JPH0228124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an improvement in a scanning method for scanning an object by rotating a reflecting mirror back and forth.

Prior Art and Problems A scanning mirror is used, for example, in an infrared thermometer to scan the surface of an object to determine its temperature distribution. FIG. 1 shows an example of an optical system including a scanning unit in an infrared thermometer. In the figure, 1 indicates a scanning unit. Infrared radiation from an object (not shown) is reflected by the scanning mirror 2 in the scanning unit 1, further reflected by the fixed reflecting mirror 3, passed through the converging lens 4, and converged on the reflecting surface of the chopper 5. The infrared rays are reflected by the lens 6. After that, it is converted into parallel light beams, and fixed reflecting mirror 7
After being reflected, the light passes through a lens 8 and enters a detector 9. The chopper 5 is rotated by a motor 10,
The infrared rays generated by the reference heat source 11 are sent to the detector 9 for a short time every rotation, and the infrared rays from the object that are incident through the converging lens 4 are incident on the detector 9 during the other periods. The detector 9 measures the surface temperature of the object by comparing the infrared intensity from the object with the infrared intensity from the reference heat source.

In the scanning unit 1, the scanning mirror 2 is fixed to shafts 13A and 13B supported by a gimbal 12, and scans within a fixed angle in the horizontal direction as the shafts reciprocate and rotate. Furthermore, the gimbal 12 is fixed to a shaft 14 that is perpendicular to the shafts 13A and 13B, and scans within a certain angle in the vertical direction as the shaft 14 reciprocates and rotates. In this way, a certain rectangular range including the object is scanned.

FIG. 2 shows the configuration of a conventional scanning unit. In this figure, the same numbers as in FIG. 1 indicate the same parts. 16 and 17 are driving electromagnets, 18 is a movable piece, 19 is a torsion bar, 20
21 is a lamp, 21 is a phototransistor, 22 is a chopper board, and 23 is a synchronous circuit. The scanning mirror 2 is rotatably supported by upper and lower shafts 13A and 13B, and the tip of the shaft 13B is fixed to the gimbal 12 via a torsion bar 19. A movable piece 18 is fixed to the torsion bar 19, and electromagnets 16, 17 are attached between the movable piece 18.
is provided. Further, the upper shaft 13A is provided with a chopper plate 22, and a lamp 20 and a phototransistor 21 placed above and below the chopper plate 22.

FIG. 3 shows a detailed structure of the electromagnets 16, 17 and the movable piece 18 in FIG. 2 in a plan view. The movable piece 18 has its center section connected to the torsion bar 1.
It is fixed at 9. The electromagnets 16 and 17 each consist of two windings, and as shown in the figure, the permanent magnet 1
For example, when the electromagnet 16 is excited, the movable piece 18 is absorbed and rotated in the direction of the electromagnet 16 as shown by the solid line, and the electromagnet 1
When magnet 7 is excited, permanent magnet 18 is attracted in the direction of electromagnet 17 and rotated as shown by the dotted line. Therefore, by alternately exciting the electromagnets 16 and 17, the movable piece 18 performs a reciprocating rotational movement around the torsion bar 19, but the excitation period at this time depends on the elasticity of the torsion bar 19 and the mass of the scanning mirror 2, etc. When the resonant frequency is close to the determined resonance frequency, the reflecting mirror 2 continues forced vibration.

FIG. 4 shows the detailed structure of the lamp 20, phototransistor 21, and chopper plate 22 in FIG. 2 in a plan view. The chopper plate 22 has a rectangular shape, is fixed to the shaft 13A, and rotates back and forth together with the scanning mirror 2. The lamp 20 and the phototransistor 21 are provided on the top and bottom of the chopper plate 22 facing each other, and one lamp 20 and a phototransistor 21 are provided on both sides of the reciprocating rotation range of the chopper plate 22.
Each pair is provided, and the chopper plates 22 alternately take the positions indicated by the solid line and the dotted line as they reciprocate and rotate.
Therefore, one of the phototransistors is blocked from light from the lamp, and the generated electromotive force becomes zero.
The lamp 20 and the phototransistor 21, which are vertically opposed, are combined to form one photocoupler, and the two photocoupler plates on both sides of the chopper board and the chopper board form a synchronizing chopper.

The synchronization circuit 23 generates a chopper signal consisting of a rectangular wave having the same period as the signal that is alternately turned off for a short time from the two photo couplers in the synchronization chopper, and calculates the period between this chopper signal and a reference signal having a constant period. By comparing the electromagnets 16 and 17 and turning them on and off, the scanning mirror 2 is forced to vibrate.

FIG. 5 explains the operation of the synchronous circuit in the scanning method shown in FIG. In the same figure, (1) indicates the reference signal (2-1), (2-2), (2-3)
are each a chiyotsupa signal.

In FIG. 6, the reference signal (1) is, for example, 60 Hz, that is, one cycle is 16.66 ms. Chiyotsupa signal (2-
1) indicates the case where the period is equal to the reference signal (1), and chopper signals (2-2) and (2-3) indicate the cases where the period is longer and shorter than the reference signal (1), respectively. It shows. The synchronization circuit 23 compares the cycle of the chopper signal and the reference signal, and when the cycle of the chopper signal is long, reduces the amplitude of the scanning mirror.
When it is short, the electromagnet 16 increases the amplitude,
The excitation current output time for 17 is controlled. Since the movement of the scanning mirror is accompanied by viscous resistance, the rotation period generally becomes shorter as the amplitude becomes smaller. Therefore, if the chopper signal period is made equal to the reference signal by controlling the amplitude, the vibration period of the scanning mirror 2 can be kept constant.

As described above, in the conventional scanning system, the reciprocating rotational movement of the scanning mirror is controlled by a chopper signal that detects the rotation period of the scanning mirror, thereby causing the scanning mirror to perform horizontal scanning. As mentioned above, the vibration of the scanning mirror uses mechanically forced vibration in the elastic system that supports it, so the angular velocity of the reciprocating rotation changes sinusoidally with respect to the rotation angle, and linear scanning is performed. The drawback was that the scope of gain was narrow.

FIG. 6 shows an example of a temporal change in the rotation angle θ of a scanning mirror in a conventional scanning method. As shown in the figure, the rotation angle θ changes sinusoidally over time, and not only is the linear range shown by A narrow, but it is also difficult to vibrate in an accurate sinusoidal shape, and the waveform is asymmetric and the reciprocating angular velocity is different, so it is difficult to move in one direction. For example, while the rotation range is ±7.2 degrees, the effective usable range is only 12.5 degrees, and only about 1/3 of the total rotation range can be used effectively.

Purpose of the Invention The present invention is intended to solve the problems of the prior art, and its purpose is to provide a scanning method that has a wide range of rotation angles that can be effectively used and that can scan in both forward and backward directions. There is a particular thing.

Embodiment of the Invention FIG. 7 shows the configuration of an embodiment of the scanning system of the present invention. In the same figure, the same parts as in FIG. 3 are indicated by the same numbers, 26 is a drive coil, 27 and 28 are permanent magnets, 29 is a rotary encoder, 30 is a light emitting diode, 31 is a phototransistor, and 32 is a reference oscillator. , 33 is an address counter, 34 is a read-only memory (ROM),
35 is a digital-to-analog (D/A) converter, 3
6 is a servo amplifier.

FIG. 8 shows an example of the detailed structure of the drive coil 26 and permanent magnets 27, 28 in the embodiment shown in FIG. The drive coil 26 has a rotatable symmetric fan shape with its central portion supported by the shaft 13B, and has windings 40 and 41 on both fan portions. Permanent magnets 27 and 28 have an N pole and an S pole above and below the drive coil 26.
They are arranged in a pair so that the poles face each other. Each permanent magnet is further divided into two parts in the rotational direction of the drive coil 26, and the poles of different names are arranged next to each other.

FIG. 9 shows an example of the detailed structure of the rotary encoder 29, light emitting diode 30, and phototransistor 31 in the embodiment shown in FIG. In this figure, the same numbers as in FIG. 7 indicate the same parts, 45 is a fixed disk, 46 is a rotating disk, 47 is a counter, and 48 is a digital-to-analog (D/A) converter.

In FIG. 9, the light emitting diode 30 and the phototransistor 31 are respectively two light emitting diodes 30 _-1 and 30 _-2 and a phototransistor 31.
_-1 and 31 _-2 , and are arranged above and below the rotary encoder 29. Light emitting diode 30 _-1 ,
The phototransistor 31 _-1 forms a photocoupler A, and the light emitting diode 30 _-2 and the phototransistor 31 _-2 form a photocoupler B.
A light emitting diode and a phototransistor forming each photocoupler are provided facing each other so that their respective optical axes coincide.

The rotary encoder 29 consists of a fixed disk 45 and a rotating disk 46. The rotating disk 46 is fixed to the shaft 13A and rotates together with the shaft 13A, but the fixed disk 45 is fixed to the gimbal 12. . The fixed disk 45 and the rotating disk 46 are provided with finely spaced slits radially and tilted at a small angle from each other. Therefore, when the rotating disk 46 rotates, the light passing through the rotating disk 46 and the fixed disk 45 due to the incident light from the photo couplers A and B forms moire fringes. Photo cutlet A, B
generates pulses by cutting these moire fringes, but since photo couplers A and B are provided with a phase shift of 90° with respect to the slit interval, the polarity of photo coupler B depends on the positive or negative rotation direction of the moire fringes. The generated pulses have different phases with respect to the pulses of the photo coupler A depending on the rotation direction of the moiré fringes.

FIG. 10 shows the phase relationship of pulses in the rotary encoder. In the same figure, (1) is the pulse generated by photo coupler A, (2) is the pulse generated by photo coupler B when the rotation direction of the moire fringe is positive, and (3) is the pulse generated by photo coupler B when the rotation direction of the moire fringe is negative. This is the generated pulse.

In FIG. 9, a counter 47 counts pulses from the photo couplers A and B, and adds them when the rotation direction of the moiré fringes is positive, and subtracts them when the rotation direction is negative. The D/A converter 48 converts the count value of the counter 47 into an analog signal, thereby generating an analog output having a magnitude corresponding to the rotation angle.

On the other hand, in FIG. 9, the ROM 34 has a scanning mirror 2.
Data corresponding to the rotation angle that the scanning mirror 2 should take is stored, which corresponds to each time period obtained by dividing one cycle of the reciprocating rotational movement into, for example, 256 equal parts. The reference oscillator 32 generates a clock with a constant period, and the address counter 33 counts this clock.
Generates a data read address for the ROM 34.

FIG. 11 shows the rotation angle data stored in the ROM 34. In the figure, the addresses for each time segment obtained by dividing the rotation period of the scanning mirror 2 into 256 equal parts are represented by addresses 00 to FF.
It is shown that data 7F to 7E are stored correspondingly.

The angle data consisting of a digital signal read from the ROM 34 is applied to a D/A converter 35 and converted into an analog signal indicating a reference angle. The servo amplifier 36 compares the signal indicating the rotation angle of the scanning mirror 2 from the D/A converter 48 with the signal indicating the reference angle from the D/A converter 35, and generates an output signal according to the error. . The output signal of the servo amplifier 36 is applied to the drive coil 26 to rotate the scanning mirror 2, thereby changing the rotation angle of the scanning mirror and the ROM 3.
Feedback control is performed so that the difference from the reference angle stored in 4 approaches zero.

FIG. 12 shows a closed loop consisting of a scanning mirror, rotary encoder, and servo amplifier as a feedback control system. In the figure, the rotational angle output θ of the scanning mirror is detected by a rotary encoder to generate a detection signal ν, the signal ν is differentially added to the reference angle signal ν _s at the servo amplifier input, and the error output is A drive signal is amplified through an amplifier and used to drive the scanning mirror via a drive coil, thereby performing feedback control and reducing the error between the rotation angle θ of the scanning mirror and the reference angle. The scanning mirror is driven so that the value approaches zero.

FIG. 13 shows the driving characteristics of the scanning mirror in the embodiment shown in FIG. In the same figure, (1) shows the digital reference angle signal generated by the ROM 34, which changes linearly in a triangular wave shape between FF and 00 with 7F as the center for each address that divides one cycle of 16.66 mS into 256 equal parts. It has been shown that
(2) shows the analog reference angle signal ν _s generated by the D/A converter 35, and corresponds to the digital angle signal shown in (1), +A[V ] and -A[V], which shows a linear change in a triangular waveform. (3) is scanning mirror 2
The angle change associated with the reciprocating rotational movement of the rotary encoder is shown by the output ν of the rotary encoder.
It is shown that the voltage changes almost linearly in a triangular wave form from +A [V] to -A [V] with the center at 0 [V] during 16.66 mS.

Effects of the Invention As explained above, according to the scanning method of the present invention, the rotation angle of the scanning mirror is detected by the rotary encoder, and data of a size corresponding to the rotation angle to be taken by the scanning mirror is transmitted in accordance with the rotation period. Each arbitrarily divided time segment is stored in memory, and an analog drive signal is generated according to the error between the data read from memory and the output of the rotary encoder, and this is fixed to the axis of the scanning mirror. The scanning mirror is rotated by the interaction with magnetic flux parallel to the axis and in opposite directions, which allows for a wide range of rotation angles that can be effectively used for scanning, as well as in both reciprocating directions. It can be used for scanning and is extremely effective.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of an optical system including a scanning unit in an infrared thermometer, Fig. 2 is a diagram showing the configuration of a conventional scanning unit, and Fig. 3 is a detailed structure of the electromagnet and permanent magnet in Fig. 2. A plan view showing
FIG. 4 is a plan view showing the detailed structure of the lamp, phototransistor, and chopper board in FIG. 2;
FIG. 5 is a diagram showing the operation of the synchronous circuit in the scanning method shown in FIG. 2, FIG. 6 is a diagram showing an example of the temporal change in the rotation angle of the scanning mirror in the conventional scanning method, and FIG. FIG. 8 is a diagram showing an example of the detailed structure of the drive coil and permanent magnet in the embodiment shown in FIG. 7. FIG. 9 is a diagram showing the configuration of an embodiment of the scanning method of the present invention. Figure 1 shows an example of detailed structures of the rotary encoder, light emitting diode, and phototransistor in the embodiment shown in
Figure 0 shows the phase relationship of pulses in the rotary encoder, Figure 11 shows the rotation angle data stored in the ROM, Figure 12 shows the scanning mirror,
FIG. 13 is a diagram showing a feedback control system consisting of a rotary encoder and a servo amplifier, and FIG. 13 is a diagram showing drive characteristics of the scanning mirror in the embodiment shown in FIG. 1...Scanning unit, 2...Scanning mirror, 3...Reflector,
4...Convergent lens, 5...Chiyotsupa, 6...Lens, 7
... Fixed reflector, 8... Lens, 9... Detector, 10...
Motor, 11...Reference heat source, 12...Gimbal, 13
A, 13B, 14... Axis, 16, 17... Driving electromagnet, 18... Movable piece, 19... Torsion bar, 20
... Lamp, 21 ... Phototransistor, 22 ... Chopper board, 23 ... Synchronous circuit, 26 ... Drive coil,
27, 28... Permanent magnet, 29... Rotary encoder, 30... Light emitting diode, 31... Photo transistor, 32... Reference oscillator, 33... Address counter, 34... Read only memory (ROM), 35
...Digital analog (D/A) converter, 36...
Servo amplifier, 40, 41... Winding wire, 45... Fixed disk, 46... Rotating disk, 47... Counter, 48... Digital analog (D/A) converter.

Claims (1)

[Claims] 1. In a scanning mirror that performs scanning by reciprocating the reflecting mirror in a fixed direction, there is a rotary encoder that detects the rotational angle of the scanning mirror and generates an output according to the rotational angle, and a rotary encoder that detects the rotational angle of the scanning mirror and generates an output according to the rotational angle. A memory that stores data of a corresponding size for each time segment that arbitrarily divides the rotation period into equal parts, and means that generates an analog drive signal in accordance with the error between the data read from the memory and the output of the rotary encoder. By passing the drive signal through a drive coil fixed to the axis of the scanning mirror and provided on a plane perpendicular to the axis, the interaction with mutually opposite magnetic fluxes parallel to the axis is achieved. A scanning method characterized by comprising means for generating rotational force to drive a scanning mirror.