Soft Pump Using Buckling of Spherical Shell Under Tension

In emerging soft robotics, a pneumatic actuator is the most common way to actuate soft robots which can safely interact with humans. Especially the soft pneumatic pump that can be used as a pneumatic actuator improves the portability and adaptability of soft robots since it can overcome many problems of the existing pump, which is often bulky and noisy. Nevertheless, this soft pneumatic pump has had apparent limitations on the maximum flow rate and the maximum mechanical power. Therefore, existing soft pneumatic pumps have difficulty actuating stiff pneumatic devices and making rapid motion. Here, we introduce the novel soft pump, which can overcome these limitations by using the snap-through instability. This soft pump is composed of a spherical shell with two opened cylindrical channels on the opposite side. One channel is designed to make only inflow, while the other channel to make only outflow using check valves. We stretch the soft pump by pulling the end of the inflow channel at a constant velocity while the other end is fixed. As the total length of the soft pump reaches a critical value, the spherical shell buckles. The soft pump generates rapid outflow with a sharp decrease in the internal volume due to the buckling under tension. We conduct finite element simulations to evaluate the maximum flow rate by controlling geometric parameters and material properties. Then, the experiment is performed with the soft pump made of Ecoflex 00-50 to validate the results of the simulations. Through the experimental method, the maximum mechanical power of the soft pump is measured to figure out the maximum stiffness of the pneumatic device that can be actuated. We also demonstrate this soft pump running pneumatic device. This work presents the potential of the novel soft pump as an advanced actuator overcoming the limitations of the existing pneumatic pump.1