Abstract:
A cleaning robot that comprises: a main case ( 2 ) having a suction port ( 6 ) opened in the lower surface thereof and an exhaust port ( 7 ) opened in the upper surface thereof, that is self-propelled on a floor surface (F); an electric fan ( 22 ) arranged inside the main case ( 2 ); a dust collection unit ( 30 ) arranged in the center of the main case ( 2 ), in a planar view, that collects dust in airflow sucked in from the suction port ( 6 ) by the driving force of the electric fan ( 22 ); and a battery ( 14 ) that supplies power to each section. The electric fan ( 22 ) is arranged on one side relative to the dust collection unit ( 30 ) and the battery ( 14 ) is arranged on the other side.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a cleaning robot that moves by itself on a floor surface. 
       BACKGROUND ART 
       [0002]    A conventional cleaning robot is disclosed in a patent document 1. In this cleaning robot, a main body housing, which has a circular shape when viewed from top, moves by itself on a floor surface to perform cleaning. Here, to perform cleaning under a table and the like, the main body housing is formed to have a thin shape that is low in height. The main body housing is provided with a drive wheel and a driven wheel that protrude from a bottom surface. The driven wheel is disposed in front of the drive wheel in a traveling direction during a cleaning time. 
         [0003]    A lower surface of a front portion of the main body housing, which is situated in front in the traveling direction during the cleaning time, is provided therethrough with a suction opening, and a circumferential surface of a rear portion of the main body housing is provided therethrough with an air exhaling opening. A dust suction portion, which has an electric fan and a dust collection portion, is disposed behind the drive wheel in the main body housing. The electric fan generates a suction air flow that is sucked from the suction opening, and the dust collection portion collects dust contained in the suction air flow. 
         [0004]    The suction opening and the dust collection portion are connected with each other by a duct, the dust collection portion and the air exhaling opening are connected by the duct, and the electric fan is disposed in the duct. Here, the dust collection portion is disposed in a freely mountable and demountable manner; accordingly, an air flow-in opening and an air flow-out opening are in tight contact with the duct via a packing. 
         [0005]    Besides, the main body housing is provided therein with a battery that supplies electric power to each portion of the electric fan, the drive wheel and the like, and with a control board that has a control circuit to control each portion. 
         [0006]    In the cleaning robot having the above structure, when a cleaning operation is started, the drive wheel and the electric fan are driven. The main body housing moves by itself on a floor surface because of rotation of the drive wheel and driven wheel, and an air flow containing dust is sucked from the suction opening disposed in the front portion because of the driving of the electric fan. The dust contained in the air flow is collected by the dust collection portion, and the air flow, from which the dust is removed, passes through the electric fan to be exhaled backward from the air exhaling opening. In this way, the floor surface is cleaned, the dust collection portion is removed, and the dust accumulated in the dust collection portion is dumped. 
       CITATION LIST 
     Patent Literature 
       [0007]    PLT1: JP-A-2007-167617 (pages 6 to 10, FIG. 2) 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    The electric fan disposed in the main body housing has a heavy weight, and the dust collection portion becomes heavy in weight because of the accumulation of dust. Because of this, according to the conventional cleaning robot that disposes the electric fan and the dust collection portion behind the drive wheel, the weight becomes heavier in the portion behind the drive wheel than in the portion in front of the drive wheel. Here, if the main body housing moves backward and stops suddenly before a step of a downward stairway and the like, there is a risk that a center of gravity shifts backward; and the main body housing falls from the step to be broken because of the weight behind the drive wheel. Besides, when dust accumulates in the dust collection portion, the weight behind the drive wheel becomes further heavier; accordingly, the main body housing becomes more likely to fall from the step. 
         [0009]    Likewise, also in a case where the weight of the portion in front of the drive wheel becomes heavier than the portion behind the drive wheel, there is a risk that the main body housing falls from a step of a downward stairway when moving forward. 
         [0010]    Besides, according to the conventional cleaning robot, the main body housing is provided with the suction opening through the front portion and with the electric fan and air exhaling opening in the back portion. Because of this, an air flow path, which connects the suction opening and the air exhaling opening with each other, is formed to extend long in the main body housing. Besides, the control board is dispersed and disposed in a left-right direction and a back-forth direction with respect to the dust collection portion, and a wiring, which connects electric components such as the electric fan, the drive wheel and the like and a plurality of the control boards, becomes long. Accordingly, there is a problem that the main body housing becomes large. 
         [0011]    Besides, if use is continued in a state where a small air leak is occurring because of deterioration of the packing and the like, the air flow containing dust flows over the control board, so that the dust accumulates on the control board. In this way, there is also a problem that the control circuit malfunctions and the reliability of the cleaning robot declines. 
         [0012]    It is an object of the present invention to provide a cleaning robot that is able to prevent a fall from a step. Besides, it is another object of the present invention to provide a cleaning robot that is able to achieve a small size and to improve the reliability. 
       Solution to Problem 
       [0013]    To achieve the above objects, the present invention comprises: a main body housing that is provided with a suction opening and an air exhaling opening; a pair of drive wheels that have a horizontal rotary shaft and allows the main body housing to move by itself; an electric fan that is disposed in the main body housing; a dust collection portion that is disposed on the rotary shaft and collects dust of an air flow which is sucked from the suction opening because of driving of the electric fan; and a battery that supplies electric power to each portion; wherein the electric fan is disposed on one side of the dust collection portion and the battery is disposed on another side of the dust collection portion. 
         [0014]    According to this structure, the main body housing moves forward and backward because of driving of the pair of drive wheels. For example, the electric fan is disposed in front of the dust collection portion that is disposed over the rotary shaft of both drive wheels, while the battery is disposed behind the dust collection portion. In this way, the weight of the main body housing is distributed in front of and behind the drive wheels. An air flow containing dust on a floor surface is sucked from the suction opening because of driving of the electric fan and collected by the dust collection portion. The air flow, from which the dust is removed by the dust collection portion, passes though the electric fan disposed in front of the dust collection portion to be exhaled from the air exhaling opening. If the main body housing stops suddenly before a step of a downward stairway or the like when moving forward and backward, the center of gravity shifts back and forth. Here, the weight of the main body housing is distributed in front of and behind the drive wheels; accordingly, a fall of the main body housing is prevented. Besides, the dust collection portion is disposed over the rotary shaft of the drive wheels; accordingly, even if the weight becomes large because of the dust collection, the weight balance of the main body housing is kept. 
         [0015]    Besides, in the cleaning robot having the above structure according to the present invention, the rotary shaft is disposed on a center line of the main body housing. According to this structure, the weight of the main body housing is distributed in front of and behind the center line. 
         [0016]    Besides, the cleaning robot having the above structure according to the present invention comprises: a rotary brush that is disposed at the suction opening arranged in front of the drive wheels; and a rear wheel that is disposed behind the drive wheels; wherein the rotary brush, the drive wheel and the rear wheel contact a floor surface, so that the main body housing moves by itself on the floor surface. According to this structure, dust on the floor surface is stirred up by rotation of the rotary brush and guided to the suction opening. If the main body housing stops suddenly when moving forward, the center of gravity of the main body housing shifts forward, and the rotary brush is deformed, so that the main body housing is inclined forward. Here, the weight of the main body housing is distributed back and forth; accordingly, the main body housing returns to the original attitude. 
         [0017]    Besides, the cleaning robot having the above structure according to the present invention comprises a control board that controls each portion; wherein the control board is disposed on the same side as the battery with respect to the dust collection portion. According to this structure, the heavy-weight electric fan is disposed on one side of the drive wheels and the battery is disposed on the other side of the drive wheels. 
         [0018]    Besides, the cleaning robot having the above structure according to the present invention comprises an air flow path that connects the suction opening with the dust collection portion, and connects the dust collection portion with the air exhaling opening; wherein the air flow path is disposed on one side with respect to the dust collection portion. 
         [0019]    According to this structure, the main body housing moves by itself on the floor surface to perform cleaning because of control by the control board disposed, for example, behind the dust collection portion. Because of the driving of the electric fan, the air flow is sucked into the air flow path from the suction opening that opens in front of the dust collection portion, and exhaled, via the dust collection portion, from the air exhaling opening that opens through the front portion of the main body housing. 
         [0020]    Besides, the present invention comprises: a main body housing that is provided with a suction opening disposed through a lower surface and an air exhaling opening disposed through an upper surface and moves by itself on a floor surface; an electric fan that is disposed in the main body housing; a dust collection portion that collects dust of an air flow which is sucked from the suction opening because of driving of the electric fan; an air flow path that connects the suction opening with the dust collection portion, and connects the dust collection portion with the air exhaling opening; and a control board that controls each portion; wherein the air flow path is disposed on one side of the dust collection portion and the control board is disposed on another side of the dust collection portion. 
         [0021]    According to this structure, because of control by the control board that is disposed, for example, behind the dust collection portion, the main body housing moves by itself on the floor surface and the electric fan is driven. Because of the driving of the electric fan, the air flow containing dust of the floor surface is sucked into the air flow path from the suction opening that opens in front of the dust collection portion. The dust contained in the air flow is collected by the dust collection portion disposed behind the suction opening. The air flow, from which the dust is removed by the dust collection portion, passes through the electric fan disposed in front of the dust collection portion and is exhaled from the air exhaling opening that opens through the front portion of the main body housing. 
         [0022]    Besides, the cleaning robot having the above structure according to the present invention comprises a dust collection chamber that houses the dust collection portion in a freely mountable and demountable manner and extends in a direction to partition an inside of the main body housing; wherein a wall surface, which extends in a longitudinal direction of the dust collection chamber, is provided with a first air inhaling path through which the air flow flows in and a second air inhaling path through which the air flow flows out; and another wall surface of the dust collection chamber is closed. 
         [0023]    According to this structure, the air flow sucked from the suction opening flows through the first air inhaling path disposed through, for example, the front wall of the dust collection chamber and flows into the dust collection portion. The air flow, from which the dust is removed by the dust collection portion, flows through the second air inhaling path disposed through the front wall of the dust collection chamber and is guided to the electric fan. 
         [0024]    Besides, in the cleaning robot having the above structure according to the present invention, the dust collection portion includes: a dust collection vessel which is provided with an air flow-in opening and in which the dust accumulates; an upper cover which opens and closes an upper surface of the dust collection vessel and is provided with an air flow-out opening; and a filter which is disposed on a lower surface of the upper cover and collects the dust. 
         [0025]    According to this structure, the air flow sucked from the suction opening flows into the dust collection vessel via the air flow-in opening, the dust accumulates in the dust collection chamber and is collected by the filter. The air flow, from which the dust is removed, flows out via the air flow-out opening disposed through the upper cover. The dust collection portion is demounted from the main body housing, the upper cover is opened, and the dust in the dust collection vessel is dumped. 
         [0026]    Besides, in the cleaning robot having the above structure according to the present invention, the opening surfaces of the air flow-in opening and air flow-out opening include an inclined surface; and a packing is disposed on circumferential rims of the opening surfaces. According to this structure, when the dust collection portion is mounted, the packing closes tightly a portion between the air flow-in opening and the wall surface of the dust collection chamber, and a portion between the air flow-out opening and the wall surface of the dust collection chamber. Here, the opening surfaces of the air flow-in opening and air flow-out opening include the inclined surface; accordingly, sliding between the packing and the wall surface of the dust collection chamber is prevented when the dust collection portion is mounted and demounted. 
       Advantageous Effects of Invention 
       [0027]    According to the present invention, the electric fan is disposed on one side and the battery is disposed on the other side with respect to the dust collection portion that is disposed over the rotary shaft of the drive wheels; accordingly, the weight of the main body housing is balanced and distributed in front of and behind the drive wheels. In this way, even if the main body housing moving forward and backward stops suddenly before a step and the center of gravity shifts back and forth, it is possible to keep the attitude and prevent the fall of the main body housing. Besides, even if the weight of the dust collection portion becomes large because of the dust collection, the weight balance of the main body housing  2  is kept, so that it is possible to prevent more surely the fall of the main body housing. 
         [0028]    Besides, according to the present invention, the air flow path is disposed on one side and the control board is disposed on the other side with respect to the dust collection portion; the air flow path and the control board are gathered and disposed. In this way, it is possible to shorten the air flow path and achieve the small size of the main body housing by reducing wirings and the like. Besides, the air flow path is far from the control board; accordingly, even if the air flow leaks, it is possible to reduce the adhering of the dust to the control board and reduce the malfunction of the control circuit. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0029]    [ FIG. 1 ] is a perspective view showing a cleaning robot according to an embodiment of the present invention. 
           [0030]    [ FIG. 2 ] is a side sectional view showing the cleaning robot according to the embodiment of the present invention. 
           [0031]    [ FIG. 3 ] is a bottom view showing the cleaning robot according to the embodiment of the present invention. 
           [0032]    [ FIG. 4 ] is a side sectional view showing a state in which a dust collection portion of the cleaning robot according to the embodiment of the present invention is demounted. 
           [0033]    [ FIG. 5 ] is a perspective view showing a motor unit of the cleaning robot according to the embodiment of the present invention. 
           [0034]    [ FIG. 6 ] is a front view showing the motor unit of the cleaning robot according to the embodiment of the present invention. 
           [0035]    [ FIG. 7 ] is a top view showing the motor unit of the cleaning robot according to the embodiment of the present invention. 
           [0036]    [ FIG. 8 ] is a side view showing the motor unit of the cleaning robot according to the embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0037]    Hereinafter, an embodiment of the present invention is described with reference to the drawings.  FIG. 1  is a perspective view showing a cleaning robot according to the embodiment of the present invention. A cleaning robot  1  has a main body housing  2  which has a circular shape when viewed from top and drives drive wheels  29  (see  FIG. 2  as to both) by means of a battery  14  to move by itself. An upper surface of the main body housing  2  is provided with a lid portion  3  that is opened and closed when a dust collection portion  30  (see  FIG. 2 ) is put in and taken out. 
         [0038]      FIG. 2  and  FIG. 3  show a side sectional view and a bottom view of the cleaning robot  1 , respectively. The main body housing  2  is provided with a pair of drive wheels  29  that protrude from a bottom surface and rotate on a horizontal rotary shaft  29   a.  The rotary shaft  29   a  of the drive wheels  29  is disposed on a center line C of the main body housing  2 . When both drive wheels  29  rotate in the same direction, the main body housing  2  moves forward and backward, while when both drive wheels  29  rotate in directions opposite to each other, the main body housing  2  rotates about the center line C. 
         [0039]    A suction opening  6  is disposed through a front portion of the main body housing  2  that is situated in front in a traveling direction when cleaning is performed. The suction opening  6  is formed to oppose a floor surface F by means of an open surface of a recessed portion  8  that is formed to be recessed on the bottom surface of the main body housing  2 . A rotary brush  9 , which rotates on a horizontal rotary shaft, is disposed in the recessed portion  8 , and side brushes  10 , which rotate on a vertical rotary shaft, are disposed on both sides of the recessed portion  8 , respectively. 
         [0040]    A roller-shaped front wheel  27  is disposed in front of the recessed portion  8 . A rear end of the main body housing  2  is provided with a rear wheel  26  that includes a universal wheel. As described later, the main body housing  2  disperses a weight in a back-forth direction with respect to the drive wheels  29  disposed at the center; the front wheel  27  goes away from the floor surface F, while the rotary brush  9 , the drive wheels  29  and the rear wheel  26  contact the floor surface F to perform the cleaning. Because of this, dust present in front in the traveling path can be guided to the suction opening  6  without being blocked by the front wheel  27 . The front wheel  27  moves onto a step that appears on the traveling path, so that the main body housing  2  can easily go over the step. 
         [0041]    A floor surface detection sensor  18  for detecting the floor surface F is disposed in front of the front wheel  27 . Similar floor surface detection sensors  19  are disposed in front of both drive wheels  29 . If a step of a downward stairway or the like appears in the traveling path, the drive wheels  29  are stopped because of detection by the floor surface detection sensor  18 . Besides, if the floor surface detection sensor  18  malfunctions, the drive wheels  29  are stopped because of detection by the floor surface detection sensors  19 . 
         [0042]    A rear end of a circumferential surface of the main body housing  2  is provided with a charge terminal  4  for charging the battery  14 . The main body housing  2  moves by itself to return to a charge stand  40  installed in a room, and the charge terminal  4  comes into contact with a terminal portion  41  disposed on the charge stand  40  to charge the battery  14 . The charge stand  40  connected to commercial power supply is usually installed along a side wall S of the room. 
         [0043]    The main body housing  2  is provided therein with the dust collection portion  30  that collects dust. The dust collection portion  30  is disposed on the rotary shaft  29   a  of the drive wheels  29  and housed in a dust collection chamber  39  that is disposed in the main body housing  2 . The dust collection chamber  39  includes an isolated chamber whose circumferential surfaces in four directions and bottom surface are covered, and is formed to extend in a left-right direction to partition an inside of the main body housing  2 . Wall surfaces of the dust collection chamber  39  are closed except for a front wall that extends in a longitudinal direction. The dust collection chamber  39  is provided, through the front wall thereof, with a first air inhaling path  11  that communicates with the recessed portion  8  and a second air inhaling path  12  that is disposed over the recessed portion  8  and communicates with a motor unit  20  described later. 
         [0044]    The dust collection portion  30  is disposed on the center line C of the main body housing  2 , and can be put into and taken out with the lid portion  3  of the main body housing  2  opened as shown in  FIG. 4 . The dust collection portion  30  is provided with an upper cover  32  that has a filter  33  on an upper surface of a bottomed cylindrical dust collection vessel  31 . The upper cover  32  engages with the dust collection vessel  31  by means of a movable engagement portion  32   a,  opens and closes an upper surface of the dust collection vessel  31  by means of operation of the engagement portion  32   a.  In this way, it is possible to dump the dust accumulated in the dust collection vessel  31 . 
         [0045]    The dust collection vessel  31  is provided, through a circumferential surface thereof, with a flow-in path  34  whose tip end is equipped with a flow-in opening  34   a  to communicate with the first air inhaling path  11 . The dust collection vessel  31  is provided therein with a flow-in portion  34   b  that communicates with the flow-in path  34  to guide an air flow downward by means of a bend. In this way, it is possible to make large dust and heavy-weight dust easily accumulate in a bottom portion of the dust collection vessel  31 . The upper cover  32  is provided, through a circumferential surface thereof, with a flow-out path  35  whose tip end is equipped with a flow-out opening  35   a  to communicate with the second air inhaling path  12 . 
         [0046]    The flow-in opening  34   a  and the flow-out opening  35   a  are provided therearound with a packing (not shown) which comes into tight contact with the front wall of the dust collection chamber  39 . In this way, the dust collection chamber  39  housing the dust collection portion  30  is tightly closed. The opening surface of the flow-in opening  34   a,  the opening surface of the flow-out opening  35   a,  and the front wall of the dust collection chamber  39  are each formed to have an inclined surface, so that it is possible to prevent the packing from being deteriorated by sliding when the dust collection portion  30  is put in and taken out. 
         [0047]    A control board  15  is disposed in an upper portion behind the dust collection chamber  39  in the main body housing  2 . The control board  15  is provided with a control circuit that controls each portion of the cleaning robot  1 . The battery  14  freely mountable and demountable is disposed in a lower portion behind the dust collection chamber  39 . The battery  14  is charged by the charge stand  40  via the charge terminal  4  and supplies electric power to each portion of the control board  15 , the drive wheels  29 , the rotary brush  9 , the side brushes  10 , the electric fan  22  and the like. 
         [0048]    The motor unit  20  is disposed in the front portion of the main body housing  2 .  FIG. 5 ,  FIG. 6 ,  FIG. 7  and  FIG. 8  show a perspective view, top view, front view, and side view of the motor unit  20 , respectively. The motor unit  20  includes a housing  21  formed of a resin and the electric fan  22  housed in the housing  21 . The electric fan  22  is formed of a turbo-fan that is covered by a motor case  22   a.    
         [0049]    The motor case  22   a  of the electric fan  22  is provided, through one end in a shaft direction thereof, with an air inhaling opening (not shown) and provided, through a circumferential surface thereof, with two air exhaling openings (not shown). The housing  21  is provided, through a front surface thereof, with an opening portion  23  that opposes the air inhaling opening of the motor case  22   a.  The electric fan  22  of the housing  21  is provided, on both sides thereof, with a first air exhaling path  24   a  and a second air exhaling path  24   b  that communicate with the air exhaling openings of the motor case  22   a,  respectively. The first and second air exhaling paths  24   a,    24   b  communicate with an air exhaling opening  7  (see  FIG. 2 ) provided through the upper surface of the main body housing  2 . 
         [0050]    Because of this, the first and second air exhaling paths  24   a,    24   b  and the second air inhaling path  12  (see  FIG. 2 ) compose air flow paths that connect the dust collection portion  30  and the air exhaling opening  7  with each other. Besides, the first air inhaling path  11  (see  FIG. 2 ) composes an air flow path that connects the suction opening  6  and the dust collection portion  30  with each other. 
         [0051]    In this way, the air flow paths including the electric fan  22  are gathered in front of the dust collection chamber  39  and disposed in the front portion of the main body housing  2 , so that it is possible to shorten the air flow paths. Besides, the control board  15  and the battery  14  are gathered behind the dust collection chamber  39  and disposed in the rear portion of the main body housing  2 , so that it is possible to reduce wirings and the like. Accordingly, it is possible to achieve the small size of the main body housing  2 . Besides, the air flow paths are far from the control board  15 ; accordingly, even if the air flow leaks, it is possible to alleviate the dust adhering to the control board  15  and to reduce the malfunction of the control circuit. 
         [0052]    Besides, the heavy-weight electric fan  22  and battery  14  are dispersed and disposed in front of and behind the rotary shaft  29   a  of the drive wheels  29 ; accordingly, the weight is balanced and distributed in a back-forth direction of the main body housing  2  with respect to the rotary shaft  29   a  that passes the center line C of the main body housing  2 . Because of this, the rotary brush  9 , the drive wheels  29  and the rear wheel  26  contact the floor surface and the main body housing  2  moves forward and backward; and even if the rotary brush  9  or the rear wheel  26  loses its foothold because of a step or the like, it is possible to prevent a fall of the main body housing  2 . 
         [0053]    The dust collection portion  30  is disposed on the center line C; accordingly, even if the weight of the dust collection portion  30  changes because of the collecting and dumping of dust, it is possible to keep the weight balance of the main body housing  2 . In the meantime, the weight of the electric fan  22  is large; accordingly, it is possible to achieve a better weight balance by disposing the control board  15  and the battery  14  behind the rotary shaft  29   a  of the drive wheels  29 . 
         [0054]    The first air exhaling path  24   a  is provided with an ion generation apparatus  28  that has a pair of electrodes  28   a.  A voltage having an a.c. waveform or an impulse waveform is applied to the electrodes  28   a,  and ions generated by a corona discharge from the electrodes  28   a  are emitted into the first air exhaling path  24   a.    
         [0055]    A positive voltage is applied to one electrode  28   a,  so that hydrogen ions due to the corona discharge combine with moisture in the air to generate positive ions formed mainly of H + (H 2 O) m . A negative voltage is applied to the other electrode  28   a,  so that oxygen ions due to the corona discharge combine with moisture in the air to generate negative ions formed mainly of O 2   − (H 2 O) n . Here, m, n are each an arbitrary natural number. H +(H   2 O) m  and O 2   − (H 2 O) n  condensate on surfaces of floating germs and odor components in the air to capture them. 
         [0056]    And as indicated by formulas (1) to (3), [▪OH] (hydroxyl radical) and H 2 O 2  (hydrogen peroxide), which are active species, are made to condensate and occur on surfaces of microbes and the like by means of collision to break the floating germs and odor components. Here, m′, n′ are each an arbitrary natural number. Accordingly, by generating the positive ions and negative ions and sending them out from the air exhaling opening  7  (see  FIG. 2 ), it is possible to perform the germ removal and deodorization of the room. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0057]    Besides, a lower portion of the first air exhaling path  24   a  is provided with a return opening  25  whose front surface is opened. An upper portion of the return opening  25  is covered by a protrusion portion  25   a  that protrudes from the front surface of the housing  21 , and an opening surface is formed to be a curved surface along a wall surface of the recessed portion  8  (see  FIG. 2 ). In this way, the return opening  25  is opened to the recessed portion  8  via a hole portion (not shown) disposed through the wall surface of the recessed portion  8 , so that a portion of the air flow, which flows in the first air exhaling path  24   a  and contains ions, is guided to the air inhaling side. 
         [0058]    In the cleaning robot  1  having the above structure, when a cleaning operation is instructed, the electric fan  22 , the ion generation apparatus  28 , the drive wheels  29 , the rotary brush  9 , and the side brushes  10  are driven. In this way, the rotary brush  9 , the drive wheels  29 , and the rear wheel  26  contact the floor surface F and the main body housing  2  moves by itself in a predetermined cleaning area, so that the air flow containing dust on the floor surface F is sucked from the suction opening  6 . At this time, the dust on the floor surface F is stirred up and guided into the recessed portion  8  because of rotation of the rotary brush  9 . Besides, dust on both sides of the suction opening  6  is guided into the suction opening  6  because of rotation of the side brushes  10 . 
         [0059]    The air flow sucked from the suction opening  6  flows backward in the first air inhaling path  11  as indicated by an arrow A 1  and flows into the dust collection portion  30  via the flow-in opening  34   a.  The air flow flowing into the dust collection portion  30  has the dust collected by the filter  33  and flows out from the dust collection portion  30  via the flow-out opening  35   a.  In this way, the dust is collected and accumulated in the dust collection vessel  31 . The air flow flowing out from the dust collection portion  30  flows forward in the second air inhaling path  12  as indicated by an arrow A 2  and flows into the electric fan  22  of the motor unit  20  via the opening portion  23 . 
         [0060]    The air flow passing through the electric fan  22  flows into the first air exhaling path  24   a  and the second air exhaling path  24   b,  and the air flow flowing in the first air exhaling path  24   a  contains ions. And the air flow containing the ions is exhaled upward and backward in an oblique direction as indicated by an arrow A 3  from the air exhaling opening  7  disposed through the upper surface of the main body housing  2 . In this way, the room is cleaned, and the ions contained in the exhaled air from the main body housing  2  moving by itself spread throughout the room to perform the germ removal and deodorization of the room. At this time, the air flow is exhaled upward from the air exhaling opening  7 ; accordingly, it is possible to prevent the dust on the floor surface F from being stirred up and to improve a cleanliness degree of the room. 
         [0061]    A portion of the air flow flowing in the first air exhaling path  24   a  is guided to the recessed portion  8  via the return opening  25  as indicated by an arrow A 4 . Because of this, the air flow guided from the suction opening  6  to the first air inhaling path  11  contains ions. In this way, it is possible to perform the germ removal and deodorization of the dust collection vessel  31  and filter  33  of the dust collection portion  30 . 
         [0062]    Besides, in a case where the main body housing  2  reaches a circumferential edge of the cleaning area or collides with an obstacle in the traveling path, the drive wheels  29  are stopped. And, both drive wheels  29  rotate in directions opposite to each other, and the main body housing  2  rotates about the center line C to change its direction. In this way, it is possible to make the main body housing  2  move by itself in the entire cleaning area and move by itself avoiding the obstacle. In the meantime, it is also possible to make the main body housing  2  move backward by rotating backward both drive wheels  29  that are rotating forward so far. 
         [0063]    If the main body housing  2  stops suddenly before a step of a downward stairway or the like when moving forward and backward, the center of gravity shifts back and forth. Here, the weight of the main body housing  2  is balanced and distributed in front of and behind the drive wheels  29 ; accordingly, the fall of the main body housing  2  is prevented. Besides, the dust collection portion  30  is disposed over the rotary shaft  29   a  of the drive wheels  29 ; accordingly, even if the weight becomes large because of the dust collection, the weight balance of the main body housing  2  is kept. 
         [0064]    When the cleaning ends, the main body housing  2  moves by itself and returns to the charge stand  40 . In this way, the charge terminals  4  come into contact with the terminal portions  41  to charge the battery  14 . 
         [0065]    Besides, when the main body housing  2  is in the return state, it is possible, by setting, to drive the electric fan  22  and the ion generation apparatus  28  during the charge and after the charge ends. In this way, the air flow containing the ions is sent out upward and backward from the air exhaling opening  7 . The charge terminals  4  are disposed at the rear end of the main body housing  2 ; accordingly, the air flow containing the ions flows toward the charge stand  40  and ascends along the side wall S. This air flow flows along a ceiling wall and side walls opposite to each other of the room. Accordingly, the ions spread throughout the room and can improve the germ removal and deodorization effects. 
         [0066]    According to the present invention, the electric fan  22  is disposed on one side and the battery  14  is disposed on the other side with respect to the dust collection portion  30  that is disposed over the rotary shaft  29   a  of the drive wheels  29 ; accordingly, the weight of the main body housing  2  is balanced and distributed in front of and behind the drive wheels  29 . In this way, even if the main body housing  2  moving forward and backward stops suddenly before the step and the center of gravity shifts back and forth, it is possible to keep an attitude and prevent the fall of the main body housing  2 . Besides, even if the weight of the dust collection portion  30  becomes large because of the dust collection, the weight balance of the main body housing  2  is kept, so that it is possible to prevent more surely the fall of the main body housing  2  from the step. 
         [0067]    Besides, the rotary shaft  29   a  of the drive wheels  29  may be deviated from the center line C of the main body housing  2  and disposed; however, it is more desirable that the rotary shaft  29   a  is disposed on the center line C as in the present embodiment. In this way, the weight of the main body housing  2  is balanced and distributed in front of and behind the center, so that it is possible to prevent more surely the fall of the main body housing  2  from the step. 
         [0068]    Besides, the rotary shaft  9  disposed at the suction opening formed in front of the drive wheels  29 , the rear wheel  26  disposed behind the drive wheels  29 , and the drive wheels  29  contact the floor surface and the main body housing  2  move by itself on the floor surface F; accordingly, the dust in front in the traveling path can be guided to the suction opening  6  without being blocked. If the main body housing  2  moves forward and stops suddenly, the center of gravity of the main body housing  2  shifts forward, and the rotary brush  9  is deformed, so that the main body housing  2  is inclined forward. Here, the weight of the main body housing  2  is distributed back and forth; accordingly, the main body housing  2  returns to the original attitude. Accordingly, even if the main body housing  2  loses its foothold in front of the suction opening  6  and is easily inclined forward at the sudden stop, it is possible to prevent the fall from the step. 
         [0069]    Besides, the control board  15  is disposed on the same side as the battery  14  with respect to the dust collection portion  30 ; accordingly, by disposing the heavy-weight electric fan  22  in front and disposing the control board  15  and the battery  14  behind, it is possible to obtain a better weight balance in front of and behind the drive wheels  29 . Accordingly, it is possible to prevent more surely the fall of the main body housing  2  from the step. 
         [0070]    Besides, the air flow paths (first and second air inhaling paths  11 ,  12  and first and second air exhaling paths  24   a,    24   b ) are disposed in front of the dust collection portion  30 , and the control board  15  is disposed behind the dust collection portion  30 . Because of this, the air flow paths and the control board  15  are gathered and disposed. In this way, it is possible to shorten the air flow paths and achieve the small size of the main body housing  2  by reducing the wirings and the like. Besides, the air flow paths are far from the control board  15 ; accordingly, even if the air flow leaks, it is possible to alleviate the dust adhering to the control board  15  and to reduce the malfunction of the control circuit. 
         [0071]    Besides, the dust collection chamber  39  extends in one direction to partition the inside of the main body housing  2   a;  accordingly, it is possible to easily isolate the air flow paths from the control board  15 . Besides, the first and second air inhaling paths  11 ,  12  are disposed through the front wall of the dust collection chamber  39  that extends in the longitudinal direction, while the other wall surfaces are closed. In this way, even if an air flow leak occurs through the flow-in opening  34   a  and flow-out opening  35   a,  the dust is confined in the dust collection chamber  39 . Accordingly, it is possible to further prevent adhering of the dust to the control board  15 . 
         [0072]    Besides, the dust collection vessel  31  is provided with the flow-in opening  34   a,  and the upper cover  32  having the filter  33  is provided with the flow-out opening  35   a;  accordingly, by opening the upper cover  32 , it is possible to easily dump the dust accumulated in the dust collection vessel  31 . 
         [0073]    Besides, the opening surfaces of the flow-in opening  34   a  and flow-out opening  35   a  are formed to have the inclined surface, and the packing is disposed on the circumferential rims of the opening surfaces; accordingly, it is possible to prevent the packing from being deteriorated by the sliding when the dust collection portion  30  is put in and taken out. 
         [0074]    In the present embodiment, the electric fan  22  is disposed in front of the dust collection portion  30 , and the battery  14  and the control board  15  are disposed behind the dust collection portion  30 ; however, the electric fan  22  may be disposed on one side and the battery  14  and the control board  15  may be disposed on the other side with respect to the dust collection portion  30 . 
         [0075]    Besides, the air flow paths are disposed in front of the dust collection portion  30  and the control board  15  is disposed behind the dust collection portion  30 ; however, the air flow paths may be disposed on one side and the control board  15  may be disposed on the other side with respect to the dust collection portion  30 . 
       INDUSTRIAL APPLICABILITY 
       [0076]    The present invention is usable for a cleaning robot that moves by itself on a floor surface. 
       REFERENCE SIGNS LIST 
       [0077]      1  cleaning robot 
         [0078]      2  main body housing 
         [0079]      3  lid portion 
         [0080]      4  charge terminal 
         [0081]      6  suction opening 
         [0082]      7  air exhaling opening 
         [0083]      8  recessed portion 
         [0084]      9  rotary brush 
         [0085]      10  side brush 
         [0086]      11  first air inhaling path 
         [0087]      12  second air inhaling path 
         [0088]      14  battery 
         [0089]      15  control board 
         [0090]      18 ,  19  floor surface detection sensors 
         [0091]      20  motor unit 
         [0092]      21  housing 
         [0093]      22  electric fan 
         [0094]      23  opening portion 
         [0095]      24   a  first air exhaling path 
         [0096]      24   b  second air exhaling path 
         [0097]      25  return opening 
         [0098]      28  ion generation apparatus 
         [0099]      29  drive wheel 
         [0100]      30  dust collection portion 
         [0101]      31  dust collection vessel 
         [0102]      32  upper cover 
         [0103]      33  filter 
         [0104]      34  flow-in path 
         [0105]      35  flow-out path 
         [0106]      40  charge stand 
         [0107]      41  terminal portion