Wheels have been commonly used for locomotion in mobile robots and transportation systems because of their simple structure and energy efficiency. However, the performance of wheels in overcoming obstacles is limited compared with their advantages in driving on normal flat ground. Here, we present a variable-stiffness wheel inspired by the surface tension of a liquid droplet. In a liquid droplet, as the cohesive force of the outermost liquid molecules increases, the net force pulling the liquid molecules inward also increases. This leads to high surface tension, resulting in the liquid droplet reverting to a circular shape from its distorted shape induced by gravitational forces. Similarly, the shape and stiffness of a wheel were controlled by changing the traction force at the outermost smart chain block. As the tension of the wire spokes connected to each chain block increased, the wheel characteristics reflected those of a general circular-rigid wheel, which has an advantage in high-speed locomotion on normal flat ground. Conversely, the modulus of the wheel decreased as the tension of the wire spoke decreased, and the wheel was easily deformed according to the shape of obstacles. This makes the wheel suitable for overcoming obstacles without requiring complex control or sensing systems. On the basis of this mechanism, a wheel was applied to a two-wheeled wheelchair system weighing 120 kilograms, and the state transition between a circular high-modulus state and a deformable low-modulus state was realized in real time when the wheelchair was driven in an outdoor environment.

中文翻译：

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受液滴表面张力启发的可变刚度变形轮


由于其结构简单和能源效率高，轮子通常用于移动机器人和运输系统的运动。然而，与在正常平坦地面上行驶的优势相比，车轮克服障碍的性能是有限的。在这里，我们提出了一种受液滴表面张力启发的可变刚度轮。在液滴中，随着最外层液体分子内聚力的增加，将液体分子向内拉的净力也增加。这导致高表面张力，导致液滴从重力引起的扭曲形状恢复到圆形形状。同样，轮子的形状和刚度是通过改变最外面的智能链条块的牵引力来控制的。随着连接到每个链轮的钢丝轮辐张力的增加，轮子的特性反映了一般圆形刚性轮的特性，在普通平坦地面上的高速运动中具有优势。相反，随着钢丝辐条张力的减小，车轮的模量也随之减小，并且车轮很容易根据障碍物的形状而变形。这使得车轮适合克服障碍，而不需要复杂的控制或传感系统。在此机构的基础上，将轮子应用于重120公斤的两轮轮椅系统中，在轮椅驱动时实时实现圆形高模量状态与可变形低模量状态之间的状态转换在室外环境中。