Twisting motion plays an important role in kinematics of soft robots. However, current twisting actuators usually suffer from complex mechanical design with multiple materials and undesired coupling with bending and stretching motions. In this letter, we propose a new class of soft twisting pneumatic actuators that purely rely on the freeform chamber geometry to achieve large bi-directional twisting rotations. The freeform chamber surface integrates geometric flexibility in the cross section, lateral profile, and axial chirality, which are parameterized as design variables. We develop a finite element analysis model and investigate the effect of the geometry parameters on the actuators’ mechanical behavior. The actuator naturally undergoes combined twisting and axial motions, and achieves a bi-directional twisting rotation of 116.7∘^\circ, blocking torque of 0.81 N ⋅\cdot m, and energy density of 1907 J/m 3^3, well in line with the theoretical prediction. When it is constrained from axial motions, the actuator delivers pure twisting motion, achieving a bi-directional twisting rotation of 72.5∘^\circ, blocking torque of 0.56 N⋅\cdot m, and energy density of 925 J/m3^3. This letter represents an important step toward leveraging the full potential of the freeform geometry design to create novel compact soft-bodied actuators and robots.

中文翻译：

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采用自由曲面设计的软扭转气动执行器


扭转运动在软体机器人的运动学中起着重要作用。然而，当前的扭转致动器通常面临采用多种材料的复杂机械设计以及与弯曲和拉伸运动的不期望的耦合。在这封信中，我们提出了一种新型软扭转气动执行器，它完全依靠自由形状的腔室几何形状来实现大的双向扭转旋转。自由形状的室表面集成了横截面、横向轮廓和轴向手性的几何灵活性，这些都被参数化为设计变量。我们开发了有限元分析模型并研究了几何参数对执行器机械行为的影响。执行器自然地进行扭转和轴向联合运动，并实现了116.7∘^\circ的双向扭转旋转，阻滞扭矩为0.81 N ⋅\cdot m，能量密度为1907 J/m 3^3，完全一致。与理论预测。当受到轴向运动约束时，执行器提供纯扭转运动，实现 72.5∘^\circ 的双向扭转旋转，阻滞扭矩为 0.56 N⋅\cdot m，能量密度为 925 J/m3^3。这封信代表了充分利用自由几何形状设计的潜力来创建新型紧凑型软体执行器和机器人的重要一步。