JPH03111741A - Optical sensor - Google Patents

Abstract

PURPOSE:To make it possible to detect a medium characterized by extreme decrease in transmittance by emitting light from a light emitting part into a transparent lightguide, reflecting the light which is propagated through the transparent lightguide, and receiving the light with a light receiving part. CONSTITUTION:One end of a transparent lightguide 11 is bonded to an optical fiber 12. The other end surface of the lightguide 11 is polished so as to obtain a mirror surface. A mirror 13 is formed on the surface by a vacuum vapor deposition method of metal material. The light emitted from a light emitting part 14 is inputted into the optical fiber 12 and propagated. The light reaches the lightguide 11. The light propagated through the lightguide 11 is reflected from the side surface of the lightguide 11. Therefore, the light reaches the mirror 13 in the confined pattern. The light reflected from the mirror 13 is propagated in the lightguide 11 again and inputted into the optical fiber 12. The incident light is propagated to reach a light receiving part 15 and detected. The attenuation rate of the light propagating through the lightguide 11 is different in correspondence with the state of a medium to be detected based on the change in total reflecting conditions of the light at the interface between the lightguide 11 and the medium to be detected, e.g. oil, and the absorption of leaking light. In this way, the state of the medium can be detected.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical sensor.

[Prior Art] Conventionally, Japanese Patent Application Laid-Open No. 111945/1983 discloses an optical sensor that can simultaneously detect the presence or absence of liquid and the contamination of the liquid. This is due to the air gap 4 between the ends of the optical fibers 1 and 2 and the mirror part 3, as shown in FIGS. 11 and 12.
This sensor utilizes the characteristic that the output changes when the tank is filled with liquid.

[Problems to be Solved by the Invention] However, since this sensor utilizes the characteristics based on the permeability of liquid, a decrease in the transmittance may cause small stains (
In the case of engine oil, the gap 4 must be extremely small (at least 0
．． 1mm or less). However, this is not possible because the mirror part 3 is tilted at 45°. Furthermore, even if a small gap can be realized, liquid tends to accumulate between them, making it impossible to detect the liquid level (detect the presence or absence of liquid).

An object of the present invention is to provide an optical sensor that can detect even a medium with a significant decrease in transmittance.

[Means for Solving the Problems] The present invention includes a transparent light guide made of a rod-shaped solid body and having a refractive index larger than a refractive index of a medium to be detected, and a light emitting device connected to one end of the transparent light guide.・Equipped with a light receiving section and a mirror that is installed at the other end of the transparent light guide and reflects the light propagating in the transparent light guide, and detects the intensity of the received light relative to the intensity of light emitted by the light emitting/light receiving section. The gist thereof is to detect the state of the medium to be detected around the transparent light guide.

[Operation] Light is emitted from the light emitting section into the transparent light guide, the light propagating through the transparent light guide is reflected by the mirror, and the light is received by the light receiving section. In this light propagation, the light propagates through the transparent light guide depending on the state of the detection medium due to changes in the total reflection conditions of the light at the interface between the transparent light guide and the surrounding detection medium and absorption of seeping light. The attenuation rate of the light emitted is different, and the state of the medium is detected based on this.

[Example] Hereinafter, an example in which the present invention is embodied in a sensor for detecting the presence or absence of engine oil and dirt will be described with reference to the drawings.

As shown in FIGS. 1 and 2, a rod-shaped transparent light guide 11
is made of solid BK7 glass. This transparent light guide 11
is connected to one end surface of the optical fiber 12 using an optical adhesive. The diameter of the transparent light guide 11 is approximately the same as that of the core of the optical fiber 12 so that light can be transmitted and received with low loss when connected to the optical fiber 12.

The other end surface of the transparent light guide 11 is mirror-polished, and a mirror 13 is formed on this surface by vacuum evaporation of a metallic material such as aluminum (A, Q>, copper (C0)). is formed on a surface perpendicular to the axial direction of the transparent light guide 11.The other end of the optical fiber 12 is branched into two, and includes a light emitting section 14 made of a light emitting diode, a semiconductor laser, etc.
- Light receiving section 15 using a diode, phototransistor, etc.
are connected to each other.

Although the light emitting section 14 and the light receiving section 15 are separated using a partially branched optical fiber in this embodiment, they may also be separated using a separating optical circuit using a beam splitter, a half mirror, etc. good. Further, the cross-sectional shape of the transparent light guide 11 may be circular or square.

Generally speaking, the mirror 13 may be formed of glass and adhered to the end surface of the transparent light guide 11 using an optical adhesive.

The light emitted by the light emitting unit 14 is transmitted through the optical fiber 1
2 and propagates to the transparent light guide 11. Since the transparent light guide 11 has a thickness comparable to the core diameter of the optical fiber 12, the light emitted from the optical fiber 12 enters the transparent light guide 11 and propagates with low loss. The light propagating within the transparent light guide 11 is reflected by the side surfaces of the transparent light guide 11 and is therefore confined therein, reaching the mirror 13.

Similarly, the light reflected by the mirror 13 returns to the transparent light guide 11.
and enters the optical fiber 12.

The incident light propagates through the optical fiber 12, reaches the light receiving section 15, and is detected. At this time, the light that can propagate within the transparent light guide 11 is determined by the refractive index n1 of the transparent light guide 11 and the light that can propagate within the transparent light guide 11.
1 and the refractive index n2 of the surrounding medium. In other words, light that is incident on the side surface (interface with the surrounding medium) of the transparent light guide 11 at an angle greater than θC θC = CO5 (n2 / n1 >) cannot propagate within the transparent light guide 11. , leaking into the surrounding medium.

As shown in Figure 3, when the surrounding medium is air, n2=1
Or, as shown in FIG. 4, n2=1.
4 to 1.6, the light intensity that can be detected by the light receiving unit 15 differs due to the difference in the critical angle θC that can propagate when the transparent light guide 11 is in air and in oil. , the presence or absence of fluids such as oil can be detected.

In addition, as shown in FIG. 5, the electromagnetic field distribution of light propagating within the transparent light guide 11 leaks out just outside the interface (into the surrounding medium), and this electromagnetic field is The degree of contamination of the fluid (engine oil) is detected by utilizing the property that oil is absorbed by contamination in the surrounding medium. In other words, the output of the light receiving section 15 is processed by a processing system (not shown) (for example,
microcomputer), the light receiving section 15 as shown in FIG.
By detecting the relative output value at , it is possible to detect the presence or absence of engine oil and the degree of contamination of the engine oil.

Next, to explain the selection of the material for the transparent light guide 11 for performing such detection, FIG.
．． 480>, the output of the light receiving section 15 was measured while changing the material of the transparent light guide 11. Here, the deteriorated oil is engine oil after traveling 5000 km.

As is clear from Fig. 7, the presence or absence of engine oil can be detected when using silica glass (refractive index 1.458> and Pyrex glass (refractive index 1.47>) whose refractive index is smaller than that of engine oil. Deterioration of the engine oil cannot be detected.In other words, if a material with a refractive index smaller than that of the engine oil is used, all of the light will leak into the engine oil, making it impossible to measure the deterioration of the engine oil.

Also, the refractive index is larger than that of engine oil, so K7 glass (
It can be seen that when a refractive index of 1.516> is used, both the presence or absence of engine oil and its deterioration can be detected. in this case,
If you use a material with a refractive index higher than that of engine oil,
Due to the strong light confinement effect, the sensitivity for detecting the presence or absence of engine oil decreases compared to when quartz glass or Pyrex glass is used.

In other words, in order to detect the deterioration of engine oil, it is necessary to make the transparent light guide 11 from a material with a higher refractive index than that of the oil, which strengthens the confinement of light and reduces the sensitivity of detecting the presence or absence of engine oil. descend. For this reason,
In order to make light confinement as weak as possible, K7 glass, which has a refractive index slightly higher than that of engine oil, is used.

To explain this in more detail, FIG. 8 shows the transmittance α of the surrounding medium when the horizontal axis represents the refractive index n1 of the transparent light guide 11 and the vertical axis represents the relative output at the light receiving section 15. −
1 and α=10'. In addition, in FIG. 9, the refractive index n1 of the transparent light guide 11 is plotted on the horizontal axis, and the residual amount detection sensitivity (sensitivity to detect the presence or absence of oil) and oil deterioration detection sensitivity are plotted on the vertical axis. Transmittance α=1 and α=10
-5 characteristics. As is clear from FIG. 9, oil deterioration cannot be detected with quartz glass or Pyrex glass, but it is possible to detect residue and oil deterioration with BK7 glass.

As described above, in this embodiment, the transparent light guide 11 is made of a rod-shaped solid body and has a refractive index larger than the refractive index of the medium to be detected (engine oil), and the light emitting member connected to one end of the transparent light guide 11 - It includes a light receiving section 14 and 15, and a mirror 13 that is provided at the other end of the transparent light guide 11 and reflects the light propagating through the transparent light guide 11. Then, light is emitted from the light emitting section 14 into the transparent light guide 11, the light propagating through the transparent light guide 11 is reflected by the mirror 13, and the light is received by the light receiving section 15. During light propagation, changes in the conditions for total reflection of light at the interface between the transparent light guide 11 and the surrounding medium to be detected (engine oil) and absorption of seeping light change depending on the state of the medium to be detected (engine oil). The attenuation rate of the light propagating through the transparent light guide 11 is different, and this makes it possible to detect the state of the medium, that is, the presence or absence of engine oil and the degree of dirt.

Therefore, since conventional sensors utilize characteristics based on the permeability of liquids, it is difficult to detect dirt (where the permeability decreases significantly).
In the case of engine oil, it is necessary to make the air gap 4 extremely small in order to detect the temperature (down to about 10-5), but since the mirror part 3 is tilted at an angle of 45 degrees, it is impossible to make the air gap 4 extremely small. Even if this could be achieved, the liquid level would not be able to be detected because the liquid would easily accumulate between them, but this example does not require any gaps, so this does not occur and the medium with a significant drop in transmittance (very dirty engine oil) ) can also be detected.

Note that this invention is not limited to the above embodiments,
It may also be implemented as shown in FIG. That is, the mirror 13 is formed on the end face of the transparent light guide 11 at an angle. This is because the sensor of the present invention utilizes changes in the total reflection conditions of light at the interface between the transparent light guide 11 and the surrounding medium and the absorption of seeping light.
By reflecting the light propagating within 1 toward the interface, it is possible to effectively perform an action at the interface. In addition, when we experimented by changing the angle θ between the axial direction L (light propagation direction) of the transparent light guide 11 made of BK7 glass and the normal line of the mirror 13, we found that when θ=6°, there was no oil or no deterioration. In both cases, a detection sensitivity of 40% or more was obtained.

Moreover, in order to exhibit the same effect, the transparent light guide 11 may be bent into an arc shape.

Furthermore, as another application example, in the above embodiment, the transparent light guide 11 is connected to the light emitting part 14 and the light receiving part 15 via the optical fiber 12, but the light emitting part 14 and the light receiving part 15 can be connected directly without using an optical fiber. The light receiving section 15 may be arranged at the end of the transparent light guide 11.

Furthermore, the transparent light guide 11 does not need to be made of a single material; for example, quartz glass and BK7 glass may be connected in series in a suitable combination of dimensions.

[Effects of the Invention] As detailed above, according to the present invention, an excellent effect is achieved in which even a medium with a significant decrease in transmittance can be detected.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the main parts of the optical sensor of the example, Fig. 2 is a diagram showing the optical sensor, and Fig. 3 is a diagram showing the propagation of light in the transparent light guide in the air. Figure 4 is a diagram for explaining the propagation of light in a transparent light guide in a liquid, and Figure 5 is a diagram for explaining the propagation of light in a transparent light guide in a dirty liquid. Figure 6 shows the relationship between the relative output value at the light receiver, the presence or absence of engine oil, and the degree of contamination of the engine oil, and Figure 7 shows the output value at the light receiver in air, new oil, and degraded oil. Figure 8 shows the relationship between the refractive index of the transparent light guide and the relative output at the light receiving part, and Figure 9 shows the relationship between the refractive index of the transparent light guide and the remaining amount detection sensitivity and oil deterioration detection sensitivity. Figure shown, 1st
FIG. 0 is a diagram showing the main parts of another example of an optical sensor, FIG. 11 is a diagram for explaining the prior art, and FIG. 12 is a diagram for explaining the prior art. 11 is a transparent light guide, 13 is a mirror, 14 is a light emitting part, 15
is the light receiving section. 1'3 mirror 14 light emitting part Figure 9) #r ratio of engine oil

Claims (1)

[Scope of Claims] 1. A transparent light guide made of a rod-shaped solid body and having a refractive index greater than the refractive index of a medium to be detected; a light emitting/light receiving part connected to one end of the transparent light guide; a mirror provided at the other end of the transparent light guide to reflect the light propagating in the transparent light guide; An optical sensor characterized by detecting the state of a medium to be detected around a body.