JPS59231412A - Detecting system of position - Google Patents

Abstract

PURPOSE:To enable the detection of a position of a moving body whose track is determined beforehand, without requiring a visual connection between an observation point and the moving body, by detecting the Faraday rotation of a plane of polarization of a linear polarized light transmitted through optical fibers, and by detecting the position of the body based thereon. CONSTITUTION:A position of a body is detected by utilizing the Faraday effect of optical fibers. Concretely, a magnet 2 is fitted to the body 1, and a number of optical fibers F1-Fn are provided in parallel so that they can be parallel with the NS direction of the magnet 2. Each of the optical fibers F1-Fn is provided with parts sensitive to magnetism (high sensitive parts) and parts not sensitive to the magnetism (low sensitive parts), which are distributed alternately. The optical fibers are made different from one another in the distribution of said parts. Since the magnet 2 is positioned close to the group of the optical fibers, the Faraday effect occurs in the optical fibers whose parts sensitive to the magnetism are in the vicinity of the magnet 2. With polarizers P1-Pn and photodetectors D1-Dn set at both ends of each optical fiber, a linear polarized light is made to fall on said optical fiber from one side, and the rotation of the plane of polarization of the light passing through the fiber is measured. The position of the body is determined when the group of optical fibers from which the Faraday rotation is detected is known.

Description

[Detailed description of the invention] (a) Technical field The present invention relates to a position detection method using an optical fiber.

The position of an object is detected by applying magnetic shielding to multiple optical fibers, creating parts that are sensitive to magnetism and parts that are not, and detecting the rotation of the plane of polarization of light propagating through the optical fibers.

(b) Conventional technology and its problems Guided radio has traditionally been one of the effective methods for detecting the position of a moving object. Since this method uses changes in high-frequency electric fields, it is easily affected by external noise and is not very accurate.

There is also a position detection method that uses light. This involves placing a bar code, mark, etc. on an object, shining light onto it, and detecting the reflected light with a sensor.

The position (address) is identified optically.

It is non-contact and has a fast reading speed. If you modulate the light,
The influence of DC disturbance light can be cut. but,
Since this method uses the reflection of light, it has the disadvantage of being susceptible to dirt.

Position detection methods that utilize laser light waves are also already known. The distance is calculated by shining a laser beam on an object and measuring the time it takes for the reflected light to return.

Since the laser beam has a constant beam diameter and propagates in a straight line, it is possible to measure the distance to a distant object. However, in the method using laser light, the distance between the observation point and the object must not be blocked by obstacles. The object must be exposed to the outside and directly visible from the observation point.

(ri) The objective of the present invention is to provide the following position detection method.

(1) Detecting the position of an object that is not necessarily exposed to the outside, has a sufficiently long range of movement, and has a predetermined trajectory.

(2) Must not be affected by noise caused by electromagnetic induction, etc.

(3) Even if the object surface is dirty, it can be detected correctly. It does not depend on the surface condition of the object.

(4) Not affected by temperature changes.

(fil) Strong against smoke and corrosive gases.

etc.

(1) Faraday Effect The inventor of the present invention came up with the idea of using the Faraday effect as a detection power formula that meets this purpose.

The Faraday effect is that when linearly polarized light is incident on an element and a magnetic field H is applied to the element in the direction in which the light travels, the plane of polarization rotates in proportion to the strength of the magnetic field. The rotation angle ψ is given by ψ−VeHβ (1). H is the magnetic field, l is the length of the element, and Ve is the Verdet constant.

The Faraday effect can be applied to lead glass and BS○ (Bi+z Si).
020) It is noticeable in single crystals.

For example, for light with a wavelength of 633 nm, the Verdet constant (d, 0.2 min/Oe am) at room temperature.

Quartz also has a slight Faraday effect.

The Verdet constant of quartz is for light with a wavelength of 589 nm,
It is 0.2 m f n /Q6 cm at room temperature. Therefore, the Faraday effect can occur even in optical fibers using quartz as a core.

In addition, the core material is FR-5 (Verdet constant -〇, 25] m
There are also research examples of fiber-type Faraday elements using i in10 e o), and it is thought that many fibers with large Verdet constants will appear in the future, and their use will be more effective.

An optical CT (current meter) has already been proposed as a measuring instrument that uses the Faraday effect of optical fiber.

A single mode optical fiber is wrapped around a power transmission line several dozen times and both ends are lowered to the ground. Lenses, polarizers, and analyzers are placed at both ends of the optical fiber, and laser light is made to enter the optical fiber.

After the laser light becomes linearly polarized, it enters the optical fiber. The plane of polarization rotates due to the magnetic field generated at the switch of the power transmission line.

The rotation of the plane of polarization can be determined from the magnitude of the output through the detector. In this way, the magnitude of the current in the power transmission line can be measured. It is safe because the only thing that connects the power lines to the ground is an insulating material such as optical fiber.

However, this has not yet been put into practical use.

The ql-mode optical fiber has a drawback in that the propagation constants βX and βy of light polarized in two axes orthogonal to the longitudinal direction cannot necessarily be equal. When there is a difference Δβ in the propagation constant, the plane of polarization rotates and shifts. The rotation due to Δβ and the rotation due to the Faraday effect should be able to be separated by calibration. However, the difference in propagation constant Δ
β is also caused by local fluctuations and bending of the paulownia wood, so it is not always constant.

Since the photometric current meter measures the current value in an analog manner, the signal/noise ratio decreases significantly due to fluctuations in Δβ, resulting in poor reliability.

(e) Configuration of the present invention The present invention detects the position of an object by utilizing the Faraday effect of an optical fiber.

To compensate for the poor polarization preservation performance of optical fibers, we give up on using the Faraday effect in an analog way and use it digitally.

A magnet is attached to the object, and a large number of optical fibers are provided in parallel so that they are parallel to the NS direction of the magnet.

The optical fiber is provided with parts that are sensitive to magnetism and parts that are not sensitive to magnetism, which are distributed alternately. This distribution is made as described in each optical fiber.

Since the magnet is close to the group of optical fibers, the Faraday effect occurs, especially when the optical fiber has a magnetic part near the magnet. A polarizer and an analyzer are placed at both ends of each optical fiber, linearly polarized light is input from one end, and the rotation of the plane of polarization of the light that has passed through the fiber is measured. If the optical fiber 1 in which the Faraday cycle was detected is known, the position of the object can be determined.

Hereinafter, for the sake of simplicity, the part that feels the magnetism of the optical fiber (~) is referred to as the full-height magnetically sensitive part, and the part that does not or hardly feels magnetism is called the low magnetically sensitive part.

The object position detection method of the present invention includes +11 a plurality of single mode optical fibers F1 in which high magnetic sensitivity parts H and low magnetic sensitivity parts are alternately provided with different distributions;
F21, Fn are provided parallel to LL, (2) polarizers P1, F2,
・, Pn and analyzers Ql , Q2, . . . , Qn are provided, (
3) Optical fibers F1, F through polarizers P11, Pn
2,...Light sources L1, L2,...L that input light to -1Fn
(4) The intensity of the emitted light from the analyzer Q, 1, on is detected by the detectors D1, D21, Dn, (5)
A magnet is installed on the moving object whose position is to be detected close to the group of optical fibers, and (]j) From the detector output, determine the group of optical fibers (Fk) in which rotation of the plane of polarization due to the Faraday effect has been detected. , (7) The position of an object is detected from a group of polarization plane rotating optical fibers (Fk).

(Force) Example 1 11th YI & Embodiment of the present invention is shown.

Optical fibers Fl 1, Fn i'j: A large number of Jl-mode optical fibers are provided in parallel along the locus of the moving body 1. The movable body 1 is mounted so that the optical fibers F+ and 8Fn are opposed to each other, and the fiber axes and the NS direction are parallel to each other.

Each optical fiber F1, -1Fn is provided with a magnetic shield 3 in a different mode. The magnetic shield 3 can be made of a ferromagnetic material such as iron. The part without the magnetic shield 3 feels magnetic when the magnet 2 approaches. In other words, the highly magnetically sensitive part H
becomes. A portion of the magnetic shield 3 does not feel magnetism even if the magnet 2 approaches it.

It has a low magnetic sensitivity part.

In the figure, from the one closest to magnet 2, optical fibers F1 and F21
, Fn are written as being lined up, but in reality, the optical fibers F1, F2,..., Fn are lined up in a cylindrical shape surrounding the locus of motion of magnet 2, at equal intervals from magnet 2. That's promising.

A polarizer P11 is attached to one end of the optical fibers F1, F2,...
, Pn, and analyzers Ql, Q2, . . . , Qn are provided at the other end. On the outer side of the polarizer, light sources L1, . . ., Ln
is installed. The light source is preferably an ID laser beam. Instead of providing n lasers, fewer lasers may be used and split by a beam splitter to be incident on each fiber. The light passes through a polarizer, is focused by a lens (not shown), and enters the optical fibers F1, . . . , Fn.

At the other end of the optical fiber is an analyzer. 1, . . . Qn and detectors D11 and Dn are provided.

It is possible to distinguish between the detector output when there is no Faraday rotation and the detector output when there is Faraday rotation.

Even if the propagation constants differ for polarized waves in the two axes x and y directions perpendicular to the fiber axis, the rotation of the plane of polarization by Δβ is constant for each fiber, so by adjusting the direction of the analyzer in advance, Set the detector output to the maximum or minimum when there is no rotation. If there is Faraday rotation, the detector output will shift. The problem is not the amount of shift, but rather a binary logic of 1-shift or no shift, so there are fewer errors.

Then, the distribution of the magnetic shield 3 (ri each fiber F1,
・, Fn are all different.

A magnetic field parallel to the optical fiber axis is generated by the magnet 2 at the location where the moving body 1 is present. In this part, only the optical fiber group ('k) without the magnetic shield 3 senses the magnetic field.The plane of polarization of the light propagating in the optical fiber (Fk) undergoes Faraday rotation.Faraday rotation causes the detector ( Dk) output changes.

Faraday rotation detected Zoko optical fiber group (Fk)
If you know, you can find out the part that these have in common with the high 1-magnetic iso part H (no magnetic shield). This is the current position of the moving body 1.

It is sufficient that the distributions of the magnetically sensitive parts H and low magnetically sensitive parts of the optical fibers F1, . . . , Fn are equal to each other. H1L by law
It is better to calculate the distribution by ′j−.

Since phino ('s) is n, it is possible to use an n-bit binary number for the digit 1.

All 15 fibers! :l is divided into 211 for Fl (is divided into F2, and for F2 is divided into 211-l. Generally, for FjK, the division I is divided into
I will do J.

ri] The number of the divided pieces is the lowest, and the even number is If.
iIhlj'< spelling part H (the complete opposite is also acceptable)
.

In this way, the position If rotation occurs, 1″° corresponds to it, and if there is no Faraday rotation, it corresponds to °゛0゛.The thus binarized outputs of the famous fibers F1, . . . , Fn are bl, b2, − If 1bn, the position of the magnet is x - = bn bo - 4 - b2b + fl)
(It is displayed as a binary number.

This is just an example.

As long as the H and L distributions of each fiber are all different, it is not necessary to do as described in 1. If it is desired to accurately detect the position of only a certain part, the H,1 distribution may be made narrower by that part.

In particular, it is more effective to use gray codes for the H and L patterns, since there are fewer errors.

The lines of magnetic force of magnet 2 are the smallest repeating pattern of H and L.
I don't want it to feel like I'm straddling two H's, so
The length of the magnet is also limited.

(G) Embodiment 2 In order to provide a high-sensitivity binding part H1 and a low-sensitivity binding part in an optical fiber, in the previous example, magnetic shields were distributed.

In order to distinguish between H and L, the light beam may be made to meander. FIG. 2 shows such an embodiment.

Since the magnet is parallel to the longitudinal direction of the fiber, the lines of magnetic force also occur parallel to the longitudinal direction of the fiber. The part parallel to the longitudinal direction of the meandering fiber has a strong magnetic field <FE=
Sign. On the other hand, in the inclined part, since the direction of the fiber and the direction of the magnetic field are not parallel, it is easier to reduce the magnetic field to most of the part.

In this manner, by providing the parallel portion and the inclined portion, a high-I binding portion H1 and a low-sensitivity binding portion can be created.

(ri) Example 3 In order to distinguish between the high magnetic part H and the low magnetic part H, a distance of 1
i'L <C' of i1ti (it is also possible to write.

The third il f-1 shows such an example. The distance between the magnet and the fiber F is changed by the diameter t of the center rod.

The part close to the magnet is the high magnetic sensitivity part H, and the part far away is the low part.
This will be the Tsuzuri section.

If the center rod 4 is made of a non-magnetic material, H and L can be distinguished by the difference in distance. When the center rod 4 is made of a ferromagnetic material, the lines of magnetic force are twisted around the center rod 4, so that there is no magnetic field at all in the part far from the magnet.

(G) Effect: The position of an object is detected by detecting the Faraday rotation of the plane of polarization of linearly polarized light transmitted within an optical fiber, so there is a lack of effect.

+1) There is no need for a visual connection between the observation point and the moving object.

(2) The position of a moving object whose trajectory is determined in advance can be detected.

(3) Strong against electromagnetic induction and noise.

(4) There is no problem even if the object is dirty.

(5) Strong against corrosive atmosphere.

(6) Not affected by temperature changes.

(7) Faraday rotation is treated as a digital signal rather than an analog signal, so there are fewer errors.

(J) Applications (1) Used for absolute position detection of moving objects, absolute position detection of +2+ rll pots, and) two-color pair position detection of industrial machines.

[Brief explanation of drawings]

Figure 1 (・'' is a schematic diagram of the optical system configuration of the position producing force type according to the present invention) Fig. 3 is a fiber front view of an embodiment in which a high-sensitivity binding part H1 and a low-sensitivity binding part are created by winding a noi fiber around the center rod. 1 Movement Body 2 ・ Magnet 3 − Magnetic shield 4 ・ Center rod ``1 ~ Fn Light Noah 1' bar P + ~ Pn −-1im So(, Child QI-
Qn~・Analyzer L1~Ln・Light source D+”=j)n・・Detector H−High magnetic sensitive part L・・・・Low magnetic sensitive part

Claims (1)

[Claims] A plurality of single mode optical fibers F1, F2, .
Fn are provided in parallel to each other, and each optical fiber F1,...,F
Polarizer P1..., Pn and analyzer Q+, ・Q on both ends of n
n, and connect each optical fiber F1 . ..., light source L1, -..., L that inputs light to Fn
n is provided at one end of the optical fiber, and analyzers Ql,...,Q
The intensity of the emitted light from N5 is detected by detectors D11 and Dn, and a magnet 2 is attached to the moving body 1 whose position is to be detected so that it is close to the group of optical fibers so that N5Jffi is parallel to the optical fibers, and the detector output Find the group of optical fibers (Fk) in which the rotation of the plane of polarization due to the Faraday effect is detected,
A position detection method characterized by detecting the position of the moving body 1 from now on.