Abstract:
Disclosed is a robot cleaner capable of reducing the material cost thereof by use of fewer motors, and performing wet cleaning while travelling in all directions and rubbing the floor surface, the robot cleaner includes a plurality of motors generating driving forces, a plurality of pad assemblies configured to rotate by receiving a driving force from one of the plurality of motors, and provided in a tilted manner so that a bottom surface of each of the plurality of pad assemblies has an uneven frictional force with respect to a floor surface, and a tilt gear unit configured to simultaneously vary tilting directions of the plurality of pad assemblies by receiving a driving force from another one of the plurality of motors, wherein the robot clean can travel in all directions depending on a tilting direction and a rotational direction of each of the plurality of pad assemblies.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the Korean Patent Application No. 10-2013-0167187, filed on Dec. 30, 2013, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Embodiments of the present disclosure relate to a robot cleaner capable of travelling in all directions. 
         [0004]    2. Description of the Related Art 
         [0005]    A robot cleaner is a device configured to perform a cleaning task by suctioning foreign substance such as dust from a floor surface while independently travelling on a cleaning area without a manipulation of a user. The robot cleaner determines the distance from an obstacle installed within a cleaning area, such as furniture, office equipment and a wall, through a distance sensor, and selectively drives a left wheel motor and a right wheel motor thereof, thereby cleaning the cleaning area while independently changing the direction thereof. 
         [0006]    In recent years, there has been introduced a robot cleaner capable of wiping off dust from a floor surface in addition to a robot cleaner capable of suctioning foreign substance, such as dust from, a floor surface. The conventional robot cleaner is provided with a pad at a lower surface thereof, and is configured to wipe off dust on a floor surface in ways that move along a floor surface while making contact with the floor surface. 
         [0007]    At this time, the robot cleaner is moved by a transportation member that is separately provided. 
       SUMMARY 
       [0008]    Therefore, it is an aspect of the present disclosure to provide a robot cleaner capable of driving in all directions by use of an uneven frictional force between a pad and a floor surface. In addition, the material cost of the robot cleaner may be reduced by use of fewer motors. 
         [0009]    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. 
         [0010]    In accordance with one aspect of the present disclosure, a robot cleaner includes a plurality of motors, a plurality of pad assemblies and a tilt gear unit. The plurality of motors may generate driving forces. The plurality of pad assemblies may be configured to rotate by receiving a driving force from one of the plurality of motors, and provided in a tilted manner so that a bottom surface of each of the plurality of pad assemblies has an uneven frictional force with respect to a floor surface. The tilt gear unit may be configured to simultaneously vary tilting directions of the plurality of pad assemblies by receiving a driving force from another one of the plurality of motors. The robot cleaner may travel in various directions depending on a tiling direction and a rotational direction of each of the plurality of pad assemblies. 
         [0011]    The plurality of motors may include a first motor connected to the tilt gear unit and a plurality of second motors mounted at each of the plurality of pad assemblies. 
         [0012]    The pad assembly may include a rotating panel, a tile spacer and a pad. The rotating panel may be configured to rotate by the second motor. The tilt spacer may be provided at a lower portion of the rotating panel and provided with a bottom surface thereof in an inclined manner. The pad may be provided at a lower portion of the tilt spacer. 
         [0013]    An elastic unit may be provided in between the tilt spacer and the pad such that the elastic unit allows a bottom surface of the pad to entirely make contact with the floor surface. 
         [0014]    The tilt spacer is connected to the tile gear unit so as to be rotated. 
         [0015]    The pad assembly may further include a mounting unit, and the rotating panel is coupled to the mounting unit by the joint shaft. 
         [0016]    The joint shaft may be provided with a locking bar at one end portion thereof, and the rotating panel may be provided with an interference unit configured to be interfered by the locking bar. 
         [0017]    The tilt spacer may be provided with a hole formed therethrough, while the joint shaft passes through the hole. 
         [0018]    A first gear may be provided at the other end portion of the joint shaft, and the first gear is connected to the second motor, so that the joint shaft and the rotating panel are simultaneously rotated by a driving force of the second motor. 
         [0019]    A second gear may be provided at the mounting unit, and the second gear may be tooth-coupled to the tilt gear unit. 
         [0020]    The driving force of the first motor is delivered to the second gear through the tilt gear unit, thereby rotating the tilt spacer. 
         [0021]    The pad assembly includes a first pad assembly, a second pad assembly positioned at the right side of the first pad assembly, a third pad assembly positioned at the front of the second pad assembly and a fourth pad assembly positioned at the left side of the third pad assembly. 
         [0022]    Tilting directions of the first pad assembly and the second pad assembly are bilaterally symmetrical to each other, and tilting directions of the third pad assembly and the fourth pad assembly to be bilaterally symmetrical to each other. 
         [0023]    Rotational directions of the first pad assembly and the second pad assembly are opposite to each other, and rotational directions of the third pad assembly and the fourth pad assembly are opposite to each other. 
         [0024]    The driving force of the first motor is simultaneously transmitted to a tile spacer included in the first pad assembly, a tile spacer included in the second pad assembly, a tile spacer included in the third pad assembly, and a tile spacer included in the fourth pad assembly through the tilt gear unit. 
         [0025]    In accordance with another aspect of the present disclosure, a robot cleaner includes a first motor provided at a base, a plurality of pad assemblies provided at the base in a tilting manner, a tilt gear unit, and a plurality of second motors. The plurality of pad assemblies may each have a mounting unit mounted at the base, a tilt spacer provided at a lower portion of the mounting unit and provided with a bottom surface thereof formed in a tilted manner, a rotating panel rotatably provided at the bottom surface of the tilt spacer, and a pad configured to clean a floor surface. The tilt gear unit may be configured to simultaneously deliver a rotating force of the first motor to the plurality of tilt spacers provided at the plurality of pad assemblies. The plurality of second motors may be each mounted at each of the plurality of pad assemblies to rotate the pad assembly clockwise or counter-clockwise. A traveling direction of the robot cleaner may be varied by an uneven frictional force between a bottom surface of the pad and the floor surface. 
         [0026]    As the rotating force of the first motor is delivered to the tilt spacer through the tilt gear unit, the tilt spacer may be rotated clockwise or counter-clockwise, so that a tilting direction of the pad assembly is varied. 
         [0027]    The tilt spacers provided at the plurality of pad assemblies, respectively, may be simultaneously rotated in the same direction by the tilt gear unit. 
         [0028]    The pad assembly may further include a joint shaft provided with a hooking unit formed configured to interfere with the rotating panel, and the joint shaft may be rotatably connected to the second motor. 
         [0029]    An elastic unit may be provided in between the rotating panel and the pad such that the elastic unit allows the bottom surface of the pad to entirely make contact with the floor surface. 
         [0030]    In accordance with one embodiment of the present disclosure, a robot cleaner can perform a wet cleaning while rubbing off a floor surface in a course of travelling in all directions, and is provided with less number of motors, thereby reducing material costs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    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: 
           [0032]      FIG. 1  is a perspective view illustrating a robot cleaner in accordance with one embodiment of the present disclosure. 
           [0033]      FIG. 2  is a side view illustrating the robot cleaner in accordance with one embodiment of the present disclosure. 
           [0034]      FIG. 3  is a drawing illustrating a bottom surface of the robot cleaner in accordance with one embodiment of the present disclosure. 
           [0035]      FIG. 4  is a drawing illustrating the robot cleaner having a cover thereof removed in accordance with one embodiment of the present disclosure. 
           [0036]      FIG. 5  is a drawing illustrating a portion of the robot cleaner in accordance with one embodiment of the present disclosure. 
           [0037]      FIG. 6  is a cross-sectional view illustrating a portion of the robot cleaner in accordance with one embodiment of the present disclosure. 
           [0038]      FIG. 7  is a drawing illustrating the robot cleaner provided with a tilt gear unit connected to a pad assembly in accordance with one embodiment of the present disclosure. 
           [0039]      FIGS. 8A and 8B  are drawings illustrating the robot cleaner driving in a diagonal direction in accordance with one embodiment of the present disclosure. 
           [0040]      FIG. 9  is a drawing illustrating the robot cleaner driving in a sideway direction in accordance with one embodiment of the present disclosure. 
           [0041]      FIG. 10  is a drawing illustrating the robot cleaner in accordance with one embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
         [0043]      FIG. 1  is a perspective view of an robot cleaner in accordance with one embodiment of the present disclosure,  FIG. 2  is a side view of the robot cleaner in accordance with one embodiment of the present disclosure, and  FIG. 3  is a drawing illustrating a bottom surface of the robot cleaner in accordance with one embodiment of the present disclosure. 
         [0044]    Referring to  FIGS. 1 to 3 , a robot cleaner  1  in accordance with one embodiment of the present disclosure includes a pad assembly  2 , a cover  10 , and a bumper  11 . The pad assembly  2  may include a plurality of pad assemblies  2 . The robot cleaner  1  is capable of travelling in various directions by use of an uneven frictional force between a bottom surface of the pad assembly  2  and the floor surface. The cover  10  is configured to cover an upper portion of the robot cleaner  1 . The bumper  11  is provided at sides of the robot cleaner  1 , and is configured to absorb an outside impact applied to the robot cleaner  1 . A sensor  110  may be provided at a side of the robot cleaner  1 . The sensor  110  is capable of detecting an obstacle positioned at the surroundings of the robot cleaner  1 . 
         [0045]    The robot cleaner  1  may include the plurality of pad assemblies  2 . As one example, the pad assembly  2  may include a first pad assembly  2   a , a second pad assembly  2   b , a third pad assembly  2   c , and a fourth pad assembly  2   d . The number of the pad assemblies  2  may differ from the above example. Hereinafter, an embodiment, in which the pad assembly  2  having the first pad assembly  2   a , the second pad assembly  2   b , the third pad assembly  2   c , and the fourth pad assembly  2   d , will be described. The first pad assembly  2   a , the second pad assembly  2   b , the third pad assembly  2   c , and the fourth pad assembly  2   d  may be disposed on the robot cleaner  1  in the order of a clockwise direction. 
         [0046]    The pad assemblies  2  may be provided in an inclined manner at a predetermined angle with respect to the floor surface. The pad assemblies  2  may be provided in an inclined manner at a predetermined angle with respect to the floor surface by tilt spacers  22  and  22 ′. One surface of each of the tilt spacers  22  and  22 ′ may be provided with a shape having a predetermined inclination angle. 
         [0047]    For example, when one surface of each of the tilt spacers  22  and  22 ′ is placed on the floor surface, the one surface of each of the tilt spacers  22  and  22 ′ may be provided in a way to form a predetermined angle with respect to the floor surface. An angle formed between the floor surface and the one surface of each of the tilt spacers  22  and  22 ′ may be referred to as an inclination angle. As one example, the inclination angle of each of the tilt spacers  22  and  22 ′ may be about 7.5°. 
         [0048]    By the tilt spacers  22  and  22 ′, the pad assembly  2  may be able to rotate while having a z-axis as a center of rotation in a state of being inclined at a predetermined angle with respect to the floor surface. That is, the pad assemblies  2  may be able to rotate while having the z-axis as a center of rotation in a tilted state by the tilt spacers  22  and  22 ′. Pads  26  and  26 ′ provided at bottom surfaces of the pad assemblies  2 , by elastic members  24  and  24 ′ interposed between the tilt spacers  22  and  22 ′ and the pads  26  and  26 ′, may be able to rotate while having the z-axis as a center of rotation, as the bottom surfaces of the pads  26  and  26 ′ as a whole are in a state of making contact with the floor surface. However, as the pad assembly  2  is rotated in an inclined manner at a predetermined angle with respect to the floor surface, the frictional forces between the bottom surfaces of the pads  26  and  26 ′ and the floor surface may be generated in an uneven manner. The frictional force between a certain portion of the bottom surfaces of the pads  26  and  26 ′ and the floor surface may be greater than when compared to the frictional force from other portions of the bottom surfaces of the pads  26  and  26 ′ and the floor surface due to the inclined one surfaces of the tilt spacers  22  and  22 ′. The robot cleaner  2  may be able to travel by the uneven frictional force between the bottom surfaces of the pads  26  and  26 ′ and the floor surface. 
         [0049]    As illustrated on  FIG. 3 , as one example, when the bottom surface of the robot cleaner  1  is viewed, with respect to the pad assembly  2 , the first pad assembly  2   a , the second pad assembly  2   b , the third pad assembly  2   c , and the fourth pad assembly  2   d  may be provided in the order of a clockwise direction. The third pad assembly  2   c  may be positioned at a front of the first pad assembly  2   a  while the fourth pad assembly  2   d  may be positioned at a front of the second pad assembly  2   b.    
         [0050]    A portion of the bottom surface of the first pad assembly  2   a  having the greater frictional force with respect to the floor surface may be positioned in symmetrical to a portion of the bottom surface of the second pad assembly  2   b  having the greater frictional force with respect to the floor surface. A portion of the bottom surface of the fourth pad assembly  2   d  having the greater frictional force with respect to the floor surface may be positioned in symmetrical to a portion of the bottom surface of the third pad assembly  2   c  having the greater frictional force with respect to the floor surface. 
         [0051]    With an assumption of a linear line I′, which is provided in a way to position the first pad assembly  2   a  and the fourth pad assembly  2   d  at a left side, and also is provided in a way to position the second pad assembly  2   b  and the third pad assembly  2   c  at a right side, a potion ‘P 1 ’ of the first pad assembly  2   a  having the greater frictional force with respect to the floor surface may be positioned in symmetric to a potion ‘P 2 ’ of the second pad assembly  2   b  having the greater frictional force with the floor surface while having the linear line I′ as a center of the symmetry. The a potion ‘P 4 ’ of the fourth pad assembly  2   d  having the greater frictional force with respect to the floor surface may be positioned in symmetric to a potion ‘P 3 ’ of the third pad assembly  2   c  having the greater frictional force with the floor surface while having the linear line ‘L’ as a center of the symmetry. 
         [0052]    On the assumption when the bottom surface of the robot clearer  1  is provided in a rectangular shape, when direction A is defined as direction in which the robot cleaner  1  advances while having the first and second pad assemblies  2   a  and  2   b  positioned at the front of the robot cleaner, direction B, C and D are defined as directions sequentially designated in the order of clockwise direction. That is, direction B is defined as direction in which the robot cleaner  1  advances while having the second and third pad assemblies  2   b  and  2   c  positioned at the front of the robot cleaner  1 , direction C is defined as direction in which the robot cleaner  1  advances while having the third and fourth pad assemblies  2   c  and  2   d  positioned at the front of the robot cleaner  1 , and direction D is defined as direction in which the robot cleaner  1  advances while having the fourth and first pad assemblies  2   d  and  2   a  positioned at the front of the robot cleaner  1 . 
         [0053]    As one example, in an initial state prior to the robot cleaner  1  being driven, the portions of the bottom surfaces of the first pad assembly  2   a  and the second pad assembly  2   b  which have the greater frictional force may be provided to be positioned at an outer side of the robot cleaner  1 . The portions of the bottom surfaces of the third pad assembly  2   c  and the fourth pad assembly  2   d  which have the greater frictional force may be provided to be positioned at an inner side of the robot cleaner  1 . 
         [0054]    That is, the first pad assembly  2   a  may be provided in a way that frictional force with respect to the floor surface is the greater at portion ‘P 1 ’ of the bottom surface of the pad  26  positioned at the direction ‘D’. The second pad assembly  2   b  may be provided in a way that frictional force with respect to the floor surface is the greater at portion ‘P 2 ’ of the bottom surface of the pad  26 ′ positioned at the direction ‘B’. The third pad assembly  2   c  may be provided in a way that frictional force with respect to the floor surface is the greater at portion ‘P 3 ’ of the bottom surface of the pad positioned at the direction ‘D’. The fourth pad assembly  2   d  may be provided in a way that frictional force with respect to the floor surface is the greater at portion ‘P 4 ’ of the bottom surface of the pad positioned at the direction ‘B’. 
         [0055]    Hereinafter, a case in which the portion having greater frictional force in between the bottom surface of the pad assembly and the floor surface is positioned at each of P 1 , P 2 , P 3 , and P 4  as the above will be described. 
         [0056]    The portion having greater frictional force at the bottom surface of the pad assembly  2  may be different from the above embodiment. However, with respect to pad assemblies which are positioned adjacent to each other at the left and right sides of the linear line I′, portions of bottom surface of the pad assemblies having greater frictional force with respect to the floor surface may be provided to be symmetrical to each other while having the linear line I′ as a center of the symmetry. 
         [0057]      FIG. 4  is a drawing illustrating an image of the robot cleaner provided with a cover thereof removed in accordance with one embodiment of the present disclosure,  FIG. 5  is a drawing illustrating a portion of the robot cleaner in accordance with one embodiment of the present disclosure, and  FIG. 6  is a cross-sectional view of a portion of the robot cleaner in accordance with one embodiment of the present disclosure. 
         [0058]    Referring to  FIGS. 4 to 6 , the robot cleaner  1  in accordance with one embodiment of the present disclosure may include a base  12 , a first motor  120  mounted at the base  12 , and second motors  121 ,  122 ,  123 , and  124  mounted at the pad assemblies  2 . The driving force of the first motor  120  may be delivered to the pad assemblies  2  through a tilting gear unit. The direction of an inclination of the pad assemblies  2  may be varied as the pad assemblies  2  are rotated by the first motor  120 . The second motors  121 ,  122 ,  123 , and  124  may be able to rotate the pad assemblies  2  in a clockwise direction or a counter-clockwise direction while having the z-axis as a center of rotation. 
         [0059]    The structures of the first pad assembly  2   a , the second pad assembly  2   b , the third pad assembly  2   c , and the fourth pad assembly  2   d  are similar, and thus hereinafter, the structure of the first pad assembly  2   a  will be described. 
         [0060]    The first pad assembly  2   a  may include a mounting unit  21 , a tile spacer  22 , a rotating panel  23 , an elastic unit  24 , a pad mounting unit  25 , and the pad  26 . The mounting unit  21  may be mounted at the base  12 . At the mounting unit  21 , the second motor  121  may be mounted. At the mounting unit  21 , an extension unit  210  provided with a hollow hole formed thereto may be provided. 
         [0061]    Into the hollow hole formed at the extension unit  210 , a joint shaft  27  connected to the rotating panel  23  may be inserted. At an inside the joint shaft  27 , a hole may be formed in a longitudinal direction. Through the hole formed at the joint shaft  27 , water that is introduced from a water tank may be supplied toward the pad  26 . 
         [0062]    At one end potion of the joint shaft  27 , a second gear  29  capable of receiving a driving force of the second motor  121  may be mounted. The second gear  29  may be tooth-coupled to connecting gears  280  and  281  that are connected to the second motor  121 . The connecting gears  280  and  281  include a first connecting gear  280  and a second connecting gear  281 . The first connecting gear  280  is connected to the second motor  121 , and the second connecting gear  281  may be tooth-coupled to the first connecting gear  280 . The second connecting gear  281  may be tooth-coupled to the second gear  29 . As the second motor  121  is driven, the connecting gears  280  and  281  are rotated, and as the connecting gears  280  and  281  are rotated, the second gear  29  may be rotated. As the second gear  29  is rotated, the rotating panel  23  connected to the second gear  29  may be rotated while having the z-axis as a center of rotation. 
         [0063]    At the other end portion of the joint shaft  27 , a locking bar  270  configured to perpendicular to the longitudinal direction of the joint shaft  27  may be formed. The locking bar  270  may be mounted at an interference unit  230  formed at the rotating panel  23 . At the interference unit  230 , an accommodating unit referred to as a space in which the locking bar  270  may be accommodated is formed, and the locking bar  270  may be accommodated in the accommodating unit. As the locking bar  270  is mounted at the interference unit  230 , the joint shaft  27  is rotated by the second motor  121  while having the z-axis as a center of rotation, and thus the rotating panel  23  may be able to rotate while having the z-axis as a center of rotation. 
         [0064]    In the case as the above, the locking bar  270  may be provided with a certain gap within the interference unit  230 , and thus even in a case when the tilt angle of the rotating panel  23  is changed, regardless of the tilt angle of the rotating panel  23 , the locking bar  270  is formed in the structure capable of delivering a rotational force to the rotating panel  23 . Other than the structure as the above, different forms of structures, which are capable of delivering a rotational force in a tilted state of the rotating panel  23 , such as a universal joint, may be employed. 
         [0065]    At a lower portion of the mounting unit  21 , the tilt spacer  22  may be positioned. At the tilt spacer  22 , a hole  220  may be formed. The joint shaft  27  may penetrate the hole  220 . Even in a case when the joint shaft  27  is rotated while having the z-axis as a center of rotation by receiving a driving force from the second motor  121 , the tilt spacer  22  may be provided in a way not to be rotated. 
         [0066]    A bottom surface  221  of the tilt spacer  22  may be formed in a way to form a predetermined angle with respect to the floor surface. The rotating panel  23  positioned at the lower portion of the tilt spacer  22  may be disposed in a way to form a predetermined angle with respect to the floor surface along the inclination of the bottom surface of the tilt spacer  22 . 
         [0067]    At an upper portion of the rotating panel  23 , the interference unit  230  at which the joint shaft  27  may be mounted may be provided. The interference unit  230  may be provided at an upper portion surface of the rotating panel  23 . At the interference unit  230 , an accommodating unit protruded from the upper portion surface of the rotating panel  23  and in which the locking bar  270  may be accommodated may be formed. The locking bar  270  may be mounted at and accommodated in the accommodating unit. As the joint shaft  27  is rotated, the interference unit  230  is interfered by the locking bar  270 , and the rotating panel  23  may be able to be rotated together with the joint shaft  27 . 
         [0068]    At a lower portion of the rotating panel  23 , the elastic unit  24  may be provided. By the elastic unit  24 , the entire surface of the pad  26  may be able to make contact with the floor surface. The elastic unit  24  may include an elastic member accommodating unit  240  and an elastic member  241 . The elastic member accommodating unit  240  may be provided in the shape of a flexible tube having a plurality of corrugations. The elastic member accommodating unit  240  may be provided with rubber material through which water may not be able to smear or penetrate. As described above, the elastic member  241  may be prevented from being wet by the water supplied to the pad  26 . The elastic member  241  may be accommodated in the elastic member accommodating unit  240 . The elastic member  241  may be provided with the material such as sponge. Even in a case when the rotating panel  23  is inclined to form a predetermined angle with respect to the floor surface, the pad  26  positioned at the lower portion of the elastic unit  24  may make contact entirely with the floor surface. 
         [0069]    At the bottom surface of the elastic unit  24 , the pad mounting unit  25  may be implemented. At the bottom surface of the pad mounting unit  25 , the pad  26  may be mounted. The pad  26  may be detachably mounted at the pad mounting unit  25 . As one example, the pad  26  may be mounted at the bottom surface of the pad mounting unit  25  by a Velcro method. 
         [0070]      FIG. 7  is a drawing illustrating an image of the robot cleaner provided with the tilt gear unit and the pad assembly connected with respect to each other in accordance with one embodiment of the present disclosure. 
         [0071]    Referring to  FIGS. 4 to 7 , the tilt spacers  22  and  22 ′ of the robot cleaner  1  in accordance with one embodiment of the present disclosure may be rotated by the first motor  120 . As the tilt spacers  22  and  22 ′ are rotated, the position of the portion having greater frictional force in between the bottom surface of the pad assembly  2  and the floor surface may be varied, and thus the travelling direction of the robot cleaner  1  may be changed. The driving force of the first motor  120  may be delivered through a tilt gear unit to the tilt spacers  22  and  22 ′. 
         [0072]    The tilt gear unit includes a tilt gear  13 , a driving gear  130 , and a first connecting gear and a second connecting gear connected to the pad assembly  2 . The tilt gear  13  may be rotated by being delivered with a driving force from the first motor  120 . 
         [0073]    The driving gear  130  is connected to the first motor  120 , and the driving gear  130  may be tooth-coupled to the tilt gear  13 . As the driving gear  130  is rotated by the first motor  120 , the tilt gear  13  tooth-coupled to the driving gear  130  may be rotated. As the driving gear  130  is rotated in a counter-clockwise direction by the first motor  120 , the tilt gear  13  may be rotated in a clockwise direction. As the driving gear  130  is rotated in a clockwise direction by the first motor  120 , the tilt gear  13  may be rotated in a counter-clockwise direction. 
         [0074]    The tilt gear  13  may be connected to a first gear  28  mounted at the tilt spacer  22  through a connecting gear. The tilt gear  13  may be connected to the first gear  28  mounted at the tilt spacer  22  through the first connecting gear  131  and the second connecting gear  135 . The tilt gear  13  is tooth-coupled to the first connecting gear  131 , and the first connecting gear  131  may be tooth-coupled to the second connecting gear  135 . The first gear  28  may be tooth-coupled to the second connecting gear  135 . The tilt spacer  22  may be rotated together with the first gear  28 . As the tilt gear  13  is rotated, the rotational force is delivered through the first connecting gear  131  and the second connecting gear  135 , and the first gear  28  is rotated. The tilt spacer  22  may be rotated together with the first gear  28 . 
         [0075]    As the tilt gear  13  is rotated in a clockwise direction, the first connecting gear  131  is rotated in a counter-clockwise direction. As the first connecting gear  131  is rotated in a counter-clockwise direction, the second connecting gear  135  is rotated in a clockwise direction. As the second connecting gear  135  is rotated in a clockwise direction, the first gear  28  is rotated in a counter-clockwise direction. The tilt spacer  22  may be rotated in a counter-clockwise direction together with the first gear  28 . The tilt gear  13  and the tilt spacer  22  may be rotated in opposite directions with respect to each other. As the tilt gear  13  is rotated in a counter-clockwise direction, the tilt spacer  22  may be rotated in a counter-clockwise direction. The tilt spacer  22  may be rotated in an identical direction with respect to the driving gear  130 . 
         [0076]    The second pad assembly  2   b , the third pad assembly  2   c , and the fourth pad assembly  2   d  may be connected to the tilt gear  13  in a similar manner as in the first pad assembly  2   a . A first gear  38  is mounted at the tilt spacer  22 ′ of the second pad assembly  2   b , and the first gear  38  may be connected to the tilt gear  13  through a first connecting gear  132  and a second connecting gear  136 . A first gear  48  is mounted at the tilt spacer of the third pad assembly  2   c , and the first gear  48  may be connected to the tilt gear  13  through a first connecting gear  133  and a second connecting gear  137 . A first gear  58  is mounted at the tilt spacer of the fourth pad assembly  2   d , and the first gear  58  may be connected to the tilt gear  13  through a first connecting gear  134  and a second connecting gear  138 . The tilt spacers provided at the second pad assembly  2   b , the third pad assembly  2   c , and the fourth pad assembly  2   d  may be rotated in opposite directions with respect to rotational directions of the tilt gear  13 . 
         [0077]    As described above, the tilt spacer provided at the pad assembly  2  may be rotated in an identical direction with respect to the rotational direction of the driving gear  130 . The tilt spacer is rotated in a different direction with respect to the tilt gear  13 , and thus the direction of inclination may be varied. That is, as the tilt spacer is rotated, the position of the portion having greater frictional force in between the bottom surface of the pad assembly  2  and the floor surface may be varied. As the position of the portion having greater frictional force in between the bottom surface of the pad assembly  2  and the floor surface is changed, the travelling direction of the robot cleaner  1  may be changed. 
         [0078]    The tilt spacer may be rotatably provided on the rotating panel  23  separately from the rotating panel  23  without being fixed to the rotating panel  23 . Thus, even in a case when the tilt spacer is rotated by the first motor  120 , the elastic member  24 , the pad mounting unit  25  and the pad  26  mounted at the rotating panel  23 , as well as the rotating panel  23  are not rotated together with the tilt spacer. The first motor  120  may be able to change the direction of inclination, which is formed by the bottom surface of the tilt spacer with respect to the floor surface, by rotating the tilt spacer. The second motors  121 ,  122 ,  123 , and  124  may be able to rotate the rotating panel  23  of the pad assembly  2  in a clockwise direction or in a counter-clockwise direction. 
         [0079]    In a case when the travelling direction of the robot cleaner  1  is needed to be changed, the first motor  120  is driven and the tilt spacer may be rotated by a predetermined angle. When the tile spacer is rotated by the predetermined angle, the position of the portion having greater frictional force in between the bottom surface of the pad assembly  2  and the floor surface may be changed within the bottom surface of the pad assembly  2 . As the position of the portion having greater frictional force in between the bottom surface of the pad assembly  2  and the floor surface is changed, the travelling direction of the robot cleaner  1  may be changed. 
         [0080]    Hereinafter, an embodiment in which the travelling direction of the robot cleaner  1  is changed will be described by referring to the drawings. 
         [0081]      FIGS. 8A and 8B  are drawings illustrating an image of the robot cleaner driving in a diagonal direction in accordance with one embodiment of the present disclosure. 
         [0082]    By referring to  FIG. 8A  and  FIG. 8B , the travelling direction of the robot cleaner  1  in accordance with one embodiment of the present disclosure may be changed during a course of driving. The tilt spacer is rotated by the first motor  120 , and the position of the portion having greater frictional force in between the bottom surface of the pad assembly  2  and the floor surface is changed, and thus the travelling direction of the robot cleaner  1  may be changed. The following description will be made in relation to a case that the travelling direction of the robot cleaner  1  having been driven in a linear direction is changed in a diagonal direction. 
         [0083]    During the course of a linear driving, the first pad assembly  2   a  may be rotated in a counter-clockwise direction by the second motor  121 . At the first pad assembly  2   a , the portion having greater frictional force in between the bottom surface of the first pad assembly  2   a  and the floor surface may be the position ‘P 1 ’. The second pad assembly  2   b  may be rotated by the second motor  122  in a clockwise direction. At the second pad assembly  2   b , the portion having greater frictional force in between the bottom surface of the first pad assembly  2   b  and the floor surface may be the position ‘P 2 ’. The third pad assembly  2   c  may be rotated by the second motor  123  in a counter-clockwise direction. At the third pad assembly  2   c , the portion having greater frictional force in between the bottom surface of the third pad assembly  2   c  and the floor surface may be the position ‘P 3 ’. The fourth pad assembly  2   d  may be rotated by the second motor  123  in a clockwise direction. At the fourth pad assembly  2   d , the portion having greater frictional force in between the bottom surface of the fourth pad assembly  2   d  and the floor surface may be the position ‘P 4 ’. 
         [0084]    As the driving gear  130  is rotated in a counter-clockwise direction by the first motor  120 , the tilt gear  13  may be rotated in a clockwise direction. As the tilt gear  13  is rotated in a clockwise direction, the first connecting gears  131 ,  132 ,  133 , and  134  are rotated in a counter-clockwise direction. As the first connecting gears  131 ,  132 ,  133 , and  134  are rotated in a counter-clockwise direction, the second connecting gears  135 ,  136 ,  137 , and  138  are rotated in a clockwise direction. As the second connecting gears  135 ,  136 ,  137 , and  138  are rotated in a clockwise direction, the first gears  28 ,  38 ,  48 , and  58  may be rotated in a counter-clockwise direction. 
         [0085]    The tilt spacer mounted at each of the pad assemblies  2  may be rotated in a clockwise direction together with each of the first gears  28 ,  38 ,  48 , and  58  mounted at each of the pad assemblies  2 . As for the diagonal driving of the robot cleaner  1 , the tilt spacer may be rotated in a clockwise direction within a range of greater than about 0° and less than about 90°. As one example, the tilt spacer may be rotated in a counter-clockwise direction at about 45°. According to the rotational angle and the rotational direction of the tilt spacer, the travelling direction of the robot cleaner  1  may be varied. Hereinafter, an embodiment in which the tilt spacer is rotated in a clockwise direction within the range of greater than about 0° and less than about 90° will be described. 
         [0086]    As illustrated on  FIG. 8B , as the tilt spacer is rotated in a counter-clockwise direction, the portion having greater frictional force in between the bottom surface of the pad assembly  2  and the floor surface may be changed in a counter-clockwise direction. The ‘P 1 ’ of the first pad assembly  2   a  is moved to a position Q 1 , the ‘P 2 ’ of the second pad assembly  2   b  is moved to a position Q 2 , the ‘P 3 ’ of the third pad assembly  2   c  is moved to a position Q 3 , and the ‘P 4 ’ of the fourth pad assembly  2   d  is moved to a position Q 4 . 
         [0087]    The first pad assembly  2   a  is rotated in a counter-clockwise direction, and a frictional force in between the position Q 1  and a floor surface may be generated in direction G 2 . The second pad assembly  2   b  is rotated in a clockwise direction, and a frictional force in between the position Q 2  and the floor surface may be generated in the direction G 2 . The third pad assembly  2   c  is rotated in a counter-clockwise direction, and a frictional force in between the position Q 3  and the floor surface may be generated in the direction G 2 . The fourth pad assembly  2   d  is rotated in a clockwise direction, and a frictional force in between the position Q 4  and the floor surface may be generated toward the direction G 2 . Due to the frictional forces in the direction G 2  generated in between the bottom surfaces of the first to fourth pad assemblies  2   a ,  2   b ,  2   c  and  2   d  and the floor surface, the robot cleaner  1  may travel in direction G 1  that is a diagonal direction. 
         [0088]    As described above, as the position of the portion having greater frictional force in between the bottom surface of the pad assembly  2  and the floor surface is moved while the tile spacer is rotated in a clockwise direction, the travelling direction of the robot cleaner  1  may be changed from a linear driving to a diagonal driving in direction G 1 . 
         [0089]      FIG. 9  is a drawing illustrating the robot cleaner driving in a sideway direction in accordance with one embodiment of the present disclosure. 
         [0090]    Referring to  FIG. 8A  and  FIG. 9 , the travelling direction of the robot cleaner  1  in accordance with one embodiment of the present disclosure may be changed to a sideway driving from a linear driving during the course of a linear driving. As the tilt spacer is rotated by the first motor  120 , the position of the portion having greater frictional force in between the bottom surface of the pad assembly  2  and the floor surface is varied, and thus the travelling direction of the robot cleaner  1  may be changed. 
         [0091]    During the course of a linear driving, the first pad assembly  2   a  may be rotated in a counter-clockwise direction by the second motor  121 . At the first pad assembly  2   a , the portion having greater frictional force in between the bottom surface of the first pad assembly  2   a  and the floor surface may be the position ‘P 1 ’. The second pad assembly  2   b  may be rotated by the second motor  122  in a clockwise direction. At the second pad assembly  2   b , the portion having greater frictional force in between the bottom surface of the second pad assembly  2   b  and the floor surface may be the position ‘P 2 ’. The third pad assembly  2   c  may be rotated by the second motor  123  in a counter-clockwise direction. At the third pad assembly  2   c , the portion having greater frictional force in between the bottom surface of the third pad assembly  2   c  and the floor surface may be the position ‘P 3 ’. The fourth pad assembly  2   d  may be rotated by the second motor  124  in a clockwise direction. At the fourth pad assembly  2   d , the portion having greater frictional force in between the bottom surface of the fourth pad assembly  2   d  and the floor surface may be the position ‘P 4 ’. 
         [0092]    As the driving gear  130  is rotated in a counter-clockwise direction by the first motor  120 , the tilt gear  13  may be rotated in a clockwise direction. As the tilt gear  13  is rotated in a clockwise direction, the first connecting gears  131 ,  132 ,  133 , and  134  are rotated in a counter-clockwise direction. As the first connecting gears  131 ,  132 ,  133 , and  134  are rotated in a counter-clockwise direction, the second connecting gears  135 ,  136 ,  137 , and  138  are rotated in a clockwise direction. As the second connecting gears  135 ,  136 ,  137 , and  138  are rotated in a clockwise direction, the first gears  28 ,  38 ,  48 , and  58  may be rotated in a counter-clockwise direction. 
         [0093]    The tilt spacer mounted at each of the pad assemblies  2  may be rotated in a counter-clockwise direction together with each of the first gears  28 ,  38 ,  48 , and  58  mounted at each of the pad assemblies  2 . As for the sideway driving of the robot cleaner  1 , the tilt spacer may be rotated by about 90° in the counter-clockwise direction. In a case when the tilt spacer is rotated by about 90° in a counter-clockwise direction, the robot cleaner  1  may drive toward a left side direction, that is, a direction ‘D’, so that the first pad assembly  2   a  and the fourth pad assembly  2   d  may be positioned at a front. On the contrary, in a case when the tilt spacer is rotated by about 90° in a clockwise direction, the robot cleaner  1  may drive toward a right side direction, that is, a direction ‘B’, so that the second pad assembly  2   b  and the third pad assembly  2   c  may be positioned at a front. 
         [0094]    The first pad assembly  2   a  is rotated in a counter-clockwise direction, and a frictional force may be generated toward the direction ‘B’ in between a position ‘R 1 ’ and the floor surface. The second pad assembly  2   b  is rotated in a clockwise direction, and a frictional force may be generated toward the direction ‘B’ in between a position ‘R 2 ’ and the floor surface. The third pad assembly  2   c  is rotated in a counter-clockwise direction, and a frictional force may be generated toward the direction ‘B’ in between a position ‘R 3 ’ and the floor surface. The fourth pad assembly  2   d  is rotated in a clockwise direction, and a frictional force may be generated toward the direction ‘B’ in between a position ‘R 4 ’ and the floor surface. As described above, by the frictional forces that are generated toward the direction ‘B’ in between the floor surface and the bottom surfaces of the first to fourth pad assemblies  2   a  to  2   d , the robot cleaner  1  may drive toward the left side direction, that is, the direction ‘D’. 
         [0095]    As described above, as the position of the portion having greater frictional force in between the bottom surface of the pad assembly  2  and the floor surface is varied while the tilt spacer is rotated in a clockwise direction or a counter-clockwise direction, the travelling direction of the robot cleaner  1  may be varied. The travelling direction of the robot cleaner  1  may be variously varied according to the rotated angle of the tilt spacer by the first motor  120 . The pad assembly  2 , by the second motors  121 ,  122 ,  123 , and  124 , may be able to wipe the floor surface by rotating while having the z-axis as a center of rotation. The travelling direction of the robot cleaner  1  may be varied according to the rotational direction of the second motors  121 ,  122 ,  123 , and  124 . The driving velocity of the robot cleaner  1  may be varied according to the rotational velocity of the second motors  121 ,  122 ,  123 , and  124 . 
         [0096]    The pad assembly  2  of the robot cleaner  1  in accordance with one embodiment of the present disclosure may be provided in a way that the position of the portion having greater frictional force in between the bottom surface of the first pad assembly  2   a  and the floor surface may be symmetrical with respect to the position of the portion having greater frictional force in between the bottom surface of the second pad assembly  2   b  and the floor surface. The first pad assembly  2   a  and the second pad assembly  2   b  may be rotated toward opposite directions with respect to each other by the second motors  121  and  122 . In the case of the third pad assembly  2   c  and the fourth pad assembly  2   d , the position of the portion having greater frictional force in between the bottom surface of the third pad assembly  2   c  and the floor surface may be symmetrical with respect to the position of the portion having greater frictional force in between the bottom surface of the fourth pad assembly  2   d  and the floor surface. The third pad assembly  2   c  and the fourth pad assembly  2   d  may be rotated toward opposite directions with respect to each other by the second motors  123  and  124 . The position of the portion having greater frictional force in between the bottom surface of the pad assembly  2  and the floor may be varied, and as the rotational direction of the pad assembly  2  is varied by the second motors, the robot cleaner  1  may be able to drive in various directions. As the rotational velocity of the pad assembly is varied by the second motors while having the z-axis as a center of rotation, the driving velocity of the robot cleaner  1  may be varied. 
         [0097]    As described above, with respect to the robot cleaner having the plurality of pad assemblies configured to clean a floor surface by wiping, by using less number of motors, a floor surface is cleaned, and the robot cleaner may be able to drive in various directions. As the plurality of pad assemblies is simultaneously manipulated by the tilt gear unit, the direction of tilting may be varied, and thereby the control needed to change the direction of the robot cleaner may be conveniently taken place. 
         [0098]    In the present disclosure, the contact portions and the rotational directions of the each of the pad assemblies, which are capable of linear driving, the diagonal driving, the sideway driving, are described as embodiments, and are not limited hereto, and through the combination of the contact portions and the rotational directions of the each of the pad assemblies having various shapes, the linear driving, the diagonal driving, the sideway driving may be possible. In addition, in the embodiments of the present disclosure, while the case of the four pad assemblies is described as an example, the embodiments of the present disclosure may also be applied to an robot cleaner applied with the two pad assemblies, for example, a case in which only the first pad assembly  2   a  and the second pad assembly  2   b.    
         [0099]    Processes according to the above-described example embodiments may be recorded in non-transitory 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. The program instructions recorded on the media may be those specially designed and constructed for the purposes of the example embodiments, or they may be of the kind well-known and available to those having skill in the computer software arts. The media may also include, alone or in combination with the program instructions, data files, data structures, and the like. Examples of non-transitory computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD ROM discs and DVDs; magneto-optical media such as optical discs; 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. 
         [0100]    The described processes may be executed on a computer or processor configured to operate as a controller to perform processes described herein. For example, a computer or processor in the robot cleaner can operate as a controller to cause the robot to travel as described herein. For example, a computer or processor in the robot cleaner can operate as a controller to cause the various mechanisms described herein (for example, motors, gears, etc) to perform specific operations described herein to cause the robot cleaner to travel in manners described herein. 
         [0101]    For example,  FIG. 10  discloses a robot cleaner in accordance with an embodiment in which the robot cleaner  1  includes a controller  300  to cause the various mechanisms described herein to perform specific operations described herein to cause the robot cleaner to travel in manners described herein. 
         [0102]    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.