JPH04351918A - Encoder - Google Patents

Abstract

PURPOSE:To obtain an optical encoder which allows high resolution. CONSTITUTION:Light emitted from a light source 4 is entered through a beam splitter 14 to a pattern plate 2 after paralleled by a lens system 6, and light reflected from the pattern of the pattern plate 2 is diaphragmed by the lens system 6, parted by the beam splitter 14 and entered to a slit plate 13 in an enlarged image area of the lens system 6. The slit plate 13 has a slit pitched equal to an entered light image and light transmitting into the slit is inputted a light-electricity converting element 8, resulting in the strength of light transmitting into the slit plate 13 which is time-modulated with the one-way movement of the pattern plate 2.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoder for detecting the position of a moving object. The present invention is applied to, for example, a rotary encoder that detects the rotational speed, rotational direction, and absolute rotational position of a servo motor or the like.

0002

2. Description of the Related Art A transmission type rotary encoder has a plurality of radially extending slits arranged at regular intervals on the surface of a rotating disk to form a transmission type non-diffraction grating, and detects light transmitted through these slits. Also, a reflective rotary encoder is provided in which a plurality of reflective bands extending in the radial direction are provided on the surface of the rotating disk at regular intervals to form a reflective non-diffraction grating, and the light reflected by the reflective bands is detected. Are known.

Furthermore, in order to measure displacements on the order of microns, a so-called Moire scale is used which has transmission type non-diffraction gratings that move relative to each other. With this Moire scale, sine wave light having a period equal to the pitch of the non-diffraction grating is obtained. The interferometric encoder disclosed in Japanese Unexamined Patent Publication No. 1-176914 inputs parallel light into a diffraction grating with a constant pitch, and detects a region where the zero-order light and the positive first-order light emitted from the diffraction grating interfere, or where the zero-order light and the positive first-order light interfere. An index scale is provided at the same pitch as the diffraction grating in the area where the negative primary light interferes, and interference light between the 0th order light and the positive primary light or interference light between the 0th order light and the negative primary light is generated. Discloses detecting spatial position changes of a diffraction grating based on.

A position detector disclosed in Japanese Patent Application Laid-Open No. 60-190812 discloses that a change in the spatial position of a diffraction grating is detected by causing only a pair of diffracted lights of the same order obtained by entering the diffraction grating to interfere with each other. ing. That is, in each encoder described above, parallel light is incident on a moving transmissive or reflective grating to spatially modulate the parallel light, and then this spatially modulated light is transmitted through a predetermined pattern of stationary slits to determine the amount of transmitted light. The position or speed of the grid is detected based on the time change of the grid.

[0005]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional encoder, it is necessary to bring the moving grating and the stationary slit close together in order to eliminate the influence of undesired diffracted light, but this has certain limitations in manufacturing. However, when the pitch of the moving grating is made finer, the pitch of the stationary slits with the same pitch is also reduced, making it difficult to manufacture and install them, making it difficult to improve resolution. .

The present invention has been made in view of the above problems, and an object thereof is to provide an optical encoder capable of improving resolution.

[0007]

[Means for Solving the Problems] The present invention includes a pattern plate that has a pattern of a predetermined shape that reflects incident light and moves in one direction, and a pattern plate that is arranged at a predetermined distance from the pattern and emits light to the pattern. a lens system disposed in the optical path from the light source to the pattern plate to make parallel light incident on the pattern; and a lens system disposed in the optical path from the light source to the lens system from the pattern. a beam splitter that shunts the reflected light of the lens system; and a beam splitter that has slits with a pitch equal to the pitch of the reflected light image output from the beam splitter in the enlarged image area of the lens system, and is spaced a predetermined distance from the converging lens along the optical axis. The device is characterized in that it includes a slit plate disposed so as to pass through the slit plate, and a photoelectric conversion element that photoelectrically converts transmitted light transmitted through the slit plate.

[0008] A preferred embodiment of the rotary encoder includes the pattern plate in which reflective diffraction grating patterns extending in the radial direction are formed at predetermined intervals in the circumferential direction and are disposed on the rotating shaft. In a preferred embodiment, the rotary encoder includes a diffracted light selection plate that is disposed near the focal point of the lens and that extracts interference light of a predetermined order component of the diffracted light reflected from the reflective diffraction grating pattern. It is equipped with

[0009] The light source consists of, for example, a laser device. A half mirror or a triangular prism can be used as the beam splitter.

0010

[Operation and Effects of the Invention] The light emitted from the light source passes through the beam splitter, is collimated by the lens system, and enters the pattern plate, and the reflected light reflected from the pattern on the pattern plate is focused by the lens system, and then The beam is shunted by the beam splitter and enters the slit plate in the magnification area of the lens system. The slit plate has slits with the same pitch as the incident light image, and the light that passes through the slits enters the photoelectric conversion element.As a result, as the pattern plate moves in one direction, the intensity of the light that passes through the slit plate decreases. Time modulated. In the case of the incremental type, the speed is determined from the modulation frequency, and the relative position within the pitch is determined from the modulation amount. Furthermore, in the absolute type, the absolute position and velocity are determined by information contained in one or more of the above-mentioned time-modulated lights.

As explained above, in the encoder of the present invention, the light emitted from the moving pattern plate is magnified by the converging lens and projected onto the slit plate, so that the slit plate can be made larger. It is possible to prevent the resolution of the encoder from deteriorating due to variations in the manufacturing accuracy of the plate. Furthermore, re-diffraction caused by the slits of the slit plate can be reduced, and the accuracy of manufacturing and mounting the slit plate can be eased.

Furthermore, compared to a transmission type encoder that transmits through the rotating disk 2, the collimating lens and the converging lens can be used in common, and the optical paths can be overlapped, so the size and weight can be reduced, and the optical positioning becomes easy.

[0013]

【Example】

(Example 1) An example of the present invention is shown in FIG. This device is a re-diffraction type rotary encoder, and one end of a rotating shaft 3 is inserted into a casing 1 and rotatably supported by a bearing 9. Inside the casing 1, a rotating disk 2 is fixed to one end of a rotating shaft 3 at right angles to its axis.

The rotating disk 2 has a width of 1 as shown in FIG.
Reflection bands 20 with a length of 1 to 1000 .mu.m and a length of 1 to 1000 .mu.m are formed radially over the entire circumference of the rotating disk 2 at a pitch of 2 to 40 .mu.m by photo-etching. reflective band 20
is a mirror, and the other parts of the rotating disk 2 are formed in black. Specifically, an aluminum film vacuum-deposited on the back surface of a disk-shaped glass plate is photo-etched in the region of the reflective band 20 to form the reflective band 20, and a black layer is applied over the entire surface. has been done.

The casing 1 further houses a detection optical system A, a light source drive circuit 11, and a light detection sensor circuit 12. The detection optical system A includes a case 5, a laser diode 4, a half mirror 14, a converging lens 6, a mask 7, a slit plate 13, and a PIN type photodiode 8 housed in the case 5. Here, the rotating disk 2 constitutes a pattern plate according to the present invention, its reflection band 20 constitutes a pattern according to the present invention, the laser diode 4 constitutes a light source according to the present invention, and the photodiode 8 constitutes a pattern plate according to the present invention. The mask 7 constitutes a diffraction light selection plate as referred to in the present invention, the converging lens 6 constitutes a lens system as referred to in the present invention, and the half mirror 14 constitutes a beam splitter as referred to in the present invention. are doing. Other structural features of the detection optical system A will be explained along with the operation description below.

The photoelectric drive circuit 11 includes a laser diode 4
This is a circuit for driving the laser diode 4.
includes a constant current circuit that supplies a constant current to the The photodetection sensor circuit 12 includes a circuit that amplifies and processes the output voltage of the photodiode 8 to detect the rotational speed of the rotating shaft 3. Mask 7 is shown in FIG. Two light-transmissible slits 70 are formed in the mask 7 at a pitch d, and specifically, a black layer is formed on the surface of the glass plate leaving the area of the slits 70. The intermediate line of the slit 70 is arranged in the radial direction of the rotating shaft 3.

In this embodiment, the slit plate 13 is provided at a position where the diffracted light emitted from the reflection band 20 of the rotating disk 2 is imaged by the converging lens 6. Since the image obtained by re-diffracting the above-mentioned diffracted light by the mask 7 is incident on the slit plate 13, the slits of the slit plate 13 are formed at the same pitch and at the same position as this re-diffracted image. A part of the slit plate 13 is shown in FIG.

The operation of the above device will be explained below with reference to the enlarged view of the main part in FIG. A laser beam of constant intensity outputted from the laser diode 4 passes through the half mirror 14, is converted into a parallel beam by the converging lens 6, enters the rotating disk 2, and is diffracted and reflected by the reflection band 20. This rotating disk 2
The light reflected from the
, 2, 3, ...) 16, and these light components are condensed by a converging lens 6, reflected by a half mirror 14,
As a result, a diffraction image is formed at the focal position of the lens 6.

In this embodiment, a mask 7 is provided at the focal position of the lens 6, and as shown in FIG. Slits 70, 70 are provided at the imaging position. Therefore, from this mask 7, the above ±1st order wave components I1,
While the re-diffraction image 15 of I-1, that is, the interference image is enlarged,
The light is incident on the slit plate 13.

In this case, the interval between the reflection bands 20 on the rotating disk 2 is observed as bright and dark fringes (energy distribution) in the re-diffraction image 15 of the ±1st-order wave components I1 and I-1 (as shown by the solid line in FIG. 6). ), apparently twice the bit information of the rotating disk can be obtained (see FIG. 6). Naturally, the slit plate 13 on which the stripes are formed has slits formed at the stripe positions (bright positions), and the light transmitted through the slits of the slit plate 13 enters the photodiode 8, and the photodiode 8 generates a signal current corresponding to the slit. Output.

[0021] The principle by which the above-mentioned double pitch is obtained will be analyzed below. FIG. 9 shows the mask 7 and the slit plate 13.
It is a figure showing each optical path length relationship between. Q is the position of the mask 7 from which P is located a distance L along the optical axis.
It is assumed that the slit plate 13 is located at the position. Q1 is a slit 70 from which the +1st order wave component I1 of the mask 7 is radiated.
, and Q0 is the 0th order (fundamental) wave component I0 of mask 7
is the virtual point from which the radiation is emitted, is the slit 70, and Q-
1 is a slit 70 from which the -1st-order wave component I-1 of the mask 7 is emitted, and each of these points is considered to be a point light source here. On the other hand, P1 and P2 are two bright points adjacent to each other in a direction perpendicular to the optical axis on the slit plate 13. Furthermore, the distance between Q1 and Q0 in the direction perpendicular to the optical axis = the distance between Q1 and Q0 in the direction perpendicular to the optical axis is d, and the distance between P1 and P2 in the direction perpendicular to the optical axis is Let it be x.

[0022] First, the ±1st order wave component I1 and the 0th order (
Basic) If we consider the interference fringes with the wave component I0,
Optical path length difference ΔL = Q1 P1 -Q0 P2 = (L2
+(x+d/2) 1/2-(L2 +(x-d/2)
2)1/2 =L(1+(x+d/2)
2/L2) 1/2-L(1+d/2)2
/L2 )1/2 If we expand this by Taylor, =L{(1+(x+d/2)2 /2L2 )
-(1+(x-d/2)2/2L2
)} =L・2・(2・x・d/2)/(2・L2
)=x・d/L. Here, since the bright spots occur at the position ΔL=nλ (λ is a positive or negative integer), the pitch x between adjacent bright spots on the slit plate 13 is x=n・λ・L/d

(a) becomes.

Next, consider the interference between the +1st order wave component I1 and the -1st order wave component I-1. Here, the distance between Q1 and Q-1 is 2d, so if the distance d in (a) is 2d, the slit plate due to the interference between the +1st-order wave component I1 and the -1st-order wave component I-1. The pitch x' between adjacent bright points on 13 is x'=n・λ・L/2・d
(b) becomes.

From the above equations (a) and (b), the pitch x' of the interference fringe between the +1st-order wave component I1 and the -1st-order wave component I-1 is determined by the pitch x' of the interference fringe between the +1st-order wave component I1 and the 0th-order (fundamental) wave. It can be seen that the distance is half the pitch x of the interference fringes with the component I0, and as a result, twice as many interference fringes are obtained. And rotating disk 2
Due to the movement of , the slit position of the rotating disk 2 moves, thereby the position of the interference fringes due to the ±1st order wave components I1 and I-1 deviates from the slit plate 13, and the intensity of the interference image output from the slit plate 13 decreases. Therefore, by detecting the change in the current of the photodiode 8, the rotation speed can be detected. Naturally, the direction of rotation can also be detected by providing a pair of slit groups on the rotating disk 2 with slit pitches that differ by 90 degrees from each other and detecting them separately.

That is, in the rotary encoder of this embodiment, the diffracted light reflected from the rotating disk 2 is passed through the converging lens 6.
Since the image is enlarged and displayed on the slit plate 13,
The slit plate 13 can be easily manufactured, and the influence of re-diffraction caused by the slit plate 13 can also be reduced. Further, in this embodiment, a mask 7 is placed near the focal point of the converging lens 6.
Since the interference fringes of the ±1st-order wave components I1 and I-1 are extracted by providing the When the reflection band 20 is provided, 2N bits of information can be obtained per revolution of the rotating disk 2, and the resolution can be doubled.

Further, in this embodiment, unlike a normal rotary encoder, since detection is performed using the coherence of light, it is possible to form a reflection band 20 on the rotating disk 2 beyond the diffraction limit. Even higher resolution can be obtained. Note that the magnification of the re-diffraction image 15 incident on the slit plate 13 can be arbitrarily determined by adjusting the position of the slit plate 13 and the like.

Further, if the mask 7 is installed so that high-order diffracted light passes through, even higher resolution can be achieved. (Modification 1) In the above embodiment, the reflection bands 2 are arranged at a constant pitch.
0 is formed on the rotating disk 2, but it is also possible to replace the rotating disk 2 and give special positional information to the position of the reflective band 20 of the rotating disk 2, or It may also be an absolute type rotary encoder that displays digital bid information using the arrangement of reflection bands 20 and detects the absolute rotational angular position. However, even in this case, although an enlarged image can be obtained on the detection surface by employing the converging lens 6, the resolution cannot be increased by using the mask 7. (Modification 2) In the embodiment of the incremental type rotary encoder described above, the mask 7 can be omitted as shown in FIG.

In this embodiment, a beam splitter 14a is used, and a slit plate 13 is attached to one surface of the beam splitter 14a, and the photodiode 8 is brought into contact with the slit plate 13. Mask 7 is omitted. Furthermore, a correction lens 60 is added so that parallel light enters the rotating disk 2. In this case, the 0th order transmitted light reflected from the reflection band 20 of the rotating disk 2 and the ±nth order diffracted light (n=1, 2,
3,...) are formed on the slit plate 13 as a diffraction image. Therefore, although the resolution cannot be doubled, the fringe pitch can be expanded by enlarging the image, and the rotating disk 2 and slit plate 13 can
Since there is no need to place the slit plate 13 in close proximity to each other, the production and arrangement of the slit plate 13 are simplified. (Variation 3) In the incremental type or absolute type rotary encoder described above, the reflection band 20 of the rotating disk 2 is enlarged (for example, the diffraction limit is 8
μm or more), and a non-diffractive rotary encoder can also be used.

In this variant, each reflection band 2 of the rotating disk 2
The 0th-order transmitted light of each reflected light is used without using the interference of the reflected light from 0. Even in this case, the reflected light image emitted from the rotating disk 2 is magnified by the converging lens 6 and sent to the slit plate 13. Since the image can be formed upwardly and there is no need to bring the rotating disk 2 and the slit plate 13 close to each other, the production and arrangement of the slit plate 13 are facilitated. (Modification 4) Another modification is shown in FIG.

In this embodiment, a beam splitter 14a made of a prism is used instead of the half mirror 14, and a mask 7 is further bonded to one surface of the beam splitter 14a. The mask 7 is placed at the focal point of the converging lens 6, and a correction lens 60 is added so that parallel light enters the rotating disk 2. In this way, the device configuration becomes simpler.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention;

[Figure 2] Figure 1
Optical path diagram showing the effect of

[Fig. 3] Front view showing the mask,

FIG. 4 is a front view showing a part of the rotating disk;

FIG. 5 is a front view showing a part of the slit plate;

FIG. 6 is an explanatory diagram illustrating the re-diffraction state,

FIG. 7 is a sectional view showing another aspect;

FIG. 8 is a sectional view showing another configuration;

FIG. 9 is an optical path length diagram showing the double pitch principle of Example 1;

[Explanation of symbols]

2 is a rotating disk (pattern board) 4 is a laser diode (light source) 6 is a converging lens 7 is a mask (diffraction light selection plate) 8 is a photodiode (photoelectric conversion element) 13 is a slit plate

Claims (3)

[Claims] 1. A pattern plate having a pattern of a predetermined shape that reflects incident light and moving in one direction; a light source disposed at a predetermined distance from the pattern and emitting light to the pattern; A lens system disposed in the optical path leading to the pattern board to make parallel light incident on the pattern; and a beam disposed in the optical path leading from the light source to the lens system to shunt reflected light from the pattern. a slit plate having slits with a pitch equal to the pitch of the reflected light image output from the beam splitter in the enlarged image area of the lens system and disposed at a predetermined distance from the converging lens along the optical axis; ,
An encoder comprising: a photoelectric conversion element that photoelectrically converts transmitted light transmitted through the slit plate. 2. The encoder according to claim 1, comprising a rotary encoder comprising a pattern plate having diffraction grating patterns extending in the radial direction formed at predetermined intervals in the circumferential direction and disposed on a rotating shaft. 3. The rotary encoder further comprises an interference plate disposed near the focal point of the converging lens and extracting interference light of a predetermined order component of the diffracted light emitted from the diffraction grating pattern. Encoder listed.