Incremental Nonlinear Dynamic Inversion Control of Long-Stroke Pneumatic Actuators

Pneumatic cylinders provide an environment-friendly actuation means by minimizing the leakage of any harmful industrial fluids, as occurs for hydraulic actuators. However, pneumatic actuation has not been utilized widely for industrial servo applications due to its highly nonlinear nature. Incremental nonlinear dynamic inversion (INDI) is a form of nonlinear dynamic inversion (NDI) that relies less on plant-model information, and is thus inherently robust to mismatches in the known plant-model, and also to external disturbances. Developing an incremental nonlinear controller for a pneumatic system is the main focus of this research article, which is accomplished by utilizing a cascaded-control approach, where the inner-loop INDI tracks a given force and the outer-loop NDI is for controlling the piston-position. Moreover, realistic sensor noises have been added in the simulation and the robustness of the incremental approach is demonstrated with respect to a baseline PID controller.