JPH0321819A - absolute rotation angle encoder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an absolute rotation angle encoder for detecting the absolute rotation angle of rotation.

BACKGROUND ART FIG. 8 is a structural diagram of an example of a conventional absolute rotation angle encoder. 1 is the rotation axis, 2 is the light source, 3 is the slit disk, 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 detecting means 4 that receives a light flux emitted from the light source 2, and as the rotating shaft 1 rotates, a slit disk 3 is placed between a light source 2 and a light detecting means 4 that receives a light beam emitted from the light source 2. Intermittent the incident light flux. Therefore, a digital value corresponding to the current absolute rotation angle is output from the output of the light detection means corresponding to each slint. company).

Problems to be Solved by the Invention However, in the above-mentioned configuration, the position of the slint changes due to the eccentricity of the rotating shaft, so the accuracy of detecting the absolute rotation angle decreases and encoding errors are likely to occur.

Means for Solving the Problems In order to solve the above problems, the present invention provides a light source, a first polarizing means attached to a rotating shaft, and a second polarizing means having polarizing axes in different directions in the circumferential direction. a plurality of light detection means arranged at approximately equal intervals around the entire circumference or half of a circle having a center on the central axis of the second polarization means; and a rotation angle determined from the plurality of outputs of the light detection means. the first polarizing means and the second polarizing means are arranged in an optical path between the light source and the light detecting means.

Operation The present invention can provide an absolute rotational angle encoder that is not affected by the eccentricity of the rotating shaft due to the above-mentioned structure.

Embodiment FIG. 1 is a block diagram showing an embodiment of the absolute rotation 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, 6 is a second polarization means, and 7 is a calculation means. The polarization axis of the first polarization stage 5 rotates as the rotation axis 1 rotates. The second polarizing means 6 is placed immediately before the photodetection stage 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 one of the light detection means 4 is determined by the difference between the polarization axis of the first thousand polarization stages 5 and the polarization axis of the second thousand polarization stages 6 at a position directly above the one light detection means. Letting the angle be θ, it is proportional to COS2θ. That is, COS2θ= (1,000 COS (2θ))
/2, the variation becomes COS (2θ) command, and two cycles of command can be taken out for each rotation of the rotating shaft.

As can be seen from this principle, the output depends only on the relative angles of the respective polarization axes and is not affected by positional deviations such as eccentricity of the rotation axis. The second polarizing means 6 has a polarizing axis oriented in different directions depending on the location 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 as shown in FIG. On the circumference of a circle whose center is on the central axis of the 1,000 stages of polarization 6, which has polarization axes oriented in different directions depending on the location in the circumferential direction created in this way, the polarization axes are arranged at approximately equal intervals corresponding to the orientation of the polarization axes. A plurality of photodetection stages 4 are arranged side by side. In addition, by dispersing needle-like crystals of herbatite 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 4 by aligning the orientation of the crystals. It is possible to make a polarizing plate. Further, 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 photodetection stages 4 may be arranged at approximately equal intervals on the half circumference of a circle having its center on the central axis of the polarization means 6. With this configuration, polyphase sine wave signals corresponding to the rotation angle can be extracted from the output of each photodetector of the photodetection means 4, as shown in FIG. By checking the output value of each light detection means, it is determined that the current first polarization stage 5 is 1
You can find out which rotational position it is within 80 degrees. In other words, the output of each phase is decoded and
It can be used as an absolute encoder (absolute rotational angle encoder) with a range of 80 degrees. In FIG. 1, reference numeral 7 denotes calculation means for converting the output of the photodetection means 4 into an absolute rotation angle. FIG. 6 is a block diagram showing an example of the operation stage 7. al, a2, . The input outputs of each photodetecting means 4 are converted into digital values of 1 and 0 by a comparator 10. For example, the decoder 1l may decode the position where the input 1.0 column changes from 0 to ■ and output a digital value corresponding to the angle. FIG. 7 is a block diagram showing another example of the calculation means 7. Sine data generating means 20
outputs a value obtained by dividing one period of a sine wave into n equal parts. The output of each of the input photodetection stages 4 is multiplied by each data of the sine data generation stage 20 in the multiplication stage 21, and then added to the addition means 22.
Calculate the sum with . That is, since the output of each input light detection means 4 is a sine wave whose phase is shifted by twice the angle of the rotation axis, its phase difference can be calculated by multiplying it with the reference sine wave. I can do it. Arcsine conversion 1,000 steps 2
3 is for correcting the linearity of the output. This structure of 1,000 stages of operations is not limited to these examples. Furthermore, if it is possible to know which half-rotation of one rotation it belongs to using a rotation detection means that generates one pulse per rotation, it is possible to expand the range to 360 degrees.

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 an absolute rotation angle encoder that is not affected by the eccentricity of the rotation axis.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram of an absolute rotation angle encoder according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing how to make the second polarizing means shown in FIG. 1, and FIGS. The second shown in Figure 1
An explanatory diagram showing the state of the polarization axis of the polarization means, FIG.
Waveform diagrams showing the output of the photodetecting means shown in Figures 6 and 7.
The figure is a Bronnoch diagram showing the inside of the calculating means shown in FIG. 1, and FIG. 8 is a block diagram of a conventional absolute rotation angle encoder. 1...Rotation axis, 2...Light source, 4...
. . . Photodetection means, 5 . . . First polarization means, 6
. . . second polarization means, 7 . . . calculation means.

Claims (5)

[Claims] (1) 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. a plurality of light detection means arranged at approximately equal intervals on the entire circumference or half the circumference of a circle having a center; and a calculation means for calculating a rotation angle from the plurality of outputs of the light detection means; An absolute rotational angle encoder characterized in that the polarizing means and the second polarizing means are located in an optical path between the light source and the light detecting means. (2) The absolute system according to claim (1), further comprising rotation detection means that generates one pulse per rotation, and the rotation angle is determined from the output of the rotation detection means and the output of the calculation means. Rotary angle encoder. (3) The absolute rotational angle encoder according to claim (1) or claim (2), wherein the second polarizing means is a polarizing plate wound in a substantially conical slope shape or a substantially truncated conical slope shape. . (4) Claim (1) or (2) characterized in that the second polarizing means is a polarizing plate that has a substantially conical slope shape or a substantially truncated conical slope shape, and whose polarization axis is radial. Absolute rotational angle encoder as described. (5) The absolute rotational angle encoder according to claim 1 or claim 2, wherein the second polarizing means is a polarizing prism having a substantially conical or truncated conical shape.