Perceptive Locomotion of Legged Robot Coupling Model Predictive Control and Terrain Mapping

Abstract

Legged robots promise an advantage over traditional wheeled systems, however, most legged robots are still confined to structured and flat environments. In this paper, we present a motion planner for the perceptive rough-terrain locomotion with quadruped robots. One of the main reasons for this is the difficulty in planning complex whole-body motions while taking into account the terrain conditions. This problem is very high-dimensional as it considers the robots dynamics together with the terrain model in a suitable problem formulation. In this work, we propose a novel trajectory and foothold optimization method that plans dynamically both foothold locations and motions (coupled planning). It jointly optimizes body motion, step duration and foothold selection, considering the terrain topology. Our model predictive controller tracks compliantly trunk motions while avoiding slippage. We test our method and comparative evaluations over a set of terrains of progressively increasing difficulty. To this end, we present a novel pose optimization approach that enables the robot to climb over significant obstacles. We experimentally validate our approach with the quadrupedal robot Panda5 autonomously traversing obstacles such steps, inclines, and stairs. The locomotion planner re-plans the motion at every step to cope with disturbances and dynamic environments.