An adaptive socket with auto-adjusting air bladders for interfacing transhumeral prosthesis: A pilot study

Comfort is a critical aspect in the application of wearable device, such as rehabilitation robots and upper limb prostheses. As a physical interface between human body and prosthetic limb, the socket and its comfort largely contribute to the user's acceptance. Traditional sockets are static, lacking dynamic adjustment mechanism for the contact pressure. To ensure a reliable suspension during daily activities, the socket is usually designed to be tightly attached, with a large stress, on the residual limb, which may introduce considerable discomfort during long-term use. In this article, we present a novel adaptive transhumeral socket, in which we employ four independent bladders contacting with the stump. Not only can these bladders provide a necessary suspension for the device but also form an air cushion (soft body) that helps relieve the pressure concentration between the biological body and physical prosthesis. In real time, this adaptive socket continuously monitors the limb posture, the operating load, and the contacting pressure between the socket and the limb, and then dynamically adjusts the clamping force to ensure a reliable attachment during various daily activities. Since well adapting to the contours of the stump, the bladders can effectively accommodate the volume change of the stump, making a balanced load distribution on load-tolerant areas. Through modeling and numerical analysis, we established a dynamic strategy for estimating the external load and an automatic scheme for adjusting the bladders' air pressure. Finally, a close-loop control was constructed based on the contact pressure measured by our self-developed force sensors. Our preliminary experiments on one normal (i.e. non-amputee) subject verified the effectiveness of the proposed method, showing that the adaptive socket can considerably reduce the socket-limb contact pressure while sustaining a secure suspension on the upper arm.