Compliant Contacts Balance-Force Controller for Legged Robots

In this letter, we propose a controller for legged robots that takes into account the individual contact compliance. This controller is able to achieve both balance stabilization and force control in the same loop in task space thanks to the use of an explicit contact flexibility model and simplified centroidal dynamics that allow exploiting the redundancy of the kinematic and force feedback, while making multiple contacts with the environment. The control problem is formulated as LQR based on a linearized model of the reduced non-linear model. The performance of the controller with regard to robustness to modeling error and external perturbations has been tested in experiments on the position-control robot HRP-2KAI, in legged contacts and multi-contact modes.