Nonlinear Control Approaches for a Pneumatically Driven Assistance System With Load Balancing

Abstract

This paper presents a model-based, cascaded control structure for a balancing manipulator actuated by pneumatic artificial muscles (PAMs). The balancer is designed to offer two operating modes: First, a balancing mode (BM) compensates for the total weight of the system so that the user feels only minimal resistance when moving the end-effector (EE) during load handling. Second, a position controller (PC) stabilizes the EE at a fixed reference position, even if the attached payload abruptly changes. The proposed cascaded control architecture consists of fast inner loops that control the pressures inside the PAMs, while an outer cascade allows for switching between BM and PC. A velocity-based backstepping approach is employed for the BM. For the position-control mode, a backstepping controller is implemented, which is extended with a cubic as well as an integral error term. An experimental validation on a test rig confirmed the effectiveness of both functions.