JPH03229189A - Optical fiber sensor - Google Patents

Abstract

PURPOSE:To use the optical fiber sensor without any adjustment in assembly or irrelevantly to a secular change by providing a zero-point correcting circuit for detecting and amplifying only reflected light from a body to be detected even if unnecessary reflected light is present. CONSTITUTION:The zero-point correcting circuit 12 is connected to a photosemiconductor device 10. Then when the body X to be detected passes nearby the sensor, the reflected light from the body X to be detected is made incident on an optical fiber cable 4, passed through a condenser lens 11 like an optical path B, and made incident on a photodetecting element 3. In this case, the zero-point correcting circuit 13 is provided, so an output value due to unnecessary reflected light generated by the optical system consisting of the photosemiconductor device 10, optical fiber cable 4, and condenser lens 11 is set to a reference potential to enable signal detection only by the reflected light from the body X to be detected even if there is the reflected light from the optical system.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical fiber sensor, and particularly to a reflective optical fiber sensor that detects the presence or absence of an object to be detected in a non-contact manner.

<Prior art> As shown in FIG. 5, a conventional reflective optical fiber sensor includes a light emitting element 2, a light receiving element 3, and a light emitting element 2 in an optical fiber sensor main body 1, and directs the emitted light from the light emitting element 2 to a detected object X. 2 cores 4a, 4. so as to guide the reflected light from the irradiated and detected object X to the light receiving element 3; It is optically coupled to an optical fiber cable 4 consisting of b.

The light emitted from the light emitting element 2 propagates through the core 4a of the optical fiber cable 4 on the light emitting element 2 side and is irradiated onto the detected object X. When the detected object X passes nearby, the detected object The reflected light from the light-receiving element 3 propagates through the core 4b on the light-receiving element 3 side and is guided to the light-receiving element 3.

Thereby, the presence or absence of the object to be detected X can be detected without contact.

<Problems to be Solved by the Invention> However, in the conventional optical fiber sensor, the optical fiber cable 4 consisting of two cores 4a and 4b requires cable processing such as special end face treatment. The use of the cable 4 increases the cost.

Furthermore, in order to avoid crosstalk between the light emitting element 2 and the light receiving element 3, it is necessary to separately mold the light emitting element 2 and the light receiving element 3 with resin and to arrange them at a certain distance D1. The number of assembly processes increases,
This is a factor leading to higher costs and larger sizes.

In view of the above, the present invention provides an optical system that can reduce manufacturing costs and downsize, and that can automatically correct variations in light-emitting element output, variations in light-receiving element sensitivity, changes over time in light-emitting element output, temperature characteristics, etc. The purpose is to provide fiber sensors.

<Means for Solving the Problems> As shown in FIGS. 1 to 4, the means for solving the problems according to the present invention is such that the light emitting element 2 and the light receiving element 3 are molded with a translucent resin in the optical fiber sensor main body i. an optical semiconductor device 10 comprising: a single-core optical fiber cable 4 for irradiating light emitted from the light emitting element 2 onto an object to be detected X and guiding light reflected from the object X to the light receiving element 3; , a condenser lens 11 is optically coupled between the optical fiber cable 4 and the optical semiconductor device 10, and the optical semiconductor device l
The output value due to unnecessary reflected light generated in the optical system of the O1 optical fiber cable 4 and the condenser lens It is set as a reference voltage, so that even if unnecessary reflected light from the optical system exists, the reflected light from the object to be detected A zero point correction circuit 12 is provided to detect and amplify only the signal.

<Operation> In the above problem solving means, the light output from the light emitting element 2 within the optical fiber sensor body 1 is focused by the condenser lens 11 and irradiated from the optical fiber cable 4.

When the detected object X passes nearby, the reflected light from the detected object X enters the optical fiber cable 4,
Condenser lens! 1 and enters the light receiving element 3.

At this time, the optical signal inputted to the light-receiving element 2 includes not only the reflected light from the object to be detected It is also man-powered.

However, the zero point correction circuit 12 sets the output value due to unnecessary reflected light generated in the optical system as a reference potential, and detects and amplifies only the reflected light from the detected object X.

Therefore, even if there is reflected light from the optical system, it is possible to detect a signal of only the reflected light from the object to be detected.

<Example> An example of the present invention will be described below with reference to Figs. 4 to 4.

FIG. 1 is a sectional view of an optical fiber sensor showing an embodiment of the present invention, and FIG. 2 is an electrical circuit diagram of its zero point correction circuit.
FIG. 3 is a diagram showing the light receiving state of the light receiving element, and FIG. 4 is a timing chart showing the operation of each part of the zero point correction circuit.

Note that the same reference numerals are given to the same functional parts as those of the prior art shown in FIG. 5.

As shown in the figure, the optical fiber sensor of this embodiment includes an optical semiconductor device 10 in which a light emitting element 2 and a light receiving element 3 are molded with a translucent resin in an optical fiber sensor main body l;
a one-core optical fiber cable 4 for irradiating the light emitted from the light emitting element 2 onto the detected object X and guiding the reflected light from the detected object X to the light receiving element 3; A condensing lens 11 is optically coupled to the optical semiconductor device IO.

The optical semiconductor device 10 and the optical fiber cable 4
The output value due to unnecessary reflected light generated in the optical system of the condenser lens 11 is set as a reference voltage, and even if unnecessary reflected light from the optical system exists, only the reflected light from the object to be detected X is detected. A zero point correction circuit 12 for amplification is provided.

As shown in FIG. 1, the optical fiber sensor main body 1 is formed into a box shape made of light-shielding resin to prevent the intrusion of disturbance light. The main body l has a storage chamber 13 for storing the light emitting element 2, a holding chamber 14 for holding the condenser lens II, and a fitting hole 15 for fitting and holding the optical fiber cable 4. We are prepared. The storage chamber 13, holding chamber 1
4 and the fitting hole 15 are connected to each other in communication with each other, the storage chamber 13 is located at the rear of the main body 1, the fitting hole 15 is located at the front of the main body 1, and the holding chamber 14 is connected to the storage chamber 13. It is arranged between the matching hole 15.

The light-emitting element 2 and the light-receiving element 3 are mounted on lead frames 16 and 17 at a constant interval 1)2 (D2<DI) within the optical semiconductor device 10, and are internally connected via bonded ink wires 18. ing. As shown in FIG. 2, the light-emitting element 2 is a light-emitting diode, and the light-receiving element 3 is a photodiode 3a and an amplifier that converts the optical signal detected by the photodiode 3a into a voltage signal and amplifies it. 3b and a pulse generating circuit 3c for driving the light emitting element 2 in pulses are integrated into the same chip.

The optical fiber cable 4 has a double structure in which an I-core core 4C having a high refractive index is covered with a cladding 4d having a low refractive index.

The condensing lens 11 is a convex compound lens, and is held by a lens frame 11a. The condenser lens II is fixed within the main body 1 by engaging the lens frame 11a with the wall of the holding chamber 13.

The zero point correction circuit 12 is connected to the optical semiconductor device 10 as shown in FIG. 2, and includes a peak hold circuit section 20, an integrating circuit section 21, an initial circuit section 22, a zero point return circuit section 23, and a differential amplifier circuit section. It consists of 24.

The peak hold circuit section 20 includes a comparator Al, a capacitor CI, and a capacitor CI to read the output value of the light receiving element 3.
C2, a rectifier diode DI, a lannostar Ql, and resistors R1 and R2.

The integration circuit section 21 includes a capacitor C4 that holds a reference voltage for amplifying only the detection signal of the detected object X, a resistor R5, and an analog switch SW so as to integrate the human input signal with respect to time.

The initial circuit section 22 includes a capacitor C3, a transistor Q2, and resistors R3, R4, and R to charge the capacitor C4 to near the power supply voltage Vce when the power is turned on.
Consists of 11.

After the detected object X has passed, the zero point return circuit unit 23 sets the holding voltage of the capacitor C4 to a peak hold output value V. It consists of a comparator A3, a transistor Q3, and a resistor R1O.

The differential amplification circuit unit 24 includes a comparator A4, which is configured to amplify and output the difference between the voltage held by the capacitor C4 and the voltage ■+ΔV, that is, the optical signal Δ■ caused by the reflected light from the detected object X. It consists of resistors R6, R7, R8, and R9.

In addition, in the figure, A2 is a comparator.

In the above configuration, the optical fiber sensor body! The light output from the light emitting element 2 is focused by the condenser lens as shown in FIG.
It is irradiated from the tip of the

When the detected object X passes nearby, the reflected light from the detected object X enters the optical fiber cable 4,
The light passes through the condensing lens 11 as shown in the optical path I3 and enters the light receiving element 3.

Note that the light emitting element 1 is equipped with a zero point correction circuit 1 in the subsequent stage in order to reduce current consumption and extend the element life.
2 and pulse driving to synchronize with signal detection.

At this time, the optical signal input to the light receiving element 2 includes not only the reflected light from the object to be detected is also entered. The situation is shown in Figure 3. In the figure, the solid line is the reflected light from the object to be detected X, the broken line is the unnecessary reflected light within the optical semiconductor device IO, and the dashed line is the unnecessary reflected light from the condenser lens 11 and the end face of the optical fiber cable 4.

However, the zero point correction circuit in the latter stage! Reference numeral 2 detects and amplifies an electrical signal based only on the reflected light from the object to be detected X shown in FIG.

Next, the detection operation of the detected object X will be explained based on FIG. 2.

When the power is turned on, when power is applied to the pulse generating circuit 3C in the light receiving element 3, the light emitting element 2 is pulse driven. Furthermore, unnecessary reflected light is input to the light receiving element 3 due to crosstalk, and the optical signal output of the optical semiconductor device 10 is a voltage pulse due to the unnecessary reflected light component due to crosstalk.

The optical signal outputs are compared in the peak hold circuit section 20 of the zero point correction circuit 12 at the subsequent stage.

At this time, the initial circuit section 22 charges the capacitor C4, which holds the reference voltage for amplifying only the detected optical signal of the object to be detected X in the integrating circuit section 21, to near the power supply voltage Vce.

This is because, in order to ensure an extremely long time constant for the operation of the integrating circuit section 21, the capacitor C4 needs to be a low leakage capacitor, and without the initial circuit section 22,
This is because when the power is turned on, by the time the charging voltage of the capacitor C4 is charged from Ov to the output voltage level of the peak hold circuit section 20, a problem occurs in which a signal is output even though the object to be detected X is not detected. be.

Furthermore, when the power is turned on, the terminal voltage of the capacitor c4 is charged to near the power supply voltage Vce, but if the output value of the peak hold circuit section 20 is smaller than the terminal voltage of the capacitor c4, the zero point return circuit as shown in FIG. The output of comparator A3 in section 23 becomes low level, transistor Q3 turns on when the pulse output is low level "L", and when the holding voltage of capacitor c4 and the peak hold voltage match, the output of comparator A3 becomes The high level "■" is reached, and the discharge of the capacitor C4 is stopped.

At this time, the terminal voltage of the capacitor c4 holds the output value due to the unnecessary reflected light and continues to hold it until the object to be detected X passes through. Its output value is V.

shall be.

Next, when the detected object The peak hold circuit unit 20 immediately holds the voltage higher by the component ΔV, and the initial circuit unit 22 starts charging the capacitor c4 in the integrating circuit unit 21 to a voltage of Vo+ΔV.

However, the time constant RXC of the integrating circuit section 21 is set to be extremely large, and the analog switch SW in the integrating circuit section 21 is turned on only when the pulse output is at a high level "H".
"The level is high, and the pulse output duty (D
If the ratio (uty) is made smaller, the time constant of the integrating circuit section 21 can be set even longer. Further, reducing the duty ratio of the pulse output is advantageous in terms of current consumption and securing the life of the light emitting element 2, and a duty ratio of 1 to 2% is selected.

Here, to explain why the integral constant of capacitor C4 must be made long, the holding voltage of capacitor C4 is considered to be the output value VO due to unnecessary reflected light, and with this point set as zero, the optical signal △V is It must be amplified by the dynamic amplification circuit section 24. In other words, the integration time to capacitor C4 needs to be set longer than the time it takes for the detected object This is because a long period of integration is required to obtain .

Then, the differential amplifier circuit unit 24 amplifies the difference between the holding voltage ■ of the capacitor C4 and the optical signal detection signal V+△V.
That is, a signal obtained by amplifying the signal ΔV due to the reflected light from the object to be detected X is output.

On the other hand, after the detected object X passes in front of the optical fiber sensor, the output of the peak hold circuit section 20 returns to the unnecessary reflected light level ■0.

At this time, the capacitor C4 is charged within the time when the signal of the detected object X is detected, and holds a voltage slightly higher than Vo. If this condition continues, it will cause a problem in the next detection operation, so
As shown in the figure, it is necessary to quickly restore the holding voltage of the capacitor C4 to the peak hold output value Vo.

This operation is realized by the operation of the zero point return circuit section 23 based on exactly the same operating principle as the operation at power-on described above.

However, the time to return to the zero point must be realized in a shorter time than the response speed of the detected object
This can be achieved by increasing the ON time of the transistor Q3 (that is, by decreasing the duty ratio of the pulse output).

As described above, since the zero point correction circuit 12 is provided, the output value due to unnecessary reflected light generated in the optical system of the optical semiconductor device 10, the optical fiber cable 4, and the condensing lens 11 is set as the reference potential, so that the optical It is possible to realize a method that enables signal detection of only the reflected light from the object to be detected X, even if there is reflected light from the system.

Therefore, the temporal change and temperature characteristics of the light emitting element output,
Variations in the output of the light emitting elements, variations in the sensitivity of the light receiving elements, variations in the dimensions of the optical system, etc. are also reflected in the level value of unnecessary reflected light, that is, the reference potential, and can therefore be automatically corrected.

For signal detection, the zero point correction circuit 12 is used as shown in FIG.
4, the output change from the reference potential Δ
This can be achieved by amplifying V, so the reference potential is O
Signal detection is possible if the signal is between the saturation voltage of the comparator (op-amp) A I - A 3 than V, a wide dynamic range can be ensured, and it can be used without adjustment during assembly or against changes over time.

Furthermore, since the condensing lens 11 is arranged between the optical semiconductor device 10 and the optical fiber cable 4, an optical fiber cable consisting of one core can be used, and the end face treatment etc. can be performed as in the case of two cores. There is no need for a special process to finish two cores at the same time, reducing manufacturing costs.

Furthermore, since the light-emitting element 2 and the light-receiving element 2 are molded with light-shielding resin, it is possible to achieve a smaller size than when the light-emitting and light-receiving elements are individually molded.

Note that when the light-emitting element 2 and the light-receiving element 3 are molded into one package, crosstalk occurs between the light-emitting element 2 and the light-receiving element 3; Regarding the talk, due to crosstalk, the operational amplifier A in the peak hold circuit section 20
If the output of the optical semiconductor device 1 is saturated, signal detection is impossible, or if the shape, structure, and arrangement of elements are designed so that the crosstalk in the optical semiconductor device IO is below a certain level of the design value. no problem.

It should be noted that the present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

<Effects of the Invention> As is clear from the above description, according to the present invention, since a zero point correction circuit is provided, the output value due to unnecessary reflected light generated in the optical system of the optical semiconductor device, optical fiber cable, and condensing lens is reduced. By setting the reference potential to the reference potential, it is possible to realize a system that enables signal detection of only the reflected light from the object to be detected even if reflected light from the optical system is present.

Therefore, the temporal change and temperature characteristics of the light emitting element output,
Variations in the output of the light emitting elements, variations in the sensitivity of the light receiving elements, variations in the dimensions of the optical system, etc. are also reflected in the level value of unnecessary reflected light, that is, in the reference potential, and can therefore be automatically corrected.

In addition, since the condenser lens is placed between the optical semiconductor device and the optical fiber cable, it is possible to use a 1-core optical fiber cable, and special processes such as end face treatment are required as in the case of 2-core optical fiber cables. There is no need for this, reducing manufacturing costs.

Furthermore, since the light-emitting element and the light-receiving element are molded with a light-shielding resin, it is possible to achieve a smaller size than when the light-emitting element and the light-receiving element are individually molded.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an optical fiber sensor showing an embodiment of the present invention, and FIG. 2 is an electrical circuit diagram of its zero point correction circuit.
FIG. 3 is a diagram showing the light receiving state of the light receiving element, FIG. 4 is a timing chart showing the operation of each part of the zero point correction circuit, and FIG. 5 is a sectional view showing a conventional optical fiber sensor. 1: Optical fiber sensor body, 2: Light emitting element, 3: Light receiving element, 4: Optical fiber cable, lO/optical semiconductor device, 1
1. Condensing lens, 12: Zero point correction circuit, 20. Peak hold circuit section, 21: Integrating circuit section, 22: Initial circuit section.
23: Zero point return circuit section, 24: Differential amplifier circuit section, X: Object to be detected. Applicant: Nyab Co., Ltd.

Claims (1)

[Claims] An optical semiconductor device includes a light-emitting element and a light-receiving element molded with a translucent resin in an optical fiber sensor body, and an optical semiconductor device that irradiates a detected object with light emitted from the light-emitting element and reflects light from the detected object. A single-core optical fiber cable for guiding the light to the light receiving element, and a condenser lens are optically coupled between the optical fiber cable and the optical semiconductor device, and a condenser lens is optically coupled between the optical semiconductor device, the optical fiber cable, and the condenser. A zero point that sets the output value due to unnecessary reflected light generated in the optical system of the optical lens as a reference voltage and detects and amplifies only the reflected light from the object to be detected even if unnecessary reflected light from the optical system exists. An optical fiber sensor characterized by being provided with a correction circuit.