JPH03211417A - Optical rotational angle measuring instrument - Google Patents

Abstract

PURPOSE:To simplify the structure and to measure the angle of rotation of a body to be measured at lower cost by varying the polarizing direction of the outgoing light from a light source part according to the rotation of the body and detecting the changed polarizing direction with a photodetector. CONSTITUTION:The light L1 of the laser light source 11 is polarized into linear polarized light L2 whose polarizing direction is fixed through a polarizer 21 and the polarized light L2 is converted into circular polarized light L3 by a discoid lambda/4 plate 23 fixed to a cylinder body 22 coupled with the body. Then the light is reflected by a corner cube 24 coaxial with the cylinder body 22 and made incident on the lambda/4 plate 23 again, and its outgoing light L4 becomes linear polarized light again, but the polarizing direction of the polarized light L4 is changed with the angle of rotation of the cylinder body 22. This polarized light L4 is split by a polarization beam splitter 22 into two light beams, which are received by 1st and 2nd photodetectors 16a and 16b; and their electric signals which are proportional to their incident light beams are inputted to an arithmetic circuit 28 to calculate the angle of rotation of the cylinder body 22.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an optical rotation angle measuring device used to measure the rotation angle of an object.

"Prior Art" Figure 5 is a principle diagram of a typical conventional optical rotary encoder, which is a type of optical rotation angle measuring device.9 light sources 11
The light passes through the fixed slit 12 and the rotating slit 14 attached to the rotating shaft 13, and enters the photodetector 16. The one-rotation slit 14, which is converted into an electrical signal, is shown in FIGS. 6 and 7. Because of the presence of the slit 14a, the amount of light passing therethrough changes periodically depending on the positions of the fixed slit 12 and the rotating slit 14, and the rotation angle of the rotating shaft 13 can be detected.

"Problem to be Solved by the Invention" In the conventional optical rotary encoder, the S/N of the signal deteriorates when the distance between the rotating slit 14 and the fixed slit I2 is increased due to the influence of light diffraction. In particular, when the pitch of the slits 14a is made small in order to achieve high resolution, the influence of diffraction is significant.

For this reason, it was necessary to align the two slits as narrowly as possible so that they would not collide.

That is, as shown in FIG. 8, if the distance between the fixed slit 12 and the rotating slit 14 is increased, the light will be diffracted and spread to the adjacent slit, and the light will always be incident on the photodetector 16. As a result, the change in the amount of light due to the rotation of the rotary pickpocket 7) 14 does not appear noticeably, making it impossible to detect the rotation angle. Therefore, as shown in FIG. 9, it is necessary to close the distance between the fixed slit 12 and the rotating slit 14 to such an extent that the influence of light diffraction can be ignored, for example, several tens of μm.
They are arranged at intervals of m.

However, the rotating slit 14 relative to the fixed slit
In order to accurately maintain the position of the rotary encoder without collision, the rotation mechanism must be configured with high precision, and the time required for alignment is also long, resulting in an expensive rotary encoder. .

The purpose of this invention is to provide a rotation angle measuring device that can be constructed at a lower cost without using a conventional rotation slit mechanism which has a complicated rotation mechanism and takes time for alignment.

"Means for Solving the Problems" (1) The optical rotation angle detection device of the present invention includes a light source section that generates linearly polarized light, and a polarization direction of the light from the light source section according to the rotation angle of the object to be measured. It consists of a rotating section that changes the polarization direction, and a detection section that detects the rotation angle of the object based on the changed polarization direction.

(2) In the above item (1), the light source unit emits linearly polarized light from a laser light source through a polarizer, and the rotating unit includes a λ/4 plate and a corner that rotate together with the object to be measured. It has a cube prism, the linearly polarized light from the light source is reflected by a corner cube prism through a λ/4 plate, and then emitted to the detection unit through the λ/4 plate, and the detection unit The light from the
A polarizing beam splitter splits the electric field components into reflected light and transmitted light that are orthogonal to each other, and each light is detected by a first and second photodetector. Preferably, the output of the second photodetector is supplied to a calculation circuit to calculate the rotation angle of the object to be measured.

(3) In the above (11) or (2), the light source section and the detection section are housed in the equipment storage chamber of the housing, and the rotating section is coaxially connected to a rotating shaft that rotates together with the object to be measured. It is preferable that the cylindrical body is housed in a cylindrical body, and that the cylindrical body is rotatably held via a bearing in a hollow cylindrical housing chamber provided in the housing.

"Embodiment" An embodiment of this invention is shown in FIG. 1, with the same reference numerals attached to parts corresponding to those in FIG. 5. Light L1 from the laser light source 11 passes through a polarizer 21 and becomes linearly polarized light L2 with a constant polarization direction. From now on, L2 is converted into circularly polarized light L3 through a disk-shaped λ/4 plate 23 fixed in a cylindrical body 22 connected to the object to be measured, and the positions of the incident light and reflected light are always point symmetrical with respect to the center. Corner cube prism 24 that is reflected so that
(attached coaxially within the cylindrical body 22), and enters the λ/4 plate 23 again. The emitted light L4 of the λ/4 plate 23 becomes linearly polarized light again, but at this time, L4 is
The polarization direction of changes.

The linearly polarized light L4 enters the polarization beam splitter 25, and is divided into two lights depending on the polarization direction. The signals are input to second photodetectors 16a and 16b, respectively. 1st. Electric signals proportional to the amount of incident light are output from the second photodetectors 16a and 16b to the calculation circuit 28, where the rotation angle θ of the cylindrical body 22 is calculated.

Polarizer 21, laser beam tA11, polarization beam splitter 25, first . Second photodetector 16a, 16b, arithmetic circuit 2
8 is installed in an equipment storage chamber 30 provided at the rear end within the fixed housing 29. The housing 29 is
It has a cylindrical body storage chamber 32 in the form of a hollow cylinder, in which the cylindrical body 22 is disposed coaxially and rotatably held via bearings 35 and 36. A rotating shaft 13 attached to the center of the front end surface of the cylindrical body 22 is led out through a through hole 31 provided at the center of the tip of the housing 29 . Ring-shaped bearings 35 and 36 are respectively installed between the front and rear end peripheral edges of the cylindrical body storage chamber 32 of the housing 29 and the cylindrical body 22.

λ/4 plate 2 sheet metal 3 complex amplitude Ei of electric field of incident light L8,
The complex amplitude Eo of the electric field of the emitted light L4 means that when the same λ/4 plate 2 sheet metal 3 reciprocates, the phase of the polarization component perpendicular to the main cross section of the λ/4 plate 2 sheet metal 3 in the crystal direction is (λ/ 4)X2
-λ/2 (-180°) delay, 2(11,(2
).

E 1=Ex+j Ey (1) E o
= E x −j E 3' (2)
Therefore, the λ/4 plate 2 for the incident light E i (Lz)
Assuming that the angle formed by the main cross section of the three-crystal sheet metal is the rotation angle θ of the rotating shaft 13, EI (L z) and Eo (L
4) is symmetrical with respect to the main cross section of the crystal, so Eo(L,
The polarization direction of Ei (L, ) is 2θ. That is, when the rotation angle θ changes due to the rotation of the cylindrical body 22, the polarization direction of Eo(L,) changes accordingly.

When the emitted light L4 from the λ/4 plate 2 and the metal plate 3 is incident on the polarizing beam splitter 25, transmitted light (p-polarized light) having only an electric field component parallel to the electric field vector defined on the needle face of the polarizing beam splitter 25 is transmitted E o It is divided into reflected light (S-polarized light) E o s having only an electric field component perpendicular to p. Now, by making the incident light Ei incident such that its polarization direction matches the p-polarized light EOP, E
o pE o s is E op = Eo cos 2θ (3) E
os = Eo sin 2θ (4). However, Eo=Eo. Therefore, the intensity signal P+P2 of the light that is split into two by the polarizing beam splitter 25, detected by the first photodetector 16a and the second photodetector 16b, and output is expressed by equations (5) and (6). Ru. However, k is a proportionality constant.

P = k Eos P, = k E o p By eliminating kEo'' from both equations, the rotation angle θ is calculated. The rotation angle θ is calculated in the arithmetic circuit 28, and an electric signal corresponding to it is output to the outside. .1st.2nd
The output signals of the photodetector PI, P! FIG. 4 shows the change in rotation angle θ.

In the above, the light source part is caused by the laser beam #11 and the polarizer 21, the rotation axis 13, the cylindrical body 22, the corner cube prism 24, the λ/4 plate 2, the metal plate 3, the rotating part, the polarizing beam splitter 25, the 1st degree 2 photodetectors 16a, 16b
, and the arithmetic circuit 18 constitute a detection section, respectively.

"Effect of the invention" In FIG. 1, linearly polarized light L2 emitted from the polarizer 21
is the λ/4 plate 23. The light enters the polarizing beam splitter 25 via the corner cube prism 24 and is diffracted in the process, but information regarding polarization is not lost due to the diffraction of the light, so the spacing between each component is similar to that of the conventional fixed slit 12.
It is not necessary to narrow the interval between the rotary slit 14 and the rotary slit 14, and it can be arranged quite freely. Therefore, in the rotation angle measuring device of the present invention, the attachment of the cylindrical body 22 to the housing 29 may not be as precise as the attachment of the rotating part including the conventional rotary slit 14 to the fixed slit. This can be realized at a low cost with an extremely simple structure that allows the coaxial core to be drawn into the cylindrical housing chamber 32 via the bearings 35 and 36.

Conventionally, a synchronizer, a resolver, etc. have been used as a means of remote angle transmission, but in the present invention, the object to be measured is completely insulated from the electrical circuit by the housing 29 and the cylindrical body 22. This is particularly advantageous in cases where explosion-proofness and its influence on the detection section of electrical noise are a problem.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, and FIG. 2 is a linearly polarized light L! which is incident on the rotating part of FIG. 1. The complex amplitude Ei of the electric field of , and the complex amplitude Eo of the electric field of the linearly polarized light L4 emitted from the rotating part
FIG. 3 is a hector diagram of the electric field hector E o p of the transmitted light and the electric field hector E o s of the reflected light output from the polarizing beam splitter 25 in FIG. 1.
The figure is No. 1 in Fig. 1. Second photodetector output P1. A diagram showing a change in Pt with respect to the rotation angle θ, FIG. 5 is a principle diagram of a typical conventional optical rotary encoder, and FIG. 6 is a front view of a rotating slit and a fixed slit of a conventional incremental optical rotary encoder. Figure 7 is a front view of the rotating slit and fixed slit of a conventional absolute type optical rotary encoder, and Figure 8 shows the principle of diffraction of light when the distance between the fixed slit and rotating slit in Figure 6 is widened. 9 are principle diagrams showing the state of light diffraction when the interval between the fixed slit and the rotating slit in FIG. 6 is narrowed.

Claims (3)

[Claims] (1) A light source section that generates linearly polarized light, a rotating section that changes the polarization direction of the light emitted from the light source section according to the rotation angle of the object to be measured, and a rotation angle of the object to be measured based on the changed polarization direction. An optical rotation angle measuring device characterized by comprising a detection section for detecting. (2) In claim (1), the light source unit emits linearly polarized light from a laser light source through a polarizer, and the rotating unit includes a λ/4 plate and a corner that rotate together with the object to be measured. The linearly polarized light from the light source unit is reflected by a corner cube prism through a λ/4 plate, and then emitted to the detection unit through the λ/4 plate, and the detection unit is configured to rotate the A polarizing beam splitter splits the light from the section into reflected light and transmitted light whose electric field components are orthogonal to each other, and each light is detected by a first and second photodetector. An optical rotation angle measuring device that supplies the output of the device to a calculation circuit to calculate the rotation angle of the object to be measured. (3) In claim (1) or (2), the light source section and the detection section are housed in an equipment storage chamber of the housing, and the rotating section is coaxially connected to a rotating shaft that rotates together with the object to be measured. The optical rotation angle type is housed in a cylindrical body, and the cylindrical body is rotatably held via a bearing in a hollow cylindrical body storage chamber provided in the housing. Measuring device.