JPH03261821A - Rotary encoder - Google Patents

Abstract

PURPOSE:To detect a rotation angle with high resolving power with use of a compact and light-weight apparatus by obtaining the rotation angle of a disc through detection of an angle of diffraction of light projected to the disc. CONSTITUTION:A light source 1 is placed above a disc 10. The light C from the light source 1 is projected at right angles to a part where slits SR and SC are formed in the disc 10. An angle of diffraction theta of the light incident upon the diffraction slit pattern is expressed by sin theta=hlambda/d wherein (h) is an order of diffraction 0, + or -1,+ or -2..., lambda is the wavelength of the incident light, and (d) is the pitch of slits. When the pitch (d) is changed, the angle of diffraction is accordingly changed. If the circumferential slit SC and the diametrical slit SR respectively having pitches dtheta1, dtheta2 are formed on the disc 10 to satisfy a specific condition, the combined diffraction light draws a circle as indicated by a chain line B. Since the rotation angle of the disc 10 corresponds to the diffraction light with 1:1, if the position of the diffraction light is detected, the rotation angle of the disc 10 can be obtained.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an absolute type rotary encoder that detects the angle of one rotation.

Conventional technology and its problems Rotary encoders include an incremental type that outputs a predetermined pulse to the outside every time the object to be inspected rotates a certain angle, and one that outputs multiple signals indicating the angular position of the object to be inspected to the outside. There is also an absolute type.

An example of an absolute type rotary encoder is shown in FIG. This rotary encoder includes a disk 40 fixed to a rotation shaft 41, and this disk 40 stores 8-bit angle information for each predetermined angle (brightness and darkness).
A slit 40A, which is expressed by light transmission and light shielding, is drawn. A slit plate 32 having eight light emitting diodes 31 and eight slits through which the light emitted from these light emitting diodes 31 passes through is arranged on one side of the disk 40, and a slit plate 32 with eight slits formed on the other side. A phototransistor 51 is arranged. Of the light emitted from the light emitting diode 31, the light transmitted through the slit 40A of the disk 40 is detected by the phototransistor 51, and information representing the rotation angle of the disk 40 is output as a bit signal.

The resolution of a rotary encoder as shown in FIG. 4 depends on the number of bits in the slit 4OA drawn on the disk 40. The resolution of a rotary encoder with 8-bit slits is 380°/28-1.4''.

A conventional absolute rotary encoder requires a number of light emitting diodes and phototransistors corresponding to the number of bits of the bright/dark slit. If the number of bits of the slit is increased in order to achieve high resolution, the number of light emitting diodes and phototransistors required will increase, making it difficult to reduce the size and weight. On the other hand, if an attempt is made to reduce the size and weight by reducing the number of light emitting diodes and phototransistors, the resolution will decrease. As described above, conventional devices have not been able to satisfy all of the requirements for miniaturization, weight reduction, and high resolution.

SUMMARY OF THE INVENTION OBJECTS OF THE INVENTION An object of the present invention is to provide a rotary encoder that can satisfy all the requirements of miniaturization, weight reduction, and high resolution.

Structure 8 of the Invention Functions and Effects In the rotary encoder according to the present invention, a diffraction pattern that causes a projected light beam to be diffracted is formed in at least one of the radial direction and the circumferential direction, and the pitch of this diffraction pattern is a rotatable disk whose angle changes, a light source that projects a light beam onto the disk, a position detection means for detecting the direction of the diffracted light generated by the diffraction pattern of the disk, and detection by the position detection means. The present invention is characterized by comprising means for outputting a signal representing the rotation angle of the disc based on the direction of the diffracted light.

According to this invention, a diffraction pattern whose pitch changes in the angular direction is formed on one disc.

When light is projected onto a disk, the diffraction angle of the light differs depending on the rotation angle of the disk. By detecting the diffraction angle of this diffracted light, the rotation angle of the disk can be determined.

The diffraction angle of the diffracted light can be detected, for example, by a position detector that detects the irradiation position of the diffracted light.

Therefore, according to the present invention, since it is sufficient to provide one light source and one position detector, it is possible to reduce the size and weight. Furthermore, since the single diffraction pattern can be made very fine and the single position detector has highly accurate position detection performance, high resolution of rotation angle detection can be obtained. Furthermore, changes in the diffraction angle of the 9-diffracted light are detected, and changes in the intensity do not pose a problem, so changes in the emission intensity of the light source do not adversely affect rotation angle detection.

Description of examples FIG. 1 is a perspective view showing an embodiment of the invention.

The disk lO is fixed to the rotating shaft 11 and rotates smoothly with the rotating shaft 11. On the disk 10, a linear diffraction slit pattern SR extending in the radial direction of one disk and an annular diffraction slit pattern Sc extending in the circumferential direction are drawn. The pitch of the diffraction slit pattern SH changes monotonically and continuously with respect to angle. The pitch of the diffraction slit pattern Sc also changes monotonically and continuously with respect to angle.

A light source 1 is arranged above the disk IO, and its emitted light C is projected perpendicularly onto the portion of the disk 10 where the slits S and Sc are drawn.

The diffraction angle θ of light incident on the diffraction slit pattern is expressed by the following equation.

sinθ−hλ/d, =・(
1) Here, h is the diffraction order (0, ±1. ±2...).

λ is the wavelength of the incident light, and d is the slit pitch.

Therefore, if the slit pitch d is changed, the diffraction angle will also change accordingly.

Since the slits S and Sc are formed in the disk lO, the incident light from the light source 1 is diffracted. Among these diffracted lights, attention is paid to the first-order (h-+1) transmitted diffracted light C9.

A position detector 20 is placed at a position where it can receive this diffracted light C1. The slits So are formed in the circumferential direction, and the pitch thereof changes depending on the angle. Therefore, the irradiation position of the diffracted light by the slit Sc changes in the X-axis direction of the position detector 20 ( radial direction of the disk IO). The slits SR are formed in the radial direction, and the pitch changes according to the angle, so when one circular plate 10 rotates, the irradiation position of the diffracted light by the slit SR is in the Y-axis direction (X-axis direction). Therefore, the light CD diffracted by the slit Sc and the slit SR draws a circle or an ellipse on the position detector 20 as shown by the chain line B as the disk lO rotates.

A position detector 20 detects the irradiation position of the diffracted light CD. A position detection signal for detecting the irradiation position of the diffracted light C9 is given to the output circuit 21. Since the angle of the disc 10 is uniquely determined by the X and Y coordinates representing the irradiation position of the diffracted light C9 on the position detector 20, the output circuit 21 outputs a signal representing the angle.

When the radius of the disk is 15 m and the pitch R of the slits S and S is varied around several μm, a circular locus with a diameter of about 4 mm is drawn on the position detector by one diffracted light. The rotation angle can be detected with a resolution of about .1', resulting in extremely high precision.

Next, the above operation will be analytically explained.

FIG. 2 shows how the incident light is diffracted by the circumferential slit Sc, and FIG. 3 shows how the incident light is diffracted by the radial slit SR.

Let O be the coordinate origin of the position detector 20. Let Q be the X coordinate of the irradiation position of the light diffracted by the circumferential slit Sc on the position detector 20, and P be the irradiation position of the incident light C on the disk 10. The distance from the disk 10 to the position detector is a5
The angle between the straight line connecting the point P and the origin O and the optical axis of the incident light C is α1.The angle between the straight line connecting the point P and the X coordinate Q and the straight line connecting the point P and the origin O is ψ. . Let G be a point where the optical axis of the incident light C intersects with the same plane as the surface of the position detector 20.

Since the diffraction angle is expressed by the equation (1) as described above, the diffraction angle of the first-order diffracted light by the slit Sc in FIG. 2 is given by the following equation.

5in(α+ψ)−λ/dθ,
-(2) dθ1 is the slit pitch of the slits Sc at the irradiation position on the disk 10.

5in2x +cos'' x -1 (7) When the relational expression (7) is used, the following expression is obtained from the equation (2).

2 2-cos(α+ψ)-(1-λ/(dθ)+2-1
3) Also, by using the relational expression tanx-5lnx/cosx, the following expression can be obtained from equations (2) and (3).

tan (α + ψ) − λ / (dθ 2 − λ2)”
-(4) Furthermore, from FIG. 2, the following equation can be obtained.

GQ −PQ 5in(a+ψ)
-(5)x Go-atana
−(6) P Q −a /eos(α+ψ
) ・(7) OQ is obtained by the following formula.

OQ - GQ - GO (8) x Equation (8) can be transformed as follows using equations (4) to (7).

OQ = PQ 5in (α+ψ) −atana
x = la/cms (α + ψ) lsln (α + ψ)
atar+α family a tan(α+ψ) -arana-
aλ/(dθ 2−λ”)2−atana−(9)O
The locus of Q and the locus of OQ, which will be described later, are combined y to form the locus of Kaden, so that OQ has the form A cos θ with respect to the rotation angle θ of the disk IO, and OQ, which will be described later.
It suffices if Q takes the form A sinθ, so the (9〉・
...(10) is obtained.

Modifying equation (lO), dθ −λ (a + (Acosθ+atanα)2
1wo/I Acosθ+atanαl −
We obtain (11).

Therefore, regarding the angle θ, the circumferential slit Sc may be formed such that the slit pitch dθ1 satisfies the equation (11).

Next, in FIG. 3, the Y coordinate of the irradiation position on the position detector 20 of the light diffracted by the radial slit SR is expressed as Q.
Let the slit pitch of the slit S at the light irradiation position on one circular plate lO be dθ2.

In the same manner as described above, the slit pitch dθ2 of the rotation angle θ of the disk lO is determined by OQ −A sin θ.
inθ12...(
12) Obtain =.

If a circumferential slit Sc and a radial slit SR with slit pitches dθ and dθ2 are formed on the disk lO so as to satisfy the equations (11> and (12)), the combined diffracted light will be A circular locus is drawn as shown by the chain line B in Fig. 1.As a result, the rotation angle of the disk 10 and the diffracted light correspond one-to-one, and by detecting the position of one diffracted light, the disk The rotation angle of lO can be known.

In the above embodiment, a radial slit S and a circumferential slit Sc are formed in one circular plate 10, and one diffracted light is caused to draw a circular locus, and the rotation angle of the circular plate 10 is detected from the irradiation position of the diffracted light. However, the slits formed in one circular plate 10 may be formed in either the radial direction or the circumferential direction.

Further, in the above-described embodiment, a slit is formed in the disk lO to generate diffracted light, but the present invention is not limited to this, and any structure that generates one diffraction may be used. For example, a grating having a rectangular pattern in cross section, a grating formed by a refractive index distribution, etc. may be used. Furthermore, although the transmitted diffracted light is used in the embodiment, the effect similar to 1.iJ can also be obtained by using reflected diffracted light.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of the invention. FIG. 2 is a perspective view showing the state of diffracted light generated by the slits formed in the circumferential direction, and FIG. 3 is a perspective view showing the state of the diffracted light generated by the slits formed in the radial direction. FIG. 4 is a perspective view showing an example of a conventional rotary encoder. 1...Light source. lO...disc. 20...Position detector. 2! ...Output circuit. Sc...Slit in the circumferential direction SR...Slit in the radial direction. C9...Diffracted light. Above Figure 1

Claims (1)

[Claims] A rotatable device in which a diffraction pattern that causes diffraction in a projected light beam is formed in at least one of the radial direction and the circumferential direction, and the pitch of this diffraction pattern changes with respect to angle. a disc, a light source that projects a light beam onto the disc, a position detection means for detecting the direction of the diffracted light generated by the diffraction pattern of the disc, and a position detection means based on the direction of the diffracted light detected by the position detection means. A rotary encoder comprising means for outputting a signal representing the rotation angle of the disc.