Passive, Reflex Response Units for Reactive Soft Robotic Systems

As robotic systems enter an ever expanding spectrum of industries, it is becoming increasingly important that they are built to respond quickly and efficiently to dynamic environments. This letter presents a passive, reflex response (PRR) unit for quick actuation of pneumatic soft robotic systems. The PRR unit consists of a pressure reservoir with a soft one way valve that can be opened by passing a pin through its aperture. The device is mechanically stimulated by the environment, leading to the release of stored pneumatic pressure into the body of a soft robotic system. Prototypes of the PRR unit were characterized with three different valve sizes (6 mm, 9 mm and 11 mm) across a range of reservoir pressures (0.2 bar to 1.2 bar). A pin, attached to a load cell, was then lowered into the valve aperture until it opened. Force and pressure dynamics were recorded, along with the curvature of a pneu-net bending actuator during successive testing of the unit when coupled with a soft structure. For all valve sizes, the force required to open the valve increased proportionally with increasing internal pressure, with a minimum force of 0.98 N and a maximum force of 4.68 N. Time to vent the system decreased with increasing valve size, from 1.30 s to vent the system with the 6 mm aperture at 1.2 bar, to 0.53 s to vent the system with an 11 mm aperture. When integrated with a pneu-net bending actuator, the force required to open the 11 mm aperture increased to 15.82 N when charged to 0.5 bar of internal pressure due to the added force required to push on the constraining layer of the pneu-net. The PRR unit actuated the pneu-net in 0.37 s when charged to 0.5 bar of internal pressure. This demonstrates how reactive soft robotic systems can rapidly respond to mechanical environmental stimuli without the need for high-level control.