JPH0776695B2 - Displacement detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a displacement detection device for converting a signal from a displacement amount detector of a phase modulation method such as a laser length measuring device into a numerical value proportional to the displacement amount. .

(Prior Art) Generally, in a displacement detection device of a detector that phase-modulates an input reference wave with a measured displacement amount and outputs a numerical value of the displacement amount, such as a resolver, an inductosyn, and a laser length measuring device, a phase-modulated wave is used. In order to detect the phase difference with respect to the reference wave, the displacement amount is detected by counting the phase difference amount with a count pulse which is synchronized with the reference wave and whose frequency is an integral multiple of the reference wave. However, this method is good when it is possible to form a reference wave by dividing the count pulse like a resolver or iductocin, but a detector such as a laser length measuring machine where the frequency of the reference wave is determined inside the laser oscillator. Then, the count pulse synchronized with the reference wave had to be generated by using a PLL (Phase Locked Loop) circuit. Therefore, 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 it is difficult to make the PLL circuit into a digital circuit and it is difficult to achieve high integration.

Here, FIG. 7 shows a configuration diagram of a laser length measuring device and a displacement detecting device by a conventional method. The laser oscillator 1 oscillates lights f ₁ and f ₂ having different frequencies with two polarization planes and outputs them. light f ₁ has, f ₂ is divided into an optically second path by the beam splitter 2, it divided light f _1, the electrical signal of the interference light intensity of the light f ₁ and f ₂ one of f ₂ at the photodetector 6 F Converted to _R. Here, the frequency of the electric signal F _R is the difference frequency between the lights f ₁ and f ₂ , and this becomes the reference wave F _R (F _R = | f ₁ −f ₂ |).
Also, the other light f ₁ split by the beam splitter 2 and
f ₂ is further optically divided into beams f ₁ and f ₂ by the beam splitter 3, the beam f ₁ is sent to the movable reflecting mirror 5, and when the movable reflecting chain 5 moves in the X direction, the beam f ₁ is emitted. Undergoes Doppler modulation of ± Δf in proportion to the moving speed and becomes reflected light f ₁ ± Δf. On the other hand, the light f ₂ which is divided by the beam splitter 3 is reflected by fixed reflecting mirror 4, and the reflected light f ₂ is combined with the reflected light f ₁ ± Delta] f by the beam splitter 3, together reflected light f ₁
± Δf and f ₂ are light f ₁ ± Δf and f _{2 by the} photodetector 7.
Is converted into an electric signal F _P of the interference light intensity of. Here, the frequency of the electric signal F _P is the difference frequency between the lights f ₁ ± Δf and f ₂ .
Therefore, when the electric signal F _R is used as the reference wave, the electric signal F _P
Is a transfer modulation wave in which the reference signal F _R is transfer-modulated by the moving displacement X of the movable reflecting mirror 5. Specifically, when λ is the wavelength of the light f ₁ , the phase of the transfer modulation wave F _P is shifted by 4π / λx.

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

First, the reference wave F _R from the laser length measuring device 1 as shown in FIG. 8 (A) is input to the phase comparator 9, and the most significant bit signal MSB of the output signal T ′ of the counter 8 (FIG. 8 (B) ) Reference), and outputs a voltage RV with a pulse width proportional to the amount of phase shift. The output voltage RV from the phase comparator 9 is LPF
It is smoothed by a (low-pass filter) 10 and is further input to a VCO (voltage controlled oscillator) 11 to oscillate and output a count pulse CLK 'as shown in FIG. 4 (C) having a frequency according to the phase difference amount. The count pulse CLK 'is input to the counter 8 and divided by 64 as shown in FIG. 8 (D) to become the most significant bit signal MSB of the counter output signal T'. From the above, the phase comparator 9, LPF10, VCO11, and counter 8 constitute a PLL circuit, whereby the count pulse CLK 'is the reference wave F.
The frequency is 64 times that of _R. Further, the output signal T ′ of the counter 8 is a signal that changes in a sawtooth shape from “0” to “63” within almost one cycle of the reference wave F _R as shown in FIGS. 8 (A) and (D). Become. Output signal T'of 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 F _P as shown in FIG. 8 (E). It becomes the phase difference within one wavelength with respect to the reference wave F _{R of P.} Therefore, the displacement X up to λ / 2 of the movable reflecting mirror 5 can be detected by the operation up to this point.

Next, the signal x ′ is stored as the signal x ″ in the latch circuit 13 at the next fall of the phase modulated wave F _P , but the signal x ″ becomes the signal immediately before the signal x ′ changes. The signal x ′ and the signal x ″ are subtracted in the up / down pulse generator 14,
Subtraction value Δx as shown in FIG. 8 (G) to output an up pulse U _P or down pulse D _P as shown in FIG. 8 under the following conditions (1) (H).

Up pulse U _P or down pulse D _P from the up-down pulse generator 14 is up-counted or down-counted up-down counter 15, the phase-modulated wave F _P reference wave F _R
The phase difference with respect to is output from the up / down counter 15 at the reference wave wavelength number x _u (see FIG. 8 (I)). Here, the signal x ′ is the lower digit, and the signal x _u is the upper digit, that is, 64 × x _u +
The signal x to be _x'becomes the phase difference x of the phase modulation wave F _{P with} respect to the reference wave F _R. Therefore, the moving displacement X of the movable reflecting mirror 5
Can be detected with a resolution of λ / 128.

The broken line characteristic A in FIGS. 8 (D), (F) and (J) is
The values in the case where there is no follow-up delay of the PLL circuit are shown, and the hatched portion B in FIG. 11 (J) shows the error due to the follow-up delay, that is, the displacement detection error.

As described above, in the conventional device shown in FIG. 7, a large displacement detection error such as the shaded portion B occurs as compared with the case where there is no tracking delay of the PLL circuit like the signal x in the timing chart of FIG.

(Problems to be Solved by the Invention) In the conventional example shown in FIG. 7, the difference frequency between the oscillation lights f ₁ and f ₂ of the laser oscillator 1, that is, the frequency of the reference wave F _R fluctuates as shown in the timing chart of FIG. Therefore, in the PLL circuit having the LPF, the count pulse CLK ′ is added to the frequency fluctuation of the reference wave F _R.
The frequency of cannot follow the synchronization accurately. Therefore, there is a problem that a displacement detection error corresponding to this tracking error occurs in the displacement detection value. In addition, it is difficult to make a low-pass filter and a voltage controlled oscillator in the PLL circuit into a digital circuit, and it is difficult to achieve high integration.

The present invention has been made under the circumstances described above, and an object of the present invention is to convert a signal from a displacement amount detector by a phase modulation method such as a laser length measuring device into a numerical value proportional to a highly accurate displacement amount. And to provide a displacement detection device that is highly integrated and easy to integrate.

(Means for Solving the Problem) 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, and the above object of the present invention is to provide an oscillator that outputs a count pulse at a constant frequency. Using a counter that measures the time with a count pulse from, the period ΔT _R of the reference wave and the delay time ΔT _{P of the} phase-modulated wave with respect to the reference wave are measured in parallel, and the delay time ΔT is almost simultaneously obtained by a divider. _This is achieved by detecting the phase difference of the phase modulation wave with respect to the reference wave, that is, the displacement amount by dividing _P by the period ΔT _R. 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 ΔT _{R of the} reference wave by the count pulse, and the count pulse for measuring the period ΔT _R in parallel. Second means for measuring the delay time ΔT _P of the phase modulated wave with respect to the reference wave,
It is achieved by providing a calculating means for dividing the delay time ΔT _P into the period ΔT _R.

(Operation) According to the solving 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 substantially at the same time. Since the phase difference of the phase modulated wave with respect to the reference wave is detected,
There is little response delay due to fluctuations in the reference wave, and because it can be configured with a digital circuit, high integration is easy.

(Example) Hereinafter, the Example of this invention is described based on drawing.

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

In FIG. 1, the laser oscillator 1, the beam splitters 2, 3
The fixed reflecting mirror 4, the movable reflecting mirror 5, and the photodetectors 6 and 7 show the same laser length measuring device as in FIG. 7, and the description thereof will be omitted here. The counter 17 uses a sawtooth-shaped time signal T (0≤T≤ (2 ⁷ as shown in FIG. 2B by a count pulse CLK having a constant frequency as shown in FIG. 2A from the count clock oscillator 16. -1) binary signal)
The time signal T is output by the latch circuit 18 in the same figure (C).
At the fall of the reference wave F _R as shown in, is stored as the fall time T _R of the reference wave F _R. In addition, the time T _R depends on the latch circuit 19
By the falling edge of the reference wave F _R, stored as falling one cycle before the time of the reference wave F _R T _R '. Time T _R and T _R ′
Are both input to the subtractor 21, and the subtractor 21 outputs 0 to
By limiting to 7 bits up to (2 ⁷ -1), T _R <T _R ′
However, the time ΔT _R from the previous fall to the next fall, that is, the reference wave period ΔT _R of the reference wave F _R is always output as shown in FIG. 2 (E). Further, the time signal T from the counter 17 is stored by the latch circuit 20 as the fall time T _P of the phase modulation wave at the fall of the phase modulation wave F _P shown in FIG. The time T _P is subtracted by the fall time T _R of the reference wave F _R in the subtractor 22 and output as the waveform fall delay time ΔT _P of the phase modulation wave F _P with respect to the reference wave F _R as shown in FIG. 2 (F). It The delay time ΔT _P is divided by the reference wave period ΔT _R by the divider 23, and a phase difference signal x ′ of one phase of the phase modulation wave F _P with respect to the reference wave F _{R is obtained} as shown in FIG.
Is output (however, the phase difference signal x ′ is ΔT _P
/ ΔT _R × 64 lower 6 bits). Therefore, by 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 x'is stored as the signal x "by the latch circuit 13 at the fall of the phase modulation wave F _P or the fall of the reference wave F _R , and the signal x" is the signal before the change of the signal x '. Becomes The up / down pulse generator 14 and the up / down counter 15 determine the phase difference wavelength number x _u of the phase modulated wave F _P with respect to the reference wave F _R based on the signals x ″ and x ′, as in the operation of FIG. Therefore, the signal x having the signal x ′ as the lower digit and the phase difference wavelength number x _u as the upper digit, that is, 64 × x _u + x ′ represents the phase difference of the phase modulated wave F _{P with} respect to the reference wave F _R. That is, the output x'of the latch circuit 13 is the second
As shown in (G), the subtraction value Δ shown in the above equation (1)
x is as shown in FIG. Also, up pulse U _P from the pulse generator 14 is output as the second diagram (I),
The output phase difference x is as shown in FIG. In addition,
A broken line characteristic C in FIG. 2 (J) shows a case where there is no follow-up delay of the above-mentioned conventional method. As a result, the displacement detector of FIG. 1 can detect the displacement X of the movable reflecting mirror 5 with a resolution of λ / 128.

As described above, according to the apparatus shown in FIG. 1, the error can be made smaller than that of the conventional method and the digital circuit which can be easily highly integrated can be formed like the signal x in the timing chart of FIG. 2 (J). It is possible to configure the device.

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

In FIG. 3, the reference wave F _R is _divided by 2 by the frequency divider 30, and the divided signal F _R / 2 is input to the logic circuit 31 and the logic circuit 31.
Reference wave F _R inverted signal and the signal F _R / 2 and logical product of the fourth view reset signal RST shown in (C) the reference wave F _R of the
Is output every two cycles. D type flip-flop 32
The AND circuit 34 counts the count pulse CLK from the count clock oscillator 16 from when the reset signal RST becomes “H” to “L” until the reference wave F _R rises.
Input to 36. The counter 36 counts up as shown in FIG. 4 (D) from immediately after the reset signal RST changes to “L” until the reference wave F _R rises after the output is cleared by the reset signal RST “H”. , Count value after counting is stopped Δ
The latch circuit 38 holds T _R as shown in FIG. 4 (G) until the reset signal RST becomes "H". Where the count value ΔT _R
Becomes a period of the reference wave F _R from the rise of the reference wave F _R to the next rising, the latch circuit 38 stores the reference wave period [Delta] T _R at the rising edge of the reset signal RST. Further, the D-type flip-flop 33 and the AND circuit 35 change the count pulse CLK from the count clock oscillator 16 to “L” after the reset signal RST becomes “H” and then the phase modulation wave F _P
Is input to the counter 37 until is started. counter
37 is after the output is cleared by the reset signal RST “H”,
Immediately after the reset signal RST changes to “L”, the phase modulated wave F
Counting up is performed until _P rises as shown in FIG. 4 (E), and the count value ΔT _P after counting is stopped by the latch circuit 39 in FIG. 4 (F) until the reset signal RST becomes “H”. Hold as shown in. Here, the count value ΔT _P is the phase modulation wave F _P
The waveform rise delay time with respect to the reference wave F _R becomes, and the latch circuit 39 stores the delay time ΔT _P at the rise of the reset signal RST. Reference wave F period [Delta] T _R and the reference wave F delay time [Delta] T _P of the phase modulation wave F _P for _R of _R in the case of Figure 1 is input to one period in the amount of similarly reference wave F _R to the divider 23 Is output from the divider 23 as the phase difference signal x '(see FIG. 4 (H)). The latch circuit 13 stores the signal x ″, which is one signal before the phase difference signal x ′ changes at the rising edge of the reset signal RST, and uses the up / down pulse generator 14 and the up / down counter 15 for the same method as shown in FIG. Thus, the phase difference x of the phase modulation wave F _{P with} respect to the reference wave F _R can be detected.

On the other hand, FIG. 5 is a block diagram showing an embodiment in which the present invention is processed by software, in which the reference wave F _R is a frequency divider.
It is converted to a signal F _R ′ divided by 128 by 40, and the phase modulated wave F
_{P is} also converted by the frequency divider 41 into a signal F _P ′ whose frequency is divided by 128.
As a result, the phase difference of the signal F _P ′ with respect to the signal F _R ′ is 1/128 of the phase difference of the phase modulation wave F _{P with} respect to the reference wave F _R. The counter 42 outputs a time signal T (a binary signal of 0 ≦ T ≦ $ 3FFF) by the count pulse CLK from the count clock oscillator 16, and the time signal T is signal F _R ′ at the rising edge of the signal F _R ′ by the latch circuit 43. It is stored as the rising time T _R of the _R '. Further, the time signal T is a latch circuit
'At the rising edge of the signal F _P' signal F _P by 44 are stored as the rising time T _P of.

Here, the microprocessor 45 operates according to the flowchart of FIG. That is, first, when the signal F _R ′ rises (step S1), the microprocessor 45 reads the rising time T _R of the signal F _R ′ from the latch circuit 43 (step S2), and sets it as the previous rising time T _R of the signal F _R ′. Difference ΔT _R is calculated (step S3), and the hexadecimal number “$ 3FF” is added.
The logical product with F "is calculated (step S4), and the processing is performed so that the difference ΔT _R is always the cycle (> 0) of the signal F _R 'even when T _R <T _R ' (step S5). After the rise of the signal F _P ′ (step S6), the microprocessor 45 reads the rise time T _P of the signal F _P ′ from the latch circuit 44 (step S7), and compares it with the rise time T _R of the signal F _R ′. Δ
T _P , that is, the waveform rising delay time of the signal F _P ′ with respect to the signal F _R ′ is obtained (step S8). Next, the delay time ΔT _P is multiplied by the hexadecimal number “$ 2000” (step S10), and the difference Δ
By taking the logical product of the T _R 16 hexadecimal after dividing "$ 1FFF" (step S11), 16 hexadecimal one period of signal F _P phase difference x 'signal F _R' for 'signal F _R of'' It is calculated in the unit of $ 2000 "and within the range of one cycle of the signal F _R ′. Further, the difference Δx between the phase difference x ′ of the signal F _P ′ with respect to the signal F _R and the previous phase difference x ″ is calculated (step S12), and the difference Δx is calculated.
It is determined whether or not x exceeds a value (± $ 1000) equal to or more than a half cycle of the signal F _R ′ (steps S14, S16), and the variable x _u is increased or decreased to increase the position of the signal F _P ′ with respect to the signal F _R ′. The number of wavelengths of the phase difference
x _u is obtained (steps S15 and S17). And the number of wavelengths x
_u is multiplied by the hexadecimal number “$ 2000” (step S20), and the result is added as the phase difference x ′ within one period to obtain the phase difference x of the signal F _P ′ with respect to the signal F _R ′ (step S21). Signal x to and output. The resolution of the phase difference signal x flowchart of FIG. 6, one period of the signal F _R '8192 ($ 200
Therefore, the phase difference signal x becomes the reference wave F _R.
For the phase difference of the phase modulated wave F _P, one period of the reference wave F _R
It can detect with a resolution of 1/64 (8192/128).

As shown in FIG. 5 explained above, the reference wave F _R and the phase modulation wave F _P
When the phase difference x of the phase-modulated wave F _P with respect to the reference wave F _F is detected from the signal obtained by dividing N by N in the same manner as the displacement detection device of FIG. 1, the reference wave F _R and the phase-modulated wave F _P are detected. By making the cycle of N times longer, it becomes easier to perform the software processing of the microprocessor 45, which is a part of the circuit, as shown in FIG. This is because the reference wave frequency is a few
When it becomes MHz, it is effective when a part of the displacement detection device is simplified by software processing of a microprocessor.

(Effect of the Invention) According to the present invention, the displacement amount of the detector that outputs the displacement amount as the phase-modulated wave with respect to the reference wave is measured by measuring the period of the reference wave and the delay time of the phase-modulated wave with respect to the reference wave at substantially the same time. ,
The phase difference of the phase modulated wave with respect to the reference wave is detected and obtained. Therefore, the error of the detected displacement amount when the frequency of the reference wave fluctuates can be reduced. In addition, since it can be configured with all digital circuits, high integration is easy compared with the device using the conventional PLL circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 4 is a timing chart showing an example of the operation, FIGS. 3 and 5 are block configuration diagrams showing another embodiment of the present invention, and FIGS. 4 and 6 are timing charts showing the respective operation examples. FIG. 7 is a block diagram showing an example of a conventional device, and FIG. 8 is a flow chart showing an example of its operation. 1 ... Laser oscillator, 4 ... Fixed reflector, 5 ... Movable reflector, 8,17,36,37,42 ... Counter, 9 ... Phase comparator, 10 ... LPF, 11 ... VCO, 12,13,18,19,20,38,39 ……
Latch circuit, 15-up / down counter, 16-oscillator, 21,22-subtractor, 23-divider, 30,40,41-divider, 32,33-flip-flop.

Claims (5)

[Claims] 1. A displacement detecting device for a detector, which outputs a displacement amount as a phase-modulated wave with respect to a reference wave, and a first means for measuring a cycle ΔT _{R of the} reference wave by an oscillator outputting a count pulse and the count pulse. And the cycle Δ
In parallel with the measurement of T _R , there are provided second means for measuring the delay time ΔT _P of the phase-modulated wave with respect to the reference wave by the count pulse, and calculation means for dividing the delay time ΔT _P by the period ΔT _R. Displacement detection device characterized by comprising. Wherein said first and second means comprises a counter for counting the count pulse, and means for storing the output value T _R of the counter at the time of rise or fall of the reference signal, the value T 'means for storing said values T _R and T _R' previous value T _R which varies between _R and subtractor for calculating outputting a difference, of the counter at the time of rising or falling of the phase-modulated wave 2. The displacement detecting device according to claim 1, comprising means for storing the output value T _P, and a subtractor for calculating and outputting the difference between the value T _P and the value T _R or T _R ′. 3. The first and second means comprise two sets of counters for counting the count pulses, and two sets at the time of rising or falling of the reference wave for every n periods (n ≧ 2). Means for clearing the counter and starting counting, a means for stopping one of the two sets of counters at the rising or falling of the reference wave after the start of counting, and the other of the two sets of counters. The means for stopping the counting at the rising or falling of the phase-modulated wave after the start of counting, and the means for storing the count output value from the stop of counting of the two sets of counters until it is cleared. 1. The displacement detection device according to 1. 4. The displacement detecting device according to claim 1, means for storing a detected displacement x ″ that is one before the detected displacement x ′ of the displacement detecting device, and the detected displacements x ′ and x ″. Displacement detecting device, comprising: a subtractor for calculating and outputting the difference Δx of the difference Δx, and a counting means for counting up or down depending on the magnitude of the difference Δx. 5. A displacement detecting device for a detector that outputs a displacement amount as a phase-modulated wave with respect to a reference wave, wherein a first frequency divider that divides the reference wave by N and the phase-modulated wave is divided by N. A second frequency divider, and the displacement detection device according to claim 1 or 4, which receives the reference wave after the N division and the phase-modulated wave after the N division as inputs. Displacement detection device.