WO2003012408A1

WO2003012408A1 - Optical condensation sensor and controller employing the same

Info

Publication number: WO2003012408A1
Application number: PCT/JP2002/007704
Authority: WO
Inventors: Hideki Imanishi; Keiji Tsunetomo; Fumitoshi Kobayashi
Original assignee: Nippon Sheet Glass Co., Ltd.
Priority date: 2001-07-30
Filing date: 2002-07-29
Publication date: 2003-02-13
Also published as: JP2004537721A

Abstract

An optical condensation sensor is provided that is capable of detecting condensation (particularly dew) adhering to a detection surface with high precision. Light emitted by a light-emitting element (2) is propagated while being subjected to total internal reflection, and light leaking out through condensation drops (5) adhering to a face of a transparent body (1) is detected by a photodetector (3). A detecting unit (6) detects the adhesion of the condensation drops (5) according to an output signal from the photodetector (3).

Description

DESCRIPTION

OPTICAL CONDENSATION SENSOR AND CONTROLLER EMPLOYING THE SAME

Technical Field

The present invention relates to an optical condensation sensor for detecting condensation adhering to a detection surface, and to a controller employing the optical condensation sensor. Particularly, the present invention relates to an optical condensation sensor that detects dew on the detection surface with high precision.

Background Art Among the prior art techniques related to optical condensation sensors, primary techniques are described below.

(1) JP5(l993)-294139A: this publication discloses a technique for detecting fogging of glass by irradiating the glass with light from the outside and receiving light diffused by condensation that forms when the fog occurs. (2) JP5(1993)-19934B: this publication discloses a technique based on the same principle as that of (l).

(3) JP2000-136998A: this publication discloses a configuration in which light is guided to enter and leave glass through a hologram provided on the glass. The technique utihzed subjects light to total internal reflection on surfaces of the glass, and senses a decrease in an amount of light having been subjected to the total internal reflection, the decrease being caused by condensation adhering to the glass.

(4) JP10(l998)-268066A: this publication discloses a configuration in which light is guided to enter and leave glass through a diffraction grating provided on the glass. The technique utilized subjects light to total internal reflection on surfaces of the glass, and senses a decrease in an amount of light having been subjected to the total internal reflection, the decrease being caused by condensation adhering to the glass. The techniques disclosed by the publications (l) and (2) have a drawback in that detection errors tend to occur in the case where dust, dirt, cigarette smoke, or the like are present in an optical path. More specifically, when light from a light source is diffused by particles of dust, dirt, cigarette smoke, or the like present in the optical path, a photodetector detects the diffused light, and misidentifies it as being caused by fog.

It should be noted that this principle itself has been brought into practical application so that dust sensors and smoke sensors have been proposed based on the principle. If necessary, JP2000-356583A should be referred to. In other words, with the techniques disclosed in the publications (l) and (2), it is difficult to distinguish a condensation-adhesion state from a state of presence of cigarette smoke, etc.

Normally, to prevent the misidentifLcation, a sensitivity of a sensor is lowered so that the sensor does not react when it senses diffused light caused by cigarette smoke, etc. This tends to make the sensor unable to detect slight fog.

To solve the foregoing problem, the publication (l) (JP5(l993)"294139A) describes an example having a configuration in which a cover is provided over the whole sensor head so as to prevent the access of smoke or the like.

However, this causes the following problem^ the provision of a cover causes a temperature difference between the inside and the outside of the cover, which causes the detection surface area to fog less as compared with a part that should be prevented from fogging, that is, the sensitivity of the sensor is deteriorated significantly.

Besides, the techniques disclosed in the publications (3) and (4) are techniques of detecting condensation according to a decrease in an amount of detected light, based on a principle common therebetween that in the case where condensation adheres to the detection surface, an amount of light subjected total internal reflection at the detection area decreases by an amount of light that leaks through the condensation. Therefore, in the case where an amount of light emitted by a light source decreases, or a transmittance decreases at some midpoint in an optical path, it is likely that condensation cannot be detected with precision.

To prevent such a problem, usually the sensitivity of a sensor is lowered so that the sensor should not react to a slight decrease in the light amount. For this reason also, sensors tend to be unable to detect slight fog.

To detect condensation, various techniques have been proposed apart from the foregoing optical types, for example, electrical resistance types, quartz oscillation types, and types that calculate a dew point according to a temperature and a humidity. In these types of methods, however, a position of measurement and a part where fog should be prevented are different, and a temperature difference therebetween leads to the deterioration of detection precision in principle. Therefore, sensors tend to malfunction, or the sensitivity of sensors has to be lowered so that malfunction should be avoided.

Disclosure of Invention

In view of the above, the object of the present invention is to provide an optical condensation sensor that is capable of detecting condensation adhering to a detection surface, particularly dew developed on the detection surface, with good precision. In order to achieve the above— mentioned object, an optical condensation sensor according to the present invention includes a light-emitting element for guiding light into a transparent body, a photodetector, and a detecting unit for detecting adhesion of condensation to the transparent body according to an output of the photodetector. In the optical condensation sensor, light emitted by the light-emitting element is guided into the transparent body so that the light propagates inside of the transparent body while being subjected to total internal reflection, and light leaking to outside the transparent body due to condensation adhering to a surface of the transparent body, among the propagating light, is detected by the photodetector, so that the detecting unit detects the adhesion of the condensation.

Brief Description of Drawings FIG. 1 is a view showing an operation principle of the present invention.

FIG. 2 is a graph showing an angle dependency of a photodetector. FIGS. 3Ato 3D are graphs showing an emission intensity of light from the light- emitting element according to an angle of incidence. FIG. 4 is a view showing a configuration of an example 1.

FIG. 5 is a view showing a configuration of an example 2. FIG. 6 is a view showing a configuration of an example 3. FIG. 7 shows an example in which a diffraction grating is employed for guiding light to a transparent plate. FIG. 8 shows an example in which a light-emitting element is embedded in a laminated glass.

FIGS. 9A and 9B show examples in which a transparent resin is used for guiding light.

FIG. 10 is a view showing an example of an optical condensation sensor of the present invention attached to a windshield.

Best Mode for Carrying Out the Invention

When condensation adheres to a surface of a transparent body, the total internal reflection conditions are not satisfied in the condensation-adhering portions, from which light propagating through the transparent body leaks out. An optical condensation sensor according to the present invention detects light leaking out the transparent body with use of a photodetector, so as to detect the adhesion of condensation to the transparent body (see FIG. l).

Without the adhesion of condensation to the surface of the transparent body, light by no means leaks from the transparent body. In other words, since an optical path in a normal state is present inside the transparent body, the configuration is immune to influences of the ambient environment. Furthermore, the leaked light hardly is affected by cigarette smoke or the like in the optical path to the photodetector. Therefore, this configuration has a characteristic in that malfunctions hardly occur due to cigarette smoke or the like.

In the present invention, in principle, no light leaks out without condensation adhering thereto, and light that leaks out due to condensation adhering thereto is detected. In other words, as long as the leaking light is detected, the presence of adhering condensation is determined. As a result, even with cigarette smoke or the like, normally there does not occur a state such that it is completely impossible to carry out the detection of light, and hence, malfunctions due to the foregoing causes hardly occur.

According to the above-described conventional techniques disclosed in the publications (l) and (2), diffusion caused by dew is detected, but since cigarette smoke or the like present in an optical path also causes diffusion at the same level as that caused by dew, there is a possibility of malfunction. Furthermore, the above -de scribed conventional techniques disclosed in the publications (3) and (4) are techniques for detecting a shght decrease in an amount of light that results from leakage of light caused by condensation adhering thereto. Therefore, it is difficult to detect dew with such a high sensitivity as that in the present invention.

The optical condensation sensor according to the present invention detects the adhesion of condensation by receiving leaking light directly, and therefore, it is unnecessary to lower the sensitivity, in particular for avoiding malfunctions, even if an amount of emitted light decreases due to the deterioration of a light source with time or temperature characteristics thereof. Accordingly, it is possible to secure a sufficient sensitivity so as to detect even a slight leaking light caused by slight fog.

Furthermore, since in principle no difference is generated between temperatures at a measurement position and on a detection surface, a malfunction resulting from a temperature difference should not occur. In the optical condensation sensor of the present invention, to maximize the light receiving efficiency, the photodetector preferably is arranged at a position such that an angle formed between a normal to a light- detecting surface of the photodetector and a normal to a detection surface of the transparent body is in a range of 50° to 90°. Furthermore, the photodetector preferably is arranged at a position such that the leaking light is detected with a maximum intensity, according to an angle of light guided into the transparent body. However, the position of the photodetector is not limited to the foregoing. The photodetector may be arranged at any position and angle as long as light is incident on the light- detecting surface of the photodetector.

In the optical condensation sensor, the photodetector preferably is arranged so as to satisfy: θ₂ = θi + 25° where θi represents the angle of incidence and satisfies 41°≤θι<60°, and Θ2 represents the angle formed between the normal to the light-detecting surface of the photodetector and the normal to the detection surface of the transparent body. In the optical condensation sensor, the light-emitting element may be arranged so that an angle of incidence when the light emitted by the light-emitting element is reflected inside the transparent body is approximately 45°, and the photodetector is arranged at a position such that the angle formed between the normal to the light- detecting surface of the photodetector and the normal to the detection surface of the transparent body is approximately 70°.

In the optical condensation sensor, the light-emitting element may be arranged so that an angle of incidence when the light emitted by the light-emitting element is reflected inside the transparent body is approximately 50°, and the photodetector is arranged at a position such that the angle formed between the normal to the light-detecting surface of the photodetector and the normal to the detection surface of the transparent body is approximately 75°.

In the optical condensation sensor, the light-emitting element may be arranged so that an angle of incidence when the light emitted by the light-emitting element is reflected inside the transparent body is approximately 55°, and the photodetector is arranged at a position such that the angle formed between the normal to the light-detecting surface of the photodetector and the normal to the detection surface of the transparent body is approximately 80°.

In the optical condensation sensor, the light-emitting element may be arranged so that an angle of incidence when the light emitted by the light-emitting element is reflected inside the transparent body is approximately 60°, and the photodetector is arranged at a position such that the angle formed between the normal to the light-detecting surface of the photodetector and the normal to the detection surface of the transparent body is approximately 90°.

The optical condensation sensor of the present invention preferably has a configuration in which the light-emitting element is arranged so that light emitted by the light-emitting element is guided through a principal face of the transparent body.

In this case, it is more preferable that a prism, a diffraction grating, or a hologram is provided on the principal face of the transparent body, at a position where the light emitted by the light-emitting element is guided into the transparent body. This allows the light emitted by the light-emitting element to be guided efficiently into the inside of the transparent body.

Alternatively, the light-emitting element may be cemented to the principal face of the transparent body with a transparent adhesive. Alternatively, the optical condensation sensor further may include a light- guiding body for guiding light emitted by the light-emitting element, and the light-guiding body is cemented to the principal face of the transparent body with a transparent adhesive. Alternatively, the optical condensation sensor further may include an optical member for collimating the light emitted by the light-emitting element so that the light enters the transparent body as a collimated light.

Alternatively, a light-emitting diode or a laser light source may be employed as the light-emitting element. With any one of the foregoing configurations, it is possible to achieve an effect that the light emitted by the light-emitting element is guided efficiently into the inside of the transparent body.

Alternatively, the optical condensation sensor of the present invention preferably has a configuration in which the light-emitting element is arranged so that light emitted by the hght-emitting element is guided into the transparent body via an end face of the transparent body, the end face being formed obliquely with respect to a principal face of the transparent body.

In the foregoing configuration, the optical condensation sensor preferably includes an optical member for collimating the light emitted by the light-emitting element so that the light as a collimated light enters the transparent body. Alternatively, a light-emitting diode or a laser light source may be employed as the light-emitting element. Alternatively, the light-emitting element may be cemented to the end face of the transparent body with a transparent adhesive. With any of these, it is possible to achieve an effect that the light emitted by the light-emitting element is guided efficiently into the transparent body.

It is also preferable that the optical condensation sensor of the present invention has a configuration in which the light-emitting element is arranged so that light emitted by the light-emitting element is guided into the transparent body via an end face of the transparent body, the end face being formed substantially perpendicularly to a principal face of the transparent body. In this case, it is more preferable that the light-emitting element is cemented to the end face of the transparent body with a transparent adhesive.

Furthermore, in the foregoing case, it is further preferable that a fight-blocking member for preventing light guided into the transparent body from the light-emitting element from leaking out is provided on at least one principal face of the transparent body in the vicinity of the end face.

The optical condensation sensor of the present invention preferably is configured so that the light-emitting element is embedded in the transparent body. In this case, it is further preferable that a light-blocking member for preventing light guided into the transparent body from the light-emitting element from leaking out is provided on at least one principal face of the transparent body in the vicinity of the end face.

The optical condensation sensor of the present invention preferably is configured so that a plurality of the photodetectors are provided. This results in an increase in the number of detection surfaces, thereby enabling the detection of the adhesion of condensation to the transparent body with a higher precision. In the optical condensation sensor according to the present invention, the condensation is, for instance, dew.

In the optical condensation sensor according to the present invention, the light-emitting element preferably is driven with pulses.

In the optical condensation sensor according to the present invention, the transparent body may be made of, for instance, glass, a synthetic resin, or silicon.

In the optical condensation sensor according to the present invention, the transparent body is, for instance, a window glass for vehicles.

Furthermore, to achieve the aforementioned object, a controller according to the present invention is mounted on a vehicle along with any one of the optical condensation sensors described above. The controller controls at least one among a defroster, a defogger, and an air-conditioner of the vehicle, according to a signal from the detecting unit of the optical condensation sensor. The transparent body used in the present invention is not particularly limited as long as it transmits light having the same wavelength as that of light emitted by a light source used. Preferable examples of the same include those made of glass or synthetic resins in terms of materials. It may be a silicon substrate that has a high transmittance with respect to infrared rays though not transmitting visible rays. Further, the shape of the transparent body is not particularly limited, and examples of the same include a plate form, a bar form, and a fiber form. The plate form is practical in particular, and therefore, favorable. Regarding glass sheets in particular, the present invention can be applied to glass in any forms, including single-sheet glass, laminated glass, etc., irrespective of the application form.

Preferably used as the light source are semiconductor light-emitting elements such as light-emitting diodes (LED), lasers, etc., or alternatively, the light source may be a lamp with a filament. For example, in the case of intended uses such that extraneous light such as sun light or room light illuminations possibly enters, a semiconductor light-emitting element that is driven with pulses easily is used suitably as a light source, with a view to distinguishing the light from the light source from the extraneous light. As a photodetector, photodiodes and phototransistors are used preferably. Regarding the position where the photodetector is arranged, it preferably is arranged at a position where hght leaking due to fog is received with the greatest light intensity.

To identify a preferable range of an angle at which the photodetector is arranged, the range of the angle for arranging the photodetector was varied and relative outputs were measured, with respect to a case where the transparent body was normal glass and the condensation adhering thereto was water. The result is shown in FIG. 2. It is evident from FIG. 2 that in the case where the photodetector was arranged at a position such that an angle formed between a normal to a light- detecting surface of the photodetector and a normal to the detection surface of the transparent body is in a range of 60° to 80°, the photodetector received leaking light with a high efficiency with respect to light that was incident at an angle of 45°. The position such that the foregoing angle is in the vicinity of 70° is particularly preferable. It should be noted that the optimal position of the photodetector varies to some extent according to a state of the surface of the transparent body (for instance, with water repellency or with hydrophilicity), and according to the material (refractive index) of the transparent body. Furthermore, a laser that emitted light with a small beam divergence was used as a light-emitting element, and the angle of incidence of light was varied stepwise from 45° to 60°. The angle dependency of emitted light intensity in these cases was examined so as to determine a preferable angle range for the arrangement of the photodetector, and the result if shown in FIGS. 3A to 3D. In FIGS. 3A to 3D, the angle of the emitted light (angle of emission) with respect to a normal to the detection surface is plotted as the horizontal axis. First, it can be seen that the emission intensity is maximized when the angle of incidence is 45°, by comparing peaks of the graphs of FIGS. 3A to 3D. The angle of emission at the peak was 70°. It is seen that as the angle of incidence increases, an angle at which the emission intensity has a peak increases. It should be noted that the angle of emission coincides with the optimal angle for the arrangement of the photodetector.

The relationship between the angle of incidence, the range of the angle of emission (preferred angle range), and the peak emission angle in the foregoing case is shown in Table 1 below. Table 1

Angle of Incidence θi Emission Angle Range Θ2 Peak Emission Angle 45° 50° - 90° 70°

50° 60° - 90° 75°

55° 60° - 90° 80°

60° 60° - 90° 90°

Hereinafter, the best mode for carrying out the present invention will be described in detail by way of illustrative examples, with reference to the drawings. (View of Principle)

First, the operation principle of the present invention is described with reference to FIG. 1. An optical condensation sensor according to the present invention is configured so that a light-emitting element 2 and a photodetector 3 are arranged with respect to a transparent body 1 as a target of detection as shown in FIG. 1, so that the adhesion of condensation is detected by a detecting unit 6 according to an output signal from the photodetector 3. The photodetector 3 is arranged at approximately 70° from a normal to a detection surface in a surface of the transparent body 1 (area shown in FIG. 5 in which condensation drops 5 adhere). It should be noted that a prism 4 having an oblique face at approximately 45° with respect to the surface of the transparent body 1 is used so as to guide light from the light-emitting element 2 into the transparent body 1. In this configuration, an emitted light 21 from the light-emitting element 2 is converted to a propagation light 22 that is subjected to total internal reflection, thereby propagating inside the transparent body 1. In the case where condensation drops 5 are developed on the surface of the transparent body 1, the conditions for the total internal reflection are not satisfied, and the light 22 that has propagated inside the transparent body 1 leaks out. When the light 23 thus leaking out is incident on the photodetector 3, the adhesion of condensation is detected by the detecting unit 6 according to an output signal from the photodetector 3.

Example 1 The following will describe an example of an optical condensation sensor according to the present invention, while referring to FIG. 4. A laminated glass 11 for automobiles was used as the transparent body. An LED with an emission wavelength of 700 nm was used as the light-emitting element 2. The guiding of light to the laminated glass 11 was carried out with the following configuration. An end of a single-sheet glass sheet 12 that is one of glass sheets composing the laminated glass 11 was cut obliquely at approximately 45° so as to form a prism section 41, and an emitted light 21 from a light-emitting element 2 was guided in through the prism section 41. A lens 42 was provided on the prism section 41, so that the emitted light 21 from the hght-emitting element 2 was colhmated and guided into the inside of the laminated glass 11.

The single-sheet glass sheet 12 and the other single-sheet glass sheet 13 were cemented with an intermediate film 14 interposed therebetween in a manner such that positions of their ends were deviated from each other, thereby forming the laminated glass 11. Aphotodiode (2506-02 manufactured by Hamamatsu Photonics K.K.) was used as the photodetector 3. The photodetector 3 was disposed at approximately 70° from a normal to the surface of the laminated glass 11, in a direction so as to face the hght source.

An experiment for determining the principle of operation was carried out using the sensor of Example 1. In the case where electric current supplied to the LED as the light-emitting element 2 was set to be DC of 30 mA, an output current of the photodetector 3 was 20 nA when the detection surface did not fog. On the other hand, when the detection surface was misted with a breath, the output current of the photodetector 3 was 200 nA.

Thus, a significant difference was found in the output values of the photodetector 3 depending on whether the detection surface fogged or not. It was found that in this case, by setting an appropriate threshold value with respect to the output of the photodetector 3, it is possible to detect the fog state of the detection surface.

Further, it was examined how the detection performance of the sensor of Example 1 varies according to a state of a space between the detection surface and the photodetector 3. More specifically, cigarette smoke was blown into the space.

It was found consequently that the output current of the photodetector 3 did not vary, irrespective of the presence or absence of the smoke. In other words, it was confirmed that the optical condensation sensor of the present invention had a constant detection capability irrespective of a state of the space between the detection surface and the photodetector 3.

Example 2 In Example 2, the sensor was configured so that light was guided into the transparent body 1 through its end surface as shown in FIG. 5. A glass sheet was used as a transparent body 1 in the present example. Further, an LED with an emission wavelength of 580 nm was used as a light-emitting element 2. As shown in FIG. 5, the light-emitting element 2 preferably is bonded to the transparent body 1 with a transparent resin or the like.

On surfaces in the vicinity of the end of the transparent body 1 at which the Hght-emitting element 2 was provided, a ceramic print 15 was provided so as to cut off light that was not subjected to total internal reflection inside the transparent body 1 but was allowed to leave the transparent body 1. Alternatively, a hght-blocking cover may be provided in place of the ceramic print. It should be noted that the ceramic print 15 or the cover provided only on one of the principal surfaces of the transparent body 1 as shown in FIG. 5 suffices, but in the case where light that is not subjected to the total internal reflection but is allowed to leave the inside of the transparent body 1 to the light-emitting element 2 side matters, the ceramic print 15 or the cover may be provided on both principal surfaces of the transparent body 1 in the vicinity of the light-emitting element 2.

When condensation drops 5 were developed by misting one surface of the transparent body 1 with a breath, leakage of light from the light source was detected (leaking hght 23 shown in FIG. 5) in a state substantially the same as that in Example 1. The leaking light was directed so that an angle formed between the light and a normal to the surface is approximately 80° or greater, where the condensation drops 5 were developed (detection surface). Since light emitted by the light-emitting element 2 as a hght source had a great beam divergence angle and hence was a divergent hght in the present example, hght was radiated at various angles. The following will be assumed in considering angles of Hght that can be employed in the present sensing technique. Transparent body: normal glass, n«1.51

Adhering condensation: water, n∞1.33

Ambient environment: air, n=l

The requirement for causing light propagating inside glass to be subjected to total internal reflection between interfaces of the glass when condensation is absent is that the light is incident on a surface of the glass so that the angle θi between the light and a normal to the surface of the glass (angle of incidence) is not less than 41°. The requirement, when water adheres to the glass surface due to condensation, for causing light propagating inside glass not to be subjected to total internal reflection but to travel into water adhering to the glass at an interface between the glass and water is that the foregoing angle θi is not more than 62°.

Therefore, the angle θi of light in a range of 41° to 62° can be used in this sensing technique. The light-emitting element 2 should be arranged so that the angle Qi falls in the foregoing range. It should be noted that the transparent body 1 is not limited to the single-sheet glass, but it may be a laminated glass, with which identical effects can be achieved.

Example 3

FIG. 6 illustrates a schematic configuration of Example 3 of the present invention. An optical condensation sensor according to Example 3 was configured as shown in FIG. 6 so that an end of a transparent body 1 (glass sheet) was cut obliquely at approximately 45° so as to form a prism section 41, and a light 21 emitted by a light-emitting element 2 was guided in through the prism section 41. A He-Ne laser was used as the emitting element 2. Further, a plurality of photodetectors (PD) 3 were provided on both principal surfaces of the glass sheet. .

Thus,_αby arranging a plurality of PDs at approximately 80° from normal to the glass surfaces at detection surfaces (all reflection points), it is possible to provide many detection surfaces on the surfaces of the transparent body 1, thereby further improving the sensitivity of the condensation sensor. Furthermore, since the light source used in the present example emits a laser light with a less divergence, an advantage is achieved in that an angle of light propagating inside the glass by total internal reflection does not increase.

The method for guiding the light from the hght-emitting element 2 so that the light propagates inside of the transparent body 1 while being subjected to total internal reflection is not limited to the aforementioned method, but it may be a method described below. For instance, as shown in FIG. 7, light may be guided in from a main surface of the transparent body 1 by an optical element 42 such as a diffraction grating or a hologram.

Furthermore, as shown in FIG. 8, a light-emitting element 2 may be embedded in an intermediate film 14 in the case where the transparent body 1 is a laminated glass. In this case, an LED chip or the like may be used as the light-emitting element 2. It should be noted that in this case as well, for the same reason as described in conjunction with Example 2, a ceramic print 15 or a light-blocking cover preferably is provided on the surface of the transparent body 1 in the vicinity of the position where the light-emitting element 2 is embedded.

Furthermore, as shown in FIG. 9A, the light-emitting element 2 and the transparent body 1 may be cemented to each other with a transparent resin 43. Alternatively, as shown in FIG. 9B, light from the light- emitting element 2 is guided into a light- guiding body 44 in a fiber form or a plate form whose end is cemented to the transparent body 1. In any case, an adhesive having a refractive index substantially equal to that of the transparent body 1 preferably is used as the adhesive 43.

Application Example

The following will describe an example of an optical condensation sensor of the present invention applied as a fog sensor for vehicles. For example, in the case where the optical condensation sensor according to Example 1 is used, the transparent body 1 is equivalent to a windshield of a vehicle. In the case where this optical condensation sensor is applied as a fog sensor for vehicles, it preferably is attached behind a rear mirror 17 as viewed from the driver's position (see FIG. 10). In this case, a light -emitting unit 20 and a photodetector unit 30 preferably are attached on an internal surface of a windshield glass 16. A detection area 18 for detecting dew is an internal surface area of the windshield glass 16. A control section for performing the following control according to an output current of a photodetector 3 (PD) preferably is mounted on the vehicle.

For example, a threshold value is set to be 40 nA, which is sufficiently greater than 20 nA as an output current in the case where the detection surface is not fogged. In the case where the output current value exceeds 40 nA, the control section, for instance, switches the climate control to a defroster mode so as to activate a fan. Furthermore, an air-conditioner may be operated. Besides, a defogger in a rear window glass may be turned on. On the other hand, it may be configured so that when the fog disappears by the effects of the defroster and the defogger and the output current decreases to not more than 40 nA, the control section stops the power supply to the fan and the defogger.

It should be noted that though an example of the optical condensation sensor of Example 1 applied as the fog sensor for vehicles is shown herein, it is possible to apply the optical condensation sensor of Example 2 or 3 as the fog sensor.

An LED is used as an example of the hght-emitting element 2 in Examples 1 and 2 described above. Light emitted by the LED has a directivity to some extent. However, it is difficult to propagate all the emitted light in the transparent body 1 while subjecting the same to total internal reflection therein. Therefore, the detection is carried out using light with an emission angle in a certain range. Here, in the case where the light having an emission angle out of the foregoing range directly leaks out from a surface of the transparent body, it will be effective to provide a light -blocking layer or a cover on a portion of the transparent body so as to prevent the light from entering the photodetector. Alternatively, it will be effective to arrange the photodetector at a sufficient distance from the light source so that the photodetector should not be affected by the leaking light.

As described above, according to the present invention, since an optical path of light emitted by the light-emitting element is inside a transparent body in a normal state, it is possible to provide an optical condensation sensor that is capable of detecting condensation with good precision without being affected by an environment.

Furthermore, the leaking light hardly is affected by cigarette smoke or the like in its optical path to the photodetector, and hence, malfunctions resulting from these hardly occur.

Furthermore, since the optical condensation sensor of the present invention detects adhesion of condensation drops by receiving leaking light directly, there is no need to lower the sensitivity for preventing malfunctions in particular, even in the case where an amount of light emitted by the light source decreases due to the deterioration of the light source with time or its temperature characteristics. Therefore, it is possible to secure the sensitivity so that even slight amounts of leaking light due to slight fog can be detected.

Furthermore, since the position where the detection is carried out is the same as the position where fog should be prevented, no temperature difference occurs between the detection position and the fog-prevented position. Therefore, there is no need to lower the sensitivity in particular for preventing malfunctions.

Industrial Applicability As described above, according to the present invention, it is possible to provide an optical condensation sensor capable of detecting fog due to condensation, with a high sensitivity and with fewer malfunctions.

Claims

1. An optical condensation sensor comprising a light-emitting element for guiding light into a transparent body, a photodetector, and a detecting unit for detecting adhesion of condensation to the transparent body according to an output of the photodetector, wherein light emitted by the Hght-emitting element is guided into the transparent body so that the light propagates an inside of the transparent body while being subjected to total internal reflection, and Hght leaking to outside the transparent body due to condensation adhering to a face of the transparent body, among the propagating light, is detected by the photodetector, so that the detecting unit detects the adhesion of the condensation.

2. The optical condensation sensor according to claim 1, wherein the photodetector is arranged at a position such that an angle formed between a normal to a fight-detecting surface of the photodetector and a normal to a detection surface of the transparent body is in a range of 50° to 90°.

3. The optical condensation sensor according to claim 2, wherein the photodetector is arranged at a position such that the leaking light is detected with a maximum intensity, according to an angle of incidence of light guided into the transparent body.

4. The optical condensation sensor according to claim 3, wherein the photodetector is arranged so as to satisfy: θ₂ = θi + 25° where θi represents the angle of incidence and satisfies 41°≤θι<60°, and Θ2 represents the angle formed between the normal to the light- detecting surface of the photodetector and the normal to the detection surface of the transparent body.

5. The optical condensation sensor according to claim 1, wherein the light-emitting element is arranged so that light emitted by the Hght-emitting element is guided through a principal face of the transparent body.

6. The optical condensation sensor according to claim 1, wherein the light-emitting element is arranged so that Hght emitted by the Hght-emitting element is guided into the transparent body via an end face of the transparent body, the end face being formed obliquely with respect to a principal face of the transparent body.

7. The optical condensation sensor according to claim 1, wherein the light-emitting element is arranged so that light emitted by the light-emitting element is guided into the transparent body via an end face of the transparent body, the end face being formed substantially perpendicularly to a principal face of the transparent body.

8. The optical condensation sensor according to claim 1, wherein the light-emitting element is embedded in the transparent body.

9. The optical condensation sensor according to claim 5, wherein a prism, a diffraction grating, or a hologram is provided on the principal face of the transparent body, at a position where the light emitted by the Hght-emitting element is guided into the transparent body.

10. The optical condensation sensor according to claim 5, wherein the light-emitting element is cemented to the principal face of the transparent body with a transparent adhesive.

11. The optical condensation sensor according to claim 5, further comprising a light-guiding body for guiding light emitted by the Hght-emitting element, the light-guiding body being cemented to the principal face of the transparent body with a transparent adhesive.

12. The optical condensation sensor according to claim 5 or 6, further comprising an optical member for colhmating the light emitted by the light-emitting element so that the light as a collimated light enters the transparent body.

13. The optical condensation sensor according to claim 5 or 6, wherein the light-emitting element is a light-emitting diode or a laser light source.

14. The optical condensation sensor according to claim 6 or 7, wherein the light-emitting element is cemented to the end face of the transparent body with a transparent adhesive.

15. The optical condensation sensor according to claim 7 or 8, wherein a Hght-blocking member for preventing light guided into the transparent body from the light-emitting element from leaking out is provided on at least one principal face of the transparent body in the vicinity of the end face.

16. The optical condensation sensor according to claim 1, wherein a plurality of the photodetectors are provided.

17. The optical condensation sensor according to claim 1, wherein the condensation is dew.

18. The optical condensation sensor according to claim 1, wherein the light-emitting element is driven with pulses.

19. The optical condensation sensor according to claim 1, wherein the transparent body is made of glass, a synthetic resin, or silicon.

20. The optical condensation sensor according to claim 19, wherein the transparent body is a window glass for vehicles.

21. A controller mounted on a vehicle along with the optical condensation sensor according to any one of claims 1 to 20, wherein the controller controls at least one among a defroster, a defogger, and an air-conditioner of the vehicle, according to a signal from the detecting unit of the optical condensation sensor.

22. A transparent body on which adhesion of condensation is detected by the optical condensation sensor according to claim 5, the transparent body comprising a prism, a diffraction grating, or a hologram on at least one principal face thereof.

23. A transparent body on which adhesion of condensation is detected by the optical condensation sensor according to claim 5 or 6, the transparent body comprising an optical member for colhmating the Hght emitted by the Hght-emitting element so that the light as a collimated light enters the transparent body.

24. A transparent body on which adhesion of condensation is detected by the optical condensation sensor according to claim 6, the transparent body comprising an end face formed obliquely with respect to a principal face of the transparent body, so that light emitted by the light-emitting element is guided therein via the end face.

25. A transparent body on which adhesion of condensation is detected by the optical condensation sensor according to claim 7, the transparent body comprising an end face formed substantially perpendicularly to a principal face of the transparent body so that light emitted by the light-emitting element is guided therein via the end face.

26. The transparent body according to claim 25, further comprising a light-blocking member for preventing light emitted by the light-emitting element from leaking out, the light-blocking member being provided on at least one principal face of the transparent body in the vicinity of the light-emitting element.

27. A transparent body on which adhesion of condensation is detected by an optical condensation sensor that detects leakage of light caused by condensation adhering to a surface of the transparent body, among light propagating inside of the transparent body while being subjected to total internal reflection therein, the transparent body comprising a light-emitting element, the light emitting element being incorporated therein.

28. The transparent body according to claim 27, further comprising a light-blocking member for preventing light emitted by the light-emitting element from leaking out, the Hght-blocking member being provided on at least one principal face of the transparent body in the vicinity of the light-emitting element.