SU1165885A1 - Device for determining displacement of object surface points - Google Patents

Abstract

1. DEVICE FOR DETERMINING SURFACE POINT SMEVSCHNY .OBEKTA comprising a source of coherent radiation and the interferogram speckle object otlichayus in that, for the purpose povysch ee performance, it is endowed .sheni Genoux xy Lurie analyzer luminance distribution of the interference fringes and recording unit, made in the form of a comparator, a pulse counter with adjustable counting time, an offset register along the X coordinate, an offset register along the Y coordinate and a switch, an optical object speckle pattern associated with a two-coordinate Fourier analyzer, the first and second outputs of which are connected to the first and second inputs of the registration unit, respectively the comparator input and the first pulse counter input, the comparator output connected to the second counter input, pulses, the first output of which is connected to the information inputs respectively, the offset register along the X coordinate and the offset register along the Y coordinate, and the second output with the input of the switch, the first output of the switch is connected to the control input of the offset register Along the X coordinate, the second output is with the control input of the offset register along the Y coordinate, and the third output is the output of the registration unit connected to the control input of the Fourier analyzer. 2. Device POP.1, characterized in that the two-coordinate Fourier analyzer contains a tunable frequency generator, (L key, acousto-optical deflector in the form of piezo exciters on two adjacent faces, a Fourier objective lens, a photogenerator and a detator, the output of the tunable frequency generator is connected to the key input, one output of which is connected to the first piezo transducer and the other to the second piezo transducer of the acousto-optical deflector, acousto-optical deflector, Fourier lens and photodetector cally bonded, the photodetector output is coupled to the detector, the outputs of the detector and tunable frequency generator are respectively first and second outputs fureanalizatora and the second key input is a control input fureanalizatora.

Description

1, the invention relates to a measurement technique and can be used to determine displacements of surface points of an object. A device is known for determining the displacements of the points of the surface of an object 1, which contains a source of radiation and a speckle interferogram of an object. The device also contains a screen. The essence of the measurement of displacement consists in determining the pitch and angle of inclination of the interference fringes obtained on the screen by illuminating the speckle interferogram, recorded by the two-exposure method, with a beam of a coherent source. The displacement of the points of the object is determined by the relation -BI M, Ur — I, where is the wavelength of the light; L is the distance from the speckle interferogram to the screen; m is the scale of the image of the object under study on a spectrinterfergram; a - step interference polo on the screen. A disadvantage of the known device is the laboriousness and the long decoding time of speckle interferograms. The aim of the invention is to improve the performance of determining displacements. The goal is achieved by the fact that a device for determining displacements of points of a surface of a volume, containing a source of coherent radiation and a speckle interferogram of an object, is equipped with a two-coordinate Fourier analyzer of the distribution of the brightness of interference fringes and a recording unit made in the form of a comparator, a pulse counter with adjustable the counting time, the X offset register, the X coordinate shift register, and the switch, the speckle interferogram of the object is optically coupled to the Fourier analyzer, the first and the outputs of which are connected to the first and second inputs of the register, which are respectively the input of the comparator and the first input of the pulse counter, 852 the output of the comparator is connected to the second input of the pulse counter, the first output of which is connected to the information inputs of the offset register X and the offset register respectively the Y coordinate, and the second output — to the input of the switch; the first output of the switch — is connected to the control input of the offset register along the X coordinate; the second output — to the control input, regis pa offset of Y coordinate, and the third output is the output register unit is connected to a control input of the Fourier analyzer. In addition, the two-coordinate Fourier analyzer contains a tunable frequency generator, a key, an acousto-optical deflector in the form of a plate with piezo exciters on two adjacent edges, a Fourier lens, a photodetector, and a detector, the output of the tunable frequency generator is connected to the key input, one the output of which is connected to the first piezoelectric transducer, and the other to the second piezoelectric transducer of an acousto-optical deflector, an acousto-optical deflector, a fourier e-objective and a photodetector are optically coupled, the output of the photodetector is connected to d detector, the detector output and frequency tunable oscillator are respectively first and second outputs of the Fourier analyzer and the second input is a control input of the key yuschim Fourier analyzer. Fig. 1 shows a block diagram of a device for determining the displacement of surface points of an object; figure 2 - the Fourier spectrum. The device contains a coherent radiation source 1, a speckle interferogram 2 located in front of it, optically coupled to a two-coordinate Fourier analyzer 3 for the distribution of the brightness of interference fringes optically coupled to a speklinterferogram 2, a recording unit 4, and two outputs of the Fourier analyzer 3 are connected respectively to the dual beam the inputs of the registration unit 4, and the output of the registration unit 4 is connected to the control input of the Fourier analyzer 3. The speckle interferogram 2 is a photographic plate with the recording x exposures of the initial and offset speckle structures of the surface under study.

The two-coordinate Fourier analyzer 3 of the distribution, the brightness of the interference fringes, consists of a generator 5 of a tunable frequency of key 6, an acousto-optical deflector 7, having a plate shape (made of optically transparent material) with piezo exciters on two adjacent faces, a Fourier lens 8, a photodetector 9 and the detector 10, and the output of the tunable frequency generator 5 is connected to the input of the key 6, one output of which is connected to one, the piezo exciter deflector 7, and the other output to the second piezo exciter 7, the output of the deflector 7 is optically coupled to the Fourier lens 8, the output of which is optically coupled to the photoreceiver 9, the output of the photoreceiver 9 is connected to the input of the detector 10, the input of the acousto-optical deflector 7 is the optical input of the Fourier analyzer 3, the second key input 6 is the control input of the Fourier analyzer 3, the outputs of the detector 10 and the tunable frequency generator 5 are respectively the first and second outputs of the Fourier analyzer.

The registration unit 4 comprises a comparator 11, a pulse counter 12 with adjustable counting time, an offset register 13 along the X coordinate and an offset register 14 along the Y coordinate, a switch 15, the first input of the registration unit 4 being the input of the comparator 11, and the second input of the pulse counter 12 , one output of the counter 12 pulses is connected to the information inputs of the registers 13 and 14 offset by coordinates X. and the second Y is connected to the input of the switch 15, the first and second outputs of the switch 15 are connected to the control inputs of the offset registers 13 and 14 along the X and Y coordinates, the third output of the switch 15 is the output of the register 4.

The device works as follows.

The source of the beam: a 1 (laser) illuminates the speckle interferogram 2 at the point of the image of the object in which it is necessary to determine the offset. AT

658854

As a result of diffraction of light on the original and displaced speckle structures when the object is displaced or deformed between two exposures on the screen in the plane located behind the speckle interferogram, Young bands are observed at a distance L. The displacement of points on the surface of an object up to a sign is determined by the formula (1).

The diffraction pattern is projected into the plane of the acousto-optic deflector 6. An acoustic wave is excited in the transparent plate of the acousto-optical reflector using piezoelectric transducers. Due to the photoelastic effect, it creates a periodic change. the refractive index in material 20 is a traveling phase grating on which it diffracts the interference pattern projected onto the deflector 6.

The alternating excitation of the piezotransducers is scanned in the selected direction X or Y. The scanning direction is switched by a control signal from the registration unit 4 to the control input 0 of the Fourier analyzer 3.

When modulating the power applied to the piezotransducer of a signal, the diffraction efficiency of the grating changes along the aperture of the deflector 6 according to the law

2.ucoJ- (Vvt) 1

(2)

 -

where is the diffraction efficiency

V is the speed of sound propagation in the material of the deflector 6; 42 - circular modulation frequency

acoustic power - coordinate (X or Y). As a result, the rejected pattern turns out to be an aperture-modulated harmonic function with a spatial frequency

, -. (3)

 ...

The intensity of the diffracted wave is then described by the expression

tUbI () Ucos 2ir;) (- Vt) 5,

(four)

where 1 (Yu is the distribution-intensity in the interference

picture.

The entire luminous flux rejected by the deflector by the Fourier objective 8 is directed to the photodetector 9. The Fourier objective 8 and the photoreceiver 9 integrate the luminous flux over the entire aperture. Then the variable component of the output signal J (-) of the photodetector 9 is the Fourier spectrum of the interference pattern.

 1 lUVco 2ir (/

.De K is a constant coefficient.

It has the form of three spectral, the average peak corresponds to a constant component in the interference picture, and the two side frequencies of the interference fringes are in the chosen direction X or Y. The spectral spikes have a symmetrical shape, and their width is determined by the number of recorded fringes.

Since the pitch of the fringes ay and the frequency of the fringes are) in the chosen direction are related by

 ig

then the displacement of the points of the object from the expression (1) can be represented as

M

(6)

LU

im

Thus, by measuring the frequencies in two orthogonal directions; Neither 9 and Si c determine the displacement at the selected point of the lens using the X and Y coordinates.

The signal from the photodetector 9 is detected by the detector 10 and is fed from the output of the Fourier analyzer 3 to the input of the comparator 11 of the recording unit 4, and the trigger level of the comparator is chosen experimentally depending on the quality of the speckle interferogram. The comparator 11 is triggered at the time when the frequency of the bands in the interference pattern coincides with the modulation frequency of the acoustic wave of the deflector 7.

The frequency of modulation of the acoustic wave is related to the frequency of modulation of the generator 5 of a tunable frequency by relation (3). Thus, by measuring the modulation frequency of the generator 5 at the time of the triggering of the comparator 11, the displacement is determined

points of the surface of the object. From expressions (3) and (6) get

-

(7)

SlTrnV

The number of pulses of the modulator signal of the variable frequency generator 5, received at the first input of the counter 12 pulses with an adjustable -Count count, is measured at the moment of arrival of the pulse from the comparator

11 at his second entrance. The measurement time is pre-entered by the operator so that the readings of registers 13 and 14 are equal to the projections of the displacement of the object point in accordance with formula (7). This time is determined only by the geometrical parameters of the optical recording scheme and the restoration of the speckle interferogram.

The switch 15 controls the operation mode of the registration unit 4. From the first output he gives the starting signal to the X register, i.e. the information is recorded by the X 13 register. Simultaneously from its third output, the control input of the key of the Fourier analyzer 3 is fed to the control signal allowing the excitation signal to pass from the tunable frequency generator 5 to the piezoelectric transducer of the deflector 7 scanning the X coordinate. After that as a counter

12 pulses will measure the offset along the X coordinate, from its output to the input of the switch 15 will receive a signal of the end of the conversion and the switch 15 will change its output signals so that scanning is now performed along the Y coordinate, and information about the offset projection will be written to the register

Thus, during one measurement cycle, the values of the projections of the displacement at a pre-selected point on the surface of the object are obtained along two orthogonal directions, for example, along the X and U coordinates. To determine the displacement at another point on the object, the operator produces a shift of the speckle interferogram, after which the measurement cycle is repeated yut.

The device allows you to automate the process of measuring the displacements of points on the surface of an object, and to speed up and simplify the process, which improves performance.

Claims (2)

1. DEVICE FOR DETERMINING DISPLACEMENTS OF SURFACE POINTS. OBJECT, containing a source of coherent radiation and a speckle interferogram of the object, characterized in that, in order to increase productivity, it is equipped with a two-coordinate Lurie analyzer of the distribution of brightness of interference fringes and a recording unit made in the form of a comparator pulse counter with adjustable counting time, shift register in X coordinate, shift register in Y coordinate and commutator, speckle interferogram of the object is optically coupled to by the Lurie analyzer, the first and second outputs of which are connected to the first and second inputs of the recording unit, which are respectively the input of the comparator and the first input of the pulse counter, the output of the comparator is connected to the second input of the counter, pulses, the first output of which is connected to the information inputs, respectively, of the offset register along the X coordinate and the displacement register in the Y coordinate, and the second output is with the input of the switch, the first output of the switch is connected to the control input of the displacement register in the X coordinate, W The second output is with the control input of the displacement register in the Y coordinate, and the third output is the output of the registration unit connected to the control input of the Fourier analyzer. 2. The device according to claim 1, characterized in that the two-axis Fourier analyzer contains a tunable frequency generator, a key, an acousto-optical deflector in the form of a plate with piezoelectric exciters on two adjacent faces, a Fourier lens, a photodetector and detector. Output The tunable frequency generator is connected to the key input, one output of which is connected to the first piezoelectric transducer, and the other to the second piezoelectric transducer of the acousto-optical deflector, the acousto-optical deflector, Fourier lens and photodetector are optically coupled, a photodetector coupled to the detector, the outputs of the detector and the tunable oscillator frequencies are respectively first and second outputs fureanalizatora and the second key input is a control input fureanalizatora. CX) SP 00 00 cl 1165885 2