JPH0641842B2 - Measurement signal conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Use The present invention is intended to measure a displacement amount with high accuracy by a simple device using a laser beam, and a frequency-modulated signal of light is generally used as a moire fringe. Reading counter,
The present invention relates to a signal conversion circuit for enabling input to a two-phase (sin, cos) input counter such as a magnetic grating reading counter.

<Prior Art> Japanese Patent Application Laid-Open No. 47-17457 “Laser length measuring device” is an example of a length measuring device that measures a change in distance using laser light.
As shown in the description of FIG. 3 in the “Detailed Description of the Invention” section, the two output beams of different frequencies are linearly polarized beams orthogonal to each other, one of which is a reference signal (REF) and the other is fixed. Interference signal (DOP) between the light reflected by the reflecting mirror and the light reflected by the moving reflecting mirror for measuring the distance.
Then, the frequency difference of the DOP signal with respect to the REF signal was read and counted through the demodulation polarizer. The counting counter for reading this frequency difference is a special one made specially, and the inside is complicated and expensive.

<Solution to the Present Invention> In the present invention, an inexpensive and simple structure device can be obtained by using a commonly used two-phase (sin, cos) input type counter without using a special counter. .

<Example> An outline of the laser interferometer used here will be described with reference to FIG. The embodiment of FIG. 1 is carried out according to FIG. 3 of the specification of Japanese Patent Application No. 59-60228 “Lightwave Interferometry Length Measuring Device” filed by the present applicant. Is divided into two by the three and four acousto-optic modulators, resulting in two different frequency output beams,
The beam emitted from the acousto-optic modulator 4 passes through the reflecting mirrors 5 and 6, passes through the beam splitter 7 and passes through the polarizing plate 13 for 1
It enters the photodetector 4 and becomes the reference signal (REF). The beam that has passed through the acousto-optic modulator 3 passes through the beam splitter 7 and is bisected by the beam splitter 8 and is reflected by the fixed mirror 9 and the beam reflected by the moving reflecting mirror 10 that measures the distance. The beam splitter 8 interferes with each other, passes through a polarizing plate 15 and enters a photodetector 16 to generate an interference signal (DOP). Here, it is widely known that the REF signal and the DOP signal have the following contents. That is, DOP = sin {2πt + σ (χ)} REF = sin (2πt) (where, is the modulation frequency, and σ (χ) is the phase corresponding to the change in distance) where DOP at time T such that 2πt = 0
The signal is DOP (t = T) = sin {2πT + σ (χ)} = (2πT) ・ cosσ (χ) + cos (2πT) ・ sinσ (χ), and this signal is applied to all Ts for which 2πt = 0. If sampled and held, it becomes a signal of sin σ (χ), that is, a signal converted into a displacement signal. As well If T is determined so that, a signal of cosσ (χ) whose phase angle is shifted by 90 ° with respect to sinσ (χ) is obtained. A circuit for implementing this concretely is shown in FIG. The third
The figure is a waveform diagram of each part. Here, the REF signal is
The DOP signal is low. The REF signal then produces a pulse signal at 90 ° and 0 ° by the pulse generation circuit. On the other hand, the DOP signal B is put into an automatic gain circuit (AGC) and its amplitude is controlled to be constant, and then put into a sample hold circuit to generate hold signals at 90 ° and 0 °. As shown in FIG. 3, this is the position a ₁ at the phase angle of 90 °,
The amplitude value of b at a ₂ , a ₃ ... Is held and b ₁ , b ₂ , b ₃ ... Are connected to form a solid line signal of c.
At the position where the phase angle is 0 °, the amplitude values of B in c ₁ , c ₂ , c ₃ ... Then, the signal is passed through a low-pass filter circuit to obtain two signals e and f of sin σ (χ) and cos σ (χ). Here, this signal can be used as an input signal of a known two-phase input counter having a displacement amount χ.

<Effect> By interposing the circuit of the present invention between the optical system of the interferometer and the counter circuit, the two-phase that has been generally used in the past can be obtained.
Since it is possible to connect to the counter of (sin, cos) input, an inexpensive laser measuring system can be realized. Also, in a laser interferometer, the environmental conditions (atmospheric pressure, temperature, humidity, etc.) at the time of measurement must be entered in the measurement data and the data must be corrected, but this can be processed by an inexpensive personal computer. is there.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an interferometer used in the present invention, and FIG.
FIG. 3 is a block diagram of the circuit of the present invention, and FIG. 3 is a waveform diagram of signals in each part of FIG. 1: light source, 2, 7, 8: beam splitter 3, 4: acousto-optic modulator, 5, 6: reflecting mirror 13, 15: polarizing plate, 14, 16: photodetector 9, 10: cube corner, 17: Counter 18: Measurement signal converter

Claims (1)

[Claims] 1. A reference signal (REF) of a laser interference signal and an interference signal (DOP) according to a displacement amount χ as inputs, and RE.
A pulse generation circuit that creates a pulse signal at phase angles 0 ° and 90 ° of the F signal, an automatic gain circuit (AGC) that controls the amplitude of the DOP signal, and a sample hold circuit that creates a sample hold signal in the pulse, and 0 °, It consists of a low-pass filter circuit that removes harmonic components from each 90 ° hold signal, and the input signal is sin σ (χ), cos σ
A conversion circuit for the measurement signal that is converted into (χ) and used as the input signal of the counter.