JPH0961394A - Rain sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely detect the start of raining by outputting a rainfall starting signal from a control circuit when the electrostatic capacity change of a prescribed threshold or more is generated a prescribed number of times within a fixed time. SOLUTION: A control circuit has an oscillating circuit 4 and a judging circuit, and the oscillating circuit 3 outputs a pulse signal based on a time constant determined by the electrostatic capacity C and feedback resistance R2 between comb-tooth electrodes of a detecting surface 3. When raindrops are adhered onto the detecting surface 3, the electrostatic capacity C is increased, and the judging circuit judges a rainfall start from the state of the change with time of the electrostatic capacity C of the detecting surface 3 inputted from the oscillating circuit 4, and outputs a rainfall signal. In electrostatic capacity changing routine, when the difference between maximum and minimum values of the period of a fixed time is a periodic value of a prescribed capacity change threshold or more on the basis of the starting time of a certain period by pulse period measuring routine, 'the presence of capacity change' on the detecting surface 3 is judged. When 'the presence of capacity change' is judged a prescribed number of times within a fixed time, 'rainfall start' is judged to output the rainfall signal.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rain sensor,
In particular, the present invention relates to a rain sensor that does not malfunction due to foreign matter adhering to or remains on the detection surface and that accurately detects the start of rain.

[0002]

2. Description of the Related Art A conventional rain sensor is provided with opposing raindrop detecting electrodes exposed in the air, and when raindrops adhere between the electrodes, a short circuit between the electrodes is used to judge the start of rainfall. Generally known are the resistance type and the electrostatic capacitance type, which is provided with opposite electrodes for detecting raindrops covered with an insulating film and determines the start of rainfall from the increase in interelectrode capacitance when raindrops adhere to the surface of the insulating film. Has been.

The latter electrostatic capacitance type rain sensor is a level judgment type which converts a change in interelectrode capacitance into a frequency through a CR oscillation circuit and judges the start of rainfall when the frequency exceeds a certain value. And a successive comparison type that converts the change in inter-electrode capacitance into a rectangular pulse signal and judges the start of rainfall when the pulse width of two consecutive pulses or the difference between the surroundings changes by a certain value or more. However, it is generally known.

[0004]

However, in the conventional rain sensor, foreign matter such as bird droppings adheres to the detection surface of the rain sensor, or water droplets adhere and remain due to dew condensation depending on the installation location. In a rain sensor of the resistance type, the electrodes are short-circuited, and in the rain sensor of the level comparison type, since it exceeds the specified capacity value, it always starts raining regardless of the actual weather conditions. There was a problem of outputting a signal.

Further, among the capacitance type rain sensors, the successive approximation type is said to be judged as rain when a temporary capacity change occurs such as when foreign matter such as bird droppings adheres. There was a problem that malfunction occurred. The present invention has been made to solve the above problems, and an object of the present invention is to provide a rain sensor that does not malfunction due to foreign matter adhering to or remains on the detection surface and that accurately detects the start of rain. To do.

[0006]

The present invention proposed to solve the above problems has the following configuration. The rain sensor according to claim 1 has a detection surface formed by arranging the comb-teeth electrodes facing each other, and detects a change in the oscillation cycle by a change in capacitance that occurs when raindrops adhere to the detection surface. Then, in the rain sensor configured to output the rainfall detection signal, a control circuit that outputs a rainfall start signal when a capacitance change of a predetermined threshold value or more occurs a predetermined number of times within a certain period of time is provided. Characterize.

The rain sensor according to a second aspect of the present invention is the rain sensor according to the first aspect, wherein it is determined that there is a capacitance change when a change in electrostatic capacitance of a predetermined threshold value or more occurs within a predetermined time. It is characterized by Hereinafter, the operation principle of the rain sensor according to the present invention will be described with reference to FIGS. 9 and 10.

FIG. 9 is a diagram showing the principle of judging the presence or absence of capacity change, and FIG. 10 is a diagram showing the principle of judging the start of rainfall. A curve A in FIG. 9 shows the time change of the capacitance of the detection unit. Given that the current time is T1, if there is a capacity change that is equal to or greater than a predetermined threshold value Cth within the past Tc, that is, between times T0 and T1, then it is determined that there is a capacity change, and such a determination is made at regular time intervals Tc. To do. For example,
In the example of FIG. 9, at the next determination time T2, it is determined that there is no capacity change because the capacity change of the threshold value Cth or more has not occurred within the past Tc.

Next, referring to FIG. 10,
Based on a certain time (time t2 shown in FIG. 10A) when the determination “capacity change” is made, a predetermined number (N times) of “capacity change” determination within a predetermined time Tr If is given, it is judged that "rainfall has started",
If the "capacity change" determination is not made a predetermined number of times (N times) within the time Tr from the time when the "capacity change" determination is made (t2 shown in FIG. 10B) (M <
N), “capacity change” for the first time after time (t2 + Tr)
The time (time ty) determined to be is set as the number of times of the first change, and the number of times of capacity change within the predetermined time Tr is counted again with reference to this time ty.

According to such a rainfall start determining method, for example, in the case of rainfall, a plurality of water droplets continuously adhere to the detecting portion at random time intervals, so that a predetermined time Tr
Since the judgment of "capacity change" occurs more than a predetermined number of times, the rainfall start signal is output. On the other hand, when foreign matter such as bird droppings or dust adheres to the surface of the detection unit, multiple pieces do not continue to adhere like raindrops, so the “capacity change” judgment is not made more than the specified number of times, so rainfall No start signal is output.

Further, when water droplets gradually adhere to the surface over a long period of time, such as dew condensation, or when foreign matter such as bird droppings and dust remains in the detection portion, a change in capacity above the threshold value Cth occurs. Since the time is longer than the set value Tc, the rain start signal is not output due to the adhesion of dew condensation.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below by taking a capacitance type rain sensor as an example.
FIG. 1 is a circuit diagram of an oscillation circuit which is a main part of the present invention, FIG. 2 is a block diagram showing a configuration of a rain sensor, and FIG. 3 is a perspective view schematically showing an external configuration of the rain sensor.

Further, FIGS. 4 to 6 are flowcharts of programs processed by the determination circuit. 1 to 3
The rain sensor 1 will be described with reference to FIG.
a and 2b have a detection surface 3 formed so as to face each other, and an electrode 2 generated when raindrops adhere to the detection surface 3
A change in the oscillation cycle of the oscillation circuit 4 is detected by a change in the capacitance between a and 2b, and a rainfall detection signal is output from the signal line L.

In FIG. 2, reference numeral 6 indicates a control circuit,
The control circuit 6 includes an oscillation circuit 4 and a determination circuit 5. Further, in FIG. 3, 11 indicates a window frame to which a rain sensor is attached, and 13 indicates a rain sensor main body (housing). The oscillation circuit 4 outputs a pulse signal based on the capacitance C between the electrodes 2a and 2b of the detection surface 3 and the time constant determined by the feedback resistance R2, and the change in the capacitance C between the electrodes 2a and 2b is The oscillation period is converted and transmitted to the determination circuit 5.

In such a structure, when raindrops adhere to the detection surface 3, the capacitance C of the detection surface 3 increases, and the detection surface 3
When the capacitance C of C does not change with time, the oscillation period and the capacitance value have a one-to-one correspondence as shown in FIG. When a capacitance value that takes a continuous value in time is converted into a periodic value that is discontinuous in time, the periodic value shows a discontinuous value in time as much as the pulse width as shown in FIG. When the period is sufficiently shorter than the time when the capacitance changes, the pulse period value can be expressed as the instantaneous value of the capacitance. For example, the capacitance at time t1 shown in FIG. 8 appears as the newest pulse period P0.

The determination circuit 5 is a state in which the pulse signal input from the oscillation circuit 4 changes with time, that is, the detection surface 3
The start of rainfall is determined from the state of the time change of the electrostatic capacitance C and the rainfall start signal is output. Such a determination circuit 5 is configured to include a CPU, and includes a pulse period measurement routine shown in FIG. 4, a capacitance change detection routine shown in FIG. 5, and a rainfall start determination routine shown in FIG. Run.

The pulse period measuring routine is executed by interruption processing, and every time the falling edge of the input signal pulse is detected, the value of the internal counter is saved, and then the counter is cleared and the counting is restarted. In this way, the cycle of the input pulse signal is saved for each cycle (above, steps 101 to 106 in FIG. 4). In the capacitance change detection routine,
The difference between the maximum value and the minimum value is calculated among the cycles stored for a certain period Pc with reference to the start time of a certain cycle stored by the pulse cycle measurement routine, and the difference ΔP is a predetermined capacity change threshold Cth. If it is equal to or greater than the cycle value Pth corresponding to, the detection surface 3 is judged as "capacity change". If it is equal to or lower than Pth, it is determined that "there is no capacity change" on the detection surface 3 (above, steps 201 to 213 in FIG. 5).

In the rainfall start determination routine, when the "capacity change" judgment is made a predetermined number of times N times within a fixed time Tr from a certain time when the "capacity change" judgment is made. Judging that "rainfall has started", a rainfall start signal is output. Further, if it is not determined that the "capacity change" has been performed N times a predetermined number of times within the time Tr from the time when the first "capacity change" determination is made, the "capacity change" is first made after the lapse of Tr. The “changed” judgment is defined as the number of times of the first change, and the number of times of capacity change within the time Tr is counted again based on this time (steps 301 to 30 in FIG. 6).
8).

As described above, the rain sensor of the present invention shows a stepwise increase as shown in FIG. 9 when, for example, bird droppings adhere to the detection surface, and "capacity change". However, since the determination is made only once, the “rainfall start determination” is not made. Further, when dew condensation, dust accumulation, or the like occurs on the surface of the detection unit, the capacity change is more gradual in time than when water droplets are attached, and therefore the determination of "capacity change" is not made.

[0020]

As described above in detail, according to the rain sensor of claim 1, even if foreign matter such as bird droppings and flying insects adheres to the rain sensor, it does not malfunction, and No malfunction occurs even if foreign matter such as water droplets due to dew condensation or bird droppings remains on the surface of the detector. Further, in the rain sensor according to claim 2,
Since it is configured to judge that there is a capacitance change when the capacitance change above the threshold value occurs within a predetermined time, it is possible to more accurately detect when foreign matter adheres to the detection surface and when it starts to rain. Can be distinguished and distinguished.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an oscillation circuit that is a main part of the present invention.

FIG. 2 is a block diagram showing a configuration of a rain sensor of the present invention.

FIG. 3 is a perspective view schematically showing an external configuration of a rain sensor of the present invention.

FIG. 4 is a flowchart of a pulse period measurement routine executed by a determination circuit.

FIG. 5 is a flowchart of a capacitance change detection routine executed by a determination circuit.

FIG. 6 is a flowchart of a rainfall start determination routine executed by a determination circuit.

FIG. 7 is a diagram showing a relationship between an oscillation period value and a capacitance value on a detection surface.

FIG. 8 is a diagram showing a relationship between an oscillation pulse signal, a cycle, and time.

FIG. 9 is a diagram showing the principle of determining whether or not the capacity of the rain sensor has changed.

FIG. 10 is a diagram showing a principle of determining the start of rainfall in a rain sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Rain sensor 2a, 2b ... Comb-shaped electrode 3 ... Detection surface 4 ... Oscillation circuit 5 ... Judgment circuit 6 ... Control circuit 8 ... Power supply (DC5V) 9 ...・ Ground part (GND) L ・ ・ ・ Signal line 11 ・ ・ ・ Window frame 13 ・ ・ ・ Rain sensor body (housing) C ・ ・ ・ Capacitance

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[Procedure amendment]

[Submission date] October 16, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction contents]

[0020]

As described above in detail, according to the rain sensor of claim 1, even if foreign matter such as bird droppings and flying insects adheres to the rain sensor, it does not malfunction, and No malfunction occurs even if foreign matter such as water drops, bird droppings, and dust due to dew condensation remains on the surface of the detection unit. Further, in the rain sensor according to claim 2, since it is configured to judge that there is a capacitance change when a capacitance change of a threshold value or more occurs within a predetermined time, foreign matter adheres to the detection surface. The case and the beginning of rain can be distinguished and distinguished more accurately.

Claims (2)

[Claims] 1. Rainfall detection is provided by having a detection surface formed by arranging comb-teeth electrodes facing each other, and detecting a change in oscillation cycle due to a change in capacitance that occurs when raindrops adhere to the detection surface. In a rain sensor configured to output a signal, a control circuit is provided that outputs a rainfall start signal when a change in capacitance of a predetermined threshold value or more occurs a predetermined number of times within a certain period of time. Rain sensor. 2. The rain sensor according to claim 1, wherein it is determined that there is a capacitance change when a change in capacitance of a predetermined threshold value or more occurs within a predetermined time.