Abstract:
A multi-unit mobile robot comprising a plurality of separate carriages or units linked together by linkages. Each unit comprises hinged first and second segments which facilitates pitch relative motion between the segments, and accordingly the units. By controlling actuators to the hinges, one can cause the robot to coil around and compress against the exterior, or compress against the interior, of an object to be traversed. The linkage between mobile units facilitates at least one of lateral pivot or yaw relative motion between units, and optionally roll. 
     Each hinged platform is carried by a pair of Mecanum wheels, which facilitate movement of the unit in any direction. Preferably, alternating units are of differing widths, and the wheels on the units are sufficiently large that they capable of overlapping, thereby enabling the robot to navigate very sharp edges or corners in the surface of an object being traversed by the robot, with the wheels always maintaining contact with the surface being traversed. 
     Among other possible uses, the multi-unit mobile robot can be used to service windmill blades and towers, and carrying cargo up and down windmill towers by directing a multi-unit mobile robot to wrap around the and traverse the tower.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/247,257 filed Sep. 28, 2011, which claims priority to U.S. Provisional Patent Application No. 61/388,204 filed Sep. 30, 2010, the contents of which are incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to multi-unit mobile robots. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention is a multi-unit mobile robot comprising a plurality of separate carriages or units linked together by linkages. Each unit comprises hinged first and second segments which facilitates pitch relative motion between the segments, and accordingly the units. By controlling actuators to the hinges, one can cause the robot to coil around and compress against the exterior, or compress against the interior, of an object to be traversed. 
         [0004]    Preferably, the linkage between mobile units facilitates at least one of lateral pivot or yaw relative motion between units. The lateral pivot and/or yaw motions allow the multi-unit mobile robot to wrap around the object in a helical fashion, and it can be long enough that its ends can overlap. 
         [0005]    Also preferably, the linkage also facilitates roll between units. The optional roll feature allows the wheels of the units to maintain contact with an irregular work surface. 
         [0006]    In a preferred embodiment, each hinged platform is carried by a pair of Mecanum wheels, which facilitate movement of the unit in any direction. In the preferred embodiment, the pitch axis is concentric with the Mecanum wheel axis of rotation. On regular work surfaces where end overlap is not required, the robot can function using pitch control only. Lateral pivot and/or yaw are or is required only if it is intended or desirable to allow the multi-unit mobile robot to lap itself in wrapping around the object to be traversed. 
         [0007]    Also preferably, alternating units are of differing widths, and the wheels on the units are sufficiently large that they capable of overlapping, thereby enabling the robot to navigate very sharp edges or corners in the surface of an object being traversed by the robot, with the wheels always maintaining contact with the surface being traversed. 
         [0008]    In another aspect of the invention, the invention comprises a method of servicing windmill blades and towers by directing a multi-unit mobile robot to wrap around and traverse the exterior of such a blade or tower, while cleaning, inspecting, resurfacing or painting the blade and/or tower. 
         [0009]    In another aspect of the invention, the invention comprises a method of carrying cargo up and down windmill towers by directing a multi-unit mobile robot to wrap around the and traverse the tower. 
         [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]      FIG. 1  is a perspective view of a preferred embodiment multi-unit mobile robot wrapped around a wind turbine blade; 
           [0012]      FIG. 2  is a side elevation of the multi unit robot wrapped around a cylindrical surface; 
           [0013]      FIG. 3  is a side elevation of the multi unit robot wrapped around a wind turbine blade; 
           [0014]      FIG. 3A  is the detail A of  FIG. 3 , showing the overlap of wheels  15  and  15 ′ as the multi-unit mobile robot rounds the edge of the wind turbine blade; 
           [0015]      FIG. 4  is a plan view of the robot traversing the surface of a wind turbine blade; 
           [0016]      FIG. 5  is a plan view of a robot unit  10  joined to the platform units  21 ′ and  22 ′ of adjacent robot units  10 ′; 
           [0017]      FIG. 6  is a perspective view of the structure shown in  FIG. 5 ; 
           [0018]      FIG. 7  is a plan view showing a robot unit linked to two adjacent units, in yaw orientation; 
           [0019]      FIG. 8  is a plan view of adjacent robot units linked in pivotal orientation; 
           [0020]      FIG. 9  is a perspective view of a yaw actuator, with adjacent link members joined to each other in rotatable orientation; 
           [0021]      FIG. 10  is a perspective view of a multi-unit mobile robot wrapped around a cylindrical object  3  in an arbitrary orientation; 
           [0022]      FIG. 11  is a side elevation of a multi-unit mobile robot pitching up and out of contact with a work surface of an object  3 , as might be done to clear an obstacle on the surface; 
           [0023]      FIG. 12  is a perspective view of an alternative robot unit having a third wheel for lateral motion control; 
           [0024]      FIG. 13  is a perspective view of an alternative embodiment in which each robot unit is supported by only one wheel instead of two; 
           [0025]      FIG. 14  is a schematic view of a control system for the multi-unit mobile robot; 
           [0026]      FIG. 15  is a schematic of the actuator control for a motion actuator, which actuates a wheel drive motor; 
           [0027]      FIG. 16  is a schematic of the actuator control for a yaw actuator; 
           [0028]      FIG. 17  is a schematic of the actuator control for a pitch actuator; 
           [0029]      FIG. 18  is a perspective view of a box representation of a payload on the robot; 
           [0030]      FIG. 19  is a graphical representation of the variables in equations (1) through (7); 
           [0031]      FIG. 20  is a perspective view of a multi-unit mobile robot transferring from one object  4  to another object  4 ′ in an arbitrary orientation; 
           [0032]      FIG. 21  is an alternate embodiment in which pitch and yaw are achieved by powered linear actuators; 
           [0033]      FIG. 22  is an alternate view of  FIG. 21  showing pitch and yaw being achieved by powered linear actuators; 
           [0034]      FIG. 23  is an alternate embodiment in which clamping force around a cylindrical surface is augmented by use of a flexible device under tension; 
           [0035]      FIG. 24  is an alternate embodiment in which clamping force around an airfoil surface is augmented by use of a flexible device under tension; 
           [0036]      FIG. 25  is an alternate embodiment in which clamping force around an airfoil surface is augmented by the use of a flexible device under tension connecting two independent robots. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    In the preferred embodiment, multi-unit mobile robot  1  is capable, given an appropriate length, of compressing around the outside of, or pushing against the inside of, a work surface of an object  2  or  3  which encompasses an arc of greater than 180° (See  FIGS. 1 ,  2 ). The multi-unit mobile robot comprises a plurality of robot units  10  and  10 ′ connected together by links  40  ( FIGS. 4-6 ). Units  10  and  10 ′ are similar in construction, except that unit  10  is slightly wider than unit  10 ′, such that units  10  and  10 ′ can be joined in alternating fashion with their wheels  15  and  15 ′ being capable of overlapping without interference to allow the multi-unit robot  1  to pass over sharp edges ( FIGS. 1 ,  3 ,  3 A and  4 - 6 ). If the object being traversed does not contain sharp edges (shown as object  3  in  FIG. 10 ), wheel overlap is not a requirement. Each unit  10  and  10 ′ includes a hinged platform  20  or  20 ′ located between wheels  15  and preferably within the confines thereof (FIGS.  1  and  4 - 6 ). 
         [0038]    Each platform  20 ,  20 ′ comprises a pair of hingedly joined platform segments  21  and  22 , or  21 ′ and  22 ′ ( FIGS. 4-6 ), respectively, which can carry any desired payload. In the embodiment of the multi-unit mobile robot shown, the payload  150  or  150 ′ (shown as a box in  FIG. 18 ) carried by each hinged platform would be a spray painting device, cleaning device, or other servicing device so that the multi-unit mobile robotic device can be used to clean, paint, or perform other maintenance to the blades of a wind turbine. For tower applications, the pay load  150  or  150 ′ would be a crane device which the multi-unit robot would transport to the desired location on the wind tower. 
         [0039]    The multi-unit robot can also be thought of as a plurality of segments  21 ,  22 ,  21 ′ and  22 ′ joined to each other alternatively by hinges which facilitate pitch motion, and linkages which optionally feature lateral pivot, yaw, and/or roll motion. 
         [0040]    Each unit  10 , 10 ′ may include quick connect/disconnect interfaces for electrical power, control communications, communication, pneumatic/hydraulic lines for use by payload and robot unit, if required, and application liquid lines for use by payload, if required. The platforms  20  and  20 ′ can be made to a size which provides room to install all equipment necessary to make it and the payload self contained (e.g. batteries, tanks, wireless communication, etc.). This would be desirable if the chassis needs to navigate around supporting structure or large obstacles that make lines impractical (e.g. pipeline supports). Each unit  10 ,  10 ′ is preferably 100% electrical for precise control capability and mass savings. However, the large forces required to enable the multi-unit mobile robot to adhere to the work surface may necessitate the use of hydraulic or pneumatic actuators in lieu of electric components. 
         [0041]    Multi-unit robot  1  is capable of movement in any direction on a work surface through the use of individually driven Mecanum wheels, as wheels  15  and  15 ′. The multi-unit robot  1  clamps (compresses) around the outside or against the interior of a work surface through control of the pitch motion between the hingedly joined platform segments  21  and  22 , and  21 ′ and  22 ′ ( FIG. 1 ). Each unit is also capable of pivot, yaw and roll motion relative to its adjacent units through control mechanisms associated with links  40  ( FIGS. 7-9 ). 
         [0042]    Compression of the device against the outside or inside of a work surface is achieved by a pitch actuator  30 , e.g. a motor, servo, or linear actuator, on each platform  20 ,  20 ′ which acts to fold the platform segments  21 ,  22  or  21 ′,  22 ′ towards one another, with a biasing torque in accordance with controller instruction (FIGS.  1  and  4 - 6 ). Links  40  do not permit pitch motion between units  10  and  10 ′, such that adjacent planar segments  22 ′ and  21 , and  22  and  21 ′, tend to be forced down (or up) against the work surface in a compressing (or outwardly forcing) motion as a result of actuator  30  causing a pitching motion between hinged segments  21  and  22 , or  21 ′ and  22 ′. This action occurring simultaneously in multiple robot units  10  and  10 ′ causes the multi-unit robot  1  to clamp against any surface which is encompassed to the extent of more than 180 degrees by the multi-unit robot  1  ( FIG. 2 ). 
         [0043]    Stated another way, the adjoining units  10  and  10 ′ thereby tend to mutually force each other against the work surface upon which they are riding, such that if the device encompasses an arc of greater than 180° to achieve clamping force equilibrium, the multi-unit robotic device as a whole tends to exert a clamping force against the work surface on either side of the arc. Through a control system, the torque exerted by pitch actuators  30  can be varied using the control system for the device. In this way, the degree of compression of the unit against the work surface can be varied. The amount of compression required is a function of the mass of robot  1  and the coefficient of friction between the Mecanum wheels and the work surface. 
         [0044]    In the embodiment shown in  FIG. 21 , pitch actuator  30  comprises a tower bracket  31  mounted on platform segment  21 , and a linear actuator  50  which is pivotally attached at one end to the top of tower bracket  31 , and at its other end to the free end of a lever  32 . The opposite end of lever  32  is mounted to platform segment  22 . Linear actuator  50  can be an electric solenoid type device, a pneumatic or hydraulic cylinder, or an electric or pneumatic or hydraulic driven screw type device (e.g. worm drive). Regardless, actuator  50  comprises a base  51  and a rod  52  which extends or retracts from the base. In so doing, actuator  50  changes the angle of the platform segments  21  and  22  relative to each other and/or the compressive force exerted by adjacent carriages  10  and  10 ′ ( FIG. 22 ). This method of pitch actuation is desired if a large amount of compression needs to be applied to the work surface to ensure wheel traction. 
         [0045]    The lateral pivot or yaw movement between adjacent units  10  and  10 ′ is achieved by each of the links  40  being pivotably connected at each end to yaw actuators  45  ( FIGS. 5 and 6 ), one of which is mounted on the platform  20  of a unit  10  and the other of which is mounted on the platform  20 ′ of an adjacent unit  10 ′. Specifically, one yaw actuator  45  mounted on the hinged platform member  21  of unit  10  is joined to one end of a link  40  and the other end of link  40  is joined to another actuator  45  is mounted on the hinged platform  22 ′ of the adjacent unit  10 ′. Similarly another link  40  is connected to and extends between a yaw actuator  45  mounted on hinged platform segment  22  of unit  10  and another yaw actuator  45  mounted on the succeeding hinged platform  21 ′ of adjacent unit  10 ′ ( FIGS. 5-9 ). 
         [0046]    Each link  40  comprises a primary link  41 , preferably “U” shaped to capture bending moments, comprising spaced legs  41   a  joined by a base member  41   b  ( FIG. 9 ). Legs  41   a  are connected at their free ends to a servo or motor driven yaw actuator  45 . The spaced legs  41   a  embrace the platform to which the free ends of legs  41   a  are connected. The base member  41   b  is spaced from the edge of the platform to allow a degree of motion of primary link  41  without interference with the edge of its platform. 
         [0047]    Primary link  41  is rotatably connected to a secondary link  42  ( FIG. 9 ), which is secured to a yaw actuator  45  mounted on the next adjacent platform segment (platform  21  in  FIG. 9 ). Secondary link  42  is a shorter version of primary link  41 , having spaced shorter legs  42   a  joined by a base member  42   b . As with primary link, the free ends of legs  42   a  are joined to a yaw actuator  45  with legs  42   a  embracing the platform and base leg  42   b  being spaced from the edge of the platform to allow a degree of motion without interference with the edge of the platform. 
         [0048]    Each yaw actuator  45  comprises a motor or servo unit  46  which differentially extends or retracts pins or pistons  47 . Pistons  47  are connected at their free ends to a plate  49  which is mounted to a pivot member  48 . The free ends of legs  41   a  or  42   a  respectively are connected to pivot member  48 . By differentially extending and retracting pistons  47 , one rotates plate  49  and pivot member  48 . This in turn causes link  40  to pivot. 
         [0049]    The free ends of the legs  41  are similarly connected to pivot member  48  in their respective yaw actuator  45 . By rotating link  40  at only one end, the adjacent units  10  and  10 ′ pivot laterally relative to one another ( FIG. 8 ). By rotating link  40  at both ends, the adjacent units yaw relative to one another ( FIG. 7 ). 
         [0050]    An alternate embodiment of yaw actuator  45  between units  10  and  10 ′ is shown in  FIG. 22 . Yaw joint  55  comprises a linear bearing  56  which moves laterally on a rod  57 . Linear bearing  56  may be driven by a worm gear, solenoid, pneumatic, or hydraulic actuator on platform  22 . This is desired if a large amount of torsion is placed on the multi-unit robot from the offset clamping forces between units  10  and  10 ′. This alternative embodiment does not facilitate lateral pivoting of the adjacent carriages relative to one another. 
         [0051]    The roll motion between adjacent units  10  and  10 ′ may be controlled or uncontrolled, and is achieved by the rotatable connection between the primary link  41  and secondary link  42  ( FIG. 9 ). This rotatable connection is made by a pin or axel  43  between the base legs  41   b  and  42   b  of primary link  41  and secondary link  42 . The rotatable connection allows adjacent units  10  and  10 ′ to roll relative to one another, to accommodate surface variations (e.g. tapered airfoil or tower). If the wheels are not in intimate contract with the work surface some degree of roll control is required to keep the robot from freely rotating. This can be as simple as a roll joint locking feature (a cylinoid with a pin on it would be sufficient) or an electric motor connected to control unit  100  ( FIG. 14 ). Cylinoids are electromagnets that act as an “on-off” actuator. 
         [0052]    Each Mecanum wheel  15  contains a series of rollers  16  attached to its circumference, each having an axis of rotation of about 45° to the vertical plane of the wheel ( FIGS. 1 and 5 ). Each wheel  15  includes its own individual drive motor, or motion actuator  17 . Each motion actuator  17 , identified by letters “a”, “b”, “c”, and “d”, is individually connected to a control unit  100  ( FIG. 14 ) such that the wheels can be instructed to rotate in the same direction at the same speed, in the same direction differentially, in opposite directions at the same speed, or in opposite directions differentially. In this way, each unit can be made to move sideways, diagonally or straightforward or straight backwards. 
         [0053]    In  FIG. 5 , the wheels  15  and their rollers  16  for two adjacent robot units  10 ′ and  10  have been labeled with the letters “a” and “b” for robot unit  10 ′ and “c” and “d” for robot unit  10 . By rotating all wheels in the same direction at the same speed, the robot units move in that direction at the same speed. By rotating wheels  15   c  and  15   d  to the right as viewed in  FIG. 5 , and wheels  15   b  and  15   a  to the left, both robot units  10  and  10 ′ will shift laterally upwardly as viewed in  FIG. 5 . By reversing those directions, the units will shift downwardly as viewed in  FIG. 5 . By rotating wheels  15   b  and  15   c  to the right, and wheels  15   a  and  15   d  to the left, the units will rotate in a clockwise direction. Reversing those directions will cause the units to rotate in a counterclockwise direction. A table indicating these motions with reference to the adjacent sketch is set forth below. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Direction of Movement 
                 Wheel Actuation 
               
               
                   
                   
               
             
             
               
                   
                 Right 
                 All Wheels Right Same Speed 
               
               
                   
                 Left 
                 All Wheels Left Same Speed 
               
               
                   
                 Up 
                 Wheels 15c, 15d Right; 15a, 15b Left 
               
               
                   
                 Down 
                 Wheels 15a, 15b Right; 15c, 15d Left 
               
               
                   
                 CW Rotate 
                 Wheels 15c, 15b Right; 15a, 15d Left 
               
               
                   
                 CCW Rotate 
                 Wheels 15a, 15d Right; 15c, 15b Left 
               
               
                   
                   
               
             
          
         
       
     
         [0054]    By thus individually controlling the speed and direction of motion actuators  17  independently, the entire multi-unit robot device can be made to traverse the work surface in any direction, forward, backward, laterally left, laterally right and any direction there between. Clockwise and counterclockwise rotation will typically be used for small adjustments only. For unbiased motion, the total number of Mecanum wheels need to be divisible by four. 
         [0055]    Through use of the pitch and yaw motions, the entire multi-unit train can wrap around a work surface with laterally offset, overlapping ends ( FIG. 10 ). The pitch motion which can be achieved by pitching the platform segments  21 ,  22  or  21 ′,  22 ′ relative to each other has been discussed above in connection with the clamping action of the device against the work surface. The pitch function can also be used to assist the robotic device in rising up to clear obstacles ( FIG. 11 ). 
         [0056]      FIG. 12  shows an alternative embodiment in which a third wheel  18  is provided for lateral motion control, instead of using Mecanum wheels. Wheel  18  is powered, and would be lowered to engage the work surface for lateral movement, or raised off of the work surface for other motion.  FIG. 13  shows an alternative embodiment in which each unit  10  or  10 ′ includes only one wheel  15  or  15 ′, with the wheels oriented on alternating sides of alternating units. 
         [0057]    For safety and operations, the multi-unit robot  1  should always envelop at least one complete revolution of the object it is traversing to ensure adequate clamping force and payload coverage. The desired length of robot  1  is determined by the largest diameter of the work object of interest. Unused units  10 ,  10 ′ will form a helix around the object for smaller diameters and payload components may be activated and deactivated as required. This embodiment is preferred but not required, as the multi-unit robot  1  only needs to envelop at least 180° to adhere to the work surface. 
         [0058]    It is thus preferable that the multi-unit robot  10  is able to wrap, or coil, around various objects with a continuous closed surface, without having the lead robot unit interfere with the trailing robot unit. This can be achieved by yawing the units with respect to each other. The number of robot units  10  and  10 ′ required for overlap at the ends without interference (T) is a function of a number of the amount of yaw movement possible from unit to unit. Assuming sufficient clearance between platform segments  21  and  22 ′, and between segments  22  and  21 ′, the gap (G) between overlapping wheels  15  is the limiting factor ( FIG. 5 ).  FIG. 19  graphically identifies all of the variables used in formulas 1-7 below. 
         [0000]        G =(( X− 2 S )− Y )/2  (1)
 
       Where: 
       [0059]    G=Mecanum Wheel Gap 
         [0060]    X=Wide Unit Width 
         [0061]    Y=Narrow Unit Width 
         [0062]    S=Mecanum Wheel Width 
         [0000]    The number of units (T) required to ensure clearance at the overlapping ends is then: 
         [0000]        T=X/G   (2)
 
       Where: 
       [0063]    T=Minimum units  10  and  10 ′ for Clearance Rounded Up to Nearest Integer 
         [0064]    X=the width of the wide unit  10   
         [0065]    G=the gap between wheels 
         [0000]    With the number of units required for overlapping clearance known, it is desirable to calculate some baseline geometry requirements for circumnavigation. Another requirement for this is the overall length (W) of robot  1 : 
         [0000]        W=NU −( V ( U− 1))  (3)
 
       Where: 
       [0066]    W=Multi-Unit Robot Length 
         [0067]    N=Number of Units 
         [0068]    V=Wheel Overlap 
         [0069]    U=Wheel Diameter 
         [0000]    The minimum cylinder diameter the multi-unit robot  1  can traverse is: 
         [0000]        D   min   =[TU −(( T− 1) V )]/ pi   (4)
 
       Where: 
       [0070]    D min =Minimum Diameter to Ensure Clearance, 
         [0071]    T=Minimum units  10  and  10 ′ for Clearance 
         [0072]    V=Wheel Overlap 
         [0073]    U=Wheel Diameter 
         [0000]    The maximum cylinder diameter the multi-unit robot  1  can traverse is: 
         [0000]        D   max =2 W/pi   (5)
 
       Where: 
       [0074]    D max =Maximum Diameter where multi unit robot  1  encompasses an arc of 180 degrees. 
         [0075]    W=Multi-Unit Robot Length 
         [0000]    The minimum flat plate chord length that can be circumnavigated is: 
         [0000]        C   min =( D   min   ·pi )/2  (6)
 
       Where: 
       [0076]    C=Minimum Flat Plate Chord 
         [0077]    D min =Minimum Diameter to Ensure Clearance, 
         [0000]    The maximum chord length is: 
         [0000]        C   max =( D   max   pi )/4  (7)
 
       Where: 
       [0078]    C max =Maximum Flat Plate Chord 
         [0079]    D max =Maximum Diameter where multi unit robot  1  encompasses an arc of 180 degrees. 
         [0000]    Table 2 below contains numerical examples of the parameters discussed above: 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Parameter 
               
               
                 Determination 
                 Description 
                 (in) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Defined by 
                 Wide Unit Width (X) 
                 11.5 
               
               
                 Chassis Geometry 
                 Narrow Unit Width (Y) 
                 7.5 
               
               
                   
                 Wheel Diameter (U) 
                 6 
               
               
                   
                 Wheel Width (S) 
                 1 
               
               
                   
                 Wheel Overlap (V) 
                 0.125 
               
               
                   
                 Number of Units (N) 
                 16 
               
               
                 Calculated 
                 Wheel Gap (G) 
                 1 
               
               
                   
                 Prototype Length (W) 
                 94.125 
               
               
                   
                 Minimum Unites for Clearance: 
                 12 
               
               
                   
                 Rounded Up (T) 
               
               
                   
                 Minimum Circumnavigate Diameter 
                 22.48 
               
               
                   
                 (cylinder) 
               
               
                   
                 Maximum Circumnavigate Diameter 
                 59.92 
               
               
                   
                 (cylinder) 
               
               
                   
                 Minimum Chord Length (flat plate) 
                 35.31 
               
               
                   
                 Maximum Chord Length (flat plate) 
                 47.06 
               
               
                   
               
             
          
         
       
     
         [0080]    The entire mobile robotic device  1  can be controlled through a “master controller” computer  100  ( FIG. 14 ). Each motion actuator  17 , pitch actuator  30  and yaw actuator  45  will preferably be independently controlled to achieve the desired movement and clamping force on the object multi-unit robot  1  surrounds. Thus master controller computer  100  will independently direct a plurality of individual actuator controls A 1 , A 2 , A 3 , AN, depending on the number required to control all of the pitch, yaw and motion actuators mounted on all of the robot units  10  and  10 ′ ( FIG. 14 ). Each actuator control is located on a unit  10  or  10 ′, and controls one of its four actuators: one motion actuator  17  for each of the two wheels  15  or  15 ′, the pitch actuator  30 , and the yaw actuator  45  ( FIGS. 15-17 ). Controller computer  100  is either independently wired to each of the actuator controls in each of the units  10 ,  10 ′, or controller computer  100  controls each actuator control through wireless connections. 
         [0081]    Actuator input from master controller computer  100  is individually directed as indicated by lines  101  to each actuator control A 1 , A 2 , A 3 , . . . AN located on the robot units  10  and  10 ′ ( FIG. 14 ). The actuator control processes the information and directs an actuator  17 ,  30  or  46  to act on its respective robot unit  10  or  10 ′. The actuator  17 ,  30  or  46  provides feedback information to the actuator control, which in turn feeds it back to master controller computer  100 , as indicated by feedback lines  102 . 
         [0082]      FIG. 15  is a schematic of actuator control system A 1 , which controls a motion actuator  17 . Master controller  100  sends angular rate instructions to a unit controller  120  in actuator control A 1 , as indicated by line  101 . This signal passes through a summing point  121  and on to unit controller  120 . At the same time, unit controller  120  is receiving a feedback signal through line  107 , summing point  121  and line  108 , from a potentiometer  123 , which is measuring the rate of rotation of motion actuator  17  through feedback line  105 . The unit controller  120  is comparing these two inputs and is sending a blended resultant signal via line  104  to motion actuator  17 . At the same time, the feedback signal is being fed back to master controller  100  through summing point  121  and feedback line  102   
         [0083]      FIG. 16  is a schematic of actuator control system A 2  which controls a yaw actuator  45 . Master controller  100  sends position input instructions to a unit controller  130  in actuator control A 2 , as indicated by line  101 . This signal passes through a summing point  131  and on to unit controller  130 . At the same time, unit controller  130  is receiving a feedback signal through line  107 , summing point  131  and line  108 , from a potentiometer  133 , which is measuring the angular position of yaw actuator  45  through feedback line  105 . The unit controller  130  is comparing these two inputs and is sending a blended resultant signal via line  104  to yaw actuator  45 . At the same time, the feedback signal is being fed back to master controller  100  through summing point  131  and feedback line  102   
         [0084]      FIG. 17  is a schematic of actuator control system A 3  which controls a pitch actuator  30 . Master controller  100  sends clamping force input instructions to a unit controller  140  in actuator control A 3 , as indicated by line  101 . This signal passes through a summing point  141  and on to unit controller  140 . At the same time, unit controller  140  is receiving a feedback signal through line  107 , summing point  141  and line  108 , from a load cell  143 , which is measuring the force exerted by pitch actuator  30  through feedback line  105 . The unit controller  140  is comparing these two inputs and is sending a blended resultant signal via line  104  to pitch actuator  30 . At the same time, the feedback signal is being fed back to master controller  100  through summing point  141  and feedback line  102 . 
         [0085]    The configuration of a surface to be cleaned, painted or otherwise treated can be loaded into the computer/controller  100  in a program similar to a CNC machining program. The controller  100  then instructs the robot  1 , through various actuator control systems A 1 -An, on how to move to cover the surface completely. The computer can determine the starting point of robot  1  by the configuration of the robot at whatever point on the work surface it starts at. If desired, robot  1  may be manually controlled by an operator if automated control is not required. 
         [0086]    Alternatively, or in addition, location control can be based on an external reference source. This source will relay global position of specific point(s) of reference on the robot units  10  and  10 ′ to the master controller  100 . By comparing the external position references to the various unit positions, the controller will have an accurate position reference for each robot unit  10  or  10 ′. There are several methods of external control. The most common being GPS or ground transmitter in a known position. 
         [0087]    Unit position can be determined by feedback from a wide array of sources (e.g. pitch and yaw angle sensors, GPS, known position transmitter, drive motor rates, inertial guidance control, etc.) The unit will relay relevant position data to the payload as required. Precise position control allows for minimal user input and thus facilitates automation of a particular task. 
         [0088]    While the multi-unit robot  1  has many uses, the use illustrated and contemplated by this multi-unit mobile robot is that of servicing wind turbine blades and towers. In use, multi-unit robot  1  can be placed on a wind turbine blade, or can simply be placed at the base of the tower. The configuration of the blade, or of the entire tower and blades, is loaded into the computer/controller  100  in a program similar to a CNC machining program. Computer/controller  100  compares the configuration of multi-unit robot  1  to the configuration of the tower or blade to determine the starting position of multi-unit robot  1 . In addition, an onboard GPS may be used to communicate position information to computer/controller  100 . The computer/controller  100  then instructs the robot  1 , through various actuator control systems A 1 -An, on how to move to proceed to and on the blade in order to cover the surface completely. The multi-unit robot  1  may carry cleaning, painting, and/or other servicing equipment on the platforms  20 / 21 , which computer/controller  100  instructs to both prepare and then paint the surface of the blades or tower. 
         [0089]      FIG. 20  illustrates how the robot can transfer from one tower or object  4  to another,  4 ′. The robot can autonomously move from the tower to the wind turbine blade provided that the blade is rotated so it is parallel with the tower so the robot can make the transfer as illustrated by  FIG. 20 . 
         [0090]    In an alternate embodiment ( FIGS. 23 and 24 ), clamping force may be augmented by use of a flexible device  60  under tension, e.g. tether, rope, or chain connecting the lead and trailing mobile units  10  and/or  10 ′ of the multi-unit mobile robot. Device  60  may contain integrated features that allow it transversely slip along the work surface such as rollers or bearings. In an alternate embodiment ( FIG. 25 ), two robots  1  and  1 ′ may be connected by flexible devices  60  and  60 ′ under tension to maintain clamping force. Note that in this configuration, it is no longer required that robot  1  envelope 180°. 
         [0091]    Of course, it is understood that the foregoing is a description of preferred embodiments of the invention, and various changes and alterations can be made without departing from the spirit of the invention.