Posture compensation of a walking assistive device using zero-moment point to stabilize motions on stairs

The main objective of this research was to stabilize the motions of a walking assistive device on the stairs. We proposed a posture-compensated method suitable for the stairs and proved the proposed theory in simulations and experiments. To adapt elderly people to daily life, an assistive device that could support the walking motion and protect the users from falls was utilized. Because the target users needed to walk on the stairs where they could easily fall, the device adjusted posture to stabilize users. Zero-moment point (ZMP) was used to quantify the stability of the device. To prevent collisions during the compensation process, the assistive device maintained the stride length because the width of the stairs is invariable. The target positions of the device feet were moved the same distance. The projection of gravity and the inertia force was kept in support polygons that varied for different walking phases to remain stable. Particularly, in simulation, the virtual slope method was quoted to calculate the location of ZMP. In experiments, pressure sensors were employed to measure ZMP. The results of the experiments showed that the assistive device, employing the proposed method, guided the user to successfully maintain the ZMP on the footplate. In conclusion, the proposed method is available for stabilizing various assistive devices, especially for slow-walking motions on stairs.