Powered knee prosthesis commonly improves locomotion of above-knee amputees by generating net positive mechanical work at the knee joint which is especially required for movements with active knee extension and flexion such as sit-to-stand maneuvers, level-ground walking with various walking speed, stair/slope ascent ambulation and so forth. These studies tend to refer and trace normal human locomotion, and have amputees move “normally”, which is quite difficult for patients with severe disability such as four-limb deficiency. In this study, a powered knee prosthesis with small-scale, light-weight and affordable series elastic actuator (PKP-SEA) is developed and adopted to a walking rehabilitation of a patient with four-limb deficiency. A subject is 45 years old and has no experience to walk on prosthetic devices in his life. During the experiment, walking performance is investigated by turning PKP-SEA control parameters. As a result, the PKP-SEA shows capability of improving his walking performance in terms of walking speed and consistency not by replicating normal human walking, but suggesting an original walking gait based on his body condition and remaining functionality.

A method of stabilizing the biped locomotion in real-time is necessary to achieve biped locomotion that is stable and practical. We propose a new walk stabilization technique. First, we define the ZMP stability index. The proposed method compensate ZMP in real-time to control of inertia force and adjust feedback parameters according to the stability index. This results in altering the speed of walk instead of the walk pattern. As a result, we can compensate ZMP without changing the walking pattern and achieve both of the robustness against disturbances and high responsiveness for ZMP error correction. In this paper, after describing the proposed real-tune ZMP compensation method, the validity of the proposed method is tested using humanoid robot named 'morph3' that is created in our laboratory. Verification experiments, including simulation are performed and their results prove the validity of the proposed method.