A complete methodology to design a safety mechanism for prismatic joint implementation

The majority of recent researches have been focused on developing compliant joint for rotary motion. Few authors contributed to the problematic of safety in pure linear motion, i.e. prismatic joint. The contribution of this work is to present a new design capable of achieving, passively, a nonlinear elastic behavior for prismatic joint implementation, the so-called Prismatic Compliant Joint (PCJ). This new device is based on a six-bar mechanism equipped with a linear spring. Hence, this structure generates the desired nonlinear stiffness behavior under a specified external force. The elastic characteristic will comply with force safety criteria of physical Human/Robot interaction (pHRI); a Hunt-Crossley model based one. In order to fit the PCJ response curve to the established safety measures, an optimization based on genetic algorithm method tunes PCJ intrinsic parameters subject to the chosen constraints.