Abstract:
A joint apparatus with two degrees of freedom and a large range of singularity-free motion is provided including a first support, a second support, a pivot coupled between the first and second supports for allowing the second support to tilt in first and second directions relative to the first support, a first linkage coupled between the first and second supports for tilting the second support in the first direction relative to the first support, and a second linkage coupled between the first and second supports for tilting the second support in the second direction relative to the first support.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Nos. 61/844,418, filed Jul. 9, 2013, 61/845,951, filed Jul. 12, 2013, and 61/846,070, filed Jul. 14, 2013, the entire disclosures of which are hereby incorporated by reference herein. 
     BACKGROUND 
     The invention relates to joints that connect a first mechanical component to a second mechanical component, allowing either component to be tilted around two perpendicular axes relative to the other. Such joints may be used for a variety of purposes—for example, transmitting rotational motion between shafts that are angled relative to each other, or orienting a gripper on the end of a robotic arm relative to the arm itself. One basic example of a two-axis joint is a universal joint. 
     Several aspects are important in two-axis joint design, such as its range of motion, complexity, robustness, and whether or not it suffers from kinematic singularities. An opportunity exists to improve upon existing joints in one or more of these areas. 
     SUMMARY 
     The opportunity described above is addressed, in one embodiment, by a joint apparatus comprising a first support, a second support, a pivot coupled between the first and second supports for allowing the second support to tilt in first and second directions relative to the first support while substantially constraining the first and second supports from translating relative to each other, a first linkage coupled between the first and second supports for tilting the second support in the first direction relative to the first support, and a second linkage coupled between the first and second supports for tilting the second support in the second direction relative to the first support. 
     The opportunity described above is addressed, in a second embodiment, by a joint apparatus comprising a first support, a second support, a pivot coupled between the first and second supports for allowing the second support to tilt in first and second directions relative to the first support while substantially constraining the first and second supports from translating relative to each other, a first linkage coupled between the first and second supports for tilting the second support in the first direction relative to the first support, a second linkage coupled between the first and second supports for tilting the second support in the second direction relative to the first support, a first actuator coupled to the first linkage for driving the first linkage to tilt the second support in the first direction relative to the first support, and a second actuator coupled to the second linkage for driving the second linkage to tilt the second support in the second direction relative to the first support. 
    
    
     
       DRAWINGS 
         FIG. 1  illustrates a perspective view of a joint apparatus in accordance with a first embodiment. 
         FIG. 2A  illustrates a cross-sectional perspective view of the joint apparatus of  FIG. 1 . 
         FIG. 2B  illustrates a cross-sectional front view of the joint apparatus of  FIG. 1 . 
         FIG. 2C  illustrates a detail view of a circular area  30  of  FIG. 2B . 
         FIGS. 3-10  illustrates perspective views of the embodiment of  FIG. 1  for a variety of movements of linkages  26 A and  26 B. 
         FIGS. 11A, 11B, and 11C  illustrate a perspective view of a joint apparatus in accordance with a second embodiment. 
         FIG. 12A  illustrates a perspective view of a joint apparatus in accordance with a third embodiment. 
         FIG. 12B  illustrates a cross-sectional front view of the joint apparatus of  FIG. 12A . 
         FIG. 12C  illustrates a detail view of a circular area  40  of  FIG. 12B . 
         FIG. 13  illustrates a perspective view of a joint apparatus in accordance with a fourth embodiment. 
         FIG. 14  illustrates a perspective view of fifth embodiment. 
         FIG. 15  illustrates a perspective view of a sixth embodiment. 
         FIG. 16  illustrates a detail perspective view of the top of the embodiment shown in  FIG. 15 . 
         FIG. 17  illustrates a perspective view of a seventh embodiment. 
         FIG. 18  illustrates a cross-sectional perspective view of the embodiment of  FIG. 17 . 
         FIG. 19  illustrates a perspective view of an eighth embodiment. 
         FIG. 20  illustrates a perspective view of a ninth embodiment. 
     
    
    
     A component in an embodiment that has a reference numeral followed by one or more apostrophes indicates that the component corresponds to or is similar in function and/or form to a component designated by the same reference numeral alone (that is, without the apostrophes) in a previous embodiment. 
     While the invention is described in this disclosure by way of several example embodiments and illustrative drawings, those skilled in the art will recognize that the invention is not limited to the example embodiments described in the detailed description or shown in the drawings; instead, the full scope of the invention is defined by the appended claims. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIGS. 1, 2A, 2B and 2C  show a first embodiment. A lower support  4  has a hemispherical cavity cut into its top, as shown in  FIG. 2A , which receives a ball  10  to form a ball and socket joint. Ball  10  is coupled to an upper support  2  via a shaft  14 , which passes through a hole in upper support  2 . Shaft  14  is retained on both sides of support  2  by dowel pins (not shown) that are press-fit into holes  42 A and  42 B, as shown in  FIG. 1 . Linkage  26 A in this embodiment comprises links  6 A and  6 B and middle links  8 A and  8 B. Link  6 A is coupled via a shoulder screw (not shown) to lower support  4  such that it can rotate around an axis  16  relative to lower support  4 . Link  6 A is coupled via a shoulder screw (not shown) to middle link  8 A such that middle link  8 A can rotate around an axis  18  relative to link  6 A. Middle link  8 A is coupled via a shoulder screw (not shown) to a second middle link  8 B such that middle links  8 A and  8 B can rotate relative to each other around an axis  20 . As shown in  FIG. 2B , it is preferable for axis  20  of linkage  26 A (as well as the corresponding axis of linkage  26 B) to lie on a plane  34  that intersects with the pivot point  35  of the joint, which in this embodiment is the center of ball  10 . A second middle link  8 B is coupled via a shoulder screw (not shown) to link  6 B such that link  6 B can rotate around an axis  22  relative to middle link  8 B. Link  6 B is coupled to upper support  2  via a shoulder screw (not shown) such that link  6 B can rotate around an axis  24  relative to upper support  2 . Linkage  26 B is substantially identical in structure to linkage  26 A, but offset 90 degrees around the joint. As shown in  FIG. 2C , a retainer  12  holds ball  10  into the cavity in lower support  4 . Preferably, in this embodiment, the center of ball  10  corresponds with the top surface  32  of lower support  4 . Therefore, ball  10  can readily be inserted and removed into the cavity of lower support  4 . Retainer  12  is held down to lower support  4  via  4  screws (not shown). 
     Referring again to  FIG. 1 , moving linkage  26 A causes support  2  to tilt. If linkage  26 A is moved alone, it causes support  2  to substantially rotate around an axis  28 A. Similarly, moving linkage  26 B causes support  2  to tilt. If linkage  26 B is moved alone, it causes support  2  to substantially rotate around an axis  28 B. If linkages  26 A and  26 B are moved together, support  2  substantially tilts between axes  28 A and  28 B. 
       FIGS. 3-10  illustrates a sequence of tilting caused by a variety of movements of linkages  26 A and  26 B. 
       FIGS. 11A, 11B, and 11C  illustrate a second embodiment incorporating a universal joint or gimbal  48  as a pivot between supports  2 ′ and  4 ′. Universal joint  48  comprises a first fork  36 A, a second fork  36 B (substantially identical to fork  36 A), and a spider  38 . Fork  36 A is rotably connected to upper support  2 ′ via shaft  14 A. Similarly, Fork  36 B is rotably connected to lower support  4 ′ via shaft  14 B, which is secured by a dowel pin (not shown) on the opposite side of lower support  4 ′. Linkage  26 A′ is comprised of links  6 A′ and  6 B′ and middle links  8 A′ and  8 B′, which are coupled substantially similarly to their counterparts in the embodiment of  FIG. 1 , with the exception of the position of attachment to upper support  2 ′ and lower support  4 ′. As shown in  FIG. 11A , the bend in links  8 A′ and  8 B′ results in a distance  19  between axes  18  and  20  and a distance  21  between axes  20  and  22 . Linkage  26 B′ is substantially identical in structure to linkage  26 A′. In operation, as shown in  FIG. 11B , upper support  2 ′ can be tilted past 90 degrees. Universal joint  48  may rotate as needed to accommodate such motion. Fork  36 A preferably has rounded inside edges, as shown in  FIG. 11C , to allow universal joint  48  to rotate as needed to more readily accommodate tilting of upper support  2 ′ relative to lower support  4 ′. 
       FIGS. 12A, 12B, and 12C  illustrate a third embodiment. A lower support  4 ″ functions similarly to support  4  of the embodiment of  FIG. 1 , but engages ball  10  at a lower position (as shown in  FIG. 12C ) to allow support  2 ″ to tilt at greater angles than the embodiment of  FIG. 1 . A magnet  42 , as shown in  FIG. 12B , is embedded in support  4 ″ to retain ball  10  (which is ferrous and magnetic) via magnetic attraction. 
       FIG. 13  illustrates a fourth embodiment comprising joints  1 A and  1 B connected back-to-back, each substantially identical to the embodiment shown in  FIG. 1 . Gears  34 A and  34 B mesh and constrain the linkage of joint  1 B sharing the same axis as Gear  34 B to rotate in the opposite direction relative to the linkage of joint  1 A coupled to gear  34 B. Gears  34 C and  34 D similarly constrain the two remaining linkages. In operation, when shaft  14 A of joint  1 A is held fixed, shaft  14 B of joint  1 B can tilt at a greater angle relative to shaft  14 A than shaft  14  can tilt relative to lower support  4  in the first embodiment. 
       FIG. 14  illustrates a fifth embodiment comprising the embodiment of  FIG. 1  with electric motors  50 A and  50 B driving linkages  26 B and  26 A respectively, with the shafts of motors  50 A and  50 B fixed to support  4  and the bodies of motors  50 A and  50 B fixed to linkages  26 B and  26 A respectively. In operation, motors  50 A and  50 B drive linkages  26 B and  26 A to rotate respectively. 
       FIGS. 15 and 16  illustrate a perspective view of a sixth embodiment comprising an upper support  2 ″ connected via linkages  26 A″ and  26 B″ to lower support  4 ′″. A link  6 A″ of linkage  26 A″ is rotated by a pushrod  58 A, which is connected to a crank arm  60 A. A motor  54 A rotates crank arm  60 A, which is mounted to its shaft. Angular position is measured by a rotary encoder  56 A mounted to the shaft of motor  54 A. Similarly, pushrod  58 B is manipulated by crank arm  60 B, which is rotated by a motor  54 B. The rotation of crank arm  60 B is measured by a rotary encoder  56 B. Support  62  mounts motors  54 A and  54 B and is connected at its top to lower support  4 ′″. 
       FIGS. 17 and 18  illustrates a seventh embodiment that allows rotation of an upper component  64 A when a lower component  64 B is rotated. Lower component  64 B is rotably attached to a lower support  4 ″″. A fork  36 B″ is rotably attached to lower component  64 B. Similarly, upper component  64 A is rotably attached to upper support  2 ″″. A fork  36 A″ is rotably attached to upper component  64 B. Fork  36 A″ is rotably attached to spider  38 , which is rotably attached to fork  36 B″. Together, forks  36 A,  36 B, and spider  38  form a joint similar to joint  48 . A linkage  66 A includes  68 A,  70 A,  70 B, and  68 B. When lower component  64 B is rotated, torque is transmitted through  66 A to upper component  64 A. 
       FIG. 19  illustrates an eighth embodiment that allows rotation of upper component  64 A to be transmitted to lower component  64 B through linkages  66 A and  66 B. Supports  72 A and  72 B rotably support upper and lower components  64 A and  64 B respectively. Support  72 A rotates relative to support  72 B around axis  74 . 
       FIG. 20  illustrates a ninth embodiment that is similar in structure to the embodiment of  FIG. 11A , except that joint  48  is replaced with forks  36 A′″ and  36 B′″ and spider  38 ′. 
     Embodiments other than those described above or shown in the drawings will become apparent to those skilled in the art with the benefit of this disclosure. Accordingly, the invention is not limited to the example embodiments described in the detailed description or shown in the drawings; instead, the full scope of the invention is defined by the appended claims.