SU1285320A1 - Device for measuring shift of interference bands - Google Patents

Abstract

The invention relates to a measurement technique and can be used to measure the profile of polished surfaces. The purpose of the invention is to increase the accuracy and noise immunity of measurements by eliminating the antiphase components of the electrical signal and its subsequent filtering. The goal is achieved by introducing an electronic key 5, a frequency dividing unit 12, a coincidence unit 13, a linear-periodic voltage generator 14, and a band-pass filter 6. As a result, interferometers with sinusoidal or linear-periodic-modulation of the path difference achieve accuracy for double-filtering the signal on the photodetector: removing the antiphase components of the interference signal with the electronic key 5 and further filtering by the active band pass filter 6. The isolated th harmonic does not depend on the amplitude of the phase components of the original signal and is substantially free of noise. 2 Il. (L

Description

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The invention relates to a measurement technique and can be used to measure the profile of polished surfaces.

The purpose of the invention is to increase the accuracy and noise immunity of measurements by eliminating the antiphase components of the electrical signal and its subsequent filtering.

Fig, 1 shows a functional diagram of the device; figure 2 - timing charts of signal processing.

The device contains a light source 1, an interferometer 2 with a modulator, a photodetector 3, a repeater 4, an electronic switch 5, made in the form of a switch, a polo-f active filter 6, zero or 7, a pulse sequence formation unit 8, consisting of RS flip-flop 9 and circuit AND 10, oscillator 11 counting pulses, frequency division block 12, coincidence block 13, sinusoidal or linear-oscillator 14, periodic, voltage, interface 15, mini-computer 16.

The light source 1 with the modulator is optically connected to the interferometer 2 and the photodetector 3, the output of the photodetector 3 is connected to the input of the repeater 4. The repeater 4, electronic key 5, active passband filter 6, the zero body 7 are connected in series, the output of the zero organ 7 connected to the S-input of the RS-trigger 9 of the pulse-shaping sequence block 8, the output of the block 13 is connected to the R-input of the RS-flip-flop 9, and the output of the RS-flip-flop 9 is connected to one of the inputs of the AND 10 circuit, the other input of which is connected with generator 11 counting impu This device is simultaneously connected to the input of the frequency division unit 12. The first output of the frequency division unit 12 is connected to the input of the coincidence unit 13, the output of which is connected to the control input of the electronic key 5. The second output of the frequency division unit 12 is connected to the input of the linear-periodic voltage generator 14, the output of which is connected to the interferometer modulator 2 light emission. The output of the circuit AND 10 of the pulse sequence formation unit 8 via the interface 15 is connected to the input of the mini-computer 16,

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The device works as follows.

In the image plane of the interference pattern of the interferometer 2, the path difference of the light rays is scanned by the modulator of the interferometer 2, for example, by a sinusoidal (linear-periodic) law (Fig. 2a, b), the photodetector 3 converts the interference signal into an electrical voltage, from the output of the photodetector 3 the signal is fed to the input of the repeater 4, and from the output of the repeater 4 to the first output of the electronic key 5, the repeater 4 at the output of the photodetector 3 is needed to match the output impedance of the photoreceiver 3 and the input resistor From the electronic key 5, the second input of the electronic key 5 is supplied with a control voltage generated from the frequency of the oscillator 11 of counting pulses using a block 12 for successive frequency division and block 13 for coincidence. The electronic switch 5 transmits the voltage from the repeater 4 to the output only in the presence of a control pulse at the control input of the electronic switch 5, at the rest of the time at its output a zero voltage (Fig. 2 g, e). Thus, the electronic key 5 transmits only a voltage on the linear portion of the sinusoid to the output (for example, a forward run). This is necessary in order to remove from the signal portions with antiphase components that occur during the reverse direction of the change in the path difference. The voltage obtained at the output of the electronic key 5 is filtered by a band-pass active filter 6, this allows to obtain at the output of the band-pass active filter 6 a harmonic component almost devoid of

noise (figure 2). From the band-pass, active filter 6, the divided harmonic is fed to the input of the zero-organ 7, which forms signals at the zero-point harmonics (Fig. 2 h). The main thing is that the double filtering is carried out: in the first stage, the antiphase components are removed from the interference signal at the output of the photodetector 3 with the electronic key 5; in the second stage, the signal is filtered in the usual way with the help of the band pass filter 1285320

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This does not depend on the antiphase components of the original signal. From the output of the zero-body 7, the pulses go to the S input of the RS flip-flop 9 of the pulse sequence generation unit 8, the R input of the RS flip-flop 9 receives the reference pulse generated by the RS flip-flop 9, the time interval goes to the first input of the AND 10 circuit, the second input of the circuit And 10 receives the pulses of the generator 11 counting pulses. In scheme 10, the time interval formed by the RS flip-flop 9 with a generator of 11 counting pulses is filled. The number of pulses in the packet at the output of the circuit And 10 is proportional to the shift of the interference band (figure 2). From the output of block 8, the signal is fed to the input of interface 15, from where the data on the shift of the interference band are transmitted to the mini-computer 16 for the reversal counting of fractional and whole parts of the interference bands and outputting the data to the display screen or plotter. The counting pulse generator 10 is also used to form the control frequency of the modulator of the path difference of the interferometer 2: the counting pulse generator 11 pulses the pulses to the input of the frequency division unit 12, where the frequency is reduced to the frequency required to control the interferometer modulator 2, the output of block 12 the square wave is fed to the input of the sinusoidal voltage generator 14, where the modulator control voltage of the interferometer 2 is formed, which controls the difference in the course of the interferometer 2. The advantage of this scheme The connection between the frequencies of the oscillator 1 1 counting pulses is rigid.

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This is due to the fact that all these signals are formed from a single oscillator frequency of 11 counting pulses.

Claims (1)

Invention Formula A device for measuring the shift of interference fringes, containing a source of light radiation, an optically coupled interferometer with a path difference modulator and a photodetector, a repeater, a zero-organ, a pulse sequence generator unit consisting of a series-connected RS flip-flop and an And circuit, a generator counting pulses, interface, mini-computer, photoreceiver output is connected to a repeater, the zero-organ output is connected to the S-input of the RS trigger, the second input of the AND circuit is connected to the output of the counting pulse generator, and you The course of the circuit And through the interface is connected to a mini-computer, characterized in that, in order to improve the accuracy and noise immunity of the measurements, it is equipped with an electronic key, a coincidence unit, a frequency division unit, a sinusoidal voltage generator, a band pass active filter, an electronic key and the band-pass active filter is connected in series, the electronic key is connected to the repeater output, the output of the band-pass active filter is connected to the zero-organ input, the output of the counting pulse generator is connected to the input of the de The frequency, the two outputs of which are connected respectively to the inputs of the linear-periodic voltage generator and the coincidence unit, the output of which is connected simultaneously to the control input of the electronic key and the R input of the RS flip-flop, and the output of the linear-periodic voltage generator at a support frequency 4 and the frequency is modulated to the modulator of the source of the luminosity of the difference in the course, this connection of the free radiation. 0 five 0 five 0 five 0 This is due to the fact that all these signals are formed from a single oscillator frequency of 11 counting pulses. Invention Formula A device for measuring the shift of interference fringes, containing a source of light radiation, an optically coupled interferometer with a path difference modulator and a photodetector, a repeater, a zero-organ, a pulse sequence generator unit consisting of a series-connected RS flip-flop and an And circuit, a generator counting pulses, interface, mini-computer, photoreceiver output is connected to a repeater, the zero-organ output is connected to the S-input of the RS trigger, the second input of the AND circuit is connected to the output of the counting pulse generator, and you The course of the circuit And through the interface is connected to a mini-computer, characterized in that, in order to improve the accuracy and noise immunity of the measurements, it is equipped with an electronic key, a coincidence unit, a frequency division unit, a sinusoidal voltage generator, a passband active filter, an electronic key and the band-pass active filter is connected in series, the electronic key is connected to the repeater output, the output of the band-pass active filter is connected to the zero-organ input, the output of the counting pulse generator is connected to the input of the de tim frequency, two outputs of which are respectively connected to the generator input linearly periodic voltage and the coincidence unit, an output of which is connected simultaneously to the control of the electronic key entry and the R-input of RS-trigger and the generator output linearly periodic voltage is connected to the modulation m radiation. but § b  y d t and  yy