse signal.

That is, in the optical scanning device according to the present invention, one end of a rotating shaft provided with an electromagnetic drive means is fixed, a scanning mirror is attached to a part of the rotating shaft, and the electromagnetic drive means is driven with a drive signal of a predetermined period. In the configuration in which the scanning mirror is vibrated by twisting the rotating shaft, a light shielding member is attached to a part of the vibration mechanism, and the light source and the light receiving element are arranged opposite to each other with the light shielding member in between. A control pulse signal having a pulse width corresponding to the vibration amplitude of the scanning mirror is obtained, and a charging/discharging circuit that is intermittently controlled by the control pulse signal is provided to generate a charging/discharging waveform having a discontinuous portion corresponding to the pulse signal. Furthermore, the output voltage waveform of the charging/discharging circuit is switched by a pulsed reference drive signal corresponding to the time width of the drive signal at a timing including the discontinuous portion, and the above-mentioned voltage waveform is switched based on the switched output signal voltage. It is characterized in that it is driven by electromagnetic driving means. Embodiments of the invention 'c' Hereinafter, preferred embodiments of the invention will be described with reference to the drawings from FIG. 2 onwards.

FIG. 2 is a system diagram showing an embodiment of the optical scanning device according to the present invention, and FIG. 3 is a circuit diagram showing details of the main parts in FIG. 2, and the same parts as in FIG. 1 are the same. It is indicated by a symbol.

The plane scanning mirror 2 is equipped with a light shielding body, such as a thin metal plate (hereinafter referred to as a blade) 13.

This blade 13 is caused by the vibration of the scanning mirror 2 to cause the light emitting element 14 to
and the light-receiving element 15, and the light-receiving element 15 is shielded from light. The light receiving element 15 has a waveform shaping and amplification circuit 16
It is connected to the. That is, the light emitting element 14, the light receiving element 15, and the circuit 16 constitute an amplitude-pulse width conversion circuit 61 that converts the amplitude pulse signal of the scanning mirror 2 into a pulse width. Note that the pulse width of this pulse signal is determined by the time during which the light from the light emitting element is blocked by the blade 13, but in the case of the present invention, the time width of the pulse signal is set to 1' below the vibration period of the scanning mirror 2. The blade 13 and the light-emitting/light-receiving element are arranged in such a relative position. The control pulse signal from the amplitude-pulse width conversion circuit 61 is input to the control circuit 10.

A reference drive signal from a reference drive signal generator 111 is input to this control circuit 1001 . The reference drive signal is a pulse-like signal with a predetermined period, and the reference drive signal drives the solenoid coil 4 via the amplifier 12 by switching a signal corresponding to the control pulse signal as described later. Next, the operation will be explained with reference to FIGS. 3 and 4.

Note that FIG. 4 shows signal waveforms at various parts in FIG. 3, and the signals at points AF in FIG. 3 correspond to the waveforms in FIG. 4 a to f. When the scanning mirror 2 vibrates as shown in Figure 4a,
The light incident on the phototransistor 5 constituting the light receiving element 15 is interrupted by the plate 13 .

The collector of the transistor 15 is connected to the base of the transistor 17 for amplification and shaping, so the transistor 17
The correct evening haze pressure in Figure 4b is caused by the vibration of the scanning mirror 2.
It changes like this. That is, it is assumed that the light emitting and light receiving elements are fixed at fixed positions, and that the blade 13 blocks light between the light emitting and light receiving elements at a deflection angle that exceeds the broken line L in FIG. 4a. Changes in the vibration amplitude of the scanning mirror 2 are eventually detected as changes in the pulse width of the pulse signal obtained from the collector of the transistor 17, and the larger the amplitude, the longer the shielding time due to the blade, and the wider the pulse width. .
In the present invention, the detection signal obtained from the amplitude-pulse width conversion circuit 61 or Z in this manner is input as a control pulse signal to the base of the transistor 18 constituting the next control circuit 100.

The control circuit 100 includes a charging/discharging circuit mainly composed of a capacitor CI, and the transistor 18 connects this charging/discharging circuit to Z.
It has an intermittent effect. In other words, since the transistor 18 repeats conduction and non-conduction states according to the control pulse signal, the capacitor CI is charged via the resistors R1 and R2 in the non-conducting state, and the capacitor CI is charged via the resistor R1 and the transistor 18 in the conductive state. is discharged as a result of transistor 1
The voltage at point C of the co-capacitor CI connected to the collector side of No.
It changes as shown in Figure c. Note that the resistor RI/R2 is semi-fixed for gain adjustment. A transistor 19 for switching the non-grounded terminal of the capacitor CI is connected to the output side of the charge/discharge circuit such as No. 2 or more, and a pulsed reference drive signal (fourth (see Figure d) is input.
The pulse of this reference drive signal is generated at a timing that includes a discontinuous portion of the charge/discharge voltage caused by the control pulse signal. Thus, the output of the charging/discharging circuit is switched by the transistor 19 in response to the reference drive signal, and the potential at the emitter of the transistor 19 changes in a manner including discontinuous portions of the charging/discharging waveform as shown in FIG. 4e. In other words, as is clear from FIG. 4e, a pulse voltage is obtained at point E on the output side of the control circuit 100, with a waveform having a larger drop during discharge as the vibration amplitude of the scanning mirror becomes larger. Therefore, if this output is connected to the solenoid 4 as a driving voltage,
The electromagnetic energy generated differs depending on the area of each pulse waveform, and as mentioned above, as the vibration amplitude of the scanning mirror increases, the drop in military pressure at the discontinuity increases and the driving force decreases. Control is automatically performed to keep the amplitude constant.

Of course, in this case, the output waveform at point E may be further amplified by the amplifier 12 shown in FIG. By the way, if the rotating shaft consisting of the torsional vibrator 1 is driven by a single electromagnetic solenoid 4 as shown in Fig. 2, the output at point E in Fig. 3 can be used as is as described above. As another configuration, two sets of electromagnetic solenoids may be used to alternately attract the iron piece attached to the vibrator from the left and right sides and apply torsional vibration.

When exploring such a driving method, in the present invention, a driving circuit surrounded by a block 50 may be added to the output side of the control circuit block 100 shown in FIG. This drive circuit includes a capacitor C2 for cutting off the DC component from the output at point E of the control circuit 100 (Fig. 4 e), and the positive and half waves of the AC output are sent to one solenoid 4a via the diode DI. In addition, the negative half wave is applied to the other solenoid 4b through the diode D2 in the opposite direction. FIG. 4f shows the drive signal waveform level-shifted through the capacitor C2, in which a positive waveform portion fa, which is typically shaded, is supplied to one solenoid 4a, and a negative waveform portion, which is also typically shaded, is supplied to one solenoid 4a. m is the other solenoid 4
It is supplied to b. In this case, the zero level is at a position where the areas of the positive and negative waveform portions fa and fb are approximately equal, so the pair of solenoids 4a and 4b are driven alternately and equally. As mentioned above, this drive signal waveform reflects the magnitude of the vibration amplitude of the scanning mirror, and control is performed such that the drive waveform becomes smaller as the amplitude increases, so the vibration amplitude is always maintained constant. It will be possible in the evening. '0 Effect of the Invention Now, as explained above, according to the present invention, '1} By detecting the magnitude of the vibration amplitude of the scanning mirror as the pulse width of the pulse signal, the detection circuit, low-pass filter , a reference voltage generation circuit, and a comparison circuit are not required, and the circuit configuration for feedback control is simplified.

[21] In particular, since a low-pass filter is not included in the feedback system, the response speed can be improved, and changes in the vibration amplitude of the scanning mirror can be quickly corrected.

t3} In addition to the small number of circuit components that make up the feedback system,
Since the amplitude change of the scanning mirror is detected using the time width of the signal pulse, compared to a method that detects the amplitude change as a voltage level, characteristic changes due to aging and temperature changes in the detection elements and circuit elements are reduced. Can be done.

It has many advantages such as, and is extremely useful especially when applied to an optical scanning device for taking infrared images to stabilize scanning vibration of a scanning mirror.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a subordinate optical scanning device, FIG. 2 is a system diagram of an optical scanning device according to the present invention, and FIG. 3 is a detailed diagram of the amplitude-pulse width conversion circuit 61 and control circuit 100 in FIG. FIG. 4 is a time chart showing the movement of the blade and the waveforms of signals at various parts in FIG. 3. In the figure, 1 is a torsional vibrator, 2 is a plane scanning mirror, 13 is a blade, 14 is a light emitting element, 15 is a light receiving element consisting of a phototransistor, 111 is a drive signal generator, 100 is a control circuit, and 50 is an additional drive The circuit 61 is an amplitude-pulse width conversion circuit. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. One end of a rotating shaft provided with an electromagnetic driving means is fixed, a scanning mirror is attached to a part of the rotating shaft, and the electromagnetic driving means is driven with a drive signal of a predetermined period to cause the rotating shaft to make a torsional movement. In the configuration in which the scanning mirror described above is vibrated, a light shielding body is attached to a part of the vibration mechanism,
A charging/discharging circuit that obtains a control pulse signal having a pulse width corresponding to the vibration amplitude of the scanning mirror by arranging a light source and a light receiving element facing each other with the light shielding body in between, and that is intermittently controlled by the control pulse signal. to generate a charging/discharging waveform having a discontinuous portion corresponding to the pulse signal, and further converting the output voltage waveform of the charging/discharging circuit into a pulse-like waveform corresponding to the time width of the drive signal at a timing including the discontinuous portion. An optical scanning device characterized in that switching is performed using a reference drive signal, and the electromagnetic drive means is driven based on the switched output signal voltage.