State-of-the-art commercial ankle prostheses enable amputees to walk on level ground replicating the passive biomechanics of able-bodied persons reasonably well. However, when navigating uneven terrains (such as slopes and stairs) these devices do not allow the ankle to adjust to the ground at each step in order to maintain stable contact. At these instances, the probability of falling is greatly increased. In contrast, the natural ankle adapts passively (i.e. no net positive power is required) just after heel strike allowing the foot to conform to the ground. This paper focuses on developing a continuously variable damper that can be paired with a carbon fiber foot in order to replicate the passive adaption dynamics of the human ankle. Presented in this paper are the performance specifications, the mathematical model, and the resulting device design for the semi-active damping system. The design consists of a hydraulic actuator, coupled to a servo control valve which modulates the damping. The system is designed to replicate the dynamic damping range of an able-bodied ankle joint by achieving flow rates as high as 2.0 liters per minute at 1.0 MPa, and operate at up to 20 MPa.
