JPH05646B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an optical encoder that can be used for position measurement in machine tools such as lathes and milling machines, and semiconductor manufacturing equipment.

(Technical background and problems to be solved) FIG. 7 is a perspective structural diagram showing an example of the optical system of a conventional optical absolute encoder.
For example, a light emitting device (LED) that emits measurement light La.
A collimator lens 12 that converts the measurement light La emitted by the light emitting element 11 into parallel light Lb, and a part that transmits the parallel light Lb that has passed through the collimator lens 12. A lattice track t ₁ , t ₂ , ..., t in which a transparent part 13A (hereinafter referred to as a transparent part) and a part 13B that does not allow transmission (hereinafter referred to as a non-transparent part) are repeated at a predetermined length (hereinafter referred to as a lattice pitch). n _o on the surface (n
is an integer) first scales 13 arranged in parallel
and the light that has passed through the transmission section 13A (not shown)
Transmission windows 14A ₁ , 14A ₂ , ..., 1 that transmit
4A _o is each grating track t ₁ of the first scale 13,
The second scale 14 provided corresponding to t ₂ , ..., t _o and each transmission window 14 of the second scale 14
Light L _c1 , L _c2 , ..., L _co transmitted through each transmission window 14A ₁ , 14A ₂ , ..., 14A _o provided corresponding to A ₁ , 14A ₂ , ..., 14A _o a photoelectric conversion element 15-1 that converts into an electrical signal according to the intensity of the
15-2, . . . , 15-n.

The first scale 1 used in the optical system 10 of the optical absolute encoder having such a configuration
3 includes adjacent grid tracks t ₁ , t ₂ and t ₂ , t ₃ and . . _. and grid pitches _{P 1 ,} P ₂ , P ₃ , An alternating binary code (Gray code) in which . . . , P _o-1 , and P _o are in a 1:2 relationship is provided. Therefore, each grid track t ₁ , t ₂ , t ₃ , ..., of this first scale 13
t _o-1 , t _o transmission part 13A, and first scale 13
Each transmission window 14A 1 , ₁ of the second scale 14 corresponds to each grid track t ₁ , t ₂ , t ₃ , ..., t _o-1 , t _o
4A ₂ , 14A ₃ , ..., 14A _o-1 , 14A _o and passes through each transmission window 14A ₁ , 14A ₂ , 14A ₃ , ...
..., 14A _o-1 , each photoelectric conversion element 15-1, 15-2, 15-3, ..., 15- corresponding to 14A _o
Light incident on n-1, 15-n L _c1 , L _c2 , L _c3 ,
..., L _co-1 and L _co change periodically as the first scale 13 moves in the longitudinal direction (arrow m in the figure), so each photoelectric conversion element 15- 1, 15-2, 15-3,...,
Each electrical signal converted by 15-n-1 and 15-n also changes periodically. In FIG. 9, the displacement amount ml of the first scale 13 in the longitudinal direction is plotted on the horizontal axis.
Each photoelectric conversion element 15-1, 15-2, 15 is shown on the vertical axis.
-3, ..., 15-n-1, 15-n indicates the electrical signals S ₁ , S ₂ , S ₃ , ..., _So-1 , _So , and each electrical signal S ₁ , S ₂ , S ₃ , ..., S _o-1 , and S _o change periodically. And these electric signals S ₁ , S ₂ , S ₃ , ..., S _o-1 ,
S _{o is} digitized by a comparator 20 _, respectively, as shown in _the block diagram of the optical absolute encoder in FIG. 10.
d _o-1 and d _o , and further converted by the decoder 30 from an alternating binary code to absolute position data D in a desired format such as a pure binary code or a BCD code.

By the way, the optical absolute encoder used for position measurement needs to improve its position detection resolution to be able to detect even smaller displacement amounts.
At the same time, it is desired to be able to detect the absolute position over a longer stroke.
However, in the optical absolute encoder described above, the minimum position detection resolution is determined by the grating pitch in the minimum divided grating track _to.
Since the absolute position detection stroke length is about the same as the grid pitch P ₁ in _the maximum divided grid track t ₁ , it is possible to increase the position detection resolution and lengthen the absolute position detection stroke length. This has disadvantages in that the number n of grating tracks increases, resulting in an increase in the size of the optical absolute encoder and an increase in the number of its components, such as photoelectric conversion elements and comparators.

(Object of the invention) The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide high position detection resolution,
Another object of the present invention is to provide a compact optical encoder that has a long absolute position detection stroke length.

(Means for Solving the Problems) The present invention relates to an optical encoder used for position measurement in machine tools such as lathes and milling machines, and semiconductor manufacturing equipment. A light source device that emits coherent parallel light; and a scale that is provided with grating tracks having the same ratio of light blocking portions and non-blocking portions and different pitches and diffracting the parallel light irradiated by the light source device; , by providing a light spot position detection device that receives positive and negative diffracted lights of the same order among the diffracted lights diffracted by this scale, detects the light spot position of each diffracted light, and converts it into an electrical signal. achieved. Furthermore, as a reading device for the optical encoder, the same order is detected from an electric signal output from the light spot position detection device that changes with relative movement between the scale, the light source device, and the light spot position detection device. This is achieved by determining the distance between the positive and negative diffracted lights, converting the distance between the diffracted lights into position data of the scale through one conversion means, and outputting the data.

(Function of the Invention) The optical encoder of the present invention performs position detection by utilizing the fact that the distance between positive and negative diffracted lights of the same order changes depending on the grating pitch pattern provided on the scale. Therefore, accurate position detection can be performed without being affected by changes in the amount of coherent light emitted from the light source section.

(Example of the invention) First, the principle of the present invention will be explained.

As shown in FIG. 5, a grating track T in which light transmitting parts and non-transmitting parts are repeated at a predetermined pitch.
When a coherent light beam L from a laser or the like is made incident on the scale 1 provided on the surface, the coherent light beam L transmitted through the transmission part undergoes a diffraction effect and becomes a plurality of diffracted lights L ₀ ,
It is divided into L± ₁ , L± ₂ , ..., L± _o , ... (hereinafter referred to as n-order diffracted light (n is an integer)). Among these diffracted lights, the positive and negative diffracted lights L _{+ o} of the n-order diffracted lights L±o,
The angle that L _-o makes with the coherent light beam L (hereinafter referred to as the diffraction angle) ±θ _o is the wavelength λ of the coherent light beam and the grating track T.
It is expressed by the following equation (1) by the pitch P of .

±θ _o = ±sin ^-1 (nλ/P) ...(1) Therefore, the positive and negative diffracted lights L _+o , L _-o irradiated on the screen 2 placed at a distance S from the scale 1
The distance d _o between them is expressed by the following equation (2).

d _o = 2S tan {sin ^-1 (nλ/P)} ...(2) Figure 6 shows, as an example, the wavelength λ of the coherent light beam L.
1μm, distance S between scale 1 and screen 2
It shows the relationship between the distance d ₁ between the ±1st-order diffracted lights L ₊₁ and L _-1 and the grating pitch P when it is 10 mm,
As is clear from the figure, the distance d ₁ between the diffracted lights differs depending on the grating pitch P, so the coherent light beam L is incident on the scale whose surface has grating tracks with different grating pitches P depending on the location. Obtained distance between positive and negative diffracted lights of the same order L _+o and L _-o
The position of the scale can be detected from d _o .

Next, examples of the present invention will be described.

FIG. 1 is a structural diagram showing an example of the optical system of the optical absolute encoder of the present invention.
A light emitting element 201 such as a diode) and this light emitting element 2
A collimator lens 202 converts the measurement light LD irradiated by the 01 into parallel light LE, and a slit 2 which partially transmits the parallel light LE made parallel by the collimator lens 202 to form a luminous flux LF with a predetermined width.
03, an elongated scale 204 having a grating track T _B on its surface in which a grating with the same ratio of transmitting portions and non-transmitting portions of the light flux from the slit 203 and different pitches is provided;
A condenser lens 205 that condenses a plurality of diffracted lights LG diffracted by T _B , and a light spot of each diffracted light LH ₀ , LH± ₁ , ..., LH± _o , ... from the condenser lens 205 The light spot position detection element 206, such as an image sensor, detects the position of the light spot and converts it into an electrical signal. Light emitting element 201, collimator lens 202, slit 203, and condensing lens 2
05 is fixedly arranged in a straight line and can be moved relative to the scale 204.
Here, the scale 204 moves linearly in the longitudinal direction of C or D.

The scale 20 used in the optical system 200 of the optical absolute encoder having such a configuration
4 has a grid pitch, for example, as shown in Figure 2.
Changes smoothly between L _ab (lattice pitch of point f P _B , g
A lattice track T _B is provided which has a lattice pitch of points P _C , a lattice pitch of h points P _D , a lattice pitch of i points P _C , and a lattice pitch of j points P _B . Therefore,
Each diffracted light LH incident on the light spot position detection element 206
The diffraction angles of ± ₁ , ..., LH± _o , ... change periodically as the grating pitch changes when the scale 204 moves in the longitudinal direction of C or D. The light spot position of each of the diffracted lights LH± ₁ , LH± _o , . . . condensed onto the light spot position detection element 206 changes accordingly. In other words, as the grating pitch becomes smaller, the diffraction angle becomes larger and the distance between the positive and negative diffracted lights of the same order becomes larger; conversely, as the grating pitch becomes larger, the diffraction angle becomes smaller and the distance between the positive and negative diffracted lights of the same order increases. distance becomes smaller. As explained in the above principle, the grating pitch is simply for changing the diffraction angle, so the grating pitch between L _ab can be changed arbitrarily, and the movement of the scale 204 Accordingly, an electrical signal that increases at a constant rate or an electrical signal that changes in a sinusoidal or triangular waveform can be easily obtained. Then, the position of the scale can be detected based on the distance between the positive and negative diffracted lights of the same order.

FIG. 3 is a block diagram showing an example of a reading circuit that obtains position data from the electric signal from the light spot position detection device 206 described above, and selects positive and negative diffracted light of the same order as described above. For example, the positions of the two light spots of the first-order diffracted light LC± ₁ are converted into electric signals S+c and S−c by the light spot position detection element 206, respectively. Then, the subtracter 211 generates an electric signal Scc representing the distance between the diffracted lights.
Therefore, the sample hold circuit 212 and A/D
It is converted into digital data _dcc by the converter 213,
It is output to the verification circuit 214. Here, the distance between the positive and negative first-order diffracted lights corresponding to the pattern of the grating track is stored in advance in the storage circuit 215 together with the corresponding position data.
The distance dm between each diffracted light read from 15 and A/
It compares the distance dcc between the diffracted lights digitized by the D converter 213 and outputs position data Dcc of the corresponding scale stored in advance.

Note that in the above embodiment, the coherent light emitted from the light emitting element is transmitted through the scale to obtain the diffracted light, but since there is no difference in nature between the transmitted light and the reflected light, the coherent light emitted from the light emitting element is reflected by the scale and diffracted. It is also possible to obtain light. In the case of a reflective type, the light emitting element, collimator, slit, condensing lens, and light spot position detection element are arranged on the same side of the scale, and the scale is formed by a light reflecting part and a light non-reflecting part. . Further, as shown in FIG. 4, if the scale is a disk 207, the grating track T _B of the present invention is provided in an annular shape on the surface of the scale, and the center of the disk 207 is rotated as the rotation axis, the angle can be changed. It is also possible to perform absolute detection. Furthermore, in the above embodiment, the light source section and the light spot position detection section are fixed and the position is detected by moving the scale, but it is possible to fix the scale and move the light source section and the light spot position detection section. However, position detection is possible.

(Effects of the Invention) As described above, according to the optical encoder of the present invention, long-stroke absolute position detection, which conventionally required multiple grating tracks, can be performed using a single grating track. As a result, the optical encoder can be made smaller, and the manufacturing cost and product cost of the optical encoder can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a structural diagram showing an example of the optical system of the optical encoder of the present invention, Fig. 2 is a diagram showing an example of its grating track, Fig. 3 is a block diagram showing an example of its detection circuit, and Fig. 4. is a perspective view showing another application example of the grating track, FIGS. 5 and 6 are diagrams each explaining the principle of the present invention, and FIG. 7 is a perspective view showing an example of the optical system of a conventional optical encoder. 8 is a diagram showing an example of the lattice track,
FIG. 9 is a diagram showing an example of the electric signal, and FIG. 10 is a block diagram showing an example of the detection circuit. 10,200...Optical system of absolute type encoder, 11,201...Light emitting element, 12,202
... Collimator lens, 13, 14, 204 ... Scale, 203 ... Slit, 205 ... Condenser lens,
206... Light spot position detection element, 211... Subtractor, 2
12...Sample hold circuit, 213...A/D converter, 214...Verification circuit, 215...Storage circuit.

Claims (1)

[Scope of Claims] 1. A light source device that emits collimated light having coherence, and a grating track with the same ratio of light blocking portions and non-blocking portions but different pitches, and irradiated by the light source device. A scale that diffracts the parallel light, and a light spot position that receives positive and negative diffracted lights of the same order among the diffracted lights diffracted by this scale, detects the light spot position of each diffracted light, and converts it into an electrical signal. An optical encoder comprising a detection device. 2. The light source device includes a light source that emits coherent light;
Claim 1 comprising: a collimator lens that converts the coherent light irradiated by the light source into parallel light; and a slit that limits the parallel light collimated by the collimator lens to a predetermined width. The optical encoder according to item 1. 3. The optical encoder according to claim 2, wherein the light source is a laser beam oscillation element that emits laser light. 4. The light source device and the light spot position detection device are on the opposite side to the scale, and the non-blocking portion of the scale transmits and diffracts the parallel light irradiated by the light source device. An optical encoder according to claim 1. 5. The light source device and the light spot position detection device are on the same side with respect to the scale, and the non-blocking portion of the scale reflects and diffracts the parallel light irradiated by the light source device. An optical encoder according to claim 1. 6. The optical encoder according to claim 1, wherein the scale is a flat plate provided with a rectangular grating track, and the relative movement is in a straight line. 7. The optical encoder according to claim 1, wherein the scale is a disk provided with an annular grating track, and the relative movement is rotation. 8. The light spot position detection device includes a condensing lens that condenses the diffracted light diffracted by the scale, and detects the light spot position of the condensed diffracted light and converts it into an electrical signal. The optical encoder according to claim 1, comprising a light spot position detection element. 9. The optical encoder according to claim 8, wherein the light spot position detection element is an image sensor that converts the light spot position into an electrical signal. 10 The relative movement between the scale, the light source device, and the light spot position detection device is such that the scale moves with respect to the light source device and the light spot position detection device. Optical encoder as described in section. 11. The relative movement of the scale, the light source device, and the light spot position detection device is such that the light source device and the light spot position detection device move together with respect to the scale. 1st
Optical encoder as described in section. 12 A light source device that emits collimated light having coherence, and grating tracks having the same ratio of light blocking portions and non-blocking portions but different pitches are provided to diffract the parallel light irradiated by the light source device. An optical system consisting of a scale and a light spot position detection device that receives positive and negative diffracted lights of the same order among the diffracted lights diffracted by the scale, detects the light spot position of each diffracted light, and converts it into an electrical signal. and between the positive and negative diffracted lights of the same order from the electrical signal output from the light spot position detection device that changes with the relative movement of the scale, the light source device, and the light spot position detection device. An optical encoder comprising a reading device that calculates a distance, converts the distance between the diffracted lights into position data of the scale through one converting means, and outputs the data. 13 a subtraction unit in which the reading device calculates a difference between electrical signals output from the light spot position detection device and representing the positions of the positive and negative diffracted lights of the same order to obtain an electrical signal representing the distance between the diffracted lights; A hold section holds the electrical signal obtained in the section, and the electrical signal held in this hold section is sent to the A/D.
13. The optical encoder according to claim 12, comprising an A/D converter that performs the conversion, and a converter that converts the output of the A/D converter into position data of the scale. 14 The converting means converts between each of the positive and negative diffracted lights of the same order corresponding to the pattern of the grating track that changes with the relative movement of the scale, the light source device, and the light spot position detection device. The distance between the diffracted lights determined by the storage unit that stores the distance in advance and the A/D conversion unit is compared with the distance between the diffracted lights stored in the storage unit to determine the corresponding scale. 14. The optical encoder according to claim 13, further comprising a verification section that outputs position data. 15. The conversion means obtains the distance between the diffracted lights obtained by the A/D conversion section, calculates it based on a predetermined calculation formula, and converts it into position data of the scale, and outputs the result. An optical encoder according to claim 13 consisting of: