Design and prototyping of a Cable-Driven Schonflies-Motion Generator

Cable-Driven Parallel Robots (CDPRs) use cables to move a moving-platform (MP) in space offering different advantages, such as high payload capability, reconfigurability, large translational workspace and high dynamic performances. However, their orientation workspace is usually limited due to cable/cable and cable/MP collisions. In this thesis, a novel Schönflies-Motion Generator (SMG) with a large translational workspace and a full rotation of its end-effector about a vertical axis is introduced. The full rotation of the end-effector is obtained using a parallelogram cable-loop. Four degrees of freedom of the end-effector are controlled by four actuators fixed to the ground thanks to three parallelogram cable structures, one cable-loop and a transmission system equipped with a differential mechanism. The three parallelograms are obtained by correctly placing the cables around the MP; this prevents the latter from oscillating, limiting the unwanted rotations. By using such a configuration, one can greatly improve the robot kinematic performance without adding the cost of extra actuators. The prototype of the abovementioned Cable-Driven Shönflies Motion Generator (CDSMG) is built and tested to validate its model. In particular, the proposed robot will be compared to a robot without parallelograms architecture, to prove its efficacy. The main contribution of this work is the design, prototyping and testing of a novel transmission system for the actuation of three winches using only two motors. This solution permits the reduction of the whole control complexity and the independent actuation of the rotational and translational motions of the MP. The adopted transmission was chosen over two others due to its compactness and low backlash (which involves high accuracy). The transmission features high torsional rigidity, extremely smooth running and low torsional backlash, thanks to the design of the differential mechanism.