Abstract:
A rotary actuator is provided which includes a first interface surface with a plurality of apertures defined therein; a plurality of interface modules, wherein each interface module includes a first portion which releasably engages one of said apertures, and a second portion which protrudes from said first interface surface; a second interface surface which releasably mates with said first interface surface; and a gear train which rotates said first interface surface about an axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority from U.S. Provisional Application No. 61/994,360, filed May 16, 2014, having the same inventor and the same title, and which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates generally to rotary actuators, and more specifically to a quick change interface for a rotary actuator. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    Electromechanical actuators (EMAs) play a key role in the performance and cost effectiveness of intelligent electro-mechanical systems. This role is underscored by the growing market for EMAs. Indeed, significant parallels exist between the market development currently unfolding for EMAs and the market development of semiconductor chips seen in the electronics industry over the past several decades. At present, it is forecasted that EMAs will see a continued growth of 50% every three years, and that the market for EMAs will exceed the market for semiconductor chips in two decades. 
         [0004]    In order for EMAs to realize their full commercial potential, it is important for the cost structure of these devices to be reduced. This, in turn, requires that EMAs become more modularized, so that a relatively small set of EMAs may be developed which span a wide range of applications. By contrast, much of the development in EMAs to date has occurred via an ad hoc approach, in which EMAs are developed for a particular end use and are unsuitable for a broader range of applications. 
         [0005]    The realization of a modularized set of EMAs requires the further development of quick-change interfaces to allow the actuators to be quickly adapted or repurposed to work with different tools and systems. Several interfaces have been developed in the art to date. The interfaces depicted in  FIG. 1  (not all of which are quick-change interfaces) are representative, and include the Nema flanged interface  101 , the Nema bolt circle interface  103 , the kinematic coupling interface  201 , the Curvic rigid coupling interface  301 , and the Tesar-Shin precision coupling interface  401 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is an illustration of various prior art actuator interfaces. 
           [0007]      FIG. 2  is an illustration of a kinematic coupling interface. 
           [0008]      FIG. 3  is an illustration of a Tesar-Shin precision coupling interface. 
           [0009]      FIG. 4  is a close-up illustration of the mating elements of the Tesar-Shin precision coupling interface of  FIG. 3 . 
           [0010]      FIG. 5  is an illustration of a portion of a C-clamp used with the Tesar-Shin precision coupling interface of  FIG. 3 . 
           [0011]      FIG. 6  is an illustration of a Curvic rigid coupling interface with close-up views of the mating elements thereof. 
           [0012]      FIG. 7  is an illustration of various pins that may be utilized in an embodiment of a variation of the Tesar-Shin precision coupling interface made in accordance with the teachings herein. 
           [0013]      FIG. 8  is an illustration of a rigid wedge module which may be utilized in an embodiment of a variation of the Tesar-Shin precision coupling interface made in accordance with the teachings herein. 
           [0014]      FIG. 9  is an illustration of a deformable wedge module which may be utilized in an embodiment of a variation of the Tesar-Shin precision coupling interface made in accordance with the teachings herein. 
           [0015]      FIG. 10  is an illustration of an embodiment of a variation of the Tesar-Shin precision coupling interface made in accordance with the teachings herein which includes a link equipped with deformable wedge modules and an actuator equipped with rigid wedge modules. 
       
    
    
     SUMMARY OF THE DISCLOSURE 
       [0016]    In one aspect, a rotary actuator is provided which comprises a first interface surface with a plurality of apertures defined therein; a plurality of interface modules, wherein each interface module includes a first portion which releasably engages one of said apertures, and a second portion which protrudes from said first interface surface; a second interface surface which releasably mates with said first interface surface; and a gear train which rotates said first interface surface about an axis. 
       DETAILED DESCRIPTION 
       [0017]    Many of the actuator interfaces developed to date have limitations that preclude them from serving as quick-change interfaces for a modularized set of EMAs. For example, although the NEMA bolt  101  and bolt/flange  103  interfaces (see  FIG. 1 ) are low cost interfaces, these devices utilize 4-8 bolts to achieve a coupling, and hence are not considered quick-change interfaces. 
         [0018]    Moreover, the NEMA interfaces  101 ,  103  provide relatively poor accuracy. Here, the term “accuracy” is used to specify the degree of repeatable assembly the interface offers, and hence indicates the degree of positional variation that occurs when the interface is disassembled and reassembled. Interfaces exhibiting poor accuracy are undesirable because their use requires metrology and calibration to ensure positional accuracy, thus precluding their use as quick-change interfaces in applications where positional accuracy is important. For sake of completeness, it is to be noted that, although the Nema flanged interface  103  is equipped with a flange that provides improved radial stiffness compared to the Nema bolt interface  101 , this modification provides only a modest improvement in accuracy. 
         [0019]    The kinematic coupling interface  201  is shown in greater detail in  FIG. 2 . As seen therein, this interface utilizes a first member  203  equipped with a series of grooves  205  and a second member  207  equipped with a series of balls  209 . In use, the ball  209  and groove  205  pairs engage to provide Hertzian contacts. The kinematic coupling interface  201  provides good accuracy in the axial direction. However, it exhibits low stiffness and low load capacity, and is overly compliant (that is, it lacks suitable stiffness) in virtually all directions. For this reason, in applications requiring accuracy and stiffness, the Curvic  301  (see  FIG. 3 ) and Tesar/Shin  401  (see  FIG. 4 ) interfaces are typically the interfaces of choice. 
         [0020]    As seen in  FIG. 3 , the Curvic rigid coupling interface  301  utilizes a pair of meshing faced toroidal gears in the form of a rotary disc  303  (disposed within a stationary disc  305 ) and a releasing disc  307  to provide a very rigid, rugged and accurate repeatable interface. The Curvic interface  301  utilizes pairs of concave  309  and convex  311  teeth to achieve contact, which ensures proper alignment when the stationary disc  305  and releasing disc  307  are pressed together. Further, because of the mating of the concave  309  and convex  311  teeth, the distance from coupling centerline to the OD of the coupling will always be the same, as will be the face of whatever the coupling is affixed to. However, despite its many advantages, the Curvic coupling requires a high closing force generated by bolts in a heavy structure, and thus is not considered a quick-change interface. 
         [0021]    The Tesar-Shin precision coupling interface  401 , which is depicted in  FIGS. 4-6 , comprises a first  403  mating member equipped with a series of split wedges  405 , and a second  407  mating member equipped with wedge mating surfaces  409  and a ring of contact flats  411 . In a typical embodiment, the interface  401  utilizes 16 flexible tooth pairs (the split wedges  405  and wedge mating surfaces  409 ), the ring of contact flats  411  and a quick-change split C-clamp  413  (see  FIG. 6 ) to achieve contact. 
         [0022]    The Tesar-Shin interface  401  interface provides high accuracy, good stiffness, and low weight. The mating surfaces in this interface  401  are contained in repeating modules (4 up to 16), all of which may be machined on standard tools. Moreover, the precision assembly of split wedges  405  represents a deformable (compliant) structure which dramatically improves closing accuracy. This result is achieved with an in-depth body of analytics which controls the relative influence of forces, deformations, and tolerances. Once it has achieved accurate closure, the contact flats  411  provide for the necessary out-of-plane stiffness. Also, the split C-clamp  413  ( FIG. 6 ), which uses tapered wedges  415  to generate the closing force, is designed to accommodate a standard commercial tightening band in its outside flat cylindrical groove  417 . 
         [0023]    As noted above, the Tesar-Shin interface  401  possesses many advantages in comparison to other known rotary actuator interfaces. However, despite its many advantages, a need exists in the art to produce an interface that is less expensive to produce and more modular in design than the existing Tesar-Shin interface  401 . 
         [0024]    It has now been found that the foregoing needs may be met the through the provision of a quick-change interface for a rotary actuator that comprises first and second mating members, each of which is equipped with a series of modules that engage one of a plurality of apertures in the member, preferably in a press-fit manner. Each of the modules contains a plurality of mating features, such that the mating features on the first member releasably engage the mating features on the second member. 
         [0025]      FIG. 7  illustrates a first particular, non-limiting embodiment of an interface for a rotary actuator in accordance with the teachings herein. As seen therein, the interface  501  comprises a first annular member  503  which has a centering ring  505  thereon which is equipped with a plurality of apertures  507 . The annular member  503  is equipped with an annular groove  509  which may be utilized to secure the first annular member  503  to a second annular member (not shown) by way of a split clamp (e.g., of the type depicted in  FIG. 6 ) or other suitable device. The interface  501  is further equipped with one or more precision cylindrical pins  511  which engage the apertures  507  in the first annular member  503 , and which provide pre-assembly alignment before large closing forces are applied (by, for example, bolts, screws or other suitable fasteners). 
         [0026]    While the use of the cylindrical pins  511  enhances radial accuracy and thus augments the accuracy provided by the centering ring  505 , it does little to assist in out-of-plane accuracy or rotary stiffness. Some improvement in centering accuracy may be obtained through the use of a 7° tapered pin  513 . In applications where it is desirable to make the tapered pin deformable, a slotted tapered pin  515  may be provided, which differs from the tapered pin  513  in that it is equipped with two perpendicular slots  517 . 
         [0027]    When a tapered pin is utilized, the hole taper is typically within the range of 5° to 10°, preferably within the range of 6° to 9°, more preferably within the range of 7° to 8°, and most preferably about 7.5°, while the pin is preferably tapered at about 0.5° less than the hole taper. The top width of the pin is typically about 0.05″ to about 0.002″ less than the hole width, and preferably 0.001″ less than the hole width (d 2 -0.001″). The bottom of the taper is preferably slightly larger in diameter than the mating hole, more preferably has a diameter within the range of about 0.0001″ to about 0.0003″, and most preferably has a diameter of about 0.0002″ (d 1 -0.0002″) to improve closing accuracy. 
         [0028]      FIGS. 8-10  depict another particular, non-limiting embodiment of a quick-change interface  601  for a rotary actuator in accordance with the teachings herein. In this embodiment, a Tesar/Shin type interface is achieved through the use of deformable wedge modules  603  and rigid wedge modules  605 , which are shown in greater detail in  FIGS. 9 and 10 , respectively. The deformable wedge modules  603  and rigid wedge modules  605  are utilized as standardized press fit plug-ins on the periphery of the first  607  and second  609  annular members forming the interface. 
         [0029]    As seen in  FIG. 9 , the deformable wedge module  603  is equipped with a pair of symmetrical, deformable wedges  621  and contact flats  623 . The deformable wedge module  603  is also equipped with a C-clamp groove  625 , which is continuous with the C-clamp groove  611  of the first  607  annular member. Similarly, as seen in  FIG. 10 , the rigid wedge module  605  is equipped with wedge mating surfaces  631  and contact flats  633 . The rigid wedge module  605  is also equipped with a C-clamp groove  635 , which is continuous with the C-clamp groove  613  of the second  609  annular member. 
         [0030]    The interface  601  depicted in  FIG. 8  is advantageous in that it allows for mass production of the modules  603 ,  605 , thus reducing their cost. Once pressed into their tapered radial grooves, these modules  603 ,  605  may be bolt fastened to prevent walking under oscillating forces. While this embodiment would not be expected to provide high rotary stiffness, a centering ring (boss) may be utilized to provide radial stiffness and a somewhat lower level of radial accuracy. 
         [0031]    One skilled in the art will appreciate that various modifications may be made to the devices and methodologies described herein. For example, while standardized press fit plug-ins have been described for Tesar/Shin type actuator interfaces, one skilled in the art will appreciate that similar press fit plug-ins may be developed to simulate the features of other interfaces, such as the kinematic coupling interface or the Curvic coupling interface. Moreover, while these press fit plug-ins are preferably disposed on the periphery of the annular members forming the interface, in some embodiments, these plug-ins may be disposed elsewhere on the interface such as, for example, on the interior surface of the annular members. 
         [0032]    One skilled in the art will also appreciate that the merits of a particular quick-change interface can change from one application to another. In particular, it would be desirable to study (analytically and experimentally) the various quick-change interfaces disclosed herein to verify their relative accuracy and stiffness in all six directions in order to best judge their merits for any given application. 
         [0033]    The above description of the present invention is illustrative, and is not intended to be limiting. It will thus be appreciated that various additions, substitutions and modifications may be made to the above described embodiments without departing from the scope of the present invention. Accordingly, the scope of the present invention should be construed in reference to the appended claims.