Patent Publication Number: US-9851711-B2

Title: Robot cleaner, docking station, robot cleaner system including robot cleaner and docking station, and method of controlling robot cleaner

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application filed under 35 USC 1.53(b) claiming priority benefit of U.S. Ser. No. 13/067,528 filed in the United States on Jun. 7, 2011, which claims priority benefit of U.S. Ser. No. 12/801,575 filed in the United States on Jun. 15, 2010, which claims the benefit of U.S. Patent Application No. 61/213,569, filed on Jun. 19, 2009 and Korean Patent Application Nos. 10-2009-0075963, filed on Aug. 18, 2009 and 10-2010-0019376, filed on Mar. 4, 2010, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     One or more embodiments of the present disclosure relate to a robot cleaner system including a robot cleaner and a docking station. 
     2. Description of the Related Art 
     The term “robot cleaner” refers to a device to perform a cleaning operation such as to suck dust, foreign matter or the like from a floor while traveling in a working area having a predetermined range without user manipulation. The robot cleaner measures distances to obstacles such as furniture, office supplies or walls located within the working area using a sensor or a camera, and performs a predetermined operation using the measured information while traveling without collision with the obstacles. 
     The robot cleaner automatically cleans while autonomously moving in an area to be cleaned and then moves to a docking station in order to charge a battery of the robot cleaner or to allow for disposal of dust contained in the robot cleaner. 
     SUMMARY 
     Therefore, it is an aspect of the present disclosure to provide a robot cleaner guided to a docking position to be docked without an overlapping area where a plurality of docking signals overlap, a docking station, a robot cleaner system including the robot cleaner and the docking station, and a method of controlling the robot cleaner. 
     It is another aspect of the present disclosure to provide a robot cleaner to measure the period of a docking signal so as to detect a reflected wave, a docking station, a robot cleaner system including the robot cleaner and the docking station, and a method of controlling the robot cleaner. 
     It is another aspect of the present disclosure to provide a robot cleaner configured to match a plurality of docking signals to the same data codes so as to indicate plural pieces of area information, a docking station, a robot cleaner system including the robot cleaner and the docking station, and a method of controlling the robot cleaner. 
     Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the disclosure. 
     In accordance with one aspect of the present disclosure, there is provided a robot cleaner system including: a docking station to form a docking area within a predetermined angle range of a front side thereof, to form docking guide areas which do not overlap each other on the left and right sides of the docking area, and to transmit a docking guide signal such that the docking guide areas are distinguished as a first docking guide area and a second docking guide area according to an arrival distance of the docking guide signal; and a robot cleaner to move to the docking area along a boundary between the first docking guide area and the second docking guide area when the docking guide signal is sensed and to move along the docking area so as to perform docking upon reaching the docking area. 
     The docking station may transmit a docking signal to a central portion of a front side of a main body thereof within the predetermined angle range so as to form the docking area. 
     The docking station may include first and second transmission units to transmit docking guide signals to both sides of a front portion of a main body thereof and a third transmission unit to transmit the docking signal to a central portion of the front side of the main body thereof within the predetermined angle range. 
     The first and second transmission units may include first and second light emitting units to generate docking guide signals and first and second shading plates to block some of the docking guide signals passing through a first lens unit or a second lens unit so as to reduce spreading angles of the docking guide signals, respectively. 
     The robot cleaner system may further include first and second lens units provided outside the first and second light emitting units so as to spread the docking guide signals. 
     The third transmission unit may include a third light emitting unit to generate the docking signal and a guide portion to guide a traveling direction of the docking signal such that the docking signal is formed within the predetermined angle range. 
     In accordance with another aspect of the present disclosure, there is provided a docking station including: at least one transmission unit to form a docking area within a predetermined angle range of a front side thereof, to form docking guide areas which do not overlap each other on the left and right sides of the docking area, and to transmit a docking guide signal such that the docking guide areas are distinguished as a first docking guide area and a second docking guide area according to an arrival distance of the docking guide signal, wherein the transmission unit forms signals directed to the first docking guide area and the second docking guide area in the form of one signal and transmits the signal. 
     The forming of the signals directed to the first docking guide area and the second docking guide area in the form of one signal may include forming a signal having a large amplitude, which reaches both the first docking guide area and the second docking guide area, and a signal having a small amplitude, which reaches only the second docking guide area, in the form of one signal. 
     The forming of the signals directed to the first docking guide area and the second docking guide area in the form of one signal may include forming signals having different amplitudes in the form of one signal, such that only a signal having a large amplitude is analyzed as a data bit in the first docking guide area and both the signal having the large amplitude and a signal having a small amplitude are analyzed as the data bit in the second docking guide area. 
     The transmission unit to transmit the docking guide signal may include a light emitting unit to generate the docking guide signal and a shading plate to block some of the docking guide signal so as to reduce a spreading angle of the docking guide signal. 
     The docking station may further include a lens unit provided outside the light emitting unit so as to spread the docking guide signal. 
     The docking station may further include a transmission unit to transmit a docking signal to a central portion of a front side of a main body thereof within a predetermined angle range such that a docking area which does not overlap the first docking guide area or the second docking guide area is formed. 
     The transmission unit to transmit the docking signal may include a light emitting unit to generate the docking signal and a guide portion to guide a traveling direction of the docking signal such that the docking signal is formed at the central portion of the front side of the main body within the predetermined angle range. 
     In accordance with another aspect of the present disclosure, there is provided a docking station including: at least one transmission unit to form a docking area within a predetermined angle range of a front side thereof, to form docking guide areas which do not overlap each other on the left and right sides of the docking area, and to transmit a docking guide signal such that the docking guide areas are distinguished as a first docking guide area and a second docking guide area according to an arrival distance of the docking guide signal, wherein delay times of a plurality of high periods included in the docking guide signal are adjusted to different lengths. 
     The adjusting of the delay times of the plurality of high periods to the different lengths may include adjusting delay times of consecutive high periods of the plurality of high periods to different lengths. 
     The docking station may further include a transmission unit to transmit a docking signal to a central portion of a front side of a main body thereof within a predetermined angle range such that a docking area which does not overlap the first docking guide area or the second docking guide area is formed, delay times of a plurality of high periods included in the docking signal may be adjusted to different lengths. 
     The adjusting of the delay times of the plurality of high periods to the different lengths may include adjusting delay times of consecutive high periods of the plurality of high periods to different lengths. 
     The transmission unit to transmit the docking signal may include a light emitting unit to generate the docking signal and a guide portion to guide a traveling direction of the docking signal such that the docking signal is formed at the central portion of the front side of the main body within the predetermined angle range. 
     The transmission unit to transmit the docking guide signal may include a light emitting unit to generate the docking guide signal and a shading plate to block some of the docking guide signal so as to reduce a spreading angle of the docking guide signal. 
     The docking station may further include a lens unit provided outside the light emitting unit so as to spread the docking guide signal. 
     In accordance with a further aspect of the present disclosure, there is provided a method of controlling a robot cleaner, the method including: checking whether the robot cleaner needs to be docked at a docking station; moving the robot cleaner toward a boundary between a first docking guide area formed a predetermined distance or more from the docking station and a second docking guide area formed within the predetermined distance from the docking station, if the robot cleaner needs to be docked; moving the robot cleaner along the boundary to reach a docking area formed at a central portion of a front side of the docking station within a predetermined angle range, if the boundary is sensed; and moving the robot cleaner along the docking area so as to dock the robot cleaner at the docking station, if the robot cleaner reaches the docking area. 
     The sensing of the boundary may include moving the robot cleaner in a direction of the docking station if the robot cleaner is first located in the first docking guide area and determining that the robot cleaner is located at the boundary when the robot cleaner reaches the second docking guide area while moving in the direction of the docking station. 
     The sensing of the boundary may include moving the robot cleaner in a direction different from a direction of the docking station if the robot cleaner is first located in the second docking guide area and determining that the robot cleaner is located at the boundary when the robot cleaner reaches the first docking guide area while moving. 
     According to the embodiments of the present disclosure, since a docking area is formed by mounting a simple component in a docking station, manufacturing costs associated with components are reduced. 
     According to the embodiments of the present disclosure, since the period of the docking signal is measured so as to distinguish the docking signal from a reflected wave, the robot cleaner is prevented from moving in an undesired direction. At this time, the docking signal is easily distinguished from the reflected wave by changing the length of the docking signal. 
     According to the embodiments of the present disclosure, the robot cleaner quickly checks area information of a docking guide signal by containing plural pieces of area information in one docking guide signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the disclosure will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is an appearance perspective view of a robot cleaner system according to an embodiment of the present disclosure; 
         FIG. 2  is a perspective view of a robot cleaner according to an embodiment of the present disclosure; 
         FIG. 3A  is a front perspective view of a docking station according to an embodiment of the present disclosure; 
         FIG. 3B  is a back perspective view of a docking station according to an embodiment of the present disclosure; 
         FIG. 4  is an enlarged view of a transmission unit included in a docking station according to an embodiment of the present disclosure; 
         FIG. 5  is a control block diagram of a docking station according to an embodiment of the present disclosure; 
         FIG. 6  is a control block diagram of a robot cleaner according to an embodiment of the present disclosure; 
         FIG. 7  is a conceptual diagram illustrating an operation principle of a robot cleaner system according to an embodiment of the present disclosure; 
         FIG. 8  is a flowchart illustrating a docking process of a robot cleaner according to an embodiment of the present disclosure; 
         FIGS. 9A, 9B, 9C, and 9D  are views illustrating a detection principle of a reflected wave according to an embodiment of the present disclosure; and 
         FIGS. 10A, 10B, 10C, and 10D  are views illustrating a principle of matching a plurality of docking signals to one data code and forming plural pieces of area information according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. 
       FIG. 1  is an appearance perspective view of a robot cleaner system according to an embodiment of the present disclosure, and  FIG. 2  is a perspective view of a robot cleaner according to an embodiment of the present disclosure. 
       FIG. 3A  is a front perspective view of a docking station according to an embodiment of the present disclosure,  FIG. 3B  is a back perspective view of a docking station according to an embodiment of the present disclosure, and  FIG. 4  is an enlarged view of a transmission unit included in a docking station according to an embodiment of the present disclosure. 
     As shown in  FIGS. 1 and 2 , the robot cleaner system includes a robot cleaner  20  and a docking station  10  to charge a battery of the robot cleaner  20 . 
     Referring to  FIG. 2 , the robot cleaner  20  includes a main body  22  forming an appearance thereof, reception units  210   a  to  210   d  mounted on front and back sides of the main body  22  to receive signals transmitted from the docking station  10 , and driving wheels  24  mounted on a lower side of the main body  22  to move the robot cleaner  20 . 
     The reception units  210   a  to  210   d  of the robot cleaner  20  receive a docking signal or docking guide signals transmitted from the docking station  10 . In the reception units  210   a  to  210   d  of the robot cleaner  20  according to the embodiment of the present disclosure, two reception units are mounted on a central portion of the front side of the main body  22  and two reception units are mounted on both sides of the back portion of the main body  22 , although other positions and quantities may be used. 
     The driving wheels  24  of the robot cleaner  20  are mounted on the left and right side of the main body  22  and are independently driven by a motor driving unit (not shown) to move the robot cleaner  20  in a desired direction. A plurality of auxiliary wheels (e.g., casters) to support the main body  22  and smoothen traveling of the robot cleaner  20  may be mounted on the front and back sides of the driving wheels  24 . 
     Referring to  FIGS. 3A and 3B , the docking station  10  includes a main body  11  forming an appearance thereof and transmission units  110   a ,  110   b  and  110   c  mounted on the main body  11  to transmit the docking signal and the docking guide signals. 
     The first transmission unit  110   a  and the second transmission unit  110   b , to transmit the docking guide signals, are mounted on both sides of a front portion of an upper end of the docking station  10 , and the third transmission unit  110   c  is mounted on a central portion of the front side of the upper end of the docking station  10  to transmit the docking signal within a predetermined angle range. 
     A slip prevention pad  14  to prevent movement of the docking station  10  is attached to a lower end of the docking station  10 . The slip prevention pad  14  is made of a material (e.g., rubber) having a high coefficient of friction. The slip prevention pad  14  includes a first slip prevention portion  14   a  obliquely extending in an opposite direction of a docking direction of the robot cleaner  20 , a second slip prevention portion  14   b  obliquely extending in an opposite direction of a separation direction of the robot cleaner  20 , and a third slip prevention portion  14   c  extending downward in a pin shape. In addition, a guide groove  15  is concavely formed in the lower end of the docking station  10  such that a connection terminal  242  (not shown) of the robot cleaner  20  is stably connected to a charging terminal  12  of the docking station  10 . 
     The charging terminal  12  to charge the battery of the robot cleaner  20  is provided on the lower end of the docking station  10 . An embossed portion  12   a  is provided on an upper surface of the charging terminal  12  such that the connection with the connection terminal  242  (not shown) of the robot cleaner  20  becomes stable. A tact switch  13  pressed when the robot cleaner  20  enters the docking station  10  is mounted on the inside of the lower end of the docking station  10 . When the tact switch  13  is pressed, power is applied to the charging terminal  12 . 
     Referring to  FIG. 4 , in the transmission units  110   a  to  110   c  included in the docking station  10 , the first transmission unit  110   a  and the second transmission unit  110   b  are mounted on both sides of the transmission unit  110   c  to externally transmit the docking guide signals, and the third transmission unit  110   c  is mounted between the transmission units  110   a  and  110   b  to transmit the docking signal within the predetermined angle range. 
     The first transmission unit  110   a  and the second transmission unit  110   b  include a first light emitting unit  111   a  and a second light emitting unit  111   b  to generate the docking guide signals, a first lens unit  112   a  and a second lens unit  112   b  to spread the docking guide signals generated by the first light emitting unit  111   a  and the second light emitting unit  111   b , and a first shading plate  113   a  and a second shading plate  113   b  mounted on the front side of the first lens unit  112   a  and the second lens unit  112   b  to block some of the docking guide signals passing through the lens units  112   a  and  112   b  so as to adjust spread angles of the signals, respectively. 
     Each of the first lens unit  112   a  and the second lens unit  112   b  includes a 180-degree spread lens to adjust the spread angle of the signal to 180° using a refractive index of the surface thereof. Outer surfaces of the first lens unit  112   a  and the second lens unit  112   b  are polyhedral and grooves  115   a  and  115   b  having curved surfaces are formed in the inside thereof so as to better spread light. 
     The third transmission unit  110   c  includes a third light emitting unit  111   c  to generate the docking signal, and a guide portion  114   a  to guide a traveling direction of the docking signal such that the docking signal generated by the third light emitting unit  11   c  is transmitted within the predetermined angle range. The guide portion  114   a  is a slit which is made of a material such as metal or a shading plate, through which infrared light may not pass, and thereby functions as an infrared light blocking device. 
     Meanwhile, the first to third light emitting units  111   a  to  111   c  include infrared light emitting elements to generate infrared signals or Light Emitting Diodes (LEDs) to generate light beams. 
       FIG. 5  is a control block diagram of a docking station according to an embodiment of the present disclosure, and  FIG. 7  is a conceptual diagram illustrating operation principle of a robot cleaner system according to an embodiment of the present disclosure. 
     As shown in  FIG. 5 , the docking station  10  includes the first and second transmission units  110   a  and  110   b  to transmit the docking guide signals, the third transmission unit  110   c  to transmit the docking signal, the charging terminal  12  to charge the battery of the robot cleaner  20 , a power supply  130  to supply power to the charging terminal  12 , a docking sensor  120  to sense docking of the robot cleaner  20 , and a controller  140  to control the overall operation of the docking station  10 . 
     Referring to  FIG. 7 , the first transmission unit  110   a  and the second transmission unit  110   b  transmit a left-area signal (L-area and W 1 -area signal) and a right-area signal (R-area and W 2 -area signal), both of which are the docking guide signals, to docking guide areas, respectively. The left-area signal and the right-area signal are distinguished from each other by a bit array. For example, the left-area signal may be set to a bit array of “01” and the right-area signal may be set to a bit array of “10”. The detailed description of the bit array of each area signal will be given later. Meanwhile, since the signals are transmitted from the first transmission unit  110   a  and the second transmission unit  110   b  at the spread angle of about 90 degrees or less by the shading plates  113   a  and  113   b , a docking area (P area) distinguished from the docking guide areas is formed in a central area of a front side of the docking station  10 . Meanwhile, the docking area (P area) may be implemented as a non-signal area without a separate signal. That is, the docking of the robot cleaner  20  may be controlled by stopping the operation of the third transmission unit  100   c  and setting an area, in which a signal is absent within a predetermined angle range of the front side of the docking station  10 , as the docking area. 
     The third transmission unit  110   c  transmits a central-area signal, which is the docking signal having a narrow transmission angle range, to the docking area. The third transmission unit  110   c  includes the guide portion  114   a  to guide the docking signal, and the guide portion  114   a  guides the traveling direction of the docking signal emitted from the third light emitting unit  111   c  such that the docking signal is formed in a predetermined area located at a central portion of a front side of the docking station  10 . 
     The charging terminal  12  is connected to the connection terminal  242  (not shown), which is electrically connected to a rechargeable battery (not shown) mounted in the robot cleaner  20 . The charging terminal  12  supplies power upon being connected to the connection terminal of the robot cleaner  20 . 
     The power supply  130  supplies power to the charging terminal  12  so as to charge the rechargeable battery of the robot cleaner  20 . 
     The controller  140  is a microprocessor to control the overall operation of the docking station  10  such that power is supplied to the charging terminal  12  through the power supply  130  according to a docking sensing signal transmitted from the docking sensor  120 . 
     The controller  140  adjusts the time lengths of high periods of data bits of the docking signal transmitted from the first to third transmission units  110   a  to  110   c  such that the robot cleaner  20  distinguishes the docking signal from a reflected wave. The robot cleaner  20  measures the time length between a start point of a high period and a start point of a subsequent high period of the docking signal transmitted from the docking station  10  so as to determine the data bits. Referring to  FIGS. 9A to 9D ,  FIG. 9A  shows the docking guide signal or the docking signal and  FIG. 9B  shows the reflected wave produced by reflection of the docking signal or the docking guide signal from an obstacle. When a signal weakens as shown in  FIG. 9B , the robot cleaner  20  measures time lengths A 2  and B 2  between a highest point of a first high period and a highest point of a second high period which is a subsequent high period so as to determine the data bits. At this time, it can be seen that the distances A 1  and B 1  between the high periods and the distances A 2  and B 2  between the high periods are equal to each other, respectively (A 1 =A 2  and B 1 =B 2 ). Accordingly, the reflected wave produced by reflection of the docking signal or the docking guide signal from the obstacle may not be recognized by the robot cleaner  20 . Therefore, the controller  140  adjusts delay times of the high periods of the data bits of the docking guide signal or the docking signal to be different from each other. Referring to  FIGS. 9C and 9D , if the signals in which the lengths of the high periods of the data bits are set to l and m are transmitted, time lengths between a start point of a high period and a start point of a subsequent period shown in  FIG. 9C  become A 3  and B 3 . At this time, the distances between the high periods of the reflected wave shown in  FIG. 9D  become A 4  and B 4 . Since the time lengths A 3  and B 3  and A 4  and B 4  are respectively different from each other, the robot cleaner  20  may recognize the signal having the time lengths A 4  or B 4  different from the stored time lengths of the high periods as the reflected wave. 
     The controller  140  adjusts the data bits of the docking signal transmitted from the third transmission unit  110   c  or the docking guide signals transmitted from the first transmission unit  110   a  and the second transmission unit  110   b  so as to contain different area signals in one signal. For example, the first transmission unit  110   a  does not separately transmit a docking guide signal directed to the first docking guide area and a docking guide signal directed to the second docking guide area at a time interval. Instead, the first transmission unit  110   a  forms the signal directed to the first docking guide area and the signal directed to the second docking guide area in the form of one signal and transmits the signal to both the first docking guide area and the second docking guide area, thereby shortening the periods of several area signals to the period of one signal. For example, as shown in Table 1, a left-area bit array is “01”, a right-area bit array is “10”, and a long-distance area bit array is “11”. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Left area (short- 
                 Right area (short- 
                 Long-distance 
               
               
                   
                 distance area) 
                 distance area) 
                 area 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Data bit 
                 01 
                 10 
                 11 
               
               
                   
               
            
           
         
       
     
     At this time, referring to  FIG. 10A , in the time length of the bit, if it is assumed that the time length of the high period of a bit “0” is 0.5, the time length of the low period of the bit “0” is 0.6, the time length of the high period of a bit “1” is 0.5, the time length of the low period of the bit “1” is 1.7, the time length of the high period of a bit “11” is 0.5, and the time length of the low period of the bit “11” is 2.8, the first transmission unit  110   a  and the second transmission unit  110   b  transmit one signal, in which the first docking guide signal and the second docking guide signal are included, as a docking guide signal, as shown in  FIGS. 10B and 10C . Referring to  FIG. 10B , the amplitudes of the high periods are differently set. A signal having an amplitude a 1  reaches the first docking guide area which is a long-distance docking guide area and a signal having an amplitude a 2  reaches only the second docking guide area which is a short-distance docking guide area. 
     For example, in the docking guide signal shown in  FIG. 10B , since both the high signal having the amplitude a 1  and the high signal having the amplitude a 2  reach the short-distance docking guide area, the high signal having the time length of 0.5 (the high signal having the amplitude a 1 ) and the subsequent low signal having the time length of 0.6 are analyzed as the bit “0” and the subsequent high signal having the time length of 0.5 (the high signal having the amplitude a 2 ) and the subsequent low signal having the time length of 1.7 are analyzed as the bit “1”. Therefore, the total bit array is “01” and is analyzed as the left-area short-distance docking guide signal. In addition, since the high signal having the amplitude a 1  reaches the long-distance docking guide area but the high signal having the amplitude a 2  does not reach the long-distance docking guide area, a signal shown in  FIG. 10D  reaches the robot cleaner  20 . Therefore, the high signal having the time length of 0.5 (the high signal having the amplitude a 1 ) and the subsequent low signal having the time length of 2.8 are input, and information “11” is input and is analyzed as the long-distance docking guide signal. 
     As another example, in the docking guide signal shown in  FIG. 10C , since both the high signal having the amplitude a 1  and the high signal having the amplitude a 2  reach the short-distance docking guide area, the high signal having the time length of 0.5 (the high signal having the amplitude a 1 ) and the subsequent low signal having the time length of 1.7 are analyzed as the bit “1” and the subsequent high signal having the time length of 0.5 (the high signal having the amplitude a 2 ) and the subsequent low signal having the time length of 0.6 are analyzed as the bit “0”. Therefore, the total bit array “10” is analyzed as the right-area short-distance docking guide signal. In addition, since the high signal having the amplitude a 1  reaches the long-distance docking guide area but the high signal having the amplitude a 2  does not reach the long-distance docking guide area, a signal shown in  FIG. 10D  reaches the robot cleaner  20 . Therefore, the high signal having the time length of 0.5 (the high signal having the amplitude a 1 ) and the subsequent low signal having the time length of 2.8 are input, and information “11” is input and is analyzed as the long-distance docking guide signal. 
     As described above, if the short-distance docking guide signal and the long-distance docking guide signal are transmitted in the period of one signal, the robot cleaner  20  more quickly distinguishes the area, compared with the related art (a time difference between area signals is reduced). 
       FIG. 6  is a control block diagram of a robot cleaner according to an embodiment of the present disclosure. 
     The robot cleaner  20  includes reception units  210   a  to  210   d  to receive docking signals or a remote control signal, an obstacle sensing unit  220  to sense a peripheral obstacle, a driving unit  230  to drive the robot cleaner  20 , a battery sensing unit  240  to sense the residue of the battery, a storage unit  250  to store a traveling pattern or the like of the robot cleaner  20 , and a control unit  260  to control the robot cleaner  20 . 
     The reception units  210   a  to  210   d  receive the docking signals transmitted from the first to third transmission units  110   a  to  110   c  of the docking station  10 . The reception units  210   a  to  210   d  include infrared reception modules to receive the docking signals, and the infrared reception modules include infrared reception elements to receive infrared signals in a specific band. 
     The obstacle sensing unit  220  senses furniture, office supplies, walls, or other obstacles located within an area in which the robot cleaner  20  travels. The obstacle sensing unit  220  may include all-direction sensors and an analog/digital converter (not shown). The all-direction sensors are provided on all sides of the robot cleaner and include RF sensors to emit RF signals and to detect signals reflected from peripheral obstacles. The obstacle sensing unit  220  receives the signals, converts the analog signals into digital signals through the analog/digital converter, and generates and transmits obstacle sensing signals to the control unit  260 . 
     The driving unit  230  controls the level of power applied to a motor (not shown) connected to the driving wheels  24  according to a control signal output from the control unit  260  so as to drive the robot cleaner  20 . 
     The battery sensing unit  240  senses the charging residue of the rechargeable battery  241  to supply driving power of the robot cleaner  20  and transmits information about the charging residue to the control unit  260 . 
     The storage unit  250  stores an operating system to drive the robot cleaner  20 , a traveling pattern, and the like, and stores location information of the robot cleaner  20 , obstacle information, and the like. A non-volatile memory such as a flash memory or an Electrically Erasable Programmable Read-Only Memory (EEPROM) may be used as the storage unit. Data stored in the storage unit  250  is controlled by the control unit  260 . 
     The control unit  260  is a microprocessor to control the overall operation of the robot cleaner  20  and determines whether the robot cleaner is docked at the docking station  10  according to a docking request signal transmitted from the battery sensing unit  240 . The control unit  260  determines the traveling direction of the robot cleaner  20  according to the docking guide signals or the docking signals received by the reception units  210   a  to  210   d  so as to dock the robot cleaner at the docking station  10 . The detailed method of docking the robot cleaner  20  at the docking station  10  will be described later. 
       FIG. 8  is a flowchart illustrating a docking process of a robot cleaner according to an embodiment of the present disclosure. 
     The robot cleaner  20  set in a cleaning mode performs a cleaning operation according to an input cleaning route or a randomly selected cleaning route. The robot cleaner  20  checks whether the residue of the battery is decreased to a predetermined level or less during the cleaning operation or whether the amount of accumulated dust or the like is equal to or greater than a predetermined amount so as to check whether the robot cleaner  20  needs to be docked at the docking station  10  ( 300  and  310 ). 
     Next, if the robot cleaner  20  needs to be docked, the cleaning mode is switched to a docking mode. If the robot cleaner  20  is in the docking mode, the robot cleaner  20  moves along a random route or a set route in order to sense a docking signal or a docking guide signal ( 320 ). 
     Next, the robot cleaner  20  checks whether a first docking guide signal is sensed. The first docking guide signal is transmitted from the first transmission unit  110   a  or the second transmission unit  110   b  to a long-distance area. The robot cleaner  20  determines that the robot cleaner is located in the first docking area which is a long-distance area, when the first docking guide signal is sensed ( 330 ). 
     Next, when the first docking guide signal is sensed, the robot cleaner  20  moves toward the docking station  10  to transmit the first docking guide signal. The robot cleaner  20  moves in the transmission direction of the first docking guide signal when the reception units  210   a  to  210   d , mounted on the front side thereof, receive the signal ( 340 ). 
     Next, the robot cleaner  20  checks whether a boundary between the first docking guide area and the second docking guide area is sensed, while moving in the transmission direction of the first docking guide signal. The first docking guide area is a wide long-distance docking guide area and the second docking guide area is a short-distance docking guide area. The robot cleaner  20  continuously senses the docking guide signal even when moving in the transmission direction of the first docking guide signal and determines that the robot cleaner is located at the boundary when the sensed docking guide signal is changed from the first docking guide signal to the second docking guide signal ( 350 ). 
     Next, the robot cleaner  20  moves along the boundary when the boundary between the first docking guide area and the second docking guide area is sensed. The robot cleaner  20  may check whether the second docking guide signal is a left-area signal or a right-area signal and determine a movement direction along the boundary according to the checked result. For example, the robot cleaner  20  moves to the right when the second docking guide signal which is the left-area signal is sensed while moving toward the docking station  10  such that the robot cleaner  20  reaches a predetermined position from the front side of the docking station  10  ( 360 ). 
     Next, when the robot cleaner  20  senses the docking signal while moving along the boundary, the robot cleaner is aligned with the docking station  10 , is moved to a docking position of the docking station  10  according to the docking signal, and is docked ( 370  and  380 ). 
     If the first docking guide signal is not sensed in Operation  330  but a second docking guide signal is sensed, the robot cleaner  20  moves in a direction (e.g., an opposite direction) different from the transmission direction of the second docking guide signal ( 390  and  400 ). 
     Next, the robot cleaner  20  checks whether the boundary between the first docking guide area and the second docking guide area is sensed, while moving in the direction different from the transmission direction of the second docking guide signal. The robot cleaner  20  continuously senses the docking guide signal even when moving in the direction different from the transmission direction of the second docking guide signal and determines that the robot cleaner is located at the boundary when the sensed docking guide signal is changed from the second docking guide signal to the first docking guide signal ( 410 ). 
     Next, the robot cleaner  20  moves along the boundary when the boundary between the first docking guide area and the second docking guide area is sensed ( 360 ). 
     Next, when the robot cleaner  20  senses the docking signal while moving along the boundary, the robot cleaner is aligned with the docking station  10 , is moved to the docking position of the docking station  10  according to the docking signal, and is docked ( 370  and  380 ). 
     If the first docking guide signal and the second docking guide signal are not sensed in Operations  330  and  390  and the docking signal is sensed, the robot cleaner is aligned with the docking station  10 , is moved to the docking position of the docking station  10  according to the docking signal, and is docked ( 420  and  380 ). 
     The method of controlling a robot cleaner according to the above-described example embodiments may be recorded in computer-readable media including program instructions to implement various operations embodied by a computer. The media may also include, alone or in combination with the program instructions, data files, data structures, and the like. 
     Examples of computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD ROM disks and DVDs; magneto-optical media such as optical disks; and hardware devices that are specially configured to store and perform program instructions, such as read-only memory (ROM), random access memory (RAM), flash memory, and the like. Examples of program instructions include both machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter. 
     The method of controlling a robot cleaner may be executed on a general purpose computer or processor or may be executed on a particular machine such as the robot cleaner described herein. 
     Although a few embodiments of the present disclosure have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.