JPH04372822A - Optical encoder - Google Patents

Abstract

PURPOSE:To obtain an optical encoder which can detect the rotating angle of a high-speed rotary body without the structural restriction of the moving plate such as the rotary plate and the restriction on the side of a light receiving unit and whose configuration can be made compact. CONSTITUTION:A rotary plate 10 or a linearly moving plate has a diffraction grating A wherein grating lines whose grating intervals P are regularly changed are aligned in a circular pattern or in a linear pattern. A laser light source 70 emits light having the planar waves and forms a light spot Q on the diffraction grating. A light receiving unit 60 comprises a plurality of photodetectors which are provided in correspondence with the individual gratings and receive the primary diffracted light from the corresponding grating.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical encoder used to detect the rotation angle and rotation speed of a rotating body such as a motor.

0002

2. Description of the Related Art FIG. 7 shows an example of a conventional optical encoder of this type. In the figure, 10A is a rotary code plate having a rotary shaft 11 connected to the motor shaft of a motor (not shown), and has four ring tracks 1 to 4 formed with a code consisting of a transparent part and a blocking part. Separated. Ring track 1 has a 45°/2 width transparent part A45/2
8 cords arranged at 45°/2 intervals are formed, ring track 2 has 4 45° wide transparent parts A45 formed at 45° intervals, and ring track 3 has 90° wide transparent parts A45. Two portions A90 are formed at 90° intervals, and the ring track 4 has a transparent portion A180 having a width of 180°. B is code board 1
A light shielding part of 0A is shown. Reference numeral 20 denotes a light projection unit that illuminates the rotary code plate 10A in the direction of the rotation axis 11, and includes light sources (light emitting elements) 21 to 21 that illuminate each of the ring tracks 1 to 4.
It is equipped with 22. 30 is a fixed slit plate disposed at a position facing the light projection unit 20 with the rotary code plate 10A in between, and has slits 31 to 34 located at positions facing each of the ring tracks 1 to 4. . Reference numeral 40 denotes a light receiving unit, which includes light receiving elements 41 to 44 that receive the light transmitted through the slits 31 to 34, respectively.

In this configuration, for example, the light that has passed through the transparent portion A180 of the ring track 4 and the slit 34 is incident on the light receiving element 44, and the light receiving element 44 outputs a signal of level H. When rotates, each track 1-4 alternately transmits light and blocks light, and the light-receiving elements 41-4
44 output pulse signals as shown in FIGS. 8(a) to 8(d), respectively. In this example, since the output of the light receiving unit 40 can be used as a 4-bit signal, one revolution of the motor can be divided into 16 parts, and by processing the output of the light receiving unit 40 in the rotation angle calculation circuit 50, the motor One rotation can be detected.

0004

[Problem to be solved by the invention] However, the bit digit 20
, 21 , 22 , 23 , 21 , 22 , 23 In the case where the rotating code plate 10A has a different number of light-transmitting parts in its ring track, there is a range in the speed at which the rotating code plate 10A turns on and off the light, and the rotational speed of the motor varies. When becomes faster, for example,
The ring track 4, which has one transparent part, transmits light at twice the speed.
However, the ring track 1, which has eight transparent parts, turns the light on and off eight times faster, and the light receiving element 44, which has a limited time constant, can turn the light on and off at this high speed. It becomes impossible to follow. As described above, the conventional encoder described above has a problem in that when it is attached to a motor rotating at high speed, it cannot be detected due to restrictions on the light receiving unit 40 side.

[0005] Furthermore, since a plurality of tracks are required and light emitting elements corresponding to the number of tracks are required, there is also the problem that it is difficult to downsize the rotary code plate or the like.

The present invention has been made to solve this problem, and it is possible to detect the rotation angle of a high-speed rotating body without being subject to structural restrictions of a moving plate such as a rotating plate or restrictions on the light receiving unit side. It is an object of the present invention to provide an optical encoder which can be made smaller in size than conventional ones.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a rotating or linearly movable plate equipped with a diffraction grating in which grating rows with regularly changing grating intervals are arranged in a circular or linear manner, and a planar wave projection plate. The structure includes a laser light source that emits light and generates a light spot on a diffraction grating, and a light receiving unit consisting of a plurality of light receiving elements provided corresponding to each of the gratings and receiving the first order diffracted light from the corresponding grating.

[0008] According to claim 2, there is provided a rotating or linearly movable plate having a diffraction grating in which grating rows with constant grating intervals are arranged in a circular or linear manner, and a laser light source that projects a plane wave to generate a light spot on the diffraction grating. , a mirror unit that generates an interference wave between the zero-order diffracted light and the first-order diffracted light of the grating rotated to the optical spot, a photodetector that receives the interference wave, and a counter that counts the number of output pulses of the photodetector. The configuration includes:

[0009]

[Operation] In the present invention, when the rotating plate is rotated by a certain angle and a laser beam is incident on a certain grating, the corresponding light receiving element receives the first-order diffracted light and generates a pulse, and the rotating plate is further rotated by a certain angle. When the laser beam is incident on another grating, another corresponding light-receiving element receives the first-order diffracted light and generates a pulse.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIGS. 1 and 2, reference numeral 10 denotes a rotating plate, and as shown in FIG. 2, a diffraction grating ring A concentric with the axis O is formed. Reference numeral 60 denotes a light receiving unit (diode array), which is composed of a row of a plurality of photodiodes 611 to 61n arranged in an arc shape. 70 is a laser light source that generates a plane monochromatic light, and 71 is a laser light (monochromatic plane wave). Q indicates a laser spot.

This diffraction grating ring A has an amplitude transmittance t of the object.
0 is a sinusoidal amplitude grating that changes sinusoidally in space, where u is the light wave just before it enters the object, and ut is the light wave just after it passes through the object. The amplitude transmittance t0 of the object of the sinusoidal amplitude grating varies sinusoidally along the y-axis as shown in FIG. The amplitude m/2 represents the magnitude of the change in transmittance, and the wave number k
represents the fineness of the notches in the grid. There is a relationship between the wave number k and the interval P between the notches of the grating.

Now, as shown in FIG. 2, a sinusoidal amplitude grating with a pitch P between the notches of the grating is placed in the xy plane at an angle θ with the x axis.
Suppose that a plane monochromatic wave traveling in the direction of i is incident,
Incident angle θi and reflection angle θn (n=1, 2, 3,...
) has the following relationship.

[0014] sinθ0 = sinθi sinθn=1 = sinθi +2π/(P
・k) sinθn=-1=sinθi-2π
/(P・k)
(4) As is clear from this equation, the first-order diffracted light u1
It is understood that the sine sin θn=1 of the angle (diffraction angle) θn=1 is inversely proportional to the grating spacing P.

Therefore, if the grating interval P of the sine wave grating A of the rotary plate 10 is sequentially varied, the angle (diffraction angle) θn of the first-order diffracted light u1 and the rotation angle θN of the rotary plate 10 become 1.
: Corresponds to 1.

In this embodiment, the grating interval P of the sinusoidal grating A is not constant, but is gradually changed, and is expressed as P1 <P2 <P3 <...<Pn.

The photodiode 611 has sinθn
=1 [=sinθi +2π/(P1 ・k)], the photodiode 61n is located at the position of sinθn=1
It is arranged at the position [=sinθi+2π/(Pn·k)].

For example, if the rotating plate 10 is rotated by θN in the direction of the arrow in the figure,
= 30 degrees and the laser beam 71 is incident on the grating interval P30 as shown in FIG. Rotate another 15 degrees (θN
=45) If the laser beam 71 is incident on the grating interval P45, the first-order diffracted light u of the photodiode 6145
1 and generates a pulse. Note that the light intensity of the higher-order diffracted light is so small that it does not pose a practical problem compared to the light intensity of the first-order diffracted light.

Therefore, when the photodiode 6130 outputs a pulse, it is detected that the rotating plate 10 has rotated by 30°, and when the photodiode 6145 outputs a pulse, it is detected that the rotating plate 10 has rotated by 45°. be able to.

As described above, in this embodiment, it is sufficient to provide one diffraction grating ring A on the rotary plate 10, and there is no need for a plurality of ring tracks as in the conventional case, so the rotary plate 10 can be made smaller. Not only that, but only one laser light source 70 is required.

Furthermore, each light receiving element 61 of the light receiving unit 60
1 to 61n only need to receive the laser beam once per rotation of the rotary plate 10 to generate one pulse, so the detection limit for the rotational speed of the rotary plate 10 is very high, and the detection limit from the light receiving unit 60 side is very high. , restrictions on rotational speed can be substantially eliminated.

In the above embodiment, the grid rows are arranged in a circular manner on the surface of the rotating plate 10, but as shown in FIG. 5, the grid rows may be arranged in a cylindrical shape.

In the above embodiment, the diffraction grating A in which the grating rows are arranged in a circular manner is used, but if it is desired to obtain a linear encoder, the diffraction grating A in which the grating rows are arranged in a straight line is used on a linear moving plate. All you have to do is set it up.

Further, in the above embodiment, the diffraction grating A is used in which the grating rows are lined up over the entire circumference, but they may be lined up at a certain interval.

Furthermore, the angular frequency ω+1 of the first-order diffracted light u1
, ω-1 and the rotational speed V of the rotating plate 10, however,
c: Speed of light ω0: Since there is a relationship between the angular frequency of the zero-order diffracted light u0, if the lattice spacing P is kept constant, the rotation of the rotating plate 10 can be achieved by utilizing the interference between the zero-order diffracted light u0 and the first-order diffracted light u1. It is possible to detect the speed V and rotation direction,
Figure 6 shows the mechanism for this purpose.

In FIG. 6, the sinusoidal grating B has a grating spacing P
It is a fixed grid. 81 is a mirror, and 82 is a half mirror, and both generate interference waves u1 to u0 between the zero-order diffracted light u0 and the first-order diffracted light u1. A photodetector 62 receives this interference wave, and a counter 83 counts the pulses output from the photodetector 62 and inputs the pulses to a speed calculator 84 . The speed calculator 84 calculates the rotational speed V of the rotating plate 10 from this pulse count value.

[0027]

Effects of the Invention As explained above, the present invention uses a diffraction grating in which the angle of the diffracted light differs for each grating, and utilizes the difference in the sine of the angle to receive and detect the diffracted light by the corresponding light receiving element. Therefore, it is sufficient to have one so-called track, and since the light receiving element receives light every rotation of the rotary plate, there are restrictions on the rotational speed of the rotary plate due to the time constant of the light receiving element described above, and manufacturing of the rotary plate. The above restrictions can be substantially eliminated, the high-speed range of the rotating body in which the angle can be detected can be expanded compared to the conventional method, and the encoder can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of the present invention.

FIG. 2 is a side view of the above embodiment.

FIG. 3 is a diagram for explaining a sine lattice.

FIG. 4 is a diagram for explaining the operation of the above embodiment.

FIG. 5 is a perspective view showing another embodiment of the present invention.

FIG. 6 is a perspective view showing another embodiment of the present invention.

FIG. 7 is a block diagram of a conventional optical encoder.

FIG. 8 is a time chart of output signals of the conventional example.

[Explanation of symbols]

10 rotating plate 60 light receiving unit 611 ~ 61n photodiode 62
Photodetector 70 Laser light source 81 Mirror 82 Half mirror 83 Counter 84 Speed calculator A, B Diffraction grating

Claims (2)

[Claims] 1. A rotating plate or a linearly moving plate equipped with a diffraction grating in which grating rows with regularly changing grating intervals are arranged in a circular or linear manner, a laser light source that projects a plane wave and generates a light spot on the diffraction grating, An optical encoder comprising a light receiving unit including a plurality of light receiving elements provided corresponding to each of the gratings and receiving first-order diffracted light from the corresponding grating. 2. A rotating plate or a linearly moving plate comprising a diffraction grating in which grating rows with constant grating intervals are arranged in a circular or linear manner, a laser light source that projects a plane wave and generates a light spot on the diffraction grating; A mirror unit that generates an interference wave between the zero-order diffracted light and the first-order diffracted light of the grating rotated to the optical spot, a photodetector that receives the interference wave, and a counter that counts the number of output pulses of the photodetector. An optical encoder characterized by: