Adaptive Ground Clearance Control for Preparation for Fall in a Wearable Assistive Device

Reducing the risks of falls is one of the main tasks for walking assistive devices. Some elderly people who fear falls tend to lower the distance between the ground and the support tip of the assistive device (ground clearance), but it is very easy to obstruct their walking and also not good for their health by always providing support because they lose the opportunities to use their muscles. However, if the ground clearance is too large, the risk of falls would also increase. In this paper, we introduced the concept of adaptive ground clearance to adjust the ground clearance dynamically during walking so that the assistive device can always prepare for falls. First, the ground reaction forces on two feet are modeled based on the symmetry walking assumption. Thus, the vertical motion on the hip during walking can be estimated. Second, a wearable device prototype was built according to the information about hip vertical displacement. Finally, a PID position control method was implemented on the prototype, using a low-cost distance sensor to enable real-time ground clearance adjustment. This work may inspire the design of rollators and walkers to reduce the reaction time and to prepare for falls.