JPH0612268B2 - Optical encoder - Google Patents

Description

The present invention relates to an optical encoder that uses a semiconductor laser to detect a rotational or linear distance displacement amount.

A conventional optical encoder of this type is shown in FIG. FIG. 1 is a perspective view showing a schematic configuration of an optical rotary encoder for detecting a rotational displacement amount using a conventional semiconductor laser. In the figure, 1 is ball pairing, 2 is a rotary shaft supported by a ball bearing 1,
3 is a pulse disk attached to the rotating shaft 2, 4 is a semiconductor laser as a light source, 5 is laser light radially generated from the semiconductor laser 4, 6 is a collimator lens for making the laser light 5 parallel, and 7 is a laser. A condenser lens for condensing the light 5 into a size of several μm, and 8 is a photodetector for detecting a change in the amount of light transmitted through the pulse disk 3, and this photodetector 8
For this, for example, a photodiode is used.
Further, as shown in FIGS. 2 (a) and 2 (b), the pulse disk 3 is
Usually, a glass disk 9 is used, and a chromium vapor deposition film which is a bright and dark lattice stripe 10 is provided on the glass disk 9 by patterning by etching.

Next, the operation of FIG. 1 will be described. When the rotation is transmitted to the rotary shaft 2 from the outside, the pulse disk 3 on which the bright and dark lattice stripes 10 are engraved is rotated, and the amount of the laser beam 5 transmitted through the pulse disk 3 changes. The changing amount,
If detected by the light detector 8, the amount of rotational displacement can be known. The laser light 5 is emitted from the semiconductor laser 4 with an intensity of about 1 to 3 mW, but since it is generated radially as shown in FIG. 1, it is collimated by the collimator lens 6 and collimated by the condenser lens 7. The light is condensed to a small size of about 2 to 10 μm and is irradiated on the bright and dark lattice fringes 10 of the pulse disk 3. Now,
As shown in FIG. 3 (a), the laser light 5 focused on the small circular spot light 11 of about 2 to 5 .mu.m is the bright and dark lattice stripes 1.
When it crosses 0, output signals having waveforms as shown in FIGS. 3 (b) and 3 (d) are generated. When the period (pitch) of the bright and dark lattice fringes 10 is large, the generated output signal has a waveform close to the rectangular wave shown in FIG. 3 (b), but the period (pitch) of the bright and dark lattice fringes 10 becomes small and the bright and dark lattice fringes 10 have a small waveform. When the width of the laser beam and the diameter of the circular spot light 11 of the laser beam 5 become substantially equal, the generated output signal has a sinusoidal waveform as shown in FIG. 3 (d).
Further, when the width of the bright and dark lattice fringes 10 becomes smaller than the diameter of the circular spot light 11 of the laser light 5, the amplitude of the generated output signal becomes small, and finally the bright and dark lattice fringes 10 cannot be detected. Therefore, if the width of the bright and dark lattice stripes 10 becomes smaller, the diameter of the circular spot light 11 of the laser light 5 must be made smaller. For example, when the pulse disk 3 having a diameter of 50 mm for generating 10,000 pulses is made, the width of the bright and dark lattice fringes 10 is about 7 μm, so that the diameter of the circular spot light 11 of the laser light 5 is about 7 μm or less. good.

In the case of an optical rotary encoder, the detection accuracy is the dimensional accuracy of the bright and dark lattice stripes 10 of the pulse disk 3 or the pulse disk 3
It is determined by the deviation (eccentricity) between the center of rotation and the center of rotation.
For this reason, the dimensional accuracy of the bright and dark lattice stripes 10 of the pulse disk 3 becomes more severe as the number of pulses increases, and for example, 10
In the case of 000 pulses, in order to keep the detection accuracy within 5%, the placement accuracy of the width of the bright and dark lattice fringes 10 must be suppressed within 3 seconds. For that purpose, in the method of producing the chromium vapor deposition film which is the light and dark lattice stripes 10 on the conventional glass disk 9 shown in FIGS.
Under the controlled conditions, one pulse disk 3 has to be patterned by electron beam exposure and manufactured by etching, which is disadvantageous in that the cost is increased.

The present invention was made to eliminate the above-mentioned drawbacks of the conventional ones, and the groove or undulation has a constant cycle, the width is 1/2 to 1/3 of this cycle, and the depth is the wavelength of light. 1/8 to 3/8 is a scale plate formed by a collection of a large number of concave grooves or a large number of convex undulations, a light source, and the light from the light source, and a predetermined number of the grooves or undulations. A configuration including a first optical system that collects light so that it can be irradiated onto an area, a second optical system that guides light reflected or transmitted from the scale plate to a photodetector, and the photodetector. It is intended to provide an optical encoder that has a low cost and high reliability, and is manufactured by molding the scale plate.

Embodiments of the present invention will be described below with reference to the drawings. Fig. 4
(a) And (b) is the one part plan view which shows the pulse disk applied to the optical encoder which is one Example of this invention, and the expanded sectional view of the BB line. In the figure, 11 is spot light, 12 is a groove formed in the pulse disk 3 as a scale plate, and 13 is a reflective film made of a metal film. Groove 12
Corresponds to a concentric circle or spiral continuous groove angle-divided according to the number of pulses. A series of grooves arranged in the radial direction of the pulse disk 3 is shown in FIG. 2 (a). It corresponds to one of the bright and dark checkered patterns 10. Therefore, the length of each groove changes depending on the size of the angle divided according to the number of pulses, and becomes shorter as it goes toward the center of the pulse disk 3. The depth d of the groove is about 1/4 of the laser wavelength used, and the period P of the groove is about 1.6 to 2 μm.
The width W of the groove may be set to 1/3 to 1/2 of the period P. As the reflection film 13 made of a metal film, a metal having high reflectance and good stability such as Cr or Al may be used.

Next, a manufacturing process of the pulse disk 3 having the groove 12 will be described with reference to FIGS. 5 (a) to (i). Fifth
As shown in FIG. 3A, a positive photo resist 15 is evenly applied on the glass disk 14 to a thickness of a quarter of the wavelength of the semiconductor laser used to form a disk 16. As the positive photoresist 15, for example, one having a large resolving power such as AZ1350 is used. As shown in FIG. 5 (b), the disc 16 is exposed to the laser beam 17 while being rotated at a constant speed. Here, an argon laser is used as the laser light 17, and spot light having a diameter of about 1 μm or less is made by the condenser lens 7 to irradiate the surface of the positive photoresist 15. At this time,
The laser beam 17 moves the irradiation position at a constant speed in the radial direction indicated by the arrow on the disk 16 while repeatedly turning on and off as many times as the number of pulses required for the pulse disk while the disk 16 makes one rotation. . Further, the timing of turning the laser light 17 on and off needs to be synchronized with the rotation of the disk 16. As shown in FIG. 5 (c), when the portion 18 exposed by the laser beam 17 is developed, FIG. 5 (d)
As shown in FIG. 4, only the exposed portion 18 melts to form the groove 12, and the arrangement is as shown in FIGS. 4 (a) and 4 (b). A replica is produced using the disc 16 thus produced as a master disc, and this replica is used as a pulse disc. Fig. 5 (e)
As shown in Fig. 5, a metal film 19 such as Ag is deposited on the surface of the master, and Ni plating is performed using this metal film 19 as an electrode, and as shown in Figs. 5 (f) and 5 (g), The master 20 is produced by peeling it off. As shown in FIG. 5 (h), several stampers 21 are produced from this master 20. Using this stamper 21, grooves are transferred to a plastic (PMMA, polycarbonate, etc.) by compression molding and injection molding, and a large number of replica disks 22 as shown in FIG. 5 (i) are manufactured. A metal film is formed on the surface of the replica disk 22 by vapor deposition or sputtering, and this is used as the reflection film 13. In order to protect the reflective film 13, this reflective film 1
You may provide a protective film on 3. Further, as a method of transferring the groove 12, there is also a method of applying an ultraviolet curable resin to a plastic plate or a glass plate, pressing the stamper 21 and curing the resin by irradiation of ultraviolet rays. Pulse disk 3 used as a scale plate, that is, replica disk 22
Can be manufactured in a large amount by molding as described above, and it is not necessary to perform etching processing one by one as in the conventional case.

Next, the replica disk 22 which is the pulse disk 3 of the present invention.
Figure 6 (a) to (c) for the method of detecting the signal from the
Will be explained. As shown in FIG. 6 (a), the laser light 5 radiated to the disk surface of the replica disk 22 through the condenser lens 7 causes the reflected light to return to its original optical path in the portion where the groove 12 does not exist. Come on. However, Figures 6 (b) and (c)
As shown in FIG. 5, in the portion where the groove 12 is present, the reflected light 23 from the bottom surface of the groove 12 causes a phase difference with the reflected light 25 from the area portions 24 on both sides of the groove 12 and interferes with each other. When the depth of the groove 12 is set to a quarter wavelength, each reflected light 23,
The phase difference of 25 becomes a half wavelength and cancels each other, and the reflected light passing through the condenser lens 7 becomes the minimum. Even if the groove depth is not a quarter wavelength, for example, a quarter wavelength, there is a quarter wavelength phase difference between the two reflected lights 23 and 25. Compared with the reflected light from the flat portion shown in (b), the reflected light from the portion having the groove shown in FIG. The depth of the groove is ⅛ centering on ¼ wavelength
The intensity of the reflected light can be detected if the wavelength is about ⅜ wavelength. Further, if the width W of the groove shown in FIG. 4 (b) is too wide, the amount of reflected light 25 shown in FIG. 6 (c) will decrease,
On the other hand, if the width is too narrow, the amount of the reflected light 23 decreases, so the width W of the groove should be selected to be ⅓ to ½ of the period. When the replica disk 22 is rotated, portions where the grooves 12 are present and portions where the grooves 12 are not present appear alternately, and the magnitude of the reflected light changes. Therefore, by detecting this, the above-described conventional disc Bright and dark checkered pattern 1 of pulse disk 3
A signal similar to 0 can be taken out. As this signal detection system, for example, a system for detecting reflected light as shown in FIG. 7 is used. The laser beam 5 is emitted from the semiconductor laser 4 via the collimator lens 6 and the condenser lens 7 to the replica disk 22.
The laser light 5 that is focused and irradiated on the replica disk 22 and reflected from the disk surface of the replica disk 22 has its optical path bent by the half mirror 26, is focused by the focusing lens 7, and is guided to the photodetector 8.

As another example, a replica disk 2 as a scale plate
When 2 is made of a metal plate having the groove 12 transferred, a signal can be taken out by the unevenness of the metal reflection surface.

As another embodiment, a system for detecting reflected light as shown in FIG. 8 can be used. In this case, the stamper 21 shown in FIG. 5 (h) is formed of transparent resin, and the transparent resin surface is not formed with the reflection film 13 made of the metal film shown in FIG. 5 (i). It is used as a replica disk 22 made of a transparent scale plate. When the replica disk 22 is focused and irradiated with the laser light 5 from the semiconductor laser 4 through the collimator lens 6 and the condenser lens 7, and hits the concave and convex grooves on the disk surface of the replica disk 22, the concave and convex grooves form the diffraction grating. And the transmitted light of the laser light 5 is separated as 0th-order light 27 and ± first-order lights 28 and 29. Therefore, by rotating the replica disk 22, the size of the 0th-order light 27 changes between the portion where the groove is present and the portion where the groove is not present, and the 0th-order light 27 is received by the photodetector 8. This can be detected as a change in amplitude.

In the above description, the operation of the replica disk 22 of the optical encoder for detecting the rotational displacement amount has been described, but the same principle can be applied to the optical linear encoder for detecting the displacement amount of the linear distance. It is clear that An embodiment will be described with reference to FIG. As shown in the figure, the scale plate 28 having a large number of concave and convex grooves 12 formed on its surface is formed in a linear shape and fixed to a fixed end. An optical system including a semiconductor laser moves on a straight line while being held by a moving object, and circular spot light 11 of laser light that irradiates a plurality of grooves 12 at the same time moves in a direction indicated by an arrow A in the drawing. The linear displacement amount can be pulsed and detected by the same principle as that of the optical rotary encoder.

Further, as another embodiment, the above-mentioned one describes the case of reading the displacement amount by counting the number of pulses of the circular spot light 11 of one laser light 5, but in general, the optical encoder In many cases, an A phase and a B phase having different 90 ° phases and a Z phase for detecting a reference position are often provided.
Phases can be provided. FIG. 10 shows a case where this embodiment is applied to an optical rotary encoder.
Circular spot light focused by a semiconductor laser
This can be achieved by individually providing each of the circular spot lights 30, 31, and 32 of the A phase, B phase, and Z phase, and receiving reflected light or transmitted light with a photodetector. The Z-phase spot light 32 can extract the reference signal once per revolution. 33 is a Z-phase groove, and this Z-phase groove 33 is
It is provided to indicate a reference position once per one rotation from a large number of grooves 12, and a signal can be detected by the spot light 32 having a circular shape of Z phase.

As described above, according to the optical encoder of the present invention, a configuration is adopted in which a scale plate formed by a flat surface portion and a large number of concave groove groups or a large number of convex undulations is applied. Light intensity weakens due to interference or diffraction of light on the uneven surface, and there is a difference in light intensity between the reflected light from the flat surface and the transmitted light. The strength and weakness can be obtained and extremely high resolution can be obtained, and since the above scale plate is manufactured by molding processing, a large amount of high quality scale plate can be obtained at low cost, and as a result, low cost and high quality optical This has an excellent effect of obtaining a rotary encoder.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of an optical rotary encoder for detecting a rotational displacement amount using a conventional semiconductor laser, and FIGS. 2 (a) and 2 (b) are optical rotary encoders of FIG. FIG. 3 (a) to FIG. 3 (d) is a partial plan view showing a pulse disk applied to
(A) and (b) each explanatory view showing the operation mode of the pulse disk,
FIGS. 4 (a) and 4 (b) are a partial plan view showing a pulse disk applied to an optical encoder according to an embodiment of the present invention, an enlarged sectional view taken along line BB thereof, and FIG. a) to (i) are
FIGS. 4 (a) and 4 (b) are explanatory views showing the manufacturing process of the pulse disk, and FIGS. 6 (a) to 6 (c) are signal detection from the pulse disk applied to the optical encoder of the present invention. FIGS. 7 and 8 are explanatory diagrams showing the principle, FIGS. 7 and 8 are explanatory diagrams showing a signal detection system of an optical encoder which is another embodiment of the present invention, and FIG. 9 is another embodiment of the present invention. Partial plan view showing a scale plate applied to an optical linear encoder,
The drawing is a partial plan view showing a scale plate applied to an optical rotary encoder which is another embodiment of the present invention. In the figure, 1 ... ball bearing, 2 ... rotating shaft,
3 ... Pulse disk, 4 ... Semiconductor laser, 5, 17 ...
Laser light, 6 ... Collimator lens, 7 ... Focusing lens, 8 ... Photodetector, 9, 14 ... Glass disk, 10 ...
... bright and dark lattice stripes, 11, 30, 31, 32 ... spot light, 12 ... groove, 13 ... reflection groove, 15 ... positive photoresist, 16 ... disk, 18 ... exposed portion, 1
9 ... Metal film, 20 ... Master, 21 ... Stamper, 22 ... Replica disk, 23, 25 ... Reflected light, 2
4 ... area portion, 26 ... half mirror, 27 ... 0th order light, 28, 29 ... ± 1st order light, 33 ... Z phase groove. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mutsuo Hirai 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Sanryu Electric Co., Ltd. Applied Equipment Research Laboratory (72) Kazuro Nishi Nishi 8-chome Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture No. 1-1 Sanryo Electric Co., Ltd., Applied Equipment Research Laboratory (56) Reference JP-A-58-135405 (JP, A)

Claims (4)

[Claims] 1. A groove or undulation has a constant cycle and a width of the cycle.
1/3 to 1/2, the depth is 1/8 to 3/8 of the wavelength of light, and a group of a large number of concave grooves or a large number of convex undulations and flat portions are formed alternately. A scale plate formed by molding into a shape, a light source, a first optical system for condensing light from the light source so that a predetermined number of grooves or undulating regions can be irradiated, and reflection from the scale plate Alternatively, an optical encoder comprising a second optical system for guiding the transmitted light to a photodetector and the photodetector. 2. The optical encoder according to claim 1, wherein the scale plate is formed of a transparent body. 3. The optical encoder according to claim 1, wherein a reflective film is formed on the surface of the concave groove or the convex undulation formed on the scale plate. 4. The optical encoder according to claim 1, wherein the scale plate is made of metal.