Design and experiment of a variable stiffness prosthetic knee joint using parallel elastic actuation

Active prosthetic knee joints are proven to provide outstanding actuating performance in various walking situations. Currently, most active prosthetic knee joints are directly actuated via motors, which have the disadvantages of high-power consumption and insufficient joint compliance. In order to solve this problem, this paper proposed an active prosthetic knee joint with a unique variable stiffness parallel elastic actuation (VSPEA) mechanism. The VSPEA prosthetic knee joint is implemented by a geared five-bar mechanism with a motor-screw system. The VSPEA mechanism is implemented via another optimized compact motor-screw-spring system controlled by an adaptive stiffness adjustment algorithm. Numerical verifications show that the VSPEA prosthetic knee joint can reduce its actuation torque and power compared to the prosthetic knee joint without the VSPEA mechanism. Further practical experiments of the VSPEA prosthetic knee joint indicate that the Root Mean Square of its actuation motor power can decline 7.36 %, 8.75 %, and 11.51 % at 1.49 m/s, 1.21 m/s, and 0.85 m/s levelground walking, respectively, which demonstrated that VSPEA could effectively reduce the energy consumption and improve the endurance of the prosthetic knee joint.