An airjet actuator system for identification of the human arm joint mechanical properties

A system for determining the mechanical properties of the human arm during unconstrained posture and movement is described. An airjet perturbation device is attached to the wrist with a special cuff, providing high-frequency stochastic perturbations in three orthogonal directions. The airjet operations as a fluidic flip-flop utilizing the Coanda effect. The design greatly reduces the mass of mechanical moving parts and enhances the frequency bandwidth dramatically. This airjet is intrinsically a bistable device that can generate arbitrary binary force sequences, such as pseudorandom binary sequences, colored white noise, and Walsh functions. The force transmissibility is identified. Cuff design and data acquisition are discussed.