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05716839 Kov\'acs, L\'aszl\'o L. Galambos, P\'eter Juh\'asz, Andr\'as St\'ep\'an, G\'abor Experiments on the stability of digital force control of robots. Awrejcewicz, Jan (ed.), Modeling, simulation and control of nonlinear engineering dynamical systems. State-of-the-art, perspectives and applications. Invited papers presented at the 9th international conference ``Dynamical systems -- theory and applications", \L \'od\'z, Poland, december 17--20, 2007. Dordrecht: Springer (ISBN 978-1-4020-8777-6/hbk; 978-1-4020-8778-3/ebook). 191-199 (2009). 2009 Dordrecht: Springer EN digital force control on-line trajectory generation of robots stability charts

doi:10.1007/978-1-4020-8778-3_17

From the text: Digital force control has a great importance in many robotic applications. For example, in automated manufacturing processes the contact force between the robot and the workpiece has to be controlled in order to achieve the desired product quality. Deburring and polishing of castings can be mentioned as typical examples for this situation. In addition, force control has an important role in contour following tasks, where the robot recognizes the contour of a given object by applying a prescribed contact force normal to the object's surface. Similarly, for on-line trajectory generation of robots (teaching-in) by a human operator, force control is a possible and obvious solution. In this case, the operator grasps the handle of the teaching-in device and leads the robot through the desired trajectory, which requires the compensation of the contact force to be zero between the handle and the robot's flange. This control technique can successfully be applied for the teaching-in of robots used in medical rehabilitation, where the physiotherapist having no robot programming skills and he/she has to teach-in complex motion trajectories to the robot depending on the patient's actual condition. The goal of this work is to contribute to the understanding of the intricate dynamic behavior of robotic devices with digital force control. The presented results are based on modeling the fundamental characteristics of a 1 Degree-of-Freedom (DoF), force controlled robotic manipulator. That is, the controller's sampling time, the mechanical impedance of the robot in contact with the environment, and the friction loss in the driving system. For the case of simple proportional force control the stable domains of mechanical and control parameters are given in the form of stability charts. In order to support the theoretical conclusions, experiments were performed with a HIRATA (MB-H180-500) DC drive robot. The experimental results reveal also the existence of stable and unstable self-excited vibrations due to friction.