JP3344637B2 - Optical interference type position measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position measuring device used for measuring the position of a work stage when it is displaced or the angle of a rotary shaft in a precision industrial machine or machine tool. The reference light from the surface and the measurement light from the measurement surface are superimposed and caused to interfere with each other, and the difference in the optical path length between the reference light and the measurement light is measured based on the light intensity of the interference light. The present invention relates to an optical interference type position measurement device for reading position data of an object.

[0002]

2. Description of the Related Art FIG. 13 shows a laser length measuring device which is an example of an optical interference type position measuring device utilizing an optical heterodyne method. This laser length measuring device is provided with a moving mirror 10 on a measuring object.
The two laser beams reflected from the mirror 11 and the fixed mirror 11 are superimposed to form interference light ML, and a change in the light intensity of the interference light ML due to the movement of the movable mirror 10 is detected to detect the relative displacement X of the measurement object. Is measured.

A laser oscillator 12, which is a light source, has a separation plane P1.
The light beam OL is emitted toward. Laser oscillator 12 is HeN
e laser, which is composed of two laser beams (light beams O1 and F2) having polarization planes orthogonal to each other and having different frequencies f1 and f2.
L) is output. The laser light is polarized beam splitter 13
At the separation plane P1, and is separated into measurement light L1 at frequency f1 and reference light L2 at frequency f2.

The measuring light L1 is applied to a measuring surface on a movable mirror 10 fixed to a measuring object. The measurement light L1 reflected by the measurement surface undergoes Doppler modulation with a frequency Δf in proportion to the moving speed of the moving mirror 10 in the X direction, and is input to the polarization beam splitter 13 again. On the other hand, the reference light L2 is reflected by the reference surface on the fixed mirror 11, and is input to the polarization beam splitter 13 again. Polarizing beam splitter 13
In the measurement light L1 and the reference light L2 are superimposed,
The measurement interference light ML is formed. When the optical path length from the separation plane P1 of the measurement light L1 to the return to P2 on the polarizing beam splitter 13 increases or decreases with the movement of the measurement target, the increase or decrease in the optical path length at P2 with respect to the reference light L2. The phase of the measurement light L1 is shifted. The light intensity of the measurement interference light ML changes due to the phase shift.

[0005] The light receiving section 14 electrically detects the interference light intensity of the measurement interference light ML. That is, in the light receiving unit 14, the measurement interference light ML is photoelectrically converted, and a measurement electric signal Fp (beat signal) having a difference frequency between f1 ± Δf and f2 is obtained.

On the other hand, the light beam OL is split by the beam splitter 15 and irradiated on the photoelectric conversion element 16. In the photoelectric conversion element 16, the two laser lights having different frequencies are photoelectrically converted, and a reference electric signal Fr (beat signal) having a difference frequency between f1 and f2 is obtained.

Here, the phase difference between the measurement electric signal Fp and the reference electric signal Fr indicates a difference in optical path length between the measurement light L1 and the reference light L2. Since the reference electric signal Fr representing the reference light L2 whose optical path length does not change has a fixed phase, the phase difference of the measured electric signal Fp with respect to the reference electric signal Fr is determined by the relative displacement X of the measurement object, that is, the relative displacement X of the movable mirror 10. Will be shown. Based on this principle, the arithmetic circuit 17
Measures the phase difference between the measurement electric signal Fp and the reference electric signal Fr while the measurement object is moving, and detects a relative displacement X as position data of the measurement object from the phase difference.

Assuming that the wavelength of the laser beam is λ, when the object to be measured is displaced X, the phase difference between the two signals Fp and Fr is 4
It is represented by π · (X / λ). As a result, the measured electrical signal F
The phase of p coincides with the phase of the reference electric signal Fr every period, that is, every time the phase difference changes by λ / 2. For this reason, the arithmetic circuit 17 includes a measuring device that specifies the measurement value Δx within the range of 0 to λ / 2, and a measurement device that specifies the measurement value Δx.
And a counter that counts the number of periods Xu of the phase difference based on the position data X, and outputs the position data X based on X = λ / 2 · Xu + Δx.

The arithmetic circuit 17 measures the phase difference between the two signals Fp and Fr according to a preset sampling time. This sampling time is set so that the change from the measurement value Δx (last) measured by the previous measurement device to the measurement value Δx (curr) measured by the current measurement device always falls within the range of ± λ / 4. Is done. According to the setting of the sampling time, the cycle number can be easily and reliably determined by comparing the measurement value Δx (last) measured by the previous measurement device with the measurement value Δx (curr) measured by the current measurement device. Xu can be counted.

The measuring instrument is Δx (curr) −Δx (la
st) ≦ −λ / 4, that is, when the current measurement value is smaller than the previous measurement value by λ / 4 or more, the cycle number Xu
Is increased by one cycle, an up pulse is output, and the count value of the counter is increased by one. For example, the current measurement value is Δx (curr) = λ / 4, and the previous measurement value Δx (l
ast) = (3λ) / 4, Δx (c
(urr) −Δx (last) = − λ / 2, and the count number of the counter increases by one. In order to reach the measured value λ / 4, there are two cases, that is, the case where the period increases from (3λ) / 4 and the period increases and the case where the period simply reaches and decreases from (3λ) / 4. Since the change to Δx (curr) is set so that the sampling time is always within the range of ± λ / 4, it is determined that the change has occurred after the cycle has changed. Similarly, the instrument measures Δx (cu
rr) -Δx (last) ≧ λ / 4, that is,
If the current measurement value is larger than the previous measurement value by λ / 4 or more, it is determined that the number of cycles has decreased by one cycle, and a down pulse is output to reduce the count number of the counter by one.

The light beam OL split by the beam splitter 15 is also input to the photoelectric conversion element 18. The electric signal obtained by the photoelectric conversion element 18 is input to a laser tuning circuit 19, which stabilizes the laser oscillator 12.

[0012]

However, in the above-described optical interference type position measuring device, since the change in the light intensity of the interference light caused by the increase or decrease in the optical path length of the measurement light is measured, the object to be measured is not measured. Need to move. That is, the above-described apparatus sets a reference point at the start of position measurement, and incrementally measures a relative displacement of a measurement target from the reference point. For this reason, if the cycle number Xu is incorrectly counted during measurement, the error is accumulated in subsequent measurements. If the optical path of the measurement light is interrupted once, the position up to that point cannot be known. At that time, the measurement target must be returned to the reference point and the origin must be found again.If the current position is erased by turning off the power, after the power is turned on, the origin must be found every time measurement starts. There is a problem that it does not.

In the above-mentioned device, for example, 2
A high-frequency HeNe laser oscillator is required, and there is a problem of large size and high price. Therefore, it is conceivable to use a small semiconductor laser as the light source. However, since the semiconductor laser has insufficient wavelength stability, for example, when a Michelson interferometer is configured, errors and fluctuations in wavelength affect measurement accuracy. There's a problem.

Further, the above-mentioned apparatus has a problem that the measurement data becomes unstable due to fluctuations in the air in the optical path due to the surrounding environment to be measured or the movement of the object to be measured.

The present invention has been made in view of the above circumstances, and has as its object to provide an optical interference type position measuring device capable of easily detecting an absolute position of a measurement object.

Another object of the present invention is to provide a small and inexpensive optical interference type position measuring device in which the measurement accuracy is not affected by the wavelength fluctuation of the semiconductor laser even when a semiconductor laser is used as a light source.

Still another object of the present invention is to provide an optical interference type position measuring apparatus which is resistant to changes in the surrounding environment of the measurement.

[0018]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
The light interference type position measuring device according to the present invention includes a light source that emits a light beam having coherence, a separation surface that separates the light beam into reference light and measurement light, a reference surface that reflects the reference light, and a measurement target. A light-interfering position measurement device that includes a measurement surface that reflects the measurement light and that overlaps the reference light and the measurement light to form interference light, and that reads position data of a measurement target based on the interference light. In, a wavelength control unit that changes the wavelength of the light beam emitted from the light source, and having the reference surface and the measurement surface, the reference light from the reference surface and the measurement light from the measurement surface are superimposed on each other to generate interference light for relative displacement. Based on the relative displacement interference unit to be sent and the reference interference light beam separated from the light beam, two lights having an optical path length difference corresponding to a predetermined reference length are superimposed on each other to produce a reference length interference beam. Reference length for sending light An interference unit, the change in light intensity generated in the relative displacement interference light and reference length for interference light when changing the wavelength of the wavelength control unit luminous flux, and based on the reference length, the absolute measurement target Absolute to calculate position data
A position data calculation unit, and the relative change accompanying the movement of the measurement target.
Absolute position of the object to be measured based on the change in the light intensity of the position interference light
Position data meter to calculate relative position data
Calculation unit and their absolute position data and relative position data
And a combining operation unit that specifies the position of the measurement target by combining

Preferably, the reference length interference portion reflects a reference light extracted from the reference interference light beam on a separation surface, and is extracted from the reference interference light beam on a separation surface. Measurement light reflecting the measurement light, the reference light from the reference surface, and the measurement light from the measurement surface having a difference in the optical path length corresponding to the reference length with respect to this reference light, It is characterized by forming interference light.

Further, preferably, the absolute position data meter
The calculation unit includes a counting circuit that measures an increase / decrease value Co of a wave number generated in the interference light for the reference length when the wavelength of the light beam is changed, and an increase / decrease of the wave number generated in the interference light for relative displacement when the wavelength of the light beam is changed. A counting circuit for measuring the value Cx, and Lx = Lo (Cx / C
o) Absolute position for calculating the position Lx of the measurement target from the separation surface in the relative displacement interference unit based on (where Lo: the reference length from the separation surface to the measurement surface in the reference length interference unit) A data calculation circuit.

[0021]

Further, preferably, the light drying device according to the present invention is used.
The interference-type position measurement device includes a wavelength-variation detecting unit that detects a wavelength variation of a light beam from the light source based on the reference-length interference light from the reference-length interference unit; and A wavelength correction unit for correcting the position data.

Still preferably, the light source is a semiconductor laser, and the wavelength controller changes the wavelength of the light beam by changing the temperature of the semiconductor laser.

Still preferably, the wavelength controller changes the wavelength of the light beam by generating a stress in the medium through which the light beam passes to change the refractive index of the medium.

Further, preferably, the wavelength control section is characterized in that an electric field or a magnetic field is applied to a medium through which the light beam passes to change the refractive index of the medium , thereby changing the wavelength of the light beam.

Still preferably, the wavelength controller changes the wavelength of the light beam by the Doppler effect when rotating a rotating plate having a predetermined refractive index.

[0027]

According to the above construction , the relative displacement interference portion can
Interfering light for relative displacement indicating a change in light intensity according to a change in the wavelength of the light beam is sent out. Also, from the interference part for the reference length,
A reference-length interference light representing a light intensity change corresponding to a similar wavelength change is sent out. The position data detector measures the increase (or decrease) of the wave number of the light wave at the measurement length and the reference length from the light intensity change in the relative displacement interference light and the reference length interference light. The position data of the measurement target is detected from the two wavenumber increases (or decreases) and the reference length. At the start of measurement, the absolute position data calculator
Measures the absolute position of the measurement object. Subsequent measurement
For displacement, the relative position data calculation unit
The relative position data to be calculated is calculated. Absolute position data calculator
Absolute position and relative position data of relative position data calculator
And the position of the object to be measured
To specify.

Further, by superimposing on the basis of the reference interference light beam separated from the light beam used for measurement in the relative displacement interference section, and the reference light reflected from a reference surface and a measurement light reflected from the measuring surface , Forming interference light for the reference length. The change in the light intensity of the reference-length interference light reflects an increase in the wave number caused by a difference in the optical path length corresponding to the reference length when the wavelength is changed.

Furthermore, counting circuit measures the wave number increases that occur on the reference length for the interference light and the relative displacement interference light when changing the wavelength of the light beam, the reduction Co, as Cx. Calculation data Co relating the measured wave number, using the Cx, absolute position data calculation circuit, the position Lx to be measured from the separating plane in the interference portion for relative displacement on the basis of the formula Lx = Lo (Cx / Co) I do.

[0030]

[0031] Furthermore, using the relative position data wavelength variation of the light beam is corrected from the light source, it calculates the relative position data with respect to the absolute position of a measured object.

[0032] Furthermore, to change the wavelength of the light beam from the light source by changing the temperature of the semi-conductor laser.

[0033] Furthermore, by generating a stress in medium passing the light beam from the light source, to change the wavelength of the light beam by varying the refractive index of the medium.

[0034] Furthermore, the medium that passes through the light beam from the light source
The wavelength of the light beam is changed by applying an electric or magnetic field to the body to change the refractive index of the light beam.

[0035] Furthermore, to change the wavelength of the light beam from the light source by the Doppler effect at the time of rotating the rotating plate of Jo Tokoro refractive index.

[0036]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of an optical interference type position measuring apparatus according to a first embodiment of the present invention. The optical interference type position measuring device 20 includes a light source 21 that emits a light beam OL. The wavelength of the light beam OL is changed at any time by the wavelength control unit 22. The relative displacement interference unit 23 superimposes, based on the light flux OL emitted from the light source 21, the reference light and the measurement light having a difference in optical path length corresponding to the distance to the measurement target, and sends out the relative displacement interference light L3. . The reference length interference unit 24 superimposes two lights having a difference in optical path length corresponding to a predetermined reference length on the basis of the reference interference light flux SOL separated from the light flux OL, and generates a reference length. And sends out the interference light L4. The position data detection unit 25 detects the position data of the measurement target based on the change in the light intensity of the relative displacement interference light L3, the change in the light intensity of the reference length interference light L4, and the reference length. In the optical interference type position measuring device 20, the relative displacement interference light L3 and the reference length interference light L3 are changed by changing the wavelength of the light beam OL emitted from the light source 21 without changing the position of the measurement target.
4 causes a change in light intensity.

As shown in FIG. 2, the light source 21 includes a GaAs type semiconductor laser 30 or the like. This semiconductor laser 30
Is driven by the semiconductor laser drive circuit 31 and outputs a light beam OL of laser light of a specific wavelength. The luminous flux OL of the outputted laser beam is divided into two beam splitters 32 and 33.
Is directed to the separation plane P3 of the relative displacement interference unit 23 through the.

The relative displacement interference unit 23 converts the light beam OL applied to the relative displacement interference unit 23 into two light beams having orthogonal polarization planes, that is, a reference light L5 and a measurement light L6.
And an interfering device 34 that separates the light beams from each other. The reference light L5 is reflected by a fixed polarizing mirror 35 serving as a reference surface,
The light is extracted from the light beam OL at the separation plane P3. Measurement light L6
Is transmitted through the polarizing mirror 35 to form the separation plane P3.
The light is taken out of the light beam OL and reflected by a reflection mirror 36 fixed to a measurement object as a measurement surface. Reference light L5 from polarization mirror 35 and measurement light L6 from reflection mirror 36
Are superimposed on each other on the separation plane P3, and the relative displacement interference light L3 is formed. The difference in the optical path length between the reference light L5 and the measurement light L6 is equal to twice the length Lx from the polarization mirror 35 to the measurement target, that is, the reflection mirror 36. As shown in FIG. 3, a light wave existing at the optical path length difference 2Lx causes a phase difference θ represented by a wave number between the measurement light L6 and the reference light L5. An interference fringe of the relative displacement interference light L3 is formed.

The reference length interference unit 24 converts the light beam SOL applied to the reference length interference unit 24 into two light beams having orthogonal polarization planes, that is, a reference light L7 and a measurement light L.
An interferometer 37 is provided which is divided into eight. The reference light L7 is reflected by a fixed polarizing mirror 38 serving as a reference surface,
The light is extracted from the reference interference light beam SOL at the separation plane P4.
The measurement light L8 is extracted from the reference interference light beam SOL at the separation plane P4 by transmitting through the polarization mirror 38, and reflected by the fixed reflection mirror 39 serving as the measurement plane. The reference light L7 from the polarizing mirror 38 and the measurement light L8 from the reflection mirror 39 are superimposed on each other on the separation plane P4, and the reference length interference light L4 is formed. The polarization mirror 38 and the reflection mirror 39 are arranged at intervals of the reference length Lo. As a result, the difference in the optical path length between the reference light L7 and the measurement light L8 becomes equal to twice the reference length. The light wave existing in the optical path length difference 2Lo causes a phase difference θ expressed by a wave number between the measurement light L7 and the reference light L8, and the phase shift due to the phase difference θ causes the interference light L4 for the reference length. Form interference fringes.

In the relative displacement interference unit 23 and the reference length interference unit 24, the polarizing mirrors 35 and 38 are controlled by the beam splitter 13 having a 45-degree angle plane with respect to the light beam as shown in FIG. You may comprise. In this case, the light beam irradiated to the beam splitter is divided into a light beam that travels straight and a light beam that travels at right angles to the beam, and the two split light beams are reflected by the reference surface and the measurement surface, and then superimposed by the beam splitter. It is sent out as interference light L3, L4.

The position data detecting section 25 is provided with a first counting circuit 40 for measuring the increase and decrease of the wave number generated in the relative displacement interference light L3 as Cx, and the increase and decrease of the wave number generated in the reference length interference light L4. Second counting circuit 41 for measuring as Co
And The wave number increase / decrease values Cx and Co measured by the first and second counting circuits 40 and 41 are input to an absolute position data calculating circuit 42, and the absolute position data calculating circuit 42
Then, based on the principle described later, Lx = Lo (Cx / C
o) (where Lo = the reference length from the separation plane P4 to the measurement plane 39 in the reference length interference unit 24), the position Lx of the measurement target from the separation plane P3 in the relative displacement interference unit 25 is calculated. . This value Lx is output as position data Pout of the measurement target.

The interference light L 3 for relative displacement applied to the position data detecting section 25 is photoelectrically converted into two light intensity signals having different phases by the light receiving section 43, and then voltage-amplified by the amplifier circuit 44. The amplified electric signal is input to the counting circuit 40, and based on the two light intensity signals, the counting circuit 40
The increase and decrease of the wave number are counted as Cx.

As shown in FIG. 4, the relative displacement interference light L3 applied to the light receiving section 43 is polarized and converted into circularly polarized light by the λ / 4 wavelength plate 45, and is split into two light beams by the beam splitter 46. . The split light beams pass through first and second polarizers 47 and 48 having polarization angles different from each other by π / 4. These two light beams are converted into electric signals S1 and S2 by the first and second photoelectric conversion elements, respectively. As shown in FIG. 5, these electric signals S1 and S2 become sine waves having a phase difference of π / 2 from each other, and one cycle thereof corresponds to a case where the measurement target is displaced by X = λ / 2. . Note that a method of extracting a two-phase signal using a λ / 4 wavelength plate and two polarizing plates is common in interference measurement. Alternatively, two polarizing plates whose polarization angles are shifted from each other by π / 2 or (3π) / 4 may be arranged to obtain an electric signal having a phase difference of π or (3π) / 2.

The amplification circuit 44 converts the electric signals S1 and S2 from current to voltage using a current-voltage circuit. This voltage is amplified to a sufficient voltage by the amplifier.

As shown in FIG. 6, the counting circuit 40 includes a comparator 51 for pulsing the two electric signals S1 and S2.
And an UP / DOWN counter 52 that counts each electric signal S1 and S2 in cycle units based on the pulse signal from the comparator 51 and outputs a cycle number N. As shown in FIG. 5, the comparator 51 compares a preset reference level, for example, the median value of the amplitude of the sine wave with the levels of the electric signals S1 and S2, respectively.
The H signal is output when the level of 1, S2 is higher than the reference level. According to the comparator 51, one cycle of the light intensity signal can be specified in the first to fourth regions by two pulse signals based on the signals S1 and S2. The UP / DOWN counter 52 measures the number of cycles N and the direction of the change from the change in the first to fourth areas.

The interpolation circuit of the counting circuit 40 outputs the electric signal S
1. Specify where S2 is in the cycle. here,
The electric signals S1 and S2 are

S1 = A1 · cos (θ) + B1 S2 = A2 · sin (θ) + B2 When the constants A1, A2, B1 and B2 are measured in advance and deleted,

S1 = cos (θ) S2 = sin (θ) is obtained. Therefore, the electrical angle θ of the electrical signals S1, S2
Is

(Equation 3) Thus, the electrical angle θ corresponding to the phase difference within the range of one cycle λ / 2 is calculated.

In the synthesizing circuit 53 of the counting circuit 40, the number of cycles N and the electrical angle θ

(Equation 4) Cx is calculated as a wave number based on A method for generating the measurable wave number will be described later.

The reference-length interference light L4 applied to the position data detector 25 via the two reflecting mirrors 55 and 56
Is converted into an electric signal by the light receiving unit 57, and then
8, the amplified electric signal is counted by a counting circuit 41.
Is input to The functions of the light receiving unit 57, the amplification circuit 58, and the counting circuit 41 are the same as those of the light receiving unit 43, the amplification circuit 44, and the counting circuit 40, and thus the description thereof will not be repeated.

The absolute position data calculation circuit 42
The wave numbers of the relative displacement interference light L3 and the reference length interference light L4 generated by the continuous change of the wavelength of the light flux OL from the laser beam and the reference interference light flux SOL (including not only analog light but also digital light). From the separation plane P3 to the object to be measured from the change Cx, Co and the reference length Lo.
Calculate x.

Now, it is assumed that the wavelength of the light flux OL from the light source 21 is continuously increased from λ1 to λ2 by the wavelength control unit 22 instead of moving the object to be measured by the displacement X.
The wavelength becomes shorter and changes from λ1 to λ2, and in the optical path 2Lx of the measurement light L6 reciprocating from the separation plane P3 in the relative displacement interference unit 23, the wave number of the light wave existing there increases from n1 to n2. At this time, if the wave number increases by λ / 2, one light / dark cycle is counted in the same manner as in the case where the measurement object moves by displacement X = λ / 2. As shown in FIG. 7, there is no phase difference between the measurement light L6 and the reference light L5 up to the separation plane P3. When the measurement light L6 of the frequency f1 is separated at the separation plane P3, only the measurement light L6 further passes through the optical path of 2Lx. When the measurement light L6 reaches the separation plane P3 again,
A phase difference θ1 is generated between the reference light L5 and the wave number existing during the period. The phase difference θ1 is shown as the light intensity of the relative displacement interference light L3. When the wavelength is increased,
The wave number n of the light wave gradually increases. As the wave number n increases, the phase of the measurement light L6 with respect to the reference light L5 at P3 gradually changes from θ1 to θ2 via θ12. The change in the light intensity accompanying the change in the wavelength is photoelectrically converted by the light receiving unit 43, and electric signals S1 and S2 are obtained. According to this principle, when the object to be measured is at the position X and the wavelength λ of the light beam OL changes and the wave number n changes by ± １ ／, the electric signals S1 and S2 change by one period as a sine wave. Become.

The data Cx regarding the wave number measured by the counting circuit 40 corresponds to the wave number increase ΔCx = n2−n1 of the light wave having the measured length Lx before and after the wavelength change. Here, the measurement length Lx is, before the wavelength change,

(Equation 5) Indicated by Here, C: speed of light; C / f1: wavelength of light wave. Similarly, the measurement length Lx after changing the wavelength is

(Equation 6) Indicated by From these two equations,

(Equation 7) Therefore, it can be seen that the change ΔCx in the measured wave number is proportional to the measurement length Lx.

Similarly, the change Co of the wave number measured by the counting circuit 41 is the reference length L before and after the wavelength change.
o The increase in the wave number of the light wave ΔCo = n4-n3 (where n
3: Wave number of light wave before change in reference length Lo; n4:
(The wave number of the light wave after the change in the reference length Lo). This wave number increase ΔCo is

(Equation 8) Is proportional to the reference length Lo. From these two equations,

(Equation 9) Holds. The absolute position data calculation circuit 42 calculates the measurement length Lx based on this equation and outputs it as position data Pout of the measurement target.

In the optical interference type position measuring device 20, the position of the object to be measured, that is, the measurement length Lx is measured at the measurement point (separation plane).
It can be obtained from the absolute position from P3. Therefore, there is no need to return the measurement target to the reference position and perform origin search,
Rapid position detection is achieved. Further, the light beam OL and the reference interference light beam SOL are sufficient if the wave number n of the light wave at the measurement length Lx and the reference length Lo fluctuates before and after the wavelength change, and the increase / decrease values Cx and Co of the wave number can be measured. There is no need to stabilize. Therefore, the displacement can be detected stably without being affected by the fluctuation of the wavelength of the light beam. Furthermore, if the measurement length Lx and the reference length Lo are set in the same environment with respect to the surrounding measurement environment, the data Cx and Co regarding the wave number are simultaneously affected by the same fluctuation, and the Lx obtained by Expression 9 Fluctuations of both are canceled out, and a measurement with strong environmental resistance can be performed.

In the above-described first embodiment, an example has been described in which two light beams are separated using polarized light or a plurality of signals having different phases are output. However, a basic Fizeau interferometer that does not use polarized light, A Michelson interferometer may be configured. In this case, the polarizing mirror may be a mere partial transmission surface, and the light receiving unit receives two beams of interference light. Further, a local transmission surface may be used. The counting circuit may count the brightness of the generated interference light. At this time, if a step of λ / 8 is provided on the reference plane to receive the interference light on each plane, the moving direction and the fine position within the half wavelength can be detected.

The optical interference type position measuring apparatus according to the second embodiment of the present invention has a feature in the configuration of the position data detecting section 60 as shown in FIG. Other configurations are the same as those described in the first embodiment.
This is the same as the optical interference type position measuring device 20 according to the embodiment, and a detailed description thereof will be omitted.

The position data detector 60 calculates the increase / decrease values Cx and Co of the wave numbers generated in the relative displacement interference light L3 and the reference length interference light L4 when the wavelength controller 22 changes the wavelength of the light flux OL. An absolute position data calculator 61 for calculating absolute position data Pabs of the measurement target based on the reference length Lo; and a relative displacement interference light L associated with the movement of the measurement target.
And a relative position data calculator 62 for calculating displacement from the absolute position of the measurement target, that is, relative position data Pinc with respect to the absolute position, based on the increase / decrease Cx of the wave number generated in 6. The absolute position data Pabs and the relative position data Pinc of the measurement target are combined by the combination calculation unit 63 and output as position data Pout indicating the position of the measurement target.

The absolute position data calculation unit 61 uses the above-described principle to calculate the absolute position data calculation circuit 4 in the first embodiment.
Similarly to 2, for example, the initial position Lini is measured by changing the wavelength of the light beam OL or the like in the initial sequence when the power is turned on.

As is well known, the relative position data calculation unit 62

(Equation 10) Is calculated based on the relative displacement Pinc from the initial position Lini.

According to the optical interference type position measuring apparatus according to the second embodiment, position data is detected by wavelength change which requires a response time in the initial sequence at the time of power-on, and then relative position data is detected. Since we only need to detect
The responsiveness of position data detection after the initial sequence at power-on can be improved by minimizing position data detection due to wavelength change. Also, unlike the case where only incremental position data is detected, the absolute position data cannot be calculated even if the original position is lost due to a count error during measurement or the light path is interrupted, or even if the power is turned on and off. There is an advantage that the absolute position can be easily detected by the re-detection in the unit 61, and it is not necessary to execute the origin search again.

In the optical interference type position measuring apparatus according to the second embodiment, when the oscillation frequency of the laser beam fluctuates with the elapse of time, the value of the relative displacement Pinc shows a non-linear tendency as compared with the detection start time. I will. In order to solve this, the optical interference type position measuring apparatus according to the third embodiment of the present invention obtains the fluctuation of the oscillation frequency f, that is, the wavelength λ, and obtains the wavelength λ.
Is corrected. Other configurations are the same as those of the second embodiment.

FIG. 9 shows a position data detecting section 70 according to the third embodiment. The position data detection unit 70 includes a wavelength variation detection unit 71 that detects a wavelength variation of the light flux OL from the light source 21 based on the reference length interference light L4 from the reference length interference unit 24, and a detected wavelength. A wavelength correction unit 72 that corrects the relative position data Pinc based on the fluctuation.

The wavelength variation detecting section 71 calculates the relative position data P
At the detection start time when the detection of inc is started, first,
The increase / decrease value Co of the wave number from the counting circuit 41 is latched and stored as the initial data CoL, and the variation Δλ of the wavelength after the lapse of a predetermined time is obtained by the following equation using the data Co measured at that time.

[0063]

[Equation 11] Subsequently, using the obtained variation Δλ, the wavelength correction unit 72
At

The wavelength λc is obtained based on λc = λ + Δλ. By performing an operation in the same manner as in Expression 10 using this wavelength λc, Pinc corrected for the wavelength variation Δλ is obtained, and as a result, position data Pout having sufficient linearity is obtained.

Here, when the optical interference type position measuring device according to the present invention is used as a relative position measuring device, it is only necessary to output a Pinc corrected for the wavelength variation Δλ. No parts are required.

When the absolute wavelength of the laser beam is obtained, the following method can be used.

Consider a case where a semiconductor laser in the λ = 780 nm band is used. In the reference length interference unit 24, the optical path length for the polarizing mirror 38 is y, the optical path length for the reflecting mirror 39 is y + β, and the optical path difference is β. The increase / decrease value Co of the wave number due to the ideal wavelength λ is Coi, whereas the increase / decrease value Co of the wave number actually obtained by using the semiconductor laser is Cor. When the ideal wavelength λ is incident, the wave number difference Δn existing between the optical path for the polarization mirror 38 and the optical path for the reflection mirror 39 is expressed by the following equation.

[0067]

(Equation 13) Here, the wavelength λ of the ideal semiconductor laser, the value Coi of the data Co based on the ideal wavelength λ, and the optical path difference β are known.

On the other hand, when the light beam of the semiconductor laser having the wavelength of (λ + α) is actually incident, the difference Δn ′ between the wave numbers existing in the optical path for the polarizing mirror 38 and the optical path for the reflecting mirror 39 is as follows. It is shown by the formula.

[0069]

[Equation 14] According to this equation, it is the same as counting the wave number when the wavelength changes from λ to (λ + α), and the relationship of the following equation is satisfied.

[0070]

(Equation 15) Thereby, the wavelength λ ′ of the semiconductor laser actually used is
Is

## EQU16 ## where λ ′ = λ + α.

That is, after setting the known optical path difference β,
If the increase / decrease value Co of the wave number is measured using a stabilized laser having a known wavelength λ as a reference, these data and the increase / decrease value C of the wave number when an actual semiconductor laser is used are obtained.
With o, the wavelength λ ′ of the semiconductor laser in use can be measured.
Therefore, highly accurate detection can be performed without receiving an error due to wavelength fluctuation.

Next, a specific example of the wavelength control unit 22 will be described in detail. The wavelength control unit 22 shown in FIG. 8 includes a temperature sensor 73 that senses the temperature of the semiconductor laser 30 and a temperature adjuster 74 that adjusts the temperature of the semiconductor laser 30 based on the sensed temperature. , The wavelength of the light beam OL is changed.

The temperature controller 74 includes a heater 75 attached to the semiconductor laser 30 and a temperature controller 76 for outputting a heating or cooling command to the heater 75. From the position data detection unit 25, the temperature control device 76
Request signal RQabs for obtaining position data Pout
Is input to the heater 75 until the temperature of the semiconductor laser 30 reaches a preset target temperature.
When the target temperature is sensed as a temperature of 0, a detection command Oabs is output to the position data detection unit 25. After outputting the detection command Oabs, a heating or cooling command may be output to return the wavelength of the semiconductor laser 30 to the normal temperature. The temperature dependence of the wavelength of the semiconductor laser 30 includes:
Depending on the fundamental wavelength and the product, for example, there is a wavelength of λ = 780 nm at a level of 2.4 nm / 10 ° C. In the present invention, it is sufficient to roughly change the wavelength λ, and the amount of change is not required to be accurate. Therefore, the temperature control of the semiconductor laser 30 is not required to be precise, and there is no need to perform the temperature feedback control by the temperature sensor 73.

As the wavelength control unit 22, there is a wavelength control unit that changes the oscillation wavelength of the output laser light through a change in the temperature of the semiconductor junction due to the excitation current of the semiconductor laser 30. The excitation current is controlled by the semiconductor laser drive circuit 31, and as the current increases, the oscillation wavelength changes to the longer wavelength side.

According to the wavelength control unit 22, when the request signal RQabs for obtaining the position data Pout is input to the wavelength control unit 22, a drive current control signal is output to the semiconductor laser drive circuit 31. The drive circuit 31 changes the drive current of the semiconductor laser 41 to change the optical output.
When the drive current reaches a desired value and the temperature changes, a detection command Oabs is output to the position data detection unit 25.
After outputting the detection command Oabs, the semiconductor laser 31
In order to return the wavelength at the time of the normal current before the change, the original drive current may be applied. The temperature dependence of the wavelength of the semiconductor laser 30 depends on the fundamental wavelength and the product. For example, when the wavelength is λ = 780 nm, 4 nm / Δ7 mW
There is a thing of the level.

Further, the wavelength controller 22 may change the wavelength of the light beam OL by generating a stress in the medium through which the light beam OL passes and changing the refractive index of the medium.

Further, the wavelength control section 22 applies an electric field to the light beam OL using so-called electro-optic modulation,
The wavelength of the light beam OL may be changed by changing the refractive index of the light beam OL. This phenomenon is called the Pockels effect. In this case, a substance in which this phenomenon is remarkable may be used in the optical path.

Further, the wavelength control unit 22 applies a magnetic field to the light flux OL using so-called magneto-optical modulation,
The wavelength of the light beam OL may be changed by changing the change in the refractive index of the light beam OL. This phenomenon is called the Faraday effect, and in this case, a larger change in wavelength can be extracted by using a substance in which this phenomenon is remarkable in the optical path.

Further, the wavelength control section 22 may rotate the rotating plate having a predetermined refractive index at a high speed to change the wavelength of the light beam OL by the Doppler effect of the light beam OL transmitted through the rotating plate.

Next, another specific example for setting the reference length Lo in the reference length interference unit 24 will be described in detail.

FIG. 11A shows that the interference device is connected to a glass flat plate 7.
7 is an example realized in FIG. The glass flat plate 77 includes a polarizing mirror 78 as an incident surface, and a reflecting mirror 79 separated from the polarizing mirror 78 by a reference length Lo. According to the glass flat plate 77, of the two light beams SOL having orthogonal polarization planes, the reference light L7 is reflected by the polarization mirror 78. The measuring light L8 passes through the polarizing mirror 78 and travels.
The light is reflected by the reflection mirror 79 and emitted from the glass flat plate 77. The reflected measurement light L8 and reference light L7 overlap each other to form reference length interference light L4, and travel toward the light receiving section 57. According to such a configuration, the reference plane and the measurement plane can be integrated with the interference device 37, and the configuration can be simplified. In the case of measurement without using polarized light, the polarization mirror 7 is used.
7 may be simply a partial transmission surface or a local transmission surface, or both the mirror surfaces 77 and 78 may use ordinary glass surface reflection or transmission. Further, the reflection mirror 79 may be of a cubic type. FIG. 11B is an example in which the interference device is realized by an optical fiber 80. This optical fiber 80
One end is provided with a polarizing mirror 81 as an incident surface, and the other end is subjected to reflection processing and functions as a mirror 82. According to the optical fiber 80, 2 having orthogonal polarization planes
Of the two light beams SOL, the reference light L7 is reflected by the polarizing mirror 81. The measurement light L8 passes through the polarization mirror 81, travels through the optical fiber 80, is reflected by the mirror 82, returns through the optical fiber 80, and exits from the entrance surface of the optical fiber 80. The reflected measurement light L8 and reference light L7 overlap each other to form reference length interference light L4, and travel toward the light receiving section 57. When it is desired to increase the reference length Lo, it may be difficult to realize the reference length Lo using the interference device 37 as shown in FIG. By adopting optical fiber, the reference length Lo
It can be easily configured without taking up space even if it is long.
As described above, the polarization mirror 81 may be a mere partial transmission surface, or both the mirror surfaces 81 and 82 may use the reflection or transmission of a normal optical fiber.

The interference device shown in FIG. 11C is a polarization mirror 8 as an incident surface attached to a housing 83.
4 and a reflecting mirror 85 for repeatedly reflecting the light beam incident on the inside of the housing 83 and finally sending it out from the incident surface. According to this interference device, the reference light L7 of the two light beams SOL having orthogonal polarization planes is reflected by the polarization mirror 84. The measurement light L8 is supplied to the polarizing mirror 84.
And is repeatedly reflected by the reflection mirror 85 in the housing 83, and then sent out from the incident surface. The reflected measurement light L8 and reference light L7 overlap each other to form reference length interference light L4, and travel toward the light receiving section 57. As in FIG. 11B, the standard length L
o can be easily configured.

In FIGS. 11A to 11C, the polarizing mirrors 78, 81 and 84 and the reflecting mirrors 79 and 8 are used.
Although 2,85 reflected lights are superimposed and sent out, they may be sent out as transmitted light. In this case, the polarizing mirrors 78, 81, 84, the reflecting mirror 79,
82 and 85 may be simply partial transmission surfaces (= partial reflection surfaces). Description will be made with the configuration of FIG. The reference interference light flux SOL from the light source 21 is partially transmitted by the polarization mirror 78 and travels to the reflection mirror 79 which is a partially transmitting surface. In the reflection mirror 79, a part of the light beam SOL is transmitted and sent out. A part of the light flux SOL reflected by the reflection mirror 79 is reflected by the polarization mirror 78, transmitted through the reflection mirror 79, and sent out. This light beam and the light beam transmitted through the reflection mirror 79 from the beginning overlap to form interference light, and
Go to 7. In the case where the transmitted lights interfere with each other in this manner, unlike the case of the reflected light, the light flux does not return toward the light source 21, so that the beam splitter 55 is not required and the configuration can be simplified. Further, the light receiving section 57 and the interference device 37 can be formed as an integrated structure, and the size of the device can be reduced.

FIG. 12 shows an optical interference type position measuring apparatus according to a fourth embodiment of the present invention. In the fourth embodiment, the principle of optical heterodyne using a two-frequency light source is adopted. Since this optical heterodyne method has been described in detail with reference to FIG. 13, it will not be described in detail in this embodiment, but only its application in this embodiment will be described. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the fourth embodiment, the light source 21 includes the acousto-optic modulator 100 for frequency-modulating the light beam OL emitted from the semiconductor laser 30. The acousto-optic modulator 100 modulates the light beam OL and sends out light beams OL of f1 and f2 having mutually orthogonal polarization planes having a frequency difference f0.

The transmitted light beam OL is supplied to the relative displacement interference unit 23 and is also applied to the photoelectric conversion element 102 of the position data detection unit 25 via the beam splitter 101. The light beam OL supplied to the relative displacement interference unit 23 is
The measurement light L6 having the frequency f1 and the reference light L5 having the frequency f2 are split, reflected by the mirrors 35 and 36, and superimposed. When the reflection mirror 36 is relatively displaced, the measurement light L6 undergoes Doppler modulation, and its frequency changes to f1 ± Δf. The relative displacement interference light L3 formed by the superimposed light beams is transmitted to the position data detection unit 2.
5 is photoelectrically converted by the light receiving unit 43, and the beat frequency f2-
An electric signal Fp1 of (f1 ± Δf) is output. As described in the conventional example, the electric signal Fp1 and the reference signal F2 of the beat frequency f2-f1 obtained by the photoelectric conversion element 102 are used.
The phase difference is measured from r and the displacement is calculated. When the wavelength of the semiconductor laser 30 is changed by Δλ by the wavelength control unit 22, the wave number of the measurement light L6 existing in the optical path between the polarization mirror 35 (separation surface P3) and the reflection mirror 36 changes, and the apparent displacement occurs. This is the same as the occurrence of X, and the increase / decrease value Cx of the wave number is obtained as the position data of the measurement target.

The reference interference light beam S separated from the light beam OL
The OL is supplied to the reference length interference unit 24, and like the relative displacement interference unit 23, the reference length interference light L4 having a phase difference corresponding to the reference length Lo is formed. The reference-length interference light L4 is photoelectrically converted by the light-receiving unit 47 of the position data detection unit 25, and the electric signal Fp2 of the beat frequency f2-f1.
Is output. As described in the conventional example, this electric signal F
p2 and the beat frequency f obtained by the photoelectric conversion element 102
The phase difference is measured from the reference signal Fr of 2-f1, and the displacement is calculated. By changing the frequency of the semiconductor laser 30, an increase / decrease value Co of the wave number is obtained.

The measured increase / decrease values Co and Cx of the wave numbers are proportional to the reference length Lo and the measured length Lx, and the measured length Lx is calculated by Expression 9 and output as the absolute position data Pout.

In the fourth embodiment, the calculation of the wave number increase / decrease values Co and Cx is different from that of the first embodiment in that the AC signal Fr,
Since it is calculated from Fp1 and Fp2, DC
It is not affected by fluctuations in level and the like, and it is possible to cut off unnecessary frequencies against noise, so that stable detection is possible.

Incidentally, as shown in the conventional example of FIG. 13, the luminous flux OL may be input to the laser tuning circuit to control the oscillation frequency. Although not shown, a HeNe laser as described in the conventional example may be used for the light source 21 instead of the semiconductor laser 30. In that case, the Zeeman effect may be used as a method of setting the frequency to two. This is known in the art, taking advantage of the fact that the spectrum is split by a strong magnetic field, and is realized by placing the laser tube in a coil to which a voltage is applied and placing it in that magnetic field. The generation of the two-frequency light flux is not limited to the above-described method, and another method may be used.

[0091]

As described above, according to the present invention, the light interference type
According to the position measurement device, when the wavelength controller changes the wavelength of the light beam, the position data of the measurement target is detected based on the change in the light intensity generated in the relative displacement interference light and the reference interference light, and the reference length. Therefore, the absolute position of the object to be measured can be easily and reliably detected. Therefore, even if accumulation of count mistakes, interruption of the optical path, power on / off, etc., occur during measurement, the current position can be known as an absolute position. Eliminating the need to find the origin eliminates man-hours and improves reliability. In addition, the initial sequence at power-on
Due to wavelength change where response time is required
Data, and then relative position data.
As much as possible, minimizing position data detection by changing the wavelength.
Position data after the initial sequence at power-on.
Response can be improved. In addition,
Unlike when only mental position data is detected, measurement
The original position may be lost due to counting mistakes during
Even if you get lost or even turn off the power,
Absolute position easily by re-detection in absolute position data calculator
Has the advantage that it is possible to detect
Having.

[0092] In addition, the wavelength is not required to be changed with high accuracy, and it is sufficient that the change in the wave number can be measured. Therefore, even if a semiconductor laser having an unstable oscillation frequency is used as a light source, highly accurate measurement can be performed. Can be realized. Therefore, it is possible to provide a small and inexpensive optical interference type position measuring device while realizing highly accurate measurement.

Further, even if there is a change in the surrounding environment such as a fluctuation occurring in the air in the optical path, stable measurement can be performed, and highly accurate measurement can be realized regardless of the surrounding environment.

Further , the light beam is separated from the reference interference light beam at the separation surface.
A reference surface for reflecting the extracted reference light,
A measurement surface that reflects the measurement light extracted from the quasi-interference light beam
With this arrangement, the reference length interference section can be realized with a simple configuration.

Further, when the wavelength of the light beam is changed, the reference length
Count for measuring the increase / decrease value Co of the wave number generated in the interference light
Path and the interference light for relative displacement when the wavelength of the light beam is changed.
A counting circuit for measuring the increase / decrease value Cx of the wave number
o (Cx / Co) (where Lo is the reference length interference part)
The reference length from the separation plane to the measurement plane)
Of the measurement object from the separation surface in the relative displacement interference portion
An absolute position data calculation circuit for calculating the position Lx.
Accordingly , the absolute position data calculation unit can be realized with a simple configuration.

[0096]

Further, the reference from the reference length interference section
Based on the interference light for the length, the wavelength fluctuation of the luminous flux from the light source is
Based on the detected wavelength fluctuation detector and the detected wavelength fluctuation
A wavelength correction unit that corrects the relative position data
Even if the wavelength of the luminous flux from the light source fluctuates over time, the value of the relative position data shows a non-linear tendency compared to the time when the detection was started, but this tendency is offset by correcting the wavelength fluctuation. Can be. Accordingly, highly accurate absolute position data can be detected regardless of the wavelength fluctuation.

Further, the light source is a semiconductor laser,
The length controller controls the temperature of the semiconductor laser by changing it.
Therefore , the wavelength of the light beam from the light source can be changed with a simple configuration by changing the wavelength of the light beam.

Furthermore , stress is applied to the medium through which the light beam passes.
Generate and change the refractive index of the medium
The wavelength of the light beam from the light source can be changed with a simple configuration by changing the wavelength of the light beam.

Furthermore , an electric field is applied to the medium through which the light beam passes.
Or applying a magnetic field to change the refractive index of the medium
Therefore, by changing the wavelength of the light beam, the wavelength of the light beam from the light source can be changed with a simple configuration.

Further, a rotating plate having a predetermined refractive index is rotated.
Changes the wavelength of the luminous flux due to the Doppler effect
Thus, the wavelength of the light beam from the light source can be changed with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical interference type position measuring device according to the present invention.

FIG. 2 is a diagram showing a specific configuration of an optical interference type position measuring device according to the first embodiment.

FIG. 3 is a diagram illustrating the formation of interference light using measurement light and reference light.

FIG. 4 is a detailed configuration diagram of a light receiving unit.

FIG. 5 is a graph showing a relationship between an electric signal from a light receiving unit and a comparator of a counting circuit.

FIG. 6 is a detailed configuration diagram of a counting circuit.

FIG. 7 is a diagram for explaining the principle of interference fringe measurement by changing the wavelength of a light beam.

FIG. 8 is a detailed configuration diagram of a position data detection unit according to a second embodiment.

FIG. 9 is a detailed configuration diagram of a position data detection unit according to a third embodiment.

FIG. 10 is a configuration diagram illustrating a specific example of a wavelength control unit.

FIG. 11 is a diagram illustrating a specific example of an interference device in a reference length interference unit.

FIG. 12 is a diagram showing a specific configuration of an optical interference type position measuring device according to a fourth embodiment.

FIG. 13 is a diagram showing a specific configuration of an optical interference type position measuring device according to a conventional example using an optical heterodyne method.

[Explanation of symbols]

Reference Signs List 20 optical interference type position measuring device, 21 light source, 22 wavelength control unit, 23 relative displacement interference unit, 24 reference length interference unit, 25 position data detection unit, 35 polarizing mirror as reference plane, 36 measurement plane Reflection mirror, L3
Relative displacement interference light, L4 reference length interference light, L5 reference light, L6 measurement light, Lo reference length, Lx measurement length, OL luminous flux, P3 separation plane, Pout position data

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-324304 (JP, A) JP-A-3-269302 (JP, A) JP-A 64-35304 (JP, A) JP-A 59- 218903 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01B 9/00-11/30 102

Claims (8)

(57) [Claims] A light source that emits a light beam having coherence;
A separation surface that separates the light beam into reference light and measurement light, a reference surface that reflects the reference light, and a measurement surface that is attached to the measurement target and reflects the measurement light, and superimposes the reference light and the measurement light Forming an interference light, and reading the position data of the measurement target based on the interference light.In the optical interference type position measurement device, a wavelength controller that changes a wavelength of a light beam emitted from a light source; and the reference surface and the measurement surface. A relative displacement interference unit that superimposes the reference light from the reference surface and the measurement light from the measurement surface and sends out the relative displacement interference light, and is predetermined based on the reference interference light flux separated from the light flux. A reference length interference unit that sends out interference light for the reference length by superimposing light having a difference in optical path length corresponding to the reference length that has been generated when the wavelength control unit changes the wavelength of the light beam.
Changes in light intensity of interference light for relative displacement and interference light for reference length
And the absolute position of the object to be measured based on the reference length.
Absolute position data calculation unit for calculating the position data , the light intensity of the relative displacement interference light accompanying the movement of the measurement target
Based on the change, the relative position
A relative position data calculation unit for calculating data, and combining these absolute position data and relative position data.
Optical interference position measuring apparatus characterized by comprising: a combining unit for specifying a position of a measured object Te. 2. The optical interference type position measuring device according to claim 1, wherein the reference length interference unit includes: a reference surface that reflects reference light extracted from the reference interference light beam on a separation surface; A measurement surface that reflects measurement light extracted from the reference interference light beam on a surface, and a measurement having a difference between a reference light from the reference surface and an optical path length corresponding to the reference length with respect to the reference light. An optical interference type position measuring device, wherein interference light is formed by superimposing measurement light from a surface. 3. The optical interference type position measuring device according to claim 2, wherein the absolute position data calculation unit measures an increase / decrease value Co of a wave number generated in the reference length interference light when the wavelength of the light beam is changed. A counting circuit for measuring the increase / decrease value Cx of the wave number generated in the interference light for relative displacement when the wavelength of the light beam is changed; Lx = Lo (Cx / Co) (where Lo: interference for the reference length) An absolute position data calculation circuit that calculates a position Lx of a measurement target from the separation surface in the relative displacement interference unit based on the reference length from the separation surface to the measurement surface of the portion). Optical interference type position measuring device. In the optical interferometric position measuring apparatus according to claim 4] claim 1, based on the reference length for the interference light from the criteria length for interference portion, the wavelength variation to detect the wavelength variation of the light beam from the light source An optical interference type position measurement device comprising: a detection unit; and a wavelength correction unit that corrects the relative position data based on the detected wavelength fluctuation. 5. The optical interference type position measuring device according to any one of claims 1-4, wherein the light source is a semiconductor laser, the wavelength control unit, the wavelength of the light beam by changing the temperature of the semiconductor laser An optical interference type position measuring device characterized by changing the following. 6. The optical interference type position measuring device according to any one of claims 1-4, wherein the wavelength control unit, to generate a stress to the medium which the light beam passes, changing the refractive index of the medium An optical interference type position measuring device characterized in that the wavelength of a light beam is changed by the method. 7. The optical interferometric position measuring device according to any one of claims 1-4, wherein the wavelength control unit, the light flux passing
The over to the medium by the action of electric or magnetic field, optical interference type position measuring apparatus characterized by varying the wavelength of the light beam by varying the refractive index of the medium. 8. The optical interference type position measuring device according to any one of claims 1-4, wherein the wavelength control unit, changes the wavelength of the light beam by Doppler effect at the time of rotating the rotary plate of a predetermined refractive index An optical interference type position measuring device, characterized in that the position is measured.