RU1711554C - Device for measuring the surface relief - Google Patents

Abstract

FIELD: instrumentation engineering. SUBSTANCE: device has an interferometer with internal phase modulation formed by laser 1, beam splitter 3 and supporting mirror 5, dissector 7 located in the output plane of the interferometer, shaper 9 of time intervals, logical block 10 and counters 11 and 13. In shaper 10 a pulse is formed whose duration is determined by the height of the controlled surface. The counting of the whole bands is exercised by analyzing the pulse duration. The decision about the passing into the whole band is made when the pulse duration is changed jumpwise. EFFECT: enhanced accuracy and high-speed response at the expense of element-by-element processing of the formed interference pattern. 2 cl, 3 dwg

Description

 The invention relates to a measurement technique and can be used to control the parameters of surface microgeometry.

 The purpose of the invention is to increase the accuracy and speed due to elementwise processing of the generated interference pattern.

 Figure 1 presents a block diagram of a device; figure 2 is a timing diagram of the voltages at the outputs of the blocks of the device; figure 3 is a block diagram of a logical block.

 The device consists of an optically coupled laser 1, a telescopic system 2, a beam splitter 3, a micro lens 4, a reference mirror 5, a telescopic system 6 and a dissector 7, a micro lens 8 optically connected to a laser 1 through a beam splitter 3 (beam splitter 3, micro lens 4 and 9, and mirror 5 are arranged according to the Linnik interferometer scheme, the analysis plane of which is the focal plane of the micro-lens 8, and the output plane is transferred by the system 6 to the input plane of the dissector 7), serially connected by the former 9 and intervals, the input of which is connected to the output of the dissector of the logical block 10, the counter 11 integer numbers of strips and block 12 of the buffer memory, the counter 13 fractional fraction of the strip included between the second output of the shaper 9 and the second input of the block 12, block 14 scan control connected between the coordinate output block 12 and the control input of the dissector 7, serially connected to the driver 15 and the piezoceramic transducer 16, mechanically connected to the mirror 5, a timer 17, the outputs of which are connected to the control inputs of the driver 15, block 10, Meters withstand 13, block 12 and reference input generator 9, respectively.

 The logical block 10 consists of series-connected pulse generator 18, the input of which is the input of block 10, counter 19, RAM register 20 and logic analyzer 21, the output of which is the output of block 10. The control inputs of the counter 19, register 20, and signaling device 21 are combined and are control input of block 10.

 The device operates as follows.

In an interferometer with a laser 1, during a linearly periodic phase modulation (see Fig. 2a) of the reference wave, a dynamic interference image of the object is formed using a piezoelectric transducer with a reference mirror 5. This image is projected onto the photocathode of the dissector 7. The coordinate of the surface working element r _i , where i is the coordinate number, is determined by the signal generated by the scan control unit 14. The signal from the dissector 7 (see Fig. 2, b) is fed to the shaper 9 time intervals, where a pulse is generated, the leading edge of which is determined by the trailing edge of the pulse at the reference input of the shaper 9 (see Fig. 2, c), the trailing edge is determined by the moment of passage through a constant level of increasing voltage from the dissector 7, and the duration is proportional to the phase difference (in the range 0-2π) of the reference and measuring waves at the point of the interference field with coordinate r _i . The duration of this pulse τ _i (see FIG. 2, d) is measured by filling it with counting pulses from timer 17 and then adding them by counter 13. Logic block 10 determines the need to change the current value of counter 11 of an integer number of bands by ± 1 when changing the phase angle ± 2π relative to the phase of the signal at the first measurement point. The counters 11 and 13 ensure the uniformity of the measurement of the integer number of bands and fractional parts of the strip at the point r _i and form a real number N _i , which is recorded in the device 12 of the buffer memory. The timer provides synchronous operation of individual blocks and a measurement of the duration τ _i .

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(1), где τ_макс - наибольшее значение временного интервала;
τ_i+1 - следующее за τ_i значение интервала, принимается решение о наличии скачкообразного перехода τ_i→ τ_i+1 и об изменении текущего значения счетчика целого числа полос (значение изменяется на +1 при выполнении неравенства (1) и условия τ_i+1 < τ_i и на -1, если при выполнении неравенства (1) выполняется условие τ_i+1 > τ_i).Registration of the moment of phase change by ± 2π is based on an analysis of the duration τ _i . In each measurement cycle, the current and previous values of τ _{i are} compared (the previous one is stored in the RAM register 20). When the phase changes by ± 2π, the duration τ _i changes stepwise, which allows you to register a phase change by 2 π. In logic block 10, the following decision-making algorithm for generating counting pulses to counter 11 is implemented. If

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(1) where τ _max is the largest value of the time interval;
τ _{i + 1} is the interval value following τ _i , a decision is made on the presence of a jump transition τ _i → τ _{i + 1} and on a change in the current value of the counter of an integer number of bands (the value changes to +1 when inequality (1) and the condition τ _{i +1} <τ _i and by -1 if, when inequality (1) is fulfilled, the condition τ _{i + 1} > τ _i ) is fulfilled.

In the logical block 10, the generator 18 generates bursts of pulses, the number of which is determined by the duration τ _i . The pulses are counted by the counter 19, the number of pulses is stored in the register 20. According to the signals from the timer 17, the analyzer 21 compares the current value of the pulses and, depending on the comparison results, gives a signal to add or subtract one to the counter 11. (56) Wyant JC, Koliopoulos CL An optical profilometer for sutface characterization of magnetic media, ASLE Transaction, v. 27, No. 2, 1983, p. 101.

Claims (3)

 1. A SURFACE RELIEF MEASUREMENT DEVICE comprising optically coupled interferometers with internal phase modulation and a coordinate-sensitive photodetector, a photodetector scan control unit, an interferometer phase modulation driver and a photodetector signal processing unit, the first and second control outputs of the signal processing unit are connected to the input of the control unit by scanning the photodetector and the driver input, respectively, characterized in that, in order to increase accuracy and speed, the signal processing unit The photodetector is made in the form of series-connected time interval shaper, a logical block, an integer counter of strips and a buffer memory block, a fractional fraction of the strip band connected between the second output of the time interval shaper and the second input of the buffer memory block, the control output of the buffer memory block is the first control the output of the signal processing block of the photodetector, and a timer, the first four outputs of which are connected to the control inputs of the counter of the fractional fraction of the strip, the buffer block memory and logical unit, respectively, the fifth timer output is the second control output of the photodetector signal processing unit, and the driver is made with a continuous periodic law of change in the output voltage.  2. The device according to claim 1, characterized in that the interferometer with internal phase modulation is made according to the Linnik interferometer with a piezoelectric drive mechanically coupled to a reference mirror.  3. The device according to claim 1, characterized in that the coordinate-sensitive photodetector is made in the form of a dissector.

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