SU1295224A1 - Device for measuring interference patterns - Google Patents

Abstract

This invention relates to a measurement technique. The aim of the invention is ytycK / ocm. This is an improvement in the accuracy of measuring the position of the centers of interference fringes by eliminating errors from measuring the scanning speed and the formation of spurious signals. The device contains an ADC 7, converts the signal into a discrete form, stores the block 9, allows you to memorize the energy value of the half-period signal (only one polarity), the divider 10 (two) and the comparison circuit 17, which allows to make a comparison (L 1C CO, sl I. is ./

Description

(in the next half-period) half of the storage value with a delayed current value and thus reveal the half-cycle energy center. Interval determination unit 5

one

The invention relates to a measuring technique and can be applied in interferometric measuring systems for measuring the distance between interference fringes, which is suitable for monitoring aspheric optical surfaces.

The purpose of the invention is to improve the measurement accuracy of the position of the centers of interference fringes by eliminating errors from varying the scanning speed and the formation of spurious signals.

Figure 1 shows the block diagram of the device; Fig. 2 is a voltage chart on the circuit elements.

The device contains sequentially installed scanning unit 1 with radiation receiver 2, amplifier-limiter 3, unit 4 for determining the center of a band, block 5 for determining intervals between the centers of the bands, recorder 6.

The strip center definition unit 4 consists of an analog-digital converter (A1DP) 7, a generator 8, a storage unit 9, a divider 10, a comparator 11 with an inverter 12, a delay element 13, a cmamator 14, a register 15, a switch 16, a circuit 17 comparing codes, second trigger 18.

Block 5 for determining the intervals between the centers of the bands consists of the first trigger 19 (with a countable input), two elements ZI-2ShSh 20 and 21, and two counters 22 and 23 of the pulse. The diagrams show signals 24-38.

The input of the ADC 7 is connected to the output of the amplifier-limiter 3 and to the input of the comparator 11, and the output to the (informational) input of block 9 and through divider 10 with the input of adder 14. The output of block 9 is combined with the output of divider 10, whose division ratio equals two. The output of the adder 14 is connected between the centers of the bands with each clock of the generator 8, taking into account the scanning speed, determines the distance between the calculated centers of the adjacent bands. 2 Il.

Not with the inputs of the register 15 and the switch 16, the outputs of which are connected to the corresponding inputs of the code comparison circuit 17. The output of the code comparison circuit 17 is connected to the second (zero) input of the second flip-flop 18 and the second reset input of the adder 14, the first reset input of which is combined with the control input of the switch 16, and connected via a serially connected delay element 13 and inverter 12 to the output of the comparator 11, to the first control input of block 9 and to the counting inputs of the trigger 19. The switching address input of the block 9 is connected to the first (single) output of the trigger 18, with the first inputs of the elements ZI-2ShZh 20 and 21. The address input of the block 9 is connected to the first output of the generator 8, clock input of the ADC 7, second and fifth inputs of ZI-2ILI elements 20 and 21. The second input of the generator 8 is connected to the input of the scanning unit 1. The input of the delay element 13 is connected to the control input of the register 15. The zero output of the trigger 18 is connected to the first the control input of the registrator 6, with the fourth inputs of the ZI-2ILI elements 20 and 21. The third input of the first 20 and sixth inputs of the second 21 ZI-2IL elements are connected to zero outputs of the first trigger 19 and the second input of the recorder 6, the sixth input of the first 20 and the third entrance at the second 21 element in the GI-2or edinichim connected to output latch 19. The outputs of elements 20 and 21 are connected via respective counters 22 and 23 input pulses informatsionnm recorder 6, which outputs are connected to inputs of the respective reset the counter 22 and 23.

The device works as follows.

3 12

The operation of the device is based on determining the center of the interference band through the energy center of the signal generated from this band and calculating the coordinates of these centers. The distance (temporary) between the centers of two adjacent bands (Fig. 2) is L + -,

where f is the period of the next two

neighboring light (dark)

bands; f 1, I - the intervals between beginnings

adjacent lanes and their centrum.

To determine the center position of the band, half the energy of each half-wave of the electric signal generated from each band is measured, and the current value of the energy of the delayed half-wave of the same signal is compared with the value obtained. The moments of equality of these energy values are taken as the time coordinates of the centers of the bands.

In the initial state, the device is set to the zero state (initial setup circuits (not shown) ADC 7, block 9 address register, counters 22 and 23, triggers 18 and 19, and register 15 to any non-zero state. With this signal 31 from the single output of the ZI-2ILI trigger 20 and 21 are prepared by the fourth input, and by signal 33 from the output of the trigger 19 these elements are prepared by the third and sixth inputs respectively.

Using the Start command, the oscillator is started using a scanning unit synchronized with the frequency of the oscillator 8, the interference pattern is scanned in the direction perpendicular to the interference fringes. At the output of the radiation receiver 2, an electrical signal is formed, the level of which is measured in accordance with the luminance of the picture elements, and the frequency is determined by the scanning speed and the intensity of the bands. The signal from receiver 2 is fed to the input of the amplifier-limiter 3, which amplifies this signal and emits a half-wave of one polarity, which is fed to the input of ADC 7 and comparator 11. ADC 7 quantizes the analog half-wave signal to a digital code with a clock frequency generator 8,

At the same time, the clock pulses from the output of the generator 8 are sent to the W2D4

The first and fifth inputs of the ZI-211LI elements are 20 and 21 and pass through one of them to the counter 23. The last starts counting pulses, the number of which is proportional to the coordinate I - the distance from the starting point of reference to the beginning of the first band. Clock impulses (signals) 37 to this counter arrive before the beginning of the first band (the first half-wave) during the time t (Fig. 2) -.

With the advent of the ADC 7 and the comparator 11 half-wave signal 25 corresponding to a light band, for example, the potential of a single level (signal 26) is formed at the output of the comparator 11 (signal 26), which enters the first control input of block 9 and sets the record mode in it, starts the counter addresses in block 9. During the time t from the output of the ADC 7, codes (signal 28) appear, which are recorded in block 9 with each clock pulse arriving at the address input of block 9 and the clock input of the ADC 7. At the same time, the code from ADC 7 through divider 10 which reduces the code value by a factor of two by shifting the code one bit towards the lower bit, enters the adder 14. In the adder 14, the codes corresponding to half the amplitude of the discrete values of the signal are summed, and a value proportional to the half of the half-wave signal energy is calculated interval t (figure 2).

At the same time, the leading edge of the signal from the output of the comparator 11 is set to one state by a trigger 19, and at its output a resolving signal 34 is formed, which prepares the sixth and third inputs of the corresponding ZI-2ILI elements 20 and 21. The clock pulses (signal 35) from the generator 8 arrive through element ZI-2ILI 20 to the input of the counter 22, which starts counting the interval t .. At this time, the input of the counter 23 is closed.

After the end of the half-wave (signal 25), a zero signal 26 is generated at the output of the comparator 11, which enters the control input of block 9 and switches it to read mode, locks the input of the address counter in block 9, and the signal 26 also goes to inverter 12 and generates its output is a single signal 27, which goes

51295224

steps on the control input of the register 15 and the leading edge allows the transfer of information from the adder 14 to the register 15, from the output of which the code goes to one of the inputs of the comparison circuit 17. At the same time, the signal 27 from the output of the inverter 1.2, delayed by the delay element 13 at time t, (FIG. 2) necessary for writing to the register 15, is fed to the first reset input of the adder 14 and the first trigger input 18. The leading edge of the delayed signal is the adder 14 is set to the zero state, and the trigger 18 is set to the single state.

The delayed signal also arrives at the control input of the switch 16, prepares it to receive a code from the adder 14. Uniform potential (signal 30) from the trigger output 18 Receives the first inputs of the ZI-2ILI elements 20 and 21, to the second control input of the block 9, code which unlocks the input of the address counter. With each clock pulse in the interval of block 9, the previously written code (signal 29) enters the adder 14, and from the output of the adder 14 the code goes through the switch 16 to the second circuit input

20

25

After the trigger 18 has been reset, when the codes are equal, the input of the counter 23 is locked and the counter 22 is unlocked. At the output of counter 23, a code (signal 37) is fixed, proportional to the interval from the starting point of reference to the center of the first band + I, LQ. This code enters the recorder 6, which, after reading the clock, issues a reset signal 38 to the counter 23 and sets its zero state. The pulses (signals 35) continue to arrive at the input of the counter 22 until the beginning of the next half-wave, the second light band.

From this point on, the calculation by the adder 14 of the half value of the signal energy of the second half-wave in the interval t.K starts recording in block 9 the current values of this signal similar to the process described for the first half-wave.

With the beginning of the half-wave (signal 25) of the second light band, a single signal 26 is formed at the output of the comparator, which sets the recording mode in block 9 and opens the input of the block 9 address counter, switches trigger 19 to the zero state. Allow 17 comparisons. As the signal 33 of the block 9 from the zero output (signal 29) from the block 9 to the summatter of the flip-flop 19 prepares the third and sixth inputs, respectively, at the ZI-2ILI elements 20 and 21. Thus, at the input of the counter 23 are coming

35 clock pulses (signal 37), which form the counter B code A, corresponding to the interval Lj - the distance between the centers of the second and third bands. Simultaneously with each tactical,

40, a pulse is written to the code (signal 28) from the output of the A / D converter 7 to block 9 and through divider 10 to the adder 14. After the half-wave ends, the authorizing signal 27 from the output of the inverter 12 rewrites the code from the adder 14 to the register 15, zero signal 26 from the output of the comparator switches the block 9 to the state of the shift. The operation of comparing the current value of the energy of the delayed second half-wave with the value of the energy recorded in the register 15 as described for the first half-wave begins. With

14, a delayed current value of the energy code of the first half-wave signal is generated, which is compared in the comparison circuit 17 with the half-energy code of this signal recorded in register 15. At the time the codes are equal, the output of the comparison circuit 17 generates a signal 32 arrives at the zero input of the trigger 18 and the adder 14, set their zero position. At the output of the trigger 18, thus, a pulse is formed (signal 30), the duration of which is equal to the time interval from the beginning of the signal 25 to its energy center, i.e. f, jL

A single signal 30 from the output of the trigger 18 through the element ZI-2ILI 21 opens the input of the counter 23, which counts the clock pulses (signal 37) in the interval I. The input of the counter 22 at this time is closed by the zero signal 31 from the output of the trigger 18, which is equivalent to that of the current

 non-value P is produced

the values of the value of I subtraction values

-2 "

THIS INPUT of the counter 23 is locked, and the 55 input of the counter 22 (The calculation of the coordinate 1 opens and begins. Thus, the formation of the code A, equivalent to the interval L between the centers of the first

0

five

After the trigger 18 has been reset, when the codes are equal, the input of the counter 23 is locked and the counter 22 is unlocked. At the output of counter 23, a code (signal 37) is fixed, proportional to the interval from the starting point of reference to the center of the first band + I, LQ. This code enters the recorder 6, which, after reading the clock, issues a reset signal 38 to the counter 23 and sets its zero state. The pulses (signals 35) continue to arrive at the input of the counter 22 until the beginning of the next half-wave, the second light band.

From this point on, the calculation by the adder 14 of the half value of the signal energy of the second half-wave in the interval t.K starts recording in block 9 the current values of this signal similar to the process described for the first half-wave.

With the beginning of the half-wave (signal 25), the second light band at the comparator output generates a single signal 26, which sets the recording mode in block 9 and opens the input of the block 9 address counter, switches the INPUT counter 23 with a trigger and locks the input of the counter 22 (Coordinate opens and starts 1. Thus, in counter 22, the generation of code A is completed, equivalent to the interval L between the centers of the first

712

and BTOpoi STRIP. After coincidence to the signals in the comparison circuit 17, the pulse from its output switches the trigger 18, from the output of which the signal 31 goes to the recorder 6. This signal from the output of the counter 22 records the code L to the recorder 6, which, after input, outputs to the counter 22 a reset pulse (signal 36) and sets it to the initial zero state. At this time, the counter 23 continues to generate a code L, counting pulses (signal 37), the number of which is equivalent to interval 1. The process continues as described until the occurrence of the Stop signal first enters the generator 8 and locks it, the scanner unit 1 is stopped, pulses (signal 24) is stopped to enter the device.

The number of pulses, counted alternately by the counters 22 and 23, is proportional to the time interval between the centers of the adjacent half-waves of the signal. If you know the pulse frequency and scanning speed of the interference pattern under study, you can recalculate this value to the distance between the centers of the interference fringes, and also determine the coordinates of the centers of all the bands in the picture .

Claims (1)

Invention Formula A device for measuring interferograms, comprising a scanning unit, a radiation receiver optically coupled to it, an amplifier-limiter connected to the output of the radiation receiver, a polo center detection unit with a comparator and a switch, and a recorder characterized by that, in order to increase the accuracy of measuring the position of the centers of the interference bands, it is equipped with a block for determining the intervals between the center of the bands, made in the form of a trigger, two ZI-2ILI elements and two pulse counters, the trigger inputs are connected to the output of the comparator, one trigger output connected to the combined and sixth input of the first element ZI-2ILI and the third input of the second element ZI-2IL, the other trigger output is connected O 5 0 0 five five 0 50 ; five 248 with the third input of the first and sixth input of the second ZI-2ILI elements, d; the other output of which is connected to the fourth inputs of the ZI-2ILI elements, and the outputs are connected via corresponding meters to the corresponding information inputs of the recorder, one control input of which is connected to the fourth inputs of the elements ZI-2ILI, the other with the sixth inputs of these elements, and the recorder's outputs connect the fjeHbi to the reset inputs of the counters, and the unit for determining the center of the band includes an analog-to-digital converter connected in series , adder, register and code comparison circuit, an inverter and a delay element connected in series, a generator, a storage unit and a second trigger, a switch is connected between the output of the adder and the second input of the code comparison circuit, the comparator input is connected to the input of the analog-digital converter and is the input of the block determining the center of the band connected to the limiting amplifier, the output of the delay element is connected to the first reset input of the adder, to the control input of the switch and to the first input of the trigger, the second input It is connected to the output of the comparison circuit, also connected to the second reset input of the adder, the output of the analog-digital converter is connected to the information OHHbBvi input of the storage unit whose output is connected to the output of the divider, the address input of the storage unit is combined with the clock input of the analog-digital converter and connected to the first output of the generator, the output of the comparator is also connected to the first control input of the storage unit, the second control input of which is connected to the first output of the second trigger, the control input The register is connected to the inverter output, the first inputs of both ZI-2IL elements are connected to the first output of the center definition block of the band, the second and fifth inputs are connected to the first output of the generator of the center band definition unit, the second output of the generator is connected to the scanning unit. delays are also connected to the register control input. Editor N. Tupitsa Compiled by E.Glazkov Tehred V, Kadar Proof-reader v.But ha Order 609/47 Circulation 678 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, st. Project, 4 (Rig.1