COMPARISON BETWEEN HYDRAULIC AND BI-STABLE SYSTEMS FOR THE MITIGATION OF THE END-EFFECTOR COLLISIONS

This paper deals with the development of special end-effectors able to mitigate the effects of collisions on the robot and on the impacted objects. This aim is achieved by avoiding the direct mechanical coupling between the end-effector and the robot flange by means of hydraulic and mechanical systems. The mathematical model of an end-effector equipped with hydraulic chambers connected by an orifice is developed and integrated with the model of a robot with compliance in the approach direction. To make a comparison, the mathematical model of the bi-stable mechanical system is integrated with the same compliant robot. Numerical simulations of one dimensional collisions are carried out. Numerical results show that, if there is a rather long dead time between the impact and the reaction of the robot, the hydraulic system generates smaller forces than the mechanical system and causes smaller initial velocities of the impacted object. Conversely, if the dead time is short, the bi-stable system generates smaller initial velocities of the impacted object and, when the object is fixed, it generates smaller forces on the robot than the hydraulic system.