Freebal: dedicated gravity compensation for the upper extremities

In most upper-extremity rehabilitation robotics, several components affect the therapy outcome. A common component is gravity compensation which alleviates upper-extremity movements. Gravity compensation by itself could improve motor control further or faster, separate from other effects of robotic therapy. To investigate the rehabilitation value of gravity compensation separately, we created the dedicated gravity compensation system, Freebal. The sling systems with ideal spring mechanisms in the Freebal are well suited for providing compensation forces. The device has steplessly scalable forces, a large range of motion with constant compensation forces, independent control of the compensation of the lower and upper arm, and low movement impedance. It also does not need external power, force sensors or active controllers. Finally, the Freebal can be easily moved, serviced and used in arm rehabilitation with either sitting or standing subjects.