Abstract:
A low profile stepper robot is described and claimed herein. The robot includes a plurality of foot assemblies. Each foot assembly includes a suction cup, a vacuum generator, and a valve, with the vacuum generator being operationally connected to the suction cup. A conduit connects a source of operational fluid flow to the vacuum generators, and the valves allow or prevent fluid flow to the vacuum generators. Actuators are positioned between the foot assemblies and the robot base. The actuators provide for linear and rotational displacement of the foot assemblies, allowing the robot to walk and turn along an inspection surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of U.S. Provisional Patent Application No. 61/893,669 filed on Oct. 21, 2013, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to robot systems, and, more particularly, the present invention relates to a stepper robot having a vacuum-based foot assembly. 
         [0004]    2. Description of the Related Art 
         [0005]    Complex industrial plants typically include several systems each having numerous pieces of equipment. Periodic inspection of such equipment is frequently necessary to ensure safe operating conditions are maintained. Automated robotic crawling systems can be used to perform labor intensive and dangerous field inspections, and to effect any necessary repairs. 
         [0006]    The complex nature of known robotic crawling systems coupled with their functionality requirements normally results in a relatively large robot system. Such size, however, can preclude operation of the robots in environments where equipment and/or structures do not allow for the clearance required by such known systems. 
         [0007]    Thus, what is needed is a low-profile robotic inspection system. 
       SUMMARY OF THE INVENTION 
       [0008]    A low profile stepper robot is described and claimed herein. The robot includes a plurality of foot assemblies. Each foot assembly includes a suction cup, a vacuum generator, and a valve, with the vacuum generator being operationally connected to the suction cup. A conduit connects a source of operational fluid flow to the vacuum generators, and the valves allow or prevent fluid flow to the vacuum generators. 
         [0009]    The foot assemblies are connected to a base of the robot. Actuators are positioned between the foot assemblies and the base. A first of the actuators is positioned so as to linearly displace one of the foot assemblies relative the base such that its suction cup can be moved, thereby allowing the robot to step or move along the inspection surface. A second of the actuators is positioned so as to rotationally displace one of the foot assemblies relative the base such that its suction cup can be rotated, thereby allowing the robot to turn along the inspection surface. By varying the attachment of this turning suction cup, the robot can be turned in either direction. 
         [0010]    Optionally, additional actuators can be included to vertically displace the suction cups from the base, thereby allowing the robot to be raised from the inspection surface. This allows the robot to pass over obstacles that may be encountered on the inspection surface. 
         [0011]    A pressure sensor is included with each foot assembly to ensure a vacuum is present prior to releasing the other foot assembly from the inspection surface. This ensures the robot does not become separated from the inspection surface. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention is described with reference to the accompanying drawings, which illustrate exemplary embodiments and in which like reference characters reference like elements. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
           [0013]      FIG. 1  shows a bottom view of a robot of the present invention with array sensors and feet aligned and in a first walking position. 
           [0014]      FIG. 2  shows a top view of a foot assembly of the robot assembly of  FIG. 1 . 
           [0015]      FIG. 3  shows a side cross-sectional view of the foot assembly of  FIG. 2 . 
           [0016]      FIG. 4  shows a bottom view of the robot assembly of  FIG. 1  with array sensors and feet aligned and in second walking position. 
           [0017]      FIG. 5  shows a bottom view of the robot assembly of  FIG. 1  with feet actuated to a turning position. 
           [0018]      FIG. 6  shows a bottom view of the robot assembly of  FIG. 1  with a linear carriage attached to a walking base. 
           [0019]      FIG. 7  shows a side cross-sectional view of the robot assembly of  FIG. 1  including optional lifting components. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The inventive vacuum stepper robot is a low-profile walking robot for inspection of any relatively smooth surface material. Exemplary inspection sensors can include ultrasound or eddy current equipment, or video cameras for visual inspections. While a variety of applications are available, the robot is particularly suited for inspection and/or repair of carbon-fiber reinforced plastics used in aircrafts and wind-turbine blades, and for stainless steel piping where magnetically coupled crawlers cannot be used. 
         [0021]      FIG. 1  shows a bottom view of a preferred embodiment of a robot  1  of the present invention, and  FIGS. 2 and 3  show top and side cross-sectional views, respectively, of a foot assembly  10  of the robot  1 . The robot  1  includes at least two vacuum foot assemblies  10 . Each vacuum foot assembly  10  includes a gasketed suction cup  12 , a vacuum generator  14 , a valve  16 , and a pressure sensor  18 . The valve  16  preferably is a remotely actuated valve, and it may be positioned on the foot  10  or in a valve manifold on the base of the robot  1 . When the valve  16  is open, operating fluid such as air or water flows through a flexible supply hose  20  to the nozzle  14 . The vacuum generated within the throat of the nozzle  14  is ported to the suction cup  12 , which is in contact with the walking or inspection surface  50 . Once a vacuum is established, the pressure sensor  18  confirms the presence of a vacuum within the suction cup  12  in known manner. The vacuum is maintained as long as fluid flows through the nozzle  14 , and the vacuum is released by shutting off the flow to the nozzle  14 . The pressure sensor  18  preferably may be a switch that is closed in the presence of a vacuum from its default open position. 
         [0022]    In a preferred embodiment, the vacuum generator  14  is based on a venturi nozzle  14 . A venturi nozzle or tube includes an inlet, a convergent cone, a throat, and an optional divergent cone. As fluid flows through the convergent portion of the nozzle  14 , the fluid velocity increases and at the same time its pressure decreases. In use, a vacuum is created within the suction cup  12  by porting the throat of the nozzle  14  thereto. A divergent zone can optionally be included downstream of the throat to reduce the overall pressure loss. 
         [0023]    Preferably, the vacuum generator  14  provides a suction force of at least 25 pounds as measured in air. This should ensure the robot  1  remains connected to the surface  50  during operation. If additional suction force is required, the flow through the nozzle  14  can be increased. Alternatively or additionally, the surface area of the foot assemblies can be increased, either by including additional feet or increasing the size of the existing feet. While oval suction cups  12  are shown in the illustrated embodiments, any shape may be used. 
         [0024]    The walking assembly  1  includes two or more vacuum foot assemblies  10  as illustrated in  FIG. 1 . The foot assemblies  10  are shown as two pairs of feet to distribute the load over a broader area. This is a preferred implementation, but is not necessary for the system  1  to perform the target stepping function. While not depicted in  FIG. 1 , it will be understood that the operational fluid flow provided by the hose  20  is connected to each foot assembly  10  by a separate valve  16 , allowing each foot assembly  10  to be controlled independent of other foot assemblies  10 . 
         [0025]    For purpose of explanation, the paired foot assemblies  10  will be designated as walking foot  10   a  and turning foot  10   b . With its valve  16  open, turning foot  10   b  is adhered by suction to the walking surface  50  to initially attach the entire assembly  1  to the walking surface  50 . The walking foot  10   a  with its valve  16  closed can then be advanced forward by an actuator  22  that pushes the foot assembly  10   a  several millimeters ahead of the robot base plate  24 . The actuator  22  may preferably be an air cylinder. This is illustrated in  FIG. 4 . If the surface roughness is extreme, this advance of walking foot may be preceded by a lifting of the foot  10   a  and followed by a lowering of the foot  10   a  using a similar actuator  25  to the actuator  22  used to advance the foot. Once the walking foot  10   a  is in contact with the surface  50  at the desired advanced location, its valve  16  is opened to start the vacuum and suck the walking foot  10   a  to the surface  50 . The presence of a vacuum in the walking foot  10   a  may be confirmed with the pressure sensor  18  prior to releasing the turning foot  10   b  so that the robot never releases the turning foot  10   b  until the walking foot  10   a  is confirmed to be connected to the surface  50 . This precludes the robot  1  from falling due to the vacuum not being established. 
         [0026]    With walking foot  10   a  firmly attached to the surface  50 , the turning foot  10   b  can be released by closing its valve  16 . This allows the turning foot  10   b  to slide along the surface  50 . If the surface  50  is rough, the same actuator discussed with walking foot  10   a  can lift and lower the turning foot assembly  10   b . Alternatively, each foot assembly  10  can be provided with a separate lifting actuator  25  as illustrated in  FIG. 7 . The turning foot  10   b  as well as the rest of the robot assembly  1  is then advanced by the walking foot actuator  23  as it shifts state. The turning foot  10   b  valve  16  is then opened, thereby allowing the turning foot  10   b  to suck and adhere to the surface  50 . Suction is confirmed by the pressure sensor  18 . Controller logic preferably will not allow either foot  10   a ,  10   b  to release until vacuum suction (and therefore connection of the robot  1  to the surface  50 ) is confirmed in the other foot  10   b ,  10   a . The walking step can then be repeated. Cycle times can be quite short (less than 1 or 2 seconds) because of the close proximity of the vacuum generators  14  to the suction feet  10   a ,  10   b . The length of each step is repeatable and adjustable as the actuators  22  drive the walking foot assembly  10   a  to a hard-stop that can be adjusted from approximately 1 mm to more than 10 mm. The robot assembly  1  can travel in the circumferential direction, which is preferred for scanning a full pipe, or the axial direction. 
         [0027]    Steering of the assembly  1  is effected with a similar set of actuators to the walking actuators  22 ,  23 . The turning feet  10   b  are mounted on a platen  26  that that can rotate from a first state of being aligned with the robot carriage ( FIGS. 1 and 4 ) to a second state of being angled few degrees in one direction relative the robot carriage ( FIG. 5 ). If the turning foot platen  26  is aligned with the robot carriage and correspondingly with the walking foot  10   a , then the robot assembly  1  will walk in a straight line. If this straight line needs to be adjusted or steered, the turning platen actuator  28  is engaged. The assembly  1  may be turned one way by engaging the turning platen actuator  28  before the walking feet  10   a  are advanced; that is, with the turning foot  10   b  engaged with the surface  50 . The assembly  1  can be turned the opposite way by rotating the turning foot  10   b  to the angled position while they are not engaged with the surface  50  and while they are being advanced by the walking feet actuator  22 . This is illustrated in  FIG. 5 . After the turning foot  10   b  is re-engaged with the surface  50  and after the walking feet  10   a  are released from the surface  50 , the turning foot  10   b  may return the turning foot platen  26  to be aligned with the robot assembly  1 . This effectively rotates the assembly  1  in the other direction by the number of degrees allowed by the turning platen hard-stop. 
         [0028]    Steering the robot  1  can be done either in an open loop simply relying on the known step distance and step turn degrees which are precisely set and controlled by an adjustable hard-stop, or with a closed loop independent position sensing system like a stereo vision position sensor or a laser tracker or an independent optical mouse encoder. Reference is made to commonly owned U.S. patent application Ser. Nos. 13/731,580 and 13/731,709, which are incorporated herein. 
         [0029]    The valve manifold  30  is connected to a flexible umbilical and tether  32  that can be more than 30 meters long without compromising function. This allows the robot  1  to crawl out of direct view of an operator to inspect parts that are difficult to access. Normally if the umbilical will be used where there is a concern for losing the robot  1 , the umbilical hoses and control wires would include a steel tether cable to pull the robot back to the operating station location. 
         [0030]    A sensor arm  34  is connected to the main body of the robot  1  and can have several embodiments. For example, as shown in  FIG. 6 , a single sensor  38  can be used. If this is the case, the stepper must steer back and forth to cover an area wider than the sensor area covered. Alternatively, as illustrated in  FIGS. 1-5 , an array of sensors  38  can be used to cover a wide swath of material with each pass of the robot  1 . Another example, a scanning arm can be used. Scanning arms typically contain a motor  36  attached to the arm  34  driving a belt or a lead-screw to translate a sensor  38  across the area to be examined. 
         [0031]    The robot  1  is a low profile robot, allowing it to operate in environments with tight spacing such as industrial piping systems. In such systems, there may only be a few inches of space between system components, precluding the use of typical crawler systems. The robot  1  has a height H that preferably is 5 inches or less, and more preferably 3 inches or less. This height H is a measurement of the total height of the system, including all components. The foot assembly components (suction cup  12 , vacuum generator  14 , valve  16 , and pressure sensor  18 ), actuators  22 , and base plate  24  are chosen and positioned to minimize their combined height. The placement of these components is also chosen to minimize the height H. While the vacuum generator  14 , valve  16 , and pressure sensor  18  are shown in the figures as being vertically in line with the suction cup  12  for illustrate purposes, these components may preferably be positioned horizontally offset from (that is, not vertically aligned with) the suction cup  12 . This placement allows the vacuum generator  14 , valve  16 , and pressure sensor  18  to be lowered and positioned more horizontally aligned with the suction cup  12  (but not impeding movement of the robot  1 ), further reducing the overall height of the robot  1 . The overall height of the robot  1  is further minimized by attaching the sensor arm  34  to a side of the base plate  24  rather than the top surface thereof. The robot  1  also has a relatively small footprint, preferably 1 ft 2  or less and more preferably 10 in 2  or less. This footprint is an overall footprint, a measurement of the total surface area covered by the robot including all components. The low profile character of the robot  1  allows the robot  1  to operate with tight spacing between components. The small footprint, and particularly using closely spaced and relatively small vacuum feet, allows the robot to navigate surfaces having a small radius of curvature. 
         [0032]    A prototype unit used four foot assembly having feet that are approximately 1.8 inches wide by 8 inches long. Allowing for the side-by-side spacing among the feet, this yields a compact total footprint that is approximately 8 in 2 . The design must trade-off stability associated with wider spacing of the feet versus the need for a small overall footprint in order to move on small radius of curvature parts. The strong vacuum provides sufficient holding force to counteract side moments without expanding or spreading the feet beyond the compact square configuration. 
         [0033]    The disclosed configuration can work on flat surfaces to surfaces having radii of curvatures of approximately 18 inches. Smaller radii of curvature can also be scanned if contoured feet are provided. The stepper robot can travel preferentially in the circumferential direction (preferred for scanning a full pipe) or axial direction. The reason the circumferential stepping is preferred is that this allows a full circumferential stepping run for scanning a circumferential weld. Axial motion to scan the transducer up to the weld or across the weld can be achieved via a low-profile linear scanner positioned on the front of the stepper platform or by a sufficient number of side-by-side transducers to cover the target inspection surface. 
         [0034]    While the preferred embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not of limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. Furthermore, while certain advantages of the invention have been described herein, it is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.