JPH0321820A - Rotation angle encoder - Google Patents

Abstract

PURPOSE:To obtain the encoder which is not affected by the eccentricity of a rotary shaft by providing a light source, a photodetecting means, and a 1st and a 2nd polarizing means. CONSTITUTION:The axis of polarization of the 1st polarizing means 5 rotates as the rotary shaft 1 rotates. The 2nd polarizing means 6 is placed right before the photodetecting means 4. Luminous flux emitted by the light source 2 passes through the 1st polarizing means 5 and 2nd polarizing means 6 and is made incident on the photodetecting means 4. The quantity of the light incident on the photodetecting means 3 is proportional to COS<2>theta, where theta is the angle between the axis of polarization of the 1st polarizing means 5 and the axis of polarization of the 2nd polarizing means 6. Namely, COS<2>theta = (1+COS(2theta))/2, so its variation is a COS(2theta) components, which is led out by two cycles in one rotation of the rotary shaft. It is evident from this principle that the output depends only upon the relative angle between the axes of polarization and is not affected by a position shift such as the eccentricity of the rotary shaft.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a rotational angle encoder that generates an electrical signal with a frequency synchronized with rotation. Conventional technology Figure 9 is a diagram of the configuration of a conventional rotary angle encoder. 1
is a rotating shaft, 2 is a light source, 3 is a Surisoto disk, and 4 is a light detection means. A slit disk 3 fixed to a rotating shaft 1 is placed between a light source 2 and a light detection stage 4 that receives a luminous flux emitted from the light source 2, and the light is incident on the light detecting means 4 as the rotating shaft l rotates. Intermittent light flux. Therefore, the light detection means 4 outputs a frequency signal associated with the rotation (g
4. For example, all the rNewton special edition sensors 1986
April issue P. 171 ■ Kyoikusha). Problems to be Solved by the Invention However, with the above configuration, the position of the slit changes due to the eccentricity of the rotating shaft, resulting in a time axis error (jitter) in the output. ! ! Means for Solving the Problem In order to solve the above problem, the present invention provides a light source;
a light detection means for receiving a luminous flux from the light source and converting it into an electrical signal; a second polarization means installed in an optical path between the light source and the light detection means; a first polarization means attached to a rotating shaft; It is equipped with Furthermore, the present invention includes a light source, a first polarizing means attached to a rotation axis, a second polarization means having a polarization axis in a different direction depending on a position in a circumferential direction around the rotation axis, and this second polarization means. A plurality of light detection means are arranged at approximately equal intervals around the entire circumference or half the circumference of a circle whose center is on the central axis of the second polarization means. Operation The present invention can provide a rotational angle encoder that is not affected by the eccentricity of the rotating shaft due to the above-described structure. Embodiment FIG. 1 is a configuration diagram showing an embodiment of a rotational angle encoder of the present invention. 1 is a rotation axis, 2 is a light source, 4 is a light detection means, 5 is a first polarization means, and 6 is a second polarization means. The polarization axis of the first polarizing means 5 rotates as the rotation axis 1 rotates. The second polarizing means 6 is placed immediately in front of the light detecting means 4. The light beam generated from the light source 2 passes through the first polarizing means 5 and the second polarizing means 6 and enters the light detecting means 4. The amount of light incident on the light detection means 4 is determined by the first polarization means 5.
Letting θ be the angle between the polarization axis of the second polarizing means 6 and the polarization axis of the second polarizing means 6, it is proportional to COS2θ. In other words, since COS2θ-(1+COS (2θ))/2, the variation is equivalent to COS (2θ), and 2 for each revolution of the rotating shaft.
It is possible to extract the precepts of the period. As can be seen from this principle, the output depends only on the relative angle of each polarization axis and is not affected by positional deviations such as eccentricity of the rotation axis. Also, since the output is a sine wave, it can be easily divided electrically for use. FIG. 2 is a block diagram showing a second embodiment of the present invention.
A and 6b are second polarizing means, respectively, and 4a and 4b are photodetecting means corresponding to the second polarizing means, respectively. Second
The polarization means 6a, 6b are shifted by the polarization axis angle Φ, and the outputs of the light detection means 4a, 4b are shifted in phase by Φ/2 accordingly. That is, the light detection means 4a
The direction of rotation can be easily determined by examining the phase of the output of 4b. FIG. 3 shows a third embodiment of the present invention, in which the second polarization means is constituted by polarization separation means using a polarization beam splitter 6c. The photodetector stages 4a and 4b are arranged at respective light exits of the polarizing beam splitter 6c.

That is, since the light beam incident on the polarizing beam splitter 6c is separated into polarized light beams that are shifted by 90 degrees from each other, signals having a phase difference of exactly 90 degrees can be extracted from the outputs of the photodetecting means 4a and 4b. I can do it. The second polarizing means is not limited to the polarizing beam splitter shown in the drawings, but there are many other possible options, such as those that utilize Brewster's angle, and those that utilize birefringence such as Nicol prisms and Glan-Thompson prisms. FIG. 4 shows a fourth embodiment of the present invention, in which the second polarizing means has different polarizing axes in the circumferential direction. Such polarizing means can be made, for example, by winding a semicircular polarizing plate into a conical shape, as shown in FIG. In this case, when viewed from above, the direction of the polarization axis changes depending on the location in the circumferential direction, as shown in Figure 6. A plurality of light detection means 4 are arranged at approximately equal intervals on the circumference of a circle whose center is on the central axis of the polarization means 6c which has polarization axes in different directions depending on the circumferential direction. are lined up. With this configuration, the light detection means 4
From the output of each photodetector, a multiphase sine wave signal corresponding to the rotation angle can be extracted as shown in FIG. In addition, by dispersing needle-shaped herabatite crystals in amyl acetate of cellulose acetate and extruding them with a conical mold, the polarization axis is oriented in the radial direction as shown in Figure 8 by aligning the orientation of the crystals. It is possible to make a polarizing plate using Furthermore, a polarizing means having such a polarization axis can also be constructed using a conical polarizing prism. In this case, since the polarization axis changes twice per rotation in the circumferential direction, the light detection means may be arranged at approximately equal intervals on the half circumference of a circle whose center is on the central axis of the polarization means 6C. By using such multiphase sine wave signals, the number of waves per revolution can be easily divided electrically and increased. Effects of the Invention As described above, according to the present invention, the first polarizing means, the second polarizing means
Since the rotation angle of the first polarization means is detected using the polarization means, it is possible to provide a rotation angle encoder that is not affected by the eccentricity of the rotation axis.

[Brief explanation of the drawing]

FIG. 1 is a composition diagram of a rotation angle encoder according to a first embodiment of the present invention, FIG. 2 is a composition diagram of a rotation angle encoder according to a second embodiment of the present invention, and FIG. FIG. 4 is a block diagram of the rotational angle encoder in the fourth embodiment of the present invention, and FIG. 5 shows how to make the second polarizing means shown in FIG. 4. 6 and 8 are explanatory diagrams showing the state of the polarization axis of the second polarizing means shown in FIG. 4, FIG. 7 is a waveform diagram showing the output of the photodetecting means, and FIG. This is a configuration diagram of a conventional rotational angle encoder.

Claims (7)

[Claims] (1) A light source, a light detection means that receives a luminous flux emitted from the light source and converts it into an electrical signal, a second polarization means installed in the optical path between the light source and the light detection means, and a rotation axis. and a first polarizing means attached thereto. (2) The second polarizing means is comprised of a plurality of polarizing means each having a polarization axis in a different direction, and a plurality of photodetecting means are provided corresponding to the plurality of polarizing means. (1) The rotational angle encoder described in (1). (3) The rotary angle encoder according to claim 1, wherein the second polarization means is constituted by a polarization separation means, and the light detection means is placed at each light exit. (4) a light source, a first polarizing means attached to a rotating shaft, a second polarizing means having a polarizing axis in a different direction depending on the position in the circumferential direction, and a polarizing means attached to a central axis of the second polarizing means; and a plurality of light detection means arranged at approximately equal intervals around the entire circumference or half the circumference of a circle having a center, and the first polarization means and the second polarization means are connected to the light source and the light detection means. A rotary angle encoder located in the optical path of the rotary angle encoder. (5) The rotary angle encoder according to claim 4, wherein the second polarizing means is a polarizing plate wound in a substantially conical slope shape or a substantially truncated conical slope shape. (6) The rotary angle encoder according to claim (4), wherein the second polarizing means is a polarizing plate having a substantially conical slope shape or a substantially conical frustum slope shape and having a polarization axis in a radial direction. (7) The rotary angle encoder according to claim 4, wherein the second polarizing means is a polarizing prism having a substantially conical shape or a substantially frustum shape.