Abstract
This study mainly aims to ensure the safety of elderly people with a walking assistive device during ground-stair transition. A system that could automatically transfer the walking mode of the assistive device after detecting the ground or stairs is proposed in this research. The assistive device utilizes impedance control to track the predefined walking motions (level and stair walking) that belong to healthy people. Therefore, the target user could be taught to walk safely while being assisted. Collisions and falls can easily happen during the transition from even ground to stairs. Thus, we propose a distance-detection system using ultrasonic sensors mounted at the toe and the heel of the feet to detect the changes in road conditions. Accordingly, the previous walking pattern automatically converses to stair climbing or level walking when the assistive device walking on the ground finds the stairs ahead or detects the ground during stair walking. The device motion is changed by switching the target trajectories. The walking trajectories during the transition for different roads are combined. When walking on stairs that are dangerous for the user, the gait is adjusted to prevent tripping and missing steps based on the measured distance from the feet to the stairs. The effectiveness of the system is verified through simulations and experiments. In the simulations, the device target trajectories could be successfully changed when the device walks toward distinct road conditions from any distance. Three subjects participated in the experiments on two types of stairs. The experimental results show that compared with the normal walking of subjects, the foot height increases after assistance, which makes stair walking safer. In conclusion, this method can solve the adaptability of walking assistive devices to different surroundings.
