SU1244485A1 - Method of measuring shift of scanning transducer - Google Patents

Abstract

This invention relates to a measurement technique. The aim of the invention is to improve the measurement accuracy by eliminating errors from external influences. The light flux, modulated according to the cosine law, is directed to the raster interface, spatially modulated according to the sinusoidal law, with the frequency of modulation of the light flux. The luminous flux that has passed the raster conjugation is converted by the photoreceiver into an electrical signal. A harmonic component is extracted from the electrical signal with a frequency equal to twice the modulation frequency of the light flux. The harmonic component phase is measured with respect to a reference signal having a frequency equal to twice the modulation frequency of the light flux. Based on the measured phase difference, the raster transducer rasters are displaced. 1 il. se IS9 4; 4 00 ate

Description

The invention relates to measuring technology and can be used in the construction of raster transducers.

The purpose of the invention is to improve accuracy by eliminating errors.

The drawing shows a functional diagram of the device that implements the method.

The device contains a generator 1, a synchronized generator 2, whose input is connected to the output of generator 1, optically coupled light source 3, the modulating input of which is connected to the first output of synchronized generator 2, raster system 4 consisting of measuring and indicator rasters modulating element associated with the indicator raster, the input of the modulating element is connected to the second output of the synchronized generator 2, the photodetector 5, the selective amplifier 6, the input of which is connected to the photodetector emniku phase meter 5 and 7, whose inputs are connected to the output of the generator 1 and the output of the selective amplifier 6.

The device works as follows.

Generator 1 generates a signal that arrives at the reference input of the phase meter 7 and the input of the synchronized generator 2, which divides the frequency into two.

The signal generated at the first output of the synchronized generator 2 is fed to the modulating input of the source 3 of the light, which forms a radiation flux, harmonically modulated. The signal generated at the second output of the synchronized generator 2 is fed to the input of the modulating element of the raster of topic 4. The modulating element, such as a piezoplate, is connected to the indicator raster. The scanning of the indicator raster with respect to the measuring raster associated with the object is carried out according to a harmonic law with a scanning amplitude shorter than the period of the measuring and indicator rasters. The frequency of modulation of the radiation flux of the light source 3 is equal to the scanning frequency of the indicator raster relative to the measurement, included in the raster system 4, and the modulation phase is shifted relative to the scanning phase by 90 °. The radiation flux from the light source 3, which has passed through the raster system 4, is incident on the photodetector 5, which converts the light flux of the radiation into an electrical signal. The harmonic component of the electrical signal with a frequency equal to twice the scanning frequency of the indicator raster relative to the measuring raster is extracted by a selective amplifier 6, the output signal from which is fed to the measuring input of the phase meter 7.

The electrical signal generated at the output of the photodetector 5 has a complex shape and is determined by the expression:

(l- -fntCos it) 1 + t2С05 (- -Al: + tzH

XsmcuO

where 1/5 is the current voltage value

output of the receiver;

Lz is the amplitude value of the voltage at the photodetector output;

m is the index of the amplitude modulation of the light source;

(O is the frequency of amplitude and phase modulation;

t2 is the coefficient characterizing the contrast of the bands formed at the exit of the raster system;

d - the period of the measuring and indicator rasters;

AJC is the magnitude of the measured displacement;

TK is the phase modulation index, determined by the scanning amplitude of the indicator raster relative to the measuring one.

The signal extracted by the selective amplifier 6 is defined by the expression:

f / 6 Ae cos (2 (at + - Al;),

where f / 6 is the current value of the voltage at the output of the selective amplifier; Lb is the amplitude value of the voltage at the output of the selective amplifier.

The value determines the phase of the signal with a frequency equal to twice the scanning frequency of the indicator raster relative to the measuring raster, which is measured by a phase meter 7, the reference input of which receives a reference signal from generator 1. The phase shift measured by the phase meter 7 is linearly related to the amount of measurement raster relative to the indicator raster included in the raster system 4.

The use of the method makes it possible to increase the measurement accuracy of the raster converter as a result of decreasing errors caused by a change in the average radiation flux of the light source and a change in the speed of movement of the measuring raster relative to the indicator one.

Claims (1)

Invention Formula The method of measuring the movement of the raster converter, which illuminates the raster interface formed by the measuring and indicator rasters, the light source, scans the indicator raster relative to the harmonically measuring with a scanning amplitude shorter than the period of rasters, converts the luminous flux that has passed the raster matching, into the electrical signal, the harmonic component of the electrical signal is extracted with often that is equal to the doubled scanning frequency of the indicator raster relative to the measuring raster, a reference signal is formed, whose frequency is equal to the doubled scanning frequency of the indicator raster relative to the measuring raster, and the measuring signal, the phase shift of the measuring signal relative to the reference signal is measured, the value of the measured phase shift is determined The amount of movement of the measuring raster relative to the indicator raster, characterized in that that, in order to improve the measurement accuracy, modulate the radiation flux of the light source according to the harmonic law with a frequency equal to the scanning frequency of the indicator raster relative to the measuring raster, and a phase shifted relative to the scanning phase by 90 °, and use the selected harmonic component as the measuring signal a frequency equal to twice the scanning frequency of the indicator raster relative to the measuring raster. 7 g