JPH10142353A - Raindrop detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a raindrop detection method capable of exactly and quantitatively detecting amount of adhering raindrop by avoiding the effects of passing wiper blade without adding any new parts. SOLUTION: A raindrop detection region 17 set on a wind shield glass 1 of a vehicle provided with a wiper is recognized by separating into a specified number of blocks. An image data obtained by photographing the raindrops in the raindrop detection region 17 is fetched for a specified time interval (T1 ) exceeding the time for passing the wiper of at least one block in the case the longest time is necessary for wiping one return of wiper. Form the fetched image data, the existence of raindrop in the raindrop detection region 17 is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting raindrops for a vehicle, and more particularly to a method for detecting raindrops attached to a windshield in a vehicle having a wiper for reciprocatingly wiping the surface of the windshield. It is about technology that is effective to apply.

[0002]

2. Description of the Related Art In recent years, as part of automation of on-vehicle equipment,
Detecting weather conditions and automatically activating the wiper,
A vehicle equipped with a so-called automatic wiper system that changes its operation speed has been developed. In this automatic wiper system, a raindrop detecting device for detecting raindrops is provided on a windshield, a radiator grill, a front bumper, etc. of a front windshield or the like of an automobile, for example, in order to detect a rainfall condition. In this case, a device that detects raindrops attached to a windshield is particularly effective for wiper control because data directly related to the driver's field of view can be obtained, and is being adopted in many vehicles.

Conventionally, such a raindrop detecting device for a windshield detects a change in resistance value caused by a water droplet adhering to a substrate, or detects the presence or absence of a water droplet by recognizing an image of a glass surface from a vehicle interior. There is something that detects In this case, in the case of detecting raindrops by changing the resistance value, a part of the electric circuit is always exposed to the outside of the vehicle. Therefore, from the viewpoint of contamination and maintenance, the raindrops are detected by image recognition from the vehicle interior. The latter device has attracted attention (for example, see Japanese Utility Model Publication No. 63-25252).

However, even in an apparatus using image recognition, if the image on the glass surface is taken as it is, the image of the wiper blade is also taken at the same time, for example, when the wiper is operated, so that the amount of the attached raindrops cannot be detected accurately.

In this case, if the capture of an image is prohibited when the wiper blade passes, detection of raindrops is not hindered by the wiper blade. However, in practice, it is not possible to accurately detect raindrops unless the position or detection timing of the raindrop detection device is appropriate.For example, almost no raindrops can be detected even if an image is captured immediately after wiping with a wiper blade, and even if it is detected. Even so, the rainfall cannot be determined quantitatively. Conversely, if an image is captured immediately before the wiper blade wipes, the amount of attached raindrops may be too large and the raindrops may flow, making it impossible to quantitatively determine the amount of attached raindrops as described above. Further, in such a system, it is necessary to separately provide a sensor for detecting the position of the wiper blade, and there is a problem in the number of parts, the assembling property, and the mounting property.

Therefore, the present inventor has studied the influence of the wiper blade and the wiping timing, and has developed the following technique. The following are not known technologies,
This is a technique studied by the inventor, and its outline is as follows.

That is, in the wiping range of the wiper, the raindrop detection area is set at one of two reversing positions where the movement of the wiper blade is reversed, for example, near the reversing position on the upper part of the windshield. Then, when the wiper blade passes the other inversion position, that is, the inversion position below the windshield, raindrop detection is performed. In this case, the wiper device is provided with a relay plate that issues a motor drive / stop signal in order to stop the wiper blade at the lower inverted position. The signal from this relay plate is taken out and the position of the wiper blade is adjusted. To detect raindrops. Thus, it is possible to detect the amount of raindrop adhesion for a half cycle of the reciprocating motion of the wiper blade without being affected by the wiper blade.

At the approximate center of the wiping range of the wiper, that is, at the center of the driver's field of view, the time from the wiping of the wiper blade on the outward path to the wiping on the return path and the time from the wiping on the return path to the forward path are determined. The time until wiping is almost the same. Therefore, the maximum amount of raindrops adhering to this area is substantially equal to a half cycle of the reciprocating movement of the wiper blade. Therefore, according to the device described above, this 1/2
It is possible to detect the raindrop adhesion amount for the cycle without being affected by the wiper blade, and it is possible to quantitatively detect the raindrop adhesion amount to be detected.

On the other hand, there has been proposed a device for analyzing the obtained image to remove the influence of a wiper blade, such as a vehicle image detecting device disclosed in Japanese Patent Publication No. 8-32509.
In this image detection device for a vehicle, the position of the wiper blade is detected by an angle sensor attached to the wiper motor. Then, a scanning line within a range intersecting with the wiper detection image in the detection image obtained from the TV camera is masked based on the value obtained from the angle sensor, and only the scanning line portion not including the wiper image is enabled. The effect has been eliminated.

[0010]

As described above, in the above-mentioned raindrop detecting device, since the raindrop detecting operation is performed by using the signal from the relay plate, the position of the wiper blade is determined. There is no need to separately provide a sensor for detection, and a raindrop detecting device with a simple structure and low cost can be realized.

However, in the above-described raindrop detecting device, the installation position of the raindrop detecting device is limited to the two reversal areas.
There is a problem that there is a design restriction on the installation position. In addition, it is necessary to newly provide a signal line in order to take in a signal from the relay plate, and there has been a problem that the number of parts, assemblability, etc. contribute to an increase in cost. Further, there has been a problem that it is not always possible to accurately detect raindrops in a region other than the substantially central region of the wiping range of the wiper.

On the other hand, the vehicle image detecting device disclosed in Japanese Patent Publication No. 8-32509 can certainly remove the influence of the wiper blade from the image data. However, this also requires an angle sensor for detecting the position of the wiper blade as described above. And Furthermore, since the scanning line range where the wiper detection image intersects is obtained from the relationship between the position (angle) of the wiper blade and the scanning line,
It requires very complicated arithmetic processing. Therefore, in order to perform such processing in a short time, a CPU having a high-speed arithmetic processing capability is required, and there is a problem that the cost is not substantial.

It is an object of the present invention to provide an accurate and quantitative installation that can be installed anywhere in a wiper wiping area and eliminates the influence of the passage of a wiper blade without adding new parts such as sensors and signal lines. It is another object of the present invention to provide a raindrop detection method capable of detecting the amount of raindrop adhesion.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0015]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, in the raindrop detection method of the present invention, the presence or absence of raindrops in the raindrop detection area is determined based on image data obtained by imaging raindrops in the raindrop detection area set on the windshield of the vehicle. A raindrop detection method for detecting a raindrop, wherein the raindrop detection area is divided into a predetermined number of blocks and recognized, and the wiper means for wiping raindrops on a windshield performs one round trip wiping of the image data. A predetermined time interval (T ₁ ) exceeding the time when the wiper means passes at least one block when the longest time is required
And detecting the presence or absence of raindrops in the raindrop detection area based on the captured image data.

In this case, the detection of the presence or absence of the raindrop is performed by dividing the longest time (T ₂ ) required for the wiper means to perform one reciprocating wiping by the predetermined time interval (T ₁ ) (T ₂ / T ₂ ). T ₁₎ is performed more, the number of times (T ₂ / T ₁₎ may be determined raindrops adhering amount on the windshield on the basis of the above predetermined number of detection results.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of a wiper control system using a raindrop detecting device to which the raindrop detecting method according to the present invention is applied. In the present embodiment, a raindrop detecting device used for controlling a wiper device that wipes raindrops attached to a windshield (windshield) of an automobile will be described as an example.

In FIG. 1, reference numeral 1 denotes a windshield as a windshield, and a CCD camera (imaging means) 2 for detecting raindrops is provided inside (a vehicle interior side). The CCD camera 2 is attached to the windshield 1 while being housed inside the hood 3, and a frosted glass screen 4 is provided on the tip side of the hood 3. In this case, the screen 4 is provided in close contact with the inner surface of the windshield 1 so that the raindrop detection area 1
The CCD camera 2 captures the shadow of the raindrop projected on the screen 4.

On the other hand, the CCD camera 2 includes an image processing section (image processing means) 5 and a wiper driving section 6 and a central control processing section (raindrop adhesion amount determining means) 7 which controls these elements and judges the amount of raindrop adhesion. Wiper control device 8 comprising
It is connected to the. In this embodiment, the CCD camera 2, the image processing unit 5, and the central control processing unit 7 correspond to a raindrop detection device to which the raindrop detection method according to the present invention is applied. Since the wiper control is inseparable, the central control processing unit 7 has a wiper operation control function.
However, it goes without saying that this does not mean that the raindrop detecting device using the raindrop detecting method according to the present invention also has a wiper control function as an essential component.

Next, the image signal from the CCD camera 2 is
The image data is sent to the image processing unit 5, where image processing such as detection of the presence or absence of raindrops and removal of the influence of the wiper blade is performed. The image processing unit 5 performs a raindrop detection process based on the data obtained by the image processing, determines the amount of raindrop adhesion, and transmits this as raindrop adhesion data to the central control processing unit 7. Then, the central control processing unit 7 determines the state of raindrop adhesion based on the raindrop adhesion data, and acts on the wiper driving unit 6 to control the start and stop of the wiper operation, the operation speed, and the like in accordance therewith.

Here, the image processing unit 5 includes the CCD camera 2
An image input unit 9 for inputting an image signal from an image processing unit, an image processing unit 10 for performing image processing such as detection of the presence or absence of raindrops, an image information storage unit 11 for storing processed data, and an image processing unit 1
And a ROM 12 for storing the image processing procedure and the like in the image processing unit 0. In this case, the image signal input to the image input unit 9 is adjusted to a predetermined signal format and input to the image processing unit 10. The image processing unit 10 performs image processing on the signal for each block described later, and stores the signal in the image information storage unit 11 as raindrop data as appropriate. Then, a raindrop detection process is performed based on the stored raindrop data to calculate raindrop adhesion data, which is sent to the central control processing unit 7.

On the other hand, the central control processing section 7 has an image processing section 9
, And acquire raindrop adhesion data to obtain RAM1
3 is stored. Further, the raindrop adhesion state is determined based on the raindrop adhesion data stored in the RAM 13. Then, based on this determination, a command is issued to the wiper driving unit 6, and the wiper motor 14 is appropriately controlled to control the wiper operation. The procedure of a series of processing operations by the central control processing unit 7 is described in ROM
15 is stored.

Next, the raindrop detecting operation of the raindrop detecting device will be described. Here, a description will be given assuming that a raindrop detection area 17 is set in a part of the windshield 1 provided with the wiper 16 as shown in FIG. In this case, the wiper blade 18 of the wiper 16
In (a), reciprocating movement is performed between the lowermost reversal storage position indicated by the solid line and the uppermost reversal position indicated by the dashed line, and the surface of the windshield 1 is wiped. On the other hand, the amount of raindrops deposited on the windshield 1 is detected in the raindrop detection area 17. At this time, if the data when the wiper blade 18 passes through the raindrop detection area 17 is used as it is,
Due to the shadow of the wiper blade itself, a larger amount of raindrops is recognized than in reality. Therefore, in the raindrop detecting device using the raindrop detecting method according to the present invention, the wiper blade 1
In order to remove the influence of the shadow of No. 8, the following detection method is adopted.

First, in the raindrop detecting device, the raindrop detection area 17 is divided into a plurality of blocks 1 as shown in FIG.
Divide into nine. Although the number of the blocks 19 is determined from the number of pixels of the CCD camera 2, the number is reduced from the actual number in the description of the present embodiment for easy understanding. Then, the presence or absence of raindrops in each block 19 is detected. That is, image data from the CCD camera 2 is fetched at a certain point in time, and image processing is performed for each block 19, and a block 19 having a shadow is set to "1" as having raindrops, and a block 19 having no shadow is not having raindrops. Is set to “0”. FIG. 2 (b)
The wiper blade 18 is positioned at the position indicated by the solid line in FIG.
This is an example showing a detection result when raindrop detection is executed at a certain time (time point A), and this is stored in the image information storage unit 11 as raindrop data at time point A.

Next, at a time point B after a lapse of a predetermined time, raindrop detection is further performed. That is, at time point B, image data is fetched from the CCD camera 2 and processed.
At this time, assuming that the wiper blade 18 is within the raindrop detection area as shown in FIG. 3A, the shadow is reflected in the raindrop detection area 17, and as a result, the raindrop data at the time point B is as shown in FIG. become.

Here, in the raindrop detecting device, the time interval for detecting raindrops (for example, the interval between the time points A and B) takes the longest time for the wiper 16 to perform one wiping, that is, When the wiper 16 operates at the latest time, a time (T ₁ ) exceeding a time that can pass at least one of the blocks 19 is set.

Therefore, if the raindrop is detected at the timing having this time interval, even if the wiper blade 18 approaches a certain block at the time of detecting the raindrop, the wiper blade 18 does not stay at that block at the next detection. Will be. Therefore, if raindrop detection is performed at this timing, it is possible to determine whether or not the influence of passing through the wiper blade 18 has been obtained by performing raindrop detection processing by comparing the raindrop data of each time with that at the time of previous detection.

That is, if it is determined that there is no raindrop on one side and there is raindrop on the other side, there is a possibility that the reflection of the wiper blade 18 is reflected. On the other hand, it is considered that the case where the result that there is raindrop on both sides is not due to the effect of the wiper blade 18 but is true that there is raindrop. Therefore, the raindrop detecting device adopts this time interval, and in the raindrop detection processing, determines that only the case where both have the raindrop is determined to be the raindrop, and removes the influence of the passage of the wiper blade.

FIG. 4 is a flowchart showing the procedure of the raindrop detection process. The presence or absence of raindrops is detected as follows. Here, first, image data is taken in (S1), a differentiation process (S2), a threshold process (S3) are performed, and an image recognition process in each block is performed (S4). next,
It is determined whether or not there is a foreign matter (raindrop) in the block (S5). If there is a foreign matter, comparison with the previous raindrop data is performed, and it is determined whether or not there is a foreign matter on the same coordinate last time. (S6). Then, if there is a foreign substance on the same coordinates last time, it is recognized that there is a foreign substance (S7). On the other hand, if there is no foreign substance in the previous time, it is recognized that there is no foreign substance (S
8). If it is determined in S5 that there is no foreign matter in this block, it is recognized that there is no foreign matter (S8). If raindrops have adhered between the previous time and this time, S6-
Although the processing is performed in step S8 assuming that there is no foreign matter, the next time the processing is performed, the foreign matter is present on the previous side, and the attachment of raindrops is recognized.

After such processing, the processing of the block is finished, and the processing moves to the next block. That is, in S9, it is determined whether or not the Y coordinate indicates the last block. If the Y coordinate does not mean the last block,
Subsequently, the same determination is made for the X coordinate (S1).
0). If the X coordinate does not mean the last block, the X coordinate is advanced by one block, and the process proceeds to the image recognition of the next block (S11). On the other hand, if the X coordinate indicates the last block, the Y coordinate is advanced by one block and the X coordinate is returned to the top, and image recognition is performed from the first block in the next column (S12, S13).

On the other hand, if the Y coordinate is the last block in S9, the X and Y coordinates are returned to the beginning, and the total amount of foreign substances is determined (S14 to S16). In other words, a block that has been recognized as having raindrops in the raindrop detection processing at a certain point in time, or raindrop adhesion data indicating the number of the blocks is created, and this processing ends.

Such a raindrop detection process is described again with reference to FIGS.
In this example, in the processing at the time point B, the raindrop data of FIG. 2B by the raindrop detection at the time point A and the raindrop data of FIG. 3B by the raindrop detection at the time point B are compared. The raindrop detection process is performed while the operation is being performed. That is, first, the raindrop data blocks 19c to 1c in FIG.
9j is determined to be "with raindrops" and compared with the data of FIG. 2 (b). At this time, in FIG. 2 (b), since "raindrops exist" in blocks 19c to 19f among them, as a result, it is recognized that "raindrops exist" in blocks 19c to 19f, and the time point B shown in FIG. Is created. Then, the raindrop adhesion data is sent to the central control processing unit 7 and stored in the RAM 14 to determine the raindrop adhesion amount.

In this case, the blocks 19a and 19b show "with raindrops" in FIG. 2A, but are wiped off with the passage of the wiper 16, and become "no raindrops" in FIG. Proceeding to S8, no raindrop is recognized. For other blocks determined as “no raindrop” in the raindrop data of FIG. 3B, raindrop adhesion data as a result of “no raindrop” is created. In addition, this raindrop adhesion data is multi-valued,
In the raindrop detection at the time point B, data “time point B: 4”, which means that raindrops are detected in four blocks, may be used.

Next, the determination of the amount of raindrop adhesion based on the raindrop adhesion data sent to the central control processing unit 7 will be described.

The central control processing unit 7 of the raindrop detecting device collects a plurality of the above-mentioned raindrop adhesion data and judges the amount of raindrop adhesion based on the collected data. In this case, in the raindrop detection device, as described above, as the time interval for the raindrop detection, at least one time T ₁ is set to exceed the time that can pass through the block 19 when the wiper 16 is actuated slowest Have been. Therefore, including the maximum value of the time required for one wiping wiper 16 to time T _2, always 1 wiping worth more data if it is determined the central control unit 7 takes in the T ₂ / T ₁ pieces of data It is possible to judge the amount of raindrop adhesion in the state.

Therefore, in the raindrop detecting device, the T ₂ /
By attracting T ₁ or more data determines raindrops adhering amount, and to perform the raindrops adhering amount determined by always inclusive form data wiping immediately preceding time near the raindrop detection region 17. That is, after the wiper 16 wipes the raindrop detection area 17, the data at the time when the amount of the attached raindrops becomes the largest between the wiper 16 and the next wipe is always included. Therefore, while the conventional device that performs the detection at the time of reversal can detect only the change in the amount of raindrop adhesion in a 周期 cycle, it is almost 1
The raindrop adhesion amount can be determined using the data for the cycle, and more accurate determination can be made. The set position of the raindrop detection area 17 can be freely changed within the wiping range of the wiper 16.

[0039] To explain such a raindrop adhesion amount determination using the example above, first, for example at each time point A~F shown in FIG. 6 (between the time point has a time interval of at least ₁ hour T) It is assumed that raindrop detection is performed, and that raindrop adhesion data at each time point is collected as shown in FIG. In the data, the data with “′” indicates the return data, and the data with “” ”indicates the second forward data. In this case, as described above, if the data is collected in a time series of T ₂ / T ₁ or more data and the judgment is made, it is possible to make a judgment in which the data of one or more wipings are collected. That is, in FIG. 7A, for example, if 11 or more pieces are collected, it is determined that data of one wipe or more is collected.

Then, these data are analyzed to change the operation state of the wiper as appropriate. That is, for example, when the data includes data having a threshold value (for example, 10) or more, the wiper operation is continued. Therefore,
In FIG. 7A, since the data “13” exists in (c) ′, the wiper operation is further continued. Also, when data of a predetermined value or more is included, it is determined that the amount of rainfall is large, and the speed of the wiper is increased. Conversely, when data of a predetermined value or less is less than a predetermined number, the wiper speed is increased. Dropping or intermittent operation is also possible. As described above, the raindrop detecting device can arbitrarily control the wiper operation based on the value and the number of the data according to the rainfall situation. These control programs are stored in the ROM 15.

On the other hand, in the raindrop detecting device, the amount of raindrops is determined while collecting data at each time point while moving the data in a predetermined number in a time-series manner. That is, after collecting data as shown in FIG. 7A and judging the amount of raindrop adhesion, as shown in FIG. 7B and FIG. The same judgment as described above is performed. Therefore, the wiper control can be performed while always taking in the latest data while referring to the past raindrop adhesion amount, and the wiper control suitable for the driver's visibility can be performed. Therefore, it is possible to realize an automatic wiper system free from malfunction such as the wiper stopping even though raindrops are present.

Although the invention made by the inventor has been specifically described based on the embodiment, the invention is not limited to the embodiment, and various modifications can be made without departing from the gist of the invention. Needless to say,

For example, in FIG.
Although 7 is divided into 7 × 5 35 blocks, the number of divisions is not limited to this. Also, the timing of raindrop detection is shown in FIG.
It is not limited to such a point. Further, the central control processing device 7 can also perform processing of image data in the image processing section 5 in a form that also serves as an image processing means and a raindrop adhesion amount determining means. In addition, CCD as imaging means
A camera other than the system can be used.

Further, it goes without saying that the control programs stored in the ROM 12 and the ROM 15 such as the image processing, the raindrop detection processing, and the control of the wiper can be stored in a predetermined medium and handled separately.

In the above description, the case where the invention made by the present inventor is applied to an automobile as a field of application has been mainly described. However, the present invention is not limited to this case. Of vehicles.

[0046]

Advantageous effects obtained by typical ones of the inventions disclosed in the present application will be briefly described.
It is as follows.

[0047] The (1) the time interval for the raindrop detection, wipers sets the block of raindrop detection region to the time T ₁ exceeding at least one time to pass when required the longest time to perform the wiping 1 Thereby, there is an effect that the influence of passing through the wiper blade can be removed. In other words, by setting the time above T ₁ time interval, even though approaching the blocks that wiper blades during rain detection, at the time of the next detection will be not remain in the block, the last of each round of raindrops data By comparing with the one at the time of detection, the influence of passing through the wiper blade can be removed. Therefore, the raindrop detection area can be installed anywhere in the wiper wiping area without considering the operation of the wiper blade.

(2) The raindrop detection is performed at least the number of times (T ₂ / T ₁ ) obtained by dividing the longest time T ₂ required for the wiper means to perform one wiping by the time interval T ₁ , and the number of times of the number or more is calculated. Judgment of the amount of raindrop adhesion based on the detection result of, it is possible to perform wiper control while always taking in the latest data while referring to the past amount of raindrop adhesion, and wiper control suited to the driver's visibility situation Can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a wiper control system using a raindrop detection device to which a raindrop detection method of the present invention is applied.

FIG. 2A is an explanatory diagram showing a relationship between a wiper blade and a raindrop detection area, and FIG. 2B is raindrop data obtained at a time point A;

FIG. 3A is an explanatory diagram showing a relationship between a wiper blade and a raindrop detection area at a time point B, and FIG. 3B is raindrop data obtained at that time.

FIG. 4 is a flowchart showing a raindrop detection processing operation in the raindrop detection device to which the raindrop detection method of the present invention is applied.

FIG. 5 is an explanatory diagram showing raindrop adhesion data obtained at a time point B;

FIG. 6 is an explanatory diagram showing raindrop detection timing in a raindrop detection device to which the raindrop detection method of the present invention is applied.

FIG. 7 is an explanatory diagram showing a state of a process of determining the amount of attached raindrops in a raindrop detection device to which the raindrop detection method of the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Windshield 2 CCD camera (imaging means) 3 Hood 4 Screen 5 Image processing part (image processing means) 6 Wiper drive part 7 Central control processing part (raindrop adhesion amount judgment means) 8 Wiper control device 9 Image input part 10 Image processing Unit 11 Image information storage unit 12 ROM 13 RAM 14 Wiper motor 15 ROM 16 Wiper (wiper means) 17 Raindrop detection area 18 Wiper blade 19 Block 19a to 19j Blocks A to F Time point T ₁ hour T ₂ hours

Claims (2)

[Claims] 1. A raindrop detection method for detecting the presence or absence of raindrops in a raindrop detection area based on image data obtained by imaging raindrops in a raindrop detection area set on a windshield of a vehicle. When the raindrop detection area is divided into a predetermined number of blocks and recognized, and the image data is processed in a case where it takes the longest time for the wiper means for wiping raindrops on the windshield to perform one round trip wiping. The wiper means captures at a predetermined time interval (T ₁ ) exceeding the time when at least one block passes through the block, and detects the presence or absence of raindrops in the raindrop detection area based on the captured image data. Raindrop detection method for a moving vehicle. 2. The method for detecting raindrops according to claim 1, wherein
Performs detection of presence or absence of the raindrop, the wiper number of means divided by the longest time required to perform wiping of one reciprocation (T ₂₎ the predetermined time interval _{(T 1) (T 2 /} T 1) or ,
Raindrop detection method for a vehicle, characterized in that to determine the raindrops adhering amount on the windshield on the basis of the number of times (T ₂ / T ₁₎ or more predetermined number of detection results.