Controle híbrido em cascata baseado em passividade

Abstract

This dissertation presents a passivity-based cascade hybrid control law whose goal is to ensure contact stability between the end-effector of an industrial manipu- lator and an unknown compliant surface on which it performs an interaction task. The cascade control law consists on two nested control loops. In the inner loop, a joint space inverse dynamics algorithm is used to make the manipulator behave kinematically. In the outer loop, an operational space kinematic position/force hy- brid control law is used so that the end-effector follows a desired position trajectory on the surface while exerting a desired contact force on the orthogonal direction to it at all times. A kinematic orientation control law is also used so that the end-effector always stays aligned with the orthogonal direction. In theory, this control allows tracking of the position, force and orientation ref- erences. However, due to practical aspects of implementation in a real manipulator, the contact between the end-effector and the surface may become unstable and large contact forces may be exerted, damaging both the manipulator and the sur- face. Many of these destabilizing factors can be attributed to the force sensor, for example, its measurement delay. The goal of the passivity control is to prevent this instability. An energy observer is introduced to monitor the energy dissipated by the system and, if loss of passivity is detected at any time, a passivity controller acts to increase its impedance so that it dissipates a larger amount of energy until passivity, and consequently stability, is recovered.