Abstract:
A three wheeled mobile robot ( 8 ) configured to be widely versatile in its use due to its novel drive unit and capability to climb ferrous surfaces regardless of the surface curvature. The drive system is based on three parallel wheels ( 12, 14, 16 ) in a fixed orientation capable of approximating the most useful traits of Omni-directional capability while also having the ability to traverse surface obstacles. The robot ( 8 ) can also have the ability to scale work surfaces regardless of orientation to the ground or curvature of the surface due to the combination of the three-wheel drive system and magneticadhesion capabilities due to an adjustable onboard magnetic unit ( 24 ), which allows the robot to carry on a diverse number of work tasks on all ferrous surfaces via unlimited system integration.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to mobile robots. More particularly, this invention relates to a mobile robot design consisting of three wheels. 
       BACKGROUND 
       [0002]    Three-wheeled robotic chassis and drive trains have existed in industry for decades. In many cases, these designs have been configured to exhibit Omni-directional capabilities. To that end, these machines have often been found to utilize (i) a system of steerable wheels in various configurations, (ii) fixed wheel hubs with Omni-directional capabilities derived from fixed, angled, Omni-wheel designs, or (iii) standard wheels in adjustable, or steerable, angled positions. 
         [0003]    Generally, in the case of steerable wheels, one or more wheels of the design have the ability to be oriented independent of, or in conjunction with, one or more other wheels of the design. Such independent/collective orientation of wheels can be found in a multitude of designs, ranging from cars to grocery carts. In more complex designs, each of the wheels is controlled via use of individual motors. For example,  FIG. 1  illustrates an exemplary steerable design utilizing three wheels (wheels A, B, and C), each of which is respectively oriented about a pivot point (pivot points A, B, and C) and controlled by a motor (motors A, B, and C). 
         [0004]    Conversely, in omni-wheel designs, the wheels are commonly affixed at angled orientations. For example, a design commonly referred to as a Holonomic drive involves three omni wheels affixed in a triangle design. The Holonomic drive is sometimes also referred to as a “fuzzy” drive based on the inherent vibrations and turbulent movement produced by the design.  FIG. 2  shows an exemplary Holonomic drive, with the omni wheels (wheels A, B, and C) being generally offset by about 120° from each other. 
         [0005]    Known three-wheeled drive systems have been found to exhibit certain limitations, particularly when called upon to climb or maneuver on curved or uneven surfaces (or navigate over surface obstacles). For example, in industrial environments, such curved and/or uneven surfaces can often be encountered when dealing with pipes, tanks, and other industrial structures. To that end, changing orientation of all three wheels in such environments (in order to bring about change in direction) has necessitated complex designs. Such designs have generally not been suited for climbing operations due to increased weight. Furthermore, such designs are generally bulky, which prevent their use in tight spaces, and even if such spaces are navigable, they can be found to adversely affect the wheels of such designs from rotating as needed. 
         [0006]    In some applications, systems are needed to navigate against gravity, such as traveling along a vertically-oriented pipe or pole, while also navigating on irregular surfaces. However, the known three-wheeled designs lack the means necessary to attach to curved or irregular surfaces, so as to provide the necessary traction to traverse such surfaces while carrying a load to accomplish useful tasks thereon. For example, regarding Holonomic drive systems, they inherently have low traction, which makes them unsuitable for climbing applications. Furthermore, these systems exhibit difficulty in traversing surface obstacles since at least one wheel is found to be nearly perpendicular to the direction of movement. 
       SUMMARY OF CERTAIN EMBODIMENTS OF THE INVENTION 
       [0007]    Embodiments of the present invention involve a mobile robot configured to be widely versatile in its use. For example, the mobile robot can be configured for being used on a wide assortment of surfaces, regardless of the orientation and/or shape of the surfaces. Alternatively or in combination, the mobile robot can be configured for effective and efficient movement on the surfaces it traverses. 
         [0008]    In certain embodiments, the mobile robot is configured with three wheels that have fixed and parallel orientation that allow stable and constant points of contact with curved and/or uneven surface. Such inherent stability benefits are combined with the robot&#39;s ability to move over surface obstacles and on curved and/or irregular surfaces. Omni directional movement of the invention is approximated by differential rotation of the wheels. Furthermore, the direction and orientation of the robot is dynamic based on the speed of travel for each wheel. 
         [0009]    In certain embodiments, the mobile robot is configured to be used on a surface, regardless of the surface&#39;s orientation with respect to gravity. For example, when designed for use on ferromagnetic surfaces, the robot can include magnets and orientation control structure therefor. In such cases, the magnets are operatively coupled to the robot so as to be held above, i.e., having no direct contact with, the ferromagnetic surfaces, yet the field strengths of the magnets are sufficient to hold the robot and its payload against the surfaces without risk of falling therefrom. In some cases, the magnets are adjustable in two or more dimensions in relation to the ferromagnetic surfaces. 
         [0010]    These and other aspects and features of the invention will be more fully understood and appreciated by reference to the appended drawings and the description of the preferred embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The following drawings are illustrative of particular embodiments of the present invention and therefore do not limit the scope of the invention. The drawings are not necessarily to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements. 
           [0012]      FIG. 1  is a top view of a known exemplary steerable wheel design; 
           [0013]      FIG. 2  is a top view of a known exemplary Holonomic drive system; 
           [0014]      FIG. 3  is a bottom view of the mobile platform design in accordance with certain embodiments of the invention; 
           [0015]      FIG. 4  is a top view of the mobile platform design of  FIG. 3 ; 
           [0016]      FIG. 5  is a top view of another mobile platform design with exemplary payload in accordance with certain embodiments of the invention; 
           [0017]      FIG. 6  is a perspective view of the mobile platform design of  FIG. 5  as shown traversing a curved work surface in accordance with certain embodiments of the invention; 
           [0018]      FIG. 6A  is an enlarged view of a portion of  FIG. 6  with respect to the mobile platform design; 
           [0019]      FIG. 7  is a photograph showing the mobile platform design of  FIG. 5  as shown in event of traversing between flat surface and curved surface in accordance with certain embodiments of the invention; and 
           [0020]      FIG. 8  is a photograph showing the mobile platform design of  FIG. 5  as shown in event of traversing between flat surfaces of differing angles in accordance with certain embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides some practical illustrations for implementing exemplary embodiments of the present invention. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements, and other elements employ that which is known to those of ordinary skill in the field of the invention. Those skilled in the art will recognize that many of the noted examples have a variety of suitable alternatives. 
         [0022]      FIG. 3  shows a mobile platform  10  in accordance with certain embodiments of the invention. As shown, the mobile platform  10  is part of a mobile robot  8 , with the platform  10  forming a chassis (for the robot  8 ) and consisting of three wheels  12 ,  14 , and  16  (such as polyurethane wheels) operatively coupled thereto. As shown, the wheels  12 ,  14 , and  16  are shown to be of similar size. Further, the wheels  12 ,  14 , and  16  are of a similar type, e.g., standard wheel design; however, the invention should not be limited to such. For example, one or more of the wheels can be of Omni-directional design. As shown, two of the wheels  12  and  14  are operatively coupled to one side  10   a  of the platform  10 , while the third wheel  16  is operatively coupled to the opposing side  10   b  of the platform  10 . 
         [0023]    In certain embodiments, as shown, each of the wheels  12 ,  14 , and  16  have fixed orientation relative to the opposing sides  10   a,    10   b  of the platform  10 , such that the wheels are each oriented in parallel directions. As further illustrated, in certain embodiments, the wheels  12  and  14  are spaced apart on the platform side  10   a,  yet aligned relative to each other in front-to-back manner. Conversely, the third wheel  16  is positioned along the opposing platform side  10   b,  so as to be centered relative to the other two wheels  12  and  14 , thereby being equidistant from the first and second wheels  12  and  14 . As shown, the wheels  12 ,  14 , and  16  are distributed about the platform  14  so as to define a plane  18  there between, defined to be the shape of a triangle, with contact points  12   a,    14   a,  and  16   a  (for contacting work surface) for each wheel  12 ,  14 , and  16 , respectively, representing points of the triangle. As shown, in certain embodiments, the spacing (or space  20 ) between the wheels  12  and  14  is of an extent substantially similar to diameter of the third wheel  16 ; however, this can vary with certain modifications being made to the robot, as further detailed herein with reference to  FIGS. 5-8 . Further, in certain embodiments as shown, one or more of the wheels  12 ,  14 , and  16  (e.g., the third wheel  16  as shown) can be operatively coupled to an interior surface of the platform  10 . 
         [0024]    The benefit of such triangular and closely-positioned locations of the wheels  12 ,  14 , and  16 , whereby only three points of contact  12   a,    14   a,  and  16   a  are facilitated (for contacting a work surface being traversed), is that all of the wheels  12 ,  14 , and  16  are always in contact with the surface, regardless of the surface&#39;s shape or geometry, e.g., whether curved or uneven. In addition, by maintaining the fixed parallel orientation of the wheels  12 ,  14 , and  16 , the robot  8  dictates a compact footprint and more reliable operating abilities, while providing maximum traction for climbing. 
         [0025]    In certain embodiments, each of the wheels  12 ,  14 , and  16  are powered via respective motors, e.g., 12 volt brushed DC motors. With further reference to  FIG. 3 , while one such motor  22  is shown as extending from wheel  16 , it should be appreciated that other motors extending from each of the wheels  12  and  14  are located internal to the platform (or chassis)  10  and hidden from view. In certain embodiments, as shown, the motors are oriented perpendicular to the wheel direction of travel, but the invention should not be limited to such. For example, the orientation of the motors may vary with changes to configuration of the platform  10  and corresponding gearbox configuration. 
         [0026]    Turning of the robot  8  is accomplished via differential rotation of the wheels  12 ,  14  on the platform (left) side  10   a  and wheel  16  on the opposing platform (right) side  10   b.  All three wheels  12 ,  14 , and  16  being driven clockwise (CW) or counterclockwise (CCW) results in the platform  10  moving forward or reverse respectively. Conversely, moving the wheels  12  and  14  (on platform left side  10   a ) counterclockwise (CW) and the wheel  16  (on platform right side  10   b ) counterclockwise (CCW) causes the platform  10  to rotate clockwise (CW). Likewise, reversing the wheel motion causes the platform to rotate counterclockwise (CCW) about a fixed point. Such movement of the robot  8  is summarized in Table 1 below. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Direction of Movement 
                 Wheel Actuation 
               
               
                   
                   
               
             
             
               
                   
                 Rearward (AFT) 
                 All Wheels CCW Same Speed 
               
               
                   
                 Forward 
                 All Wheels CW Same Speed 
               
               
                   
                 CW Rotate 
                 Left Wheels CW; Right Wheel CCW 
               
               
                   
                 CCW Rotate 
                 Left Wheels CCW; Right Wheel CW 
               
               
                   
                   
               
             
          
         
       
     
         [0027]    In certain applications, the mobile robot  8  may need to rotate in tight spaces. As such, in certain embodiments as noted above, one of the wheels  12  or  14  may be replaced with an Omni wheel. Such substitution would allow slippage of rollers of the Omni wheel, while still maintaining  3  points of contact with the surface being traversed. In such embodiment, the two wheels of standard type (the other of wheels  12  and  14 , as well as wheel  16 ) maintain sufficient traction (create friction) with underlying surface(s) to keep the robot  8  stable during climbing operations, even when the Omni wheel rollers are free to roll in the direction of gravity. 
         [0028]    Continuing with  FIG. 3 , the platform  10  is shown to include a magnet  24 , such as a neodymium magnet. With reference to  FIG. 4 , showing a top view of the robot  8 , the magnet  24 , in certain embodiments, can be operatively coupled to an enclosure  26  of the robot  8  such that its lower surface  24   a  is suspended slightly above a ferrous surface to allow the platform to drive in any direction and in any orientation on such a work surface. To that end, the magnet  24  is held relative to lower surface  10   c  of the platform  10 , while being offset from work surface being traversed by robot  8 , to prevent contact with such surface and corresponding friction there between. 
         [0029]    In certain embodiments, the magnet  24  is adjustably coupled to the robot enclosure  26 . It should be appreciated that such adjustable coupling can take a variety of forms. For example, with reference to  FIG. 3 , the magnet  24  is operatively coupled to the robot enclosure  26  via an adjustment bolt  28 , whereby the height of the magnet lower surface  24   a  relative to the work surface can be adjusted via tightening/loosening of corresponding screw  30  (see  FIG. 4 ) on bolt  28 . Thus, the gap between the magnet  24  and the work surface can be varied based on the particular work surface. Additionally, in certain embodiments, the magnet lower surface  24   a  can be angularly shifted relative to the work surface via various means. While the robot  8  is shown with only one magnet  24 , the invention should not be so limited, as more magnets can be added so long as their location(s) comply with the description below. 
         [0030]    Continuing with  FIG. 3 , in certain embodiments as shown, the magnet  24  has a central axis  24   b  (shown as dashed line) that extends through the plane  18  defined between the wheel contact points  12   a,    14   a,  and  16   a.  Such extension of the magnet central axis  24   b  through the plane results in corresponding forces from the magnet  24  being exerted on the three wheels  12 ,  14 , and  16  sufficient to maintain contact with a work surface of ferromagnetic material, regardless of varying shape of such surface or orientation of the robot  8  when navigating such surface. As shown, the magnet  24  is situated so as to be centered between the two wheels  12 ,  14  on platform side  10   a  (and in line with the wheel  16  on opposing platform side  10   b ). To that end, in certain embodiments, the magnet  24  can be spaced equally between the wheels  12 ,  14 , and  16  to equalize the downward force of the magnet on all three of the wheels  12 ,  14 , and  16 . However, such equal spacing of the magnet  24  is not required, so long as the central axis  24   b  of the magnet  24  is situated within plane defined between the wheel contact points  12   a,    14   a,  and  16   a.  Such configuration for the magnet  24  relative to the wheels  12 ,  14 , and  16  provides an ideal center of gravity, which would provide for sufficient stresses on the wheel motors so the mobile platform tracks straight. To that end, if, for example, position of the magnet  24  were to be instead shifted toward one of the wheels (e.g., wheel  16 ) yet within plane between wheels  12 ,  14 , and  16 , the corresponding motor (e.g., motor  22 ) for such wheel would need to work harder to keep the platform  10  (and robot  8 ) driving straight, and such would lag behind other wheel motors (e.g., of platform side  10   a ) if there were no control compensation. 
         [0031]    Continuing with the above, if the magnet  24  were positioned outside the position described above, the platform  10  would still function as long as the magnet  24  is located within the triangle  18  drawn between (contact points of) each of the three wheels  12 ,  14 , and  16  (see  FIG. 3 ). To that end, if the magnet  24  were located outside this triangle  18 , one of the wheels  12 ,  14 , and  16  would not have any positive force exerted on it, and it would be possible for the platform  10  (and robot  8 ) to foreseeably shift on two of the three wheels  12 ,  14 , and  16 , thereby becoming temporarily inoperable. Particularly, the magnetic force created would overwhelm the center of gravity location for stability on ferrous surfaces, so the center of gravity could fall slightly outside the triangle  18  in this situation. 
         [0032]    Turning back to  FIG. 4 , in certain embodiments as described above, the platform  10  supports an enclosure  26  for the robot  8 . Such enclosure  26 , in certain embodiments, is used for housing electronic controls for the robot  8 . For example, such controls can include power source  32 , such as one or more batteries, and a controller  34 , e.g., for controlling motor speed, which in certain embodiments, is further controlled by an electronic receiver  36 . In such embodiment, all controls are operated wirelessly with an electronic controller (e.g., located remote from robot  8  and configured to wirelessly communicate with receiver  36 ). In alternate applications, wireless communication may not be available. In such applications, the electronic controller can be further located in enclosure  26  and part of a wired design allowing for control of the robot  8 . 
         [0033]    It should be understood that various payloads and control sensors may be operatively coupled to the mobile platform  10  so as to perform various tasks. To that end, while only baseline components for operation are depicted in  FIGS. 3 and 4 , the invention should not be so limited. Furthermore, the configurations of these baseline components can be altered as desired, while still abiding by the design requirements regarding wheels  12 ,  14 ,  16  and magnet  24  already detailed herein. 
         [0034]    For example,  FIG. 5  shows another mobile platform  10 ′ (of further robot  8 ′) with exemplary payload (shown as wireless camera  38  and pan/tilt system  40 ) in accordance with certain embodiments of the invention. As shown, the enclosure  26 ′ (e.g., for the electronic controls with optional external power switch  42 ) has been reduced in size (compared to enclosure  26  of robot  8 ), whereby orientation of the motors for wheels  12 ′ and  14 ′ (wheel  12 ′ and corresponding motor  44  being shown, while wheel  14 ′ and corresponding motor  45  are mostly hidden in  FIG. 5 , but shown in  FIG. 6 ) can be altered to allow the two wheels  12 ′ and  14 ′ to be spaced closer together, so as to correspondingly enable the wheels  12 ′,  14 , and  16 ′ to be collectively positioned closer to (and more closely surround) the magnet  24 ′ (with reduced spacing between the magnet&#39;s central axis  24   b ′) . It should be appreciated that the configuration of contact points  12   a ′,  14   a ′, and  16   a ′ of the wheels  12 ′,  14 ′, and  16 ′ (and corresponding center of gravity center) as well as parallel setup for the wheels  12 ′,  14 ′, and  16 ′ are similar to that already described with regard to robot  8 ; however, the above-described design modifications (facilitating closer positioning of the wheels  12 ,  14 ′, and  16 ′ relative to the magnet  24 ′) of the robot  8 ′ enhance its performance. For example, such configuration enables the robot  8 ′ to bump into protruding objects (e.g. walls and pipes) and subsequently transition over them. In certain embodiments, via such configuration, the robot  8 ′ is able to transition between surfaces having angular difference of up to 135° (e.g., traversing from horizontal surface of 0° to vertical surface of 90° plus 45° additional angular difference) while its wheels  12 ′,  14 ′, and  16 ′ provide continual contact with the surfaces. 
         [0035]    Transitioning between such surfaces with such severe angular difference, even when against gravity, is made possible (based on the combination of the further protruding wheels  12 ′ and  14 ′ and the altered three-wheel geometry), which permits the magnet  24 ′ to remain in close proximity to the work surface when making such transition. To that end,  FIGS. 6-8  illustrate differing transition environments (and differing transition angles  46  and  48 ) for such robot  8 ′, e.g., between differing angled surfaces, whether one flat and the other curved, or both being flat, despite gravitational force  50  acting upon the robot  8 ′. 
         [0036]    The advantages of the present invention overcome many of the limitations of known three-wheeled machines. Particularly, the mobile platforms  10 ,  10 ′ (of corresponding robots  8 ,  8 ′) allow contact by all wheels regardless of surface orientation. The parallel wheel design for the platforms  10 ,  10 ′ also provide an accurate and compact way to approximate Omni-directional capabilities without additional mechanical design or bulk involved in wheel hubs which require turning capabilities. 
         [0037]    Thus, embodiments of a THREE-WHEELED MOBILE ROBOT are disclosed. While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the embodiments (and examples thereof) described herein. To that end, one skilled in the art will appreciate that the invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the invention is limited only by the claims that follow.