Cable Joint Differential for Robot

A method for moving a joint in two degrees of freedom, the method comprising, in any order:

• rotating a first input pulley around a first axis while rotating a second input pulley around the first axis in the same direction and in the same amount as the first input pulley, thereby causing an output pulley and idler pulley to rotate around the first axis;
• and
• rotating one of the first input pulley or the second input pulley around the first axis while rotating the other input pulley in an opposite direction in the same amount, thereby causing the output pulley and the idler pulley to rotate around a second axis that is orthogonal to and offset from the first axis;
• and
• rotating one of the first input pulley or the second input pulley around the first axis while rotating the other input pulley in a different amount, thereby causing the output pulley and the idler pulley to rotate around both the first axis and the second axis.

A motor-drivable two degrees of freedom joint comprising:

• a first input pulley that rotates around a first axis;
• a second input pulley that rotates around the first axis, wherein the second input pulley is spaced apart from the first input pulley along the first axis, wherein the second input pulley can rotate independent from the first input pulley;
• an intermediate link that is disposed between the first and second input pulleys along the first axis, wherein the intermediate link rotates around the first axis, wherein the intermediate link defines a second axis that is orthogonal to and offset from the first axis;
• an output pulley that rotates around the second axis of the intermediate link;
• an idler pulley that rotates around the second axis of the intermediate link, wherein the idler pulley is spaced apart from the output pulley along the second axis;
• a driving cable which, along its length and in this order or the reverse order, is in contact with the first input pulley, the output pulley, the second input pulley, and the idler pulley;
• wherein the driving cable is coupled to a point on each pulley.