Pressure Control of Rolling-Seal Tape Spring Actuators

Tape spring mechanisms are useful in soft robotics for their ability to extend long distances and exhibit both high strength and high flexibility. In this work we introduce a new tape-spring based actuator concept that uses internal fluidic actuation to achieve: 1) stiffness control of tape-spring beams, and 2) shape modulation of a length-constrained tape-spring actuator. This concept relies on the ability of sealed tape-springs to form a rolling pressure seal when the mechanism is bent, and thus through differential pressure control across the bend we can reconfigure the actuator shape. We first describe the fabrication methods for sealed tape-spring actuators and then characterize their mechanical and hydraulic properties. Three-point bend tests of open and hydraulically sealed tape-spring beams enable us to determine how fluid pressure influences mechanical stiffness. We measured the sealing characteristics of the rolling bend seal by measuring mass-flow through the bend at different input pressures. These characterization experiments allowed us to build a length-constrained actuator which can change stiffness, and actuate through differential pressure control. Fluidic control of rolling-seal tape spring actuators presents new opportunities for using tape-spring mechanisms in situations where electromagnetic actuation may be unfavorable or infeasable.