JPH052183B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a water droplet detection method for detecting the presence or absence of water droplets adhering to a window glass and automatically starting and stopping an anti-fog device. .

[Conventional technology]

Conventional optical water droplet detection devices of this type include:
For example, a structure disclosed in Japanese Patent Laid-Open No. 167945/1983 is known. The configuration of this known device is that an input waveguide with a light emitter and an output waveguide with a receiver are provided on one side of a transparent plate material, which is the surface to be detected. When a light beam is introduced at an angle that forms a total reflection angle and is totally reflected on the inner surface of the plate material, if water droplets adhere to the surface of the plate material, the amount of light leaks to the outside due to disturbance of the reflective surface. The adhesion of water droplets is detected from the decrease, and the total reflection is performed an odd number of times to guide the light beam to the output side waveguide provided on the same surface and detect it with a light receiver.

However, the means for detecting dew condensation and water droplet adhesion in this conventional device detects only a decrease in the amount of light on the receiver side, and in order to ensure reliable detection, detection can only be made at a level where the amount of light has decreased considerably. Because of this configuration, there was a problem in that condensation and water droplets could not be detected unless they were at a level that was noticeable to human vision, making it difficult to automatically maintain a safe field of vision.

[Problems to be Solved by the Invention] The present invention attempts to solve the problem of temporary visibility instability due to dew condensation and a delay in detection of water droplets in the conventional example.

[Means for solving problems]

As a specific means for solving the above-mentioned problems, the present invention includes a light emitting element and a light receiving element, and reflects light from the light emitting element multiple times in a detection member provided on a detection surface to detect the light receiving element. In the water drop detection means for detecting the presence or absence of water droplets based on the degree of light intensity, the output signal of the light emitting element is driven in a triangular wave or sawtooth shape, and the output signal of the light receiving element is formed correspondingly. A water droplet detection method comprising: comparing an output signal at a constant level and converting it into a digital signal; and detecting initial condensation or adhesion of water droplets by measuring the rate of change over time of the width of the digital signal. This makes it possible to accurately detect dew condensation and water droplet adhesion at an early stage, and to drive an auto defroster, defogger, wiper, etc. at a certain level.

〔Example〕

Next, the water droplet detection method according to the present invention will be explained in more detail with reference to the illustrated embodiment. FIG. The water droplets are detected only on the surface 1a side of the plate 1. A prism 2 made of a transparent material having the same refractive index as the plate 1 is attached to the surface 1a side of the plate 1, and the prism 2 is made of a material such as balsam resin or epoxy resin. 2
It has a refractive index similar to , and is bonded to the surface 1a, which is the detection surface. Further, a back surface 1 of the plate material 1 opposite to the surface 1a to which the prism is bonded.
b, the modulation generating circuit 3 and the amplifying light receiving circuit 4 are placed adjacent to each other and are attached by an appropriate method. A light emitting element 3a and a light receiving element 4a are provided in each circuit.

In another embodiment shown in FIG. 2, a detection member 5 having a circular or square cross section for detecting water droplets is attached to the modulated light emitting circuit 3 and the amplified light receiving circuit 4 in an arch shape.

In any of the embodiments, the light 6 emitted from the light emitting element 3a is inside the prism 2 or the detection member 5.
If there is condensation or water droplets 7 on the outer surface of the prism 2 or the outer surface of the detection member 5 where the reflection takes place, the light will be reflected through the water droplets 7. A part of the light 6a leaks to the outside, and the amount of light reaching the light receiving element 4a decreases, thereby detecting dew condensation or adhesion of water droplets.

As the detection means, the measuring method shown in FIG. 3 can be used. In other words, the output signal a of the light emitting element
is driven in a triangular waveform with a constant period T, and the output signal b based on the amount of light received by the light receiving element in each period is amplified to form a similar triangular waveform. When the output signal b from the light receiving element side is compared at a constant level s and the high level "H" and the low level "L" are converted into digital signals, a rectangular waveform g is obtained.
When measuring the time Δt of this square wave, if there is no condensation or water droplets attached, it will continue to show Δt for a certain period of time, but when dew condensation or water droplets start to adhere, light leaks to the outside and the amount of light reaching the light receiving element decreases. As a result, the triangular waveform of the output signal b becomes smaller, the rectangular wave g becomes narrower, and the measurement time Δt becomes shorter. Therefore, the width time Δt for forming the rectangular wave g
Dew condensation or water droplet adhesion can be detected by measuring , and if a certain period T is repeated and time Δt is not detected even once, extreme dew condensation or water droplet adhesion can be detected. Further, in the above description, an example was shown in which the output a of the light emitting element was driven as a triangular wave signal, but the same result can be obtained even if the output a is driven as a sawtooth wave signal, for example.

〔Effect of the invention〕

As explained above, in the dew condensation or water droplet detection method according to the present invention, in the detection means consisting of a light emitting element and a light receiving element, the output signal of the light receiving element is sampled at a timing synchronized with the output signal of the light emitting element. Since the data is extracted and detection is performed based on the rate of change of the data, accurate and reliable detection can be performed from the initial stage of dew condensation or water droplet adhesion.

Furthermore, the output signal of the light emitting element is driven in a triangular wave or sawtooth shape, and the corresponding output signal of the light receiving element is compared at a constant level and converted into a digital signal.
Since detection is performed based on the rate of change over time of the waveform width of the digital signal, it has an excellent effect of being able to accurately detect dew condensation or water droplet adhesion at an early stage.

Additionally, since it is possible to detect dew condensation and water droplet adhesion at the initial stage, the auto defroster, defroster, air conditioner, wiper, etc. can be operated at a predetermined timing, so visibility will not become unstable even temporarily. This has an excellent effect in that it can be avoided and contribute to safe driving.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing an example of a detection device for carrying out the method of the present invention, FIG. 2 is a schematic sectional view showing another detection device, and FIG. 3 is a schematic sectional view showing another detection device. This is a graph showing the principle. 1... Surface to be detected, 2, 5... Detection member, 3...
Modulated light emitting circuit, 3a...Light emitting element, 4...Modulated light receiving circuit, 4a...Light receiving element, 6...Light, 7...Dew condensation or water droplets, a...Output of the light emitting element, b...Output of the light receiving element .

Claims (1)

[Claims] 1 Comprising a light-emitting element and a light-receiving element, the light from the light-emitting element is reflected multiple times in a detection member provided on a detection surface and guided to the light-receiving element, and the presence or absence of water droplets is detected based on the degree of the amount of light. In the water droplet detection means, the output signal of the light emitting element is driven in a triangular wave or sawtooth shape, the output signal of the light receiving element is formed correspondingly, and the output signal is compared at a constant level to convert it into a digital signal. A water droplet detection method, characterized in that initial condensation or adhesion of water droplets is detected by measuring the rate of change over time of the width of a digital signal.