Intermittent control model for ascending stair biped robot using a stable limit cycle model

Abstract

Among the different functional movements can be carried out by humanoid biped robots, stair climbing is considered an important functional activity. Although many papers have been published on the planning and executing walking gaits for humanoid robots, most of them were concerned with walking on level ground. This is because the fundamental mechanisms that are needed to fulfill these requirements are still scarcely understood.Thus, in this research, we focused on another perspective of this problem and are inspired by the human control system. The proposed hypotheses were to develop an innovative bio-inspired model based on human dynamic during stair ascent. The model has been established as a reference trajectory model representing the desired coordination pattern between the ankle, knee and hip joints during human stair ascending. An intermittent controller devised such that it keeps the system’s dynamic in a close neighborhood of the desired dynamic and become on/off based on the distance between the model output and the reference trajectory of each joint.The evaluation was carried out through some computer simulation studies on a five-link biped robot. Results show that the reference model follows the desired synergy pattern of lower extremities joints and coordinates joints such that the postural stability is achieved. It has been also proved that the proposed intermittent controller successfully maintains the balance of the robot during movement and can simulate the human ascending stair behavior steadily. It also supports the biped in DSP, SSP and impact phases very well.