Control Architecture of a Variable Stiffness Prosthetic Knee for Energy Absorption and Restoration

This study presents a control architecture for a powered variable stiffness prosthetic knee joint, which relies on a state machine and an impedance controller. The state machine guarantees to reliably discriminate between the stance phase, and the flexion/extension of the knee joint during the swing phase. The impedance controller tunes the variable stiffness joint and, namely, its equilibrium angular position and mechanical stiffness. To assess the impact of the impedance control and of the variation of the walking speed on the energy absorption and restoration of the prosthetic joint, experiments were conducted with a healthy participant wearing the pros-thetic knee by means of an able-bodied testing adaptor. Results demonstrate that a greater equilibrium position, lower stiffness, and higher walking speed are associated with enhanced energy absorption and restoration within the mechanical springs of the knee joint, along with increased knee flexion and extension during the stance. These findings provide valuable insights into the control of the powered variable stiffness prosthetic knee joint for enhancing gait dynamics and overall functionality.