JPH02287109A - Displacement detector - Google Patents

Abstract

PURPOSE:To reduce an error in displacement quantity detection at the time of fluctuating a reference frequency by measuring the period of a reference wave and the delay time of a phase-modulated wave behind the reference wave at the same time, and dividing the delay time by the period. CONSTITUTION:A displacement measurement system outputs the reference wave FR and phase-modulated wave FP to a processing circuit. A counter 17 counts pulses CLK of an oscillator 16 and outputs a time signal, and latches 18 and 19 and a subtracter 21 measure the period TR of the reference wave FR. A time signal, on the other hand, is stored in a latch 20 as the falling time of the modulated wave in the falling of the phase-modulated wave FP and a subtracter 22 subtracts the falling time TR of the reference wave FR from the time, and outputs the delay time TP of the phase-modulated wave FP behind the reference wave FR. Then a subtracter 23 subtracts the delay time TP by the period TR to detect the quantity of displacement from the phase difference, so the error is small.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention particularly relates to a displacement detection device that converts a signal from a displacement detector using a phase modulation method such as a laser length measuring device into a numerical value proportional to the amount of displacement. .

(Prior art) Generally, in a displacement detection device of a detector such as a resolver, an inductosin, a laser length measuring device, etc., which phase-modulates an input reference wave with a measured displacement amount and outputs a numerical value of the displacement amount, a phase-modulated wave In order to detect the phase difference with respect to the reference wave, the amount of displacement was detected by counting the amount of phase difference using count pulses that were synchronized with the reference wave and whose frequency was an integral multiple of the reference wave. However, this method is good if the reference wave can be formed by dividing the count pulse, such as with a resolver or inductosyn, but if the frequency of the reference wave is determined inside the laser oscillator, such as with a laser length measuring device, this method is fine. The detector uses a PLL (Phase Locked Loop) to generate count pulses synchronized with the reference wave.
) had to be generated using a circuit. For this reason,
In a laser oscillator in which the frequency of the reference wave is unstable, a detection error occurs due to the response delay of the PLL circuit, and the PLL circuit is difficult to convert into a digital circuit, making it difficult to achieve high integration.

Here, FIG. 7 shows a configuration diagram of a laser length measuring device and a conventional displacement detection device, in which the laser oscillator 1 oscillates light fin t2 with different frequencies in two polarization planes, and the output light f ,, f2 is optically split into two paths by the beam splitter 2, and one of the split lights f and f2 is converted by the photodetector 6 into an electric signal FR representing the interference light intensity of the light f and f2. Here, the electrical signal FR
The frequency is the difference frequency between the lights f1 and f2, and this becomes the reference wave FR (FR=lt+-tzl). Further, the other light beams f1 and f2 split by the beam splitter 2 are further optically split into lights f1 and f2 by the beam splitter 3, and the light f1 is sent to the movable reflecting mirror 5, and the movable reflecting mirror 5 is moved in the X direction. , the light f1 undergoes Doppler modulation of ±Δf in proportion to the moving speed and becomes reflected light f1±Δf. On the other hand, the light f2 split by the beam splitter 3 is reflected by the fixed reflecting mirror 4, and the reflected light f2 is combined with the reflected light f1±Δf by the beam splitter 3, and the combined reflected light f, ±Δf and f2 is light f at photodetector 7
It is converted into an electrical signal FP with an interference light intensity of 1±Δf and f2. Here, the frequency of the electrical signal FP is the difference frequency of the light f, ±Δf, and f2. Therefore, when the electric signal PR is used as a reference wave, the electric signal F becomes a phase modulated wave obtained by phase modulating the reference signal F8 by the movement displacement X of the movable reflecting mirror 5. Specifically, if λ is the wavelength of light f, then the phase modulated wave F
, will be out of phase by 4π/λX.

The above is the basic principle of the laser length measuring device. Next, the operation of the displacement detecting device shown in FIG. 7 will be explained with reference to the timing chart shown in FIG.

First, the reference wave FR of the laser length measuring device 1h)' as shown in FIG. 8(A) is inputted to the phase comparator 9, and the most significant bit signal MSB (FIG.
(See B)) and outputs a voltage of 1V with a pulse width proportional to the amount of phase shift. The output voltage Rν from the phase comparator 9 is smoothed by an LPF (low-pass filter) 10, and is further inputted to a νCO (voltage controlled oscillator) 11 to generate a frequency according to the amount of phase difference as shown in FIG. 4 (C). It oscillates and outputs ° to the count pulse CL. The count pulse CL is inputted to the counter 8 and frequency-divided by 64 as shown in FIG. 8(D), resulting in the most significant bit signal tosB of the counter output signal T°. From the above, phase comparator 9
, LPF 10. VCO11 and counter 8 are PL
It constitutes an L circuit, which allows the count pulse CL
The output signal T of the counter 8 is almost synchronized with the reference wave FR and has a frequency 64 times higher than that of the reference wave FR.
And as shown in (D), within approximately one cycle of the reference wave FR, “
This is a signal that changes in a sawtooth pattern from 0" to "B3". Output signal T of the counter 8.

is stored in the latch circuit 12 as a signal x' as shown in FIG. 8(F) at the falling edge of the phase modulated wave FP as shown in FIG.
, is the phase difference within one wavelength with respect to the reference wave Fll. Therefore, the displacement X of the movable reflecting mirror 5 up to λ/2 can be detected by the operations up to this point.

Next, the signal X° is stored in the latch circuit 13 as a signal
" is the signal immediately before the signal X° changes.

The signal X° and the signal X" are the up-down pulse generator 14
The subtracted value Δ× as shown in FIG. 8(G) outputs an up pulse UP or a down pulse DP as shown in FIG. 8(II) under the condition of equation (1) below.

Up pulse UP from Araftaran pulse generator 14
Or, the down pulse D causes the up/down counter 15 to count up or down, and generates a phase modulated wave FP.
The phase difference with respect to the reference wave FR is outputted from the up/down counter 15 as the number of reference wave wavelengths (X) (see FIG. 8 (1)). Here, the signal X' is the lower digit, and the signal x. The signal X whose upper digits are 64Xx, +x' becomes the phase difference X between the phase modulated wave F and the reference wave FR. therefore,
The displacement X of the movable reflecting mirror 5 can be detected with a resolution of λ/128.

The broken line characteristic A in Figure 8 (D), (F) and (J) shows the value when there is no tracking delay in the PLL circuit, and the shaded area B in Figure 8 (J) shows the error due to the tracking delay, that is, Indicates displacement detection error.

As described above, in the conventional device shown in FIG. 7, a large displacement detection error as shown in the shaded area B occurs compared to the case where there is no follow-up delay of the PLL circuit like signal X in the timing chart of FIG.

(Problem to be Solved by the Invention) In the conventional example shown in FIG.
2, that is, the frequency of the reference wave FR, tends to fluctuate as shown in the timing chart in Figure 8. Therefore, in a PLL circuit with an LPF, the frequency of the count pulse CLK' is accurately adjusted to the frequency fluctuation of the reference wave FR. Unable to follow synchronously.

Therefore, there is a problem in that a displacement detection error corresponding to this tracking error occurs in the displacement detection value. Furthermore, it is difficult to convert the low-pass filter and voltage-controlled oscillator in the PLL circuit into digital circuits, making it difficult to achieve high integration.

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to convert a signal from a displacement detector using a phase modulation method such as a laser length measuring device into a highly accurate numerical value proportional to the displacement. The object of the present invention is to provide a displacement detection device that is easy to integrate and can be highly integrated.

(Means for Solving the Problems) The present invention relates to a displacement detection device for a detector that outputs a displacement amount as a phase modulated wave with respect to a reference wave. The period ΔTR of the reference wave and the delay time ΔTP of the phase modulated wave with respect to the reference wave are measured in parallel using a counter that measures time using count pulses from . The period ΔT
This is achieved by performing a division operation by R to detect the phase difference of the phase modulated wave with respect to the reference wave, that is, the amount of displacement. That is, an object of the present invention is to provide an oscillator that outputs a count pulse, a first means for measuring the period ΔTR of the reference wave using the count pulse, and a method for measuring the period ΔTR of the reference wave using the count pulse in parallel with the measurement of the period ΔTR. a second means for measuring a delay time ΔT of the phase modulated wave relative to the period ΔTR;
This is achieved by providing an arithmetic means for dividing by .

(Operation) According to the solution means of the present invention, the period of the reference wave and the delay time of the reference wave and the phase modulated wave are measured in parallel, and the delay time is divided by the period of the reference wave at approximately the same time. Since the phase difference of the phase modulated wave with respect to the reference wave is detected by
It has less response delay than a PLL circuit due to fluctuations in the reference wave, and can be configured with a digital circuit, making it easy to achieve high integration.

(Example) Hereinafter, an actual example of the present invention will be described based on the drawings.

FIG. 1 is a configuration diagram showing an embodiment of a laser length measuring device and a displacement detecting device according to the present invention, corresponding to FIG. 7, and its operation will be explained with reference to the timing chart of FIG. 2.

In FIG. 1, a laser oscillator 1. Beam splitter 2
．． 3 and fixed reflector 4. The movable reflecting mirror 5.degree. photodetector 6.7 shows a laser length measuring device exactly the same as in FIG. 7, and its explanation will be omitted here. The counter 17 is activated by a count pulse CLX of a constant frequency as shown in FIG. 2 (8) from the count clock oscillator 16 as shown in FIG. 2 (B).
A sawtooth time signal T (0≦T≦(2'-1
) is output, and the time signal T is stored by the latch circuit 18 as the falling time Tn of the reference wave Fe at the falling edge of the reference wave FR shown in FIG.

Further, the time Tn is determined by the latch circuit 19 at the falling edge of the reference wave FR, and the time Tn is one cycle before the falling edge of the reference wave pi.
It is stored as n゛. Both times TR and TR' are input to the subtracter 21, and the subtracter 21 outputs O~(2'-
By limiting to 7 bits up to 1), TR<Tn'
However, the time ΔTR% from the previous falling edge to the next falling edge, that is, the reference wave period ΔTR of the reference wave FR, is always outputted as shown in FIG. 2(E). Also, counter 17
The time signal T from
) is stored as the fall time T of the phase modulated wave. The time T is subtracted by the fall time TR of the reference wave FR in the subtracter 22, and is output as the waveform fall delay time ΔT of the phase modulated wave F with respect to the reference wave FR, as shown in FIG. 2(F). The delay time ΔTP is calculated by dividing the reference wave period ΔTR by the divider 23.
The phase difference signal X° within one period of the phase modulated wave F with respect to the reference wave Fn is output as shown in Fig. 2 (6) (however, the phase difference signal X° is ΔTp/ΔT
(lower 6 bits of RX64). Therefore, with the above operation, the displacement X of the movable reflecting mirror 5 up to λ/2 can be detected with a resolution of λ/128.

Next, the signal ×° is converted into a phase modulated wave FP by the latch circuit 13.
The falling edge of the reference wave FR or the falling edge of the reference wave FR is stored as the signal X'', and the signal X'' becomes the signal immediately before the signal X° changes. The up-down pulse generator 14 and the up-down counter 15 operate similarly to the operation shown in FIG.
Based on the signal X', the number x of phase difference wavelengths of the phase modulated wave F and the reference wave FR is output. However, signal X
° is the lower digit, and the number of phase difference wavelengths xu is the upper digit, that is, 6
A signal X of 4Xx, +x' represents the phase difference of the phase modulated wave FP with respect to the reference wave FT1. That is, the output X' of the latch circuit 13 becomes as shown in the second (G), and the subtracted value Δ× shown in the equation (1) becomes as shown in ()I) of the same figure. In addition, the up pulse II from the pulse generator 14
P is output as shown in FIG. 2 (1), and the output phase difference X is as shown in FIG. 2 (J). Note that the broken line characteristic C in FIG. 2(J) shows the case where there is no follow-up delay of the conventional method described above. Thereby, the displacement detection device shown in FIG. 1 can detect the movement displacement X of the movable reflecting mirror 5 with a resolution of λ/128.

As explained above, according to the apparatus shown in FIG.
), the error can be made smaller than in the conventional method, and the device can be configured with digital circuits that can be easily integrated.

FIG. 3 is a configuration diagram showing another embodiment of the present invention, and FIG.
The figure is a timing chart showing an example of the operation.

In FIG. 3, the reference wave FR is frequency-divided by 2 by a 2-frequency divider 30, and the frequency-divided signal FR/2 is input to a logic circuit 31.
The logic circuit 31 generates an inverted signal of the reference wave FR and a signal FR/
A reset signal R5T as shown in FIG. 4(C) is outputted every two cycles of the reference wave FR. The D-type flip-flop 32 and the AND) circuit 34 send the count pulse CLK from the count clock oscillator 16 to the counter 36 from when the reset signal R5T goes high until the reference wave FR rises after it goes low. After the counter 36 clears the output with “H” of the reset signal R5T, the counter 36 clears the output with “H” of the reset signal R5T, and then clears the output with the fourth pulse from immediately after the reset signal R5T changes to “L” until the reference wave FR rises.
The count is counted up as shown in FIG. 4(D), and the counted value ΔTR after the counting is stopped is held in the latch circuit 3B as shown in FIG. 4(G) until the reset signal rlST becomes "H." Here, the count value ΔTll is the period of the reference wave F from the rising edge of the reference wave FR to the next rising edge, and the latch circuit 38 stores the reference wave period ΔTR at the rising edge of the reset signal R5T. In addition, D type flip-flop 3
3 and the AND circuit 35 receives the count pulse CLK from the count clock oscillator 16 when the reset signal R5T is "
After it becomes "H" and "L" until the phase modulated wave FP rises, the counter 37 is manually inputted.

After the output of the counter 37 is cleared by the H'' of the reset signal R5T, the period from immediately after the reset signal R5T changes to "L" until the rise of the phase modulated wave F is shown in FIG.
The count value ΔTp after counting is stopped is held in the latch circuit 39 as shown in FIG. 4(F) until the reset signal R5T becomes "H". Here, the count value ΔTP is a waveform rise delay time of the phase modulated wave FP with respect to the reference wave FR, and the latch circuit 39 stores the delay time ΔTP at the rise of the reset signal R5T. The period ΔTR of the reference wave PR and the delay time ΔT of the phase modulated wave FP with respect to the reference wave FR are input to the divider 23, and as in the case of FIG. 1, the phase difference signal for one period of the reference wave FR× is output from the divider 23 as (see FIG. 4(H)). The latch circuit 13 outputs the signal X before the phase difference signal X° changes at the rising edge of the reset signal R5T.
The phase difference X between the phase modulated wave F and the reference wave FR can be detected using the up-down pulse generator 14 and the up-down counter 15 in the same manner as shown in FIG.

On the other hand, FIG. 5 is a block diagram showing an embodiment in which the present invention is processed by software. In this example, the reference wave FR is converted into a signal FR' whose frequency is divided by 128 by a frequency divider 40, and a phase modulated wave FP is also a signal F whose frequency is divided by 128 by the frequency divider 41.
It is converted to P'. As a result, the phase difference between the signal F,'' and the signal FR' becomes 1/128 of the phase difference between the phase modulated wave FP and the reference wave FR.

The counter 42 receives a count pulse CL from the count clock oscillator 16 to generate a time signal T (0≦T≦$3
FFF binary signal) is output, and the time signal T is output by the latch circuit 43 at the rising edge of the signal PR', and the time signal T is output as the signal FR.
' is stored as the rise time TR.

Further, the time signal T is converted into a signal F by a latch circuit 44.

At the rising edge of , the rising time TP of the signal F,° is stored as 4.

Here, the microprocessor 45 operates according to the flowchart shown in FIG. M6. That is, first, the signal FR'
rises (step Sl), the microprocessor 45 reads the rise time Tn of the signal FR' from the latch circuit 43 (step s2), and calculates the difference ΔTR from the previous rise time T of the signal FR' (step S3).
, and the hexadecimal number "$3FFF" (step S4), and even if TR<Tn', the difference ΔTR is always obtained.
Processing is performed so that the period becomes the period (>0) of the signal FR' (step S5). Further, after the rising of the signal FP° (step S6), the microprocessor 45 reads the rising time TP of the signal FP' from the latch circuit 44 (step s7), and the rising time Tn of the signal FR'.
The difference ΔTP%, that is, the waveform rise delay time of the signal FP' with respect to the signal Fn' is calculated (step s8
). Next, the delay time ΔTP is multiplied by the hexadecimal number "$2000" (step 510), and the signal FR of the signal FP' is ' The phase difference X° with respect to the signal FR° is one period of the hexadecimal number
Step 512 , it is determined whether the difference Δx exceeds a value (±$1000) equal to or more than half the period of the signal FTI' (steps 514, 516), and the signal F is increased or decreased by increasing or decreasing the variable x.
The number of wavelengths of the phase difference of P' with respect to the signal PR' is calculated by dividing by x (steps 515 and 517).

Then, the number of wavelengths x is multiplied by the hexadecimal number "$ 2000" (step 520), and the phase difference X within the period is added to obtain the phase difference X of the signal FP' with respect to the signal FR' (step 521). , the resolution of the 0 phase difference signal X to be outputted to the outside as a signal
) will be 1/1. Therefore, the phase difference signal X is the reference wave F
The phase difference between the phase modulated wave F and the phase modulated wave F can be detected with a resolution of 1/64 (81927128) of one cycle of the reference wave FR.

As explained above in FIG. 5, from a signal obtained by dividing both the reference wave FR and the phase modulated wave FP by N, the position of the phase modulated wave FP relative to the reference wave F is calculated using the same method as the displacement detection device shown in FIG. 1. When detecting the phase difference X, a reference wave FR and a phase modulated wave F,
By making the cycle N times longer, it becomes easy to perform part of the circuit by software processing of the microprocessor 45 as shown in FIG.

This is because the reference wave frequency is several M11 like a laser length measuring device.
□ is effective when a part of the displacement detection device is simplified by software processing of a microprocessor.

(Effects of the Invention) According to the present invention, the displacement amount of a detector that outputs the displacement amount as a phase modulated wave with respect to the reference wave can be measured almost simultaneously with the period of the reference wave and the delay time of the phase modulated wave with respect to the reference wave. ,
It is obtained by detecting the phase difference between the phase modulated wave and the reference wave. Therefore, the error in the detected displacement amount when the reference wave changes in frequency can be reduced. Furthermore, since it can be constructed entirely from digital circuits, it is easier to achieve higher integration than devices using conventional PLL circuits.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
3 and 5 are block configuration diagrams showing other embodiments of the present invention, respectively. FIGS. 4 and 6 are timing charts showing each operation example, respectively. FIG. 7 is a block diagram showing an example of a conventional device, and FIG. 8 is a flowchart showing an example of its operation. 1... Laser oscillator, 4... Fixed reflecting mirror, 5...
Movable reflecting mirror, 13.17, 36, 37.42... Counter, 9... Phase comparator, 10-L'PF, 1l
-V(:0, 12, 13, 18, 19, 20, 38° 39...Latch circuit, 15...Up/down counter, 16...Oscillator, 21.22...Subtractor, 23
...divider, 3G. 40.41... Frequency divider, 32.33... Flip-flop.

Claims (1)

[Claims] 1. In a displacement detection device for a detector that outputs a displacement amount as a phase modulated wave with respect to a reference wave, an oscillator that outputs a count pulse and a first oscillator that measures the period ΔT_R of the reference wave using the count pulse. and the period ΔT_
a second means for measuring a delay time ΔT_P of the phase modulated wave with respect to the reference wave using the count pulse in parallel with the measurement of R;
1. A displacement detection device comprising: arithmetic means for dividing by . 2. The first and second means include a counter for counting the count pulses, a means for storing an output value T_R of the counter at the time of rising or falling of the reference wave, and a rate at which the value T_R changes. means for storing the previous value T_R'; a subtracter for calculating and outputting the difference between the values T_R and T_R'; and means for storing the output value T_P of the counter at the time of the rise or fall of the phase modulated wave. , and a subtracter that calculates and outputs the difference between the value T_P and the value T_R or T_R'. 3. The first and second means include two sets of counters that count the count pulses, and n periods of the reference wave (n≧
means for clearing the two sets of counters and starting counting at the rising or falling edge of each integer of 2); and means for clearing one of the two sets of counters at the rising edge or falling edge of the reference wave after starting counting; means for stopping the counting at the rising or falling edge of the phase modulated wave after the other of the two sets of counters starts counting; 2. The displacement detecting device according to claim 1, further comprising means for storing a counted output value between. 4. A displacement detecting device according to claim 1, a means for storing a detected displacement x'' immediately before the detected displacement x' of the displacement detecting device changes, and a difference Δx between the detected displacements x' and x''. A displacement detection device comprising: a subtracter for calculating and outputting the difference Δx; and a counting means for counting up or down depending on the magnitude of the difference Δx. 5. A displacement detection device for a detector that outputs a displacement amount as a phase modulated wave with respect to a reference wave, a first frequency divider that divides the frequency of the reference wave by N, and a second frequency divider that divides the frequency of the phase modulated wave by N. A displacement detector comprising: a frequency divider; and the displacement detection device according to claim 1 or claim 4, which inputs the reference wave after the frequency division by N and the phase modulated wave after the frequency division by N. Detection device.