JP2002286629A - Raindrop detecting device and method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a raindrop detecting device and a method thereof which are simple in constitution and capable of reducing cost in the detection of raindrops immediately after starting. SOLUTION: The raindrop detecting device 6 is provided with a setting means (a CPU 12) for setting the gradient of output values of a light receiving means (a PD9 and a detector/amplifier 14) in the state of the absence of the adhesion of raindrops to an object (windshield 1) as a gradient in sunny weather through the use of a light emitting means (an LED 8 and an LED drive circuit 13) capable of emitting light in such a way that luminance is proportional to a driving current with an approximately constant gradient, an operation means (the CPU 12) for computing the gradient of the output values of the light receiving means by changing the driving current immediately after starting, and a determining means (the CPU 12) for determining the adhesion of raindrops by comparing the computed gradient with the gradient in sunny weather. As the determination is performed in a short time immediately after the raindrop detecting device 6 is started by the gradient of the output values, it is possible to eliminate the need for temperature correction, facilitate operation, simplify the constitution, and reduce cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raindrop detecting apparatus and method for detecting raindrops, and more particularly to a raindrop detecting apparatus and method for easily detecting raindrops immediately after startup.

[0002]

2. Description of the Related Art A conventional raindrop detecting device is disclosed in
As disclosed in JP-A-326186, the degree of the amount of raindrops adhering to a raindrop-attached object and the output of the light-receiving means are obtained by changing the light emission output level of the light-emitting element and the output signal level of the light-receiving element depending on the ambient temperature. To cope with the problem that the correspondence relationship with the signal level fluctuates, there is known a raindrop detecting device that performs temperature characteristic correction by changing the gain of an amplifier circuit that constitutes a light receiving unit in accordance with a change in ambient temperature. .

[0003]

However, Japanese Patent Application Laid-Open No.
The raindrop detecting device disclosed in Japanese Patent No.
For example, connecting the diode as a negative resistance element in parallel to the feedback resistance of a DC amplifier changes the gain of the amplifier circuit according to the fluctuation of the ambient temperature, which complicates the configuration and raises the cost. there were.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a raindrop detecting device having a simple configuration and capable of reducing costs in detecting a raindrop immediately after startup, and an object thereof.

[0005]

According to a first aspect of the present invention, there is provided a raindrop detecting apparatus according to the present invention. Can emit light in proportion to a constant slope,
Alternatively, it is possible to emit light in proportion to a substantially constant slope for each predetermined drive current section, and the slope of the output value of the light receiving means with respect to the drive current in a state where raindrops are not attached to the target object, in a sunny time Setting means for setting as a slope; calculating means for changing the drive current to emit light by the light emitting means immediately after the start; calculating means for calculating the slope of the output value of the light receiving means with respect to the drive current; And determining the attachment of the raindrop to the target object by comparing the inclination with the inclination in (1).

Thus, the measurement of the output value is performed immediately after the start-up, and since the measurement time is short, the ambient temperature becomes substantially constant during the measurement. For this reason, it is not necessary to consider a change in the slope of the output value due to a change in the ambient temperature. Therefore, there is no need for a circuit configuration in consideration of the temperature characteristics or correction by software. Further, when raindrops are attached to the target object, the slope of the output value of the light receiving means is smaller than that at the time of sunny because a part of the emitted light is transmitted to the outside by the raindrops and is not received by the light receiving means. Is also smaller. Therefore, it is possible to easily determine the attachment of raindrops only by comparing the inclination of the output value with the inclination at the time of sunny, so that a complicated comparison operation or the like becomes unnecessary. From these facts, it is possible to provide a raindrop detecting device having a simple configuration and capable of reducing costs. Further, when the inclination of the light emission output changes with respect to the ambient temperature due to the characteristics of the light emitting element, the raindrop can be detected with higher accuracy by storing the output gradient with respect to the ambient temperature in advance.

According to the raindrop detecting device of the second aspect of the present invention, the light emitting means can emit light such that the light emission luminance is proportional to the drive current for causing the light emitting element to emit light at a substantially constant slope, or is predetermined. And the output value of the light receiving means with respect to the drive current in a state where no raindrop is attached to the target object is represented by a first slope in a sunny state. Setting means for setting a slope smaller than the first slope as the second slope at the time of clearing in consideration of a reduction factor of the amount of received light; By calculating the slope of the output value of the light receiving means with respect to the drive current, comparing the calculated slope with the first slope, and comparing the calculated slope with the second slope. And having a determination means for attachment of raindrops to the object.

[0008] Thus, not only the first inclination at the time of fine weather, but also the reduction of the amount of received light, such as dirt, is taken into consideration and compared with the second inclination set in accordance with the actual situation. Therefore, it is possible to prevent a determination error such that it is determined that raindrops are attached due to dirt or the like even though raindrops are not actually attached,
A raindrop detection device with high determination accuracy can be provided. When the inclination of the light emission output changes with respect to the ambient temperature due to the characteristics of the light emitting element, the raindrop can be detected with higher accuracy by storing the output inclination with respect to the ambient temperature in advance.

According to the raindrop detecting method of the third aspect of the present invention, it is possible to emit light such that the emission luminance is proportional to the drive current for causing the light-emitting element to emit light at a substantially constant slope, or to a predetermined light-emitting element. A light emitting means capable of emitting light with a linearly interpolated slope for each drive current section, and a light receiving means for receiving light emitted by the light emitting means and reflected by the object and outputting an output value substantially proportional to the amount of received light By using, the inclination of the output value of the light receiving means with respect to the driving current in the state where no raindrops are attached to the target object is set as the inclination at the time of clearing, and immediately after startup, the driving current is changed to emit light. Means for emitting light, calculating the slope of the output value of the light receiving means with respect to the drive current, and comparing the calculated slope with the slope at the time of clearing to determine the attachment of raindrops to the object. And wherein the Rukoto.

As a result, the output value is measured immediately after the start-up, and the measurement time is short, so that the ambient temperature is substantially constant during the measurement. For this reason, it is not necessary to consider a change in the slope of the output value due to a change in the ambient temperature. Therefore, there is no need for a circuit configuration in consideration of the temperature characteristics or correction by software. Also, when raindrops are attached to the object, a part of the emitted light is transmitted to the outside by the raindrops and is not received by the light receiving means. Is also smaller. Therefore, it is possible to easily determine the attachment of raindrops only by comparing the inclination of the output value with the inclination at the time of clearing, and a complicated comparison operation or the like becomes unnecessary. From these, it is possible to provide a raindrop detection method that can easily detect raindrops immediately after startup. When the inclination of the light emission output changes with respect to the ambient temperature due to the characteristics of the light emitting element, the raindrop can be detected with higher accuracy by storing the output inclination with respect to the ambient temperature in advance.

According to the raindrop detecting method of the present invention, it is possible to emit light such that the light emission luminance is proportional to the drive current for causing the light emitting element to emit light at a substantially constant slope, or to a predetermined light emitting element. A light emitting means capable of emitting light with a linearly interpolated slope for each drive current section, and a light receiving means for receiving light emitted by the light emitting means and reflected by the object and outputting an output value substantially proportional to the amount of received light And the gradient of the output value of the light receiving means with respect to the drive current in a state where no raindrop is attached to the target object is set as the first gradient at the time of sunny, and the gradient of the output value is taken into consideration in consideration of the reduction factor of the received light amount. A slope smaller than the slope of 1 is set as a second slope at the time of fine weather. Immediately after the start, the drive current is changed to emit light by the light emitting unit, and the output value of the light receiving unit with respect to the drive current is changed. It calculates the can, computed slope and first
By comparing the calculated inclination with the second inclination, it is determined that the raindrop is attached to the target object.

With this arrangement, not only the first inclination at the time of fine weather but also the second inclination which is set in accordance with the actual situation in consideration of factors such as dirt and the like, which reduces the amount of received light, makes it possible to attach raindrops. Therefore, it is possible to prevent a determination error such that it is determined that raindrops are attached due to dirt or the like even though raindrops are not actually attached,
A raindrop detection method with high determination accuracy can be provided. When the inclination of the light emission output changes with respect to the ambient temperature due to the characteristics of the light emitting element, the raindrop can be detected with higher accuracy by storing the output inclination with respect to the ambient temperature in advance.

The term "inclination" in the present invention indicates a rate of increase or decrease in emission luminance, output value, or the like with respect to an increase or decrease in drive current, and includes a proportional coefficient, an increase / decrease rate, and the like.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

The raindrop detecting apparatus and method according to the present invention are for detecting raindrops attached to, for example, a windshield of a vehicle, a ship, an aircraft, or the like, or a window glass of a house, and are used in a windshield of a vehicle or the like. Or used in a system for opening and closing windows in a house. In the following embodiments, a case will be described in which the raindrop detection device of the present invention is applied to an automatic wiper control device of an automobile.

The automatic wiper control device W shown in FIG. 1 includes a raindrop detecting device 6 and a wiper driving device 3.
The raindrop detecting device 6 is for detecting raindrops attached to a front windshield (hereinafter, referred to as a front window) 1 which is an object of raindrop detection.
Is for driving the wiper 2 disposed on the front window 1 when raindrops adhere to the front window 1. Power supply to the wiper automatic control device W
The operation is performed from the battery 30 through the ignition switch 31, and the power is distributed to the CPU 12 in the raindrop detecting device 6, the wiper motor 4 in the wiper driving device 3, and the like.

The wiper driving device 3 includes a wiper motor 4 for driving the wiper 2, a wiper motor drive circuit 5,
And a wiper switch 7. The wiper switch 7 is stopped (OFF), in the auto mode (AUT
O), low-speed operation (Lo), and high-speed operation (Hi)
When the automatic mode is selected, the wiper 2 is automatically controlled by the automatic wiper control device W.

The raindrop detector 6 includes a front window 1
Light-emitting unit (light-emitting means) for optically detecting raindrops above
And a light receiving section (light receiving means). The light emitting section
It comprises an LED driving circuit 13 and a light emitting element (light emitting diode which emits infrared light, hereinafter, LED) 8,
The light receiving part is a light receiving element (photodiode, hereinafter, PD)
9 and a detection / amplification circuit 14. Although one set of the light emitting unit and the light receiving unit can detect raindrops, a plurality of sets (three sets) are installed in the present embodiment in order to increase detection accuracy.

Further, as shown in FIG. 1, the raindrop detecting device 6 is provided with a CPU 12 for controlling a light emission timing of the LED 8 and a drive current for causing the LED 8 to emit light. When detecting a raindrop, the CPU 12 sets the drive current to L
The light is supplied to the ED drive circuit 13 to cause the LED 8 to emit light and to cause light (infrared light) to enter the front window 1. This light is reflected by the front window 1 and received by the PD 9, and the amount of the received light is subjected to light-to-voltage conversion by the detection / amplification circuit 14 and input to the CPU 12 as an output signal (output value) from the light receiving unit. The CPU 12 has a setting function (setting means) for setting (storing) the inclination at the time of fine weather in advance, an arithmetic function (arithmetic means) for calculating the inclination of the output value from the light receiving section, and
A judgment function (judging means) for judging the attachment of raindrops by comparing the calculated inclination with the inclination at the time of clearing is also provided, and a wiper control signal is transmitted to the wiper motor drive circuit 5 based on the judgment result. Have been.

The raindrop detector 6 includes a prism 23
A heater 20 for preventing dew condensation (see FIG. 2), a heater circuit 21, and a prism temperature sensor 22 are provided. The CPU 12 controls the heater circuit 21 in accordance with a temperature signal from the prism temperature sensor 22 to control the heater. Send a signal,
The power supply state to the heater 20 is controlled.

Further, as shown in FIG.
Has a base portion 17 that supports the LED 8 and the PD 9;
A circuit board 15 having the LED drive circuit 13 and the detection / amplification circuit 14 described above is provided. These L
The ED 8, the PD 9, the base 17, and the circuit board 15 are housed and integrated in the sensor case 16, are further covered by the cover 11, and cover the inner wall of the front window 1 (in the vehicle interior side) The surface 1b is attached to a portion that does not obstruct the driver's view by using, for example, a transparent adhesive that transmits light. And LED8 and PD9
Are arranged so as to face the front window 1 from an oblique direction.

A prism 23 as a transmission member is adhered to the inner wall 1b of the front window 1 using a transmissive adhesive (a silicon sheet in this embodiment) 18, and the LED 8 and PD 9 and the front window 1 are connected to each other. It is located between. The prism 23 is for refracting the light of the LED 8 so that the light from the LED 8 is surely incident on the PD 9 and for preventing the solar radiation from outside the vehicle compartment from entering the PD 9. The prism 23 is formed with a plate-like reflecting portion 23a at the center, and the reflecting portion 23a
Are formed on both sides of each of the projections, and a lens is formed on a surface of each projection facing the LED 8 and the PD 9. Thereby, the light emitted from the LED 8 is reflected by the prism 23 as shown by the line with the arrow in FIG.
, The light is totally reflected on the inner surface of the outer wall 1a of the front window 1, then is totally reflected by the reflector 23a, is totally reflected again on the inner surface of the outer wall 1a of the front window 1, and then enters the PD 9. In addition, the heater 20 described above is disposed behind the reflecting portion 23a (inside the vehicle compartment).

Further, between the prism 23 and the PD 9, there is provided a visible light cut filter 19 for blocking the incidence of visible light to the PD 9 in order to cancel the influence of solar radiation which cannot be prevented by the prism 23.

The LED 8 has a characteristic that the light emission luminance (light emission intensity) is substantially proportional to the drive current, and this characteristic is the same whether the drive method is a pulse or DC (direct current). This characteristic will be described with reference to FIG. 3. FIG. 3 is a graph in which the luminous intensity with respect to the drive current when the LED is illuminated by pulse driving at an ambient temperature of 25 ° C. is measured and is shown in a graph. It can be seen that the intensity (relative light intensity) is substantially directly proportional to the drive current. It is known that this proportional coefficient (slope θ _C ) is substantially constant regardless of the ambient temperature. The present invention utilizes this characteristic, and the principle of the determination will be described with reference to FIGS.

When the LED 8 is made to emit light in a state where no raindrops are attached to the front window 1 (when there is no raindrop or when it is sunny), the emitted light is, as described above, the outer wall of the front window 1 (outside the vehicle interior). Surface) 1a, is totally reflected at the inner surface of the outer wall 1a, is totally reflected again at the inner surface of the outer wall 1a, and is incident on the PD 9 again. Therefore, L
When the emission current is increased by increasing the drive current of the ED 8, the amount of light received by the PD 9 also increases at a substantially constant slope in accordance with the slope of the emission brightness.
4 (hereinafter, sensor output) increases with a substantially constant slope in proportion to the amount of received light. When the inclination theta ₁ during sunny slope at this time, LED during sunny
The relationship between the drive current and the sensor output is a straight line as shown by A in FIG.

On the other hand, as shown in FIG. 5, since when the raindrop R ₁ is attached to the front window 1, at its attachment portion which transmits to the outside without being totally reflected light from the LED 8, P
The light receiving amount at D9 decreases, and the sensor output decreases accordingly. Here, the detection area in accordance with the emission luminance is increased gradually expands as shown in FIG. 5 (a) (b) ( c) , and for example in the detection area from the beginning is attached section of the raindrops as raindrops R ₁ If it is included, the straight line B in FIG.
So that the sensor output increases in theta ₁ is less than the inclination theta ₂ from the beginning as shown in.

Also, for example, the raindrop R shown in FIG._Two Like the rain
Detected when the brightness of the drop is low (Fig. 5 (a))
When the brightness increases to the middle without entering the area (FIG. 5)
(B)) When entering the detection area from
, The sensor output initially has a slope θ as shown in FIG.
₁ , But from the middle (when the brightness is medium)₁ Than
Small inclination θ_Four Will increase. In this case,
For example, sensor output when brightness is high and sensor when brightness is 0
A straight line C connecting to the output (that is, 0)
You. ), The slope θ of the straight line C_Three Is θ₁ Smaller than
So that θ _Four Instead of θ_Three May be used
No.

As described above, when raindrops adhere to the detection area, the inclination θ of the sensor output with respect to the drive current
₂ , θ ₃ and θ ₄ are all smaller than the inclination θ ₁ at the time of sunny. Therefore, by changing the drive current, changing the emission luminance, measuring the sensor output, calculating the slope, and comparing the slope with the clear slope, it can be determined whether or not raindrops are attached. .

The CPU 12 performs a determination process based on the above-described determination principle, and this determination process will be described with reference to FIGS.

[0030] Figure 6, the inclination theta _C1 during sunny sensor output for the LED drive current, and, more theta _C1 consideration of decrease factor of the light receiving amount of dirt in the slope of the variation and the front window 1 at sunny The inclination θ _C2 set to be small is illustrated. These inclinations are set (stored) in the CPU 12 in advance as constants on software.

First, a description will be given of a first embodiment in which the determination is made using only the inclination θ _C1 at the time of sunny, with reference to the flowchart of FIG. When the operator turns on the ignition switch 31 (S01), if the wiper switch 7 is in the automatic mode, the automatic wiper control device W performs raindrop determination processing immediately after startup as follows (S02).

The CPU 12 causes the LED 8 to emit light immediately after startup, and measures the sensor output from the light receiving section. At this time,
The drive current of the LED 8 is increased within a short time to increase the light emission luminance of the LED 8, and the sensor output is measured when the light emission luminance is low and when the light emission luminance is high (S03).
The CPU 12 calculates the inclination θ of the sensor output with respect to the drive current from the measured sensor output (S04) and compares it with the inclination θ _C1 at a sunny time (S05). If θ is smaller than θ _C1, it is determined that there is a raindrop. A drive signal is output to the wiper motor drive circuit 5 (S06), and normal rain determination processing is started (S07). If θ is not smaller than θ _C1 ,
The CPU 12 does not output the wiper drive signal, and enters a normal rain determination process (S07). Note that the normal rain determination process is L
This is a conventional rain determination process performed while maintaining the drive current of the ED 8 at a constant level.

In the first embodiment, when the inclination θ of the sensor output is smaller than the inclination θ _C1 in FIG. 6, the wiper 2 is driven. As described above, in the first embodiment, the adhesion of raindrops can be determined only by a simple calculation and comparison of calculating the slope θ and comparing it with the predetermined slope θ _C1 . Also,
The measurement of the sensor output is performed in a short time immediately after startup, and the ambient temperature is considered to be almost constant during the measurement. Therefore, the fluctuation of the light emission luminance and the inclination θ due to the fluctuation of the sensor output due to the fluctuation of the ambient temperature are considered. No need to do. For this reason,
The circuit configuration taking into account the temperature characteristics and the correction by software become unnecessary. Therefore, the hardware configuration and software are simplified, and the cost can be reduced.

Next, a description will be given, with reference to the flowchart of FIG. 8, of a second embodiment in which a judgment is made using the inclination θ _C1 at the time of fine weather and the inclination θ _{C2 in} consideration of dirt / variation. Note that S11 to S14 in FIG. 8 are the same as S01 to S04 in FIG.

In the second embodiment, the CPU 12
Compares the calculated inclination θ with the inclination θ _C1 at the time of fine weather (S 15). If θ is smaller than θ _C1 , the inclination θ is further increased.
Compare with _C2 (S16). If θ is not larger than θ _C2 , a wiper drive signal is output to the wiper motor drive circuit 5 as the presence of raindrops (S17), and normal rain determination processing is started (S18). If θ is not smaller than θ _C1 , or if θ is smaller than θ _C1 but larger than θ _C2 , the CPU 12 does not output the wiper drive signal and enters normal rain determination processing (S17).

In the second embodiment, when the inclination θ of the sensor output is equal to or smaller than the inclination θ _C2 in FIG. 6, the wiper 2 is driven, and when the inclination θ is smaller than the inclination θ _C1 but larger than θ _C2. In the case (in the case of entering the shaded portion in FIG. 6), the wiper 2 is not driven. In this embodiment, the first
As in the embodiment, the presence or absence of raindrops can be determined only by simple calculations and comparisons, eliminating the need for temperature characteristic correction, simplifying the hardware configuration and software, reducing costs, and reducing the amount of received light. Is determined by comparison with the inclination θ _C2 set in consideration of the above, so that although the raindrops are not actually attached, the received light amount is reduced due to dirt and the like, and the raindrops are attached. Can be prevented, and the determination accuracy can be increased.

When the driving current is small, the LED 8
Since the light emission luminance of the detection / amplification circuit 14 is insufficient, a sufficient sensor output may not be obtained. Therefore, CPU
A circuit and software for amplifying the sensor output to a level detectable by the circuit 12 are added to make the amplification factor (amplifier gain) of the detection / amplification circuit 14 variable, and to increase the amplification factor when the driving current is small. Is also good.

In each of the above embodiments, the present invention is applied to the wiper automatic control device W for automatically controlling the wiper 2 according to the detection result of the raindrop detecting device 6, but the present invention is applied to, for example, a ship or an aircraft. Alternatively, any device that detects raindrops can be applied.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an automatic wiper control device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a raindrop detecting device in the embodiment of FIG. 1;

FIG. 3 is a diagram illustrating an example of light emission intensity with respect to a drive current of an LED.

FIG. 4 is a diagram illustrating an example of a sensor output with respect to a drive current of an LED.

FIG. 5 is a diagram showing a case where raindrops are attached to the raindrop detecting device of FIG. 2;

FIG. 6 is a diagram illustrating a gradient of a sensor output with respect to a drive current of an LED according to the embodiment of the present invention.

FIG. 7 is a flowchart illustrating a process according to the first embodiment of the present invention.

FIG. 8 is a flowchart illustrating a process according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Front window (target object) 6 ... Raindrop detector 8 ... Light emitting element (LED) 9 ... Light receiving element (PD) 12 ... CPU 13 ... LED drive circuit 14 ... Detection / amplification circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G059 AA05 BB20 CC11 EE02 GG02 GG08 JJ12 KK01 MM05 MM09 MM10 MM14 NN02 NN05 NN08 3D025 AC01 AD02 AG31 AG42

Claims (4)

[Claims] 1. A light emitting means having a light emitting element which emits light toward an object to be detected for raindrop detection, and a light emitted by the light emitting means and reflected by the object is received. A light-receiving unit that outputs an output value substantially proportional to the light-emitting element, wherein the light-emitting unit emits light from the light-emitting element. It is possible to emit light in such a manner that the emission luminance is proportional to the drive current to be applied with a substantially constant slope, or to emit light with a slope that is linearly interpolated for each predetermined drive current section to the light emitting element. Setting means for setting a slope of an output value of the light receiving means with respect to the drive current in a state where no light is adhered, as a slope at the time of a sunny day, and immediately after activation, changing the drive current to the light emitting means. Calculating means for calculating the slope of the output value of the light receiving means with respect to the drive current, and comparing the calculated slope with the slope at the time of the fine weather, whereby raindrops on the target object are generated. A raindrop detection device comprising: a determination unit configured to determine adhesion. 2. A light-emitting means having a light-emitting element which emits light toward an object to be detected for raindrop detection, and light received by the light-emitting means and reflected by the object is received. A light-receiving unit that outputs an output value substantially proportional to the light-emitting element, wherein the light-emitting unit emits light from the light-emitting element. It is possible to emit light in such a manner that the emission luminance is proportional to the drive current to be applied with a substantially constant slope, or to emit light with a slope that is linearly interpolated for each predetermined drive current section to the light emitting element. The slope of the output value of the light receiving means with respect to the drive current in a state where no light is adhered is set as a first slope at a sunny time, and a slope smaller than the first slope is set in consideration of a decrease factor of a received light amount. ,Sunny Setting means for setting as a second slope in the above, and immediately after startup, changing the drive current to cause the light emitting means to emit light, and calculating means for calculating a slope of an output value of the light receiving means with respect to the drive current. Determining means for comparing the calculated inclination with the first inclination and comparing the calculated inclination with the second inclination to determine the attachment of raindrops to the object;
A raindrop detecting device comprising: 3. A light-emitting element which emits light toward an object to be detected for raindrop detection, wherein the light-emitting element can emit light in such a manner that emission luminance is proportional to a drive current for emitting the light-emitting element with a substantially constant slope. Or, a light emitting means capable of emitting light with a linearly interpolated slope for each predetermined drive current section to the light emitting element; and receiving light emitted by the light emitting means and reflected by the object, and the amount of light received is substantially reduced. A light-receiving unit that outputs a proportional output value, a raindrop detection method for detecting raindrops attached to the object based on the output value, wherein the raindrops are not attached to the object. The slope of the output value of the light receiving means with respect to the drive current is set as a slope at a sunny time, and immediately after startup, the drive current is changed to emit light by the light emitting means, and the drive is performed. Calculating the inclination of the output value of the light receiving means with respect to the flow, and comparing the calculated inclination with the inclination at the time of the fine weather to determine the attachment of the raindrop to the object. Method. 4. A light-emitting element which emits light toward an object to be subjected to raindrop detection, wherein the light-emitting element is capable of emitting light such that emission luminance is proportional to a drive current for causing the light-emitting element to emit light at a substantially constant slope. Or, a light emitting means capable of emitting light with a linearly interpolated slope for each predetermined drive current section to the light emitting element; and receiving light emitted by the light emitting means and reflected by the object, and the amount of light received is substantially reduced. A light-receiving unit that outputs a proportional output value, a raindrop detection method for detecting raindrops attached to the object based on the output value, wherein the raindrops are not attached to the object. The slope of the output value of the light receiving means with respect to the drive current is set as a first slope at a sunny time, and a slope smaller than the first slope is set at a second time at a sunny time in consideration of a factor of reduction in the amount of received light. Tilt and Immediately after startup, the drive current is changed to emit light by the light emitting means, and the slope of the output value of the light receiving means with respect to the drive current is calculated. A method for detecting raindrops, comprising: comparing a first slope with the calculated slope and comparing the calculated slope with the second slope to determine whether raindrops adhere to the object.