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

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 79-82).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.by Nina T. Petelina.S.M.S.M. Massachusetts Institute of Technology, Department of Mechanical Engineerin

Design of a Passive, Shear-Based Rotary Hydraulic Damper for Single-Axis Prosthetic Knees

With over 30 million people worldwide in need of assistive devices, there is a great need for low-cost, high performance prosthetic technologies in the developing world. A majority of the hydraulic dampers used in prosthetic knee designs are highly specialized, expensive, require regular maintenance, and are incompatible for use with low-cost, single-axis prosthetic knees popular in developing countries. In this study, optimal damping coefficients were computed based on a theoretical analysis of gait, specifically during the transition from the stance to swing phase of human walking when a large damping torque is needed at the knee. A novel rotary hydraulic damper prototype was designed using high-viscosity silicone oil and a concentric meshing of fins for shearing the oil. The prototype was validated experimentally to provide the desired damping torque profile. For preliminary, user-centric validation of the prototype, a gait study on one above-knee amputee in India was conducted with four different damping magnitudes. Feedback from the subject validated the optimal damping torque magnitude predicted for minimizing gait deviations and for enabling able-bodied knee kinematics. The new rotary hydraulic damper design is novel, passive, and compatible with low-cost, single-axis knee prostheses. Topics: Shear (Mechanics) , Dampers , Design , Artificial limbs , Kne

Knee Swing Phase Flexion Resistance Affects Several Key Features of Leg Swing Important to Safe Transfemoral Prosthetic Gait

We systematically investigate in-vivo the effect of increasing prosthetic knee flexion damping on key features of the swing phase of individuals with transfemoral amputation during walking. Five experienced prosthesis users walked using a prototype device in a motion capture laboratory. A range of interchangeable hydraulic rotary dampers was used to progressively modify swing phase flexion resistance in isolation. Toe clearance (TC; vertical distance toe to floor), effective leg length (ELL; distance hip to toe), and knee flexion angle during swing phase were computed, alongside the sensitivities of vertical toe position to angular displacements at the hip, knee and ankle. Key features of these profiles were compared across 5 damping conditions. With higher damping, knee extension occurred earlier in swing phase, promoting greater symmetry. However, with implications for toe catch, minimum TC reduced, and minimum TC and maximum ELL occurred earlier; temporally closer to mid-swing, when the limb must pass the stance limb. Further, TC became less sensitive to changes in hip flexion, suggesting a lesser ability to control toe clearance without employing proximal or contralateral compensations. There is a trade-off between key features related to gait safety when selecting an appropriate resistance for a mechanical prosthetic knee. In addition to highlighting broader implications surrounding swing phase damping selection for the optimization of mechanical knees, this work reveals design considerations that may be of utility in the formulation of control strategies for computerized devices