Design and Modeling of Generalized Fiber-Reinforced Pneumatic Soft Actuators

Soft actuators comprised of fluidic structures with fiber-reinforced elastomeric enclosures are seen throughout nature, exhibiting strength, power density, resilience, and diverse motions and forces. However, these structures are rarely used by engineers, in part due to the absence of a generalized understanding of their kinematics and forces. A small subset of soft actuators generating only extension or compression, popularly known as McKibben actuators, has been thoroughly investigated. This paper introduces the entire design space of actuators built with two families of fibers, of which McKibben actuators occupy a subset. The helix angle of the actuator's translation and rotation deformation is determined from the kinematics of the fiber deformation for all fiber angles as the actuator is pressurized. The volumetric transduction of the actuators, relating the output motion to change in contained volume, is analytically determined. The results are discretized to provide a designer with an easy to use design selection chart. The kinematics, force, and moment of the actuators are experimentally validated for all fiber angles.