JPS6333645A - Optical liquid detector - Google Patents

Abstract

PURPOSE:To detect the attaching of water drops or the like selectively at a high accuracy, by making two luminous fluxes, large and small, incident on a transparent medium such as glass at an critical angle in the interface between an object to be detected such as water drop and the medium from the opposite side of a surface to be detected. CONSTITUTION:In a transparent medium 1 such as front glass of an automobile, light emitting elements 21 and 22 and light receiving elements 31 and 32 are arranged at a fixed angle on the opposite side of a surface 1a intended to detect the attaching of water drops. The elements 21 and 22 are so arranged as to receive incident lights therefrom through a prism 4 at different angles. That is, one element is set at such an angle that incident light is not totally reflected on the interface when water drops attach to the surface 1a being inspected but done so when they do not and the other element is set at such an angle that total reflection conditions thereof will not break with the attaching of water. The light, which has repeated the total reflection in the medium 1 is received by the elements 31 and 32 through a prism 5 and a lens 6 and thus, the attaching of water drops is detected from the attenuation of the one element only.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an optical sensor that detects liquid such as raindrops with good selectivity and high accuracy.

<Prior art and its problems> Liquid detection or liquid identification sensors are particularly useful for detecting rain in automobiles and automatically operating wipers, power windows, sunroofs, etc., and for detecting rain from indoors in ordinary homes. Dew condensation sensors, sensors using piezoelectric elements, and the like are conventionally known. The former is due to 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 due to the electromotive force generated due to the piezoelectric effect when water droplets collide with the piezoelectric element while the car is running. , respectively, to detect raindrops. However, in either case, the sensor is 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 mud to the sensor element, collision of small stones, etc., and the sensor life is significantly affected by fluctuations in natural conditions. Therefore, as shown in Fig. 4, a method has been proposed that detects the change in capacitance between two electrodes (42) when raindrops (43) adhere to the outer surface of a windshield (41) of a car. ing. Since the sensor components are placed inside the car, this configuration is not susceptible to the effects of the external environment, but does it have sufficient detection output? In order to achieve this, it is necessary to reduce the spacing between the electrodes [42], and therefore the area for detecting raindrops becomes quite small, or it is necessary for large I raindrops to adhere, which poses a problem in terms of detection sensitivity. Furthermore, if liquid other than raindrops adheres to the sensor, the output may change, resulting in poor liquid discrimination ability. Therefore,
It is possible to consider a sensor that detects all water (rain) droplets by making full use of optical methods as a whole detection surface such as a windshield of a car.

That is, as shown in Fig. 5, the light source light is incident on the windshield (51) from the inside, and the incident light is always propagated by total reflection within the windshield (51) and reaches the light receiving element (52) at the final end. When many raindrops adhere to the outer surface of the windshield (51), the total internal reflection condition is broken due to the difference in the refractive index between the air and the raindrops, and the incident light passes through the light receiving element (52). Sensors with optical configurations that do not receive light are being considered. The detection surface is the windshield (51), and all the optical components that make up the sensor can be placed inside the windshield [51], that is, inside the vehicle, so that the sensor life is not affected by dust, mud, etc. It is possible to obtain a sensor with 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 under 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. In this case, disturbance light caused by sunlight, etc. other than that emitted from the light emitting element may be incident on the light receiving element, and this poses major problems in improving measurement precision, identifying the detected liquid, etc.

<Purpose of the invention> The invention was made in order to eliminate all the drawbacks of the conventional liquid detection or liquid identification sensors as described above. It performs detection with excellent selectivity.

The configuration of the device (sensor) is that two light beams are incident on a transparent medium such as glass, polymer resin, or a prism that has a detection surface at different incident angles from the opposite side of the detection surface, and the two light beams are combined. First, set the luminous flux above the critical angle at the interface between the transparent medium and the object to be detected, such as water droplets adhering to the detection surface of the transparent medium, and set the other beam at an angle smaller than the critical angle. A water droplet is detected by comparing the reflection characteristics at the interface between the transparent medium and the water droplet, that is, the digital reflected light intensity change detected by the light receiving element, and the refractive index n- 1
, 33) and liquids with a higher refractive index than water.In addition, during actual operation, shadows are generated as ambient light.
Jt-For sunlight, etc., it is necessary to provide a shielding plate when packaging the optical components of the device, and for some of the light that is expected to enter from the detection surface of the transparent medium and reach the photodetector, use a front cover lens of the photodetector. By arranging this, the disturbance light can be focused outside the light-receiving element, and the two detected light beams can be focused on each light-receiving element with high precision.

Furthermore, by loading an optical filter in front of the light-receiving element that transmits only light in the emission wavelength band of the light-emitting element, the power level of ambient light can be significantly reduced, and when used in combination with the above lens, the effect of ambient light can be almost ignored. and a good output can be obtained.

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 outside of the car windshield is used as the detection surface, the entire sensor can be installed inside the car, which improves environmental resistance. An excellent configuration can be achieved.

Furthermore, since the light source and light receiving element are installed 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 fully expanded, and the High-sensitivity detection can be performed even with water droplets, and the sensor structure is simple and can be made at low cost, making it an extremely useful structure in practice. The object of this great invention is to provide an optical liquid detection sensor having many of the advantages mentioned above.

<Example> Figure 1 shows an optical liquid detection device (
FIG. 2 is a configuration diagram of a sensor (hereinafter referred to as a sensor). Light-emitting elements (21), (22) and light-receiving elements (31), (32)'i are arranged on the inner surface (IT) opposite to the detection surface (la) of the transparent medium (1).
A light emitting element (21
), (22) d, etc. are emitted from the inner surface (lb) of the transparent medium.
are introduced into the transparent medium (1) at different angles through prisms (4) that are optically coupled to M (coupled). As shown in the figure, the incident light propagated through the transparent medium (1) by total reflection is similarly led out of the transparent medium (1) through the prism (5) optically bonded to the inner surface (lb) and is received. The light is incident on the elements (31) and (32). In addition, a shielding plate (
7) and lens (6) are partially packaged with the above optical components and jig (8), and the respective light receiving elements (11) and (32
) is output as an electrical signal and compared in a well-known comparison circuit (comparator) to detect the presence or absence of water (rain) drops, etc.

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 used.
After the emitted beam from each of (22) passes through the prism (4), the incident angle θ1=50°, θ
The angles of the light emitting elements (21) and (22) are set so that 2=70°.

The best place to decide these two angles of incidence is glass (1)
It can be derived by considering the total internal reflection conditions when air or water is attached to the surface. That is, the refractive index n of glass l
For a=1.47, air nA=1.00-water nw=1
．． 33, therefore air.

Critical angles Bh and Ow when water is attached to glass respectively
is determined by Snell's law as the following straight line.

s 1nJ2ffA1 s inow 1
．． 33sin90° 1,47 5in90°
1.47” 15A-42,9°, jlw=
64.8° Therefore, when there is nothing attached to the detection surface of the glass (1), the distance from the light source to the glass (1) is 42°.
．． Everything that enters the glass (1) at an incident angle of 9 degrees or more is totally reflected and propagates in the opposite direction, while the glass (1)
When a water droplet adheres to the detection surface in 1), the angle of total reflection on the surface to which the water droplet adheres is determined by the respective refractive indexes of glass (1) and water, so as mentioned above, the angle of incidence is 64.8°. The above objects propagate within the glass (1) by total internal reflection, but most of the objects whose incident angle is 42.9°≦fli (incident angle) <64.8° propagate within the glass (1). become unable.

Therefore, in this sensor configuration, the incident angle of the emitted light from each of the two light sources on the glass (1) is determined based on the total reflection condition in the water trowel glass (1). angle of receiving (4
2.9°≦θl<64.8°), and the other is an angle (θ
2≧64.8°), and by comparing the light intensities of two light beams incident at different angles of incidence when water is attached (this makes it possible to identify whether there is a nail in the water. Therefore, θ1= 50°, and θ2=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, if a water droplet adheres to the glass detection surface and the incident angle is θ, there will be a large light loss in the case where the water droplet is attached, and almost no incident light will reach the light receiving element (31), and the other light beam with the incident angle θ2 will be Light-receiving element (32) that repeats total reflection regardless of the water droplet weight
The incident light reaches the If liquids other than water droplets are attached to the glass detection surface, such as oil contained in car exhaust, car wax, engine oil, and oils such as salad oil used in general households, these oils will not be present. The refractive index is considerably larger than that of water, and since the refractive index of glass is relatively close, the critical angle for total reflection is also a large value (2≧~80°), and when oil is attached, the angle of incidence increases. θ1. In the case of θ2, an optical loss sound occurs at the lower part of the index plate, and almost no incident light reaches the light receiving element. Therefore, the angle of incidence θ
1. Of the two beams of light at θ2, the attachment of water droplets can be recognized when only the light incident at θ□ 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. In addition, FIG. 2 shows the sensor configuration shown in FIG. 1, with the horizontal axis representing the incident angle θit of the light source on the glass (1), and the vertical axis representing the respective incident angle numbers for water and oil (thick example). Here, the photodetector (31) when attached (engine oil).

The light intensity detected in (32) is normalized to the light intensity incident on the light receiving element with respect to air at the same incident angle, and is taken as the reflectance (chi). As is clear from this result75), what was stated earlier, that is, the angle of incidence (θi) is 4
When 2.9°≦θi<64.8°, a large optical loss occurs due to adhesion of water (corresponding to the solid line in the figure), and θi≧64.8°.
It was confirmed that this has nothing to do with water adhesion. Furthermore, the angle of incidence of oil (corresponding to the broken line in the figure) is θi≧~80°
It became clear that nearby areas were not affected. However, the reflectance (detected light intensity) fluctuates sharply, so Table 1 shows the normalized reflectance.
), (32), only when the light intensity of only one of them is attenuated, that is, when (θ1.θz)=(0,1), it is possible to determine that it is a water (rain) drop and operate the sensor. In this way, the wood-based sensor uses two light beams at different incident angles and compares their respective reflection characteristics, so that it is not affected by adhesion of liquids other than water, and detects only water droplets with high precision and sensitivity. can be detected. As the transparent medium (1), other than Pyrex glass, various optical glasses, polymer resins, automobile windshields, rear glasses, etc. can also be used as they are.

Furthermore, the settings of the light source incident angles θl and θ2 are determined based on the critical angle of total reflection when water adheres to the transparent medium (1), taking into account the entire refractive index of the transparent medium (1) to which it is applied.

θ1 is an angle smaller than the critical angle, and θ2 is 8 above the critical angle.
It is sufficient to set it to about 0° or less.

Next, when considering reducing the influence of disturbance light such as sunlight, the first
When optical components are integrated into a package as shown in the figure, even if a shielding plate (7) is provided as shown in the figure, disturbance light such as sunlight will enter the glass detection surface at all angles. Some of them reach the light receiving element. However, glass, which is a transparent medium, is a parallel flat plate, and when considering light incidence at a point on the detection surface, the maximum angle of incidence is 42.9° due to the relationship between the critical angles of air and glass, as described above, and schematically, The situation can be considered as shown in Figure 3a. Therefore, the passing angle is different from that of the two detected light beams, and it becomes possible to spatially separate the detected light and the disturbance light by the lens. FIG. 3b shows the convergence state of the two detected light beams (solid line) and the disturbance light (broken line) after exiting the prism by the respective lenses. Since the maximum emission angle of the disturbance light is 42.9 degrees compared to the respective emission angles θ1=50° and θ2−70° of the two detected light beams, clear separation is possible. On the other hand, most of the disturbance light emitted from the (b) surface of the prism reaches only a portion far from the light-receiving element and does not reach the center. Furthermore, as shown in FIG. 3b, the two signal light beams are sufficiently discriminated based on the difference in their advancing angles, and are focused on the respective light receiving elements, so that a good output signal can be obtained.

Furthermore, if a light source with a narrow emission spectrum such as a laser diode or LED is used as the sensor's primary light source, the disturbance light is natural light (white light), so the front surface of the light receiving element is By installing an optical filter that transmits only light in the wavelength band, it is possible to sufficiently attenuate natural light within the detection sensitivity of the light receiving element, thereby reducing the power level of the disturbance light. As described above, by spatially separating the disturbance light using a lens and also using a filter to separate it in the optical wavelength range, the influence of the disturbance light on the sensor output can be almost ignored.

Regarding the mounting position of the sensor, for example, if the sensor is mounted inside the windshield of a car and the rear glass, the glass has a certain slope, so a small amount of raindrops may fall outside the sensor mounting part of the detection surface. Even if raindrops adhere to the sensor, they will run down to the sensor part and improve the detection of raindrops.Also, by installing the sensor inside the detection surface as a part that can be wiped off with a wiper, the wiper will operate when raindrops are detected and wipe away the raindrops. This means that raindrops do not stay on the force sensor detection surface, and therefore, it is possible to reliably recognize that the rain has stopped.

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

<Effects of the Invention> As detailed above, the optical liquid detection device according to the present invention (
(sensor) has the following properties which are extremely useful in practice.

(1) In order to detect water droplets using optical methods, especially when detecting water droplets for various automatic controls in automobiles or recognizing rainfall in the home, the sensor components should be placed on the detection surface such as inside the automobile. Since it can be set inside the 300°C, it has good resistance to external environmental changes.

(2) Comparison of the reflection characteristics (reflected light intensity) of each of the two light beams when a water droplet is attached using two light beams with different incident angles 2 When a liquid other than water adheres to the detection surface of the sensor to detect water droplets The lens has excellent selectivity of the detection target without being affected by it, and the lens
This effect can be removed by using an optical filter.

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

As mentioned above, the uninvented optical liquid detection device can be manufactured at low cost, has good environmental resistance, and has two
Since water droplets are detected by utilizing total reflection of light using a luminous flux, it has high sensitivity and excellent selectivity in detecting water droplets, and also enables highly accurate detection that is almost unaffected by ambient light. That is.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical liquid detection device packaged with a jig using two light beams, showing one embodiment of the present invention. FIG. 2 is a characteristic diagram showing the characteristics in case of water and oil adhering to the detection surface in the configuration shown in FIG. 1. Are the lenses in Figures 3a and ab based on uninvented devices? FIG. 2 is a schematic diagram illustrating the principle of spatial separation (removal) of disturbance light. FIG. 4 is a diagram showing the principle of a capacitive raindrop sensor, and FIG. 5 is a diagram showing the configuration of an optical sensor that detects raindrops based on changes in total reflection characteristics with one beam of light. l...glass, la...detection surface, lb...4.2
1.22.53...Light emitting element-31, 32, 52...
・Light receiving element-4... Prism for light incidence, 5... Prism for light output, 6... Lens, 7... Shielding plate, 8...
...Fixing jig, 41.51...Automobile windshield, 42...Parallel electrode, 43...Raindrop. Agent Patent Attorney Takeshi Sugiyama (((II 1 person) Atsushi
l Figure ANGLE (dekutsu'$2

Claims (1)

[Claims] 1. The incident angle of the light beam emitted from the light emitting element with respect to a transparent medium having a detection surface is determined by determining the critical angle of total reflection at the interface formed by the liquid to be detected that is in contact with the detection surface and the transparent medium. an optical system configured to be set at an angle smaller than , and at an angle that causes total reflection and propagation in a transparent medium when there is no liquid to be detected attached to the detection surface, and a change in the reflection characteristics of the light beam on the detection surface. An optical system comprising a light receiving element and a lens that condenses disturbance light incident from the outside of the detection surface onto a portion that does not enter the light receiving element due to the difference in the traveling angle between the detected light flux and the disturbance light. Liquid detection device. 2. The optical system according to claim 1, wherein an optical filter is loaded on the front surface of the light-receiving element, which selectively transmits light in the emission wavelength band of the light-emitting element and reflects or absorbs light in other wavelength bands. Liquid detection device. 3. The light beams incident on the detection surface of the transparent medium are two light beams set at different incident angles, one of which is at an angle greater than or equal to the critical angle of total reflection when the liquid to be detected comes into contact with the detection surface, and the other. is an optical system set at an angle smaller than the critical angle of total reflection, a light receiving element that detects a change in the reflection characteristics of each of the two light beams, and the presence or absence of a liquid to be detected by comparing the detection signal of the light receiving element. The optical liquid detection device according to claim 1 or 2, comprising comparison means for detecting. 4. The optical liquid detection device according to claim 1, 2 or 3, wherein the liquid to be detected is raindrops, snowflakes or other water droplets. 5. The mounting position of the detection device is the inside of the portion of the windshield or rear glass of an automobile or train that is wiped by a wiper, that is, the wiper wipes the detection surface of the detection device. The optical liquid detection device according to item 2, 3, or 4.