Abstract
High performance pick-and-place applications having large performance levels require high dynamic characteristics that can only be achieved by parallel robots. Mechanisms having four degrees of freedom give the best flexibility, but the range of the angular motion is often the weak point of these architectures. However, introducing articulated traveling plates overcomes this drawback. As such, three new architectures of four degree of freedom pick-and-place robots are presented in this document: Par4, Heli4 and Dual4. A complete study of these mechanisms is proposed, and their prototypes are presented in order to validate the architectures and to estimate their performances. Then, a simplified dynamic model applied to robots having articulated traveling plates is presented. This method is applied to the Par4 to identify an imbalance of its motor torques. Then, a minor modification on the platform kinematics is shown to create a 30% reduction of these torques. Therefore, a new "balanced" version of the robot based on the dynamic study is proposed. Finally, two optimizations are applied to pick-and-place robots. First, the geometric parameters of the Par4 are optimized for pick-and-place operations. Second, path planning which uses clothoids and an adaptive time law is presented in order to optimize the movements of the robot during a pick-and-place motion with high accelerations.