Modelling and identification of a pneumatically actuated balancer for collaborative load handling

This paper deals with a comprehensive modelling and identification approach for a pneumatically actuated serial manipulator dedicated for the collaborative handling of loads attached to the end-effector, employing pneumatic artificial muscles (PAMs) as driving elements. The overall system is decomposed into two interconnected subsystems. The pneumatic subsystem covers the characteristic behaviour of the PAMs, and the air-mass-flow characteristic of the associated valves. Two different polynomial formulations replicate both the force and volumetric changes of the muscles with high fidelity. To address the hysteresis of the PAMs, a generalized Bouc-Wen model is incorporated. For a control-oriented design, the valves characteristic air-mass-flow map and its inverse are obtained using the C-b method for the purpose of compensating its nonlinear behaviour. The mechanical subsystem captures the descriptions for the manipulator geometric configuration. The complete model has been validated at a balancer test rig and provides a reliable foundation for a subsequent nonlinear control design.