SBOR: a minimalistic soft self-burrowing-out robot inspired by razor clams
SBOR: a minimalistic soft self-burrowing-out robot inspired by razor clams
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DOI：
10.1088/1748-3190/ab8754
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发表时间：
2020-04
影响因子：
3.4
通讯作者：
J. Tao;Sichuan Huang;Yong Tang
中科院分区：
文献类型：
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作者：
J. Tao;Sichuan Huang;Yong Tang
我们观察到，大西洋剃刀蛤（Ensis directus）通过简单地伸展和收缩其肌肉足迅速地从沙子中钻出来。这与其众所周知的向下挖掘策略或双锚机制明显不同，其中还涉及壳的闭合/打开和足部的扩张。受此启发，我们设计了一个简单的自挖掘机器人（SBOR）的纤维增强硅管驱动器和外部控制板的单段组成。增强纤维将致动器的运动限制为在充气/放气下的轴向延伸/收缩。对于垂直埋在沙子中的致动器，循环的充气和放气自然地将其从沙子中驱动出来，模仿剃刀蛤的运动。我们通过改变驱动周期和相对密度（填料）的沙子的驱动器的挖洞行为的特点。每个洞穴循环的特点是在膨胀期间最初向上推进，然后在紧缩期间向下滑动，导致净向上步幅。在掘出过程中，由于上覆岩层压力、端部拔出阻力和侧摩阻力的减小，步长首先增大;当致动器顶部移出砂层后，由于致动器的有效长度减小，步长减小。研究结果还表明，平均挖掘速度随沙子相对密度的增加而减小，并随驱动压力的变化而变化。基于土力学原理建立了一个简化的模型，用于预测相对松散的干砂中的掘出过程，模型计算结果与试验结果吻合较好。从这个模型中，挖洞的行为很容易解释的不对称性质的阻力两端的致动器和流动性质的沙子屈服。我们的研究结果意味着，剃刀蛤利用沙沉积物的自然应力梯度向上挖掘。另一个观点是，为了向下钻入沙子，需要额外的破坏阻力的特征，如不对称的几何形状、摩擦、应力状态或外部载荷，以增加向上方向的阻力（锚固），并减少向下方向的阻力（阻力）。
We observe that the Atlantic razor clam (Ensis directus) burrows out of sand rapidly by simply extending and contracting its muscular foot. This is notably different from its well-known downward burrowing strategy or the dual-anchor mechanism, where closing/opening of the shell and dilation of the foot are also involved. Inspired by this burrowing-out strategy, we design a simple self-burrowing-out robot (SBOR) consisting of a single segment of fiber-reinforced silicone tube actuator and an external control board. The reinforcing fibers limit the motion of the actuator to axial extension/contraction under inflation/deflation. For an actuator that is vertically buried in the sand, cyclic inflation and deflation naturally drives it out of the sand, mimicking the motion of a razor clam. We characterize the burrowing-out behavior of the actuator by varying the actuation period and the relative density (packing) of the sand. Each burrowing cycle features an initial upward advancement during inflation, followed by a downward slip during deflation, resulting in a net upward stride. During the burrowing-out process, the stride length first increases due to a drop in the overburden pressure, the end pull-out resistance, and the side frictional resistance; the stride length then decreases after the top of the actuator moves out of the sand layer, due to a reduction in the effective length of the actuator. The results also indicate that the average burrowing-out speed decreases with the relative density of the sand and changes with the actuation pressure. We developed a simplified model based on soil mechanics to predict the burrowing-out processes in relatively loose dry sands, and the modeling results match well with the experiment results. From this model, the burrowing-out behavior is readily explained by the asymmetric nature of the resistant forces on the two ends of the actuator and the flowing nature of sand upon yielding. Our findings imply that razor clams leverage the natural stress gradient of sand deposits to burrow upward. Another insight is that in order to burrow downward into the sand, additional symmetry-breaking features such as asymmetric geometry, friction, stress state or external load are needed to increase the resistant force (anchorage) in the upward direction and to reduce the resistant force (drag) in the downward direction.