FI80521C - Fiber optic location sensor - Google Patents

Description

80521

Fiber optic position sensor 5

The invention relates to an optical position sensor for optically measuring small displacements. The sensor is based on the coupling of light from an optical light waveguide, e.g. an optical fiber, to the light waveguides of the integrated optics and the sensor part is formed by an optical light waveguide.

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Previous fiber optic position sensors are based on the coupling of light from one optical fiber to another, with the intensity of the coupled light depending on the position of the fibers relative to each other. The weakness of the sensors is their sensitivity to displacements in all 15 directions, so the direction of the displacement cannot be measured. In addition, small changes in the light intensity level affect the measurement results.

The position sensor according to the invention provides a decisive improvement in the above-mentioned drawbacks. The optical position sensor according to the invention is characterized in that the position is measured by those connected to the light waveguides by a light waveguide (e.g. a single-mode optical fiber). a ratio of light powers which depends on the position of the light waveguide only in the other direction and which is not affected by the light power propagating in the light waveguide.

More specifically, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

The position sensor according to the invention, in turn, is characterized by what is set forth in the characterizing part of claim 2.

Thanks to the use of integrated optics fluorescent tubes, the sensor is only sensitive to one-way transitions. In addition, when measuring the ratio of the intensities coupled to two isolated light tubes, changes in the intensity level are eliminated. Based on the measurement results, the sensitivity of the sensor is in the same class as previous fiber optic position sensors.

In the following, the invention will be explained in more detail with reference to the accompanying drawings.

Figure 1 shows one optical position sensor according to the invention, which has two light waveguides in the branch structure of the integrated optics.

Figure 2 shows another optical position-15 sensor according to the invention, which has four light waveguides in the branching structure of the integrated optics.

The sensor according to Fig. 1 consists, for example, of a single-mode fiber 1 and a branching structure 3 of the integrated optics, which has been previously used in backscatter measurements of multi-mode fibers. The light is connected to a light waveguide 1 transmitted from a light source (e.g. a laser), e.g. a single mode fiber, the output end of which is placed at a distance of about 10 μm from the common end of the light waveguides 2 of the integrated optics 3. The 25 optical waveguides 2 of the integrated optics 3 are arranged side by side. Formed on the surface of the glass substrate, the interfaces of the light waveguides against each other are substantially straight and parallel, and the insulator is a layer of adhesive about 5 .mu.m thick with a refractive index lower than that of the waveguides. By measuring the ratio of the intensities obtained from the output of the light tubes 2, the displacement of the optical fiber with respect to the common end of the light tubes is determined. The sensor is sensitive to displacements in only one direction, because the dimensions of the waveguides 2 are about 10 times the size of the core of the single-mode fiber 1.

The sensor according to Figure 2 has two devices according to Figure 1.

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35 3 80521 light waveguide arrangement 2 arranged in parallel, whereby information on the position of the moving fiber 1 is obtained both vertically and horizontally by measuring the ratio of the light powers connected to the light waveguides from the fiber.

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The optical position sensors shown in the figures are only examples of a position sensor according to the invention. Of course, embodiments of the invention may vary widely within the scope of the claims.

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Claims (3)

An optical displacement measurement method, according to which method - a light signal is passed along an emitting optical light tube (1) to a sensor (3) comprising at least two receiving light tube 10 (2), - the light effect that hit each one of the receiving light tubes (2) is detected with corresponding detectors for determining the light effect in the light tubes, characterized in that - the relationship between the light effect that hit each of the receiving light tubes (2) and the light effect which when the other receiving light-tube tubes (2) are determined, the displacement can be determined and the variation in the incoming light output is eliminated from these relative light effects. 2. Optical position sensor, comprising - an emitting, movable light-tube (1) 30 and - at least two receiving light-tube (2), arranged side by side, characterized in that - the receiving, arranged side-by-side (2) tubes (2) are formed of integrated optics, such that adjacent edge surfaces of the receiving light wave tubes <23 are substantially straight and parallel to provide directional sensitivity. (I 7 80521 3. An encoder according to claim 2, characterized in that it has four receiving lightweight tubes (2).