JP2567934B2 - Rotation detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a rotation detection device for detecting the position or speed of a rotating body in order to control the rotational position or speed by an electric motor or the like.

(Prior Art) The third conventional rotation detection device is
A method called an optical pulse encoder shown in the figure is typical. A disk is recorded with a rotary slit 31 in which light-transmitting portions and light-shielding portions in the circumferential direction are alternately arranged with the same width.
It is composed of 30 and a detector 40 that optically reads the rotation of the rotary slit, and the disk 30 is coupled to a rotating body (rotated detection body, not shown) whose rotation is desired to be detected. The detector 40 includes a light source 41 such as a light emitting diode, a fixed slit 42 for detection, and a phototransistor 43 that converts an optical signal into an electric signal. When the disk 30 rotates and the permeation part of the rotary slit 31 and the fixed slit 42 for detection match, the phototransistor 43 of the light from the light source 41 arrives, and the light from the light source 41 when the transmission part and the blocking part of each match. Will not reach the phototransistor 43. The movement of the rotary slit recorded on the disk in this way makes the intensity of the light reaching the phototransistor 43 from the light source 41, and the phototransistor 43
Is converted into an electric signal.

1 to rotate the disk by the amount corresponding to one slit
It is called a pulse encoder because it can obtain a pulse-shaped electric signal with a varying size. With this basic configuration, the same electrical signal will be generated in both forward and reverse rotations, so two sets of detectors with fixed slits for detection that are shifted by 1/4 of the slit interval are used to identify the rotation direction. Optical two-phase pulse encoders that are capable of obtaining two-phase electrical signals are often used. Further, the pulse encoder is provided with a zero position detector that can generate a pulse only once per rotation because it can detect a relative position from the number of pulses but cannot detect an absolute position.

As such a pulse encoder, a magnetic pulse encoder using a magnetic slit recorded by alternately magnetizing an S pole and an N pole on a magnetic disk is also used, but an optical pulse encoder uses a slit. The number of pulses per rotation can be increased, that is, the resolution can be increased.

(Problems to be solved by the invention) Recently, in driving a robot or the like, conventionally, the rotation of a servomotor was driven by decelerating the rotation of the gear, but it is possible to remove the gear and directly drive the servomotor (direct drive). Attention has been paid. Play with gear,
There is no decrease in rigidity, and high-precision and fast operation is possible. The servomotor used for such a direct drive rotates at a very low speed, and the rotation control of this motor requires a rotation detecting device having a high resolution, which is equivalent to deceleration of the gear as compared with a case with a gear.

Even in the optical pulse encoder, when the slit spacing is several tens of μm or less, the effect of the diffraction phenomenon of light cannot be ignored, and the spacing between the rotary slit and the fixed slit for detection must be very close to each other. The mechanical assembly of is very difficult. As a disc with a diameter of 10 cm, it has about 6,000 slits with a slit interval of 50 μm.

On the other hand, as a method of recording data at a very high density using a rotating disk, it is called an optical disc method used for a CD (compact disc) for recording music and an LD (laser disc) for recording video. There is a way. This is a method of optically reading pits recorded on a disk with a laser beam. Figure 4 shows the principle of CD (compact disc). Reference numeral 50 is a part of a CD (compact disc), which is enlarged and shown. Width of about 0.5 μm and depth of about 0.11 μm called a pit 52 on one side of the disk of transparent plastic 51.
4 is engraved (FIG. 4 is a view seen from the side opposite to the surface with the pits, so that it can be seen protruding), and a reflecting mirror film 53 is attached to the surface. Furthermore, a protective film 54 is provided on the outer side.
Is attached. The laser light having a wavelength of about 0.78 μm emitted from the laser diode 11 of the photodetector 10 (called an optical pickup) for reading the pit 52 passes through the beam splitter 12 and becomes parallel light by the collimator lens 13.
Further, the disk is irradiated through the objective lens 14 from the side opposite to the surface where the pid 52 is present. The laser light is adjusted by the objective lens 14 in the photodetector 10 so as to be focused at the pit position, and the diameter of the laser light beam 15 at the pit position is narrowed to about 1.4 μm. This laser light is reflected by the reflection film 53.
The light is reflected by, passes through the objective lens 14 and the collimator lens 13 in the photodetector 10, is changed in direction by the beam splitter 12, and is guided to the photodiode 13 to be converted into an electric signal. When the laser light hits a place without the pit 52, most of the laser light is reflected and a large electric signal is obtained. When the laser light hits the pit 52, the width of the pit is less than half the beam diameter of the laser light, so the laser light reflected from the pit and the laser light reflected from outside the pit are combined. Return to photodetector 10.
The optical path difference between the reflected laser light from the pit portion and the reflected laser light from outside the pit is twice the pit depth.
The depth of the pit 52 is 1 / wavelength of the laser light in the plastic.
Since it is selected as 4, the reflected laser light from the pit part and the reflected laser light from the outside of the pit have a 180 ° phase difference, and they interfere and cancel each other. Therefore, the amount of laser light returning to the photodetector 10 is greatly reduced, and the obtained electric signal is also small. In this way, the presence or absence of the pit 52 is converted into the magnitude of the electric signal and read. The pits are lined up one after another on the circumference and spirally arranged at a radial pitch (track pitch) of 1.6 μm, and a very large number of pits are recorded on the disk. With the large number of these pits, music data is recorded with the presence or absence of pits and the shortest combination thereof, and the music is reproduced by reading the data. According to the CD (Compact Disc) standard, the minimum pit length and the length between pits is 0.9 μm. Therefore, a maximum of approximately 17
It has the potential to record 10,000 pits.

If this technology is used, it is possible to construct a high-resolution rotation detection device, or it is necessary to perform tracking in the radial direction (tracking) so that the laser beam accurately hits a narrow pit, It requires a mechanism for moving the objective lens in the radial direction, which has the drawback of complicating the structure. Further, since the rotation detector is used by being attached to an electric motor or the like, there is a possibility that tracking cannot be performed due to the influence of vibration, and it is difficult to improve reliability.

The present invention has been made in consideration of the above points, and an object of the present invention is to obtain a rotation detection device having a high resolution, a simple structure, and a high reliability by using the technique of an optical disk.

[Structure of the Invention] (Means for Solving the Problems) According to the present invention, a rotating disk having slits in which irregularities having substantially equal widths are radially engraved is recorded on one surface, and a laser beam is read through the slits. It is composed of a photodetector, and the width of the concave portion and the convex portion forming the slit is made substantially equal to or wider than the beam diameter of the laser light of the photodetector.

(Operation) In the rotating disk of the rotation detecting device of the present invention, the unevenness has a slight width in the circumferential direction, but the slits of sufficient length are formed in the radial direction. There is no need for a tracking function in the radial direction, and there is no concern that reading will fail because tracking cannot be performed due to vibration or the like.

Also, when the rotating disk rotates and the beam of laser light emitted from the photodetector reaches the position of the boundary between the concave and convex portions of the slit, reflected light from both the concave and convex portions is generated. Interfere with each other, the laser light hardly returns to the photodetector, and the obtained electric signal is small. On the other hand, when the beam of laser light reaches the center of the concave or convex portion of the slit, most of the laser light is reflected by either the concave or convex portion and returns to the photodetector. The electric signal sent is also large. The slit interval can be reduced, a large number of slits can be recorded, and when the rotating disk rotates by one slit, two cycles of electric signals can be obtained, and a rotation detector with extremely high resolution can be realized.

(Embodiment) FIG. 1 is a configuration diagram of a first embodiment of a rotation detecting device of the present invention. Reference numeral 10 is a photodetector, and 20 is a rotating disk, which is roughly divided into two parts. A part of the rotating disk 20 is shown enlarged for the purpose of explanation. The photodetector 10 has the same structure as a photodetector (optical pickup) of an optical disc such as a CD (compact disc), 11 is a laser diode, 12 is a beam splitter, 13 is a collimator lens, and 14 is a collimator lens.
Is an objective lens, 15 is a beam of laser light, and 16 is a photodiode. The rotating disk 20 is coupled to a rotation shaft of a rotation detection body (not shown) and rotates with the rotation of the rotation detection body. Reference numeral 21 is plastic, 22 is a slit, 23 is a reflective film, and 24 is a protective film. The slit 22 has a radial depth of 0.11 μm and a width of 1.1 on one side of the plastic 21 of the rotating disk.
3 μm recesses of appropriate length (Fig. 1 is a view seen from the reflection side of the surface with slits, so the part that can be seen protruding) are spaced at 2.6 μm intervals (the remaining protrusions are 1.3 μm), and the It is a slit with irregularities made by attaching a reflective film 23 to the irregular surface.

The laser light having a wavelength of about 0.78 μm emitted from the laser diode 11 of the photodetector 10 passes through the beam splitter 12,
The collimator lens 13 collimates the light, and the collimator lens 13 irradiates the rotating disk 20 through the objective lens 14 from the reflection side of the surface having the slit 22. The laser light is adjusted by the objective lens 14 so as to be focused at the position of the slit 22, and the diameter of the laser light beam 15 at the position of the slit 22 is about 1.4 μm.
It is squeezed. This laser light is reflected by the reflection film 23, returns to the photodetector 10, passes through the objective lens 14, the collimator lens 13, and is changed in direction by the beam splitter 12.
It is guided to the photodiode 16 and converted into an electric signal.
When the center of the laser beam 15 is aligned with the boundary between the concave portion and the convex portion of the slit 22, half of the laser light is reflected by the concave portion, and the other half is reflected by the convex portion. The light is synthesized and returned to the photodetector 10. The optical path difference between the reflected laser light from the concave portion and the reflected laser light from the convex portion is twice the depth of the concave portion. Since the recess depth of 0.11 μm is selected to be 1/4 of the wavelength of the laser light in the plastic 21, the reflected laser light from the concave portion and the reflected laser light from the convex portion are 18
They are 0 ° out of phase and interfere with each other to cancel each other out. Therefore, the amount of laser light returning to the photodetector 10 is greatly reduced, and the electric signal obtained from the photodiode 16 is also small. When the center of the beam 15 of the laser light is aligned with the center of the projection or recess of the slit 22, the width of the recess or projection of the slit is 1.3 μm, which is almost equal to the beam diameter of the laser light of 1.4 μm. The laser light is reflected by the concave portion or the convex portion and returns to the photodetector 10, and a large electric signal is obtained from the photodiode 16. In this way, the slit
The unevenness forming 22 can be converted into a magnitude of an electric signal and read by the photodetector 10. The boundary between concave and convex is 1
Since there are two positions for the set of slits, the strength signal is obtained twice each time the slit 22 rotates by the slit interval (2.6 μm) by the rotation of the rotary disk 20.

If the beam diameter of the laser light is 1.4 μm, the rotating disk 20
If the width of the concave and convex parts of the slit is 1.4 μm or more,
A larger amplitude electrical signal is obtained from the photodetector 10.
However, if the width of the convex portion and the concave portion is widened, the number of slits engraved on the circumference of the rotating disk is reduced, and the resolution as a rotation detection device cannot be increased. The width of the convex portion and the concave portion is 1.3 μm, which is slightly narrower than the beam diameter of the laser light. About 210,000 slits can be carved on a rotating disk with a diameter of 10 cm, and an electrical signal of about 420,000 cycles can be obtained per rotation. Also, it is difficult to make the slit shape into a perfect rectangle as shown in the figure,
Since the reflection of the laser light at the concave portion and the convex portion changes depending on the shape, when the beam of the laser light arrives at each position, the magnitude of the electric signal obtained from the photodetector differs. By slightly changing the widths of the concave portion and the convex portion, the magnitude of this electric signal can be made equal.

As described above, according to the embodiments of the present invention, it is possible to obtain a very high-resolution rotation detecting device using the technology of optical disks such as CD (compact disk) and LD (laser disk). By using the slits formed by the unevenness and the reflection film similar to the pits in the optical disk, the tracking in the radial direction is not required, the structure is simplified, and the reliability of the rotation detection device is significantly improved. Further, by making the widths of the concave portion and the convex portion forming the slit substantially equal to each other and making the width approximately equal to or wider than the beam diameter of the laser light, the rotary disc rotates from the photodetector by a distance corresponding to one slit. Each time, an electric signal whose amplitude greatly changes twice is obtained,
It can be reduced to about 2.6 μm, and a rotation detection device with a resolution higher than that of conventional optical pulse encoders by one digit or more can be obtained.

FIG. 2 is a block diagram of a second embodiment of the present invention. 10 is a photodetector and 20 is a rotating disk. The photodetector 10 is the same as that of the first embodiment shown in FIG. The rotating disk 20 is also the first
The same configuration as the embodiment of, but the slit 22 has a radial height of 0.11μ on one surface of the plastic 21 of the rotating disk.
m, 1.3 μm wide with appropriate length of “convex part” (Fig. 2 is a view seen from the side opposite to the surface with slits, so it looks concave) with a gap of 2.6 μm (the remaining convex part is 1.3 μm is there.)
It is made by engraving with, and attaching an opposite film 23 to the uneven surface. Although the method of forming the slits of the rotary disk is different, the width of the unevenness is 1.3 μm, and the same operation and effect as in the first embodiment can be obtained.

In addition, as an example of the present invention, an example of the same configuration as a CD (compact disc) or an LD (laser disc) in which a transparent disc is engraved with transparent plastic on a rotating disc and a reflective film is attached to the surface thereof is explained. It is also possible to have a structure in which irregularities are engraved on the disk and reflected directly. In addition, laser light is allowed to pass through the rotating disk without attaching a reflective film, and the phase of the transmitted laser light changes due to the unevenness (thickness difference) engraved on the rotating disk, which causes interference, A configuration may be used in which the intensity of the transmitted laser light is read by a photodetector.

In order to manufacture these rotary disks of the rotation detector of the present invention, almost the same method as that for manufacturing a CD (compact disk) or an LD (laser disk) can be used. For a CD (compact disc), first make a master. Photoresist material is applied to a disk such as glass whose surface has been polished to a uniform thickness, and while rotating this disk, the laser light beam focused by a lens to about 0.5 μm is intermittently applied according to the pit pattern to be recorded. Irradiation. At the same time, the laser light beam is moved in the radial direction at a rate of 1.6 μm in the pitch (track pitch) of the pits in the radial direction for one rotation of the disk. A pit pattern is engraved as an exposure mark on the photoresist material of the disk. When this phenomenon occurs, the photoresist material in the portion corresponding to the pit is removed, and the pit appears as a concave portion to complete the master.

After plating a metal such as nickel on this master, the master is removed to make a master mold (stamper). Using this mold (stamper), plastic is molded by injection molding or the like to make a replica having the same unevenness as the master. Aluminum or the like is vapor-deposited on this uneven surface and a reflective film is attached. Furthermore, a CD (compact disc) is completed by attaching a plastic protective film.

In order to make a master of the rotating disk of the present invention, intermittent irradiation of a laser light beam is applied to a disk, such as a glass whose surface is polished, with a photoresist material applied in a uniform thickness, at a constant frequency. The number of revolutions obtained by dividing the intermittent frequency is controlled to synchronize the intermittent frequency of the laser light beam with the rotational speed of the disk. The movement of the laser light beam in the radial direction is extremely small (about 0.1 μm). Therefore, the disk is irradiated with a laser light beam on the circumference of the disk at a constant number of intervals, which is the ratio of the intermittent frequency to the number of revolutions. When the disk makes one revolution, it is slightly (about 0.1 μm) in the radial direction at almost the same position. ) Is irradiated at a position shifted by only. Since this radial deviation is small with respect to the laser light beam diameter (about 0.5 μm), it is connected in the radial direction, and by repeating this, a radial slit is formed as an exposure mark with respect to the center of the disk. The width of the slit can be controlled by controlling the interruption time of the laser light beam. By developing this, a master having slits formed by unevenness is completed. By changing the characteristics (negative or positive) of the photoresist material, it is possible to reverse the concavo-convex relationship.

It is possible to manufacture a large number of rotary discs of the rotation detection device at low cost by duplicating this original disc in the same manner as a CD (compact disc).

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain a highly reliable and highly reliable rotation detection device that uses the technology of optical disks such as CD (compact disk) and LD (laser disk). Eliminating the need for tracking in the radial direction, which was necessary in high discs,
The structure is simplified and the reliability of the rotation detection device is greatly improved. In addition, by appropriately selecting the relationship between the width of the concave and convex portions forming the slit and the beam diameter of the laser light,
An electric signal whose amplitude greatly changes twice each time the rotating disk rotates by the amount corresponding to the slit spacing can be obtained, and the slit spacing can be reduced to about 2.6 μm, which is a single digit compared to conventional optical pulse encoders. The above high resolution can be obtained. In addition, most of the basic constituent elements of the present invention are suitable for an optical disk, and a rotary disk can be mass-produced similarly to an optical disk, and a high-resolution, highly reliable, and inexpensive rotation detection device can be realized.

Similar to the conventional optical pulse encoder, it is easy to provide a plurality of photodetectors so as to generate a two-phase pulse or a pulse once for one rotation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, and FIG. 3 is a block diagram of a conventional optical rotation detection device (optical pulse encoder). FIG. 4 is a block diagram of a CD (compact disc) of a technique closest to the present invention. 10: Photodetector, 11: Laser diode 12: Beam splitter 13: Collimator lens 14: Objective lens, 15: Laser light beam 16: Photodiode, 20: Rotating disk 21: Plastic, 22: Slit 23: Reflective film, 24 : Protective film 30: Disc, 31: Slit 40: Detector, 41: Light source 42: Slit for detection 43: Phototransistor 50: CD (Compact disc) 51: Plastic, 52: Pit 53: Reflective film, 54: Protective film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-60-46414 (JP, A) JP-A-60-100013 (JP, A) JP-A-62-144024 (JP, A) JP-A-63- 144212 (JP, A) JP 63-201520 (JP, A) JP 63-289403 (JP, A)

Claims (1)

(57) [Claims] 1. A reflective film provided on one surface of a rotating disk connected to a detected object to be rotated is arranged in a radial pattern with respect to the center of the rotating disk in a concave and convex shape, and the concave and convex portions have substantially equal widths. A slit and a photodetector that irradiates the slit with a laser beam whose beam diameter is substantially equal to or narrower than the width of the slit and reads the reflected light, and the laser beam straddles the concave portion and the convex portion. The height difference of the slits is determined so that the irradiation light and the reflected light interfere with each other and weaken each other when the light is detected, and a signal having a pulse number twice the number of the slits per one rotation of the rotating disk is obtained from the photodetector. A rotation detection device characterized in that