Design for underactuated sequencing of bistable inflatable structures

In inflatable soft robots, every individual actuator is an underactuated structure since it transduces a single pressure input to a deformation with essentially unlimited degrees of freedom. On a system level, however, soft robots usually are not underactuated as the pressure in each actuator is controlled independently. This requires a large volume of valves and tubing which compromises the softness and performance of the robot.

In this talk, we present the design an underactuated system of soft actuators that inflate and deflate in a fixed sequence from a single controlled pressure supply. The system consists of multiple actuators each featuring a shell that buckles on inflation resulting in pressure-volume relationships with peaks and valleys in pressure. When the pressure in the shared supply line crosses a peak or valley, the corresponding actuator transitions between a low- and high-volume state. We propose a method to find the dimensions of the buckling shells that yield a desired set of peak and valley pressures. This allows us to design an underactuated system with one pressure input and six actuators that inflate in the precise sequence that renders Ludwig van Beethoven’s Ode to Joy when interfaced with a piano keyboard.