Impedance control of a small treadmill with sonar sensors for automatic speed adaptation

Automatic speed adaptation in treadmill training plays an important role in gait rehabilitation and virtual reality (VR) environments, where the user can adjust his/her speed for improved motivation and an enhanced sense of reality during walking interactions. To implement automatic speed adaptation of a treadmill belt, we have developed a novel impedance control scheme that accommodates natural movements without mechanical attachments to the user, and can estimate user-treadmill interactive forces to directly detect user intention, while simultaneously maintaining the user’s position on the treadmill platform. The proposed impedance control is realized via user interaction with a fixed virtual spring-damper component, allowing direct acceleration control of the treadmill belt in proportion to user displacement. The technique was applied to a small commercial treadmill (with a belt length of 1.2 m and a width of 0.5 m), which is easily installed and economical to operate, and is widely used in homes and health centers. Inexpensive sonar sensors with a Kalman filter algorithm were employed to measure user motions. To identify the characteristics of the proposed control scheme, a set of experiments was conducted and preliminary user studies with VR interactions were performed. The results of these experiments indicate that our impedance control scheme can provide a non-intrusive, intuitive method for implementing user-selected speed on a small treadmill. The proposed technique is cost-effective, and could potentially be applied to any type of locomotion interface or gait rehabilitation system, without the use of expensive, sophisticated sensors or special treadmills.