JPH0593625A - Optical displacement gage - Google Patents

Abstract

PURPOSE:To make it possible to perform high-speed measurement by limiting the emitting time of the optical beam from a processing circuit, which integrates the detected signals when the scanning speed of the optical beam is approximately constant and generates a center-of-gravity signal, to only an integrating section. CONSTITUTION:A processing circuit 50 has an oscillator 22, a laser driving circuit 24, amplifiers 54c and 54d, synchronous detectors 56c and 56d, an integration timing circuit 66 and the like. The circuit 24 is turned ON and OFF not with the pulse modulating signal outputted from the oscillator 22 but with an integration timing signal (f) outputted from the circuit 66. Thus, the emitting time of a laser beam 14 is limited to only an integrating section. At the same time, the detection timings of the detectors 56c and 56d are changed with the ON/OFF of the circuit 24. Furthermore, integrating circuits 64c and 64d and sample/hold circuits 68c and 68d are provided at the front stage of a subtractor 58, an adder 60 and divider 62. Since the emitting time of the optical beam is limited to only in the integrating section of the detected signals, the high-speed measurement can be performed without using expensive special electric parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement meter,
In particular, an illumination system that irradiates the measurement surface while scanning a pulse-modulated light beam, which is suitable for non-contact measurement of the thickness and displacement of a remote object by a triangulation method,
A light receiving lens that collects the reflected light of the light beam from the measurement surface to form an image, a photoelectric sensor that generates a detection signal corresponding to the light amount distribution of the formed image, and a scanning speed of the light beam that is substantially constant. A processing circuit that integrates the detection signal at a certain time to generate a center-of-gravity signal corresponding to the center-of-gravity position of the light-quantity distribution, and calculates the position or displacement of the measurement surface from the change of the center-of-gravity signal. Regarding improvement.

[0002]

2. Description of the Related Art With the automation of production in the industrial world, introduction of robots, etc., there is a rapid demand for in-process measurement, high speed, and high accuracy. There is also a great need for a displacement meter that can measure the thickness and displacement of a remote object in a non-contact manner like process measurement.

As an example of such a non-contact displacement meter, as previously proposed by the applicant in Japanese Patent Laid-Open No. 63-200011, the measuring surface 10 is irradiated with a light beam such as a laser beam 14 as shown in FIG. As a result, there is known an optical displacement meter that detects a position and a displacement by a triangulation method.

The optical displacement meter shown in FIG. 4 forms an image by collecting an illumination system 20 for irradiating the measurement surface 10 while reciprocally scanning the pulse-modulated laser beam 14 and reflected light of the laser beam from the measurement surface 10. A light receiving lens 40 that forms an image on a surface, and a semiconductor position detector (PSD) 4 as a photoelectric sensor that generates detection signals c 1 and d 2 corresponding to the light amount distribution of the formed image.
2 and a processing circuit 50 that integrates the detection signals c 1 and d 2 when the scanning speed of the laser beam 14 is substantially constant to generate a centroid signal e 2 corresponding to the centroid position of the light amount distribution. It is configured.

The illumination system 20 includes, for example, an oscillator 22 for pulse-modulating the laser beam 14 and the oscillator 2.
A laser drive circuit 24 that is periodically turned on and off by a two-output pulse modulation signal, and a semiconductor that is driven by a pulsed laser drive signal a output from the laser drive circuit 24 and generates a pulse-modulated laser beam 14. A laser 26 and an oscillating mirror 28 for reciprocally scanning the laser beam 14 generated from the semiconductor laser 26.
And a tuning fork 30 for vibrating the vibrating mirror 28,
From a tuning fork driving circuit 32 for driving the tuning fork 30 by a sinusoidal tuning fork driving signal b, and a projection lens 34 for making the laser beam 14 reciprocally scanned by the vibrating mirror 28 parallel to each other. It is configured.

Further, the processing circuit 50 is, for example, the P
A current-voltage (IV) converter 5 for converting the detection (current) signals c and d from SD42 into voltage signals, respectively.
2c and 52d, and amplifiers 54c and 54d for amplifying the outputs of the IV converters 52c and 52d, respectively.
The output signals of the amplifiers 54c and 54d are detected in synchronism with the output signal of the oscillator 22 to obtain a detection signal.
synchronous detectors 56c and 56d for removing the direct current component contained in c and d, that is, the disturbance light component, and the synchronous detector 5
6c and 56d, the difference and the sum of the outputs are calculated by a subtracter 58 and an adder 60, respectively. By dividing the output of the subtractor 58 by the output of the adder 60, the center of gravity of the light amount distribution on PSD 42 is calculated. The divider 62 for obtaining the center of gravity signal e corresponding to the position, and the output of the divider 62 are integrated in the neutral region of the tuning fork where the scanning speed of the laser beam 14 by the tuning fork 30 is substantially constant to obtain an integrated signal g. Integrating circuit 64 for obtaining
According to the outputs of the tuning fork drive circuit 32 and the oscillator 22, the tuning fork 30 is in the neutral region, and the laser beam 1
4 is emitted only when the integrating circuit 64 is irradiated.
An integration timing circuit 66 for outputting an integration timing signal f for turning on, a sample / hold (S / H) circuit 68 for sampling and holding the output of the integration circuit 64, and the S / H circuit An A / D converter 70 for converting the output (analog signal) of 68 to a digital signal, and a linear corrector 72 for correcting the linearity of the output of the A / D converter 70 and outputting it as a measurement value. It consists of and.

When the measurement surface 10 is displaced from Z1 to Z2 in the vertical direction (Z direction) in the figure, the irradiation point of the laser beam 14 also changes in the vertical direction, and accordingly the light receiving lens 4 is moved.
The center of gravity of the image forming position due to 0 moves on the PSD 42 in the left and right direction of the figure, and the center of gravity signal e also changes from e ₁ as illustrated in FIG.
Change to e ₂ . Therefore, the displacement ΔZ of the measurement surface 10 can be measured.

Further, in the optical displacement meter of FIG.
As shown in, the oscillator 22 pulse-modulates the laser beam 14, and the synchronous detectors 56c and 56d detect only the detection signals c and d when the laser beam 14 is irradiated. The effect of can be eliminated.

Further, since the laser beam 14 is reciprocally scanned by the tuning fork 30 and the region in which the reciprocating movement of the vibrating mirror 28 is unstable is eliminated, the integration timing circuit 66 and the integration circuit 64 use the integration timing circuit 66 and integration circuit 64 as shown in FIG. Since the center of gravity signal e is integrated only in the neutral region of the tuning fork 30 where the scanning speed of the laser beam is substantially constant, the measurement error due to the surface texture of the measurement surface 10 can be eliminated.

That is, microscopically irregular irregularities are formed on the measurement surface 10, and the light quantity distribution on the image plane is also irregularly distributed accordingly. Therefore, the measurement surface 10
Even if the position in the Z direction is the same, if the surface texture is different, the light amount distribution is also different, and a kind of noise signal is mixed in the center-of-gravity signal e, which deteriorates the measurement accuracy.

On the other hand, as in the optical displacement meter of FIG. 4, if the laser beam 14 is scanned on the measurement surface 10 and the detection signal is integrated, the light quantity distribution due to the difference in surface texture is obtained. Differences are averaged and less susceptible to surface texture.

[0012]

However, as described above, the laser is pulse-modulated to remove ambient light,
In addition, when a laser beam is scanned to eliminate measurement errors due to surface texture, in order to obtain a large amount of data, as shown in FIG.
As shown in the structure of the output signal from the PSD 42, the pulse modulation frequency needs to be considerably (about 100 times) faster than the scanning frequency. Further, in this case, since the reciprocating movement of the vibrating mirror 28 is unstable in the area where the scanning speed is changing, the measurement data is valid only in the neutral area where the scanning speed is substantially constant.

On the other hand, since the measuring speed is determined by the scanning frequency, the scanning frequency must be increased in order to increase the measuring speed. In this case, since the pulse modulation frequency of the laser is further increased, a general-purpose operational amplifier has a problem in electric response, and expensive electric parts must be used. Further, it becomes difficult to increase the measurement speed because it becomes difficult to take electrical timing at high speed.

The present invention has been made to solve the above-mentioned conventional problems. In an optical displacement meter in which a light beam is pulse-modulated and the light beam is scanned, expensive special electrical parts are used. The purpose is to enable high-speed measurement without using it.

[0015]

SUMMARY OF THE INVENTION The present invention is directed to an illumination system for irradiating a measurement surface with a pulse-modulated light beam while scanning, and a light receiving device for collecting and forming an image of reflected light of the light beam from the measurement surface. A lens, a photoelectric sensor that generates a detection signal corresponding to the light amount distribution of the formed image, the detection signal when the scanning speed of the light beam is substantially constant, and the barycentric position of the light amount distribution is integrated. In the optical displacement meter, which includes a processing circuit that generates a center-of-gravity signal corresponding to, and obtains the position or displacement of the measurement surface from the change of the center-of-gravity signal, the irradiation time of the light beam is limited to the integration section. The above-mentioned object is achieved.

The pulse modulation frequency of the light beam is
The scanning frequency of the light beam is approximately doubled.

[0017]

In the present invention, the irradiation time of the pulse-modulated light beam is such that the scanning speed of the light beam is substantially constant.
Since only the integration section of the detection signal is used, it is not necessary to increase the pulse modulation frequency even if the scanning frequency is increased, and the pulse modulation frequency of the light beam is set to 2 times the scanning frequency of the light beam.
It can be doubled.

Therefore, general-purpose electric parts can be used, and the timing is not difficult to set, so that the measurement speed can be increased.

Particularly, in the case where the irradiation time of the light beam is made to substantially coincide with the integration section and the pulse modulation frequency of the light beam is set to be approximately twice the scanning frequency of the light beam,
All the irradiated light beam will be used for measurement,
Good efficiency.

On the other hand, conventionally, as shown in FIG.
Since it is necessary to obtain a large amount of data even in the integration section, the pulse modulation frequency needs to be considerably faster than the scanning frequency, and the light beam needs to be emitted even in the section where measurement is not performed. Yes, it was inefficient.

[0021]

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

In this embodiment, as shown in FIG. 4, the illumination system including the oscillator 22, the laser driving circuit 24, the semiconductor laser 26, the vibrating mirror 28, the tuning fork 30, the tuning fork driving circuit 32, and the light projecting lens 34 is used. 20, light receiving lens 40, PSD
42, IV converters 52c and 52d, an amplifier 54c,
54d, synchronous detectors 56c and 56d, subtractor 58, adder 60, divider 62, integration timing circuit 66, A / D
A processing circuit 50 including a converter 70 and a linear corrector 72,
In the optical displacement meter having the above, as shown in FIG. 1, the laser drive circuit 24 is turned on and off not by the pulse modulation signal of the oscillator 22 output but by the integration timing signal f of the integration timing circuit 66 output. The irradiation time is limited to the integration section, and the detection timings of the synchronous detectors 56c and 56d are also changed accordingly, and further the integration circuits 64c and 64d and the S / H circuit 6 are used.
8c and 68d are added to a subtractor 58, an adder 60 and a divider 6
It is provided not in the second stage but in the first stage.

The rest of the configuration and the overall operation are the same as in the prior art example, so a description thereof will be omitted.

In the configuration of the output signal from the PSD 42 in the present embodiment, as shown in FIG. 2, the laser scanning component includes a laser pulse modulation component having a frequency twice that of the laser scanning component. In comparison, the frequency of the laser pulse modulation component is significantly reduced.

FIG. 3 shows an example of waveforms of the output signal from the PSD 42, the signal after synchronous detection, and the integrated signal in this embodiment.

In the above embodiment, the tuning fork 30 is used as a scanner for scanning the laser beam 14, but the type of scanner is not limited to this.
For example, as proposed by the applicant in Japanese Patent Laid-Open No. 63-200011, a magnetic body frame, a permanent magnet 38, a coil to which a sinusoidal alternating current is applied as an excitation signal, and a rotating shaft including an iron piece are provided. It is also possible to use a galvanometer-type vibration exciter that is configured to include a vibration mirror and is fixed to the rotation shaft.

Although the PSD 42 is used as the photoelectric sensor in the above embodiment, the type of the photoelectric sensor is not limited to this, and a two-divided photodiode or the like can be used.

[0028]

As described above, according to the present invention, the light beam is pulse-modulated in order to remove ambient light, and the light beam is scanned in order to eliminate a measurement error due to surface texture. Even with an optical displacement meter, high-speed measurement is possible without using expensive special electric parts. Therefore, high-speed and highly accurate measurement can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram including a partial optical path diagram showing a configuration of an embodiment of an optical displacement meter according to the present invention.

FIG. 2 is a diagram showing a configuration of an output signal from a PSD in the above embodiment.

FIG. 3 is a diagram similarly showing an example of signal waveforms of respective parts.

FIG. 4 is a block diagram including a partial optical path diagram showing a configuration example of a conventional optical displacement meter proposed by the applicant in JP-A-63-200011.

FIG. 5 is a diagram showing an example of a change state of a center-of-gravity signal in the conventional example.

FIG. 6 is a diagram similarly showing a configuration of an output signal from the PSD.

FIG. 7 is a diagram similarly showing an example of signal waveforms of respective parts.

[Explanation of symbols]

 10 ... Measuring surface, 14 ... Laser beam, 20 ... Illumination system, 22 ... Oscillator, 24 ... Laser drive circuit, a ... Laser drive signal, 26 ... Semiconductor laser, 28 ... Vibration mirror, 30 ... Tuning fork, 32 ... Tuning fork drive circuit , B ... Tuning fork drive signal, 34 ... Emitter lens, 40 ... Light receiving lens, 42 ... PSD (photoelectric sensor), c, d ... Detection signal, 50 ... Processing circuit, 56c, 56d ... Synchronous detector, 58 ... Subtraction Integrator, 60 ... Adder, 62 ... Divider, 64c, 64d ... Integrator circuit, 66 ... Integral timing circuit, f ... Integral timing signal.

Claims (2)

[Claims] 1. An illumination system for irradiating a measurement surface while scanning a pulse-modulated light beam, a light-receiving lens for collecting reflected light of the light beam from the measurement surface to form an image, and A photoelectric sensor that generates a detection signal corresponding to the light amount distribution, and a process that integrates the detection signal when the scanning speed of the light beam is substantially constant to generate a center of gravity signal corresponding to the center of gravity position of the light amount distribution. An optical displacement meter, including a circuit, for determining the position or displacement of a measurement surface from a change in the center-of-gravity signal, wherein the irradiation time of the light beam is limited to the integration section. 2. The optical displacement meter according to claim 1, wherein the pulse modulation frequency of the light beam is approximately twice the scanning frequency of the light beam.