Sequential Trajectory Generation for Dynamic Multi-Contact Locomotion Synchronizing Contact

This paper proposes a new framework to generate 3D multi-contact locomotion with low computation cost. The proposed framework consists of (a) the derivation of the prospect centroidal dynamics by introducing a force distribution ratio, where it can be represented with a formulation similar to the inverted pendulum's one, and (b) the development of a fast computation method for generating a 3D center-of-mass (CoM) trajectory. Then (c) the ZMP reference is modified so that feasible contact wrench can be generated by a force distribution using the centroidal dynamics with the approximated friction cone. The proposed method allows to generate a trajectory sequentially and to change the locomotion parameters at any time even under variable CoM height. Then, the contact timing of each end-effector can be adjusted to synchronize with the actual contact with the environment by shortening or extending the desired duration of the support phase. This can be used to improve the robustness of the locomotion. The validity of the proposed method is confirmed by several numerical results in dynamic simulator: a CoM motion while changing the contact timing, a multi-contact locomotion considering a transition between biped and quadruped walking on an horizontal floor to move below obstacles. Finally, we also show a climbing stairs using handrail which requires dynamic changes of unilateral and bilateral contacts.