JPH0434443Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a wiper drive raindrop sensor that detects rainfall and automatically starts the wiper of a vehicle.

[Conventional technology]

Optical raindrop sensors are sometimes used to automatically activate a car's wipers when it rains.

Figure 3 is a diagram of the principle of a raindrop sensor, where 1 is a light emitting element such as a light emitting diode, 2 is a light receiving element such as a photodiode, and 3 is an approximately 10 cm gap formed between the two.
4 is a raindrop falling across the raindrop detection area. If a constant amount of light is always output from the light emitting element 1, the amount of light incident on the light receiving element 2 decreases each time a raindrop 4 passes. Therefore, the amount of rain can be calculated from the integrated value of the decrease in the amount of incident light per unit time.

FIG. 4 is a block diagram showing a conventional configuration of an auto wiper device using this type of raindrop sensor.

In the figure, light from a light emitting element 1 is pulse-modulated by the output of a modulation drive circuit 5 in order to distinguish it from peripheral light. Emitted from the light emitting element 1,
The light that passes through the raindrop detection area 3 and enters the light receiving element 2 is converted into an electrical signal here, and the output of the light receiving element 2 is input to a bandpass filter 6 that passes only the modulated wave, and is further amplified by an amplifier 7. After that, the envelope is detected by the wave detector 8. The output of this detector 8 shows a level drop in a portion 15 corresponding to raindrops.
The low-pass filter 9 removes ripple components caused by pulse modulation from the detection output, and for example,
It has a cutoff frequency of about 20KHz. The low-pass filter 9 is configured to obtain a level-inverted output using, for example, an active filter, and therefore, a portion 16 of the output corresponding to raindrops has a pulse waveform. low pass filter 9
After the output is amplified by an amplifier 10, it is input to an analog integrator 11, where the raindrop pulse output is integrated and input to the + terminal of a comparator 12.

The reference level _L1 is input to the - terminal of the comparator 12, and the comparator 12 compares the integrated output of the integrator 11 with the reference level _L1 , and if it becomes > _L1 , its output (wiper activation signal ) to high level and switch wiper drive switch _S1 from b to a. As a result, the motor M of the wiper motor section 14 receives power +
Current flows through the path B→a→S ₁ →M→ground, and motor M starts rotating. When the motor M starts rotating, a wiper (not shown) starts one reciprocating operation,
After a certain period of time, the cam switch _S2 switches from d to c. As a result, power is supplied to the reset circuit 13 via the path +B→c→S ₂ →b, and the reset circuit 13
resets the integrator 11, that is, makes its contents zero. When the integrator 11 is reset, the integrated output becomes zero, so the output of the comparator 12 becomes low level, and the switch _S1 returns from a to b. However, since the path +B → c → S ₂ → b → S ₁ → M → ground is formed, motor M continues to rotate, and when cam switch S ₂ returns from c to d at the end of one reciprocation, motor M Stop.

Since the integrator 11 starts the integration operation immediately after the above-mentioned reset, the above-described operation is repeated every time the output of the comparator 12 becomes high level. Therefore, the intermittent operation cycle of the wiper changes in proportion to the time when the integrated output reaches the reference level _L1 , that is, in inverse proportion to the amount of rainfall.

[Problems to be Solved by the Invention] Incidentally, in the raindrop sensor described above, the detection sensitivity decreases due to the following various factors.

Attachment of dirt, etc. to the receiving and emitting surfaces due to changes over time Changes in the characteristics of the receiving and emitting elements due to changes in ambient temperature Variations in the receiving and emitting intensity of individual receiving and emitting elements, radiation and reception directions, and chip mounting position accuracy Light when combining the receiving and emitting elements If the axis misalignment detection sensitivity decreases, various problems will occur, such as the wiper not moving even though it is raining, or the intermittent operation cycle of the wiper being too long for the amount of rain. However, conventional raindrop sensors have not been provided with compensation means for such a decrease in sensitivity.

Therefore, an object of the present invention is to provide a wiper drive raindrop sensor that can always provide constant sensitivity.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention makes the light emitted from a light emitting element driven by a pulse signal received by a light receiving element across a raindrop detection area, and envelopes the modulated wave component extracted from the output of the light receiving element. A raindrop sensor for driving a wiper receives a wiper activation signal from a comparator that extracts a variation component due to raindrops after line detection and compares an integrated value of the variation component due to the raindrop with a reference value. a differential amplifier that amplifies the difference between the output of the first low-pass filter and a reference value; and a second low-pass filter that receives the output of the differential amplifier as an input. circuit, and a modulation drive circuit that changes the light emission power when driving the light emitting element in pulses according to the output of the power control circuit, and further includes a modulation drive circuit that changes the amount of variation in the envelope detection output due to temperature in the power control circuit. A temperature compensation circuit is provided that adds a variation amount having a characteristic opposite to that of the envelope detection output to the envelope detection output and supplies the result to the differential amplifier as an output of the first low-pass filter.

[Effect]

If the detection sensitivity decreases, the average level of the output of the detector will decrease. This average level is taken out as the output of the first low-pass filter,
The differential amplifier generates a voltage according to the difference from the reference value, and the modulation driver circuit adjusts the light emission power of the light emitting element so that the detection sensitivity is always constant. The influence of minute fluctuations in the output of the detector when detecting raindrops is removed by the first low-pass filter, and the fluctuation in light emission power due to overcompensation of the light-emitting element drive current is removed by the second low-pass filter.

Furthermore, when the envelope detection output varies due to temperature, the variation is removed by the temperature compensation circuit and input to the differential amplifier, so the input to the envelope detection stage remains constant regardless of temperature.

〔Example〕

FIG. 1 is a block diagram of essential parts of an embodiment of the present invention, where the same reference numerals as in FIG. 4 indicate the same parts, and 20 is a power control circuit.

The raindrop sensor of this embodiment includes the detector 8 shown in FIG.
A low-pass filter 21 that receives the output of the low-pass filter 21 and a reference voltage setter 23
A power control circuit 20 is provided, which includes a differential amplifier 22 that amplifies the difference between the output of The light emitting power of the light emitting element 1 is increased in accordance with the decrease in the average value of the output level of the detector 8.

As mentioned above, the output of the detector 8 includes ripple components due to modulated waves and fluctuation components due to raindrops, so in order to remove these effects and extract only the average level, the cutoff frequency of the low-pass filter 21 is set as follows. For example, it is set to about 5Hz. Further, in order to prevent fluctuations in the light emitting power due to overcompensation of the light emitting element drive current, the cutoff frequency of the low pass filter 24 is set to, for example, about 1 Hz.

Since this embodiment has such a configuration, when the sensitivity decreases due to factors such as those mentioned above, the average output level of the detector 8 (this is equivalent to the average level of received light power) decreases, and the reference voltage Since the difference with the output value of the setter 23 becomes large, the output of the differential amplifier 22 becomes large, the light emission power during pulse modulation of the light emitting element by the modulation drive circuit 5 is increased, and the average output level of the detector 8 is increased. Feedback is applied so that the output is equal to the output of the reference voltage setter 23. Therefore, the received light power is always kept constant and the detection sensitivity is maintained at a desired value.

FIG. 2 is a circuit diagram of a more detailed embodiment of the present invention, in which the same symbols as in FIGS. 1 and 4 indicate the same parts, R ₁ to _{R 12} are resistors, C ₁ to C ₆ are capacitors,
D ₁ to D ₃ are diodes, ZD is a zener diode,
AMP is an amplifier, TR is a transistor, V _S is the output voltage of the detector 8, V _B1 is the reference voltage, V _B2 is the bias addition voltage, V _B3 is the temperature compensation voltage, and V _PC is the output voltage of the amplifier AMP.

In this embodiment, the detector 8 is a diode D ₁
and a detection section consisting of a diode _{D 2 ,} a resistor R ₅ , and a capacitor C ₂ , and its output V _S is input to a low-pass filter 21 consisting of a resistor R ₁ and a capacitor C ₁ . . Since the output V _S is generally a small value, the power supply +B is connected to the output of the low-pass filter 21 through resistors R ₇ and R ₈
The bias addition voltage V _B2 obtained by voltage division is added, and in order to compensate for the forward voltage drop V _F due to temperature changes of the diodes D ₁ and D ₂ in the detector 8, the power supply +B is connected to the resistor R ₆ and the diode. After the voltage V _B3 obtained by dividing the voltage by D ₃ is further added, the voltage is inputted to the - terminal of the amplifier AMP constituting the differential amplifier 22 .

On the other hand, the reference voltage V _B1 obtained by dividing the voltage of the Zener diode ZD by resistors R ₉ and R ₁₀ is input to the + terminal of the amplifier AMP, and the voltage difference with the - terminal is amplified and output. . The output of this amplifier AMP is applied to the modulation drive circuit via a low pass filter 24 consisting of a resistor R ₁₁ and a capacitor C ₅ .

In this embodiment, the modulation drive circuit 5 includes a pulse oscillator OSC, a transistor TR connected in series between the light emitting element 1 driven by the output of the pulse oscillator OSC, and ground, and a base of the transistor TR. The output of low pass filter 24 is added. When the output voltage of the low-pass filter 21 decreases, the output voltage of the amplifier AMP increases, the resistance value of the transistor TR decreases, a large voltage is applied to the light emitting element 1, and the light emitting power is increased.

In Figure 2, the output voltage V _PC of the amplifier AMP is: V _PC = V _B1 − R ₄ [{(V _B3 − V _B1 )/R ₁ } + {(V _B2 − V _B1 )/R ₂ } + {( V _S −V _B1 )/R ₃ }]. Here, if R ₁ = R ₂ = R ₃ , then V _PC = V _B1 − (R ₄ /R ₁ ) × {V _S − (3V _B1 − V _B2 − V _B3 )}. Let the target voltage of V _S be V _SO , and its value is 3V _B1
−V _B2 −V _B3 , when V _S = V _SO , V _PC
= V _B1 . Therefore, the reference voltage V _B1 may be set in advance according to the desired detection sensitivity to be obtained.

Also, when the ambient temperature changes, V _S = V _S ±ΔV _S
However, if the characteristics of the diodes D ₁ to D ₃ are selected so that V _B3 ±ΔV _B3 and ΔV _S =ΔV _B3 ,
Temperature fluctuations due to the diode in ΔV _S will be canceled out.

[Effect of idea]

As explained above, the wiper drive raindrop sensor of the present invention is susceptible to dirt, etc. attached to the light receiving and emitting surfaces due to changes over time, and variations in the light receiving and emitting intensity of the light receiving and emitting elements, the direction of radiation and light reception, and the accuracy of the chip mounting position. If the sensor detection sensitivity becomes lower than desired due to the above-mentioned factors, the power control circuit changes the light emission power when pulse-driving the light emitting element so as to obtain the desired detection sensitivity. Therefore, constant detection sensitivity can be maintained at all times. Additionally, when the envelope detection output fluctuates due to the ambient temperature, the temperature compensation circuit removes the fluctuation and supplies it to the differential amplifier, so the input level of the envelope detection stage is always constant and the detection sensitivity is improved. It can be kept constant regardless of the ambient temperature. Therefore, it is possible to reliably carry out controls such as starting to move the wiper at a preset amount of rainfall, or driving the wiper intermittently at intervals appropriate for the amount of rainfall.

In addition, in the present invention, since the first low-pass filter is provided in the power control circuit to remove modulation components and fluctuation components caused by raindrops from the detected output, minute fluctuations in the detector output when raindrops are detected are provided. In addition, since the output power of the differential amplifier is further smoothed by the second low-pass filter and the output power is changed, the emission power does not change due to overcompensation of the emission power. The fluctuation can be minimized.

[Brief explanation of drawings]

Figure 1 is a block diagram of the main parts of an embodiment of the present invention, Figure 2 is a detailed circuit diagram of an embodiment of the present invention, Figure 3 is a principle diagram of a raindrop sensor, and Figure 4 is a diagram of a conventional raindrop sensor. FIG. 2 is a configuration diagram of an automatic wiper device. In the figure, 1 is a light emitting element, 8 is a detector, 20
2 is a power control circuit, 21 and 24 are low-pass filters, 22 is a differential amplifier, and 23 is a reference voltage setter.

Claims (1)

[Scope of Claim for Utility Model Registration] Light emitted from a light emitting element driven by a pulse signal is received by a light receiving element across a raindrop detection area, and the modulated wave component extracted from the output of the light receiving element is subjected to envelope detection. Extract the fluctuation component due to raindrops,
A wiper drive raindrop sensor that obtains a wiper activation signal from a comparator that compares the integrated value of the fluctuation component due to the raindrops with a reference value, the wiper drive raindrop sensor comprising: a first low-pass filter receiving the envelope detection output as input; a power control circuit including a differential amplifier that amplifies the difference between the output of the low-pass filter and a reference value, and a second low-pass filter that receives the output of the differential amplifier as an input; a modulation drive circuit that changes the emission power of the envelope detection output according to the output of the power control circuit, and the power control circuit changes the amount of variation that has an opposite characteristic to the amount of variation in the envelope detection output due to temperature. A raindrop sensor for driving a wiper, comprising a temperature compensation circuit that adds the envelope detection output to the differential amplifier as an output of the first low-pass filter.