Modeling of Pneumatic Artificial Muscle with Kinetic Friction and Sliding Mode Control

Abstract

A nonlinear lumped-parameter state-space model of a pneumatic artificial muscle that accounts for kinetic friction is developed. Model simulations are reported for square-wave command signals at different frequencies. Comparisons to experimental results demonstrate the fidelity of the model. A new sliding mode control tuning parameter is introduced that increases the gradient of the error dynamic poles of the sliding surface with respect to lower order errors. With this method input-output feedback linearization and model observation are not needed. A third-order integral sliding mode control law exhibits steady-state errors of ±15 μm or less with a maximum error of 0.29 mm or less when tracking a 7th-order square-wave position trajectory with an amplitude of 5.40 mm. This simplified sliding mode control law shows advantages compared to a conventional approach.