Abstract:
A rain sensor using light scattering, and more particularly to, a rain sensor for detecting an amount of moisture particles, such as raindrops or fog, accumulated in a front windshield of a vehicle, and applying the amount of moisture particles to an operation of a wiper of the vehicle.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2009-0117094, filed on Nov. 30, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a rain sensor using light scattering, and more particularly to, a rain sensor for detecting an amount of moisture particles, such as raindrops or fog, accumulated in a front windshield of a vehicle, and applying the amount of moisture particles to an operation of a wiper of the vehicle. 
         [0004]    2. Description of the Related Art 
         [0005]    If moisture is accumulated in a transparent material, such as glass or plexiglass, the transparent material may prevent a persons&#39; field of vision. A vehicle is equipped with a motor drive type windshield wiper used to remove moisture from a wider area of the external surface of a windshield within a range of a driver&#39;s field of vision so as to improve the field of vision through the windshield. 
         [0006]    Although most vehicles are not equipped with unlimitedly various windshield wipers, vehicles include a multi-switch or a variable speed switch that allows a driver to select a wide range of speeds according to the circumstances. 
         [0007]    A wiper is manually controlled and exhibits typical delay characteristics so that the wiper inadvertently operates at a selected time delay interval. 
         [0008]    A recently developed wiper control system includes a moisture sensor or a rain sensor that is installed in one of vehicle windows and automatically operates a wiper motor when moisture is formed on the surface of a window. 
         [0009]    Although the wiper control system including the moisture sensor or the rain sensor is generally installed in a windshield, it may be installed in a rear window or in another glass surface intended to remove moisture. 
         [0010]    A driver does not need to frequently adjust a wiper speed according to a change in the driving conditions using the wiper control system. 
         [0011]    The wiper control system includes conductivity, electrical capacity, and piezoelectric and light sensors, and uses a plurality of different technologies for detecting a moisture status that occurs in a vehicle. 
         [0012]    If moisture is accumulated in the external surface of a windshield, the light sensor operates based on a principle that a light beam is scattered by being deflected from a normal path. 
         [0013]    Although various methods has been proposed for a rain sensor, electronic methods, other than a optoelectronic method, are not generally used due to reliability that falls short of obtaining an electrical output in proportional to the size of large or small water particles. Most vehicles currently use the optoelectronic method. 
         [0014]      FIG. 1  is a conceptual diagram of a conventional optical waveguide type rain sensor. Referring to  FIG. 1 , if light radiated from a light source  100  is collected to be askew incident onto a glass window  140  having a specific thickness or a windshield, an optical waveguide is formed in the glass window  140  within a specific angle range to transfer light. 
         [0015]    In this regard, if rain drops or water drops  130  fall down on the glass plate  140 , since the inner guiding conditions of the optical waveguide are broken, the light is leaked to the outside, and thus an amount of light received by a light receiving element  120  changes, which is used as a parameter for determining the size of raindrops. 
         [0016]    The optical waveguide type rain sensor needs complicated geometrical optical systems shown in  FIG. 3  in order to form guiding condition inside waveguide. 
         [0017]    The optical waveguide type rain sensor needs optical systems, such as input lenses  350   a  and  350   b  of  FIG. 3 , between the light source  100  and the glass window  140  in order to collect the light radiated from the light source  110  and make the light incident onto the windshield, and necessarily needs output lenses  360   a  and  360   b  to transfer guiding light output from the glass window  140  to the light receiving element  120 , which makes the structure of the optical waveguide type rain sensor complicated. 
         [0018]      FIG. 2  is a conceptual diagram of a conventional direct reflective type rain sensor. Referring to  FIG. 2 , light radiated from a light source  210  is collected to be irradiated onto a specific part of the surface of a glass window  240  in order to measure an amount of light directly reflected by raindrops. If water drops or raindrops  230  fall down on the specific part of the surface of the glass window  240 , the amount of reflected light changes, which is detected in a light receiving element  220 . 
         [0019]    The conventional direct reflective type rain sensor needs complex geometrical optical systems, such as the input lenses  350   a  and  350   b  and the output lenses  360   a  and  360   b , in order to transfer most of light radiated from the light source  210  to the light receiving element  220 . 
         [0020]    The conventional direct reflective type rain sensor collects the light radiated from the light source  210  and measures the amount of light reflected from a specific point, which reduces a detection range of the raindrops  230 . 
         [0021]      FIGS. 3A and 3B  illustrate geometrical optical systems of a conventional rain sensor. Referring to  FIGS. 3A and 3B , the geometrical optical systems of the conventional rain sensor increase an area for detecting raindrops and maintain a limited number of light source  310  and light receiving elements  320 . 
         [0022]    When the light source  310  is driven by a discharge driving circuit, the light source  310  emits light having predetermined characteristics. 
         [0023]    Light is radiated from the light source  310  and is incident onto the surface of input side planoconvex les segments  350   a  and  350   b.    
         [0024]    Light that moves within an irradiation angle θ 11  is incident onto the surface of the input side planoconvex les segments  350   a  and  350   b.    
         [0025]    The light emitted by the light source  310  is refractive to form an input side collimated light beam through the surface of the input side planoconvex lens segments  350   a  and  350   b.    
         [0026]    The input side collimated light beam moves toward a front glass  340  through a light guide body  370 . 
         [0027]    The input side collimated light beam collimated by the input lens  350  is applied to an external wall surface  380   a  from an internal wall surface  380   b . The input side collimated light beam of the external wall surface  380   a  is applied to a raindrop detection area. 
         [0028]    The input side collimated light beam is reflected from the external wall surface  380   a  of the raindrop detection area. Thereafter, the reflected light moves forward output side planoconvex les segments  360   a  and  360   b  through the light guide body  370 , as a reflected collimated light beam. 
         [0029]    The reflected collimated light beam is incident onto the output side planoconvex les segments  360   a  and  360   b  and is refractive from the surface of the output side planoconvex les segments  360   a  and  360   b  to be converged forward the light receiving element  320 . 
         [0030]    The light receiving element  320  receives light that moves within a light receiving angle θ 21 . 
         [0031]    An optical path of the light emitted by the light source  310  is formed as follows. 
         [0032]    The input side planoconvex les segments  350   a  and  350   b  obtained by dividing a planoconvex lens into two lens segments are formed on corresponding output side inclination planes  395   a  and  395   b.    
         [0033]    A single optical axis is formed on an input side image and another single optical axis is formed on an output side image, thereby reducing the number of light sources and light receiving elements necessary for a rain sensor. 
       SUMMARY OF THE INVENTION 
       [0034]    The present invention provides a rain sensor using light scattering in order to simplify a complicated structure of a conventional light waveguide type rain sensor or a conventional direct reflective type rain sensor that has a narrow detection range and needs geometrical optical system 
         [0035]    According to an aspect of the present invention, there is provided a rain sensor using light scattering including: a light receiving element for receiving light that is radiated from a light source, penetrates through a windshield, and is scattered in water drops; and a light blocking material for blocking the radiated light that is directly reflected from the windshield. 
         [0036]    The light receiving element may be attached to the windshield, and the light source may maintain a reference distance from the windshield. 
         [0037]    The light blocking material may seal the light receiving element except for a surface of the light receiving element attached to the windshield. 
         [0038]    A reference distance between the light source and the light receiving element may be maintained in order to reduce an amount of the radiated light that is guided inside the windshield and is received by the light receiving element. 
         [0039]    The light source may be a light emitting diode (LED) having a center wavelength within an infrared ray region. 
         [0040]    The light source may maintain a reference incidence angle and a horizontal distance from the light blocking material. 
         [0041]    The light source may further include an oscillator that oscillates a sine wave and a modulator that modulates a light source according to an oscillation signal of the oscillator. 
         [0042]    The light source may further include an amplifier that amplifies a photoelectrically converted signal and a band pass filter that filters the same frequency component as an oscillation frequency of the oscillator. 
         [0043]    The light blocking material may be a totally opaque material with respect to the radiated light, except the scattered light. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]    The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0045]      FIG. 1  is a conceptual diagram of a conventional optical waveguide type rain sensor; 
           [0046]      FIG. 2  is a conceptual diagram of a conventional direct reflective type rain sensor; 
           [0047]      FIGS. 3A and 3B  illustrate geometrical optical systems of a conventional rain sensor; 
           [0048]      FIG. 4  is a diagram of a structure of a rain sensor according to an embodiment of the present invention; 
           [0049]      FIG. 5  is a diagram for explaining a total reflection in a windshield of a rain sensor according to an embodiment of the present invention; 
           [0050]      FIG. 6  is a diagram of a reference distance between a light source and a light receiving element according to an embodiment of the present invention; and 
           [0051]      FIG. 7  is a diagram for explaining the operation of a rain sensor according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0052]    Hereinafter, the present invention will be described in detail by explaining exemplary embodiments of the invention with reference to the attached drawings. 
         [0053]      FIG. 4  is a diagram of a structure of a rain sensor according to an embodiment of the present invention. Referring to  FIG. 4 , the rain sensor of the present embodiment uses light scattering and does not need a geometrical optical system, unlike the conventional rain sensor. 
         [0054]    The rain sensor of the present embodiment includes a light source  410 , a light receiving element  420 , and a light blocking material  440  for preventing light directly reflected from a windshield  430  or light directly output from the light source  410  from being received. 
         [0055]    The light reflected from the light source  410  spreads over the entire area of a radiation angle  480  and thus a raindrop detection area of the rain sensor of the present embodiment is much wider than the conventional rain sensor. 
         [0056]    The light reflected from the light source  410  scatters in water drops or raindrops  460  through the windshield  430 . The light receiving element  420  receives the scattered light. 
         [0057]    The more the number of water drops, the greater the amount of scattered light received by the light receiving element  420 . 
         [0058]    The light receiving element  420  is disposed to contact the windshield  430  in order to prevent the light receiving element  420  from receiving the light that is radiated from the light source  410  and is directly reflected from the windshield  430 , and the light receiving element  420  is sealed by using the light blocking material  440  in order to prevent the light directly output from the light source  410  from being received in the light receiving element  420 . 
         [0059]    The light source  410  is a light emitting diode (LED) having a center wavelength within an infrared ray region. The light blocking material  440  is a totally opaque material in order to block the light directly reflected from the windshield  430  or the light directly radiated from the light source, except the light scattered against the water drops. 
         [0060]    The light source  410  is spaced apart from the windshield  430  by a distance h so that the light source  410  is disposed farther from the windshield  430  than the light receiving element  420 . 
         [0061]    The light receiving element  420  and the light source  410  are spaced apart from each other by a recommendation distance in order to receive the minimum amount of the light that is radiated from the light source  410  and is guided in the windshield  430 . 
         [0062]    The recommendation distance between the light source  410  and the light receiving element  420 , a horizontal distance w between the light source  410  and the light blocking material  440 , and a distance h between the light source  410  and the windshield  430  will now be described in more detail with reference to  FIGS. 5 and 6 . 
         [0063]      FIG. 5  is a diagram for explaining a total reflection in a windshield  510  of a rain sensor according to an embodiment of the present invention. Referring to  FIG. 5 , the light reflected from the light source  410  is incident in a predetermined incidence angle  520 . An inside reflection angle  530  by which the incident light is not guided inside the windshield  510  and penetrates through the windshield  510  is calculated according to an equation below, 
         [0000]        n   1* sin θ= n   2 *sin θ
 
         [0000]      sin 90°=1.5*sin θ r  
 
         [0000]      θ r =41.8°  1)
 
         [0064]    wherein, a refractive index n 1  of air is 1, and a refractive index n 2  of a windshield is 1.5. 
         [0065]    In more detail, the maximum value of the inside reflection angle  530  by which the incident light is not guided inside the windshield  510  and penetrates through the windshield  510  is 41.8 according to the Snell&#39;s law of equation 1 above. 
         [0066]    The predetermined incidence angle  520  by which the light radiated from the light source  410  is incident must be smaller than the inside reflection angle  530  by which the incident light is not guided inside the windshield  510  and penetrates through the windshield  510 . 
         [0067]    When the inside reflection angle  530  is smaller than 41.8, a part of the incident light penetrates through the windshield  510  and a part thereof is guided inside the windshield  510 . 
         [0068]    If the light receiving element  420  receives the light guided to the windshield  510 , the rain sensor malfunctions. 
         [0069]    In more detail, if the light receiving element  420  receives the light directly reflected from the windshield  510  or the light guided inside the windshield  510 , except the light scattered against the water drops  460 , an error with the water drops detection result occurs. 
         [0070]    Thus, the light source  410  and the light receiving element  420  must maintain the minimum distance therebetween in order to minimize the amount of guided light received by the light receiving element  420 . 
         [0071]    The minimum distance between the light source  410  and the light receiving element  420  is shown in  FIG. 6 . 
         [0072]      FIG. 6  is a diagram of a reference distance between the light source  410  and the light receiving element  420  according to an embodiment of the present invention. Referring to  FIG. 6 , when the inside reflection angle  630  is smaller than 41.8, a part of the incident light penetrates through a windshield  610  and a part thereof is guided inside the windshield  610 . 
         [0073]    Power of the light guided inside the windshield  610  is calculated according to an equation below, 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       P 
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                         = 
                         
                           
                             
                                
                               
                                 
                                   1 
                                   - 
                                   1.5 
                                 
                                 
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                             2 
                           
                           = 
                           
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                           0.0064 
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         [0074]    wherein, a refractive index n 1  of air is 1, and a refractive index n 2  of a windshield is 1.5. 
         [0075]    The power of the light guided inside the windshield  610  is 4% in a first reflection, 0.0064% in a third reflection, and 1*10̂−7% in a fifth reflection as shown in equation 2 above and  FIG. 6 . 
         [0076]    Thus, the light source  410  and the light receiving element  420  must maintain a recommendation distance  650  in order to receive the guided light in the light receiving element  420  through the fifth reflection. 
         [0077]    The rain sensor of the present embodiment has a structure in which the light receiving element  420  is disposed to contact the windshield  610  and the light receiving element  420  is sealed by using the light blocking material  440  in order to reduce the influence of the light directly reflected from the windshield  610  and the light source  410  and the light receiving element  420  are spaced apart from each other by the recommendation distance  650  in order to reduce the influence of the light guided inside the windshield  610  as shown in  FIG. 6 . 
         [0078]    Table 1 below shows recommendation distances between the light source  410  and the light receiving element  420  when the inside reflection angle  630  is smaller than 41.8. 
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 P r  (power 
                   
               
               
                   
                 θ l  (external 
                 θ r  (internal 
                 l (minimum 
                 of reflected 
                 recommendation 
               
               
                 case 
                 incidence angle) 
                 incidence angle) 
                 distance) 
                 light) 
                 distance 
               
               
                   
               
             
             
               
                 1 
                   90° 
                 41.8° 
                 3.56d 
                 1 × 10 −7  P i   
                 27 mm 
               
               
                 2 
                 48.6° 
                   30° 
                 2.32d 
                 1 × 10 −7  P i   
                 18 mm 
               
               
                 3 
                 32.3° 
                 20.9° 
                 1.53d 
                 1 × 10 −7  P i   
                 12 mm 
               
               
                 4 
                 22.8° 
                   15° 
                 1.07d 
                 1 × 10 −7  P i   
                  8 mm 
               
               
                 5 
                   10° 
                  6.7° 
                 0.47d 
                 1 × 10 −7  P i   
                  4 mm 
               
               
                   
               
             
          
         
       
     
         [0079]    In Table 1 above, d denotes a thickness of the windshield  610  and d=6 mm. 
         [0080]    In Table 1 above, a recommendation distance is based on an arrival distance of a guided light in the fifth reflection. 
         [0081]    In the rain sensor of the present embodiment, since an external incidence angle  620  is a main factor for determining the recommendation distance, the horizontal distance w between the light source  410  and the light blocking material  440  and the distance h between the light source  410  and the windshield  430  are calculated in Table 2 below. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 θ i  = 10° 
                   
                 θ i  = 32.3° 
                   
                 θ i  = 48.6° 
                   
               
             
          
           
               
                   
                 h 
                 w 
                 h 
                 w 
                 h 
                 w 
               
               
                   
                   
               
               
                   
                 4 mm 
                 0.7 mm 
                 4 mm 
                 2.5 mm 
                 4 mm 
                 4.6 mm 
               
               
                   
                 5 mm 
                 0.9 mm 
                 5 mm 
                 3.2 mm 
                 5 mm 
                 5.7 mm 
               
               
                   
                 6 mm 
                 1.1 mm 
                 6 mm 
                 3.8 mm 
                 6 mm 
                 6.8 mm 
               
               
                   
                   
               
             
          
         
       
     
         [0082]      FIG. 7  is a diagram for explaining the operation of a rain sensor according to an embodiment of the present invention. Referring to  FIG. 7 , an oscillator  741  oscillates a sine wave between 40 kHz and 60 kHz. 
         [0083]    A modulator  742  modulates a light source  710  according to an oscillation signal of the oscillator  741 . 
         [0084]    Light radiated from the light source  710  is scattered in water drops or raindrops through a windshield. A light receiving element  720  receives the scattered light. 
         [0085]    The light receiving element  720  photoelectrically converts the received light. 
         [0086]    An amplifier  751  amplifies a photoelectrically converted signal. A band pass filter  752  filters the same frequency component as an oscillation frequency of the oscillator  741 . 
         [0087]    The rain sensor using light scattering of the present invention does not collimate light radiated from a light source and radiates light onto a wide area, requiring no complicated geometrical optical system and recognizing raindrops on a relatively wide  2 D plane. 
         [0088]    The rain sensor using light scattering of the present invention can simplify a complicated structure of the conventional direct reflective type and light waveguide type rain sensors that detect raindrops contacting the surface of glass and need optical systems for collimating radiated light in a beam format and an optical system for collimating reflected or guided light into a light receiving element again. 
         [0089]    The rain sensor using light scattering of the present invention needs no complicated optical system and uses a wide raindrop detection area, unlike the conventional direct reflective type rain sensor or the conventional light waveguide type rain sensor. 
         [0090]    The rain sensor using light scattering of the present invention solves interference of light that is radiated from a light source and is directly reflected from a windshield or guided in the windshield by means of a relative arrangement of light receiving elements, thereby simplifying the structure thereof and achieving an excellent raindrop detection performance. 
         [0091]    While this invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.