SU1427179A1 - Device for checking rectilinearty - Google Patents

Abstract

The invention relates to the field of measurement technology. The aim of the invention is to increase productivity, accuracy and reliability by applying the mode of spatial modulation of the light flux in the acousto-optic cell. During the propagation of the light flux 15 through the acousto-optic cell 2, diffraction beams 14 are produced, which contain information on the envelope of the diffraction beam 14 The phase of the generator signal 8 reference oscillations. When moving the measuring carriage 3 along the measured profile, due to its irregularity, the phase of the envelope of the signal of the diffraction beam 14 will change. Measure the change of the phase of the envelope of the signal of the diffraction beam 14 with a phase meter 7, determine the amount of roughness of the measured profile. 1 il. §

Description

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The invention relates to a measurement technique and can be used to control deviations from a linearity and a plane.

The purpose of the invention is to increase the productivity, accuracy and reliability by locating the photodetector and the lens on the measuring cell and applying the mode of spatial modulation of the light flux in the acousto-optic cell.

The drawing shows the functional diagram of the device for monitoring the linearity. : A device for controlling the linearity contains optically coupled light source 1, an acousto-optic cell 2 installed on the measuring carriage 3 for modulating the light beam and a positioning-sensitive phototransducer 1 designed to detect deviations of the light beam. amplifier 5, connected in series with actuator 6, kinematically connected with light source 1. The feedback circuit from the position-sensitive photovoltaic converter A, amplifier, 5 and actuator 6 is designed to stabilize the position of the reference light beam of the source of light I. In addition, the device has a phase meter 7 for measuring the phase shift, a generator 8 of reference oscillations, a selective amplifier 9 designed to amplify the first harmonic of a signal with a frequency O., a recording unit 10 and a generator 11 of carrier oscillations with a frequency co modulated by reference oscillations of the frequency , The lens 12 and the photodetector 13 are installed on the measuring carriage 3 in the zone of the diffraction leg of the beam 14 of the acousto-optic cell 2. The photodetector 13 is located in the focal plane of the lens 12, the generator output 8 of the reference oscillations 5 is connected to the first input of the phase meter 7 and the modulation input of the carrier 11 oscillation, the output of which is connected to the input of the acousto-optic cell 2. The output of the photoreceiver 13 is connected to the input of the selective amplifier 9, the output of which is connected to the second input of the phase meter 7, the output of which is connected to 10 uyuschim unit.

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Lens 12 is designed to focus the diffraction beam 14 on the photosensitive area of the photodetector 13 and eliminate the possible displacement of the light spot from the photosensitive area with parallel movements of the measuring carriage up and down on the unevenness of the monitored profile. The photodetector 13 is designed to detect the envelope of the light signal with a frequency Si and feed it to the phase meter 7 for measuring the phase shift.

The device works as follows.

The light source 1, installed at the beginning of the controlled profile, emits a reference flat network beam 15 with a flat wave front (parallel beam), which passes through the acousto-optic cell 2 and hits the position-sensitive phototransducer 4. The light beam 15 sets a reference straight line that coincides with its axis of symmetry, with respect to which the profile is monitored and measured by the linearity of the profile. When random deviations of the light beam 15, caused by the drift of the radiation pattern of the light source 1 or by the fluctuation changes in the refractive index gradient of the air, the output of the position-sensitive photovoltage converter 4 is generated by an error signal, which is amplified by the amplifier 5 and sets in motion actuator 6. The actuator 6 rotates the source, 1 light so that the light beam 15 occupies the initial position and the error signal is equal to zero. In this way, the position of the reference light beam 15 is stabilized. The oscillator 8 of the reference oscillations with frequency Q modulates in amplitude the signal of the oscillator 1 1 of oscillation carriers with frequency se, affecting its modulation input. The amplitude-modulated signal excites in an acousto-optic cell 2 an ultrasonic wave of the following type:

S (t, x) - l + mco8 (nt-Kx) cos (ot-Kx) j

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Q where K ---- the wave number of the wave envelope;

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K --- is the wave number of the carrier wave;

m is the modulation index; t is the current time; X is the coordinate along the direction of movement of the ultrasound wave. The ultrasonic wave is excited at the entrance end of the acousto-optic cell 2 and passes some distance X to the intersection of the axis of the light beam 15, while undergoing a deceleration in time. This delay results in a phase shift in the envelope (reference oscillation) of the signal.

P

to x

(2)

In order for the acousto-optic cell 2 to work in the diffraction mode, it is necessary that the wavelength of the carrier oscillation is much smaller than the width of the light beam. With this, the following inequality should be fulfilled:

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The ultrasound wave of the SCt, co6 (Qt-Kx) type, in accordance with the elasto-optic effect, modulates the refractive index of the material of the acousto-optic cell 2 and, in the intersection zone of the light beam 15, is a traveling phase diffraction grating.

As a result, at the output, in addition to the reference light beam 15 (zero order), diffraction beams appear. One of them (14), corresponding to the first diffraction order, is focused by lens 12 on the photodetector 13. Due to the fact that the signal creating the diffraction grating is modulated by the amplitude by a reference oscillation with frequency fl, the amplitude of the electric field strength in the diffraction beam 14 also varies with time with frequency and phase shift, defined by expression (2), Since everything is. the photodetectors have a quadratic characteristic, the output signal, in addition to the component with frequency Q, also contains a constant component and a second harmonic, which are suppressed in the selective amplifier. As a result, after amplifier 9, the input of phase meter 7 receives a signal of the form:

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5 50 55 The second input of the phase meter 7 receives a signal from the generator 8 reference oscillations of the form:

2 (t) cosQt.

Phase meter 7 measures the phase shift tf, linearly related to the distance XjjjB according to the extrusion (2). The recording unit 10 fixes a signal proportional to the offset value X. During the movement of the measuring carriage 3 along the monitored profile as a result of irregularities of the latter, the measuring carriage 3 periodically rises and falls. In this case, the value of X varies accordingly. The values of these measurements are recorded in the recording unit 10 and allow us to determine the degree of linearity of the monitored profile. At the same time, the reference light beam 15, which has passed the acousto-optic cell 2, is not subjected to distortions, its phase front remains flat, which significantly increases the length of the controlled profile,

The operation of the acousto-optic cell in the diffraction mode does not require high acoustic signal powers. Relatively low acoustic signal powers do not lead to rapid destruction of the cell material. Due to this, the device has a high reliability.

Claims (1)

Invention Formula A device for controlling the pitch of a non-linearity, containing a series-arranged and optically coupled light source, an acousto-optic cell and a position-sensitive photo-converter, a series-connected amplifier and an actuator, a series-connected oscillator reference oscillator. 5U Research institutes and a phase meter, a selective amplifier, a registering unit and a measuring carriage on which an acousto-optic cell is installed, the output of the selective amplifier is connected to the second input of the phonometer, the output of which is connected to the input of the recording unit, the actuator is kinematically connected to the light source, characterized by the fact that, in order to increase Productivity, accuracy and reliability, it is equipped with a generator of non-oscillations, optically coupled with a lens and a photodetector. 796 installed on the measuring carriage in the zone of action of the diffraction beam of the acousto-optic cell, the photoreceiver is located in the focal plane of the lens, the output of the photoreceiver is connected to the input of the selective amplifier, the output of the reference oscillator is connected to the modulation input of the carrier oscillation, the output of which is connected to the input of the acousto-optical cell, The frequency Q of the carrier oscillator is selected from the conditions for ensuring the diffraction mode of the acousto-optic cell.