Recent progresses in powered lower-limb prostheses have the potential of enabling amputee users to conduct energetically demanding locomotive tasks, which are usually beyond the capability of traditional unpowered prostheses. Realizing such potential, however, requires responsive and reliable control of the power provided by prosthetic joints. In this paper, an integrated walking-stair climbing control approach is presented for transfemoral prostheses with powered knee joints. Leveraging the similarities between walking and stair climbing, this new approach adopts the general finite-state impedance control framework. Furthermore, important modifications are introduced to model the biomechanical characteristics that are beyond the capability of standard impedance control. The transition between the walking and stair-climbing modes is triggered through the real-time measurement of the spatial orientation of the user's thigh, which provides a reliable indicator of the user's intention of making such transition. This new control approach has been implemented on a powered knee prosthesis, and its effectiveness was demonstrated in human subject testing.
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