Abstract:
The ice maker for refrigerator and driving method thereof disclosed herein have advantages over a full ice level detection method using mechanical device in that an ice height can be more accurately detected by a detection signal reflected from ice, wherein an ultrasonic signal is transmitted to the ice to sense the height of ice in the ice storage bin using the reflected ultrasonic signal, enabling to precisely detect the ice height, prevent the overflow of ice, prolong the life and prevent the failure of the ice maker for refrigerator.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is based on, and claims priority from, Korean Application Numbers 10-2007-0106524, filed Oct. 23, 2007, the disclosure of which is incorporated by reference herein in its entirety. 
       BACKGROUND 
       [0002]    The following description relates to an ice maker for refrigerator and a driving method thereof capable of precisely detecting a height of ice. 
         [0003]    Generally, a refrigerator is an apparatus which supplies cool air generated by a refrigeration cycle to a storage chamber which stores food such that various storage products can be stored while being cooled or frozen. The conventional refrigerator includes an ice maker which makes ice by using the cool air of a freezer. 
         [0004]      FIG. 1  is a perspective view illustrating an ice maker for refrigerator according to prior art, where the ice maker is installed at a door for opening/closing a freezer of refrigerator or inside a space of the freezer. 
         [0005]    The ice maker ( 20 ) may include an ice container ( 21 ) from which ice is made and a water supplier ( 22 ) formed at one side of the ice container ( 21 ) for supplying water to the ice container ( 21 ). 
         [0006]    When water is supplied to the ice container ( 21 ) from the water supplier ( 22 ), the water contained in the ice container ( 21 ) is frozen by the cold air of the freezer. The ice container ( 21 ) is made of material having excellent heat conductivity and is installed thereunder with a heater. The ice thus made may be extracted from the ice container ( 21 ) by operating the heater. 
         [0007]    The ice separated from the ice container ( 21 ) by the heat of the heater may be dropped by rotation of an ice separation lever installed at an upper end of the ice container into an ice storage installed underneath the ice container. At this time, an ice detection lever ( 23 ) installed at a bottom lateral surface of the ice container may check whether ice is fully stored in the ice storage before the ice is separated from the ice container. The ice detection lever ( 23 ) checks if ice is fully packed inside the ice storage by operation of the driving motor connected to the ice separation lever. 
         [0008]    However, the conventional ice maker suffers from disadvantages in that the ice fully packed in the ice storage is detected by the ice detection lever moving up and down within a predetermined angle to prevent an accurate detection of whether the ice is fully packed. Consequently, the conventional ice maker may result in discomfort in use according as ice is less made or over-made. 
       SUMMARY 
       [0009]    The present disclosure is intended to solve the aforementioned disadvantage and to provide an ice maker for refrigerator and a driving method thereof capable of precisely detecting an ice height. 
         [0010]    One general aspect of the present general inventive concept may be achieved by an ice maker for refrigerator, comprising: an ice making bin for making ice with water fed from a water supplier; a heater for detaching the ice made by the ice making bin by applying heat; an ice storage bin for storing the ice detached from the ice making bin; an ice separating lever for dropping the ice detached from the ice making bin into the ice storage bin; and an ultrasonic sensor for transmitting an ultrasonic signal to the ice in the ice storage bin and receiving the ultrasonic signal transmitted from the ice and measuring the height of ice stored in the ice storage bin. 
         [0011]    Another general aspect of the present general inventive concept may be achieved by an ice maker for refrigerator, comprising: an ice making unit in which ice is made; a water supplier supplying water to the ice maker; an ice storage storing the ice made by the ice making unit; and a full ice level detector sending an ultrasonic signal or an optical signal to the ice stored in the ice storage and detecting the full ice level by receiving the ultrasonic signal or the optical signal reflected from the ice and processing the received ultrasonic signal or the optical signal. 
         [0012]    Still another general aspect of the present general inventive concept may be achieved by an ice maker for refrigerator, comprising: an ice making unit in which ice is made; an ice storage storing the ice made by the ice making unit; an ultrasonic sensor transmitting an ultrasonic signal to the ice in the ice storage and receiving the ultrasonic signal transmitted from the ice; and an ice height converter converting an ice height in the ice storage using the ultrasonic signal received from the ultrasonic sensor and outputting the converted ice height. 
         [0013]    Still further general aspect of the present general inventive concept may be achieved by a driving method of an ice maker for refrigerator, comprising: making ice using water in an ice making bin; storing the ice by separating the ice made by the ice making bin and storing the ice in an ice storage bin; and detecting a height of ice stored in the ice storage bin. 
         [0014]    Still further general aspect of the present general inventive concept may be achieved by a driving method of an ice maker for refrigerator, comprising: transmitting an ultrasonic signal from an ultrasonic transmission sensor to the ice stored in the ice storage bin; receiving, by an ultrasonic reception sensor, the ultrasonic signal reflected by the ice; time-counting from a time of the ultrasonic signal transmitted by the ultrasonic transmission sensor to a time of the ultrasonic signal received by the ultrasonic reception sensor; converting a height of ice using the counted time; determining whether the converted ice height is more than a predetermined ice height; and stopping the ice making in the ice making bin if the converted ice height is more than a predetermined ice height. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a perspective view illustrating an ice maker for refrigerator according to prior art. 
           [0016]      FIG. 2  is a schematic cross-sectional view illustrating an ice maker for refrigerator according to a first exemplary implementation. 
           [0017]      FIG. 3  is a schematic cross-sectional view illustrating an ice storage bin and an ultrasonic sensor according to the present invention. 
           [0018]      FIG. 4  is a block diagram illustrating an ice maker for refrigerator according to a second exemplary implementation. 
           [0019]      FIG. 5  is a block diagram of other configurations of an ice maker for refrigerator according to a second exemplary implementation. 
           [0020]      FIG. 6  is a block diagram illustrating an ice maker for refrigerator according to a third exemplary implementation. 
           [0021]      FIG. 7  is a block diagram of other configurations of an ice maker for refrigerator according to a third exemplary implementation. 
           [0022]      FIG. 8  is a schematic view illustrating an ice height of a display according to the present invention. 
           [0023]      FIG. 9  is a block diagram of still other configurations of an ice maker for refrigerator according to a third exemplary implementation. 
           [0024]      FIGS. 10   a  and  10   b  are schematic views explaining an ultrasonic sensor in an ice maker for refrigerator according to the present invention. 
           [0025]      FIG. 11  is a block diagram explaining function of a controller installed at an ice maker for refrigerator according to the present invention. 
           [0026]      FIG. 12  is a flowchart explaining a first driving method of an ice maker for refrigerator according to the present invention. 
           [0027]      FIG. 13  is a flowchart explaining a second driving method of an ice maker for refrigerator according to the present invention. 
           [0028]      FIG. 14  is a flowchart explaining a third driving method of an ice maker for refrigerator according to the present invention. 
           [0029]      FIG. 15  is a flowchart explaining a fourth driving method of an ice maker for refrigerator according to the present invention. 
           [0030]      FIG. 16  is a waveform of a signal received by an ultrasonic sensor according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Exemplary implementations of an ice maker for refrigerator and a driving method thereof according to the present novel concept will be described in detail with reference to the accompanying drawings. 
         [0032]    Referring to  FIG. 2 , an ice maker for refrigerator may include an ice making bin ( 100 ) for making ice with water fed from a water supplier ( 110 ); a heater ( 120 ) for detaching the ice made by the ice making bin ( 100 ) by applying heat; an ice storage bin ( 160 ) for storing the ice detached from the ice making bin ( 100 ); an ice separating lever ( 130 ) for dropping the ice detached from the ice making bin into the ice storage bin ( 160 ); and an ultrasonic sensor for transmitting an ultrasonic signal to the ice in the ice storage bin ( 160 ) and receiving the ultrasonic signal transmitted from the ice and measuring the height of ice stored in the ice storage bin ( 160 ). 
         [0033]    Reference numeral  170  is a control box installed with a motor and may control the ice maker for refrigerator. The ice maker for refrigerator according to the first exemplary implementation is such that when water is supplied from the water supplier ( 110 ) to the ice making bin ( 100 ), the water in the ice making bin ( 100 ) is turned into ice by the cooling air inside a freezing chamber of the refrigerator. 
         [0034]    When the ice making is finished by the ice making bin ( 100 ), the heater ( 120 ) may be operated to detach the ice made from the ice making bin ( 100 ). In other words, an interface between the ice making bin ( 100 ) and the ice are detached by the heat from the heater ( 120 ). The heater ( 120 ) is preferably installed at a bottom surface of the ice making bin ( 100 ). 
         [0035]    Successively, the motor installed at the control box ( 170 ) may be driven to rotate the ice separating lever ( 130 ) for dropping the ice separated from the ice making bin ( 170 ) into the ice storage bin ( 160 ), whereby the ice is stored in the ice storage bin ( 160 ). 
         [0036]    The ice is heaped in the ice storage bin ( 160 ) through the repeated processes, and in the midst of the process, a storage degree of ice in the ice storage bin ( 160 ) should be checked to keep ice making or stop the ice making. The ultrasonic sensor ( 150 ) is used as a means for measuring the storage degree of ice in the ice storage bin ( 160 ). In other words, the ultrasonic sensor ( 150 ) may transmit an ultrasonic signal to the ice in the ice storage bin ( 160 ) and receive the ultrasonic signal reflected from the ice to measure a height of ice stored in the ice storage bin ( 160 ) using the ultrasonic signal received by a controller installed in the control box ( 170 ), where the controller may control the water supplier ( 110 ) supplying the water to the ice making bin ( 100 ). If the water is not supplied to the ice making bin ( 100 ), the ice making bin ( 100 ) cannot make the ice. 
         [0037]    It could be said that the ice maker for refrigerator according to the first exemplary implementation has a feature of being installed with the ultrasonic sensor ( 150 ) capable of measuring the height of ice stored in the ice storage bin ( 160 ). 
         [0038]    Now, referring to  FIG. 3 , it is preferable that the ultrasonic sensor ( 150 ) is structurally located at an upper surface of the ice storage bin ( 160 ), so that the ultrasonic sensor can transmit an ultrasonic signal to ice ( 161 ) in the ice storage bin ( 160 ) and receive the ultrasonic signal reflected from the ice ( 161 ) to measure a height of ice stored in the ice storage bin ( 160 ). 
         [0039]    The ice maker for refrigerator according to the first exemplary implementation may further include an ice height converter for converting the height of ice inside the ice storage using an ultrasonic signal received by the ultrasonic sensor and outputting the ice height. 
         [0040]    It is preferable that the ice maker for refrigerator according to the first exemplary implementation further include a controller for receiving a signal relative to the ice height outputted from the ice height converter and outputting to the water supplier a signal for stopping the water supplied to the ice making bin, when the ice height indicates a full ice level in which the ice is fully stored in the ice storage. 
         [0041]    In other words, the controller may output a signal for stopping water supplied to the ice making bin if the ice in the ice storage reaches a full ice level, because there is no need of making the ice any more. The water supplier having received the signal for stopping the water supplied to the ice making bin may stop the water supply to the ice making bin. 
         [0042]    If the full ice level in the ice storage is released, the controller is preferred to output a signal to the water supplier for supplying water to the ice making bin. The water supplier having received from the controller the signal for supplying water to the ice making bin may re-start the supply of water to the ice making bin. 
         [0043]    If the ice height converter and the controller are installed in the ice maker for refrigerator according to the first exemplary implementation, the full ice level may be automatically detected, the ice making may be stopped during the full ice level state, and a series of operations starting the ice making may be automatically conducted when the fall ice level is released. As a result, the ice maker for refrigerator according to the novel concept can provide an added convenience to a user. 
         [0044]    Meanwhile, the ice maker for refrigerator according to the first exemplary implementation may further include a heater for detaching an interface between the ice making bin and the ice thus made by using the heat from the heater, or an ice making temperature detecting sensor for detecting an ice making temperature of the ice maker. 
         [0045]    Now, referring to  FIG. 4 , an ice maker for refrigerator according to the second exemplary implementation may include an ice making unit ( 200 ) in which ice is made; a water supplier ( 210 ) supplying water to the ice making unit ( 200 ); an ice storage ( 230 ) storing the ice made by the ice making unit ( 200 ); and a full ice level detector ( 240 ) sending a detection signal to the ice stored in the ice storage ( 230 ) and detecting the full ice level using the detection signal reflected from the ice. 
         [0046]    It is preferable that the ice maker for refrigerator according to the second exemplary implementation further include a controller ( 250 ) for outputting a control signal to the water supplier ( 210 ) in order to stop supplying water to the ice making unit ( 200 ) when the full ice level in the ice storage bin is detected by the full ice level detector ( 240 ). The controller ( 250 ) may control the ice making unit ( 200 ), the water supplier ( 210 ) and the full ice level detector ( 240 ). 
         [0047]    The detection signal is an ultrasonic signal or an optical signal, and the full ice level detector is preferred to be a device for detecting a full ice level by processing the received ultrasonic signal or the optical signal. In other words, the ice maker for refrigerator according to the second exemplary implementation is disposed with the full ice level detector ( 240 ) capable of detecting a full ice level in the ice storage bin. 
         [0048]    Therefore, the ice maker for refrigerator according to the second exemplary implementation is such that when water is supplied from the water supplier ( 210 ) to the ice making unit ( 200 ), the water of the ice making unit ( 200 ) is made an ice by the cooling air inside the freezing chamber of the refrigerator, and the ice made by the ice making unit ( 200 ) is stored in the ice storage ( 230 ). 
         [0049]    The full ice level detector ( 240 ) may send a detection signal to the ice storage ( 230 ) and detect a full ice level in the ice storage ( 240 ) using the detection signal reflected from the ice. The full ice level detector ( 240 ) may determine which level in the ice storage bin corresponds to the height of ice stored in the ice storage bin. 
         [0050]    As a result, if the full ice level is detected by the full ice level detector ( 240 ), the controller ( 250 ) may output a control signal to the water supplier ( 210 ) in order to stop water supply to the ice making unit ( 200 ). 
         [0051]    Accordingly, there is an advantage in the ice maker for refrigerator according to the second exemplary implementation in that the full ice level can be more accurately detected by the full ice level detector ( 240 ) capable of detecting the full ice level using the detection signal reflected from the ice, as compared with the mechanical full ice level detection configuration, thereby preventing overflow of ice from the ice storage ( 230 ). 
         [0052]    Meanwhile, if the ice overflows from the ice storage ( 230 ), a shock may be applied to the refrigerator by physical force of ice to generate a frosting phenomenon or a failure of the refrigerator. However, the ice maker for refrigerator according to the second exemplary implementation can accurately detect the full ice level and prevent the overflow of ice to thereby prolong the life of the ice maker for refrigerator and prevent the failure of the ice maker for the refrigerator. 
         [0053]    Referring now to  FIG. 5 , the ice maker for refrigerator according to the second exemplary implementation may further include an indicator ( 260 ) in addition to the configuration of the ice maker in  FIG. 4 . In other words, if the full ice level is detected by the full ice level detector ( 240 ), the controller ( 250 ) may output a control signal to the water supplier ( 210 ) in order to stop water supply to the ice making unit ( 200 ) and to simultaneously output a signal for the indicator ( 260 ) to indicate the full ice level. 
         [0054]    Referring to  FIG. 6 , the ice maker for refrigerator according to the third exemplary implementation may include an ice making unit ( 300 ) in which ice is made; an ice storage ( 310 ) storing the ice made by the ice making unit ( 300 ); an ultrasonic sensor ( 320 ) transmitting an ultrasonic signal to the ice in the ice storage ( 310 ) and receiving the ultrasonic signal transmitted from the ice; and an ice height converter ( 330 ) converting an ice height in the ice storage ( 310 ) using the ultrasonic signal received from the ultrasonic sensor ( 320 ) and outputting the converted ice height. 
         [0055]    The ice maker for refrigerator according to the third exemplary implementation is such that the ultrasonic sensor ( 320 ) transmits an ultrasonic signal to the ice stored in the ice storage ( 310 ) and receives the ultrasonic signal reflected from the ice. 
         [0056]    The ultrasonic signal received by the ultrasonic sensor ( 320 ) may be inputted into the ice height converter ( 330 ) which in turn converts the height of ice inside the ice storage ( 310 ) and outputs the converted ice height. The ice height outputted from the ice height converter ( 330 ) may be used to determine the full ice level inside the ice storage ( 310 ) and how much (which level) of ice is stored inside the ice storage ( 310 ). 
         [0057]    Therefore, it could be said that the ice maker for refrigerator according to the third exemplary implementation has a feature of being installed with the ultrasonic sensor ( 320 ) and the ice height converter ( 330 ), where information of ice height outputted by the ice height converter ( 330 ) may be used to perform additional functions such as stopping water supply to the ice making unit ( 300 ) and indication of ice height using the indicator. Design of the additional functions may be freely changed. 
         [0058]    Referring to  FIG. 7 , a controller ( 340 ) may receive a signal relative to the ice height outputted from the ice height converter ( 330 ) in the ice maker as illustrated in  FIG. 6 , and transmit the signal relative to the ice height to an indicator ( 350 ), where the indicator ( 350 ) may indicate the ice height. Preferably, the indicator ( 350 ) indicates in percentage the degree of height of ice stored in the ice storage ( 310 ). 
         [0059]    In other words, as shown in  FIG. 8 , if 50% is displayed on the indicator ( 350 ), it can be discerned that the ice storage ( 310 ) stores 50% of ice out of a total capacity of the ice storage ( 310 ). The indicator ( 350 ) may also display a full ice level indicating that ice is fully stored in the ice storage ( 310 ). The display state of the indicator may be freely designed. 
         [0060]      FIG. 9  is a block diagram of still other configurations of an ice maker for refrigerator according to a third exemplary implementation, where the ice maker further includes a comparator ( 370 ), a controller ( 340 ) and a water supplier ( 360 ). 
         [0061]    In other words, the ice maker for refrigerator according to  FIG. 9  may include the water supplier ( 360 ) for supplying water to the ice making unit ( 300 ), the comparator ( 370 ) comparing the ice height converted by the ice height converter ( 330 ) with a predetermined height, and the controller ( 340 ) receiving a signal outputted from the comparator ( 370 ) to control the water supplier ( 360 ) so that water supply to the ice making unit ( 300 ) can be stopped. 
         [0062]    Meanwhile, the ice maker according to  FIG. 9  may be applied to an ice maker structure capable of rotating and twisting the ice making bin to drop the ice, albeit no ice separating lever and a heater. 
         [0063]      FIGS. 10   a  and  10   b  are conceptual drawings explaining an ultrasonic sensor in an ice maker for refrigerator according to the present invention, where the ultrasonic sensor may include a transmitting ultrasonic sensor ( 510 ) and a receiving ultrasonic sensor ( 511 ), as shown in  FIG. 10   a.    
         [0064]    Furthermore, as illustrated in  FIG. 10   b,  the ultrasonic sensor structure may comprise a plurality of ultrasonic reception sensors ( 511 ,  512 ). In other words, when an ultrasonic emitted from one ultrasonic transmission sensor ( 511 ) is reflected from ice ( 520 ) stored in an ice storage bin ( 550 ), the reflected ultrasonic is received by the ultrasonic reception sensor ( 511 ) as shown in  FIG. 10   a,  or received by the plurality of ultrasonic transmission sensors ( 511 ,  512 ) as illustrated in  FIG. 10   b.    
         [0065]      FIG. 11  is a block diagram explaining function of a controller ( 600 ) installed at an ice maker for refrigerator according to the present invention, where the controller ( 600 ) may control a water supplier ( 610 ) to stop water supply to an ice making bin. 
         [0066]    The controller ( 600 ) may control an ice making temperature detection sensor ( 620 ) to detect an ice making temperature of the ice making bin. The controller ( 600 ) may also output to a heater ( 630 ) a signal instructing to separate from the ice making bin the ice made from the ice making bin. The controller ( 600 ) may also control an ultrasonic sensor ( 640 ) to detect a height of ice. The controller ( 600 ) may also output a signal for driving a driving motor for dropping the ice of the ice making bin into an ice storage bin. 
         [0067]      FIG. 12  is a flowchart explaining a first driving method of an ice maker for refrigerator according to the present invention, where water is made ice by an ice making bin (S 10 ). 
         [0068]    The ice made by the ice making bin is separated to be stored in an ice storage bin (S 20 ). That the ice made by the ice making bin is separated to be stored in an ice storage bin (S 20 ) is conducted by a heater driven to separate an interface between the ice making bin and the ice, and by a ice separating lever for dropping the ice into the ice storage bin and storing the ice therein. 
         [0069]    Successively, the height of ice stored in the ice storage bin is detected (S 30 ). In other words, that the height of ice stored in the ice storage bin is detected is conducted by an ultrasonic sensor transmitting an ultrasonic signal to the ice stored in the ice storage bin, receiving the ultrasonic signal reflected from the ice and detecting the height of ice using the ultrasonic signal received from the ultrasonic sensor. The stored degree of ice in the ice storage bin may be discerned by the detected height of ice. Methods of detecting the height of ice using the received ultrasonic signal may be variably designed. 
         [0070]      FIG. 13  is a flowchart explaining a second driving method of an ice maker for refrigerator according to the present invention, where water is first supplied from a water supplier to an ice making bin (S 110 ), and the water in the ice making bin is made ice (S 120 ). 
         [0071]    The ice made by the ice making bin is separated to be stored in an ice storage bin (S 130 ). The height of ice stored in the ice storage bin is detected (S 140 ). 
         [0072]    Successively, determination is made to check whether the detected height of ice is higher than a predetermined height (S 150 ). If it is determined that the detected height of ice is higher than a predetermined height, a water supplier may stop supplying water to the ice making bin (S 160 ). 
         [0073]      FIG. 14  is a flowchart explaining a third driving method of an ice maker for refrigerator according to the present invention, where water in an ice making bin is first made ice (S 210 ), and an ice temperature in the ice making bin is detected (S 220 ). Successively, determination is made to check if the detected ice temperature is lower than a predetermined temperature (S 230 ). The predetermined temperature is a temperature under which the ice making is completed, and if the detected ice temperature is lower than the predetermined temperature, it defines that the ice making has been completed. If it is determined that the detected ice temperature is lower than the predetermined temperature, the ice is separated from the ice making bin and the ice is stored in the ice storage bin (S 240 ). 
         [0074]    Successively, the height of ice stored in the ice storage bin is detected ( 250 ). In other words, the driving method is the same method as that of  FIG. 12  but added by steps  220  and  230 . 
         [0075]      FIG. 15  is a flowchart explaining a fourth driving method of an ice maker for refrigerator according to the present invention, where an ultrasonic transmission sensor first transmits an ultrasonic signal to the ice stored in the ice storage bin (S 300 ), and an ultrasonic reception sensor receives the ultrasonic signal reflected from the ice (S 310 ). 
         [0076]    Successively, time is counted from a time of the ultrasonic signal transmitted by the ultrasonic transmission sensor to a time of the ultrasonic signal received by the ultrasonic reception sensor (S 320 ), where the counted time is defined as ‘ΔT’. The height of ice is converted using the counted time (S 330 ), where the height of ice may be defined as “a×ΔT+b” (described later). Determination is made to check whether the converted height of ice is more than a predetermined ice height (S 340 ). If it is determined that the converted height of ice is more than the predetermined ice height, the ice making in the ice making bin is stopped (S 350 ). 
         [0077]      FIG. 16  is a waveform of a signal received by an ultrasonic sensor according to the present invention. 
         [0078]    When an ultrasonic signal (A) is transmitted from an ultrasonic transmission sensor, an ultrasonic reception sensor receives the ultrasonic signal reflected from the ice stored in the ice storage bin. The ultrasonic signal received by the ultrasonic reception sensor has a waveform of ‘B’ as shown in  FIG. 16 . 
         [0079]    In  FIG. 16 , ‘T 1 ’ is a time on which the ultrasonic transmission sensor transmits the ultrasonic signal, ‘T 2 ’ is a time on which changes of ultrasonic signal received by the ultrasonic reception sensor starts, ‘T 3 ’ defines a time on which inclination changes of ultrasonic signal received by the ultrasonic reception sensor start, and ‘T 4 ’ defines a time on which size of the ultrasonic signal received by the ultrasonic reception sensor is maximized. Therefore, the following equation is used to convert the height of ice. 
         [0000]        H (ice height)= a×ΔT+b,    
         [0000]    where, ‘a’ is an inclination of graph, ‘b’ is an intercept which is constant, and ΔT is the time counted from a time of the ultrasonic signal transmitted by the ultrasonic transmission sensor to a time of the ultrasonic signal received by the ultrasonic reception sensor. 
         [0080]    In other words, the time (ΔT) counted from a time of the ultrasonic signal transmitted by the ultrasonic transmission sensor to a time of the ultrasonic signal received by the ultrasonic reception sensor is one of T 2 −T 1 , T 3 −T 1  and T 4 −T 1 . 
         [0081]    While the present disclosure has been particularly shown and described with reference to exemplary implementations thereof, the general inventive concept is not limited to the above-described implementations. It will be understood by those of ordinary skill in the art that various changes and variations in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.