JPS61204577A - reflective optical sensor - 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] [Industrial Application Field] The present invention relates to a reflective optical sensor using an optical fiber.
In particular, the present invention relates to a reflective optical sensor that measures the amount of displacement of a reflector due to pressure or the like from the output ratio of reflected light incident on a light receiving fiber from the reflector and reflected light incident on a light transmitting fiber.

[Prior Art] A conventional reflective optical sensor will be described with reference to FIG. The light emitted from the light emitting element 1 is guided to the light transmitting fiber 2, is emitted to the reflecting plate 3, and is reflected by the reflecting plate 3. Reflector plate 3
The reflected light is received by the light-receiving fiber 4, passes through the light-receiving fiber 4, enters the light-receiving element 5, and is photoelectrically converted. Note that 6 is a drive circuit for driving the light emitting element 1, 7 is a temperature compensation circuit for keeping the optical output of the light emitting element 1 constant, 8 is an amplifier circuit for amplifying the electrical output of the light receiving element 5, and 9 is an amplifier circuit for amplifying the electrical output of the light receiving element 5. This is a display circuit that displays the amplified electrical signal level.

When the reflection plate 3 is displaced due to pressure, vibration, temperature, etc., the intensity of the reflected light incident on the light receiving fiber 4 changes. Therefore, by detecting the change in the intensity of this reflected light, the physical quantity to be measured (pressure, vibration, displacement, temperature, etc.) can be measured.

[Problems to be Solved by the Invention] However, the intensity of the light emitted from the light emitting element 1 as a light source varies depending on the temperature of the surrounding water, etc., and this variation in the intensity of the light emitted from the light source appears as a measurement error. For this reason, when performing precise measurements, a compensation circuit such as the temperature compensation circuit 7 is required to keep the intensity of the light emitted from the light source constant, which complicates the measurement.

[Object of the Invention] The present invention was devised to solve the problems of the prior art described above, and an object of the invention is to provide a reflective optical sensor that can perform highly accurate measurement with a simple configuration. There is a particular thing.

[Summary of the Invention] In order to achieve the above object, the present invention includes a light source, a light transmitting fiber having an optical branching part and guiding light emitted from the light source, and a light transmitting fiber that guides the light emitted from the light source. a light-receiving fiber that receives the light reflected from the reflector; and a first light-receiving fiber that photoelectrically converts the light emitted from the light-receiving fiber.
a second light-receiving element that charges and converts the light that is reflected by the reflector, enters the light-transmitting fiber again, is split at the light branching section, and is emitted; the first light-receiver and the second light-receiver; The device includes an arithmetic circuit that calculates the amount of displacement of the reflector from the ratio of the electric outputs of the elements.

[Embodiment 1] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, 10 is a light emitting element as a light source,
The light emitting element 1o is driven by a drive circuit 11. Also,
Reference numeral 12 denotes a light transmitting fiber that guides the light emitted from the light emitting element 10 to a reflecting plate 13 as a reflector.
They are set up facing each other. The reflecting plate 13 reflects the light emitted from the light transmitting fiber 12, and the input end of the light receiving fiber 14 is provided facing the reflecting plate 13 in order to receive this reflected light. Furthermore, the output end of the light-receiving fiber 14 is provided facing the first light-receiving element 15 . Further, the light transmitting fiber 12 is provided with an optical branching section 16 for branching the light propagating therethrough, and an optical branching fiber 18 is connected to guide the branched light to the second light receiving element 17. ing. First and second light receiving elements 1
Amplifying circuits 19 and 20 for amplifying the photoelectrically converted electrical output are connected to 5° 17, respectively.

Further, the electrical signals amplified by the amplifier circuits 19 and 20 are input to the arithmetic circuit 21.
A display circuit 22 is connected to display the results of the arithmetic processing. Note that the light transmitting fiber 12, the light receiving fiber 14, and the light branching fiber 18 may be a bundle of a plurality of optical fibers instead of one.

Next, the operation of this embodiment will be described.

The light emitted from the light emitting element 10 is transmitted through the light transmission fiber 12.
The light is guided to the reflection plate 13 and emitted from its output end. The light emitted from the light transmitting fiber 12 is reflected by the reflecting plate 13, a part of the reflected light enters the light receiving fiber 14, and the rest enters the light transmitting fiber 12 again. The light incident on the light-receiving fiber 14 is guided to the first light-receiving element 15 and photoelectrically converted, and then amplified by the amplifier circuit 19. On the other hand, the light incident on the light transmitting fiber 12 returns to the light receiving element 10 side through the light transmitting fiber 12 and returns to the light branching section 16.
The light is branched at , guided to an optical branching fiber 18 , photoelectrically converted by a second light receiving element 17 , and further amplified by an amplifier circuit 20 .

The electrical signals of the first and second light receiving elements 15.17 amplified by the amplifier circuits 19.20 are input to the arithmetic circuit 21, and the output ratio e6 of these electrical signals is determined by the dividing section of the arithmetic circuit 21. It will be done. Since the reflected light that enters the light-receiving fiber 14 and the reflected light that enters the light-transmitting fiber 12 are from the same light emitting element 10, even if the intensity of the light emitted from the light emitting element 10 fluctuates, the difference between the two reflected lights will change. By taking the ratio, the influence of fluctuations in the light intensity of the light emitting element 10 serving as the light source is eliminated. That is, now, the intensity of the light entering the light transmitting fiber 12 from the light emitting element 10 is P, the coupling coefficient of the OX light branching section 16 is Ca,
The light coupling coefficient between the light transmitting fiber 12 and the reflecting plate 13 is Cr (g), the light coupling coefficient between the light receiving fiber 14 and the reflecting plate 13 is C5 (g), and the light transmitting fiber 12 Let lr be the optical transmission loss occurring in the light receiving fiber 14, and Ls be the optical transmission loss occurring in the light-receiving fiber 14, the above output ratio eo obtained by the arithmetic circuit 21 will be as follows.The fluctuation in the light intensity of the child 10 is canceled out. In this manner, the present invention is not affected by fluctuations in the light intensity of the light source, so a temperature compensation circuit or the like of the light source is not required, the structure can be simplified, and stable and accurate measurement can be performed.

In addition, when the reflection plate 13 is distorted, moved, rotated, etc. due to changes in physical quantities to be measured such as pressure, imaging, displacement, temperature, etc., the light enters the light receiving fiber 14 and the light transmitting fiber 12. However, the intensities of both reflected lights change in opposite ways with respect to the distance Q between the ends of the transmitting/receiving fibers 12 and 14 and the reflecting plate 13. That is, as the distance Q becomes larger, as shown in FIG. The light intensity B increases.

In this way, the reflected light that enters the light-receiving fiber 14 and the reflected light that enters the light-transmitting fiber 12 show opposite increases and decreases with respect to the displacement of the reflection plate 13, so the output ratio eo of these reflected lights is It changes greatly depending on the displacement of the reflection plate 13. Therefore, the position 9 of the reflecting plate 13 can be determined with high accuracy from the output ratio eo, and the sensitivity of the sensor can be improved.

[Effects of the Invention] In summary, the present invention provides the following excellent effects.

(1) By taking the ratio of the light reflected from the light receiving fiber to the light reflected from the light transmitting fiber, which includes intensity fluctuations of the same light source, it is not affected by the intensity fluctuations of the light source, and the temperature of the light source can be compensated. This eliminates the need for circuits, simplifies the structure, and enables stable and accurate measurements.

(B) Since the amount of light reflected to the light transmitting fiber and the amount of light reflected to the light receiving fiber show opposite increases and decreases with respect to the displacement of the reflector, the displacement of the reflector can be detected more sensitively than the output ratio of these reflected lights. detection and highly sensitive measurement.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing an embodiment of a reflective optical sensor according to the present invention, and Fig. 2 shows the relationship between the intensity of reflected light incident on the transmitting/receiving fiber of the sensor and the displacement of the reflecting plate. The graph shown in FIG. 3 is a schematic configuration diagram showing a conventional reflective optical sensor. In the figure, 10 is a light emitting element, 11 is a drive circuit, 12 is a light transmitting fiber, 13 is a reflection plate, 14 is a light receiving fiber, 15
1 is a first light receiving element, 16 is an optical branching section, 17 is a second light receiving element, 18 is a fiber for optical branching, 19.20 is an amplifier circuit, 21 is an arithmetic circuit, 22 is a display circuit, and 9 is an optical fiber end. This is the distance between the reflector and the reflector. Patent Applicant Hitachi Cable Co., Ltd. Representative Patent Attorney Nobuo Kinuya C Report ~

Claims (1)

[Claims] A light source, a light transmitting fiber having a light branching part and guiding the light emitted from the light source, a reflector for reflecting the light emitted from the light transmitting fiber, and the light reflected from the reflector. A light-receiving fiber for receiving light, a first light-receiving element for photoelectrically converting the light emitted from the light-receiving fiber, and a light receiving fiber that is reflected by a reflector, enters the light-transmitting fiber again, and is split at a light branching section. a second light-receiving element for photoelectrically converting the light emitted by the light-receiving element; and an arithmetic circuit for calculating the displacement amount of the reflector from the ratio of the electrical outputs of the first light-receiving element and the second light-receiving element. A reflective optical sensor characterized by: