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.
Robotic assembly of emergency-stop buttons
Author Andreas Stolt, Magnus Linderoth, Anders Robertsson, Rolf Johansson
Video ID : 692
Industrial robots are usually position controlled, which requires high accuracy of the robot and the workcell. Some tasks, such as assembly, are difficult to achieve by using using only position sensing. This work presents a framework for robotic assembly, where a standard position-based robot program is integrated with an external controller performing with force-controlled skills. The framework is used to assemble emergency-stop buttons which had been tailored to be assembled by humans.
This work was published in
A. Stolt, M. Linderoth, A. Robertsson, R. Johansson: Force controlled assembly of emergency stop button, Proc. Int. Conf. Robot. Autom. (ICRA), Shanghai (2011), pp. 3751–3756