Exploring the role of damping in a passive prosthetic knee through modeling, design, and testing

Abstract

With about 440,000 people with an above-knee amputation in India alone, there is a great need for high performance prosthetic knee. Due to socio-economic stigma associated with amputation, one of the main requirements for a lower limb prosthesis is achieving able-bodied kinematics. However, the prostheses available in developing countries, such as India, primarily focus the design on stability and low cost. This study presents a shear-based rotary viscous damper design for late stance and swing flexion for a passive single-axis knee prosthesis. The optimal normalized damping coefficient range of 0.012 - 0.014 ... was determined by optimizing a set of passive components to replicate a knee moment for an able-bodied subject and transtibial amputee wearing a fully characterized prosthetic foot. Dampers with a stacked fin architecture, where a highly viscous fluid is sheared between neighboring disks, were built with a range of damping coefficients from 0.37 to 1.80 Nm/(rad/s). The performance of dampers was evaluated through field and clinical testing with unilateral transfemoral amputees. The results of the studies showed that not only damping is required to prevent hyper flexion, but the optimal damping range allows achieve a peak knee flexion close to able-bodied. In future design, the validated damping selection framework will be used to expand the prosthetic knee design to other gait activities such as walking at different speeds, on slopes or uneven terrains.