LAUSR

Abstract The use of pneumatic linear actuators is generalised in engineering applications because of their many advantages, but modelling the force they supply may become more of a challenge due to their nonlinear behaviour and the hysteresis their energy losses cause. The authors propose a straightforward model to accurately predict force–displacement behaviour using as a basis experimental observations for several pressures and harmonic displacements of the rod. The model proposed includes two dissipative terms: one due to Coulomb friction and another due to structural damping. The force is proportional to relative pressure when acting as an actuator but nonlinear (modelled as a polytropic transformation) when acting as a pneumatic spring (with a closed pressurised chamber). The model accurately reproduces experimental results (Normalised Root Mean Square Errors lower than 2.5%) and may be used in control systems as well as in adaptive stiffness systems.