JPH0646186B2 - Water drop detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water drop detection device for detecting water drops such as drizzle, raindrops, snow and the like.

[Conventional technology]

BACKGROUND ART Conventionally, a water drop detection device is known in which a piezoelectric element is used as a sensor and the energy of raindrops that strike the sensor is converted into an electric signal. Further, it is provided with two electrodes insulated from each other on the side where raindrops and the like come in, and it is detected that the resistance value or the capacitance value between these electrodes changes due to the attachment of raindrops,
There is a water drop detection device that detects that a raindrop has adhered when the value reaches a predetermined level.

[Problems to be solved by the invention]

However, in the conventional water drop detection device, there is a problem that a device using a piezoelectric sensor cannot detect minute rain drops such as drizzle. Furthermore, the one that detects the raindrop by comparing the resistance value or the electrostatic capacitance value between the electrodes with a predetermined level, when foreign matter or the like adheres and accumulates as dirt between the electrodes,
Due to this influence, the electrostatic capacitance value between the electrodes becomes equal to or higher than a predetermined value level, and there is a problem of malfunction in that the same detection as that of raindrop attachment is performed even when raindrops are not attached.

The present invention has been made in view of the above problems, and detects a raindrop using electrostatic capacitance, and a waterdrop detection device that is not affected by dirt or stains deposited by foreign matter between electrodes. For the purpose of providing.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention has two electrodes, which are arranged on the same plane with a predetermined inclination angle at a portion where water droplets fly, and are insulated from each other, and between the electrodes due to the attachment of water droplets. Detecting means for generating a frequency component according to the capacitance of the detection signal as a detection signal, frequency change detecting means for receiving the detection signal and sending out a frequency change amount signal according to the change amount of the frequency, the frequency change amount Water drop adhesion determination means for sending out a signal indicating a water drop adhesion state based on the signal.

[Action effect]

According to the present invention, it is possible to detect a frequency component corresponding to a change in capacitance between two electrodes, and detect a water droplet adhesion state based on a frequency change signal corresponding to a change amount of the frequency component. For this reason, the amount of change in the frequency component of the detection signal appears for each newly attached minute water droplet without being affected by foreign matter or dirt already attached between the electrodes. Therefore, the present invention can provide a highly sensitive water droplet detection device that can detect minute water droplets without being affected by a long-term change in capacitance due to dirt between electrodes.

Further, according to the present invention, since the electrodes are arranged on the same plane with a predetermined inclination angle with respect to the electrodes existing in the portions where the water droplets fly, the electrode portions are large enough to be completely covered with the water droplets. It is possible to prevent a large amount of water droplets from adhering to each other, thereby preventing saturation in detection and preventing deterioration in detection accuracy.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

First, FIGS. 2 and 3 show structural diagrams of the detection means of the water droplet detection device. Reference numeral 6 denotes a ceramic substrate on which electrode patterns 50a and 50b for detecting water droplets having a comb structure which are insulated from each other are formed as shown in FIG. The ceramic substrate 6 is arranged with a predetermined inclination angle as shown in FIG. The ceramic substrate 6 is press-fitted into the housing 1 by using a drip-proof O-ring 3. The printed circuit board 7 is provided with the oscillation circuit 9 shown in FIG. 1, and the printed circuit board 7 is fixed to the housing 1 by machine screws 4. The detection electrodes 50a and 50b of the ceramic substrate 6 are connected to the oscillation circuit 9 by the lead wire 8.
It is connected to the. The wire harness 5 is connected to the printed board 7 and includes a line for taking out the output of the oscillation circuit 9 and supplying a power source and a ground line. 2 is a code push. The oscillation output 9a of the oscillation circuit 9 is transmitted to the controller 16 shown in FIG. 1 by a wire harness.

The controller 16 includes a one-shot circuit 20, an FV conversion circuit 23, a differentiation circuit 25, a voltage comparison circuit 26, a monostable multivibrator 29, a drive circuit 33 such as an alarm device, a constant voltage circuit 35, and a power ON reset circuit 36. To be done.

The oscillator circuit 9 has four inverter gates 1 directly connected to each other.
0, 11, 12, 13, the resistor 14, the capacitor 15, and the detection electrodes 50 a, 50 formed on the ceramic substrate 6.
It is composed of the interelectrode capacitance C ₀ of b. Oscillator circuit 9
The oscillation output 9a is transmitted to the controller 16, received by the PNP transistor 17, and input to the wasshot circuit 20 through a low-pass filter composed of a resistor 18 and a capacitor 19. The output 20a of the one-shot circuit 20 becomes a pulse having a constant time width determined by the time constant of the resistor 21 and the capacitor 22. The output 20a of the one-shot circuit 20 is input to an FV conversion circuit 23 including an OP amplifier 24 and the like, and the oscillation output 9a of the oscillation circuit 9 is converted into a voltage output 23a. Output 23a of F-V conversion circuit 23
Is connected to a voltage comparison circuit 26 including an operational amplifier 27 and the like via a differentiation circuit 25. The voltage comparison circuit 26 receives the D-flop flip 30 via the inverter gate 28.
And the like are connected to a monostable multivibrator 29.

The monostable multivibrator 29 has a clock input 29a.
At the rising edge of, an output pulse 29b having a constant time width determined by the time constants of the resistor 31 and the capacitor 32 is generated. The output pulse 29b is input to the drive circuit 33. The drive circuit 33 is connected to an alarm device (not shown), a relay of a wiper drive motor, and the like. Reference numeral 36 is a power-ON reset circuit, and when a power switch (not shown) is turned on and the constant-voltage circuit 35 is supplied with the power V _B , the power is turned on.
A reset pulse is generated to reset the output 29b of the D flip-flop 30 to low level.

Next, the operation will be described based on the above configuration.

When water droplets adhere to the detection electrodes 50a and 50b and the inter-electrode capacitance C ₀ changes due to the relative dielectric constant, the oscillation frequency of the oscillation output 9a of the oscillation circuit 9 changes. This oscillation output 9
The value a is transmitted to the controller 16 and input to the one-shot circuit 20 through a low-pass filter including a resistor 18 and a capacitor 19. The output 20a of the one-shot circuit 20 becomes a pulse having a constant time width determined by the time constant of the resistor 21 and the capacitor 22, and this output 20a is F-V.
The conversion circuit 23 converts the voltage output 23a. When the oscillation output 9a changes, the voltage output 23a also changes, and the differentiating circuit 25 inputs only the change 23b of the voltage output 23a to the voltage comparing circuit 26. When the voltage change 23b exceeds the comparison voltage 26a, the output 27a of the OP amplifier 27 is output.
Is inverted from the high level to the low level and is inverted again by the inverter gate 28, and the clock input 29a of the D flip-flop 30 rises from the low level to the high level. Output pulse 2 of monostable multivibrator 29
9b turns on the NPN transistor 34 of the drive circuit 33.
Then, an alarm device (not shown) is driven.

In the case of detecting the rainfall state, the amount of rainfall attached to the detection electrodes 50a and 50b changes as long as the rainfall continues, so that the inter-electrode capacitance C ₀ changes and the same as described above. The output pulses are sequentially output from the monostable multivibrator 29, and the alarm device and the like are driven. Here, when the amount of rain attached to the detection electrodes 50a and 50b increases, the inter-electrode capacitance C ₀ may be saturated, but
Since the detection electrodes 50a and 50b are inclined as shown in FIG. 2, the amount of rain adhering between the electrodes is limited and the saturation of the interelectrode capacitance C ₀ is suppressed. Therefore, as long as the electrode portion is not completely covered with rain due to heavy rain or the like, it is possible to detect a change in the interelectrode capacitance C ₀ . Further, even when the intensity of rain changes, the inter-electrode capacitance C ₀ changes according to the amount of rainfall due to it,
Thereby, raindrop detection can be performed.

In the above-described embodiments, the inter-electrode capacitance change of the detection electrodes is used as the frequency change of the oscillator and further converted into the voltage change for detection, but a method of detecting the frequency change may be used. FIG. 4 shows another embodiment. In this embodiment, the oscillation output 9a of the oscillation circuit 9 is input to the PLL circuit 43.
The phase output 43a of the PLL circuit 43 generates a pulse having a pulse width corresponding to a phase change caused by a change in the oscillation output 9a. The counter 41 is normally reset by the phase output 43a, but the reset is released only when the phase output pulse is generated due to the change in the oscillation output 9a, and counts the output pulse 40a of the reference oscillator 40. The pulse width of the phase output pulse 43a is the output 41a of the counter 41.
If the time width is sufficient to output the signal, the output 41a generates a pulse, the monostable multivibrator 29 is triggered, and the drive circuit 33 operates.

As described above, in this example, the change in the capacitance value between the detection electrodes 50a and 50b due to the attachment of the water drop is detected as the output signal of the frequency component according to the change amount, and the frequency component is detected. Since the attached state of water droplets is detected based on the change amount of, it is possible to detect minute water droplets, for example, minute raindrops in the form of drizzle. Further, there is an advantage that the detection state with high sensitivity can be maintained without being affected by the contamination of the electrode that is attached due to the change with time.

In the above-mentioned embodiment, the electrode of the water drop detecting means is an electrode having a comb-like structure, but the two electrodes are insulated from each other even if they have other shapes. Anything that causes a capacitance change of Although the ceramic substrate is used as the substrate for forming the electrodes, a printed substrate such as glass epoxy may be used.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a partial cross-sectional view showing the structure of the detection portion of the water droplet detection device, and FIG. 3 is a front view showing the electrode shape of the water droplet detection device. The drawing is a circuit diagram showing another embodiment of the present invention. 9 ... Oscillation circuit (electrode and detection means), 20 ... One shot circuit, 23 ... FV conversion circuit, 25 ... Differentiation circuit, 26 ... Voltage comparison circuit, 29 ... Monostable multivibrator. 33 ... Driving circuit, 40 ... Reference oscillator, 4
1 ... Counter, 43 ... PLL circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-85949 (JP, A) JP-A-54-100797 (JP, A) Actual development: JP-A-59-34354 (JP, U)

Claims (3)

[Claims] According to a capacitance between two electrodes, which are arranged on the same plane with a predetermined inclination angle at a portion where the water droplets fly, and are insulated from each other, and the electrode between the electrodes due to the attachment of the water droplets. Detecting means for generating a frequency component as a detection signal, frequency change detecting means for receiving the detection signal and sending out a frequency change amount signal according to the temporal change amount of the frequency, and based on the frequency change amount signal A water drop detection device, comprising: a water drop adhesion determination means for transmitting a signal indicating the water drop adhesion state. 2. The frequency change detection means includes a one-shot circuit for converting the detection signal of the frequency component into a predetermined pulse signal, a frequency-voltage conversion circuit for converting the pulse signal into a voltage signal, and the voltage signal conversion circuit. The water droplet detection device according to claim 1, further comprising a differentiating circuit for extracting the amount of change as a frequency change amount signal. 3. The frequency change detecting means is a PLL circuit which sends out from the detection signal of the frequency component as a frequency change amount signal having a pulse width corresponding to the amount of change of the frequency. Water drop detector.