ZMP Reference Trajectory Generation for Biped Robot with Inverted Pendulum Model by Using Virtual Supporting Point

Motion planning of a biped robot based on ZMP is quite popular in recent years. In this method, ZMP reference trajectory is planned at first so that ZMP stays inside of the support polygon. Then, walking pattern is generated based on the trajectory. Conventional methods based on ZMP reference trajectory did not take the dynamics of bipedal locomotion into account. Therefore, the basis of the motion planning was ambiguous and the biped robot did not get human-like walking. This paper proposes ZMP reference trajectory generation with inverted pendulum model by using VSP (Virtual Supporting Point). VSP, which was proposed by our research group, is the method to design the position of the supporting point of inverted pendulum model with mechanical constraint relaxation. Walking with the proposed trajectory generation is schematically explained in Fig. 1. The robot is modeled as one mass point system and both COG and ZMP reference trajectory are generated along the movement of the inverted pendulum. With this, a smooth ZMP reference trajectory based on the dynamics of the inverted pendulum is generated uniquely according to the desired stride and walking cycle. In addtion, the trajectory is able to defined on any plane. Some bipedal walking were simulated and experimented in this