Abstract:
A robotic mechanical manipulator structure includes a first link, a second link rotatably coupled to the first link, a first cable connected between the first link and the second link and coupled to the first link by a spring anchored to the first link, passing through cable guides on the first link and the second link and anchored to the second link, and a second cable connected between the first link and the second link and anchored to the first link, passing through cable guides on the first link and the second link and coupled to an actuator. The cables each have a length selected to provide a selected range of motion between the second link at a selected angle with respect to the first link when the actuator is in a rest position. The cable guides are formed from a high hardness material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 62/041,332 for “Cable Guide System for Robotic Mechanical Manipulator Structure,” filed Aug. 25, 2014; Provisional Patent Application No. 62/087,664 for “Tendon Configuration for Under-Actuated Robotic Manipulator With Progressive Wrapping Links,” filed Dec. 4, 2014; Provisional Patent Application No. 62/165,080 for “Tendon Configuration for Under-Actuated Robotic Manipulator With Progressive Wrapping Links,” filed May 21, 2015; and Provisional Patent Application No. 62/165,074 for “Apparatus and Method for Attaching Apparatus to Robotic Fingers,” filed May 21, 2015 the contents of all of which are incorporated in this disclosure by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates in general to mechanical manipulators and appendages for use in robotics applications. 
         [0004]    2. The Prior Art 
         [0005]    The mechanical manipulator of an industrial robot is commonly implemented as a serial link structure utilizing revolute joints. The links are the rigid members coupled to each other by the joints. The joints (also called axis) are the movable components of the robot that enable relative motion between adjacent links. 
         [0006]    Joint rotation is usually powered by motors, hydraulics or pneumatic actuators. In larger mechanical manipulators, these actuators can be directly connected to or within the joint to directly impart torque when actuated. When mechanical manipulators get very small, such as in use for “fingers” in mechanical hands, providing the motors, hydraulics and pneumatics directly attached to the joint is impractical due to size constraints and mass impacts on the moment of inertia. An alternative that is widely used is to utilize cables as artificial tendons that transfer the rotational force back to remotely located actuation such as a motor or pneumatic actuator. 
         [0007]    When cables are used in mechanical manipulators, the cables need to be routed through the links and joints to the remotely located actuators. The cables may move in the links and joints when the mechanical manipulators are moving. The cables pass through the links and joints and may change direction at various points. At these points where the direction of the cable must change, it is important to reduce friction as much as possible to minimize wear and maximize resulting forces through the cable. 
         [0008]    Routing tension cables in mechanical manipulators as described above requires overcoming friction while directing the path of the cable throughout any rotation of the links. There are three primary solutions for routing tension cables in mechanical manipulators: pulley based systems, the use of a Bowden cable or routing the cable over pins and bearings. 
         [0009]    A very low friction configuration utilizes pulleys to route the cables. However, because a pulley is required wherever a cable must change direction, this can result in a large number of pulleys, which are mechanically complicated to implement, have high costs, and consume significant volume. In addition, if the cable falls off the pulley, the system has broken. 
         [0010]    A more common configuration utilizes a Bowden cable, which is a cable mechanism utilizing a thin stranded cable that moves inside of a flexible outer housing. A Bowden cable provides an easy mechanism to route a cable through a confined area with little regard to position and obstacles. However, Bowden cables are relatively high friction and their performance degrades significantly over time. 
         [0011]    Another common configuration is to run cables over metal pins or bearing races. This approach generally does not provide adequate alignment of the cable and can allow rubbing of the cable against the body of the link. This can result in high friction and wear in the mechanical manipulator reducing performance and operating lifetime. 
         [0012]    Many other mechanical systems utilize cables to transmit tension between moving parts unrelated to link and joint based movement. These systems may experience similar challenges to those described above including: friction, wear, cost, and weight. 
         [0013]    Ceramic guides have been widely used in the textile industry to route thread and yarn through machines. The primary reason for using ceramic guides has been to reduce lint build-up in textile factories. 
         [0014]    Ceramic guides are used in fishing rods to reduce wear on the fishing line and rod. 
       SUMMARY 
       [0015]    According to a first aspect of the invention, the cables used to transmit tension in a robot are routed through a series of high hardness cable guides to direct the cable path and force. 
         [0016]    According to a second aspect of the invention, cables assemblies can be pre-assembled including the high hardness cable guides, termination rings, springs, if required, and other components into finished, calibrated cables. 
         [0017]    According to a third aspect of the invention, the pre-assembled cables can be terminated with knots, rings, blocks or other methods to allow connection of the cable to the link, actuator, or another cable. 
         [0018]    According to a fourth aspect of the invention, each link may be constructed out of two or more mating pieces. The pieces have pre-molded locations for the eyelets, and additionally if required anchor points for the cables, locations for springs and paths for the cables to traverse the link, joint hardware such as bearings and any other hardware such as sensors. When joined, the pieces securely embed the eyelets, springs, anchor points, cables and joint hardware. 
         [0019]    According to a fifth aspect of the invention, each link may be constructed from a rod or bar, on which cable guides and terminations, and joints may be affixed. 
         [0020]    According to a sixth aspect of the invention, the cables with cable guides can be used to apply tension between any two points in a structure where cable movement at intermediate points in the cable relative to the structure is expected. 
         [0021]    According to a seventh aspect of the invention, the routing of the cable can utilize a combination of the cable guides as well as other methods to route the tension of the cable through a structure including the outside race surface of a ball bearing joint, a post or pin, a pulley or any other methods. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0022]      FIG. 1  is a diagram showing an embodiment of the present invention wherein two links are connected together through a joint and cables are in place to rotate the link around the joint. 
           [0023]      FIG. 2  is a diagram showing an embodiment of the present invention wherein two cables are configured to fit into the two links and a joint shown in  FIG. 1   
           [0024]      FIG. 3  is a diagram showing an embodiment of the present invention applied to a link, joint and cable configuration developed by Stanford University and the Jet Propulsion Laboratory. 
           [0025]      FIG. 4  is a diagram showing an embodiment of the present invention wherein two cable assemblies with high hardness cable guides and termination points are shown that address the configuration in  FIG. 3 . 
           [0026]      FIG. 5  is a diagram showing an embodiment of the present invention wherein a single link assembly is shown partially disassembled. No cable is shown in this picture. 
           [0027]      FIG. 6  is a diagram showing an embodiment of the present invention wherein two assembled links are shown. 
           [0028]      FIG. 7  is a diagram showing an exploded isometric view of an exemplary link in accordance with an embodiment of the present invention including a shaft and two end pieces. 
           [0029]      FIG. 8  is a diagram showing an assembled isometric view of the link of  FIG. 7  including an exploded view of the end pieces to show interior detail. 
           [0030]      FIG. 9  is a diagram showing an isometric view of two links of the type shown in  FIGS. 7 and 8  coupled together at a center joint. 
           [0031]      FIG. 10  is a diagram showing an assembled isometric view of an illustrative embodiment of the present invention wherein a link includes a shaft, two cable guide holders, two end pieces, and a cable anchor piece. 
           [0032]      FIG. 11  is a diagram showing an exploded isometric view of the embodiment of  FIG. 10 . 
           [0033]      FIG. 12  is a diagram showing an isometric view of two links of the type shown in  FIGS. 10 and 11  coupled together at a center joint. 
           [0034]      FIG. 13  is a diagram showing an embodiment of the present invention wherein two links are connected by a joint and controlled by two cables. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Persons of ordinary skill in the art will realize that the following description of the present invention is illustrative only and not in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons. 
         [0036]    Referring now to  FIG. 1 , a diagram shows an illustrative embodiment of the present invention wherein two links  10  and  12  connected by a joint  14  and controlled by two cables  16  and  18 . The links  10  and  12  rotate about the joint  14  controlled by torques induced by the cables  16  and  18 . The cables  16  and  18  have termination fittings  20  secured to the links  10  and  12  at anchor points  22 . In one embodiment of the invention, the attachment points are in the form of attachment rings that nest into anchor points  22  in links  10  and  12 . The cables  16  and  18  pass through cable guides  24  secured into the links  10  and  12  at points where the cables  16  and  18  need to be guided through the links  10  and  12  or exert force on the links  10  and  12 . No-limiting examples of cable materials suitable for use in the present invention include super strong and low stretch synthetic materials, such as sold under the trademark Dyneema, available from Royal DSM of Heerlen, Netherlands, and ultra-high molecular weight polyethylene braided line sold under the trademark Spectra, available from Honeywell International, Inc., of Morristown, N.J. 
         [0037]    In one embodiment of the invention, the cable guides  24  are high hardness cable guides. As used herein, the term “high hardness” refers to a material having a hardness greater than 600 HB (HBW 10/3000) on the Brinell Hardness scale. High hardness cable guides can be implemented using a variety of very hard materials. Non-limiting examples of such materials include ultra-hard ceramics including aluminum oxide, zirconium dioxide, titanium dioxide, polycrystalline sapphire and silicon carbide. 
         [0038]    In the different embodiments of the invention, the cable guides  24  may take the form of eyelets and permutations thereof including, but not limited to, slotted, grooved, flanged, double flanged, tube, and other configurations. The cable guides  24  may also take the form of other types of guides and permutations thereof, including, but not limited to, traverse, trap, slit, roller, bearing rollers, pigtails, faller eyes and other configurations. Illustrative cable guides that are suitable for use in the present invention are disclosed in the publication Ascotex, Ceramic Yarn Guides, available at the web page http://www.ascotex.com/Binder2.pdf. 
         [0039]    In the exemplary embodiment depicted in  FIG. 1 , one of the cables  18  is attached to an inline spring  26 . The other cable  16  is connected to an actuator  28  that exerts tension on the cable  16  to cause rotational movement of the links  10  and  12  around the joint  14 . Persons of ordinary skill in the art will appreciate that cable  18  can be eliminated and the end of spring  26  can instead be anchored to link  10 . Such skilled persons will also appreciate that spring  26  can be eliminated and cable  18  can be controlled by a second actuator (not shown) working in cooperation with actuator  28 . 
         [0040]    The cables  16  and  18  transfer forces between their termination fittings  20  which can be attached to links  10  and  12 , springs  26 , actuators  28 , or other sources of passive or active tension on the cables  16  and  18 . The cables  16  and  18  are thus constructed to connect to these various points of the structure including links  10  and  12 , the actuators  28  and the springs  26  to transfer and apply that force through the structure. The force of the cables  16  and  18  will be applied to the link  10  and  12  and joint  14  structure through its termination points  22  and also where the cable is redirected through cable guides  24 . These points where the cables  16  and  18  are redirected generally require dynamic movement of the cable relative to the structure including links  10  and  12  and joint  14 . At these points, the cable guides  24  are used to provide a low wear and low resistance method to change the direction of cables  16  and  18 . The cable guides  24  are securely attached to the links  10  and  12 . At these points of redirection, forces are also applied to the structure including links  10  and  12  and joint  14 . When the tension applied to cables  16  and  18  is increased, the stiffness of the structure including links  10  and  12  and joint  14  increases as well. In this configuration, when the actuator  28  increases tension on the cable  16 , the link  10  on the left will rotate counter clockwise relative to the link  12  on the right. When the tension in the cable  16  is reduced by the actuator  28 , the force of the spring  26  will rotate the link  10  on the left in the clockwise direction relative to the link  12  on the right. 
         [0041]    While in the particular embodiment of  FIG. 1 , the anchor points  22  are positioned symmetrically around the joint  14  and the cable guides  24  are symmetric around the joint  14 , the positioning of the anchor points  22  and cable guides  24  is entirely design dependent and do not need to be symmetric around the joint  14  or the same distance from the joint  14 . The location of the anchor points  22  for the cables  16  and  18  do not need to be next to each other on the link  10 . The cables  16  and  18  could be implemented to share an anchor on the link  10 . The joint  14  can be offset from the horizontal centerline of the links  10  and  12 . As will be readily appreciated by persons of ordinary skill in the art, the positioning of the cable guides  24  relative to the joint  14  affects the torque exerted by the cables  16  and  18  and is design dependent. The positioning of the anchor points  22  also affects the torque applied to the links  10  and  12  and joint  14 . 
         [0042]    Referring now to  FIG. 2 , a diagram shows an aspect of the present invention wherein the cables depicted in  FIG. 1  may be pre-assembled before being further assembled with the links and joints. According to one illustrative embodiment of the invention, the cables  16  and  18  include termination fittings  20  are shown in the form of rings connected to the ends of cables  16  and  18 , although persons of ordinary skill in the art will appreciate that a wide variety of other termination fittings can be employed in the present invention. The cable guides  24  are pre- assembled in the correct order onto the cables  16  and  18  by threading the cables  16  and  18  through them. Any springs  26  that are used may also be pre-assembled on the cables  16  and  18  and positioned in the correct order with respect to the cable guides  24 . The pre-assembled cables  16  and  18  shown in  FIG. 2  may be manufactured having pre-specified lengths between the termination fittings  20 . Persons of ordinary skill in the art will appreciate that the assembly shown in  FIG. 2  is configured specifically for the link assembly depicted in  FIG. 1 , and is thus illustrative and non-limiting, as different numbers of cables and particular configurations will be required for various link arrangements. 
         [0043]    One method for assembling the cables  12  is to attach a termination fitting such as a termination fitting  20  to the cable  12  using, for example, a Palomar knot, slide the necessary cable guides  24  onto the cable, cut the cable to the correct length and attach another termination ring  24  is attached to the second end of the cable. A Palomar knot  14  is particularly useful because it can be tied in a manner that consistently provides a known length consumption of cables  16  and  18 . Therefore a cable can be assembled to desired lengths. Tying termination fittings  24  to a cable is one method to terminate a cable. Other options to terminate a cable can include gluing, fusing, crimping or any other method to attach a cable termination fitting  24  to the end of cables  16  and  18 . Attaching the springs  26  can also be included as step in pre-assembling the cable. A pre-configured cable can then be assembled into a link and joint structure in a separate step from the assembly of the cable. 
         [0044]    Referring now to  FIG. 3 , a diagram shows an embodiment of the present invention applied to the Stanford JPL cable configuration (J. K. Salisbury and J. J. Craig. Articulated hands: Force control and kinematic issues,  IJRR,  1(1), Spring 1982) wherein a robotic hand  30 , in which four links  32 ,  34 ,  36 , and  38  are connected at three joints  40 ,  42 , and  44  with four cables  46 ,  48 ,  50 , and  52 . In this example configuration, each cable  46 ,  48 ,  50 , and  52  is terminated at an individual actuator  54 ,  56 ,  58 , and  60 . This configuration including links  32 ,  34 ,  36 , and  38 , joints  40 ,  42 , and  44  and cables  46 ,  48 ,  50 , and  52  allows full control of the relative joint angles between each link. 
         [0045]    Referring now to  FIG. 4 , a diagram shows that, in this configuration, multiple cables may share one or more cable guides.  FIG. 4  is a diagram that shows an embodiment of the present invention showing an illustrative example of pre-configured cables in an arrangement that addresses the requirements of  FIG. 3  (StanfordJPLTendonConfiguration). There are a total of four cables  46 ,  48 ,  50 , and  52 . There is only a single cable  52  that uses a single cable guide  62  and does not share any cable guides with the other cables  46 ,  48 , and  50 . Three of the cables  46 ,  48 , and  50  share a common subset of cable guides  64  and  66 . Cable  50  includes two single cable guides  62 . 
         [0046]    A method to pre-assemble the set of three cables  46 ,  48 , and  50  includes assembling a single cable  50 , assembling the second cable  48  by sharing some of the cable guides  64 , and assembling the third cable  46 , again sharing some of the cable guides  64  and  66  with the other two cables  48  and  50 . Once assembly of the three cables  46 ,  48 , and  50  is complete, they constitute a single completed pre-assembled cable assembly. 
         [0047]    Referring now to  FIG. 5 , a diagram shows an illustrative embodiment of the present invention wherein a link  70  is composed of pre-molded mating link sections  72  and  74 . Cable guides  76  fit snugly into pre-formed locations  78 . The cables are not shown in  FIG. 5 . In the illustrative example of  FIG. 5 , the cable guides are in the form of eyelets or grommets. A bearing  80  is seated into appropriately-formed recesses  82  in the link sections  72  and  74 . Bolts  84 ,  86 , and  88  pass through the link sections  72  and  74  and mate with nuts  90  to fasten link sections  72  and  74  to one another. As shown in  FIG. 5 , the nuts  90  may fit snugly into pre-formed locations  92  in link section  74 . A cable termination ring  94  is shown without the cable. The termination ring  94  may be anchored to the link  70  by passing one of the bolts  86  through it or, for example, may rest in a recessed area as shown in some of the other embodiments. In the embodiment depicted in  FIG. 5 , one of the bolts  84  through a joint acts as an axle for the bearing of the next link (not shown). It is straightforward to assemble the link joint system using the cable assemblies as disclosed herein, avoiding any difficulty that might otherwise be encountered in assembling the cables after the links, bearings, cable guides, termination rings, bolts and nuts have been assembled. 
         [0048]    Referring now to  FIG. 6 , a diagram shows an embodiment of the present invention wherein two links of the type illustrated in  FIG. 5  are assembled. Links  70   a  and  70   b  are shown joined together as was indicated above with reference to  FIG. 5 . A cable  94  is visible passing between links  70   a  and  70   b.  Only the visible cable is shown and identified by reference numeral  96 . The cable  96  passes through embedded cable guides  76 , only two of which are visible in the view of  FIG. 6 . As previously noted with reference to  FIG. 5 , the bolt  84  may be employed to provide the axle for the joint between links  70   a  and  70   b.  A bearing  98  is visible at the joint where link  70   a  would be attached to other links (not shown). The cable  96  is shown at arrow  99  continuing beyond links  70   a  and  70   b  to connect to actuators, springs, other cables or other termination (not shown). 
         [0049]    Referring now to  FIG. 7 , a diagram shows an exploded view of an embodiment of the present invention wherein a link  100  is formed from a shaft  102  and two end pieces  104  and  106 . A cover  108  is shown removed from end piece  104  and a cover  110  is shown removed from end piece  106 . Cable guides  112  are seated in preformed recesses  114  (two of which are shown prior to placement in recesses  114 ). 
         [0050]    Bolts  116  and  118  are used to secure cover  108  to end piece  104  using nuts  120  and  122 , respectively. Nuts  120  and  122  may fit into recesses (one is shown at reference numeral  124 ) pre-formed in cover  108 . Bolt  116  also serves as an axle for a bearing (not shown) used to couple link  100  to another link that would be located to the left of the figure. Bolt  126  is used to secure cover  110  to end piece  106  using nut  128 . Nut  128  may fit into recess  130  pre-formed in cover  110 . 
         [0051]    A bearing  132  sits in bearing seat  134  formed in end piece  106  and is used to couple link  100  to another link that would be located to the right of the figure. Such a link would be secured to link  100  on a bearing shoulder identical to shoulder  136  using a bolt such as bolt  116  shown in the left side of  FIG. 6 . 
         [0052]    Referring now to  FIG. 8 , a diagram shows an assembled view of the link  100  shown in  FIG. 7 . The same reference numerals used in  FIG. 7  are used to designate corresponding structure in  FIG. 8 . The link is shown with shaft  102  fastened to the two end pieces  104  and  106 , such as by gluing or use of other known fastening techniques. End pieces  104  and  106  are shown assembled to secure the hardened eyelets  114 . The joint bearing  132  fits into molded shoulders  136  in the right most end piece  106  (as seen on the left hand side of  FIG. 8 ). The left most end piece  104  has an axle formed from bolt  116  in shoulder  136  (seen most easily in  FIG. 7 ) onto which the bearing in the next link (not shown) fits. The end piece  104  and its cover (seen in  FIG. 7 ) are secured by bolts  116  and  118  and nuts  120  and  122 . The right most end piece  106  and its cover (seen in  FIG. 7 ) are secured by bolt  126  and nut  128 . Nuts  120 ,  122 , and  128  fit into pre-molded locations ( 124  in  FIG. 7 ). 
         [0053]    There are three cables  138 ,  140 , and  142  shown passing through the link  100  in  FIG. 8 . Cable  138  is anchored in the left most end piece  104  by bolt  122 . Cable  140  is shown passing through cable guides  114 . Cable  142  passes through cable guides that are not visible in the drawing. 
         [0054]    Referring now to  FIG. 9 , a diagram shows an embodiment of the present invention wherein two links of the type shown in  FIGS. 7 and 8  are assembled together at a center joint  144 . Four cables at reference numeral are shown exiting the right most end piece  106   b.  One of the cables is anchored into the right most end piece  102   b  by a bolt  146 . In the center joint, a cable (not visible) is anchored by bolt  148 , serving as the axis of the joint. In the center joint a cable  150  passes between cable guides  152  embedded into the joint. Two cables exit the left most end piece  104   a  at reference numeral  154 . 
         [0055]    Referring now to  FIG. 10 , a diagram shows an embodiment of the present invention wherein a link  160  is formed from a shaft  162 , two cable guide holders  164  and  166 , two end pieces  168  and  170 , and a cable anchor piece  172 . Cables (not shown) pass through the link. The cables pass through cable guides  176  and one or more of the cables may be anchored by a bolt  174  in the cable anchor piece  172 . Persons of ordinary skill in the art will appreciate that cable anchor piece  172  could be located between one of the cable guide holders  164  and one of the end pieces  168  or  170 . 
         [0056]    Referring now to  FIG. 11 , a diagram shows an exploded view of the link  160  of  FIG. 10 . The shaft  162  is connected to end pieces  168  and  170  by inserting shaft  162  into holes in the end pieces  168  and  170 . In the illustrative embodiment shown in  FIGS. 10 and 11 , the end pieces  168  and  170  are complementary. One end piece  168  accepts a bolt  178  held by nut  180 . Bolt  178  provides an axis for a bearing  182  seated in the other end piece  170 . The cable guide holders  164  and  166  fit onto the shaft  162  through mounting holes  184 . The cable guides  176  snap into holes  186  in the cable guide holders  164  and  166 . The joint bearing  182  snaps into the right most end piece  170 . The right most end piece  170  has molded shoulders  188  that hold the edges of the outer race of joint bearing  182 . This allows the use of a concave joint bearing  182  to provide centering alignment when a tendon passes over the outer bearing race. Cable anchor  172  is coupled to shaft  162  by a bolt  190  and nut  192  to secure a cable. 
         [0057]    Referring now to  FIG. 12 , a diagram shows shows an embodiment of the present invention wherein two links of the type shown in  FIGS. 10 and 11  are assembled together at a joint  194 . The cables pass through cable guides  176 . A cable is shown anchored at reference numeral  190 . Two cables are shown passing over the joint bearing outer race  188 . Persons of ordinary skill in the art will appreciate that if cable anchor piece  172  is located between one of the cable guide holders  164  and the one of the end pieces  168  or  170  at joint  194 , that the cable anchored to it will not need to pass through the cable guides connected to shaft  162   a    
         [0058]    Referring now to  FIG. 13 , a diagram shows an embodiment of the present invention wherein two links  202  and  204  connected by a joint  206  and controlled by two cables  206  and  208 . The links  202  and  204  rotate about the joint  206  controlled by torques induced by the cables  206  and  208 . The cables  206  and  208  have termination fittings  210  secured to the links  206  and  208  at anchor points  212 . In one embodiment of the invention, the attachment points are in the form of attachment rings that nest into anchor points  212  in the link  202 . The cables  206  and  208  pass through a cable guide  214  secured into link  204  at the points where the cables  206  and  208  need to be guided through the link  204 . 
         [0059]    The present invention allows building very small mechanical manipulators with the following benefits over the prior art: reduced component cost, reduced assembly cost, reduced part count, reduced friction, longer wear life, great shock resistance, light weight and decreased moment of inertia. 
         [0060]    This invention allows building small robots with “legs” or appendages, large robots, such as humanoids as well as improved prosthetic hands and robotic mechanical manipulators. The invention can be further applied where ever forces can be applied over a distance using a Bowden cable, cable or rope to transmit tension. 
         [0061]    The use of ultra-hard ceramic to implement highly polished high hardness cable guides and the use of super strong synthetic braided line create a very cost effective and robust cable tension system that uses few inexpensive parts that are easy to assemble and have excellent wear and low friction characteristics. 
         [0062]    The reduced component costs result from the combined costs of the hard ceramic guides and cable. The high hardness cable guides are simple components and can be sourced for less expense than pulleys. Cable, such as braided Dyneema or similar materials, is a widely-available inexpensive commodity. 
         [0063]    Reduced assembly cost can be achieved by separating assembly into sub-systems such as the pre-configured cables including cable guides and termination rings, from the assembly of the link and joint structure. 
         [0064]    The present invention provides a system having reduced friction at points where the cable is redirected. The friction of the cable is reduced as compared to the Bowden cable solution. 
         [0065]    The present invention separates actuators from links and joints, and minimizes mass and moment of inertia for links and moves mass and moment of inertia to a better location (centralized body, for example, in an embodiment). Links and joints can be smaller. Links and joints are more shock resistant. 
         [0066]    In various embodiments, joints can be implemented using bearings, bushings, rods or similar elements. This present invention can also be used in mechanical manipulators that utilize springs as the joints instead of having a sliding or rolling joint. Examples include metal or rubber spring joints. 
         [0067]    The invention can be used where joints are multi-dimensional, such as a universal joint or a rubber joint. 
         [0068]    The invention can be applied to non-robotic structures such as a cable actuation system in bicycle gears and brakes or other applications utilizing Bowden cables or pulleys. 
         [0069]    Although the invention has been described in detail by illustrative embodiments, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements. For example, it is to be understood that the present invention contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.