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This paper introduces a real-time dynamic-model-based feedback framework for controlling pneumatic soft actuators, addressing the challenges posed by their nonlinearities and distributed deformation. By employing a non-minimal coordinate discrete elastic rod model, the authors achieve efficient task-space control while maintaining high precision across various tasks, including digit drawing and periodic motion tracking. Experimental results show that their approach yields a root mean square error (RMSE) of 1.5-2.3 mm for precision tasks, demonstrating the effectiveness of structured dynamic models in enhancing control capabilities of soft actuators.
Real-time control of pneumatic soft actuators can achieve precision within 1.5-2.3 mm, even in complex tasks like drawing digits and tracking motion.
Soft actuators enable dexterous and compliant interaction, but closed-loop task-space control remains challenging due to strong nonlinearities, distributed deformation, and uncertainty in their dynamics. This paper presents a real-time dynamic-model-based task-space feedback and estimation framework based on a non-minimal coordinate discrete elastic rod model formulated in absolute coordinates with holonomic constraints. The resulting structure preserves distributed mechanics while maintaining computational efficiency through sparse system matrices, enabling real-time control with up to 10 discretized rods. A quasi-static feedforward inverse model is combined with a task-space PI controller and a dynamic observer that fuses measurement residuals as virtual forces, enabling full-state estimation from sparse sensing. The approach is experimentally validated on three planar pneumatic soft actuators with varying geometries. Across five tasks, including drawing the digits 0-9 across the workspace (3-18 mm/s tip speed), tracking periodic motion (up to 37 cm/s), cross-platform generalization, reduced sensing conditions, and real-time user-defined references, our method achieves 1.5-2.3 mm root mean square error (RMSE) for precision motions and 5.5-12.4 mm RMSE at 1-2 Hz. Results demonstrate that structured, non-minimal dynamic models can enable real-time, high-precision, moderate-bandwidth task-space control of planar soft pneumatic actuators in free space.
