A fundamental requirement for the success of a manipulation task is the capability to handle the physical contact between a robot and the environment. Pure motion control turns out to be inadequate because the unavoidable modeling errors and uncertainties may cause a rise of the contact force, ultimately leading to an unstable behavior during the interaction, especially in the presence of rigid environments. Force feedback and force control becomes mandatory to achieve a robust and versatile behavior of a robotic system in poorly structured environments as well as safe and dependable operation in the presence of humans. This chapter starts from the analysis of indirect force control strategies, conceived to keep the contact forces limited by ensuring a suitable compliant behavior to the end effector, without requiring an accurate model of the environment. Then the problem of interaction tasks modeling is analyzed, considering both the case of a rigid environment and the case of a compliant environment. For the specification of an interaction task, natural constraints set by the task geometry and artificial constraints set by the control strategy are established, with respect to suitable task frames. This formulation is the essential premise to the synthesis of hybrid force/motion control schemes.
Experiments of spatial impedance control
Author Fabrizio Caccavale, Ciro Natale, Bruno Siciliano, Luigi Villani
Video ID : 686
The videod results of an experimental study of impedance control schemes for a robot manipulator in contact with the environment are presented. Six-DOF interaction tasks are considered that require the implementation of a spatial impedance described in terms of both its translational and its rotational parts. Two
representations of end-effector orientation are adopted, namely, Euler angles and quaternions, and the implications for the choice of different orientation displacements are discussed. The controllers are tested on an industrial robot with open-control architecture in a number of case studies.
This work was published in
A. Casals, A.T. de Almeida (Eds.): Experimental Robotics V, Lect. Note. Control Inform. Sci. 232 (Springer, Berlin, Heidelberg 1998)