JPH05272990A - Drum-type encoder - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a rotary encoder that can reduce a mounting space and can detect a rotation angle of a rotating body more accurately. [Structure] A rotating body 1 having a diffraction grating 4 formed on an outer peripheral surface thereof has a drum shape and is formed integrally with a rotating shaft 2 by, for example, an aluminum tachy cast. This diffraction grating 4
In addition, the light L ₁ and L _{2 obtained} by splitting the light of the light emitting element 5 into two by the half mirror 6 are focused on one point via the mirrors 7 and 8. A light receiving element 9 is arranged at a position where the first-order diffracted light of the reflected light from the diffraction grating 4 can be received, and a processing circuit 10 is connected to the light receiving element 9, and this processing circuit 10 divides the divided lights L ₁ and L ₂ into one. The number of changes in the intensity of the interference fringes caused by the interference of the secondary diffracted light is counted to detect the rotation angle of the rotating body 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drum type encoder for detecting a rotation angle of a rotating body by using diffracted light.

[0002]

2. Description of the Related Art Conventionally, as a rotary encoder using diffracted light, for example, FIG.
The ones shown in are known. In the figure, reference numeral a denotes a shaft cylinder, which is hung vertically on a collar c whose tilt can be adjusted by a leveling screw b. The shaft cylinder a is integrated with a casing d of a rangefinder. For example, a vertical shaft e made of aluminum is rotatably fitted. Flange portion f of the shaft cylinder a
As shown in FIG. 7, a ring-shaped fixed disk i made of glass on which a diffraction grating in which a light transmitting portion g and a light non-transmitting portion h are arranged at equal intervals is formed is fixed. A ring-shaped rotating disk k having a diffraction grating in which light transmitting portions and light non-transmitting portions are arranged at equal intervals is fixed to the flange portion j of the axis e. A light emitting element 1 and a light receiving element m are arranged across the fixed disk i and the rotating disk k, and the light from the light emitting element 1 is branched into two on the way, although not shown in the drawing. Respectively pass through a single grating position of the fixed disk i and the rotating disk k, and the first-order diffracted light enters the light receiving element m.

With the above construction, when the vertical axis e rotates, the light receiving element m outputs a signal corresponding to the intensity change of the interference fringes caused by the interference of the first-order diffracted light of the two branched lights, and from this signal the casing The rotation angle of d can be detected.

In FIG. 6, n is a collimating telescope.

[0005]

In the conventional rotary encoder described above, since the outer diameters of the fixed disk i and the rotary disk k are larger than that of the vertical axis e, the space for a device for mounting them is large. Further, since the rotating disk k and the vertical shaft e are formed of separate members, and a fixing means for connecting them is indispensable, the structure is complicated and the size becomes large. In addition, since there is a connecting and fixing portion of the rotating disk k and the vertical axis e, the center of the rotating disk k and the center of the vertical axis e may deviate, and the rotating disk k may be eccentric with respect to the center of rotation. Therefore, the rotation speed of the diffraction grating may fluctuate, and accurate angle detection may not be possible. Further, since the light transmission part g forming the conventional diffraction grating is fan-shaped, it is difficult to form a diffraction grating having a uniform pitch. An object of the present invention is to provide a rotary encoder that solves these conventional problems.

[0006]

In order to achieve the above object, the present invention provides a drum-shaped rotating body which is integrally formed with a rotary shaft and has a reflection type diffraction grating formed on the outer peripheral surface thereof. Rotation of the rotator from a light-receiving element arranged at a position where the first-order diffracted light of the light reflected by the reflection type diffraction grating can be received, and an output signal corresponding to the interference fringes of the first-order diffracted light output from the light-receiving element. And a detecting means for obtaining a corner.

[0007]

In the above-mentioned structure of the present invention, the rotating body forming the diffraction grating is formed integrally with the rotating shaft, so that the rotating body is different from the conventional one in which separate members are connected and integrated. The degree of eccentricity with respect to the center of rotation is small, and the rotational speed of the diffraction grating does not fluctuate so that the angle detection of the rotating body becomes more accurate. Further, the drum-shaped rotating body having the reflection type diffraction grating formed on the outer peripheral surface becomes smaller than that using the conventional rotating disk. Also,
Since the diffraction grating is formed on the outer peripheral surface of the drum-shaped rotating body, the grating shape can be formed in a rectangular shape, so that it can be formed at a higher accuracy and at equal intervals as compared with the conventional one. Is eliminated and the angle detection of the rotating body becomes more accurate.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In the figure, reference numeral 1 is a drum-shaped rotating body made of, for example, aluminum die-cast formed integrally with the rotating shaft 2, and has a vertically long rectangular mask 3 on its outer peripheral surface, that is, black as shown in FIG. Diffraction grating 4 is formed by arranging masks 3 in which the above paint is applied in a vertically long rectangular shape.

Reference numeral 5 is a light emitting element, and the light emitted from this is divided into two by a half mirror 6 and two divided lights L are obtained.
₁ , ₁ and ₂ are reflected by mirrors 7 and 8, respectively, and are focused on one point on the diffraction grating 4 on the outer peripheral surface of the rotating body 1. A light receiving element 9 is arranged at a position where the first-order diffracted light of the light reflected by the diffraction grating 4 can be received.

When the rotator 1 rotates, a signal corresponding to a change in the intensity of interference fringes caused by interference between the + _1st-order diffracted light of the split light L _{1 and} the -1st-order diffracted light of the split light L ₂ incident on the light receiving element 9 is generated. Output. That is, the complex amplitude A (+1) of the + 1st-order diffracted light is as follows, where the amplitude of the split light L ₂ is 1.

[0011]

[Equation 1]

(Where ωt + φ ₀ is the initial phase,
p is the pitch of the diffraction grating 4, x is the rotation angle of the rotating body 1), −
If the amplitude of the split light L ₁ is 1, the complex amplitude A (−1) of the first-order diffracted light is

[0013]

[Equation 2]

It is represented by The intensity distribution of the interference fringes when the + 1st-order diffracted light and the -1st-order diffracted light interfere with each other is

[0015]

[Equation 3]

As is clear from this equation, the intensity of light in the light receiving element 9 fluctuates as shown in FIG. 3 according to the rotation angle x, that is, the position of the rotating body 1. That is, the rotating body 1
When the diffraction grating 4 is rotated by one pitch p, light and darkness of light occurs twice. The interference light is detected by the light receiving element 9, the output pulse thereof is counted by the processing circuit 10, and the rotation angle of the rotating body 1 is detected from the counted number. As shown in FIGS. 4 and 5, the diffraction grating 4 of the rotating body 1 is formed by forming an aluminum vapor deposition film 11 on the outer peripheral surface of the rotating body 1 and forming recesses 12 and 12A at equal intervals on the surface by etching. But it's okay.

[0017]

Since the present invention is constructed as described above, the mounting space for the encoder can be made smaller than that of the conventional one, and the eccentricity of the rotating body on which the diffraction grating is formed with respect to the rotating shaft. Therefore, it is possible to accurately detect the turning angle of the rotating body. Furthermore, since the grid shape can be made rectangular, it can be formed at even intervals with higher accuracy than the conventional fan shape, and as a result, the error in the interval of the interference fringes is eliminated and the rotation angle of the rotating body can be detected more accurately. Has the effect of becoming.

[Brief description of drawings]

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

FIG. 2 is a sectional view of a part of the rotating body of the embodiment shown in FIG.

FIG. 3 is a diagram showing an intensity distribution of interference fringes with respect to a rotation angle of a rotating body.

FIG. 4 is a sectional view showing a modification of the diffraction grating of the embodiment shown in FIG.

5 is a sectional view showing another modification of the diffraction grating of the embodiment shown in FIG.

FIG. 6 is a cross-sectional view of a conventional rotary encoder provided on a rangefinder.

7 is a partially enlarged perspective view of the rotating body shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 rotator 2 rotation axis 3 mask 4 diffraction grating 5 light emitting element 9 light receiving element 10 processing circuit 11 aluminum vapor deposition film 12, 12A recess

Claims (1)

[Claims] 1. A drum-shaped rotating body integrally formed with a rotating shaft and having a reflective diffraction grating formed on an outer peripheral surface thereof, and first-order diffracted light of the reflected light from the reflective diffraction grating can be received. A drum-type encoder comprising: a light-receiving element arranged at a position; and detection means for obtaining a rotation angle of the rotating body from an output signal corresponding to an interference fringe of the first-order diffracted light output from the light-receiving element.