Due to the lack of support area during tiptoe support phase, the virtual force control method is applied to planning dynamically stable bipedal sprinting. However, this landing pattern introduces a redundant degree-of-freedom, which leads to the uncontrollable inner motion of the support leg. To solve this problem, the virtual force of the body and the work output of support leg joints are analyzed, and then the conditions and method of driving coordination between the knee and ankle joints are put forward to maximize the total power of virtual forces. The proposed approach not only solves the uncontrollable inner motion of the support leg motion by balancing the driving load on ankle and knee joints, but also makes full use of the ankle drive capability. The planar bipedal robot achieves a higher speed by the locomotion pattern of sprinting, while the drive capacity of the other leg joints keeps unchanged. Finally, the effectiveness of the proposed method is verified with simulations.
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