Abstract:
A robotic device may include a plurality of concatenated assemblies, a tendon slidably connected to the plurality of concatenated assemblies, and an actuator that moves the tendon. Each assembly of the concatenated plurality may include a joining member that neighbors an adjacent assembly, a linkage that may fixedly connect to the joining member and may pivotably connect to the adjacent assembly, and an appendage that may extend from the joining member to a length. The appendage may include a connector through which the tendon may be connected to slide through. The connector may be adjustably disposable along the length of the appendage to a specified position thereon. The appendage may extend in a direction at a specified angle relative to the linkage.

Description:
This nonprovisional application claims the benefits of U.S. Provisional Application No. 60/636,533, filed Dec. 17, 2004. The entire disclosure of the prior application is incorporated herein by reference in its entirety. 
   BACKGROUND 
   This invention relates to an articulated robotic serial mechanism. 
   Highly articulated snake-like robots may be formed from several concatenated segments having connection interfaces. Such “snake-bots” typically require many actuators to move the robot in a desired manner. These actuators may include motors that supply the force for moving the segments. 
   The distribution of the motors along the segments, provide an even weight distribution. However, because the motors form comparatively massive components, a plurality of actuators (especially motors) produces a heavy and slow robot that is inhibited from executing actions that require the robot to lift much of itself against gravity. 
   For snake-like arms, heavy actuators may be disposed at a base of the arm, with separate tendons or cables connected to each joint for transmitting forces. While such an arrangement facilitate lighter-weight arms, particularly for fixed structures, total weight considerations render them impractical for mobile robots. Examples of tendon-driven robot arms include U.S. Pat. Nos. 6,593,907, 6,413,229 and 6,432,112, each of which is incorporated by reference in its entirety. 
   SUMMARY 
   Various exemplary embodiments provide a robotic device that includes a plurality of concatenated assemblies, a tendon slidably connected to the plurality of concatenated assemblies, and an actuator that moves (e.g., pulls) the tendon. Each assembly of the concatenated plurality may include a joining member that neighbors an adjacent assembly, a linkage that fixedly connects to the joining member and pivotably connects to the adjacent assembly, and an appendage that connects to the tendon and extends from the joining member along a lateral direction at a specified angle to the linkage. The appendage may extend in a direction at a specified angle relative to the linkage. The appendage may include a connector through which the tendon may be slidably connected for at least one of the assemblies. 
   In various exemplary embodiments the appendage may extend linearly from the joining member. The connector may be positioned manually or by an auxiliary actuator. Alternatively, the appendage may extend radially from the joint to form a rim of the appendage having a variable outer radius from the joint. A variable lateral distance between the joining member and the connector for separate assemblies may enable variable moments to be exerted for the same tensile load through the tendon. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various exemplary details are described below with reference to the following figures, wherein: 
       FIG. 1  shows an exemplary tendon-driven arm having linearly adjustable moment members in a first embodiment; 
       FIG. 2A  shows an exemplary tendon-driven arm of  FIG. 1  before executing an exemplary operation tendon-driven arm; 
       FIG. 2B  shows an exemplary tendon-driven arm of  FIG. 1  after executing an exemplary operation tendon-driven arm; and 
       FIG. 3  shows an exemplary tendon-driven arm having rotatable moment members in a second embodiment. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   The following detailed description refers to a tendon-driven robot. The robot may refer to any automatic assembly, for example, articulated arms, for sake of clarity and familiarity. However, it should be appreciated that the principles described herein may be equally applied to any known or later-developed robots, beyond the examples specifically discussed herein. 
     FIG. 1  shows an exemplary robot arm  100  having a plurality of concatenated assemblies  110 . In the example illustrated, a series of five such assemblies  110  are provided. The assembly  110  may include a joining member or joint  120  having a center  125 , a linkage  130  that connects the center  125  of the joint  120  with an adjacent joint  120 ′, and a linearly adjustable moment member or appendage  140  appended from the joint  120 . To facilitate its movement, the appendage  140  may be less massive than the joint  120 . Each assembly  110  may have the same, similar or different components, with linkages and appendages of extending the same or different lengths as compared to their adjacent neighbors. 
   The assembly  110  may dispose the linkage  130  and the appendage  140  at a specified angle θ, e.g., fixed at 90°, as shown. However, the connection between the appendage  140  and an adjacent linkage  130 ′ may pivot, such that an angle φ between the appendage  140  and the adjacent linkage  130 ′ may be varied (typically within the same plane as θ) upon application of an appropriate force. Alternatively, this relationship can be expressed as an angle ψ at the joint  120  between the linkage  130  and the adjacent linkage  130 ′. 
   The appendage  140  may extend rigidly from a root  141  to a tip  142 , and may include an adjustable connector  145  therebetween. This may provide a variable distance between the joint  120  and the connector  145  for each assembly  110  that enables variable moments to be exerted for the same tensile load through a tendon  150 , described below. 
   The root  141  may connect the appendage  140  to the joint  120 . The tip  142  may provide a surface with which to articulate an object to be manipulated by the robot. The tendon  150  may be slidably attached to the connector  145  to provide a moment (force times distance) to be applied to the linkage  120  by tensioning the tendon  150 . The connector  145  may be positioned along the length of the appendage  140  to enable the distance between the center  125  and the connector  145  to be varied as desired. The tendon  150  may terminate at an end  155 , which may be attached to the connector  145  of one of the concatenated assemblies and/or fixed to an alternate location relative to the robot arm  100 . 
   A tendon motor or actuator  160  may controllably apply a tensile force  165  to the tendon  150 , thereby pulling the tendon  150 , in response to a command signal. This force  165  may enable the angle ψ at the joint  120  to be reduced. A coil spring  170  may provide a counteracting torsional force  175  between the appendage  140  and the adjacent linkage  130 ′ in order to return them to a default or preload angular position. 
   The connector  145  may be disposed at a specified distance from the center  125  either by manual adjustment or by an auxiliary actuator  180  that may be located at the joint  120 , or at separate location and connected to the connector  145  by cables (not shown). Alternatively, the connector  145  may be fixed in position relative to the appendage  140 . The moment depends on the distance between the center  125  at the joint  120  and the connector  145  through which the tendon  150  attaches to the appendage  140 . The distance between the center  125  and the connector  145  may be independent of the corresponding distance between an adjacent center  125 ′ and an adjacent connector  145 ′ on the adjacent appendage  140 ′. 
     FIGS. 2A and 2B  show an example of an object  300  (shown as an oval tape dispenser) being manipulated by the robot arm  100  to turn in an arc direction  310  from a first orientation or position to a second orientation or position by the robot arm  100  during actuation. The appendages  140  may be positioned to engage, by their respective tips  142 , the object  300  at the first position. 
   Prior to actuation, the joints  120  (relative to their adjacent linkages) and the tendon  150  may be relaxed or in minor tension from the tendon motor  160 , as shown in  FIG. 2A . Upon actuation, the motor  160  may pull the tendon  150  taut so that the joints  120  and linkages  130  are translated and rotated (relative to their adjacent linkages), as shown in  FIG. 2B . 
   This movement produced by tension in the tendon  150  enables the tips  142  of the appendages  140  to apply force to push against the object  300  to the second position. Those having skill in the art will recognize that the joints, linkages, appendages and connectors shown are exemplary and may encompass arbitrary shapes within the scope of the invention. These forces from the tips  142  may conform to engage various shapes of object  300  naturally, without explicit commands to each joint  120 . 
     FIG. 3  shows another exemplary robot arm  200  having a plurality of concatenated assemblies  210 . The assembly  210  may include a ball (or universal) joint  220 , a linkage  230  that connects the ball joint  220  with an adjacent ball joint  220 ′, and a rotatable cam member  240  extending from the joint  220 . The assembly  210  may angularly dispose the linkage  230  and the cam member  240  at a specified joining angle θ, e.g., fixed at 90°, as shown. A linking angle φ between an adjacent cam member  240 ′ and the linkage  230  may be varied upon application of appropriate force. A countervailing force between the adjacent cam member  240 ′ and the linkage  230  may be provided to return them to a default or preload angular position. 
   A rim or periphery  245  of the cam member  240  exhibits a radial profile having radius R that may vary angularly with a cam angle ζ around the cam circumference as a radial function R(ζ). The rim  245  may have a similar or different radial profile than an adjacent rim  245 ′ of the adjacent cam member  240 ′. The rim  245  may serve to interface with an object to be manipulated. The radial distance between the rim  245  and the ball joint  220  may vary depending on the angular orientation of the cam member  240 . 
   A first tendon  250  may connect or attach to the rim  245  by a follower (not shown, but for example a clip connected to the ball joint  220 ) that enables the first tendon  250  to glide along the rim  245  as the cam member  240  rotates. A second tendon  255  may also connect to the rim  245  by another follower (not shown). The optional second tendon  255  may provide an additional degree of freedom for flexing the cam members  240 , and thereby enable the linking angle φ to vary with the cam angle ζ as an angular function φ(ζ). 
   The first and second tendons  250 ,  255  may be angularly separated from each other by a displacement angle η. In the example shown, the angular separation for displacement angle η may be substantially perpendicular. Alternatively, a larger plurality of tendons may be employed to provide a greater number of degrees of freedom with specified or variable relative angles of separation. 
   A first tendon motor  260  may apply a first tensile force  265  to the first tendon  250 . A second tendon motor  270  may apply a second tensile force  275  to the second tendon  255 . These first and second tensile forces  265 ,  275  applied to the first and second tendons  250 ,  255  may enable the rim  245  of the cam member  240  to be brought in greater proximity to the rim of an adjacent cam member  240 ′ by changing the linking angle φ. 
   A flexible transmission cable  280  may connect the cam member  240  and may pass through the ball joint  220 . A cam motor  290  may connect at one end of the transmission cable  280  to provide torsional force  295  to rotate the cam member  240 . The angular position of the cam member  240  may orient the rim  245  to produce controlled radial distances between the ball joint  220  and the first and second tendons  250 ,  255 . 
   It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, and are also intended to be encompassed by the following claims.