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In our previous works, we have proposed "virtual passive dynamic walking" with virtual gravity for biped robots in order to realize active walking on level ground without any gait design in advance. In this paper, we discuss some control problems of a kneed biped robot and propose "modified compass-like virtual passive dynamic walking" with active knee-lock algorithms in order to avoid the "foot scuffing" problem during the single support phase. Furthermore, a virtual coupling control law is proposed which can realize a variable walking pattern with respect to the robot's energy levels. By the effect of the control law, the robot, which is a hybrid dynamical system, can be regarded as a passive system which does not include any collisions, and a variable walking pattern can be realized without loss of the properties of a virtual passive walk. The validity of the proposed methods has been examined by numerical simulations.
Asano et al. (Mon,) studied this question.