Robust impedance control of pressure-sensor free pneumatic servo systems

The paper presents an impedance controller with the support of the function approximation technique (FAT) based multiple-surface sliding control (MSSC) for highly nonlinear pressure-sensor free pneumatic servo systems with mismatched uncertainties. A transformative model is firstly cited so that the pressure sensor feedback can be avoided without deteriorate the closed loop performance. The target impedance is then used to reformulate the system equation so that a normal form can be obtained for the FAT based MSSC design. All uncertainties and disturbances are then covered in a backstepping-like procedure where rigorous proof is derived. Experimental results show that the proposed strategy is able to give good performance in both free-space tracking and compliant motion phases.