A 4-degree-of-freedom powered exercise and/or rehabilitation machine has been designed for studies in physical human-machine interaction. The machine, called CSU 4OptimX, is fitted with 4-axis motion and force sensors and a robust impedance control system. A visualization system is used to provide motion reference paths for the human to follow. The control system uses real-time optimization to generate human motion reference paths, machine reference paths and a set of impedance parameters for each axis.

The project aims to advance both foundations and enabling technologies in the field of human-machine systems, with a focus on exercise and rehabilitation machines. A human interacting with an advanced (actively-controlled) exercise machine is the ultimate cyber-physical system due to the presence of multi-level loop closures, large-scale, coupled musculoskeletal dynamics, conflicting objectives between human vs. machine controllers, uncertain dynamics and limited sensing.