JPH054615B2 - - 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 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 transparent 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, 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 , 14 _o , and each transmission window 14A ₁ , 14A ₂ , 14A ₃ , ...,
14A _o-1 , each photoelectric conversion element 1 compatible with 14A _o
5-1, 15-2, 15-3, ..., 15-n-
Light incident on 1,15-n L _c1 , L _c2 , L _c3 ,...,
Since the intensities of L _co-1 and L _co change periodically as the first scale 13 moves in the longitudinal direction (arrow m in the figure), each photoelectric conversion element 15-1, 15 -2,15-3,...,15-n
The electrical signals converted by -1 and 15-n also change periodically. In FIG. 10, the horizontal axis represents the displacement amount ml of the first scale 13 in the longitudinal direction, and the vertical axis represents each photoelectric conversion element 15-1, 15-2, 15-3,
It shows the electric signals S ₁ , S ₂ , S ₃ , ..., S _o-1 , S _o converted by ..., 15-n-1, 15-n,
It can be seen that each of the electrical signals S ₁ , S ₂ , S ₃ , ..., S _o-1 , S _o changes periodically. and,
These electrical signals S ₁ , S ₂ , S ₃ , ..., S _o-1 , S _o are
As shown in the block diagram of the optical absolute encoder in Fig. 11, each comparator 2
Digitized by 0 d ₁ , d ₂ , d ₃ , ...d _o-1 , d _o
Then, the decoder 30 converts the alternating binary code into 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; a scale that is provided with grating tracks of the same pitch and different ratios of light blocking portions and non-blocking portions and diffracting the parallel light irradiated by the light source device; This is achieved by providing a photoelectric conversion device that receives a plurality of diffracted lights of different orders among the diffracted lights diffracted on this scale and converts them into electrical signals according to the intensity of each diffracted light. Furthermore, as a reading device for the optical encoder, an electric signal output from the photoelectric conversion device corresponding to a pattern of the grating track that changes with relative movement between the scale, the light source device, and the photoelectric conversion device This is achieved by determining the ratio of the scale, converting the ratio into position data of the scale through one converting means, and outputting the result.

(Function of the Invention) The optical encoder of the present invention performs position detection by utilizing the fact that the intensity ratio of diffracted light of different orders changes depending on the pattern of the aperture ratio between one pitch of the grating 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. 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)). FIG. 6 shows the above-mentioned grating track T. Letting the length of the transparent part 1A be la, the length of the non-transparent part 1B be lb, and the grating pitch be P, the length of the transparent part 1A between one pitch of the grating is The ratio (hereinafter referred to as aperture ratio) Q is expressed by the following equation (1).

Q=la/P...(1) Also, the n-th diffracted light L± _o for _the 0th-order diffracted light L0
The intensity ratio I of is expressed by the following equation (2) using the aperture ratio Q.

I=sin ² (nπQ)/(nπQ) ² ...(2) Figure 7 shows, as an example, the aperture ratio Q and the 0th order diffracted light.
1st-order diffracted light L± ₁ , 2nd-order diffracted light L± ₂ for L ₀ ,
This shows the relationship between the intensity ratio I of each of the third-order diffracted lights L± ₃ , and as is clear from the figure, each diffracted light L± ₁ , L± ₂ , L± ₃
Since the intensity ratio I also differs, the aperture ratio Q
The position of the scale is detected by detecting the intensity ratio I of diffracted light of two arbitrary different orders obtained by making a coherent light beam L incident on a scale whose surface is provided with different grating tracks. be able to.

Next, examples of the present invention will be described.

FIG. 1 is a perspective structural diagram showing an example of the optical system of the optical absolute encoder of the present invention,
emit coherent measurement light LA, e.g. LD
A light emitting element 101 such as a laser diode, a collimator lens 102 that converts measurement light LA emitted by the light emitting element 101 into parallel light LB, and parallel light made parallel by the collimator lens 102.
A slit 103 that partially transmits the LB to produce a luminous flux (not shown) of a predetermined width, and a grating track T _A in which the transmitting part and the non-transmitting part of the luminous flux from the slit 103 are repeated at a predetermined grating pitch. A plurality of diffracted lights (not shown) diffracted by the elongated scale 104 provided on the surface and the grating track T _A
a condenser lens 105 that condenses the respective diffracted lights LC ₀ , LC± ₁ , ...,
It is provided corresponding to LC± _o ,..., and each diffracted light _LC0 ,
It consists of photoelectric conversion elements PL ₀ , PL± ₁ , ..., PL± _o , ... such as photodiodes that convert into electrical signals according to the intensity of LC± ₁ , ..., LC± _o , ... ing. Light emitting element 101, collimator lens 1
02, the slit 103 and the condensing lens 105 are fixedly arranged in a straight line, and the scale 104
In this case, the scale 104 is designed to move linearly in the longitudinal direction of A or B.

The scale 10 used in the optical system 100 of the optical absolute encoder having such a configuration
4 has a grid pitch, for example, as shown in Figure 2.
P _A is constant over the entire scale length (several μm to several +
μm), but the aperture ratio Q changes smoothly between the lengths l _ab (aperture ratio 0.5 at point a, aperture ratio 0.75 at point b, c
A lattice track T _A is provided with an aperture ratio of 0.5 at a point, an aperture ratio of 0.25 at a point d, and an aperture ratio of 0.5 at a point e. Therefore, each photoelectric conversion element PL ₀ , PL± ₁ , ...,
Each diffracted light incident on PL± _o , LC ₀ , LC± ₁ ,
The intensities of ..., LC± _o , ... change periodically as the aperture ratio Q changes when the scale 104 moves in the longitudinal direction of A or B. Conversion element PL ₀ , PL± ₁ , ...,
Each electrical signal converted by PL± _o , ... also changes periodically.

As explained in the above principle, the aperture ratio is simply used to find the intensity ratio of the diffracted light, so the aperture ratio between l _ab can be changed arbitrarily, and the aperture ratio of the scale 104 can be changed as desired. Electrical signals that increase at a constant rate as the robot moves, or electrical signals that change in a sinusoidal or triangular waveform can be easily obtained. Then, the position of the scale can be detected based on the intensity ratio of diffracted light of two arbitrary different orders, that is, the ratio of electric signals.

FIG. 3 is a block diagram showing an example of a reading circuit that obtains position data from the electric signal from the photoelectric conversion element described above. As described above, it is sufficient to select two arbitrary different orders of diffracted light. For example, the electrical signals Sa and Sb from the photoelectric conversion elements PL ₀ and PL ₊₁ that convert the 0th-order diffracted light LC ₀ and the 1st-order diffracted light LC ₊₁ into electrical signals are sent to the sample and hold circuits 111a and 1111b and the A/D, respectively. converter 11
2a and 112b are converted into digital data d _a and d _b . Then, each A/D converted digital data d _a and d _b is divided by a division circuit 113 to obtain digital data d _ab representing a ratio,
It is output to the verification circuit 114. Here, the storage circuit 115 stores in advance the ratio of electrical signals representing the intensities of the diffracted lights LC ₀ and LC ₊₁ of two different orders corresponding to the pattern of the grating track, together with the corresponding position data. , the ratio dm of each electric signal read from this memory circuit 115 and the division circuit 11
Compare the electrical signal ratio d _ab obtained in step 3,
The position data D _ab of the corresponding scale stored in advance is output.

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 photoelectric conversion element are arranged on the same side with respect to the scale, and the scale is formed of a light reflecting part and a light non-reflecting part. Further, as shown in FIG. 4, the scale is made into a disk 106, and the grating track of the present invention is formed on the surface of the disk.
If T _A is provided in an annular shape and rotated using the center of the disk 106 as the rotation axis, it is also possible to detect the angle absolutely. Furthermore, in the embodiments described above, the light source section and the photoelectric exchange section are fixed and the position is detected by moving the scale.
Position detection is also possible by fixing the scale and moving the light source section and photoelectric conversion 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. The smaller size allows the optical encoder to be made smaller, and since there are now two optical conversion elements instead of the conventional multiple photoelectric conversion elements, the number of parts is reduced, reducing the manufacturing cost of the optical encoder and the product cost. You can try to bring it down.

[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. The figure is a perspective view showing another application example of the grating track, Figures 5 to 7 are diagrams each explaining the principle of the present invention, and Figure 8 is a perspective view showing an example of the optical system of a conventional optical encoder. A structural diagram, FIG. 9 is a diagram showing an example of the lattice track,
FIG. 10 is a diagram showing an example of the electrical signal, and FIG.
The figure shows an example of the detection circuit. 10,100...Absolute type encoder optical system, 11,101...Light emitting element, 12,1
02... Collimator lens, 13, 14, 104
...Scale, 103...Slit, 105...
Condensing lens, 15, PL...Photoelectric conversion element, 11
1a, 111b...Sample hold circuit, 11
2a, 112b...AD converter, 113...Division circuit, 114...Verification circuit, 115...Storage circuit.

Claims (1)

[Scope of Claims] 1. A light source device that emits collimated light having coherence, and a grating track of the same pitch with different ratios of light blocking portions and non-blocking portions. It consists of a scale that diffracts parallel light and a photoelectric conversion device that receives multiple diffracted lights of different orders among the diffracted lights diffracted by this scale and converts them into electrical signals according to the intensity of each diffracted light. Features of optical encoder. 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 a laser beam. 4. A patent in which the light source device and the photoelectric conversion 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. A patent in which the light source device and the photoelectric conversion 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 photoelectric conversion device includes a condensing lens that condenses the diffracted light diffracted by the scale;
The optical encoder according to claim 1, further comprising a photoelectric conversion element that converts the focused diffracted light into an electric signal according to the intensity thereof. 9. The method according to claim 1, wherein the relative movement between the scale and the light source device and the electro-photoelectric conversion device is such that the scale moves with respect to the light source device and the photoelectric conversion device. optical encoder. 10. According to claim 1, the relative movement between the scale, the light source device, and the photoelectric conversion device is such that the light source device and the photoelectric conversion device move together with respect to the scale. Optical encoder as described. 11 A scale that is provided with a light source device that emits collimated light having coherence and grating tracks of the same pitch with different ratios of light blocking portions and non-blocking portions and diffracting the parallel light irradiated by the light source device. and a photoelectric conversion device that receives a plurality of diffracted lights of different orders among the diffracted lights diffracted on this scale and converts them into electrical signals according to the intensity of each diffracted light, and The ratio of each electrical signal output from the photoelectric conversion device corresponding to the pattern of the grating track that changes with the relative movement of the scale, the light source device, and the photoelectric conversion device is calculated, and the ratio is converted into one. An optical encoder comprising a reading device that converts and outputs the position data of the scale through a converting means. 12. The reading device includes a hold unit that holds each of the electrical signals output from the photoelectric conversion device, and an A/D conversion unit that A/D converts each of the electrical signals held by the hold unit.
Claim 11 is comprised of a division unit that calculates the ratio of values output from each A/D conversion unit, and conversion means that converts the output of the division unit into position data of the scale. optical encoder. 13 The converting means generates each electrical signal representing the intensity of the plurality of diffracted lights of different orders corresponding to the pattern of the grating track that changes with relative movement between the scale, the light source device, and the photoelectric conversion device. a storage unit configured to store in advance a ratio of the scale, and a verification unit that compares the ratio obtained by the division unit with the ratio stored in the storage unit and outputs position data of the corresponding scale. The optical encoder according to claim 12, comprising: 14. Claim 1, wherein the conversion means comprises a calculation unit that inputs the ratio obtained by the division unit and calculates it based on a predetermined calculation formula to convert it into position data of the scale and output it. The optical encoder according to item 12.