JPS59224514A - Optical encoder - Google Patents

Abstract

PURPOSE:To obtain high resolution and improve reliability by forming a scale plate of an assembly of numbers of recessed or projecting grooves. CONSTITUTION:The scale plate of a pulse disk 3 is formed of the assembly of numbers of recessed or projecting grooves 12 which have constant slit pitch P, slit width W 1/2-1/3 as large as the pitch P, and slit depth (d) about as large as the wavelength of light. Then, Spot light 11 formed by converting light from a light source illuminates a specific area of a specific number of grooves 12 and light reflected by or transmitted through the scale plate is guided to a photodetector to detect the amount of variation, detecting the extent of rotational displacement. Consequently, the manufacture is facilitated, the high resolution is obtained, and the reliability is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an optical encoder that uses a semiconductor laser to detect rotational or linear displacement.

A conventional optical encoder of this type is shown in FIG. FIG. 1 is a perspective view showing a schematic configuration of a conventional optical rotary encoder that uses a semiconductor laser to detect the amount of rotational displacement.

In the figure, 1 is a ball bearing, 2 is a rotating shaft supported by a ball bearing IK, 3 is a pulse disk attached to the rotating shaft 2, 4 is a semiconductor laser as a light source, and 5 is a laser emitted radially from the semiconductor laser 4. 6 is a collimator lens for collimating the laser beam 5, 7 is a condensing lens for condensing the laser beam 5 into a size of several μm,
Reference numeral 8 denotes a photodetector that detects changes in the amount of light transmitted through the pulse disk 3. As this photodetector 8, for example, a photodiode is used. In addition, Fig. 2 (a) and (
As shown in bl, the pulse disk 3 is usually a glass disk 9.
The glass disk 9 is provided with a chromium vapor deposited film, which is a light and dark checkered stripe 10, by patterning by etching.

Next, the operation shown in FIG. 1 will be explained. When rotation is transmitted to the rotating shaft 2 from the outside, the pulse disk 3 on which the bright and dark lattice fringes 10 are formed is rotated, and the amount of laser light 5 passing through the pulse disk 3 changes. The amount of change,
The rotational displacement i can be known by detecting it with the photodetector 8. The laser beam 5 is emitted from the semiconductor laser 4 with an intensity of about 1 to 3 mW, but as it is generated radially as shown in FIG. The light is focused to a small diameter of approximately 2 to 10 μm, and is irradiated onto the bright and dark lattice stripes 10 of the pulse disk 3. Now,
As shown in FIG. 3(a), when the laser beam 5 focused into a small circular spot light 11 of approximately 2 to 5 μm crosses the bright and dark lattice stripes 10, it appears as shown in FIGS. 3(b) and 3(d). Each output signal with the waveform shown is generated.

When the pinch of the bright and dark checkered stripes 10 is large, the generated output signal has a waveform close to the rectangular wave shown in FIG.
Light and dark plaid 10 has a small pinch, light and dark plaid 10
When the zero width and the diameter of the circular spot light 11 of the laser beam 5 are equal, the generated output signal has a sinusoidal waveform as shown in FIG. 3 fd). In addition, 100 bright and dark checkered stripes
When the width becomes smaller than the diameter of the circular spot light 11 of the laser beam 5, the amplitude of the generated output signal becomes small, and eventually the bright and dark lattice fringes 10 become undetectable. Therefore, when the width of the bright and dark checkered stripes 100 becomes smaller, the laser beam 50
The diameter of the circular spot light 11 must be small. For example, if a pulse disk 3 with a diameter of 50 and generating 10,000 pulses is made, the width of the bright and dark lattice stripes 10 will be about 7 μm, so the diameter of the laser beam 50 and circular spot light 11 should be about 7 μm or less. .

In the case of an optical rotary encoder, its detection accuracy is within the 100 dimensions of bright and dark lattice stripes on the pulse disk 3.
The difference between the center of the button and the center of rotation (eccentricity) is determined by the button.

Therefore, the dimensional accuracy of the bright and dark lattice stripes 10 on the pulse disk 3 becomes more severe as the number of pulses increases.
In the case of 00 pulses, in order to keep the detection accuracy within 5%, the placement accuracy of the width of the bright and dark checkered stripes 10 must be kept within 3 seconds. For that purpose, Figure 2 (a), (b
In the conventional method shown in ) in which a chromium vapor deposited film, which is a light and dark lattice stripe 10, is produced by etching on a glass disk 9,
It is necessary to pattern 1 & 1 pulsed disks 3 under controlled conditions by electron beam exposure and to fabricate them by etching, which has disadvantages such as high cost.

This invention was made to eliminate the above-mentioned drawbacks of the conventional ones.The slits have a constant pitch, the width is 1/2 to 1/3 of the pinch, and the depth is about the wavelength of light. a scale plate formed by converging a large number of concave or convex grooves, a light source, and a first optical system that condenses light from the light source so that it can irradiate a predetermined number of groove areas; A second device that guides the light reflected or transmitted from the scale plate to a photodetector.
has a configuration comprising an optical system and the photodetector,
The purpose is to provide a highly reliable optical encoder.

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 4(a) and 4(bl) are a partial plan view and an enlarged sectional view taken along the line B--B of a pulse disk to which an optical encoder according to an embodiment of the present invention is applied.

In the figure, the 11th company spot light 't12 is a groove carved in the pulse disk 3 serving as a scale plate, and a reflective film made of a 13th metal film. The grooves 12 correspond to continuous concentric or spiral grooves divided into angles according to the number of pulses. This corresponds to 1001 conventional bright and dark lattice stripes. Therefore, the length of each groove becomes shorter as the pressure toward the center of the pulse disk 3 increases. Also, the depth d of the groove is approximately 1/4 of the laser wavelength used. The size of the groove, the pinch P of the groove, is approximately 1.6 to 2 μm, and the width of the groove W is approximately 0.2 to 2 μm.
Just set it to 1.0PK. Reflective film 13 made of metal film
For this purpose, a metal sound with high reflectance and good stability, such as Cr or At, may be used.

Next, the above $12'! The mounting process of the pulse disk 3 having the number i will be explained with reference to FIGS. 5(a) to 5(i)'. As shown in FIG. 5(a), a glass disk 14 is coated with Bosiphotoresist (15k) uniformly to a thickness of one-fourth the wavelength of the semiconductor laser used to form a disk 16. As the positive photoresist 15, for example, A
Use a lens with high resolution such as Z1350. As shown in FIG. 5), the disk 16' is exposed to laser light 17 while rotating at a constant speed. Here, the laser beam 17i
C is an argon laser with a diameter of about 1 μm around the entire circumference and a condensing lens 7.
The surface of the positive photoresist 15 is irradiated with a spot light having a diameter of m or less. At this time, the laser beam 17 is transmitted so that the disk 16 is 1
While rotating, the irradiation position is moved at a constant speed in the radial direction indicated by the arrow on the disk 16 while repeating ON and OFF'e as many times as the number of pulses required for the pulse disk. Also, the laser beam 17t-ON.

The timing of turning off must be synchronized with the rotation of the disk 16. As shown in FIG. 5(C), the laser beam 17
When the exposed portion 18 is developed, only the exposed portion 18 is melted to form grooves 12, as shown in FIG. 5(d), and the grooves 12 are arranged as shown in FIG. ) as shown below. Using the disk 16 produced in this way as a master disk,
A replica is made and used as a pulse disk.

As shown in FIG. 5(e), a metal film 19 such as At is deposited on the surface of the master, and Ni plating is performed using this metal film 19 as an electrode, as shown in FIG. 5(f), @. As,
A master 20 is produced by peeling it off from the master disc. Figure 5 (1
As shown in 1), several stampers 21 are produced from this master 20.

Using this stamper 21, grooves are transferred to plastic (PMMA, polycarbonate, etc.) by compression molding or injection molding, and replica disks 22 as shown in FIG. 5(i) are produced in large quantities. A metal film is formed on the surface of this replica disk 22 by vapor deposition or sputtering, and this is used as a reflective film 13. Note that in order to protect the reflective film 13, a protective layer may be provided on the reflective film 13. Also,
As a method for transferring the grooves 12, there is also a method in which an ultraviolet curable resin is applied to a plastic plate or a glass plate, a stamper 21 is pressed against the resin, and the resin is cured by irradiation with ultraviolet rays.

Next, 1 the replica disk 22 which is the pulse disk 3 of this invention
A method of detecting a signal from a signal will be explained using FIGS. 6(a) to 6(c). As shown in FIG. 6, the laser beam 5 irradiated onto the disk surface of the replica disk 220 through the condensing lens 7 returns along the original optical path in the portion where the groove 12 is not present. . However, as shown in FIGS. 6(b) and 6(e), in the area where the groove 12 exists, the reflected light 23 from the bottom surface of the groove 12 is combined with the reflected light 25 from the area portions 24 on both sides of the groove 12. They create a phase difference and interfere with each other.

If the depth of this groove 12 is set to 1/4 wavelength, each reflected light 2
A phase difference of 3.25 becomes a half wavelength and cancels each other out, so that the reflected light passing through the condenser lens 7 is minimized. As the replica disk 22 rotates, portions where the grooves 12 are present and portions where the grooves 12 are not present alternately appear, and the magnitude of the reflected light changes. By detecting this, the above-mentioned A signal similar to that of the bright and dark checkered stripes 1o of the conventional pulse disk 3 can be extracted. As this signal detection system, for example, a system for detecting reflected light as shown in FIG. 7 is used. Laser light 5 from the semiconductor laser 4 is focused on the replica disk 22 via the collimator lens 6 and the condensing lens 7, and the five laser beams reflected from the disk surface of the replica disk 22 are reflected on the optical path by the half mirror 26. The light is bent, focused by a condensing lens 7, and guided to a photodetector 8.

As another example, a replica disk 2 as a scale plate
If 2 is made of a metal plate on which the grooves 12 have been transferred, the unevenness of the metal reflective surface allows the signal to be extracted without being extracted.

Further, as another embodiment, it is also possible to use a system for detecting reflected light as shown in FIG.

In this case, a stamper 21 shown in FIG. 5 (hl) is formed using transparent 8A resin, and the stamper 21 shown in FIG.
The reflection made of the gold film shown in [13] is not formed;
It is used as a replica disk 22 made of a transparent scale plate. Laser light 5 from the semiconductor laser 4 is focused and irradiated onto the replica disk 22 via the collimator lens 6 and the condensing lens 7, and when it hits the uneven grooves on the disk surface of the replica disk 22, the uneven grooves form a diffraction grating. Works as a laser beam 5
The transmitted light is O-order light 27. It is separated as ±1st order light 28.29. Therefore, by rotating the replica disk 22, the area where the groove exists and the area where the groove does not exist can be
The magnitude of the order light 27 changes, and by receiving this O order light 27 with the photodetector 8, this can be detected as a change in amplitude.

In the above explanation, we have described the action of the replica disk 220 of the optical encoder that detects the amount of rotational displacement, but the same principle can also be applied to the optical linear encoder that detects the displacement i: of distance on a straight line. It is clear that this can be done. Referring to FIG. 9, an example thereof will be described. As shown in the figure, a scale plate 28 having a large number of uneven grooves 12 formed on its surface is formed into a linear shape and is fixed to a fixed end.

An optical system including a semiconductor laser is held by a moving object and moves in a straight line, and the circular spot light 11 of the laser light that simultaneously irradiates the plurality of grooves 12 moves in the direction shown by the arrow A in the figure. Using the same principle as the optical rotary encoder, linear displacement can be converted into pulses and detected.

Further, as another embodiment, the above described method uses a method of reading the amount of displacement by counting the number of pulses from one laser beam 50 and circular spot light 11, but generally an optical method is used. In many cases, an encoder is provided with two phases, A phase and B phase with 90° different phases, and two phases for detecting the reference position, and the scale plate in this invention also has two phases.
A phase can be provided. FIG. 10 shows a case where this embodiment is applied to an optical rotary encoder.

A circular spot light focused by a semiconductor laser is
This can be achieved by receiving reflected light or transmitted light with a photodetector as a signal of circular spot lights 30, 31, and 32 of A phase, B phase, and two phases, respectively. The two-phase spotlight 32 can generate a reference signal once every - cycle. 33 is a 2-use groove, and this 2-phase groove 33 is
A signal can be detected by a two-phase circular spot light 32, which is provided to indicate a reference position once per rotation from a large number of grooves 12.

As described above, the optical encoder of the present invention has an extremely high resolution because it is configured using a scale plate formed of a large number of concave or convex grooves.
This provides an excellent effect in that a highly reliable optical encoder can be easily obtained at low cost.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing a schematic configuration of an optical rotary encoder that detects rotational displacement ik using a conventional semiconductor laser, and Fig. 2 (+l) and (b)! -t, 1st I￥
A partial plan view showing a pulse disk applied to the optical rotary emitter of No. 1 and an enlarged sectional view of A-AM thereof, Fig. 3 (a) to d) fi, Mouse Fig. 2 (a) and ( b
Figure 14 (al and (b)) is a partial plan view showing a pulse disk applied to an optical encoder which is one embodiment of the present invention ff+, +, and a partial plan view thereof. The enlarged sectional view of B-B@, Fig. 5 (a) to i) is each explanatory diagram showing the manufacturing process of the pulse disk of Fig. 4 (a) and (b), and Fig. 6 (a) is not shown. Shikuel
a, each explanatory diagram showing the principle of signal detection from a pulse disk applied to the optical encoder of the present invention, FIGS. 7 and 8
Figure 9 shows the scale plate applied to the optical +7 near encoder which is another embodiment of the present invention. Figure 1 is a partial plan view showing a scale plate used in an optical rotary encoder Km which is another embodiment of the present invention. ... Rotating shaft, 3... Pulse disk, 4... Semiconductor laser, 5.
17... Laser light, 6... Collimator lens, 7.
...Condenser lens, 8...Photodetector, 9.14 Glass disk, l. ...Bright and dark checkered stripes, 11, 30, 31.32 Spot light, 12...Groove, 13...Reflection film, 15...Positive photoresist, 16...Disc, 18...Exposed part,
19... Gold IKM, 20... Master, 2 toss tambour, 22- Replica disc, 23.25 - Reflected light, 2
4. Area part, 26. Half mirror-227-0th order light,
28.29・11th order light, 33・Z phase groove. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Daikun Masuo Figure 1 Figure 2 (a) (0) 0 Figure 3 II+! Light Dark Funeral Figure 4 (0) Figure 5 (9) 1 piece, □20 5th μm□]〒- (i) γ℃2:=R71 Husband A-A-Duni 5 (b) 13 ; 21 22. 13 22 7 3 22 (c) Figure 9 2nd Figure 10 0

Claims (1)

[Claims] txt Thrift is formed by a collection of many concave or convex grooves having a constant pitch, a width of 1/2 to 1/3 of the pinch, and a depth of about the wavelength of light. a scale plate, a light source, a first optical system that focuses the light from the light source so as to irradiate a predetermined number of the groove areas, and optically detects the light reflected or transmitted from the scale plate. a second optical system that guides the
Optical type 1 characterized in that it comprises the above-mentioned photodetector.
encoder. (2) The light according to claim 1, wherein the scale plate is made of a transparent material. Academic encoder. (3) The optical encoder according to claim 1, wherein a reflective film is formed on the surface of the concave or convex groove formed on the scale plate. (4) The optical encoder according to claim 1, wherein the scale plate is made of metal.