Patent ID: 6840127

Claim:
A method for creating a variable-length mechanism link possessing pivoting freedom about an invariable-and-known end point, comprising the steps of: a. joining a first link to a second link with a first revolute joint having a first axis of rotation, and b. joining a third link to said second link with a second revolute joint having a second axis of rotation, such that said second axis of rotation is orthogonal to, and intersects, said first axis of rotation, and such that said third link's line vector intersects said first axis of rotation and said second axis of rotation at their point of intersection, and c. attaching a tendon-length-controlling actuator and a first segment of a constrained tendon path to said first link, such that said first segment proceeds from said actuator to become collinear with said first axis of rotation, and d. attaching a second segment of said constrained tendon path to said second link, such that said second segment changes from being collinear with said first axis to become collinear with said second axis of rotation, and e. attaching a third segment of said constrained tendon path to said third link, such that said third segment changes from being collinear with said second axis to become collinear with said third link's line vector, and f. attaching a tendon to said actuator, and threading said tendon along said first segment and then along said second segment and then along said third segment, for a distance determined by said third link's required length, to terminate with a tensile force load, whereby said tendon remains in tension throughout said path.