Control of Contact Forces: the Role of Tactile Feedback for Contact Localization

Abstract

This paper investigates the role of precise estimation of contact points in force control. This analysis is motivated by scenarios in which robots make contacts, either voluntarily or accidentally, with different parts of their body. Control paradigms that are usually implemented in robots with no tactile system, make the hypothesis that contacts occur at the end-effectors only. In this paper we try to investigate what happens when this assumption is not verified. First we consider a simple feedforward force control law, and then we extend it by introducing a proportional feedback term. For both controllers we find the error in the resulting contact force, that is induced by an hypothetic error in the estimation of the contact point. We show that, depending on the geometry of the contact, incorrect estimation of contact points can induce undesired joint accelerations. Moreover, we design a parallel control law that controls the position of the end-effector while controlling the norm of the force applied on a generic link of the robot. Experiments with the iCub humanoid robot support the presented analysis. In order to estimate contact points and contact forces on the forearm of the iCub we do not use any model of the environment, but we exploit its 6-axis force/torque sensor and its sensorized skin.

Publication
IEEE International Conference on Intelligent Robots and Systems
Date
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