A parallel-actuated robot with two end-effector degrees-of-freedom: Application as a novel wearable head-neck traction brace

This paper describes a parallel-actuated robotic mechanism designed to provide two degrees-of-freedom (DOF) to the end-effector relative to a fixed base. In a potential application as a head-neck traction brace, these two independent DOFs are the vertical translation of the head with respect to shoulders and a specified orientation of the head in lateral bending. Motivated by recommended clinical methods to apply traction forces on the head, it is designed to provide vertical traction force on the head while tilted in a specific orientation. The design has four chains starting from a base stationed at the shoulders, each chain having 5 DOFs. Each chain imposes a single constraint on the motion of the end-effector. Together, four chains would apply four constraints, allowing only two DOFs of motion to the end-effector. Two out of four component chains are actively driven by linear actuators. Our kinematic studies show that the achievable workspace of this mechanism with a specific stroke length of actuators of ± 50 mm results in 175-222 mm of vertical translation and up to ± 9 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">◦</sup> of lateral bending. The lateral bending is coupled to the flexion/extension angle of the end-effector. A physical prototype was constructed to investigate the functional realization of the design in hardware. Overall, the physical prototype validated the motion of the theoretical model despite potential errors in the fabrication, making the design a candidate for potential head-neck traction application.