JPS62163949A - Optical type liquid detection sensor - Google Patents

Abstract

PURPOSE:To enable the detection of a liquid especially water drops with excellent selectivity by optical method, by projecting two luminous fluxes into a transparent medium at a different incident angles from the side opposite to a detecting surface to compare changes in intensity of reflected light detected with a light receiving element. CONSTITUTION:Light emitting elements 21 and 22 are arranged on an inner surface 1b opposite to a detecting surface 1a of a transparent medium 1 while light receiving elements 31 and 32 are arranged at a fixed angle. Moreover, light emitted from the light emitting elements 21 and 22 as a light source are introduced into the transparent medium 1 at a different angle with a prism 4 optically bonded on the inner surface 1b of the transparent medium. A incident light propagating through the transparent medium 1 by total reflection is led out of the transparent medium 1 through a prism 5 optically bonded on the inner surface 1b to irradiate light receiving elements 31 and 32. The intensity of the detection light with the light receiving elements 31 and 32 is outputted as electrical signal and compared with a comparator circuit to detect presence of water (rain drops or the like).

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an optical sensor that detects liquids such as water (rain) drops with good selectivity and high accuracy.

<Prior art and its problems> Liquid detection or liquid identification systems are used especially in cases such as detecting rainfall and automatically operating wipers, power windows, sunroofs, etc. in automobiles, and in applications such as indoor operation in ordinary homes. It is useful for rain recognition, etc., and dew condensation sensors and sensors using piezoelectric elements are conventionally known. The former is caused by a sudden change in electrical resistance between the element electrodes due to water adhering to the surface of the dew condensation sensor, and the latter is caused by the electromotive force generated by the piezoelectric effect when water droplets collide with the piezoelectric element while the car is running. This is to detect. However, in either case, the sensor must be installed outside the vehicle or outdoors in order to detect raindrops, and the environmental conditions in which the sensor is placed are quite severe. For example, there are many factors that can cause sensor malfunctions, such as adhesion of conductive dust or the like to the sensor element, splashing of mud, and collisions with small stones, and changes in natural conditions can significantly affect the sensor's lifespan. Therefore, as shown in Fig. 4, two parallel electrodes (42) are formed inside the windshield (41) of the automobile.
) Two electrodes (4) when raindrops (43) adhere to the outer surface.
2) A method has been proposed that detects the change in capacitance between the two. This is a configuration in which the sensor components are placed inside the car, making it less susceptible to the effects of the external environment. However, in order to obtain sufficient detection output, it is necessary to reduce the spacing between the electrodes (47J), so raindrops The detection area is quite small or a large amount of raindrops must be attached, which poses a problem in terms of detection sensitivity.Furthermore, when liquid other than raindrops adheres, the output changes and the liquid discrimination ability is also poor. .

Therefore, it is possible to consider a sensor that detects water (rain) droplets by making full use of optical techniques using an automobile windshield or the like as a detection surface. That is, as shown in FIG.
), and is set so that it propagates through total reflection and enters the light receiving element ω at the final end, and when raindrops adhere to the outer surface of the windshield (51), the total reflection occurs due to the difference in refractive index between the air and the raindrops. Sensors with optical configurations have been considered in which the conditions are broken and the incident light is not received by a group of light-receiving elements. The detection surface is the windshield (51), and all the optical parts that make up the sensor can be placed inside the windshield (51), that is, inside the car, so that dust, mud, etc. can affect the sensor life. It is possible to provide a sensor that is reduced and has excellent environmental resistance. However, if a liquid other than raindrops, such as oil such as automobile wax, adheres to the detection unit that is trying to detect the total reflection condition, the total reflection condition will be disturbed, and the output will change in the same way as in the case of raindrops, making it difficult to identify the detected liquid. It has a big problem.

<Object of the Invention> The present invention has been made to overcome the drawbacks of conventional liquid detection or liquid identification sensors as described above. It performs detection with excellent selectivity.

The configuration of the sensor is such that a transparent medium such as glass, polymer resin, or prism has a detection surface, and two beams of light are incident on the transparent medium at different incident angles from opposite sides of the detection surface.
By setting one of the two light beams at an angle greater than or equal to the critical angle at the interface between the transparent medium and the object to be detected, such as a water droplet adhering to the detection surface of the transparent medium, and setting the other beam at an angle smaller than that critical angle, the detection surface The water droplet is detected by comparing the reflection characteristics of the two light beams at the interface between the transparent medium and the water droplet, that is, the change in digital reflected light intensity detected by the light receiving element, when the water droplet is attached to the water (refractive index n). = 1.33), which enables highly accurate discrimination between liquids with a higher refractive index than water, resulting in good output.

In addition, since the light source, light receiving element, prism, etc. that make up the sensor can be placed on the opposite side of the detection surface, if the detection surface is on the outside of the car windshield, the sensor can be installed inside the car, improving environmental resistance. An excellent configuration can be achieved.

Furthermore, since the light source and the light receiving element are provided so that the detection light beam propagates through multiple reflections while repeating total reflection within the transparent medium, the detection area on the detection surface of the transparent medium can be expanded. Even minute water droplets can be detected with high sensitivity, and the structure of the sensor is simple and inexpensive, making it an extremely useful structure in practice. Thus, it is an object of the present invention to provide an optical liquid detection sensor having many of the advantages mentioned above.

<Example 1. > FIG. 1 is a configuration diagram of an optical liquid detection sensor showing one embodiment of the present invention. Light emitting elements (21), (2
2) The light receiving element +31+, (32) is arranged at a certain angle, and the light emitting element (21+,
The emitted light from (22) is introduced into the transparent medium (1) at different angles by prisms (4) optically bonded (coupled) to the inner surface (1b) of the transparent medium. Transparent medium (
1) As shown in the figure, the incident light propagated by total internal reflection is similarly guided out of the transparent medium (1) via the prism (5) optically bonded to the inner surface (1b) and then to the light receiving element (31).
, (32). Each light receiving element (31)
The detected light intensity in (32) is output as an electric signal, and the presence or absence of water (rain) drops etc. is detected by comparing it in a well-known comparison circuit (comparator).

Next, the principle of detecting water droplets in the above-described sensor configuration and the details of the sensor configuration will be explained. The transparent medium (1) is made of Pyrex glass (hereinafter simply referred to as glass) with a refractive index of n=1.47, and the light emitting element (21,) of the light source is
After the emitted beams from each of (22) pass through the prism (4), the incident angle θ1=50° with respect to the glass (1).

Light emitting elements +21+, (22
) The angle of incidence can be determined by taking into account the conditions for total reflection when air or water is attached to the glass (1). That is, for the refractive index n of glass 1 = 1.47, air nA
= 1.00.

Since water nw=1.33, the critical angles A and ΩW when air and water are respectively attached to the glass are determined as the following values according to Snell's law.

, °, 0A = 42.9°, 115w = 64.8° Therefore, when nothing is attached to the detection surface of the glass (1), the incident angle from the light source to the glass (1) is 42.9° or more. All the light incident at the corner propagates while repeating total reflection within the glass (1).On the other hand, when a water droplet adheres to the detection surface of the glass (1), the angle of total reflection on the surface to which the water droplet adheres is the same as that of the glass (1). Since it is determined by the refractive index of (1) and water, as mentioned above, anything with an incident angle of 64.8° or more will propagate within the glass (1) by total internal reflection. 42.9°
≦8i (incidence angle) <64.8° is all glass (1
), a large optical loss occurs at the point where the water droplets adhere to the glass (1
) becomes almost impossible to propagate within. Therefore, in this sensor configuration, the incident angle of the emitted light from each of the two light sources on the glass (1) is set to one angle (42,9 ≦θ, (64
, 8°), and the other is set at an angle (θ2 ≧ 64.8°) that is not affected by the total reflection condition within the glass (1) even when water adheres, and the angle of incidence is different when water adheres. By comparing the light intensities of the two luminous fluxes, it is possible to identify the presence or absence of water. Therefore θ1=50°, θ2=
It is set at 70°.

The detailed operating mechanism of the sensor is as follows.

In a normal case where there are no water droplets or the like attached to the glass detection surface, the respective incident lights from the two light sources propagate within the glass (1) and reach the light receiving elements (31) and (32). However, when a water droplet adheres to the glass detection surface, a large optical loss occurs at the part where the water droplet adheres, and the light receiving element (31)
Almost no incident light reaches the light-receiving element (Ω
The incident light reaches the Furthermore, liquids other than water droplets can be detected on the glass detection surface, such as oil contained in car exhaust, car wax, and engine oil.

Even if we consider the case where oil such as salad oil used in general households is attached, the refractive index of these oils is considerably larger than that of water and relatively close to the refractive index of glass, so it is critical to form total internal reflection. The angle also takes a large value (Ω≧~80°), and when oil is attached, the incident angle θ1. For both θ2, optical loss occurs at the attachment portion, and almost no incident light reaches the light receiving element. Therefore, the incident angle θ4. Of the two luminous fluxes of θ2, θ
The adhesion of water droplets can be recognized when only the incident light is attenuated.

Next, the above contents are shown in Figure 2 and Table 1, which are the actual measurement results.
Explain using.

[Table 1] Table 1 shows the normalized values of reflectance. Furthermore, in FIG. 2, the horizontal axis represents the incident angle θi of the light source light on the glass (1) using the sensor configuration shown in FIG. 1, and the vertical axis represents water or oil (in this example, engine oil) at each incident angle. The light intensity detected by the light receiving element (311, (Incorporated) at the time of attachment is normalized to the light intensity incident on the light receiving element with respect to air at the same incident angle and taken as the reflectance (%). As is clear from the results, the incident angle (θi) is 42.9°≦θi〈64, which causes a large optical loss due to adhesion of water (corresponding to the solid line in the figure). θi
It was confirmed that ≧64.8° has nothing to do with water adhesion. Furthermore, the oil (corresponding to the broken line in the figure) also has an incident angle of θ
It became clear that there was no effect up to i≧~80°. In addition, the variation in reflectance (detected light intensity) is steep, so Table 1. As shown by normalizing the reflectance, two light-receiving elements + 31), (water ( This makes it possible to operate the sensor by determining that it is a raindrop.In this way, the sensor of this embodiment uses two light beams at different angles of incidence and compares the reflection characteristics of each, thereby preventing the adhesion of liquids other than water. However, it is possible to detect only water droplets with high precision and sensitivity without being affected by this.In addition to Pyrex glass, various optical glasses can be used as the transparent medium (1).

Furthermore, polymer resins such as automobile windshields, rear glass, etc. can also be used as they are. Still light source incident angle θ
1. The setting of θ2 is also determined by the critical angle of total reflection when water adheres to the transparent medium (1), considering the refractive index of the applied transparent medium (1), and θ is an angle smaller than the critical angle, θ2 may be set to be greater than or equal to the critical angle and less than or equal to 80°.

The sensor of this embodiment can be applied to a wide range of applications, such as automatic control of automobile wipers, power windows, sunroofs, etc., and rain recognition in the home.

<Example 2. 3 shows a configuration in which a transparent medium prism (BK-7) (6) is used and light is reflected once on the detection surface of the prism (6). The light emitted from each light emitting element (7) is reflected by a prism (6) and then reaches each light receiving element (8). The principle or method of detecting water droplets is the same as that explained in Example 1, but since the prism itself is used as the transparent medium with the detection surface, the number of parts of the sensor can be reduced, and the amount of incident light can be reduced. Optical coupling to a transparent medium is also facilitated, resulting in a more inexpensive sensor.

<Effects of the Invention> As detailed above, the optical liquid detection sensor according to the present invention has the following practically extremely useful characteristics.

(1) Since water droplets are detected using an optical method, the sensor components are set inside the detection surface, such as inside the car, especially when detecting water droplets in various automatic controls in cars or recognizing rain in the home. Therefore, it has good resistance to external environmental changes.

(2) Water droplets are detected by comparing the reflection characteristics (reflected light intensity) of each of the two light beams when a water droplet adheres using two light beams with different incident angles, so when a liquid other than water adheres to the detection surface of the sensor. It also has excellent selectivity for the detection target without being affected by this.

(3) The sensor has a simple configuration and can be inexpensive.

As described above, the optical liquid detection sensor of the present invention can be manufactured at low cost and has good environmental resistance. This enables highly accurate detection with high sensitivity and excellent selectivity for detecting water droplets.

[Brief explanation of drawings]

□'1. The first figure is a configuration diagram of a multiple reflection type optical liquid detection sensor using two light beams, showing one embodiment of the present invention. FIG. 2 is a characteristic diagram showing the characteristics of the sensor shown in FIG. 1 when water and oil are attached. FIG. 3 is a configuration diagram of a single reflection type optical liquid detection sensor using two light beams, showing another embodiment of the present invention. FIG. 4 is a diagram showing the principle of a capacitive raindrop sensor. FIG. 5 is a configuration diagram of an optical sensor that detects raindrops based on changes in total reflection characteristics with one light beam. 1.Glass, la, detection surface, lb,...
Inside, 7. 21. ．． 22, . . . light emitting element, 8. ．． 3
1-, 32. . . . Light receiving element, 4. . . . Prism for light incidence, 5. ...Light-emitting prism, 6, ... Prism agent Patent attorney Aihiko Fukushi (and 2 others) Figure 2

Claims (1)

[Claims] 1. At different angles of incidence on a transparent medium having a detection surface; 2.
A light beam from a book is incident from the opposite side of the detection surface, and the angle of incidence of one light beam is set to be equal to or greater than the critical angle of total reflection at the interface between the transparent medium and the liquid to be detected that is in contact with the detection surface, and the angle of incidence of the other light beam is is set to an angle smaller than the critical angle; a light receiving element that detects a change in the reflection characteristics of each of the light beams on the detection surface when the detection surface is in contact with the liquid to be detected; 1. An optical liquid detection sensor comprising: comparison means for detecting the presence or absence of a liquid to be detected by comparing detection signals of the elements. 2. The optical system according to claim 1, which identifies the liquid to be detected by comparing the respective reflected light intensities of the two light beams when the liquid to be detected or a substance other than the liquid to be detected comes into contact with the detection surface. Liquid detection sensor. 3. The optical liquid detection sensor according to claim 1 or 2, wherein the liquid to be detected is raindrops, snowflakes, or other water droplets. 4. The optical liquid detection sensor according to claim 1, 2, or 3, wherein the transparent medium is a window glass of an automobile or a train. 5. The optical liquid detection sensor according to claim 1, wherein the number of total reflections on the detection surface of the two light beams incident on the transparent medium is one or multiple reflections.