Speed adaptation control of a small-sized treadmill with state feedback controller

Variable velocity in treadmill training may play an important role in gait rehabilitation where a patient can practice variable walking velocity while the treadmill adjusts to it. In order to adjust the treadmill velocity to the subject´s variable walking velocity, we have developed an automatic gait velocity adaptation algorithm implemented on a small-sized commercial treadmill (belt length of 1.2 m and width of 0.5 m) which is widely used at home and health centers. The control objective is to automatically adjust the treadmill velocity so that the subject´s position is maintained within the track when the subject walks at a variable velocity. The subject´s position with respect to a reference point is measured by a low-cost sonar sensor located on the back of the subject. Based on a encoder sensor measurement at the treadmill motor, a state feedback control algorithm with Kalman filter was implemented to determine the velocity of the treadmill. In order to reduce the unnatural inertia force felt by the subject, a predefined acceleration limit was applied, which generated smooth velocity trajectories. The experimental results demonstrate the effectiveness of the proposed method in providing successful velocity changes in response to variable velocity walking including starting (accelerating) and stopping (decelerating) periods of treadmill exercise without causing significant inertia force to the subject. In the pilot study with three subjects, users could change their walking velocity easily and naturally with small deviations during slow, medium, and fast walking. The proposed automatic velocity adaptation algorithm can potentially be applied to any locomotion interface in an economical way without having to use sophisticated and expensive sensors and larger treadmills.