JPH0762622B2 - Optical encoder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is used in a so-called optical rotation detection device,
The present invention relates to an optical encoder having a pit formed on a rotating disk.

(Prior Art) FIG. 8 is an external perspective view of a conventional optical encoder, FIG. 9 is a partially enlarged view of the optical encoder shown in FIG. 8, and FIG. 10 is an optical system utilizing a conventional optical encoder. It is a front sectional view of a rotation detection device.

As shown in FIGS. 8 and 9, the conventional optical encoder 1 includes a disk-shaped glass plate 2, a metal layer 3, a plurality of slits 4,
It is composed of a central hole 5, a shaft 6 and a housing 7.

A metal layer 3 is vapor-deposited on the upper surface of the disk-shaped glass plate 2,
The metal layer 3 is made of a metal such as aluminum or chrome that reflects light rays from a light emitting element 11 which will be described later, and a large number of slits 4 are formed in an annular shape by etching in the vicinity of the outer periphery thereof.

A central hole 5 is formed in the central portion of the disk-shaped glass plate 2, and a shaft 6 is inserted and fixed therein through a housing 7.

The conventional optical encoder 1 having the above structure is rotatably supported by the case 8 of the optical rotation detecting device shown in FIG. 10 via bearings 9 and 10. The light emitting element 11 and the light receiving element 12 are arranged in the case 8 so as to face each other via the metal layer 3 and the disk-shaped glass plate 2 of the optical encoder 1, and these are attached to the shaft 6 and are not shown. When the disk-shaped glass plate 2 is rotated by the rotation of a spindle motor or the like, the light beam from the light emitting element 11 is directly incident on the light receiving element 12 through the slit 4 of the metal layer 3.
An amplification / waveform shaping circuit 13 for amplifying the output signal of the light receiving element 12 and shaping the waveform is also arranged in the case 8.

In the optical rotation detection device having such a configuration, when the optical encoder 1 is rotated by the rotational force of the spindle motor or the like (driving means), the light beam from the light emitting element 11 is emitted from the metal layer 3
The light beam is incident on the light receiving element 12 as a light beam that is interrupted by the slit 4. The light receiving element 12 that receives the intermittent light beam outputs an electric signal whose level changes according to the incident light. This output signal is supplied to the amplification / waveform shaping circuit 13, where it is amplified and waveform-shaped, and the pulse signal is output to the output terminal 14.
Is output from. Then, by counting the pulses of this signal with a counting circuit (not shown) connected to the output terminal 14, a rotation detection signal corresponding to the rotation speed or rotation angle of the optical encoder 1 can be detected.

(Problems to be Solved by the Invention) In the optical encoder having the slits as described above, in order to obtain a highly accurate detection signal for rotation, the slits formed on the disk-shaped glass plate 2 constituting the optical encoder are provided. Four
Need to increase the number of. However, when the number of slits 4 is increased, the change of the light rays from the light emitting element 11 to the light receiving element 12 is reduced due to the influence of the diffraction of light, and the intermittent change of the light amount due to the rotation of the slit cannot be detected.

Further, if minute dust or the like adheres to the slit 4, the light beam is blocked, so that there is a problem in that the rotation detection signal cannot be obtained with an accuracy higher than a predetermined limit.

Further, there is a problem that manufacturing a high-precision optical encoder is expensive and not suitable for mass production.

The present invention has been made in view of the above points, and an object thereof is to provide an inexpensive optical encoder capable of highly accurate rotation detection.

(Means for Solving the Problems) In order to solve the above problems, the present invention is an optical encoder including a reflective member having a plurality of pits formed at equal angles in the circumferential direction, a protective member, and a transparent member that are stacked. Given that the wavelength of the laser light used is λ and the numerical aperture of the optical pickup used is NA, the small pit width is 0.25λ / NA.
Larger and smaller than 0.35λ / NA, small pit pitch is 0.4λ / N
An optical encoder having a pit composed of a plurality of small pits larger than A and smaller than 0.7λ / NA.

(Example) The optical encoder of the present invention can be manufactured using a well-known compact disc (hereinafter abbreviated as CD) recording / production apparatus.

FIG. 1 is a partially enlarged pattern view of a pit of a first embodiment of an optical encoder of the present invention, FIG. 2 is a partially enlarged sectional view of an optical encoder, and FIG. 3 is a relation between a light beam, a pit and a detection signal. 4 and 5 are block system diagrams showing an embodiment of an optical rotation detecting device using the optical encoder of the present invention, and FIG. 5 is a waveform diagram for explaining the operation of FIG.

The optical encoder 16 of the present invention has substantially the same structure as a known CD. As shown in FIG. 2, a protective film 17 made of an ultraviolet curable resin or the like and a metal such as aluminum is formed by vapor deposition or sputtering. The reflective film 18 and a transparent plastic 19 made of a polycarbonate resin or the like are laminated and adhered to each other.

The pits 20 are arranged in the optical encoder 16 at equal intervals α, α, ... In the circumferential direction as shown in FIG.
Is twice the amount of eccentricity when the
A length X that is sufficiently longer in the radial direction than the sum of the distance L between e and 22f
Are formed on a concentric circle, the width Q of the pits 20 on the same circumference and the pit gap P are equal (P =
Q) Since it is formed, the pit pitch is 2P.

Although the optical encoder 16 is not shown in FIG. 4, the optical encoder 16 is rotatably supported so as to face the optical pickup 31, and the transparent plastic of the optical encoder 16 is provided. The 19 side (lower side in FIG. 2) faces the optical pickup 31.

The optical pickup 31 has substantially the same structure as that of a known compact disc player, and includes a semiconductor laser,
Optical system such as half mirror, drive system for focus servo,
It is composed of a grating plate (diffraction grating plate) (none of which is shown) and a photodetector composed of a photodiode or the like.

The grating plate divides the laser light beam from the semiconductor laser into three beams, and photodetectors Da, Db, Dc, Dd for detecting signals for focus control.
Are arranged in the shape of a letter, and the electric output signals from the four photodetectors Da to Dd are A, B, C, and D, and the electric output signals from the photodetectors De and Df that obtain the rotation detection signals are output. Let E and F respectively.

The electric output signals A to D are supplied to the focus control unit 32, and the electric output signals E and F are supplied to the encoder signal processing unit 33.

The signal E supplied to the encoder signal processing unit 33 is supplied to the amplifier circuit 36 via the current / voltage conversion circuit 34 and the buffer circuit 35 in series. Similarly, the signal F is sent to the current / voltage conversion circuit 37, the buffer circuit 38 through the series, and the amplification circuit.
39 have been supplied.

The output signals of the amplifier circuits 36 and 39 are supplied to the comparison circuits 40 and 41, respectively.

Then, the output signal of the comparison circuit 40 is supplied to the mono multivibrator 42 and the mono multivibrator 44 separately via the inverter 43, and similarly, the output signal of the comparison circuit 41 is separated from the mono multivibrator 45 and this. It is supplied to the mono-multivibrator 47 via the inverter 46, respectively.

Here, the comparison circuits 40 and 41, the mono-multi vibrators 42 and 4
4, 45, 47 and the inverters 43, 46 constitute a pulse generation circuit 48, and the respective output signals of the mono-multivibrator 42, 44, 45, 47 are supplied to the OR circuit 49, and the OR circuit 49 The output signal is output from the output terminal 50 as an encoder output.

Further, 51 is a Z-phase detector for detecting a pit indicating a zero address provided on the inner or outer circumference of an increment type optical encoder 16 described later, and 52 is an output terminal of this Z-phase detection signal. .

Further, although not shown, the output signal of the optical pickup 31 is supplied to a rotation servo detection circuit for controlling the rotation of the optical encoder 16 and a rotation direction detection circuit for detecting the rotation direction.

The operation of the optical rotation detecting device having such a configuration will be described with reference to FIGS. 1 to 5.

When the optical encoder 1 is rotated at a constant speed by the rotational force of a driving means such as a spindle motor, a laser light beam having a wavelength of 0.78 μm, which is output from the semiconductor laser element of the optical pickup 31, is divided into three by a grating plate. After going through the optical system of the optical pickup 31 built-in,
As shown in the figure, the surface of the optical encoder 16 is irradiated here with beams 22a, 22e, 22f having a diameter of 1.5 μm (these three beams are collectively referred to as beam 22).

The irradiated beam 22 passes through the transparent plastic 19 of the optical encoder 16 and the surface of the reflection film 18 (pit 20).
Then, the light beam 22 is reflected and again enters the photodetectors Da to Df through the optical system built in the optical pickup unit 31, but the beam 22a is emitted to the photodetectors Da to Dd. The beam 22f enters the photodetector De and the beam 22f enters the photodetector Df.

Here, since the depth 23 of the pit 20 is approximately 1/4 of the wavelength of the laser light to be used, interference of the laser light occurs at the boundary portion of the pit 20.
Changes at the boundary of. Therefore, the photodetectors Da, Db, Dc, Dd,
De and Df can obtain the pit 20 as electric signals A, B, C, D, E, and F.

FIG. 3 is a diagram showing the relationship between the light beam, the pit, and the detection signal. FIGS. 3 (A), (B), and (C) show the diameter of the light beam, the cross section of the pit, and the detection of this pit. This is an electric signal obtained. Here, since the width Q and the pit gap P on the same circumference of the plurality of pits 20 of the optical encoder 16 are formed to be equal to the diameter of the light beam 22, the electric signals A to As for the waveform of F, as shown in FIG. 3 (C), a signal having a small wave height difference but a frequency of twice the number of pits arranged on the same circumference and having the same duty ratio of polarity change can be obtained.
3 (B) and 3 (C) show the case where the width Q of the pit 20 is equal to the diameter of the light beam 22.
If the width Q of 20 is equal to or larger than the diameter of this light beam 22, a detection signal having a frequency twice the number of pits arranged on the same circumference can be obtained.

Based on the electric signals A to D obtained in this way, the focus control unit 32, which is well known in CD players and the like, adjusts the focus of the optical pickup 31 so that the difference between (A + C) and (B + D) becomes zero. Adjust. Further, the rotation servo for keeping the optical encoder rotating at a constant speed or the rotation angle and the detection of the rotation direction are performed.

Further, the focus control unit 32, when the light beam 22a is focused on the pit 20 of the optical encoder 16, the buffer circuit 35,3.
8 is designed to work.

On the other hand, the signals E and F supplied to the encoder signal processing unit 33 are converted into voltages by the current / voltage conversion circuits 34 and 37, respectively, and then amplified to a predetermined level by the amplification circuits 36 and 39, and then the fifth level.
A signal a (referred to as an A-phase signal) and a signal b (referred to as a B-phase signal) illustrated in FIGS.

Here, by rotating the grating plate so that the phase difference between the A-phase signal and the B-phase signal becomes π / 2 radian in electrical angle, the beams 22e and 22f have a mechanical angle β in the rotation direction. It is adjustable.

The signals a and b are shaped by the comparison circuits 40 and 41 into rectangular wave signals c and d shown in FIGS. 5C and 5D, respectively. These signals c and d are respectively
Inverted by 3,46, the rectangular wave signals c'and d'shown in FIGS. 5 (C ') and (D') are obtained.

The mono-multi vibrators 42, 44, 45 and 47 send out one pulse at the rising edge of the supplied rectangular wave, and their output signals are signals e to e shown in FIGS. 5 (E) to 5 (H).
h. From the signals e to b, the fifth signal is obtained by the OR circuit 49.
A signal i obtained by dividing the A-phase signal (B-phase signal) shown in FIG.

Therefore, it is possible to obtain an encoder output signal with four times higher accuracy by using the signal i than using the A-phase signal and the B-phase signal as they are as the encoder output signal.

It is also possible to electrically divide the A-phase signal and the B-phase signal sent from the amplifier circuits 35 and 38 to obtain an encoder output signal with higher resolution.

FIG. 6 is a partially enlarged pattern diagram of the pits of the second embodiment of the optical encoder of the present invention, in which the angle α, the pit width Q and the pit gap P are different in addition to the pit 20 of FIG. The pits 24, 25 or more pits are formed on concentric circles different from the pit 20, respectively.

Since the second embodiment has a plurality of patterns with different pit widths Q (pit gaps P) in one encoder, it is optimal to immediately obtain a desired encoder signal by selecting the patterns.

In FIG. 1, the pit width Q (pit gap P) is used, for example, as shown in FIG. 3 (D).
When it is sufficiently larger than the diameter of the pit width, the detected electric signal has a small wave height difference as shown in FIG. 3 (E) and the duty ratios are not equal. It is not a good idea to make it sufficiently larger than the diameter of the beam 22.

FIG. 7 is a partially enlarged pattern diagram of pits of the third embodiment of the optical encoder of the present invention, which is made in order to obtain the maximum wave height difference and an appropriate waveform even in the above case.

In the figure, a plurality of arc-shaped small pits 26 having a small pit width W smaller than the beam 22 used are grouped to form one pit 27. Here, the plurality of small pits 26 have an arc shape, but even if they are arranged in the radial direction,
It may be arranged at an angle to the radial direction.

Here, when the wavelength λ of the laser light used is 0.78 μm and the numerical aperture NA of the pickup is 0.47, the small pit width W that maximizes the electric signal level obtained can be expressed by λ / (3NA). It is known that the result is about 0.5 μm.

Under these conditions, the small pit pitch R of the small pits 26 that minimizes the signal level fluctuation obtained by the small pit portion and the gap between the small pits is approximately 1 μm as a result of simulation. It was

As a result of the above simulation, the optimum range is that the small pit width is larger than 0.25λ / NA and smaller than 0.35λ / NA, and the pitch of the small pits is larger than 0.4λ / NA and smaller than 0.7λ / NA.

When the above optical encoder 16 is used as an incremental encoder that detects the rotation speed by incrementally counting the number of pulses from the encoder output, it is not shown here, but is zero on the inner or outer circumference of the optical encoder 16. Needless to say, a pit indicating an address is formed.

(Effect of the Invention) As described above, the optical encoder of the present invention can improve the accuracy of rotation detection by forming an extremely large number of pits as compared with the conventional encoder.
It can be manufactured using a CD recording and production device, and the same product can be mass-produced and is inexpensive.

By lengthening the pits in the radial direction, there is a feature that a rotation detection signal of a certain level can be obtained even when eccentricity or the like occurs when the optical encoder is attached to the rotation detection device and used.

By having a plurality of patterns having different pit widths (pit gaps) in one encoder, a versatile optical encoder can be obtained.

Since the width of the pit is set to be equal to or larger than the diameter of the light beam of the laser light used, a detection signal having a frequency twice the number of pits arranged on the same circumference can be obtained.

By forming a pit pattern with a small pit width that maximizes the detected signal level and a small pit group that minimizes the signal level fluctuation, the rotation detection accuracy can be improved. .

[Brief description of drawings]

FIG. 1 is a partially enlarged pattern view of a pit of a first embodiment of an optical encoder of the present invention, FIG. 2 is a partially enlarged sectional view of an optical encoder, and FIG. 3 is a relation between a light beam, a pit and a detection signal. 4 and 5 are block system diagrams showing an embodiment of an optical rotation detecting device using the optical encoder of the present invention, FIG. 5 is a waveform diagram for explaining the operation of FIG. 4, and FIG. , FIG. 7 is a partially enlarged pattern view of pits of the second and third embodiments of the optical encoder of the present invention, FIG. 8 is an external perspective view of a conventional optical encoder, and FIG. 9 is shown in FIG. FIG. 10 is a partially enlarged view of the optical encoder, and FIG. 10 is a front sectional view of an optical rotation detection device using a conventional optical encoder. 16 ... Optical encoder, 17 ... Protective member, 18 ... Reflective member, 19 ... Transparent plastic (transparent member), 20, 24, 2
5,27 …… pit, 26 …… small pit, α, α ′ …… center angle, λ …… wavelength, NA …… numerical aperture, P …… pit gap, Q
…… Small pit width, R …… Small pit pitch, W …… Pitch width.

Continuation of front page Examiner Atsushi Ozaki (56) References JP-A-60-100013 (JP, A) JP-A-63-201521 (JP, A)

Claims (1)

[Claims] 1. An optical encoder comprising a reflective member having a plurality of pits formed at equal angles in the circumferential direction, a protective member, and a transparent member, wherein the wavelength of laser light used is λ. When the numerical aperture of the optical pickup is NA, the small pit width is larger than 0.25λ / NA and smaller than 0.35λ / NA,
An optical encoder characterized by having a pit composed of a plurality of small pits having a pitch of smaller than 0.4λ / NA and smaller than 0.7λ / NA.