JPH0581649U - Optical fiber sensor - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to an optical fiber sensor for measuring a physical quantity of an object to be measured by using an optical fiber, and a light quantity of light emitted from a light source changes with temperature and time. It is possible to prevent the occurrence of a correction error when the correction is performed so as to cancel. [Structure] The light emitted from one light source is branched and one is used for measurement and the other is used for monitor.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an optical fiber sensor that measures a physical quantity of an object to be measured using an optical fiber.

[0002]

[Prior Art]

 When measuring various physical quantities of an object to be measured using light, an optical fiber sensor that guides light with an optical fiber to measure light has been conventionally used because of explosion proof or because it is necessary to place the sensor in a narrow place. Has been. A conventional optical fiber sensor using an optical fiber will be described with reference to FIG. 2 by taking a so-called encoder as an example.

The encoder 10 shown in FIG. 2 is roughly divided into a measurement unit 11 and a light amount correction unit 12. In the measuring unit 11, the light emitted from the light source 13 is transmitted through the optical fiber 16 having one end held by the ferrule 14 and guided to the sensor unit 18. The sensor unit 18 is provided with a fixed slit 18a and a moving slit 18b, and the moving slit 18b moves in accordance with the movement of the object to be measured (not shown), whereby the light passing through the slits 18a, 18b is moved. Is light that carries information about the movement of the object to be measured. The light passing through the slits 18a and 18b is transmitted through the optical fiber 20, emitted from the end portion held by the ferrule 22, received by the signal photodetector 24, passed through the signal circuit 26, and not shown. For example, it is input to a counter or the like and the movement of the measured object is detected.

Here, the amount of light emitted from the light source 13 of the measuring unit 11 changes with changes in the ambient temperature and the passage of time, so that the amount of light guided to the sensor unit 18 also changes, and as a result thereof. That is, the signal carrying the information on the movement of the object to be measured, that is, the signal detected by the signal photodetector 24 is not stable. For this reason, a light amount correction unit 12 is provided to correct the above-mentioned light amount and the like so that this optical signal becomes stable and to minimize the measurement error. The light quantity correction unit 12 is provided with a light source 30 having the same characteristics as the light source 13, and the light emitted from the light source 30 is held in the optical fiber 34 by the end portion held by the ferrule 32. The light enters from the side, is transmitted through the optical fiber 34, is emitted from the end portion held by the ferrule 36, and is guided to the monitor photodetector 38. The monitor signal obtained by the monitor photodetector 38 is input to the control circuit 40. The control circuit 40 is a circuit that controls the light sources 13 and 30 so that the light sources 13 and 30 always emit a constant amount of light based on the input monitor signal. The amount of light emitted is corrected so that it is stable regardless of changes in ambient temperature and the passage of time. Therefore, the amount of light guided to the sensor unit 18 is stable, and the signal obtained by the signal photodetector 24 is also stable.

Although the control circuit 40 has been described here as controlling the amount of light emitted from the light source 13, the control circuit 40 controls the signal circuit 26 as shown by the broken line in FIG. The amplification factor of the signal obtained by the photodetector 24 may be changed so that the signal has a predetermined magnitude. Further, both the amount of light emitted from the light source 13 and the amplification factor of the signal obtained by the signal photodetector 24 may be adjusted.

[0006]

[Problems to be solved by the device]

 In the conventional encoder 10 described above, two light sources, a measurement light source 13 and a correction light source 30, are used and controlled so that the amount of light guided to the sensor unit 18 is stable. Since there are variations in characteristics such as the rate of change in the amount of light of two light sources over time and the rate of change in the amount of light with respect to temperature and humidity, the amount of change in the amount of light emitted from the light source 13 and the amount of change in the amount of light emitted from the light source 30 are different, An error may occur in the correction of the light source 13 performed based on the amount of the emitted light. When this error occurs, the signal obtained by the signal photodetector 24 is not stable, and therefore a measurement error occurs.

In view of the above circumstances, the present invention prevents the occurrence of a correction error when correcting the light amount of the light emitted from the light source so as to cancel the change in the light amount due to the temperature change or the passage of time, and stabilizes the light output. An object is to provide an optical fiber sensor for obtaining a signal.

[0008]

[Means for Solving the Problems]

 An optical fiber sensor of the present invention for achieving the above object transmits an optical fiber to a sensor unit for measuring a physical quantity of an object to be measured using the optical fiber, and from the sensor unit to the optical fiber, In an optical fiber sensor that guides and receives light carrying a physical quantity, (1) a light source (2) a monitor light-receiving section equipped with a monitor photodetector (3) a signal light-receiving section equipped with a signal photodetector ( 4) Extends between the light source and the sensor unit, which is equipped with a ferrule that holds the end portions of the light source side together so that the light emitted from the light source is simultaneously incident on both, and is emitted from the light source. A first optical fiber or a plurality of first optical fibers that transmit the emitted light to the sensor unit, and a first optical fiber that extends between the light source and the light receiving unit for monitoring and guides the light emitted from the light source to the photodetector for monitoring. 2 optical fibers (5) Sensor part One or a plurality of third optical fibers that extend between the signal light receiving section and guide the light carrying the physical quantity to the signal light detector (6) Based on the monitor signal obtained by the monitor light detector It is characterized by comprising a control circuit for controlling the amount of light emitted from the light source and / or the amplification factor of the signal obtained by the signal photodetector.

In the above-described optical fiber sensor, either the light amount of the light emitted from the light source or the amplification factor of the signal obtained by the signal photodetector may be controlled, or both of them may be controlled. It may be controlled. . When both of these are control targets, either one may be for coarse adjustment and the other may be for fine adjustment.

[0010]

[Action]

 The light emitted from the light source is simultaneously incident on the first optical fiber and the second optical fiber, and the light incident on the first optical fiber is transmitted to the sensor unit and is incident on the second optical fiber. Is received by the monitor photodetector. Therefore, the monitor signal obtained by the monitor photodetector directly carries the information on the amount of light transmitted to the sensor unit. The control circuit controls the light quantity of the light emitted from the light source based on this monitor signal. Therefore, even if the light quantity of the light emitted from the light source changes due to the ambient temperature change or the passage of time, this change does not occur. It is canceled with high accuracy, and as a result, a stable signal can be obtained and the physical quantity of the measured object can be measured stably and with high accuracy compared to the conventional method.

[0011]

【Example】

 Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an encoder according to an embodiment of the present invention. The encoder 50 is provided with an LED 52. The encoder 50 is also provided with an optical fiber 54 that transmits light to the sensor unit 60 and an optical fiber 56 that guides light to the monitoring optical sensor 66. The LEDs 52 of these optical fibers 54 and 56 are provided. The end portions on the side are collectively held by a ferrule 58 so that the light emitted from the LED 52 is incident on both ends at the same time. The light emitted from the LED 52 and incident on the optical fiber 54 is transmitted to the sensor unit 60, and the transmitted light is measured by a fixed slit 60a and a moving slit 60b provided in the sensor unit 60 (not shown). Is subjected to intensity modulation by the movement of the optical fiber, is emitted from the end held by the ferrule 69 via the optical fiber 68, is guided to the signal optical sensor 70, and is converted into an electric signal by the signal optical sensor 70. .. This signal is input to the signal circuit 76, is appropriately amplified in the signal circuit 76, and the movement of the measured object is detected based on the signal.

On the other hand, the light incident on the optical fiber 56 passes through the inside of the optical fiber 56, is emitted from the end portion held by the ferrule 57, is received by the monitoring optical sensor 66, and is converted into a monitor signal. The monitor signal is input to the control circuit 78, and the control circuit 78 controls the LED 52 based on the input monitor signal so that the emitted light amount of the LED 52 is always constant. Since this monitor signal is a signal obtained by receiving the light emitted by the LED 52 itself, the change over time in the amount of light emitted from the LED 52 and the change due to temperature and humidity are directly corrected based on this signal. Therefore, the signal obtained by the signal light sensor 70 is stable, and an encoder capable of highly accurate measurement is realized. The control circuit 78 may control the amount of light emitted from the LED 52 based on the monitor signal obtained by the monitor optical sensor 66 as described above. The amplification factor of the generated signal may be controlled, or both the amount of emitted light and the amplification factor may be controlled. The optical fiber 54 for transmitting light to the sensor section 60 and the optical fiber 68 for returning the light from the sensor section 60 are provided one by one in the above embodiment, but these optical fibers 54, 68 are provided. Needless to say, it is not necessary to provide one each, and it is needless to say that a plurality of each may be provided depending on the measurement principle, the structure of the sensor unit 60, and the like.

Although the above embodiment is an example of an encoder, the optical fiber sensor of the present invention is not limited to an encoder, but various devices for transmitting light using an optical fiber to measure a physical quantity of a measured object. Can be applied to.

[0014]

[Effect of the device]

 As explained above, in the optical fiber sensor of the present invention, the light emitted from one light source is branched and one is used for measurement and the other is used for monitoring. The rate can be controlled with high precision, resulting in a high precision sensor. In addition, the number of light sources is smaller than in the past and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an encoder according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a conventional encoder.

[Explanation of symbols]

 50 encoder 52 LED 54, 56, 68 optical fiber 57, 58, 69 ferrule 66 monitor optical sensor 70 signal optical sensor 76 signal circuit 78 control circuit

Claims (1)

[Scope of utility model registration request] 1. An optical fiber transmits light to a sensor unit for measuring a physical quantity of an object to be measured by using light, and the optical fiber guides the light carrying the physical quantity from the sensor unit to receive the light. In a fiber sensor, a light source, a monitor light-receiving unit having a monitor photodetector, a signal light-receiving unit having a signal photodetector, and light emitted from the light source are incident on both at the same time. A ferrule that holds the end portions on the light source side together, extends between the light source and the sensor portion, and transmits one or more light emitted from the light source to the sensor portion. A first optical fiber, and a second optical fiber extending between the light source and the monitor light-receiving unit and guiding the light emitted from the light source to the monitor photodetector; the sensor unit and the signal light-receiving unit Extends between the front and One or a plurality of third optical fibers for guiding the light carrying the physical quantity to the signal photodetector, and the light emitted from the light source based on the monitor signal obtained by the monitor photodetector. An optical fiber sensor, comprising: a control circuit for controlling an amount of light and / or an amplification factor of a signal obtained by the signal photodetector.