ZeroG: Overground gait and balance training system

1. ZeroG: Overground gait and balance training system Joseph Hidler, PhD; David Brennan, MBE; iian Black, MBE; Diane Nichols, PT; Kathy Brady, MSPT; Tobias Nef, PhD

2. Study Aim • Present ZeroG, a new overground, body-weight support (BWS) system that helps patients practice safe and controlled gait, balance, and postural activities. Relevance • Incorporating BWS into gait therapy allows patients to safely practice high number of steps. • Current BWS gait training often restricted to treadmill because of limitations with commercially available systems.

3. Design • ZeroG : • Provides both static and dynamic BWS. • Rides along overhead track, allowing practice while using walking aids and walking on flat surfaces, rough terrain, or stairs. • Uses active trolley system that automatically follows patients as they walk, so they feel vertical unloading forces but very little horizontal forces. (a) Side and (b) top view of ZeroG illustrating custom-series elastic actuator that controls rope force. Top and bottom assemblies have been removed from (b) for clarity. DC = direct current.

4. Experimental Tests • System maintained constant forces, producing much more normal ground reaction forces. • Active trolley minimized horizontal forces experienced by patient during gait. Subject descended approximately 16 in. with level of unloading set to 30 lb. (a) Desired movement speeds: 20, 40, 60 in./s (0.5, 1.0, 1.5 m/s). (b) Resulting rope angle averaged over 10 trials.

5. Conclusions • Performance of custom-series elastic actuator and trolley tracking was well within original design goals. • Training with ZeroG will allow patients to practice activities critical to functional independence at home and in community.