JP2001147105A - Position detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a position detecting device capable of preventing a malfunction caused by a rapid change of a laser beam or amplitude fluctuation of a phase detection signal or the like, and having high resolution of position detection. SOLUTION: In this position detecting device for detecting the position of a detection target optically by using an interferometer, the phase of an interference fringe is detected by a phase detector, and a modulation signal for modulating an angular frequency ωs according to a moving quantity of the detection target is obtained. An operation processing is given to the modulation signal to obtain a signal (ωc≫ωs) having an angular frequency (ωc+ωs). The signal is pulsed and divided by a comparator. The frequency of the divided signal is measured to obtain the position of the detection target based on the measured frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device for optically detecting the position of a detection target using an interferometer.

[0002]

2. Description of the Related Art A position detecting apparatus using an interferometer has an advantage that it can detect a position with high accuracy and without contact.

FIG. 2 is a configuration diagram of a conventional example of a position detecting device using an interferometer. In FIG. 2, the position of the target mirror 1 is fixed, and the optical circuit unit 2 moves in the CC ′ direction together with the detection target (not shown). The laser light source 21 emits laser light having a polarization component perpendicular to the plane of the drawing. Lens 22
Turns the light emitted from the laser light source 21 into parallel light. The half mirror 23 splits the light passing through the lens 22 into transmitted light and reflected light.

The mirrors 24 and 25 whose positions are fixed receive the light transmitted through the half mirror 23, reflect the received light, and return the reflected light to the half mirror 23. The mirror 24 is arranged at an angle of 45 ° with the optical axis of the laser light source 21. On the other hand, the mirror 25 is at 45 ° + θa
Are arranged at an angle. The polarization beam splitter (PBS) 26 reflects the light reflected by the half mirror 23. The reflected light passes through the λ / 4 plate 261 and proceeds to the target mirror 1. By passing the light twice through the λ / 4 plate 261, the light is converted from vertically polarized light to horizontal polarized light and from horizontal polarized light to vertical polarized light. By providing the λ / 4 plate 261, transmitted light and reflected light can be selected by the PBS 261. After being reflected by the target mirror 1, the corner cube 27 reflects the light transmitted through the λ / 4 plate 261 and the PBS 26 and returns the light to the PBS 26. The phase detector 28 detects an interference fringe generated by the light returning to the half mirror 23. Let L be the distance between the target mirror 1 and the corner cube 27.

The light emitted from the laser light source 21 in the position detecting device shown in FIG. 2 includes light taking the following path. Lens 22 → half mirror 23 → mirror 24 → mirror 2
5 → half mirror 23 → phase detector 28 Light taking this route is defined as light. Lens 22 → half mirror 23 → PBS 26 → λ / 4 plate 261 → target mirror 1 → λ / 4 plate 261 → PBS
26 → Corner cube 27 → PBS26 → λ / 4 plate 2
61 → Target mirror 1 → λ / 4 plate 261 → PBS2
6 → half mirror 23 → phase detector 28 Light taking this path is defined as light.

Since the arrangement angle of the mirror 25 is shifted by θa with respect to the arrangement angle of the mirror 24, the wavefront of the light a returning along the path and the wavefront of the light b returning along the path Are shifted by θa. Lights a and b interfere with each other due to the shift of the wavefront to form an interference fringe S. FIG. 3 shows the pattern of interference fringes. The pitch P of the interference fringes is given by the following equation. P = λ / θa (λ is the wavelength of the laser beam)

[0007] The phase detector 28 detects interference fringes by two light receiving elements arranged with a phase shifted by P / 4 pitch along the arrangement direction of the interference fringes. The light receiving element is, for example, a photodiode. FIG. 3 shows the arrangement of the two light receiving elements 281 and 282. The two light receiving elements 281 and 282 output detection signals according to the amount of received light. The detection signals of the light receiving elements 281 and 282 are K1 sin θ and K1 cos θ (K1
Is a constant, and θ is a phase). The phase θ is modulated according to the movement amount ΔL of the optical circuit unit 2. θ is given by the following equation. θ = 2π · 4ΔL / λ (1) In equation (1), “4” means that light travels back and forth between the target mirror 1 and the corner cube 27 twice, and the optical circuit unit 2 moves by ΔL. This is because the optical path length changes by 4ΔL. From the equation (1), the moving amount ΔL is given by the following equation. ΔL = θλ / 8π (2)

The comparator 29 includes light receiving elements 281 and 2
The detection signals K1sinθ and K1cosθ at 82 are converted into pulse signals. The converted pulse signals are referred to as pulse A and pulse B. The phase counter 30 measures the phases of the pulse A and the pulse B, and calculates the moving distance ΔL from the measured phase based on the equation (2). The position of the detection target is obtained from the moving distance ΔL. The phase counter 30 determines the moving direction of the detection target from the relationship between the phases of the pulse A and the pulse B.

FIG. 4 is a waveform diagram of each signal in the apparatus of FIG. In FIG. 4, the horizontal axis represents the movement amount ΔL. The phase counter 30 measures the phase of the pulse A or the pulse B with a resolution of 1/4 cycle of the pulse A and the pulse B.

The conventional example shown in FIG. 2 has the following problems. (Problem 1) The phase counter 30 detects the input pulse A
Since the moving direction of the detection target is determined based on the phase difference between the pulse B and the pulse B, it is necessary to ensure a sufficient phase difference between the two pulses. However, there has been a problem that the phase difference is reduced due to the following factors, which may cause a malfunction.

When the wavelength of the laser oscillation in the laser light source changes sharply, the output of the phase detector also changes sharply,
The phase difference may be reduced.

An error may occur in the phase and amplitude of the detection signal of the light receiving element due to the disturbance of the laser wavefront, and the phase difference may be reduced.

When the optical circuit section 2 and the slider on which the object to be detected are moved at a high speed, the output frequency of the phase detector 28 is about several MHz because the wavelength of the laser is short. Must be used. Conversely, when the slider stops or moves at a low speed, the frequency of the output of the phase detector 28 decreases to about 0 or several tens Hz. At this time, it is necessary to provide the comparator with hysteresis so as not to oscillate the high-speed comparator. If hysteresis is provided, a large error may occur in the phase difference between the pulse A and the pulse B when the amplitude of the comparator input fluctuates.

(Problem 2) In the conventional example of FIG. 2 in which the position is obtained by measuring the phase of the output of the phase detector 28, when the output of the phase detector 28 changes by 2.pi. The count changes by four. Therefore, the detection resolution is (the cycle of the output of the phase detector 28) /
It is fixed to 4.

[0015]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and can prevent malfunction due to a sharp change in laser light, amplitude fluctuation of a phase detection signal, and the like. It is an object of the present invention to realize a position detecting device having a high resolution.

[0016]

SUMMARY OF THE INVENTION The present invention is a position detecting device having the following configuration.

(1) An optical circuit unit that generates interference fringes of a constant pitch that moves with the movement of a detection target by using light interference, and a plurality of light receiving units that are arranged to be displaced along the arrangement direction of the interference fringes. A phase detector that detects interference fringes by an element and generates two types of modulation signals that are modulated in accordance with the amount of movement of the detection target, wherein an original clock is added to the two types of modulation signals. A phase detection device, comprising: a multiplier for multiplying each of the reference signals generated based thereon; and an adder for adding the two multiplied signals.

(2) In a position detection device that optically detects the position of a detection target using an interferometer, interference fringes having a pitch P that moves with the movement of the detection target are generated by using light interference. P along the optical circuit portion and the arrangement direction of the interference fringes
Interference fringes are detected by a plurality of light receiving elements arranged with phases shifted by / 4 pitch, and modulation signals K1 sin ωst and K1 cos ωst (in which the angular frequency ωs is modulated according to the moving amount of the detection target from the detection signals of these light receiving means). K1 is a constant, t is time), a reference signal K2cosωct and K2si generated based on the original clock for the modulated signals K1sinωst and K1cosωst.
multipliers that respectively multiply nωct (ωc≫ωs);
A signal K1 · K2 sin is obtained by adding the two multiplied signals.
An adder for obtaining (ωc + ωs) t, a comparator for converting the added signal into a pulse signal, a frequency divider for dividing the converted pulse signal by a frequency division ratio n (n is an integer), and The cycle of the obtained divided signal n / (fs + fc) (ωc =
2πfc, ωs = 2πfs) synchronized with the original clock and measuring with a clock whose cycle is sufficiently shorter than the frequency-divided signal, and the difference between the measurement cycle of the cycle counter and the cycle n / fc of the reference signal. , An integrator that integrates the subtracted value of the subtractor for each cycle n / (fs + fc), and a position calculating unit that calculates the position of the detection target from the integrated value of the integrator. Characteristic position detection device.

(3) A source clock generator for generating a source clock having a frequency equal to or higher than fc, an oscillator for generating and generating a signal K2cosωct or K2sinωct based on the source clock, and a signal generated by the oscillator And a phase shifter for generating signals K2cosωct and K2sinωct. The signals K2cosωct and K2sinωct generated by the phase shifter are supplied to the multiplier, and the original clock is sent to the cycle counter as a cycle measuring clock. (2)
The position detecting device as described in the above.

(4) The multiplier outputs the modulated signal K1 sin
The reference signal K2sinωct is added to ωst and K1cosωst.
And K2cosωct, respectively, and the adder
The signals K1 and K2cos (ωc
-Ωs) The position detection device according to (2), wherein t is obtained.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the present invention. 1 that are the same as those in FIG. 2 are given the same reference numerals. For simplicity of explanation, it is assumed that the optical circuit unit 2 is moving at a constant speed V together with the detection target. Phase detector 28
Outputs the detection signals K1 sin θ and K1 cos θ. Since the optical circuit unit 2 is moving at a constant speed,
K1 sin θ = K1 sin ωst, K1 cos θ = K1
cosωst (ωs is angular frequency, t is time).

Since the optical circuit 2 is moving at a constant speed V, ΔL = Vt. From equation (1), θ = 2π · 4ΔL / λ = 2π · 4Vt / λ = 8πVt / λ. From θ = ωst, ωs = 8πV / λ. Assuming that ωs = 2πfs (fs is a frequency), fs = 4V / λ (3)

The original clock generator 40 has a frequency fc.
Generate an original clock that is sufficiently larger than the original clock. Oscillator 41
Is a signal K2cosωct (K2
Is generated by generating a constant, ωc≫ωs). The phase shifter 42 shifts the phase of the signal K2cosωct,
2sinωct is generated. The multiplier 43 outputs the modulated signal K
The reference signal K2co is applied to 1 sinωst and K1cosωst.
sωct is multiplied by K2sinωct. The adder 44 adds the two multiplication signals to generate a signal K1 · K2s.
in (ωc + ωs) t is obtained.

The comparator 45 converts the addition signal into a pulse signal. The frequency divider 46 divides the converted pulse signal by a frequency division ratio n (n is an integer). A signal (ωc = 2πfc) having a frequency of (fc + fs) / n is obtained by the frequency divider 46. The period counter 47 measures the period n / (fs + fc) of the frequency-divided signal obtained from the frequency divider 46 using the original clock. The frequency of the original clock is frequency (fc + fs) / n
Because it is sufficiently large compared to, the period can be measured with high resolution. Note that the cycle may be measured using a clock other than the original clock.
The cycle of the measurement clock is the cycle of the frequency-divided signal n / (fs + f)
It suffices if it is sufficiently shorter than c). The subtractor 48 calculates the period n / fc of the reference signal and the measurement period n / (fs) of the period counter.
+ Fc). Thereby, the period difference nfs
/ Fc (fs + fc) is obtained.

The integrator 49 calculates a subtraction value nfs / f of the subtractor.
c (fs + fc) is integrated every cycle n / (fs + fc). As a result, an integrated value fst / fc is obtained. The scale converter 50 adds λfc / 4 to the integrated value fst / fc.
Is multiplied to calculate the moving distance ΔL. This operation is as follows. From equation (3), fst / fc × λfc / 4 = 4V / λ × t / fc × λfc / 4 = Vt = ΔL Thus, the movement amount ΔL is obtained. The calculating means 51 calculates the position of the detection target from the movement amount ΔL. The position calculating means referred to in the claims is a scale converter 5
0 corresponds to the calculating means 51.

The moving direction of the detection target is expressed by two modulated signals K
The polarity of ωs differs depending on the relationship between the phase of 1 sinωst and the phase of K1cosωst, and it is determined whether the frequency fs + fc is higher or lower than fc.

The multiplier 43 outputs the modulated signal K1 sin
The reference signal K2sinωct is added to ωst and K1cosωst.
And K2cosωct, respectively, and the adder 44
The signals K1 and K2cos (ωc
−ωs) t may be obtained.

In the embodiment, the case where the optical circuit unit 2 moves has been described. However, the target mirror moves,
The position of the optical circuit unit 2 may be fixed.

[0029]

According to the present invention, the following effects can be obtained.

According to the first aspect of the present invention, two types of modulated signals modulated according to the amount of movement of the detection target are respectively multiplied by a reference signal generated based on an original clock, and the two multiplied signals are added. By doing so, an addition signal having a higher frequency than the modulation signal is generated. For this reason, even when the detection target stops or moves at a low speed, a high-frequency signal is input to the comparator that pulses the addition signal. This eliminates the need for the comparator to have hysteresis. Since there is no hysteresis, no malfunction occurs even if the amplitude of the comparator input fluctuates.

According to the second and fourth aspects of the present invention, the following effects can be obtained. Apply arithmetic processing to the detection signal obtained from the phase detector,
Since a high-frequency signal is input to the comparator after being input, a high-frequency signal is input to the comparator even when the detection target stops or moves at a low speed. Therefore, it is not necessary to provide the comparator with hysteresis. Since there is no hysteresis, no malfunction occurs even if the amplitude of the comparator input fluctuates. In addition, since the cycle is measured after dividing the detection signal of the phase detector, it is not affected by the duty distortion of the comparator output. This makes it difficult to malfunction even when the output of the phase detector changes sharply. A position is detected by generating a modulation signal whose period is modulated in accordance with the amount of movement of the detection target, and measuring the period of the modulation signal with a measurement clock whose period is sufficiently shorter than the period of the modulation signal. Thus, position detection can be performed with high resolution.

According to the third aspect of the present invention, a signal for multiplying the output of the phase detector and a measurement clock for the period counter are generated by sharing the original clock. Therefore, the output of the phase detector and the timing of the cycle measurement can be synchronized with high accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional example of a position detection device using an interferometer.

FIG. 3 is a diagram showing a pattern of interference fringes;

FIG. 4 is a waveform diagram of each signal in the device of FIG.

[Explanation of symbols]

 2 Optical Circuit Unit 28 Phase Detector 40 Original Clock Generator 41 Oscillator 42 Phase Shifter 43 Multiplier 44 Adder 45 Comparator 46 Divider 47 Period Counter 48 Subtractor 49 Integrator 50 Scale Converter 51 Calculation Means

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Ryuichi Jimbo 2-93-2, Nakamachi, Musashino-shi, Tokyo F-term in Yokogawa Electric Corporation (reference) 2F064 AA03 BB05 CC04 DD01 DD08 FF01 FF05 GG16 GG22 GG38 GG53 HH01 HH05 JJ01 JJ13 2F065 AA09 BB25 DD03 FF13 FF51 GG04 GG12 GG22 HH04 HH13 JJ01 JJ18 LL12 LL17 LL36 MM03 NN05 PP22 QQ25 QQ27 QQ51

Claims (4)

[Claims] An optical circuit unit that generates interference fringes at a constant pitch that moves with the movement of a detection target by using light interference, and a plurality of light receiving elements that are arranged so as to be shifted along an arrangement direction of the interference fringes. And a phase detector that generates two types of modulated signals that are modulated in accordance with the amount of movement of the detection target. And a multiplier for multiplying each of the generated reference signals, and an adder for adding the two multiplied signals. 2. A position detecting apparatus for optically detecting the position of a detection target using an interferometer, wherein the optical system generates interference fringes having a pitch P that moves with the movement of the detection target by using light interference. The interference fringes are detected by a circuit unit and a plurality of light receiving elements arranged with a phase shift of P / 4 along the arrangement direction of the interference fringes. Modulated signal K1 sinωst modulated according to the amount
And a phase detector for generating K1cosωst (K1 is a constant and t is time), and a reference signal K2cosωct generated based on the original clock for the modulated signals K1sinωst and K1cosωst.
And K2sinωct (ωc≫ωs), respectively, and a signal K1 · K2sin by adding the two multiplied signals.
An adder for obtaining (ωc + ωs) t; a comparator for converting the added signal into a pulse signal; a frequency divider for dividing the converted pulse signal by a frequency division ratio n (n is an integer); Period n / (fs + fc) of obtained divided signal
(Ωc = 2πfc, ωs = 2πfs) synchronized with the original clock and measured with a clock whose cycle is sufficiently shorter than the frequency-divided signal; a measurement cycle of this cycle counter and a cycle of the reference signal n / fc
And a position calculating means for calculating a position of a detection target from the integrated value of the integrator, and an integrator for integrating the subtracted value of the subtractor every cycle n / (fs + fc). A position detecting device characterized by the above-mentioned. 3. An original clock generator that generates an original clock having a frequency equal to or higher than fc; an oscillator that generates and generates a signal K2cosωct or K2sinωct based on the original clock; The phase is shifted and the signal K2cos
ωct and a phase shifter for generating K2sinωct, and a signal K2cosωct generated by the phase shifter.
3. The position detecting device according to claim 2, wherein the multiplier outputs the original clock to the period counter as a period measuring clock. 4. The multiplier outputs a modulated signal K1 sinωs
Reference signals K2sinωct and K are added to t and K1cosωst.
2cosωct, and the adder adds two multiplied signals to obtain a signal K1 · K
3. The position detecting device according to claim 2, wherein 2 cos (ωc−ωs) t is obtained.