Body Temperature-Triggered Mechanical Instabilities for High-Speed Soft Robots

Abstract

Nature offers bionic inspirations for elegant applications of mechanical principles such as the concept of snap buckling, which occurs in several plants. Exploiting mechanical instabilities is the key to fast movement here. We use the snap-through and snap-back instability observed in natural rubber balloons to design an ultrafast purely mechanical elastomer actuator. Our design eliminates the need in potentially harmful stimulants, high voltages, and is safe in operation. We trigger the instability and thus the actuation by temperature changes, which bring about a liquid/gas phase transition in a suitable volatile fluid. This allows for large deformations up to 300% area expansion within response times of a few milliseconds. A few degree temperature change, readily provided by the warmth of a human hand, is sufficient to reliably trigger the actuation. Experiments are compared with the appropriate theory for a model actuator system; this provides design rules, sensitivity, and operational limitations, paving the way for applications ranging from object sorting to intimate human-machine interaction.

Phase Transition Actuators Inspired by Plants Exploiting Soft Materials Mechanical Charcteristics

“…Combining mechanical instability and phase transition enables a significantly faster actuation than that of the Mimosa inspired phase transition actuator. With an actuation speed of 4 ms the Venus flytrap inspired actuator even outperforms it's plant counterpart [14] with an actuation time of <100 ms.…”

“…The second plant inspired actuator relies on a mechanical instability mimicking the Venus flytrap (Dionaea muscipula) [14]. The Venus flytrap's trapping structure [17] is formed by the terminal portion of each of the plant's leaves with each of being deflected outward into a concave (open) shape while awaiting its prey.…”

“…This conformation change due to the instability is as fast as 100 ms, while the recovery back to the open concave shape is achieved by means of swelling/shrinking and takes up several hours. Challenged by the speed of the mechanical instability a phase transition actuator utilizing a mechanical instability is conceived [14].…”

“…Owing to this "softness", actuation and deformation can happen throughout the soft robots' structure and provide an unlimited number of degrees of freedom [1]. Due to this mechanical paradigm shift, actuation of this soft robots explores a wide range of physical stimuli and phenomena [5] such as pneumatics [6], electric fields [7,8,9], shape memory alloys [10], phase transitions [11,12] or mechanical instabilities [13,14]. This offers a wide field to play for scientists and engineers.…”

Bio-inspired physical intelligence for soft robotics

“…受捕蝇草利用机械不稳定性实现叶片快速闭合的启发, 软体机器 人还可以利用机械不稳定性进一步提高驱动速度. Stadlbauer 等人 [38] 基于天然橡胶气球充气过程 中出现的机械不稳定性, 设计了一种体温触发的超高速纯机械软体驱动器. 当用手握住储液罐时, 罐内的低沸点液体会发生液-气相变, 触发机械不稳定性, 在不到 4 ms 的时间内使气球尺寸迅速 变大.…”