Design Study of Low-Profile Fluidic Actuators for Origami-Inspired Folding Structures

Soft actuators leverage material compliance to achieve complex motions beyond what is typically possible for more classical motor architectures. One common category of soft actuators uses a pressurized working fluid to drive the deformation of an elastomeric pouch. This class of inflatable fluidic soft actuators has practical benefits due to simple construction from quasi-2D sheets, enabling rapid and low-cost prototyping of energy-dense low-profile actuators compatible with challenging applications in self-folding origami-based devices. The proposed pouch actuators combine elastomeric pouches of nearly arbitrary geometries with flexure-based folding mechanisms to apply controlled torques to drive self-folding. In prior work, flexure-based folding mechanisms employed the torque generated from a single pouch, which has been improved upon through various designs such as pleating structures, force conversion mechanisms, and series balloon configurations. For example, soft inflatable microactuators have demonstrated bending actuation by converting pouch expansion to torque by way of a compliant tendon.<br/>This presentation will describe efforts to build on past demonstrations of pouch-based folding actuators to examine the impact of the inflation chamber geometry on resulting motion and torque programmability. We leverage laminate-based 2D fabrication processes involving bonding thermoplastic elastomers to rigid substrates to construct inflatable fluidic actuators and simultaneously integrate with mechanical components that guide motion. We developed two actuators, the “thin-film pouch hinge” (TPH) and the “thin-film bellows hinge” (TBH), where the expansion of the pouch chamber volume drives contraction and generates angular displacement of the attached flexure hinge. We present a characterization of actuator and hinge displacement as a function of multiple geometric parameters. We find that, in the TPH designs, the pouch width determines the baseline angular deflection. In addition, we find that more complex pouch geometries (e.g., hourglass-shaped pouches) can further enhance displacement through 3D effects such as kinking of the pouch. Furthermore, we find that TBH actuator deflection depends critically on the tendon attachment distance to the hinge joint and the height achieved by the stacked inflatable pouches. We conclude with demonstrations of pouch actuators integrated with self-folding origami mechanisms, including flower-inspired designs that achieve multiple fold angles from a single pressure source.