Patent Publication Number: US-2020275811-A1

Title: Wheel support structure for self-propelled electronic device

Description:
TECHNICAL FIELD 
     The present invention relates to a wheel support structure for a self-propelled electronic device. 
     BACKGROUND ART 
     As a traditional self-propelled electronic device, for example, PTL 1 discloses a self-propelled transport vehicle comprising the following members; front and rear body framings; a plurality of casters supporting the body framings; right and left frames provided between the front body framing and the rear body framing; and a pair of drive wheels supporting the right and left frames. Each of the frames of this self-propelled transport vehicle is swingably joined with one of the front and rear body framings through an oscillation shaft extending in a right-left direction and also is joined with the other body framing through a junction shaft so as to be swingable up and down. Each of the body framings and each of the frames have a compression spring provided therebetween that allows each of the junction shafts to penetrate through the compression spring so that the drive wheels are pushed downward by the compression springs through the frames. In case a floor surface is uneven where this self-propelled transport vehicle travels on, the drive wheels are configured to go up and down with use of the oscillation shafts as fulcrum shafts in response to the unevenness of the floor surface and to rotate along the uneven floor surface. 
     Furthermore, PTL 2 discloses a self-propelled electronic device including wheel support structures that cause drive wheels to protrude downward from a bottom part of a housing using tension springs. The self-propelled electronic device has a configuration in which the drive wheels protrude downward through right and left holes in the bottom part of the housing. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] Japanese Unexamined Patent Application Publication No. H09-286337 
         [PTL 2] Japanese Unexamined Patent Application Publication No. 2016-143231 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In a self-propelled electronic device including wheel support structures that use springs to cause drive wheels to protrude outward through holes in the bottom part of the housing as disclosed in PTL 2, the drive wheels are biased by the springs so as to be always protruding outward. Furthermore, this wheel support structures maintain strong biasing force of the springs to enable the drive wheels to protrude outward with force strong enough to climb a floor level difference. That is, the biasing force of the springs toward the drive wheels is maintained so strong as to give a protrusion length greater than a protrusion length necessary for the drive wheels to climb the floor level difference (i.e., an elevation step, an elevation change, or a floor step). 
     As such, if a child toys around with the self-propelled electronic device by turning it over and pushing or spinning any of the drive wheels with a finger, for example, the drive wheel may pop out through the corresponding hole with a great protrusion amount (strong force) In such a case, the child may get injured clue to the drive wheel scratching the finger or the hole and the drive wheel catching the finger therebetween. 
     The present invention was made in view of the above-described problem, and it is an object of the present invention to provide a wheel support structure for a self-propelled electronic device that prevents, in consideration of safety, a drive wheel from popping out with strong force when the drive wheel is caused to protrude outward. 
     Solution to Problem 
     The present invention therefore provides a wheel support structure for a self-propelled electronic device, comprising: a drive wheel supporting a housing to cause the housing to run on a floor surface; a swinging support unit rotatably supporting the drive wheel and pivoting the drive wheel to a bottom part of the housing in such a way that the drive wheel is swingable upward and downward about a swinging axle; and a biasing mechanism including a biasing member configured to give a downward bias to the swinging support unit to cause the drive wheel to swing downward, wherein 
     the biasing mechanism gives the downward bias to the swinging support unit using the biasing member while the housing is on the floor, and release the downward bias while the drive wheel is off the floor surface. 
     Advantageous Effects of Invention 
     According to the wheel support structure for the self-propelled electronic device of the present invention, the bias from the biasing member toward the swinging support unit is released while the drive wheel is off the floor surface as a result of the housing being lifted or turned over. That is, the drive wheel becomes free from the load from the biasing member once the drive wheel protrudes from the bottom part of the housing to a certain degree. This reduces the risk of injury to a child, for example, due to the drive wheel popping out through a hole in the housing with a great protrusion amount (strong force) and scratching the child&#39;s finger or the hole and the drive wheel catching the child&#39;s finger therebetween, when the child is toying around with the self-propelled electronic device by turning it over and pushing or spinning the drive wheel with the finger. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of external appearance of a self-propelled electronic device including a wheel support structure according to the present invention. 
         FIG. 2  is a bottom view of the self-propelled electronic device illustrated in  FIG. 1 . 
         FIG. 3  is a vertical cross-sectional view of the self-propelled electronic device illustrated in  FIG. 1  taken along a front-back direction. 
         FIGS. 4(A) to 4(C)  are each an explanatory diagram of a wheel support structure according to a first embodiment, among which  FIG. 4(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 4(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 4(C)  illustrates a state in which the drive wheel is off the floor surface. 
         FIGS. 5(A) to 5(C)  are each an explanatory diagram of a wheel support structure according to a second embodiment, among which  FIG. 5(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 5(B)  illustrates a state in which the drive wheel is climbing a floor level difference, arid  FIG. 5(C)  illustrates a state in which the drive wheel is off the floor surface. 
         FIGS. 6(A) to 6(C)  are each an explanatory diagram of a wheel support structure according to a third embodiment, among which  FIG. 6(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 6(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 6(C)  illustrates a state in which the drive wheel is off the floor surface. 
         FIGS. 7(A) to 7(C)  are each an explanatory diagram of a wheel support structure according to a fourth embodiment, among which  FIG. 7(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 7(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 7(C)  illustrates a state in which the drive wheel is off the floor surface. 
         FIGS. 8(A) to 8(C)  are each an explanatory diagram of a wheel support structure according to a fifth embodiment, among which  FIG. 8(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 8(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 8(C)  illustrates a state in which the drive wheel is off the floor surface. 
         FIGS. 9(A) to 9(C)  are each an explanatory diagram of a wheel support structure according to a sixth embodiment, among which  FIG. 9(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 9(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 9(C)  illustrates a state in which the drive wheel is off the floor surface. 
         FIGS. 10(A) to 10(C)  are each an explanatory diagram of a wheel support structure according to a seventh embodiment, among which  FIG. 10(A)  illustrates a state which a drive wheel is running on a floor surface,  FIG. 10(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and.  FIG. 10(C)  illustrates a state in which the drive wheel is off the floor surface. 
         FIGS. 11(A) to 11(C)  are each an explanatory diagram of a wheel support structure according to an eighth embodiment, among which  FIG. 11(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 11(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 11(C)  illustrates a state in which the drive wheel is off the floor surface. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes embodiments with reference to the drawings taking, as an example, a case where the self-propelled electronic device according to the present invention is a self-propelled vacuum cleaner. However, the self-propelled electronic device according to the present invention is not limited to the self-propelled vacuum cleaner. 
     First Embodiment 
       FIG. 1  is a perspective view of external appearance of a self-propelled electronic device including a wheel support structure according to the present invention.  FIG. 2  is a bottom view of the self-propelled electronic device illustrated in  FIG. 1 .  FIG. 3  is a vertical cross-sectional view of the self-propelled electronic device illustrated in  FIG. 1  taken along a front-back direction.  FIGS. 4(A) to 4(C)  are each an explanatory diagram of the wheel support structure according to a first embodiment, among which  FIG. 4(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 4(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 4(C)  illustrates a state in which the drive wheel is off the floor surface. It should be noted that the front-back direction in the following description means a direction collinear with a straight line along which the self-propelled vacuum cleaner moves straight ahead on a floor surface G, and a left-right direction means a direction collinear with a horizontal straight line orthogonal to the front-back direction. 
     &lt;Configuration of Self-Propelled Vacuum Cleaner&gt; 
     As illustrated in  FIGS. 1 to 3 , a self-propelled vacuum cleaner  1  includes wheel support structures  3 L according to the first embodiment and a housing  2  having a disc-like shape. It should be noted that the housing  2  is not limited to a circular, disc-like shape as in the case of the first embodiment but may for example have an elliptical shape or a polygonal shape in a plan view. 
     The housing  2  includes a circular top plate. The top plate includes a top plate front part  2   b   1  being a front of the top plate, and a lid part  2   b   2  being a middle and a rear of the top plate. The lid part  2   b   2  opens upward by pivoting about a hinge, not shown, disposed on a side thereof at a boundary between the lid part  2   b   2  and the top plate front part  2   b   1 . A front end of the top plate front part  2   b   1  has a plurality of air holes  2   b   11  for releasing heat from a circuit board (not shown) disposed inside. 
     The housing  2  also includes an annular side plate and a bottom plate  2   a.  The housing  2  further includes an inner structural wall  2   d  as illustrated in  FIG. 3 . The bottom plate  2   a  has a front end  2   a  rising frontward, and thus providing a curved surface or an inclined surface (see  FIG. 3 ). 
     The side plate includes an arc-shaped side plate front half  2   c   1  and an arc-shaped side plate rear half  2   c   2 . The side plate front half  2   c   1  is movably engaged with the inner structural wall  2   d  with an elastic material, not shown, therebetween in order to function as a bumper. An obstacle contact sensor (not shown) that detects collision of the side plate front half  2   c   1  is provided inside the side plate front half  2   c   1 . Furthermore, ultrasonic receivers  14 A are disposed in three positions on the side plate front half  2   c   1 —a front position, a left front position, and a right front position, and ultrasonic transmitters  14 B are disposed in two (2) positions between the three positions of the ultrasonic receivers  14 A. 
     Furthermore, a guide signal receiver  24  and a charging connector  13  are disposed in respective positions on a front surface of the housing  2  that are visible from the exterior. 
     The housing  2  has a suction port  31  in the bottom plate forming a bottom part and an exhaust port  32  extending obliquely upward in a rear part. A dust collection section  15  and an electric air blower (not shown) are disposed inside the housing  2 . The dust collection section  15  collects dust from a room being vacuumed. The dust collection section  15  includes a dust container  15   a  and a dust collecting filter  15   b.  The dust container  15   a  has an inlet port leading to an inlet channel in communication with the suction port  31  and an exhaust port leading to a duct  114  in communication with the electric air blower (not shown). 
     A front half of a bottom face of the self-propelled vacuum cleaner  1  is provided with a rotary brush  9  disposed behind the suction port  31 , a side brush  10  disposed diagonally in front of the suction port  31  to the left, a side brush  10  disposed diagonally in front of the suction port  31  to the right, and a drive wheel unit (see  FIGS. 4(A) to 4(C) ) including a drive wheel disposed diagonally behind the suction port  31  to the left (a left drive wheel  22 L) and a drive wheel disposed diagonally behind the suction port  31  to the right (a right drive wheel  22 R). It should be noted that lower portions of the respective drive wheels protrude outward through left and right holes  2   a   11  in the bottom plate  2   a  of the housing  2 . 
     The rotary brush  9  and the side brushes  10  are driven to rotate by a brush motor (not shown). A rear half of the bottom face is provided with a pivotable rear wheel  26  in a middle position in the left-right direction. The rear wheel  26  is rotatable. It should be noted that  FIGS. 2 and 3  show the rear wheel  26  pivoted forward by 180° using a dashed-two dotted line. 
     The self-propelled vacuum cleaner  1  has floor surface detection sensors  18  disposed in four (4) positions in total on the bottom part of the housing  2 , four (4) positions are at front and rear ends in the front-back direction, and at axial centers of the left and right brushes  10 . 
     Furthermore, a circuit board  11 S is disposed in a front half of the self-propelled vacuum cleaner  1 , and a rechargeable battery  12  and an ion generator  120  are disposed in a rear half of the self-propelled vacuum cleaner  1 . 
     The self-propelled vacuum cleaner  1  cleans a floor surface on which the self-propelled vacuum cleaner  1  has been placed (a surface for the self-propelled vacuum cleaner  1  to run on) by sucking air including dust from the floor surface and exhausting the air from which the dust has been removed while autonomously running on the floor surface. The self-propelled vacuum cleaner  1  runs while autonomously avoiding an obstacle detected by any of the ultrasonic receivers  14 A serving as obstacle detectors. The self-propelled vacuum cleaner  1  also runs while autonomously avoiding a drop below the level of the floor surface by detecting such the drop using the floor surface detection sensors  18 . The self-propelled vacuum cleaner  1  has a function of autonomously returning to a charging dock, not shown, once the self-propelled vacuum cleaner  1  finishes cleaning. 
     &lt;Wheel Support Structure&gt; 
     As illustrated in  FIGS. 2 to 4 (C), the self-propelled vacuum cleaner  1  according to the first embodiment includes the left and right wheel support structures  3 L, of which the right wheel support structure is not shown, supporting the left and right drive wheels  22 L and  22 R, respectively. 
     The following describes the left wheel support structure  3 L. The left and right wheel support structures are symmetrical to each other with respect to a center line P (see  FIG. 2 ) extending in the front-back direction of the self-propelled vacuum cleaner  1 . Description of the right wheel support structure is therefore omitted. 
     The wheel support structure  3 L includes the drive wheel  22 L, a swinging support unit  21 L, and a biasing mechanism  23  including a biasing member  23   a.  The drive wheel  22 L supports the housing  2  and causes the housing  2  to run on the floor surface. The swinging support unit  21 L rotatably supports the drive wheel  22 L and pivots (mounts) the drive wheel  22 L to the bottom plate  2   a  of the housing  2  in such a way that the drive wheel  22 L is swingable upward and downward direction indicated by arrow A) about a swinging axle  21   a  extending in the left-right direction. The biasing member  23   a  gives the downward bias to the swinging support unit  21 L to cause the drive wheel  22 L to swing downward. 
     The wheel support structure  3 L also includes, as described below, a fixing section that is provided. on the bottom plate  2   a  and fixes the swinging support unit  21 L and the biasing mechanism  23  to the bottom plate  2   a  of the housing  2 . 
     The fixing section provided on the bottom plate  2   a  includes a swinging axle mounting rib  2   f   1  provided in the vicinity of a front end of the hole  2   a   11  in the bottom plate  2   a  and a biasing member mounting rib  2   f   2  provided in front of the swinging axle mounting rib  2   f   1  on the bottom plate  2   a.  It should be noted that an abutment rib  2   f   3  that comes in abutment with the swinging support unit  21 L to restrict the swinging support unit  21 L from swinging upward may be provided between the swinging axle mounting rib  2   f   1  and the biasing member mounting rib  2   f   2  on the bottom plate  2   a.    
     The swinging support unit  21 L includes a swinging arm  21   b  and the swinging axle  21   a  attached to a lower surface of one end of the swinging arm  21   b.  The swinging support unit  21 L is attached to the bottom part  2   a  of the housing  2  in a swingable manner about the swinging axle  21   a  in an direction fro downside to upside (the direction indicated by arrow A). 
     The drive wheel  22 L is rotatably attached to another end of the swinging arm  21   b,  and a projection  21   b   1  projecting upward is provided on an upper surface of the one end of the swinging arm  21   b.  The biasing member  23   a  pushes the projection  21   b   1 . It should be noted that the projection  21   b   1  is unnecessary as long as the swinging arm  21   b  has a total height enough to be pushed by the biasing member  23   a.    
     The swinging support unit  21 L may be further provided with a drive motor  21   c  and a rotational force transmitting mechanism (not shown) that transmits rotational force of an output shaft of the drive motor  21   c  to the drive wheel  22 L. In this case, for example, the rotational force transmitting mechanism is provided within the swinging arm  21   b  having a case shape, and the drive motor  21   c  is fixed to a side face of the swinging arm  21   b.    
     The rotational force transmitting mechanism for example has a configuration including an output gear, an input gear, and one or more transmission gears in meshing engagement with the output gear and the input gear. The output gear is fixed to the output shaft, which projects into the swinging arm  21   b  having a case shape, of the drive motor  21   c.  The input gear is fixed to a supporting shaft, which projects into the swinging arm  21   b,  of the drive wheel  22 L. The transmission gears are rotatably provided within the swinging arm  21   b.  Alternatively, the rotational force transmitting mechanism has a configuration including a first grooved pulley, a second grooved pulley, and a timing belt wound around the first and second grooved pulleys. The first grooved pulley is fixed to the output shaft, which projects into the swinging arm  21   b,  of the drive motor  21   c.  The second grooved pulley is fixed to the supporting shaft, which projects into the swinging arm  21   b,  of the drive wheel  22 L. It should be noted that the wheel support structure  3 L may have a configuration in which the rotational force transmitting mechanism reduces the rotational speed of the output shaft of the drive motor  21   c  or a configuration in which the drive motor  21   c  is able to adjust the rotational speed. 
     The drive wheel  22 L has a wheel  22 L 1 , the supporting shaft C fixed to a center hole of the wheel  22 L 1 , and a rubber tire  22 L 2  fitted in an outer periphery of the wheel  22 L 1 . It should be noted that an outer periphery of the rubber tire  22 L 2  has a tread pattern (see  FIGS. 2 and 3 ), which is omitted in  FIGS. 4(A) to 4(C) . 
     The biasing mechanism  23  gives the downward bias to the swinging support unit  21 L using the biasing member  23   a  while the housing  2  is on the floor surface G (see  FIGS. 4(A) and 4(B) ). The downward bias from the biasing member  23   a  toward the swinging support unit  21 L is released while the drive wheel  22 L is off the floor surface G (see  FIG. 4(C) ). 
     More specifically, the biasing member  23   a  according to the first embodiment is a compression spring having a proximal end  23   a   1  fixed to the biasing member mounting rib  2   f   2 , which is the fixing section provided within the housing  2 , and a distal end  23   a   2  enabled to abut the swinging support unit  21 L. In this case, the distal end  23   a   2  of the compression spring may be provided with an abutment member  23   b  that is to abut the projection  21   b   1  of the swinging arm  21   b  of the swinging support unit  21 L. Preferably, the abutment member  23   b  is made from a material (for example, rubber) that resists slipping against the projection  21   b   1  of the swinging arm  21   b.  In addition, the projection  21   b   1  may be microtextured for slip resistance in a surface thereof to be in contact with the abutment member  23   b.    
     The following describes operation of the wheel support structure  3 L with reference to  FIGS. 1 to 4 (C). 
     As illustrated in  FIG. 4(A) , the drive wheel  22 L is kept in a state reached after having swung upward relative to the bottom plate  2   a  of the housing  2  against the biasing force of the biasing member  23   a,  while the self-propelled vacuum cleaner  1  is moving straight ahead (moving forward) on the floor surface G in a direction indicated by arrow F. In this state, the one end of the swinging arm  21   b  is in abutment with the abutment rib  2   f   3  to restrict the swinging arm  21   b  from swinging upward, keeping a protrusion length H 1  of the drive wheel  22 L protruding from the bottom plate  2   a  of the housing  2  to a minimum. Furthermore, in the state illustrated in  FIG. 4(A) , the projection  21   b   1  of the swinging arm  21   b  pushes the biasing member  23   a  with the abutment member  23   b  therebetween, compressing the biasing member  23   a.    
     When the self-propelled vacuum cleaner  1  comes to a floor level difference that is higher than the level of the bottom plate  2   a  and that is high enough to touch the front end  2   a   1  (see  FIG. 3 ) of the bottom plate  2   a,  the front end  2   a   1  of the housing  2  abuts an edge of the floor level difference. The front end  2   a   1 , which is curved or inclined, of the housing  2  then slides over the edge of the floor level difference to climb the floor level difference as the self-propelled vacuum cleaner  1  further moves forward after having abutted the floor level difference. Thus, the housing  2  moves forward with the bottom plate  2   a  sliding on the edge of the floor level difference. While in sliding contact with the edge of the floor level difference, the bottom plate  2   a  of the housing  2  is slightly inclined with the front end  2   a   1  leaving the floor level difference. As a result, a gap between the floor surface G and a portion of the bottom plate  2   a  in the vicinity of the drive wheel  22 L increases as illustrated in  FIG. 4(B) . It should be noted that the bottom plate  2   a  of the housing  2  and the floor surface G are parallel to each other in  FIG. 4(B)  for convenience of illustration. 
     The biasing member  23  (compression spring), meanwhile, gives the downward bias to the swinging arm  21   b  of the swinging support unit  21 L to cause the drive wheel  22 L to greatly protrude downward relative to the bottom plate  2   a.  Thus, the drive wheel  22 L climbs the floor level difference S while greatly protruding downward. The biasing member  23  has not yet reached a fully stretched state, still biasing the drive wheel  22 L downward. Under this continued bias, the drive wheel  22 L protruding from the bottom plate  2   a  of the housing  2  reaches an approximately maximum protrusion length H 2 . 
     Once the self-propelled vacuum cleaner  1  is lifted and the drive wheel  22 L leaves the floor surface G as illustrated in  FIG. 4(C) , for example, the swinging support unit  21 L is no longer coupled to the biasing member  23   a.  Accordingly, the drive wheel  22 L swings downward due to its own weight to reach a maximum protrusion length H 3 , and the biasing member  23   a  reaches the fully stretched state. At the same time, a lower surface of the swinging arm  21   b  abuts a front end of the hole  2   a   11  in the bottom plate  2   a  of the housing  2  to restrict downward swing of the drive wheel  22 L to the maximum protrusion length H 3 . The drive wheel  22 L is stopped from swinging downward beyond the maximum protrusion length H 3  by the swinging arm  21   b  and an edge X of the hole  2   a   11  in the bottom plate  2   a  being in contact with each other (see  FIG. 4(C) ). Alternatively or additionally, a member for stopping the drive wheel  22 L may be attached to the bottom plate  2   a.    
     That is, according to the wheel support structure  3 L, it is possible to bias the swinging support unit  21 L using the biasing member  23   a  to cause the drive wheel  22 L to protrude downward to the extent that the drive wheel  22 L can climb the floor level difference S, and it is possible to release the bias from the biasing member  23   a  toward the swinging support unit  21 L when the drive wheel  22 L is to protrude further outward. 
     When the self-propelled vacuum cleaner  1  is turned over, therefore, the drive wheel  22 L protrudes outward until the drive wheel  22 L reaches a protrusion length equal to the protrusion length H 2  illustrated in  FIG. 4(B)  plus a margin (until the biasing member  23   a  reaches the fully stretched state) but is prevented from easily popping out beyond the approximately maximum protrusion length H 2  since the biasing force from the biasing member  23   a  is not applied when the drive wheel  22 L is to protrude further outward. This reduces the risk of injury to a child, for example, due to the drive wheel popping out through the hole in the bottom part with a great protrusion amount (strong force) and scratching the child&#39;s finger or the hole and the drive wheel catching the child&#39;s finger therebetween, when the child is toying around with the self-propelled electronic device by turning it over and pushing or spinning the drive wheel with the finger. 
     Second Embodiment 
       FIGS. 5(A) to 5(C)  are each an explanatory diagram of a wheel support structure according to a second embodiment, among which  FIG. 5(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 5(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 5(C)  illustrates a state in which the drive wheel is off the floor surface. It should be noted that elements in  FIGS. 5(A) to 5(C)  that are the same as the elements in  FIGS. 4(A) to 4(C)  are labelled using the same reference signs. 
     A wheel support structure  103 L according to the second embodiment is substantially the same as the wheel support structure  3 L according to the first embodiment other than including a biasing mechanism  123  having a different configuration from the biasing mechanism  23  in the first embodiment. The following mainly describes differences between the second embodiment and the first embodiment. 
     The biasing mechanism  123  in the second embodiment includes a stopper  123   c  that restricts stretching of the biasing member  23   a  in addition to the biasing member  23   a  (compression spring) having the abutment member  23   b  at the distal end thereof and having a proximal end  23   b   1  fixed to the biasing member mounting rib  2   f   2 . 
     The stopper  123   c  has a function of stopping the distal end (the abutment member  23   b  in this case) of the biasing member  23   a  from pushing the swinging support unit  21 L once the drive wheel  22 L protrudes downward from the bottom plate  2   a  of the housing  2  beyond a predetermined protrusion length. 
     It is sufficient that the stopper  123   c  be provided on the fixing section within the housing  2 . In the second embodiment, a proximal end of the stopper  123   c  being an L-shaped projection is attached to an upper end of the biasing member mounting rib  2   f   2 . A distal end of the stopper  123   c  bends downward for abutment with the abutment member  23   b.    
     Furthermore, in the second embodiment, a projection  121   b   1  of a swinging arm  121   b  of a swinging support unit  121 L has a vertical slit  121   b   11 , so that the distal end of the stopper  123   c  can pass through the slit  121   b   11  of the projection  121   b   1 . It should be noted that the abutment member  23   b  of the biasing mechanism  123  can abut both left and right sides of the slit  121   b   11  in the projection  121   b   1  of the swinging arm  121   b.    
     According to the wheel support structure  103 L having such a configuration, as in the case of the first embodiment, the swinging arm  121   b  is biased by the biasing member  23   a  to swing downward while the self-propelled vacuum cleaner is moving straight ahead on the floor surface G as illustrated in  FIG. 5(A) . 
     The swinging arm  121   b  biased by the biasing member  23   a  greatly swings downward when the self-propelled vacuum cleaner is climbing the floor level difference S as illustrated in  FIG. 5(B) , but the projection  121   b   1  of the swinging arm  121   b  does not abut the stopper  123   c  because of the slit  121   b   11 . It should be noted that the abutment member  23   b  of the biasing member  23   a  in this state is in proximity to the distal end of the stopper  123   c.    
     Furthermore, once the self-propelled vacuum cleaner is lifted and the drive wheel  22 L leaves the floor surface G as illustrated in  FIG. 5(C) , the swinging support unit  121 L is no longer coupled to the biasing member  23   a.  Accordingly, the drive wheel  22 L is released from the bias from the biasing member  23   a  and swings downward due to its own weight to reach the maximum protrusion length H 3 . 
     However, the abutment member  23   b  of the biasing member  23   a  is not in the fully stretched state as abutting the distal end of the stopper  123   c.  That is, the biasing member  23   a  in this state has remaining biasing force, because the biasing member  23   a  has not fully stretched and the biasing force thereof is not zero. 
     That is, the wheel support structure  103 L according to the second embodiment can transmit strong pushing force to the swinging support unit  121 L using the biasing member  23   a  (compression spring). Specifically, the biasing force gradually increases from zero as the compression spring gradually compresses from the fully stretched state, and therefore the compression spring is enabled to maintain strong pushing force while biasing the swinging support unit  121 L by being designed to abut the stopper  123   c  once the compression spring has stretched to a predetermined length (a predetermined biasing point). According to such a configuration, therefore, it is possible for the compression spring to push the swinging support unit  121 L at the predetermined biasing point when the housing  2  is climbing the floor level difference, enhancing the floor level difference climbing ability of the self-propelled vacuum cleaner. It is also possible to easily set the pushing force of the biasing member  23   a  (compression spring). 
     The second embodiment also produces the same effect as the first embodiment, which in other words is the effect of preventing, in consideration of safety, the drive wheel  22 L from popping out with strong force when the drive wheel  22 L is caused to protrude outward to exceed the protrusion length H 2  to a certain degree. 
     Third Embodiment 
       FIGS. 6(A) to 6(C)  are each an explanatory diagram of a wheel support structure according to a third embodiment, among which  FIG. 6(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 6(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 6(C)  illustrates a state in which the drive wheel is off the floor surface. It should be noted that elements in  FIGS. 6(A) to 6(C)  that are the same as the elements in  FIGS. 6(A) to 6(C)  are labelled using the same reference signs. The following mainly describes differences between the third embodiment and the first embodiment. 
     A wheel support structure  203 L according to the third embodiment includes a biasing member  223   a  that is an tension spring. The biasing member  223   a  (tension spring) has one end  223   a   1  slidably attached to a biasing member mounting rib  202   f   2 , which serves as the fixing section provided within the housing  2 , and the other end  223   a   2  attached to a swinging support unit  221   b.    
     Specifically, the one end  223   a   1  of the biasing member  223   a  has a ring shape with an elongate hole, and the other end  223   a   1  of the biasing member  223   a  has a ring shape with a circular hole. 
     The biasing member mounting rib  202   f   2  is stood in the vicinity of a rear end of the hole  2   a   1  in the bottom plate  2   a  of the housing  2 , and an upper end thereof has a recess  202   f   21  to be engaged. with the one end  223   a   1  of the biasing member  223   a.    
     Furthermore, one end (an end adjacent to the winging axle  21   a ) of a swinging arm  221   b  of the swinging support unit  221 L is provided with an L-shaped hook  221   b   1 , and the other end  223   a   2  of the biasing member  223   a  is put on the hook  221   b   1 . 
     According to the wheel support structure  203 L having such a configuration, the tension spring serving as the biasing member  223   a  pulls the hook  221   b   1  of the swinging area  221   b  rearward, and thus the swinging arm  221   b  is biased downward in a swinging direction (the direction indicated by arrow A) while the self-propelled vacuum cleaner is moving straight ahead on the floor surface G as illustrated in  FIG. 6(A) . 
     The swinging arm  221   b  biased by the biasing member  223   a  greatly swings downward when the self-propelled vacuum cleaner is climbing the floor level difference S as illustrated in  FIG. 6(B) . 
     Furthermore, once the self-propelled vacuum cleaner is lifted and the drive wheel  22 L leaves the floor surface G as illustrated in  FIG. 6(C) , the drive wheel  22 L swings downward due to its own weight to reach the maximum protrusion length H 3 . The bias from the biasing member  223   a  toward the swinging arm  221   b  is released once the drive wheel  22 L exceeds the protrusion length H 2  to a certain degree. The biasing member  223   a  then fully compresses and is pushed rearward by the hook  221   b   1 , and thus the one end  223   a   1  thereof slides rearward on the recess  202   f   2   1  of the biasing member mounting rib  202   f   2 . This creates a gap between the ring shape of the one end  223   a   1  and the recess  202   f   21  to eliminate the biasing force of the biasing member  223   a.    
     The third embodiment also produces the same effect as the first embodiment, which in other words is the effect of preventing, in consideration of safety, the drive wheel  22 L from popping out with strong force when the drive wheel  22 L is caused to protrude outward to exceed the protrusion length H 2  to a certain degree. 
     Fourth Embodiment 
       FIGS. 7(A) to 7(C)  are each an explanatory diagram of a wheel support structure according to a fourth embodiment, among which  FIG. 7(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 7(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 7(C)  illustrates a state in which the drive wheel is off the floor surface. It should be noted that elements in  FIGS. 7(A) to 7(C)  that are the same as the elements in  FIGS. 1 and 4 (A) to  4 (C) are labelled using the same reference signs. The following mainly describes differences between the fourth embodiment and the first and third embodiments. 
     A wheel support structure  303 L according to the fourth embodiment has a biasing mechanism  323  including a guide  323   b,  a stopper  323   c,  a sliding member  323   d,  and a tension spring serving as a biasing member  323   a.  The guide  323   b  is provided on a guide mounting rib  302   f   3 , which serves as one of a pair of front and rear fixing sections provided within the housing  2 , and projects in the front-back direction. The stopper  323   c  is provided on a distal end of the guide  323   b.  The sliding member  323   c   1  is attached to the guide  323   b  and enabled to slide in the front-back direction and abut the swinging support unit  21 L. The biasing member  323   a  has two ends respectively attached to the sliding member  323   d  and the biasing member mounting rib  202   f   2 , which serves as the other of the pair of front and rear fixing sections. 
     The guide mounting rib  302   f   3  is provided at the front end of the hole  2   a   11  in the bottom plate  2   a  of the housing  2 , and the biasing member mounting rib  202   f   2  is provided at the front end of the hole  2   a   11  as in the case of the third embodiment. 
     The guide  323   b  of the biasing mechanism  323  is a rod-shaped member having a non-circular (for example, square) transverse cross-section. The stopper  323   c  is a projection projecting outward from an outer periphery of the guide  323   b.  The sliding member  323   d  is a plate-shaped member having a hole (for example, a square hole) receiving insertion of the guide  323   b.    
     According o the wheel support structure  303 L having such a configuration, the tension spring serving as the biasing member  323   a  pulls the sliding member  323   d  rearward, and thus the swinging arm  21   b  is biased downward in the swinging direction (the direction indicated by arrow A) while the self-propelled vacuum cleaner is moving straight ahead on the floor surface G as illustrated in  FIG. 7(A) . In this state, the sliding member  323   d  is located between the guide mounting rib  302   f   3  and the projection  21   b   1  of the swinging arm  21   b.    
     The swinging arm  21   b  biased by the biasing member  323   a  greatly swings downward when the self-propelled vacuum cleaner is climbing the floor level difference S as illustrated in  FIG. 7(B) . In this state, the sliding member  323   d  is not in abutment with the stopper  323   c.    
     Furthermore, once the self-propelled vacuum cleaner is lifted and the drive wheel  22 L leaves the floor surface G as illustrated in  FIG. 7(C) , the drive wheel  22 L swings downward due to its own weight to reach the maximum protrusion length H 3 . The bias from the biasing member  323   a  toward the swinging arm  21   b  is released once the drive wheel  22 L exceeds the protrusion length H 2  to a certain degree, but the biasing member  323   a  does not fully compress because of abutment with the stopper  323   c.  That is, the biasing member  323   a  in this state has remaining biasing force, because the biasing member  323   a  has not fully compressed and the biasing force thereof is not zero. 
     That is, the wheel support structure  303 L according to the fourth embodiment can transmit strong pushing force to the swinging support unit  21 L using the biasing member  323   a  (tension spring). Specifically, the biasing force gradually increases from zero as the tension spring gradually stretches from the fully compressed state, and therefore the tension spring is enabled to maintain strong pushing force while biasing the swinging support unit  21 L by being designed to abut the stopper  323   c  once the tension spring has compressed to a predetermined length (a predetermined biasing point). According to such a configuration, therefore, it is possible for the tension spring to push the swinging support unit  21 L at the predetermined biasing point when the housing  2  is climbing the floor level difference, enhancing the floor level difference climbing ability of the self-propelled vacuum cleaner. It is also possible to easily set the pushing force of the biasing member  23   a  (compression spring). 
     The fourth embodiment also produces the same effect as the first embodiment, which in other words is the effect of preventing, in consideration of safety, the drive wheel  22 L from popping out with strong force when the drive wheel  22 L is caused to protrude outward to exceed the protrusion length H 2  to a certain degree. 
     Fifth Embodiment 
       FIGS. 8(A) to 8(C)  are each an explanatory diagram of a wheel support structure according to a fifth embodiment, among which  FIG. 8(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 8(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 8(C)  illustrates a state in which the drive wheel is off the floor surface. It should be noted that elements in  FIGS. 8(A) to 8(C)  that are the same as the elements in  FIGS. 4(A) to 4(C)  are labelled. using the same reference signs. The following mainly describes differences between the fifth embodiment and the first embodiment. 
     A wheel support structure  403 L according to the fifth embodiment includes a roller section  23   c  that is rotatable while in sliding contact with the swinging support unit  21 L. The roller section  23   c  is provided on the distal end  23   a   2  of the compression spring serving as the biasing member  23   a.    
     The roller section  23   c  has a roller main body  23   c   1  and a roller holding member  23   c   2  rotatably holding the roller main body  23   c   1  at a shaft  23   c   3  thereof extending in the left-right direction, and the roller holding member  23   c   2  is attached to the distal end  23   a   2  of the compression spring. 
     In the case of the fifth embodiment, the swinging support unit  21 L slides on the roller main body  23   c  of the roller section  23   c  when the biasing member  23   a  pushes and causes the swinging support unit  21 L to swing via the roller section  23   c.  The roller main body  23   c  rotates as the swinging support unit  21 L slides thereon to facilitate smooth swing of the swinging support unit  21 L. 
     Sixth Embodiment 
       FIGS. 9(A) to 9(C)  are each an explanatory diagram of a wheel support structure according to a sixth embodiment, among which  FIG. 9(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 9(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 9(C)  illustrates a state in which the drive wheel is off the floor surface. It should be noted that elements in  FIGS. 9(A) to 9(C)  that are the same as the elements in  FIGS. 5(A) to 5(C) and 8(A) to 8(C)  are labelled using the same reference signs. The following mainly describes differences between the sixth embodiment and the second embodiment. 
     A wheel support structure  503 L according to the sixth embodiment includes the roller section  23   c  that is rotatable while in sliding contact with the swinging support unit  121 L. The roller section  23   c  is provided on the distal end  23   a   2  of the compression spring serving as the biasing member  23   a.    
     As in the case of the fifth embodiment, the roller section  23   c  has the roller main body  23   c   1  and the roller holding member  23   c   2 . 
     In the case of the sixth embodiment, as in the case of the fifth embodiment, the swinging support unit  121 L slides on the roller main body  23   c   1  of the roller section  23   c  when the biasing member  23   a  pushes and causes the swinging support unit  121 L to swing via the roller section  23   c.  The roller main body  23   c   1  rotates as the swinging support unit  121 L slides thereon to facilitate smooth swing of the swinging support unit  121 L. 
     It should be noted that the roller main body  23   c   1  abuts the stopper  123   c  before the biasing member  23   a  has fully stretched. 
     Seventh Embodiment 
       FIGS. 10(A) to 10(C)  are each an explanatory diagram of a wheel support structure according to a seventh embodiment, among which  FIG. 10(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 10(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 10(C)  illustrates a state in which the drive wheel is off the floor surface. It should be noted that elements in  FIGS. 10(A) to 10(C)  that are the same as the elements in  FIGS. 7(A) to 7(C)  are labelled using the same reference signs. The following mainly describes differences between the seventh embodiment and the fourth embodiment. 
     A wheel support structure  603 L according to the seventh embodiment includes a roller that is rotatable while in sliding contact with the swinging support unit  21 L and that serves as a roller section  623   c.  The roller is rotatably attached to a downward opening cutaway portion  623   d   1  in a lower end of a sliding member  623   d  with a shaft extending in the left-right direction. 
     In the case of the seventh embodiment, the swinging support unit  21 L slides on the roller section  623   c  when the tension spring serving as the biasing member  323   a  pushes and causes the swinging support unit  21 L to swing via the sliding member  623   d  and the roller section  623   c.  The roller section  623   c  rotates as the swinging support unit  21 L slides thereon to facilitate smooth swing of the swinging support unit  21 L. 
     Eighth Embodiment 
       FIGS. 11(A) to 11(C)  are each an explanatory diagram of a wheel support structure according to an eighth embodiment, among which  FIG. 11(A)  illustrates a state in which a drive wheel is running on a floor surface,  FIG. 11(B)  illustrates a state in which the drive wheel is climbing a floor level difference, and  FIG. 11(C)  illustrates a state in which the drive wheel is off the floor surface. It should be noted that elements in  FIGS. 11(A) to 11(C)  that are the same as the elements in  FIGS. 8(A) to 8(C)  are labelled using the same reference signs. The following mainly describes differences between the eighth embodiment and the fifth embodiment. 
     A wheel support structure  703 L according to the eighth embodiment includes a swinging support unit  721 L including a swinging arm  721   b.  The swinging arm  721   b  has a projection  721   b   1  and, for abutment with the roller section  23   c,  an abutment surface  721   b   1  including the projection  721   b   1 . The abutment surface  721   b   1  is inclined toward the roller section  23   c  at a specific angle θ relative to a vertical line P orthogonal to the floor surface G when the self-propelled vacuum cleaner is placed on the floor surface G ( FIG. 11(A) ). 
     According to this configuration, the biasing force of the biasing member  23   a  can be transmitted in the vertical direction to the abutment surface  721   b   1  of the swinging arm  721   b  when the self-propelled vacuum cleaner is climbing the floor level difference ( FIG. 11(B) ), readily transmitting great biasing force to the swinging arm  721   b  and advantageously helping the drive wheel  22 L climb the floor level difference. 
     Other Embodiments 
     1. The first embodiment may omit the rotational force transmitting mechanism, and the output shaft of the drive motor  21   c  may be directly coupled to the drive wheels  22 L and  22 R. In this case, a rotational speed-adjustable, reversible motor may be used. The same is true for the second to eighth embodiments. 
     2. The positions of the left and right wheel support structures in the first to eighth embodiments may be left-right reversed. In this case, the drive wheels are swingable about the swinging axle in an upward and rearward direction. 
     3. The roller sections in the fifth to eighth embodiments ( FIGS. 8(A) to 11(C) ) may each have a rubber roller including the roller main body and a rubber ring surrounding an outer circumferential surface of the roller main body. 
     According to this configuration, the roller section is less slippery for the swinging support unit because of the rubber roller, and thus ensures reliable rotation when the swinging support unit swings. 
     4. A ball section may be adopted instead of any of the roller sections in the fifth to eighth embodiments ( FIGS. 8(A) to 11(C) ). The ball section includes a ball main body and a ball holding member having a fastening portion rotatably holding the ball main body, and the ball holding member is attached to the distal end of the compression spring serving as the biasing member. 
     According to this configuration, the swinging support unit slides on the ball main body of the ball section when the biasing member pushes and causes the swinging support unit to swing via the ball section. The ball main body rotates as the swinging support unit slides thereon to facilitate smooth swing of the swinging support unit. 
     5. The configuration described for the eighth embodiment ( FIGS. 11(A) to 11(C) ) in which the abutment surface  721   b   1  of the swinging arm  721   b  of the swinging support unit  721 L is inclined at the specific angle θ is also applicable to the first to seventh embodiments ( FIGS. 4(A) to 10(C) ). 
     (Summarization) 
     The wheel support structure for a self-propelled electronic device according to the present invention comprises: a drive wheel supporting a housing to cause the housing to run on a floor surface; a swinging support unit rotatably supporting the drive wheel and pivoting the drive wheel to a bottom part of the housing in such a way that the drive wheel is swingable upward and downwardabout a swinging axle; and a biasing mechanism including a biasing member configured to give a downward bias to the swinging support unit to cause the drive wheel to swing downward, wherein 
     the biasing mechanism gives the downward bias to the swinging support unit using the biasing member while the housing is on the floor, and release the downward bias while the drive wheel is off the floor surface. 
     The wheel support structure for a self-propelled electronic device according to the present invention may have any of the following configurations, which may be combined as appropriate.
     (1) The biasing member may be a compression spring having a proximal end fixed to a fixing section provided within the housing and a distal end enabled to abut the swinging support unit.   

     According to this configuration, it is possible to cause the swinging support unit to swing downward by pushing and biasing the swinging support unit using the distal end of the compression spring while the housing is on the floor surface, making the wheel support structure simple.
     (2) The biasing mechanism may further include a stopper configured to stop the distal end of the biasing member from pushing the swinging support unit once the drive wheel protrudes downward from the bottom part of the housing beyond a predetermined protrusion length.   

     According to this configuration, it is possible to transmit strong force to the swinging support unit using the compression spring in the above-described configuration (1). That is, the biasing force gradually increases from zero as the compression spring gradually compresses from the fully stretched state, and therefore the compression spring is enabled to maintain strong pushing force while biasing the swinging support unit by being designed to abut the stopper once the compression spring has stretched to a predetermined length (a predetermined biasing point). According to this configuration, therefore, it is possible for the compression spring to push the swinging support unit at the predetermined biasing point when the housing is climbing a floor level difference, enhancing the floor level difference climbing ability of the self-propelled electronic device.
     (3) The biasing member may be a tension spring having one end slidably attached to a fixing section provided within the housing and the other end attached to the swinging support unit.   

     According to this configuration, the swinging support unit is pulled and biased by the tension spring to swing downward while the housing is on the floor surface, and the bias toward the swinging support unit is released as a result of the one end of the tension spring sliding on the fixing section while the drive wheel is off the floor surface.
     (4) The biasing mechanism may further include a guide that is provided on one of a pair of front and rear fixing sections provided within the housing and that projects in a front-back direction, a stopper provided on a distal end of the guide, and a sliding member attached to the guide and enabled to slide in the front-back direction and abut the swinging support unit. The biasing member may be a tension spring having two ends respectively attached to the sliding member and the other of the pair of front and rear fixing sections.   

     According to this configuration, the sliding member is pulled by the tension spring and the swinging support unit is pushed and biased by the sliding member to swing downward while the housing is on the floor surface, and the sliding member abuts the stopper to be stopped from pushing the swinging support unit to release the bias toward the swinging support unit once the drive wheel protrudes downward from the bottom part of the housing beyond a predetermined protrusion length. 
     Furthermore, according to this configuration, it is possible to transmit strong pushing force to the swinging support unit using the tension spring. That is, the biasing force gradually increases from zero as the tension spring gradually stretches from the fully compressed state, and therefore the tension spring is enabled to maintain strong pushing force while biasing the swinging support unit by being designed to abut the stopper once the tension spring has compressed to a predetermined length (a predetermined biasing point). According to this configuration, therefore, it is possible for the tension spring to push the swinging support unit at the predetermined biasing point when the housing is climbing a floor level difference, enhancing the floor level difference climbing ability of the self-propelled electronic device.
     (5) The distal end of the biasing member may be provided with a roller section or a ball section that is rotatable while in sliding contact with the swinging support unit.   

     According to this configuration, the roller section or the ball section rotates while in sliding contact with the swinging support unit when the swinging support unit swings under biasing force of the biasing member (compression spring). It is therefore possible to facilitate smooth swing of the swinging support unit.
     (6) The sliding member may be provided with a roller section or a ball section that is rotatable while in sliding contact with the swinging support unit.   

     According to this configuration, the roller section or the ball section rotates while in sliding contact with the swinging support unit when the swinging support unit swings under biasing force of the biasing member (tension spring). It is therefore possible to facilitate smooth swing of the swinging support unit. 
     It should be noted that the disclosed embodiments are merely examples in all aspects and should not be construed to be limiting. The scope of the present invention is indicated by the claims, rather than by the description given above, and includes all variations that are equivalent in meaning and scope to the claims. 
     INDUSTRIAL APPLICABILITY 
     The wheel support structure for a self-propelled electronic device according to the present invention is for example applicable to devices such as a self-propelled ion generator that runs while spreading ions and a self-propelled transport vehicle that transports things, as well as to the self-propelled electronic devices described in association with the embodiments above. 
     REFERENCE SIGNS LIST 
     
         
           1 : self-propelled vacuum cleaner (self-propelled. electronic device) 
           2 : housing 
           2   a:  bottom plate (bottom part) 
           2   f   2 ,  202   f   2 : biasing member mounting rib (fixing section) 
           3 L,  103 L,  203 L,  303 L: wheel support structure 
           21   a:  swinging axle 
           21 L,  121 L,  221 L: swinging support unit 
           22 L,  22 R: drive wheel 
           23 ,  123 ,  223 ,  323 : biasing mechanism 
           23   a,    223   a,    323   a:  biasing member 
           23   b:  abutment member 
           23   b   1 : proximal end 
           123   c,    323   c:  stopper 
           223   a   1 : one end 
           223   a   2 : other end 
           302   f   3 : guide mounting rib (fixing section 
           323   b:  guide 
           323   d:  sliding member 
         G: floor surface