A General Whole-Body Compliance Framework for Humanoid Robots

In this paper we present a novel whole-body compliance framework. It is based on the Multi Spring Model, a set of virtual springs interconnecting the limb extremities and the trunk as well. More specifically, six virtual springs connect the trunk of the robot to the feet and the hands and other six springs interconnect the limb extremities. By selecting the stiffness values of each individual spring, complex behaviors can be generated, opening the way for more challenging tasks. The framework is implemented in a multi-layer architecture that distributes the computation on the different control units available on the robot. The proposed method was tested in two different tasks using the COmpliant huMANoid (COMAN), a full-body torque-controlled humanoid robot. For the first task, the robot was able to grasp a box, lift it up and firmly hold it. In the second task, the robot balanced itself while having the hands in contact with two walls. COMAN was able to successfully perform both tasks while perturbed by external disturbances and environmental uncertainties.