Design and Assist-As-Needed Control of a Lightly Powered Prosthetic Knee

Abstract

This paper presents the design of a swing-assist prosthetic knee capable of providing stabilizing passive torques during the stance phase of walking and supplementing the passive swing phase behavior of the prosthetic knee with small active torques. The prosthesis design utilizes a novel actuator which integrates a symmetric multi-chamber hydraulic cylinder and a highly backdrivable linear electromechanical drive system into a single compact package. This actuator is implemented in a self-contained prosthesis design (including batteries and embedded system) which weighs 1.7 kg and is 28 cm in length, making this design comparable in size/mass to commercially available microprocessor-controlled prosthetic knees. The device is controlled using a finite state machine with a novel assist-as-needed controller operating during the swing phase. This assist-as-needed controller supplements a nominally passive swing phase behavior with small amounts of active power to enhance user safety. The device and controller were assessed on a single participant who took part in level ground walking experiments with both the swing-assist prosthesis and his daily-use device. Results indicate that the swing-assist prosthesis increases maximum swing phase knee flexion angle relative to the subject’s daily-use device. Furthermore, the swing-assist prosthesis was shown to automatically vary its assistance across walking speeds.