APAM: Antagonistic Pneumatic Artificial Muscle

We present a pneumatic actuator capable of changing length by 1000%, applying both pushing and pulling forces, and independently modulating its length and stiffness. These characteristics are enabled by individually addressable internal and external chambers that work antagonistically against one another. The high deformation with low hysteresis is achieved by wrinkling of thin materials that are assumed to be inextensible but flexible, as opposed to stretchable. A model for the actuator is presented and validated with experimental results, showing capabilities of high strain, pushing and pulling, and independent control of length and stiffness. These characteristics are motivated by the application of a compliant truss robot. Accordingly, we show a simple grounded tetrahedron with three actuator elements and three static elements. We demonstrate motion of the tetrahedron apex against external loads and the ability of the structure to vary its stiffness. The actuator offers a unique set of characteristics that could increase the capabilities of soft robotic devices.