Kinematics and work-space analysis of a novel active joint using cable driven parallel mechanism

In this paper, the structure of a novel 6 DOF active joint using cable driven parallel mechanisms is designed, analyzed and presented. This joint consists of two fixed and mobile frames, and unlike all the commonly used cable driven parallel mechanisms, for first time the outer frame is mobile and the interior frame is considered to be fixed. The mobile frame is attached to the fixed frame by the 8 cables and moves through the tensioning and lengthening of the cables. This new structure can be applied to the wrist mechanism, motion simulators, power balances, haptic interfaces, and Etc. Since the parallel mechanism is a closed loop system and its equations cannot be separated regards to the Cartesian space variables, forward kinematics cannot be solved easily and analytically. Several methods have been proposed to solve the forward kinetic of parallel mechanisms, including numerical optimization and methods, in which the Newton-Ruffson numerical method is used here. Due to the unilateral nature of cables that are only effective in pulling, cables must always be tension. For this purpose, a tension optimization algorithm is presented and, by solving this algorithm for all possible positions of the mobile frame, the workspace of the mechanism is obtained. The results show that the Newton-Raphson method has an appropriate convergence rate and the tension algorithm is capable of determining the tension forces of the cables in the desired range.