Curved Soft Actuators
University of Illinois at Urbana-Champaign
What is a FREE?
Fiber-reinforced elastomeric enclosures (FREEs) are a type of pneumatic soft actuator consisting of an elastomer bladder surrounded by helical networks of inextensible fibers, with air supplied through a fitting attached at one end. The angle of the fibers relative to the longitudinal axis of the FREE control the FREE’s deformation when pressurized. FREE fiber angles can be set to produce contraction, extension, axial rotation, rigidity, or bending.
(a) A FREE with symmetric fiber angles less than 54° (b) contracts axially and expands radially under pressure. (c) Unpressurized and (d) pressurized contracting FREE.
Curved FREEs
Development of the soft robotic heart demanded a novel type of FREE that was pre-formed to allow for contraction along tightly curved surfaces. Actuator bladders were cast from silicone rubber from 3D printed molds with predetermined grooves for the fiber wrap. Each fiber follows the path of a helix with a curved center axis.
Curve paths were defined in Blender, and then transferred to CAD for mold modeling.
Curved FREE Kinematics
I developed parametric design software to explore curved FREE kinematics. A Python script defines and meshes the FREE geometry based on input parameters from the user such as FREE length, arc radius, fiber angle, and elastomer material properties. The model is then solved using Abaqus/CAE, and post-processed in Python. Curved FREEs can follow any three-dimensional discretized path.
The code for this project can be found here.
