Soft pneumatic actuators have seen applications in many soft robotic systems, and their pressure-driven nature presents unique challenges and opportunities for controlling their motion. In this work, we present a new concept: designing and controlling pneumatic actuators via end geometry. We demonstrate a novel actuator class, named the folded Pneumatic Artificial Muscle (foldPAM), which features a thin-filmed air pouch that is symmetrically folded on each side. Varying the folded portion of the actuator changes the end constraints and, hence, the force-strain relationships. We investigated this change experimentally by measuring the force-strain relationship of individual foldPAM units with various lengths and amounts of folding. In addition to static-geometry units, an actuated foldPAM device was designed to produce continuous, on-demand adjustment of the end geometry, enabling closed-loop position control while maintaining constant pressure. Experiments with the device indicate that geometry control allows access to different areas on the force-strain plane and that closed-loop geometry control can achieve errors within 0.5% of the actuation range.

翻译：软体气动执行器已广泛应用于众多软体机器人系统中，其压力驱动特性为运动控制带来了独特的挑战与机遇。本文提出了一种新概念：通过末端几何结构设计并控制气动执行器。我们展示了一类新型执行器——折叠式气动人工肌肉（foldPAM），其特征为两侧对称折叠的薄膜气囊。改变执行器的折叠部分可改变末端约束条件，进而影响力-应变关系。我们通过实验研究了不同长度与折叠量的单个foldPAM单元的力-应变关系。除静态几何单元外，还设计了可驱动foldPAM装置，能连续按需调整末端几何结构，在保持恒定压力的同时实现闭环位置控制。装置实验表明，几何控制可访问力-应变平面上的不同区域，且闭环几何控制可实现致动范围0.5%以内的误差。