An adaptable prosthetic socket: Regulating independent air bladders through closed-loop control

During grasping or natural movement a prosthesis experiences varying loads, which can directly impact the comfort and fit of a socket on the user's residual limb. To alleviate this issue, four independent air bladders were integrated in a custom prosthetic socket, which contacted a model residual limb. The purpose of the bladders was to maintain specific pressures on the model residual limb to counteract pressure changes caused by an applied load. To sense pressure, calibrated custom piezoresistive sensors were placed between the air bladder and the model residual limb. A closed-loop algorithm was implemented to utilize sensor feedback and update airflow into each bladder to achieve a pressure equilibrium that maintains a static socket-limb system. The RMS error of internal pressure using pulse width modulation (PWM) bladder regulation decreased by 33% when compared no pressure regulation on the top bladder. We showed that this adaptive biomedical system for the human machine interface between a residual limb and socket can improve stability for prosthesis users using real-time pressure feedback.