Model-Based Control of Antagonistic Pair of Pneumatically Actuated Pouch Motors

Pneumatic pouch motors are soft actuators that contract when inflated. Their low cost and ease of fabrication make them ideal choices for disposable systems such as those used in robotic surgery. However, the dynamics of pouch motors are highly nonlinear, which complicates control. In this paper, we investigate the position control of an antagonistic pair of soft pneumatic pouch motors. An analytical model of system dynamics, including the pressure dynamics in the pouches, is proposed. To compensate for uncertainties and disturbances, a nonlinear observer is constructed based on the Immersion and Invariance methodology. A new model-based nonlinear controller, constructed using a nested sliding variable, is designed for tracking tasks. Stability conditions are discussed, and the effectiveness of the new controller is demonstrated in simulations and experiments. The new controller is compared with a reduced-order version that neglects pressure dynamics. The results indicate that both controllers are effective in tracking tasks, with the new controller showing improved accuracy by up to 33.3% in experiments.