On the Design, Control, and Prospective Value of a Swing-Assist Low-Impedance Transfemoral Prosthesis

Abstract

This dissertation details the mechanical design, benchtop testing, controller development, and participant experiments of the Stance Control Swing Assist (SCSA) V2 Knee, a hydraulic semi-powered prosthetic knee prototype. Using a conventional resistive hydraulic cylinder in parallel with a flooded brushless DC motor with a low gear reduction, the SCSA V2 can provide powered swing in addition to the low and high impedance behaviors typical of hydraulic microprocessor-controlled knees. The SCSA V2 is used to demonstrate homogeneous dynamic control, which is a new class of swing phase control for semi-powered prosthetic knees. Homogeneous dynamic control is the first method of powered prosthetic knee control that is mathematically shown to not potentially override or conflict with the motion intent of the user. One example of this class of control, negative damping, is experimentally validated during slow walking, fast walking, and upslope walking. Negative damping is shown to improve relevant swing phase gait parameters including peak knee flexion angle, minimum toe clearance, knee angle at heel strike, and the temporal latency between full knee extension and heel strike. Participants with transfemoral amputation responded favorably to the SCSA V2’s negative damping controller during i) slow walking, stating that the knee felt lighter, ii) upslope walking, stating they felt safer with the extension assistance, and iii) fast walking, stating that the knee’s powered swing extension felt like it assisted their prosthesis side hip during swing. Results indicate that the SCSA V2’s low swing phase impedance combined with the presented novel swing assist controllers make the SCSA V2 more capable and safer than state-of-the-art microprocessor-controlled knees without sacrificing natural coordination with the user.