Abstract:
A rotary actuator mechanism for applying torque to a shaft and comprising an actuator housing forming an actuator path that includes an actuator pinion rotatably supported in said housing and having said shaft secured thereto. The pinion having peripheral notches of a selected shape and positioned within the actuator path. The mechanism having a train of discrete actuator elements having opposite ends and positioned in the actuator path, each of the actuator elements being of said selected shape to enable reception in the peripheral notches, a plurality of the elements engaging the notches. The mechanism having at least one linear actuator supported by the housing and engaging one of the ends of the train of actuator elements, the linear actuator being selectively activated to push the train of discrete actuator elements through the actuator path to thereby serially engage the actuator elements with the notches of the pinion and thereby apply torque to the shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/279,853, filed Oct. 27, 2009 and incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention is broadly directed to actuator mechanisms and, more particularly, to embodiments of a ball and piston rotary actuator mechanism using linear actuators to pivot a first structure relative to a second structure. 
         [0003]    Many robotic devices utilize robotic arms or arm like structures (herein generally referred to as arms) for conducting work at a site of use. Often such robotic arms are utilized in environments which are dangerous or hazardous to humans, such as deep sea construction or exploration, chemical or explosives handling, outer space construction and the like. An example of such use of robotic arms is described in U.S. Pat. No. 4,648,782, which is incorporated herein by reference. 
         [0004]    A robotic arm generally includes an elongated arm member which is pivotally connected to another structure, such as a support base or another robotic arm member. Some sort of motor is engaged between the arm member and the other structure to cause relative pivotal movement therebetween. The type of motor used depends on the intended function of the robotic arm. For high torque applications, it has been common to provide parallel sets of push/pull hydraulic cylinder arrangements which linearly move a rack gear engaged with a pinion gear secured to a shaft to which another arm is attached. One problem with such an arrangement is that one set of cylinders typically projects from the end of the arm. In some situations, such projecting cylinders can limit range of motion of the attached arm and are also vulnerable to damage by unintended contact with other structures. 
         [0005]    Another approach to robotic arm articulation has involved vane motors. A vane motor typically has an annular chamber in fluid pressure between a fixed vane member and a movable vane connected to a shaft causes the movable vane to move thereby applying torque to the shaft. A problem with vane motors is a rotary stroke of less than 360 degrees because of space taken up by the fixed and movable vanes. In some robotic applications, a pivot range of greater than 360 degrees is desirable. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides an improved rotary actuator mechanism which is compact and which can be implemented with a range exceeding 360 degrees. 
         [0007]    The rotary actuator mechanism includes a notched actuator pinion rotatably mounted in an actuator housing which defines an actuator path impinging on the notched pinion secured to an output shaft, a train of discrete actuator elements having opposite ends and positioned in the actuator path with at least one actuator element engaging a notch in the pinion, and at least one linear actuator engaging an end of the train of actuator elements. The linear actuator is activated to push the train of actuator elements to serially engage the notches of the pinion to thereby apply torque to the shaft. 
         [0008]    More particularly, an embodiment of the rotary actuator includes an actuator housing forming a U-shaped actuator path. An actuator pinion is rotatably mounted in the housing and has a plurality of spherical notches formed in a periphery of the pinion. The pinion is positioned in the housing such that the U-shaped portion of the path passes around a portion of the pinion. A train of discrete, spherical actuator elements or actuator balls are positioned in the actuator path with a plurality of the actuator balls engage the spherical notches in the pinion. A pair of hydraulic actuators or cylinders are secured in spaced apart parallel relation on the housing and communicate with the actuator path. Each of the cylinders includes a piston which is engaged with a respective end of the ball train. The actuator path may be partially defined by a ramp structure to guide the balls onto the pinion and from the pinion back into straight legs of the U-shaped actuator path. Thus, the housing and the pinion form a curved or bight section of the actuator path, while the ramp structure and portions of the cylinders form straight leg sections of the actuator path. 
         [0009]    The cylinders are activated in coordination to reversibly push the balls through the actuator path and serially engaging the notches in the pinion to rotate it and thereby apply torque to a shaft or other torque transfer element secured to the shaft. The cylinders are provided with suitable valves so that as one cylinder is being filled with hydraulic fluid, the other cylinder is exhausting fluid from its chamber. 
         [0010]    An actuator housing is secured to one or both ends of a robotic arm and is activated to pivot the arm relative to another structure or to pivot another structure, such as a second robotic arm, relative to the first arm. The cylinders may be mounted entirely within the robotic arm structure so as to form a compact rotary actuator mechanism for a robotic arm. 
         [0011]    While the present invention is quite useful as an actuator over a wide range of external pressures and in conjunction with the need for more or less tight control (precision control) over the device in which the actuator is used, the actuator of the present invention provides special advantages where used in environments under comparatively high pressure (for example, 3000 pounds per square inch pressure) and/or where very precise movements are to be controlled by the actuator. In particular, in some embodiments the piston driver can be hydraulically locked in position without leakage, so that a position can be precisely held while applying force or under load. In other embodiments, because the individual actuator elements are generally inelastic in both compression and stretch, movement is controlled precisely and without compression or stretch that can occur in some types of actuators. Therefore, for some embodiments the present actuator provides one or more of the advantages of being lockable in position, stiff and precise in movement under control of a user, operates with zero leakage when locked and/or may operate under high external pressure conditions. 
         [0012]    Various objects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
         [0013]    The drawings constitute a part of this specification, include exemplary embodiments of the present invention, and illustrate various objects and features thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view of a multi-link robotic arm assembly in which an embodiment of a ball and piston rotary actuator mechanism of the present invention is installed. 
           [0015]      FIG. 2  is a perspective view of an embodiment of a ball and piston rotary actuator mechanism according to the present invention, shown with an annular torque transfer element. 
           [0016]      FIG. 3  is a perspective view of another embodiment of a ball and piston rotary actuator mechanism with a pinion gear torque transfer element. 
           [0017]      FIG. 4  is an enlarged cross sectional view taken on line  4 - 4  of  FIG. 2  and illustrates internal details of an embodiment of the ball and piston rotary actuator mechanism. 
           [0018]      FIG. 5  is an enlarged cross sectional view similar to  FIG. 4  and shows the ball train in an alternative position within an actuator path of the actuator mechanism. 
           [0019]      FIG. 6  a diagrammatic side elevational view of a multi-link robotic arm assembly with walls broken away to illustrate the incorporation of three ball and piston rotary actuator mechanisms according to the present invention, including internal details of the mechanisms. 
           [0020]      FIG. 7  is a perspective view of the actuator mechanism of  FIG. 2  with exterior portions shown in phantom to better illustrate the interior thereof. 
           [0021]      FIG. 8  is a perspective view of the actuator mechanism of  FIG. 2 , similar to the view of  FIG. 7  except with an outer U-shaped pathway removed and with the exterior portion shown in phantom to better illustrate the interior thereof. 
           [0022]      FIG. 9  is an enlarged perspective view of a wall and recup block structure of the actuator mechanism of  FIG. 2 . 
           [0023]      FIG. 10  is a cross-sectional view of the actuator mechanism, taken along the line  10 - 10  of  FIG. 8  with the exterior phantom lines removed to better show interior structure thereof. 
           [0024]      FIG. 11  is a side elevational view of an actuator rotor assembly of the actuator mechanism of  FIG. 2  on a reduced scale, also showing a single ball shaped actuator element in phantom, so as to better illustrate the relationship of actuator elements with the rotor assembly. 
           [0025]      FIG. 12  is a cross-sectional view of the actuator rotor assembly, taken along line  12 - 12  of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
         [0027]    Referring to the drawings in more detail, the reference numeral  1  (in  FIGS. 1-11 ) generally designates an embodiment of a ball and piston rotary actuator mechanism according to the present invention. The mechanism  1  is controlled to cause relative pivoting between structures interconnected by the mechanism  1 , such as between components of a robotic arm assembly  2  ( FIG. 1 ). 
         [0028]    The illustrated robotic arm assembly  2  includes a base link or base  5  to which is pivotally connected a first robotic arm member  6  and a second robotic arm member  7  pivotally connected to the first arm member  6 . The second arm member  7  may have an additional robotic arm member (not shown) connected to its outer end, a robotic gripper or hand assembly (not shown) or the like. The mechanism  1  is applied to the illustrated robotic arm assembly  2  in multiple locations to form a first pivotal arm joint  10  between the first arm member  6  and the base link  5 , a second pivotal arm joint  11  between the first arm member  6  and the second arm member  7 , and a third pivotal arm joint  12  between the second arm member  7  and another structure (not shown). 
         [0029]    Referring to  FIG. 2 , the illustrated actuator mechanism  1  includes an actuator housing  15  including a U-shaped main wall  17 , a pair of opposite side walls  18 , and a rectangular end wall  19 . The main wall  17  encloses top and bottom sides and an outer end  19  of the housing  15 . The side walls  18  of the enclosure  15  rotatably support an actuator rotor assembly  22  including at least one externally accessibly torque transfer element  24  and an internal shaft  26  ( FIGS. 4 and 5 ) for rotation about an actuator rotor axis  27 . The embodiment of the mechanism  1  illustrated in  FIG. 2  has a torque transfer element  24  in the form of a torque transfer ring  28 . In many configurations, the housing  15  has torque transfer elements  24  accessible through both side walls  18 , as is shown in  FIG. 1  in which joint connection yokes  30  and  32  that are secured respectively to robotic arm members  5  and  7 , are secured to pairs of torque rings  28  accessible at opposite sides of the robotic arm member  6  at joints  10  and  11  of the robotic arm assembly  2 . Alternatively, the torque transfer element  24  can be provided in other forms, such as a splined or other non-round shaft  34 , as shown alternatively in  FIG. 3 , a cylindrical shaft (not shown), a gear member, or the like. The end wall  19  completes the housing  15  and provides support for a pair of linear actuator members  36  and  38 . 
         [0030]    Referring to  FIGS. 4 and 5 , the housing  15  cooperates with the linear actuators  36  and  38  to form or define a U-shaped actuator path  40 , see especially  FIG. 10 , extending from the linear actuator  36  and around the actuator rotor  22  to the linear actuator  38 . The actuator rotor  22  includes an actuator pinion member  42  which is secured to the internal shaft  26 . The pinion member  42  has a plurality of pinion notches  44  formed radially thereinto, spaced circumferentially about the pinion member  42 , and positioned to impinge or be tangent with the U-shaped actuator path  40 . The notches  44  are sized and shaped to receive discrete actuator elements  48  therein. The actuator elements  48  collectively form an actuator train  50  which is positioned within the U-shaped actuator path  40  from one linear actuator  36  to the opposite linear actuator  38 . In the embodiment of the mechanism  1  shown in  FIGS. 4 and 5 , the actuator elements  48  are spherical elements in the nature of ball bearings or actuator balls. Thus, the pinion notches  44  are also spherical in shape, and the U-shaped path  40  has a circular cross-sectional shaped. It is foreseen that the actuator elements  48  could have alternative shapes, such as cylindrical that are suitable for rolling along an approximately shaped U-shaped path. 
         [0031]    The illustrated linear actuators  36  and  38  are hydraulic cylinders, each having an elongated cylindrical fluid chamber  54  and a piston  56  sealingly positioned within the chamber and slidable therealong. Each chamber  54  communicates with a hydraulic fluid port  58  through which pressurized hydraulic fluid is injected into the chamber  54  to linearly move the piston  56  or through which fluid can be exhausted by the coordinated action of hydraulic valves (not shown), in a conventional manner. Each of the pistons  56  has a spherically cupped contact surface  60  which engages a respective end element  62  of the train  50  of actuator elements  48 . 
         [0032]    The linear actuators  36  and  38  are illustrated as positioned in spaced apart parallel relation to align respectively with straight portions  64  and  65  respectively of the U-shaped path  40 , which are interconnected by a substantially 180 degree curved or bight section  66  of the path  40 . The illustrated mechanism  1  is provided with a recup or ramp block  68  with opposite parallel surfaces  70  to guide the balls  48  into the notches  44  of the pinion  42  and from the notches  44  back into the straight portions  64  and  66 , of the path  40 . The ramp block  68  is shown joined to end wall  19  in  FIG. 9  separate from the remainder of the mechanism  1  to better show the detail thereof. The ramp block  68  has a curved wall  71  opposite the end wall  19  that operably slidably abuts or is positioned closely adjacent to the internal shaft  26 , as seen in  FIG. 10 . It is foreseen that the linear actuators  36  and  38  could have angular relationships other than 180 degrees. And while the linear actuators  36  and  38  are illustrated as both being active actuators, it is foreseen that one of the linear actuators could be replaced by a return spring (not shown). 
         [0033]    In operation of the ball and piston rotary actuator mechanism  1 , the linear actuators  36  and  38  operate in opposition to reversibly push the train  50  of discrete actuator elements or balls  48  through the U-shaped path  40 , serially engaging the balls  48  with the notches  44  in the actuator pinion  42 , thereby creating a moment about the actuator rotor axis  27 , resulting in torque applied to the actuator rotor assembly  22 . As hydraulic fluid is injected under pressure into the chamber  54  of the actuator  36 , the piston  56  engages the cupped surface  60  with the end ball  62  of the ball train  50 , thereby pushing the ball train  50  about the pinion  42  and against the piston  56  of the actuator  38  and creating counterclockwise torque (as viewed in  FIGS. 4 and 5 ) in the rotor  22 , as fluid is exhausted from the actuator  38 . The operation to create clockwise torque in the rotor  22  is reversed as the chamber  54  of the actuator  38  is pressurized as the chamber  54  of the actuator  36  is exhausted. 
         [0034]    Torque applied to the actuator rotor  22  causes a structure secured to the torque transfer element  24  to be pivoted, such as the robotic arm member  7  relative to the arm member  6 , or causes the structure in which the mechanism  1  is mounted to pivot, such as the arm  6  relative to the base link  5 . As is shown particularly in  FIG. 6 , the linear actuators  36  and  38  are mounted entirely within the arm members  6  and  7  to provide a compact configuration of a rotary actuator mechanism. 
         [0035]    The end wall  19  has a pair of spaced bores or apertures  74  sized sufficiently large to allow passage of the actuator elements  48  therethrough.  FIG. 7  shows the mechanism  1  with the actuator housing  15  in phantom showing the inner surface  76  of the housing  5  to provide greater detail of the interior.  FIG. 8  shows both the actuator housing  15  and its inner surface  76  in phantom to show even greater detail of the interior of the mechanism  1 .  FIG. 10  is a cross-section of  FIG. 8  showing interior detail with all phantom lines removed.  FIG. 9  is an enlarged and separated view of the end wall  19  and ramp block  68  to better illustrate their detail and  FIG. 11  is a similar stand alone view of the rotor assembly  22 . 
         [0036]    While the illustrated linear actuators  36  and  38  are hydraulic in operation, it is foreseen that the linear actuators  36  and  38  could be of other configurations, such as pneumatic, electromotive, or the like. And while the rotary actuator mechanism  1  is described in association with a robotic arm assembly  2 , other advantageous applications of embodiments of the ball and piston rotary actuator mechanism  1  are foreseen. 
         [0037]    In use the mechanism  1  works by utilizing the actuator members  36  and  38  to alternatively drive to actuator members  48  (here balls) about the U-Shaped path  40 . The path  40  is defined by a portion of each actuator member  36  and  38 , the bores  74  in the end wall  19  and the space between U-Shaped main wall  17 , the rotor assembly  22  and the side walls  18 . As the actuator members  48  traverse the path  40  each engages and is received in a pinion notch  48  of the actuator rotor assembly  22 . Movement of the actuator members  48  in either direction along the path  40  causes corresponding movement (here rotation) of the actuator rotor assembly  22  and subsequently any element joined to the assembly  22  rotates about the axis thereof. 
         [0038]    It is to be understood that while certain forms of the present invention have been described and illustrated herein, it is not to be limited to the specific forms or arrangement of parts described and shown.