JPH05647B2 - - 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. 8 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 light emitting element 11 such as a diode or lamp, 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 that is provided corresponding to A ₁ , 14A ₂ , ..., 14A _o and transmitted through each transmission window 14A 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, adjacent grid tracks t ₁ , t _{2 and} t ₂ , t ₃ and . . . and t _{o-1 ,} t _o as _shown in FIG. 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 Figure 10, the horizontal axis shows the displacement amount ml of the first scale 13 in the longitudinal direction.
The vertical axis represents each photoelectric conversion element 15-1, 15-2,
15-3, ..., 15-n-1, 15-n shows the electrical signals S ₁ , S ₂ , S ₃ , ..., S _o-1 , S _o , and each electrical signal S ₁ , S ₂ , S ₃ , ..., S _o-1 ,
It can be seen that S _o changes periodically. And these electric signals S ₁ , S ₂ , S ₃ , ...,
S _o-1 and S _o are respectively digitized by a comparator ₂₀ as shown in _the block diagram of the optical absolute encoder in FIG. 11 _.
. . , d _o-1 , d _o and further converted by the decoder 30 from the alternating binary code to absolute position data D in a desired format such as pure binary code or 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 grating track having the same ratio and pitch of light blocking portions and non-blocking portions and different grating line directions are provided to emit the parallel light irradiated by the light source device. A scale for diffraction and 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 is provided. This is achieved by 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 rotation angle of the light spot of the positive and negative diffracted lights, converting the rotation angle 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 detects a position by using the fact that the light spots of positive and negative diffracted lights of the same order move (rotate) according to a pattern in the direction of the grid lines 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.

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

As shown in FIG. 7, 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 which is provided on the surface, the coherent light beam L transmitted through the transmission part is subjected to the diffraction effect and becomes a plurality of diffracted light beams L ₀ in a plane perpendicular to the grating lines. ,L± ₁ ,L± ₂ ,...,L± _o ,
... (hereinafter referred to as n-order diffracted light (n is an integer)). Among these diffracted lights, the angle (hereinafter referred to as diffraction angle) between the positive and negative diffracted lights L _{+o and} L _-o of the n-th order diffracted light L±o and 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 pitch P of the lattice track T, as shown in the following equation (1).

±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 light spots are located on a line perpendicular to the grid line direction at a distance d _o expressed by the following equation (2).

d _o = 2S tan {sin ^-1 (nλ/P)} ...(2) Therefore, an arbitrary light beam L can be obtained by making the coherent light beam L incident on a scale whose surface has grating tracks with different grating line directions depending on the location. The position of the scale can be detected from the movement (rotation) angle of the light spot of the positive and negative diffracted lights L _+o and L _-o of the same order.

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 301 such as a diode), and this light emitting element 3
A collimator lens 302 converts the measurement light LI irradiated by 01 into parallel light LJ, and a slit 3 that partially transmits the parallel light LJ made parallel by this collimator lens 302 to form a luminous flux LK of a predetermined width.
03, an elongated scale 304 whose surface is provided with a grating track T _C in which gratings are repeated in different directions with the same ratio and pitch of the transmitting part and non-transmitting part of the light beam from the slit 303, and the grating. Multiple diffracted lights diffracted by track T _C (not shown)
A condensing lens 305 condenses the respective diffracted lights LL ₀ , LL± ₁ , ..., from the condensing lens 305 .
Of these, there is a 0th-order diffracted light shielding plate 306 that blocks only the 0th-order diffracted light LL ₀ , and a light point LP of positive and negative diffracted light of the same order (the figure shows the 1st-order diffracted light) LM± ₁ that has passed through this shielding plate 306. It is comprised of a light spot position detection element 307, such as an image sensor, which detects the position of ± ₁ and converts it into an electrical signal. Light emitting element 301, collimator lens 302, slit 30
3. It is sufficient that the condensing lens 305 and the shielding plate 306 are linearly fixed and movable relative to the scale 304, but here the scale 304 is linearly arranged in the longitudinal direction of E or F. It is starting to move to .

The scale 30 used in the optical system 300 of the optical absolute encoder having such a configuration
4 includes, for example, a light transmitting part as shown in FIG.
The ratio of the non-transparent part and the pitch P _E are the same, and the grid line direction changes between l _AB (it rotates counterclockwise as it moves from point k → point l → point m → point n, and at point 0 it becomes point k. A lattice track T _C is provided which returns in the same direction.

Therefore, 1 incident on the light spot position detection element 307
Light spots LP ₊₁ and LP _-1 of the next diffracted light LM± ₁ are scale 3
As the grating line direction changes when moving in the longitudinal direction of E or F of 04, the light spot rotates on the circumference of the light spot position detection element 307 with a constant distance of 180° on the circumference of diameter d ₁ (see Fig. 2).
k', l', m', n', 0'), the position of the scale 304 can be detected from this rotation angle. Note that, as explained in the above principle, the grid line direction is simply for rotating the light spot, so the grid line direction between l _AB can be changed arbitrarily. Then, the position of the scale can be detected based on the rotation angle of the light spot of 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 element 307 described above, and selects positive and negative diffracted light of the same order as described above. For example, the light points LP ₊₁ , LP _-1 of the first-order diffracted light LM± ₁
The position of the light spot position detection element 3 is as shown in FIG.
07 into electrical signals (x ₊₁ , y ₊₁ ) and (x _-1 , y _-1 ) representing respective (x, y) coordinates. Then, the subtracters 311A and 311B calculate the X component = (x ₊₁ - x _-1 ) and Y component Y = (y ₊₁ - y _-1 ) of the distance between each light spot, and the magnitude comparator 312 and the divider 313. And the size comparator 3
12 compares the magnitude of the If /, |
If |<||, / is determined and output to the data converter 314. Here, Figure 5 shows
The relationship between the division value/or/obtained by the divider 313 and the position of the scale 304, and the corresponding light spot LP ₊₁ on the light spot position detection element 307,
It shows an example of the position of LP _-1 and the comparison result CR of the magnitude comparator 312. This example is scale 304
In the case where the scale 304 is provided with a grating track T _c in which the position of and the change in the grid line direction are in a proportional relationship, the change in the position of the scale 304 causes the change in the range of ||≧|| The division value Y/ is a tan curve, and the division value / within the range of ||<|| is a cot curve. Therefore, the data converter 314 receives the comparison result from the magnitude comparator 312.
When CR′ is ||≧||, tan ^-1 (/) is calculated and the comparison result from the magnitude comparator 312 is
When CR' is ||<||, calculate cot ^-1 (/) to find the slope φ of the straight line connecting the light points LP ₊₁ and LP _-1 , and scale the scale corresponding to the pre-stored slope φ. Outputs the corresponding position data D _P from among the position data 304. Furthermore, even if the scale 304 is provided with a lattice track T _C in which the position of the scale 304 and the change in the direction of the lattice lines are not proportional to each other, the position data of the scale 304 corresponding to the division value / or / Data converter 3
If the position data D p is stored in advance in 14, the position data D _p can be obtained.

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. When using a reflective type, the light emitting element, collimator, slit, condensing lens, 0th order diffraction light shielding plate, and light spot position detection element are arranged on the same side of the scale, and the scale is placed on the same side as the light reflecting part and the light non-reflecting part. It is formed by the parts. Further, as shown in FIG. 6, if the scale is a disk 308, the grating track T _C of the present invention is provided in an annular shape on the surface of the scale, and the center of the disk 308 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 if the scale is fixed,
Position detection is also possible by moving the light source section and the light spot position detection section.

(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 perspective 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. 5 and 5 are diagrams each explaining the detection method, FIG. 6 is a perspective view showing another application example of the lattice track, FIG. 7 is a diagram explaining the principle of the present invention, and FIG. FIG. 9 is a perspective structural diagram showing an example of the optical system of an optical encoder, FIG. 9 is a diagram showing an example of its grating track, FIG. 10 is a diagram showing an example of its electrical signal, and FIG. 11 is an example of its detection circuit. FIG. 10,300...Absolute type encoder optical system, 11,301...Light emitting element, 12,302
...Collimator lens, 13, 14, 304...Scale, 303...Slit, 305...Condenser lens,
306... 0th order diffraction light shielding plate, 307... Light spot position detection element, 310... Reading circuit, 311A, 311
B...subtractor, 312...size comparator, 313...divider, 314...data converter.

Claims (1)

[Scope of Claims] 1. A light source device that emits collimated light having coherence, and a grating track having the same ratio and pitch of light blocking portions and non-blocking portions and different grating line directions; A scale that diffracts the parallel light irradiated by the scale, and a scale 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. 1. An optical encoder comprising: a light spot position 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, a shielding plate that blocks only the 0th-order diffracted light of the condensed diffracted light, and The optical encoder according to claim 1, further comprising a light spot position detection element that detects the light spot position of the diffracted light transmitted through the shielding plate and converts it into an electrical signal. 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 a grating track having the same ratio and pitch of light blocking portions and non-blocking portions and different grating line directions, and providing the parallel beams irradiated by the light source device. A scale that diffracts light, 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. and detects the positive or negative 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. What is claimed is: 1. An optical encoder comprising: a reading device for determining a rotation angle of a light spot of diffracted light, converting the rotation angle into position data of the scale through one conversion means and outputting the data. 13 The reading device determines each orthogonal component of a line segment connecting each of the light points based on the difference in the orthogonal coordinates of the light points of the positive and negative diffracted lights of the same order output from the light point position detection device. a subtraction unit; a comparison unit that compares the magnitude of the orthogonal component obtained by the subtraction unit;
It is composed of a division section that divides each of the orthogonal components from the subtraction section based on the comparison result from the comparison section, and a conversion means that converts the division value from the division section into position data of the scale. An optical encoder according to claim 12. 14. The conversion means rotates the light spot of the positive and negative diffracted light of the same order in accordance with 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 rotation angle is determined from a storage unit that stores angles in advance and the division value determined by the division unit, and this rotation angle is compared with the rotation angle stored in the storage unit to determine whether the rotation angle corresponds to the rotation angle stored in the storage unit. 14. The optical encoder according to claim 13, further comprising a collation section that outputs position data of the scale. 15. A memory in which the conversion means stores in advance the division value corresponding to the pattern of the lattice track that changes as the scale, the light source device, and the light spot position detection device move relative to each other. and a collation unit that compares the division value obtained by the division unit with the division value stored in the storage unit and outputs the corresponding position data of the scale. The optical encoder according to item 13.