Design

The fiber-reinforced bending actuator documented here consists of a core bladder reinforced with a strain-limiting layer and inextensible fibers. This section of the documentation describes some of the design considerations involved in making your own actuator, followed by a detailed tutorial on designing the required molds. Solid model files of the actuator and molds can be downloaded here (SolidWorks 2013) and .stl files of the molds can be downloaded here.

Since design decisions are closely tied to the fabrication process, here we provide a brief overview of the steps involved (a more detailed explanation is available in the Fabrication section).

1. The actuator core is a hollow semi-cylindrical tube molded out of elastomer. 2. The inextensible, strain-limiting layer is a sheet of fiberglass attached to the flat face of the actuator core, preventing that face from lengthening when inflated. 3. The entire actuator is wrapped with inextensible Kevlar thread, which restricts radial expansion. 4. This thread wrapping is secured in place by molding an additional outer "skin" layer which encapsulates the threads and the actuator core. 5. Finally, the actuator is plugged at both ends, forming a closed chamber. A vented screw is installed in one of the end caps to provide access for an air source to inflate the chamber.

This fabrication approach involves a multi-step molding process. The actuator core is cast on a steel half-round which serves multiple purposes: providing the hollow central chamber, aligning the actuator within the molds, and providing structural reinforcement during the attachment of the strain limiting layers.