JPH0381688A - Laser length measuring device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser length measuring device that measures length using laser light.

[Conventional technology]

Regarding the method of measuring the distance to an object using laser light, see Japanese Patent Application Publication No. Sho 62-251686 and Japanese Unexamined Patent Publication No. Sho 62-251686.
There are some proposals such as in Publication No.-147384.

To outline the method, the optical frequency of a semiconductor laser is linearly frequency-modulated and output, the laser output light is irradiated toward the surface to be measured, the reflected light and reference light are mixed, and optical heterogain detection is performed. The distance to the object is measured by measuring the period of the beat signal generated by the object.

That is, if the measurement distance n (optical path difference) is R and the beat signal frequency is f, the following relational expression can be obtained.

r b = 1 / T b = f・2R/C...
・・・・・・・・・(1) However, 1 is the optical frequency change rate, T
b is the beat signal period, and C is the speed of light.

In this way, by measuring the beat signal period T using a clock frequency that is sufficiently higher than the beat signal frequency, the measured distance R can be determined from the relationship expressed by equation (1).

[Problem to be solved by the invention]

This method is effective when the reflected signal from the object to be measured is continuous and large enough, but if the beat signal amplitude fluctuates or attenuates due to vibrations of the object to be measured, noise in the signal processing circuit etc. Due to the influence of this, there is a risk that large errors and malfunctions may occur in period measurement and abnormal values may be output.

In particular, when this measuring device is used as a control sensor for a positioning device or the like, there is a risk that the positioning device may run out of control.

The present invention prevents the output of an abnormal value even when the beat signal fluctuates or attenuates transiently as described above, and furthermore, when this abnormal state continues,
The purpose of the present invention is to provide a laser length measuring device with an additional function of outputting an alarm.

[Means to solve the problem]

In order to achieve this objective, the laser length measuring device of the present invention includes:
Semiconductor laser light whose frequency is modulated so that it continuously increases and decreases at a certain rate is split into two directions, one light beam is directed to a reference mirror installed at the end of the reference optical path, and the other light beam is directed to the object to be measured. The amplitude of the beat wave is detected in a laser length measurement device that measures the distance between the reflectors by irradiating each fixed reflector, mixing the respective reflected lights, and measuring the distance of the reflector based on the cycle of the beat wave generated by light interference. means for outputting a distance signal calculated based on the measured cycle and outputting a distance signal immediately before the amplitude attenuates when the amplitude value is less than a certain threshold; and an amplitude attenuation time. The present invention is characterized by comprising means for measuring and outputting an abnormality alarm after a certain period of time has elapsed.

[Effect]

In the present invention, the amplitude of the detected beat signal is detected by means such as full-wave rectification, and it is determined whether this amplitude is above a certain level, and if the signal level is below this level, period measurement is performed. Stop outputting the distance data converted from , and hold and output the output value immediately before the error occurred.

On the other hand, regarding the alarm output, the time in the hold output state is measured using a timer counter or the like, and an alarm is output when the hold output state continues for a certain period of time.

Therefore, even if the amplitude of the beat signal is attenuated due to vibration of the object to be measured, it is possible to prevent output values with large errors or abnormal values, and to detect abnormal conditions such as the posture of the object to be measured. , alarms can be issued.

〔Example〕

The present invention will be explained in detail below using examples.

FIG. 1 is a diagram showing the configuration of a laser length measuring device according to the present invention. In the figure, 1 is a frequency modulation circuit, which frequency-modulates the laser light emitted from the semiconductor laser oscillator 2.

3 is a collimator lens for collimating the emitted light from the semiconductor laser oscillator 2, and 4 is for distributing the laser light to both the reference mirror 5 and the moving mirror 6 and mixing the reflected light from each mirror. Beam splitter; 7 is a light receiver that detects the beat signal generated by mixing; 8 is a waveform shaper with a high-pass filter function for amplifying the beat signal and cutting the DC component; 9 is a waveform shaper A period counting circuit counts the period of the beat signal output from 8 using a sufficiently high frequency clock, 10 a distance calculation circuit that calculates the distance to the movable mirror 6 from the period data, and 13 detects the amplitude of the beat signal. 14 is a comparator that compares the amplitude of the beat signal with a certain threshold;
11 is a latch circuit that latches the output of the distance calculation circuit 10 when the output of the comparator circuit 14 is "1", and 12 is an output circuit.

15 is an alarm circuit, which is composed of a clock and a counter.

The operation will be explained below using FIG. 2.

Linear frequency modulation from semiconductor laser 2 (Figure 2 (a)
) is emitted, the period T of the obtained beat signal (Fig. Outputs as shown in figure (e). This measurement method includes, for example,
Patent application No. 62-102847 filed earlier by the applicant of the present application
The method described in the specification can be used.

At this time, when the amplitude of the beat signal becomes small like between A and 8, the output of the comparator 14 becomes "0" as shown in FIG. The signal is held for this period. After this, during the B-C period, the beat signal amplitude returns to normal, so the distance output follows and changes.

During the CD period, the amplitude of the beat signal similarly decreases, the output signal is held, and the counter circuit of the alarm circuit 15 operates to output an alarm at point D.

Note that the output of the comparator 14 serves as a reset signal for the counter circuit of the alarm circuit 15. That is, when the output of the comparator 14 is ``1'', the counter circuit is reset.An alarm output can be easily generated using the signal of the upper bit of the counter.

〔Effect of the invention〕

The present invention achieves the following effects with the configuration described above.

■ With conventional measurement methods that use FM modulation of semiconductor lasers, electrical noise appears when the beat signal amplitude attenuates due to vibrations, changes in posture, etc. of the object to be measured, which may increase errors in periodic measurements. However, in the present invention, the amplitude of the beat signal is detected, and if there is a risk of a large error occurring when the amplitude attenuates, period measurement - distance measurement is performed. By ceasing to output the data on which the calculation has been performed and holding and outputting the immediately previous value, abnormal values such as those described above will not be output.

■ By measuring the time when the amplitude decays and issuing an alarm output after a certain period of time, it is now possible to detect abnormal conditions related to the posture, vibration, etc. of the object to be measured.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram showing an example of the operation of each part. 1: Frequency modulation circuit 2; Semiconductor laser oscillator 3: Collimator lens 4: Beam splitter 5: Reference mirror 6: Moving mirror 7: Photo receiver 8: Waveform shaper 9: Period counting circuit 10: Distance calculation circuit 11: Latch circuit
12: Output circuit 13: Full wave rectifier circuit 14: Controller 15: Alarm circuit

Claims (1)

[Claims] 1. A semiconductor laser beam whose frequency is modulated so that it continuously increases and decreases at a certain rate is split into two directions, and one beam is sent to a reference mirror provided at the end of the reference optical path, and the other beam is split into two directions. A laser length measurement device that irradiates each of the light beams onto a reflecting mirror fixed to an object to be measured, mixes the respective reflected lights, and measures the distance of the reflecting mirror based on the period of a beat wave generated by light interference. A means for detecting the amplitude of a beat wave, and a means for detecting the amplitude of a beat wave when the amplitude value is below a certain threshold, stops outputting a distance signal calculated based on the measured period, and outputs a distance signal immediately before the amplitude attenuates. What is claimed is: 1. A laser length measuring device characterized by comprising means for outputting an output, and means for measuring an amplitude attenuation time and outputting an abnormality alarm after a certain period of time has elapsed.