Estimation of Energy Minimizing Series Elastic Spring Stiffness for an Active Knee Prosthesis

Minimizing the mechanical motor output work or power required to create the desired actuator behavior in a quasi-static manner is a widely used, but incomplete method for actuator design. Here we use a dynamic electric and mechanical motor model combined with constrained output kinematics to find spring parameters for an active knee prosthesis using a series elastic actuator. This simulation was used to examine the landscape of motor torque tracking ability, motor electrical consumption, and the mechanical output of the system to determine spring stiffness ranges that should be further examined in the real device. Even though the task is negative net work, the actuator seems to benefit from having a elastic design, with a range of stiffness that improve energy consumption and torque tracking compared to a stiff device.