SU1479831A1 - Device for measuring angular displacement of member - Google Patents

Abstract

The invention relates to a measurement technique and can be used to accurately measure the angular displacement of an object. The purpose of the invention is to expand the range of measurement of the angular displacement of an object by modulating the frequency of an acousto-optic modulator and filtering the corresponding electrical signals. The beams diffracted by the acousto-optic modulator 2 and the zero order beam during the passage of a plane-parallel plate 3 experience different phase incursions depending on the angle of rotation of the plane-parallel plate. The diffraction grating 4 combines the indicated beams on the photodetector 5, at the output of which the signal phase will be proportional to the angle of rotation of the plane-parallel plate 3. Phase meters 7 and 10 carry out a coarse and accurate angle measurement, respectively. 1 il.

Description

4i

sj

with

00

WITH

The invention relates to a measurement technique and can be used to accurately measure the angular position of an object in a wide range of angles.

The purpose of the invention is to expand the range of measurement of the angular displacement of an object by modulating the frequency of an automatic opto-modulator and filtering the corresponding electrical signals.

The drawing shows a functional diagram of the device.

The device contains a series-connected laser 1, an acousto-optic modulator 2, a plane-parallel plate 3 connected with an object, a diffraction grating 4, a photo-receiver 5, a filter 6, a phase meter 7, an output of the photo-receiver 5 through a filter 8 and a mixer 9 are connected to a phase meter 10, the first inputs of the phase meters 7 and 10 are connected to the output of the low-frequency generator 11, the output of the high-frequency generator 12 is connected to the second inputs of the mixer 9 and the modulator 13, the output of which is connected to the input of the acoustic modulator 2,

The device works as follows.

The beam of laser light 1 falls on an acousto-optic modulator 2. A beam diffracted by an acousto-optic modulator 2 and a zero-order beam are fed to a plane-parallel plate (SPT) 3, the angle of rotation of which must be measured. Let in be the angle of diffraction of light on modulator 2, when one frequency is applied to it. If SPT 3 is perpendicular to the optical axis, then the angle of incidence of the beam on the plate is at. If SPT 3 is rotated by angle ei, then the angle of incidence y, 0, d. Similarly, the angle of incidence of the zero-order beam on the plate y2 d. Both beams, when passing the SPT 3, depending on the angle of rotation d, acquire different phase incursions.

The angles of refraction of the beams of the first and zero orders

, sin (6 + al) sin y;

i sine sinTl --- (O

where n is the refractive index of the SPT,

Phase raids during the passage

SPT

v,

2iTL-n 2ff

Ln

cosj-i L I Pn2

- 2 | TL- n 2 L-n Lose and

ZT (2)

sin2

PG Sln J1 and

Decomposition of these expressions in the Taylor series is obtained

2i L-nГ1-cos2 (e + oO I

V G I1n U

“. , + j

0 LLn2 J

(3)

where h is the wavelength of light;

L is the thickness of the SPT. The diffracted beam passes through the diffraction grating 4 and hits the photodetector 5, and the beam

zero order diffracted by

diffraction grating 4 and also enters the photodetector 5, where both beams interfere. Incremental diffraction order of light that

occur when the diffracted beam passes through the diffraction grating 4, can be eliminated by installing a slit in front of the photodetector (not shown). Modulator 2 from modulator 13 is given a signal

U (1 + t taken by coswftt cosw8t +

+ - cos (ui8 + uiK) t + - COS (U) B-WH) t, (4)

where t is the modulation depth;

WH- generator frequency 11. From expression (4) it can be seen that the modulator 2 is supplied with signals of three frequencies. Therefore, after the modulator 2, there are three diffracted beams, each of which, when passing through the plate 3, acquires a different phase shift in accordance with expression (3),

50

as the angle of diffraction of light on the modulator

i - Ј. f

 - v-

v ъъ

(five)

where Vift is the speed of sound in modulator 2;

f is the frequency of the signal. The modulator 2 is assumed to perform a shallow phase modulation,

314798314

You can get the following expression, i, to be filtered by a device for voltage at the output of the photodetector-after the photodetector 5 of the capacitor):

nick 5 (constant constituting the mo

and you iostn 5 / ftexP (i4 + kxsin6t) + iexp (+ + kxsin62 + -an p

+ H. | (we + wH) t + + kxsin6j) + Y | exp fi (SW) t Hf (l + kxsin 4 J | Jx "Urn, B t + ifa- (/, + - | (sin 64-sin 0, + UmlCos (u) & WH) t tifj -if

+ - | (sin03- sin01) J + it3soz (i) B- and, H + if 4 L + f (sin e4- -sin6,) I + Um4cos (2o) Mt + i / 4- i / 3 + - | (si / i03) j + Umfcos wHt +

+ -5- + a (sin 93- sin e4) J, - (6)

where a is the photo-aperture aperture 5; This signal is fed to the mixer

10 - light intensity at mod-9, after which a signal is received

l torus 2; 20 u, Urancos u) Ht + 4 -4i + (sines-sine,) J.

5 - sensitivity photoreception-, l z / y

 using filter 6 is allocated

 - diffraction efficiency signal

modulator 2; U U T t i ± -4j

p - diffraction efficiency 25 5 COSLU) H 2 +

diffraction grating 4 :. .

ttt ttt tt ™ ka (sin 0s-sin64) t, „, Um.Unij,, Um3, j (9)

Uma, TJm K - amplitudes of the frequency coefficients eq for compensating constant phase

signaling signals at the output

the course of the photodetector; gn shifts a (sin 65- sin 6,);

, -, izcosW.ka (sin9s-sine)

H (- An2 Gna top ° Dah Filter ilЈos2j, 6 + c {21 poB 6 and 8 can be set with the F1 ALn2 J hooks (not shown).

2 jrLg1-cos2 (0з +) 1 Therefore, we can assume that the phase meter

ALn J 7 Izmet e b b ew spvig ----

7 measures the phase shift

q, 2ЈЬп р + Iicos2 e j + o (} |. Phase meter 10 - phase shift V3-H,.

 Ln2. Allowing (6) and believing that the angles of differential, L l L40, the light is small, get

 i j; yi v- f in 5

, 4i / l. . . ,, 1ПЧ

.Л А «: Ч. f И

6E v fB + fH 52nV

382fL

Vo ,,

M e - - - (f6 + fH) ain2ef. (eleven)

64 v (n 4 f

V38 Since f e f n, the steepness of the 2ff phase change in the expression (11) is equal to; more than in expression (10).

Therefore, the phase meter 7 can be realized - the step of the diffraction grating 4., Q is a rough measurement of the angle c / within wide limits, and the phase meter 10 From expression (6) it can be seen that it is accurate. By calibrating the phase meters, with the output of the photodetector 5, there are all known angles d, you can form signals of several frequencies. By using two measurement channels, the fine filter 8 extracts the ' and coarse signal. Moreover, the measuring range

the coarse channel is much higher, U, Um cos (ыв + w) t + ijs-if, + than the prototype. Indeed, is, favor ratio (10) dl Chprot

ka / l t / -

+ - (sin bj sin sin,) (7) from the expression:

7 izmete et gb spovig ----

7 measures the phase shift

phase meter 10 - phase shift V3-H,

 U sin (w t

П1D

,

prog

),

(12)

if

prot

w

fsine

l ™ a

- frequency of the high frequency generator; a - aperture of the photodetector; 9 - the angle between the beams, from

razhennymi from reflectors in the plane of the photodetector; light wavelength; voltage amplitude

get

M-Jofrp - - ".... J

nV3B- a

m Pr01

Suppose that lead molybdate with n 2, V, 4 -104 mm / s is selected as the modulator material,

L 3 mm, Receive

-e

N

And 0.63-10 um, and 2 mm.

YU

with

20, a diffraction grating and a photodetector, a first phase meter, the output of which is the first output of the device, and a high frequency generator, characterized by

. s

Vnpor

25 that, in order to expand the range of ee. Therefore, in comparison with the measurements of the angular displacement of an object, it is equipped with the first filter, 1

the input of which is connected to the output of the photodetector, and the output to the input of the first phase meter, serially connected by a second filter, the input of which is connected to the output of the photodetector, a mixer and a second phase meter, the output of which is the second

35 by the output of the device, by a modulator, the output of which is connected to an acousto-optic modulator, a low-frequency generator, the output of which is connected to the inputs of the first and second phase meters 40 of the ROV and a modulator, and the output of the high-frequency generator is connected to the inputs of the modulator and mixer .

The range of angle measurements is greatly expanded. Moreover, adjustment and adjustment of the measurement range can be made by selecting the frequency Јn. A phase meter 10 performs an accurate angle measurement.

The steepness of phase measurement in the prototype (12) and in the proposed device (11):

prot

a a

(13)

2fL ()

5 КЭо5р

Equating these expressions with the given data f B v

798316

4-10 Hz, which is quite achievable for modern acousto-optic modulators. Thus, two measurement channels are formed in the device - accurate and coarse, the conversion range is expanded while maintaining accuracy at the prototype level, and the optical layout of the device is also simplified, since there are no reflectors in it.

Claims (1)

Invention Formula A device for measuring the angular displacements of an object, containing an optically coupled laser, an acousto-optic modulator, a plane-parallel plate associated with the object, a diffraction grating and a photodetector, the first phase meter whose output is the first output of the device, and a high-frequency oscillator characterized by ,