US Patent 9782621 Exercise device providing automatic braking

An exercise device comprises a flywheel, a driving assembly, and a control assembly. The driving assembly drives the flywheel to rotate. The control assembly comprises an angle sensor for measuring the change of angular displacement of the flywheel during a specific period of time. The control assembly calculates the angular velocity or the angular acceleration of the flywheel by the measured angular displacement during the specific period of time. The control assembly determines if the flywheel is to be stopped according to at least a criterion.