JPH0810145B2 - Optical encoder and its optical scale - Google Patents

Description

The present invention relates to a machine tool such as a lathe and a milling machine, and
The present invention relates to an optical encoder and an optical scale thereof that can be used for position measurement of a semiconductor manufacturing device.

(Prior Art) FIG. 9 is a perspective structural view showing an example of an optical system of a conventional optical absolute type encoder, which emits measurement light La, for example, a light emitting element 11 such as an LED (Light Emitting Diode) or a lamp. And the measurement light emitted by the light emitting element 11.
A collimator lens 12 that makes La parallel to Lb, a portion (hereinafter, referred to as a transmission portion) 13A that transmits the parallel light Lb that has transmitted through the collimator lens 12 and a portion that does not transmit (hereinafter,
Lattice tracks t ₁ , t ₂ , ..., t _{n in which a} non-transmissive portion 13B is repeated with a predetermined length (hereinafter, referred to as a lattice pitch)
Light transmitted through the first scale 13 and the transmissive portion 13A that are arranged in parallel on the surface of n (n is an integer) parallel to each other (not shown)
Second scale 14 in which transmission windows 14A ₁ , 14A ₂ , ..., 14A _{n for} transmitting light are provided corresponding to the respective lattice tracks t ₁ , t ₂ , ..., t _n of the first scale 13, Each transparent window of the second scale 14
14A ₁ , 14A ₂ , ..., 14A _n provided corresponding to each transmission window 14A
_1, 14A _2, ......, light Lc ₁ came through the 14A _n, Lc _2, ......, a photoelectric conversion element for converting into an electric signal corresponding to the intensity of Lc _n 15-1,15
-2, ..., 15-n.

In the first scale 13 used in the optical system 10 of the optical absolute type encoder having such a configuration, adjacent grating tracks t ₁ , t ₂ , and t ₂ , t ₃ and so on as shown in FIG. The alternating binary code (Gray code) in which the lattice pitches P ₁ , P ₂ , P ₃ , ..., P _n-1 , P _{n of} t _n-1 , t _n are in a 1: 2 relationship with each other is It is provided. Therefore, the transmission portion 13A of each of the lattice tracks t ₁ , t ₂ , t ₃ , ..., T _n-1 , t _n of the first scale 13 and each of the lattice tracks t ₁ , t ₂ , t ₃ , ……,
Each transmission window 14A ₁ , 14 of the second scale 14 corresponding to t _n-1 , t _n
A ₂ , 14A ₃ , ..., 14A _n-1 , 14A _n are transmitted, and each transmission window 14A ₁ , 1
4A ₂ , 14A ₃ , ......, 14A _n-1 , 14A _n corresponding to each photoelectric conversion element 1
Light incident on 5-1,15-2,15-3, ..., 15-n-1,15-n
Lc ₁ , Lc ₂ , Lc ₃ , ..., Lc _n-1 , Lc _n have the first scale 13
Each of the photoelectric conversion elements 15 changes periodically with the movement in the longitudinal direction (arrow x in the figure).
Each of the electric signals converted by -1,15-2,15-3, ..., 15-n-1,15-n also changes periodically. In FIG. 11, the horizontal axis represents the displacement amount ml in the longitudinal direction of the first scale 13, and the vertical axis represents the photoelectric conversion elements 15-1, 15-2, 15-3, ..., 15-n-1, 1
Electric signal converted by _{5-n S 1, S 2} , S 3, ......, show the S _n-1, S _n, each of the electric signals _{S 1, S 2, S 3} , ......, S n _It can be seen that _-1 , S _n change periodically. And these electric signals _{S 1, S 2, S 3} , ......, S n-1, S n are digitized d ₁ by the respective comparators 20 as shown in the block diagram of the optical absolute encoder of Figure 12 , d ₂ , d ₃ ,…
, D _n−1 , d _n, and is further converted by the decoder 30 into absolute position data D of a desired format such as alternating binary code or pure binary code or BCD code.

(Problems to be Solved by the Invention) An optical absolute encoder used for position measurement is capable of increasing its position detection resolution to detect a smaller displacement amount, and at the same time, its absolute position over a longer stroke. Is required to be detectable. However, in the optical absolute encoder as described above, the minimum position detection resolution is about the same as the grating pitch P _n in the minimum divided grating track t _n , and the absolute position detection stroke length is the maximum divided grating track. Since it is about the same as the grating pitch P _{1 at} t ₁ , if the position detection resolution is increased and the absolute position detection stroke length is increased, the number of grating tracks n increases and the optical absolute encoder becomes larger,
There is a drawback that the number of photoelectric conversion elements, comparators, etc., which are the parts, increases.

The present invention has been made under the circumstances as described above,
An object of the present invention is to provide a compact optical encoder having a high position detection resolution and a long absolute position detection stroke length, and an optical scale thereof.

(Means for Solving the Problems) The present invention relates to a machine tool such as a lathe and a milling machine, an optical encoder used for position measurement of a semiconductor manufacturing apparatus, and an optical scale thereof. The purpose is that in an optical encoder, grating windows made up of diffraction gratings are arranged at predetermined intervals in the longitudinal direction, and the diffracted light generated in each grating window is
It emits parallel light that has coherence with an optical scale that has a unique diffraction angle or direction or diffraction intensity distribution different from that of other grating windows, and has one or more rays in its light flux. A light source device including the grating window, a light spot position detection device that receives diffracted light diffracted by the lattice window, detects a light spot position of each diffracted light, and changes into an electric signal, and the electric signal A reading device for obtaining and outputting position data of the optical scale, or
A grating window group including two or more grating windows composed of diffraction gratings is arranged in the longitudinal direction, and a combination of diffracted light generated in each grating window in each grating window group is set in another grating window group. Emitting parallel light that has coherence with an optical scale that has a unique diffraction angle, diffraction direction, or diffraction intensity distribution combination that is different from the combination of diffracted light generated in each grating window, and A light source device including one or more of the lattice window groups, and a light spot position detection device that receives diffracted light diffracted by the lattice window groups, detects the light spot position of each diffracted light, and converts the diffracted light into an electric signal. And a reader for obtaining and outputting the position data of the optical scale based on the electric signal.

Further, in an optical scale used for detecting displacement of a moving body, grating windows made of diffraction gratings are arranged at a predetermined interval in the longitudinal direction, and diffracted light generated in each grating window is Is arranged so as to have a unique diffraction angle, diffraction direction, or diffraction intensity distribution different from that of the grating window, or a grating window group including two or more grating windows composed of diffraction gratings is arranged in the longitudinal direction. And a unique diffraction angle different from the combination of the diffracted light generated in each grating window in the individual grating window group and the diffracted light generated in each grating window in the other grating window group, or This is achieved by arranging so as to be a combination of diffraction directions or diffraction intensity distributions.

(Operation) The optical encoder and the optical scale thereof of the present invention are
By utilizing the fact that the position of the diffracted light moves due to the displacement of the grating window and the fact that the grating window can be specified by the way of diffraction at the grating window, it is possible to accurately obtain position data with high resolution over a long stroke. Obtainable.

(Embodiment) FIG. 1 is a perspective structural view showing an example of an optical system of an optical absolute encoder of the present invention, which emits coherent measurement light LI, for example, a light emitting element 301 such as an LD (Laser Diode) 301. And the measurement light LI emitted by the light emitting element 301.
Is a parallel light LJ, a slit 303 that partially transmits the parallel light LJ collimated by the collimator lens 302 to form a light beam LK having a predetermined width, and a grating window T having a diffraction grating is constant. Arranged at a distance W, each diffracting element has the same ratio of the light transmitting portion and the non-transmitting portion and the same lattice line direction and different pitches, and the elongated scale 304 that diffracts the light flux LK from the slit 303, A cylindrical lens 305 that condenses a plurality of diffracted lights diffracted by the grating window T of the scale 304, and diffracted lights LL ₀ , LL ± ₁ , ..., LL ± _n ,. Light spot of LP ₀ , LP
Detects the position of ± ₁ , ..., LP ± _n , ... and converts it to an electric signal, for example, a light spot position detection element 306 such as an image sensor.
It consists of and. The light emitting element 301 fixedly arranged on the straight line, the collimator lens 302, the slit 303,
The cylindrical lens 305 may move relative to the scale 304, but in this example, the scale 304 moves linearly in the longitudinal direction (arrow X in the drawing).

In the optical system 300 of the optical absolute encoder having such a configuration, the _0th-order diffracted light LL among the diffracted lights LL ₀ , LL ± ₁ , ... LL ± _n ... From the cylindrical lens 305.
_The angle formed by ₀ and the positive and negative nth-order diffracted light LL ± _n (hereinafter referred to as a diffraction angle) ± θ _n is determined by the pitch PP of the diffraction grating of the grating window T of the scale 304 and the wavelength λ of the light flux LK from the slit 303. It is expressed by the following equation (1).

± θ _n = ± sin ⁻¹ (nλ / PP) (1) Then, the light spots LP + _n and LP _−n on the light spot position detecting element 306 of the positive and negative n-th order diffracted light are the scale 304 and the light spot position. Detector element 3
The distance dd _n expressed by the following equation (2) where SS is the distance from 06
Located apart from each other.

dd _n = 2SStan (sin ^-1 (nλ / PP)) (2) For example, as shown in FIG. 2, the scale 304 moves to the left in the figure and the irradiation range of the light flux LK from the slit 303 is a.
→ When b is changed, the light spots LP _1TO , LP _2TO , LP _{3TO of the 0th-order} diffracted light and the light spot LP _{1T of the} 1st-order diffracted light on the light spot position detection element 306
± ₁ , LP _2T ± ₁ , LP _3T ± ₁ is as shown in the figure, and the distances dd _1T , dd _2T , dd _3T between the light spots of each 1st-order diffracted light are expressed by the following equation (3),
(4) and (5).

dd _1T = 2SStan (sin ^-1 (λ / PP _1T )) …… (3) dd _2T ＝ 2SStan (sin ^-1 (λ / PP _2T )) …… (4) dd _3T ＝ 2SStan (sin ^-1 (λ / PP _3T )) ...... (5) Therefore, the distance dd _nT between these light spots is calculated from the position of the light spot LP _nT ± ₁ of the positive and negative first-order diffracted light on the light spot position detection element 306, and the distance between these light spots is calculated. The pitch PP _{nT of the} diffraction grating is obtained from the distance dd _nT to specify the grating window T _nT on the scale 304, and the distance W from the position of the light point LP _nT0 of the 0th-order diffracted light on the light spot position detecting element 306 to the grating window W _n. By finding the absolute position in the scale 304
The absolute position data above can be determined.

FIG. 3 is a block diagram showing an example of the optical absolute type encoder of the present invention, which is composed of the above-described optical system 300 and the reading device 310 including the first conversion unit 320, the second conversion unit 330, and the calculation unit 340. Has been done.

The diffraction determination unit 322 is, for example, 1 on the light spot position detection element 306.
Input the coordinate values (x _{nT + 1} , y _{nT + 1} ), (x _nT-1 , y _nT-1 ), as shown in FIG. 4, which represents the position of the light point LP _nT ± ₁ of the next-order diffracted light, and The distance dd _nT between the light spots is obtained by the equation (6), and the pitch PP _nT of the diffraction grating is obtained by the equation (2).

In the storage unit 321, each lattice window T _1T , T _2T , ..., T on the scale 304 is stored.
_nT, the position of ... data _{P OSH1, P OSH2, ...,} P OSHn, ... and pitch PP _1T of the diffraction grating, PP _2T, ..., PP _nT, ... and is stored in association with, the matching unit 323 Position data P _OSHn of the grating window T _nT corresponding to the diffraction grating pitch PP _nT from the diffraction determining unit 322 is read from the storage unit 321 and sent to the arithmetic unit 340.

On the other hand, the second conversion unit 330 outputs 0
By _inputting coordinate values (x _nTO , y _nTO ) representing the position of the light point LP _nTO of the next-order diffracted light, the absolute position P _OSLn in the gap W of the lattice window T _nT on the scale 304 is obtained. And outputs it to the calculation unit 340. Incidentally, 0 coordinates of the light spot LP _NTO order diffracted light (x
_nTO , y _nTO ), instead of the light spot LP _nT ± ₁ of the first-order diffracted light, the coordinate value (x _{nT + 1} −x _nT-1 ) / 2, (y _{nT + 1} −y _nT-1 ). / 2)
It is also possible to obtain the absolute position P _OSLn by using.

Since the position data P _OSHn and the absolute position P _OSLn described above change as shown in FIG. 5 with respect to the displacement of the scale 304, the calculation unit 340 adds the position data P _OSHn and the absolute position P _OSLn to the scale 304. The absolute position data P _{OSn of} is _calculated and output.

FIG. 6 is a diagram showing another pattern example of the grating window provided on the scale 304 of the optical system of the optical absolute type encoder shown in FIG. 1, in which a pair of grating windows T _nA and T _nB having a diffraction grating are provided. The diffraction gratings are arranged with a constant gap WW, and the diffraction gratings have the same ratio of the light transmitting portion and the non-light transmitting portion and the same grating line direction but different pitches. With such a configuration, the number of grid windows can be increased by the number of combinations of grid windows, and thus the scale 304 can be elongated.

The reading device for obtaining the absolute position data on the scale 304 may be modified by changing the first conversion unit 320 of the reading device 310 shown in FIG. 3 as shown in FIG. That is, the two diffraction determination units 322 are arranged such that the coordinate values (x _{nA + 1} , y _nA) representing the positions of the light spots LP _nA ± ₁ and LP _nB ± ₁ of, for example, two first-order diffracted lights on the light spot position detection element 306. ₊₁ ), (x _{nA-1 ,,} y _nA-1 ) and (x _{nB + 1} , y
_{nB + 1) (x nB-} 1, y nB-1) were respectively inputted, the diffraction grating by inter obtained point distance dd _nA and dd _nB pitch PP _nA and PP
_{Find nB} respectively.

The combination determination unit 324 uses the pitch PP from each diffraction determination unit 322.
The combination of _nA and PP _nB is determined, and as a result, PP _nAB is compared with the matching unit 3
Send to 23.

A pair of lattice windows T _1A , T _1B on the scale 304 are stored in the storage unit 321.
Position data P _OSH1 , P _OSH2 , ..., P of T _2A , T _2B ; ...; T _nA , T _nB ; ...
_{Combination of OSHn} ,… and grating pitch PP _1AB , PP _2AB ,…, PP
_nAB , ... _Are stored in association with each other.
Is the combination PP of the diffraction grating pitches from the combination determination unit 324.
grille T _nA that corresponds to the _NAB, and sends the position data P _OSHn of T _nB reads from the storage unit 321.

In each of the above-described embodiments, the pitch of the diffraction grating of the grating window on the scale 304 is different for each grating window, but the ratio of the transmissive portion and the non-transmissive portion is different for each lattice window, and the grating Absolute position data on the scale can be obtained by using a scale whose line direction is different for each lattice window. That is, when the ratio of the transmissive part and the non-transmissive part is changed, the intensity ratio of diffracted light of different orders changes depending on the ratio of the transmissive part and the non-transmissive part. Since the diffraction determination unit 322 has the, the grating window can be specified. Further, when the lattice line direction is changed, the fact that the light spot positions of the positive and negative diffracted lights of the same order move (rotate) according to the lattice line direction is used, and the determination criterion based on this principle is used as the diffraction determination unit. The lattice window can be specified by having 322.

Further, for example, as shown in b in FIG. 2 or c in 6 in FIG.
When two sets of lattice windows are included in the irradiation range of LK, the reader 310 may obtain and average absolute position data on the scale 304 for each lattice window. When performing this averaging process, by weighting each absolute position data, it is possible to reduce the error component having the gap W or WW of the lattice window as a period.

Furthermore, the coherent light emitted from the light emitting element is transmitted to the scale to obtain diffracted light. However, since there is no difference in properties between the transmitted light and the reflected light, the scale reflects the diffracted light to obtain diffracted light. It is also possible. In the case of the reflection type, the light emitting element, the collimator lens, the slit and the cylindrical lens, and the light spot position detecting element are arranged on the same side with respect to the scale, and the scale is formed of a light reflecting portion and a light non-reflecting portion. .

Then, as shown in FIG. 8, the scale is a disc 307, and the lattice window T of the present invention is annularly provided on the surface of the disc 307.
If the center of 307 is rotated about the axis of rotation, the angle can be detected absolutely.

(Effects of the Invention) As described above, according to the optical encoder of the present invention, long stroke absolute position detection, which has conventionally required a plurality of grid tracks, can be performed with a linearly arranged grid window. Therefore, it is possible to reduce the size of the optical encoder by reducing the number of parts, and it is possible to reduce the manufacturing cost and the product cost of the optical encoder.

[Brief description of drawings]

FIG. 1 is a perspective structural view showing an example of an optical system of an optical encoder of the present invention, FIG. 2 is a view showing an example of an optical scale thereof, FIG. 3 is a block diagram showing an example of a reading device thereof, and FIG. FIG. 5 and FIG. 5 are views for explaining reading by the optical encoder of the present invention, FIG. 6 is a view showing another example of the optical scale of the present invention, and FIG. 7 is a block showing a main part of the reading device. FIG. 8 is a diagram showing still another example of the optical scale of the present invention, FIG. 9 is a perspective structural view showing an example of an optical system of a conventional optical encoder, and FIG. 10 is an example of its grating track. 11 is a diagram showing an example of the electric signal, and FIG. 12 is a diagram showing an example of the reading device. 10,300 …… Optical absolute encoder optical system, 11,301 …… Light emitting element, 12,302 …… Collimator lens, 13,14,304,307 …… Scale, 303 …… Slit, 30
5: Cylindrical lens, 15: Photoelectric conversion element, 20
...... Comparator, 30 …… Decoder, 306 …… Light spot position detection element, 310 …… Reading device, 320 …… First conversion unit, 321
...... Memory unit, 322 ...... Diffraction determination unit, 323 ...... Verification unit, 324
...... Combination determination unit, 330 …… Second conversion unit, 340 …… Calculation unit.

Claims (5)

[Claims] 1. A grating window composed of a diffraction grating is arranged at a predetermined interval in the longitudinal direction, and diffracted light generated in each grating window has a unique diffraction angle different from those of other grating windows, or An optical scale that has a diffraction direction or a diffraction intensity distribution, a light source device that emits parallel light having coherence and includes one or more of the grating windows in its light flux, and the grating window A light spot position detecting device that receives the diffracted diffracted light, detects the light spot position of the diffracted light and changes it into an electric signal, and a reading device that obtains and outputs position data of the optical scale based on the electric signal. An optical encoder comprising: 2. The diffraction grating constituting the grating window is configured so that the diffracted light generated in each grating window has a unique diffraction angle or diffraction direction or diffraction intensity distribution different from those of other grating windows. The grating window is provided in which the reading device reads the light point positions of positive and negative diffracted lights of the same or higher order than the first order by an electric signal output from the light point position detection device and diffracts the diffracted light. A first exchange means for identifying
0 according to the electric signal output from the light spot position detection device
Second conversion means for reading the light spot position of the next diffracted light to obtain the position within the interval of the grating window, and the position of the optical scale by the outputs from the first conversion means and the second conversion means. The optical encoder according to claim 1, further comprising a calculating unit that obtains data. 3. A grating window group including two or more grating windows composed of a diffraction grating is arranged in the longitudinal direction, and a combination of diffracted light generated in each grating window in each grating window group is Emitting parallel light having coherence with an optical scale that has a unique combination of diffraction angle or direction or diffraction intensity distribution different from the combination of diffracted light generated in each lattice window in the lattice window group. , A light source device including one or more of the lattice window groups in its light flux, and the diffracted light diffracted by the lattice window groups is received, and each diffracted light detects a light spot position and is converted into an electric signal. An optical encoder comprising: a light spot position detection device; and a reading device that obtains and outputs position data of the optical scale based on the electric signal. 4. In an optical scale used for detecting displacement of a moving body, grating windows made of diffraction gratings are arranged at predetermined intervals in the longitudinal direction, and diffracted light generated in each grating window is The optical scale is characterized in that it is arranged so as to have a unique diffraction angle, diffraction direction, or diffraction intensity distribution different from other grating windows. 5. In an optical scale used for detecting displacement of a moving body, a grating window group including two or more grating windows made of a diffraction grating is arranged in the longitudinal direction, and each grating window group is provided. The combination of the diffracted light generated in each grating window of is a unique combination of the diffraction angle or the direction or the diffraction intensity distribution different from the combination of the diffracted light generated in each grating window in the other grating window group. An optical scale, which is characterized in that it is arranged in.