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Design of a Semipowered Stance-Control Swing-Assist Transfemoral Prosthesis

This article describes the design of a new type of knee prosthesis called a stance-control swing-assist (SCSA) knee prosthesis. The device is motivated by the recognition that energetically passive stance-controlled microprocessor-controlled knees (SCMPKs) offer many desirable characteristics, such as quiet operation, low weight, high-impedance stance support, and an inertially driven swing-phase motion. Due to the latter, however, SCMPKs are also highly susceptible to swing-phase perturbations, which can increase the likelihood of falling. The SCSA prosthesis supplements the behavior of an SCMPK with a small motor that maintains the low output impedance of the SCMPK swing state, while adding a supplemental closed-loop controller around it. This article elaborates upon the motivation for the SCSA prosthesis, describes the design of a prosthesis prototype, and provides human-subject testing data that demonstrate potential device benefits relative to an SCMPK during both nonperturbed and perturbed walking.