An experimental comparison of tradeoffs in using compliant manipulators for robotic grasping tasks

Controllers developed for control of exible-link robots in hybrid force-position control tasks by a new singular perturbation analysis of exible manipulators are implemented on an experimental two-robot grasping setup. Performance criteria are deened for the grasping task. We present preliminary experimental data to show the tradeoos between controller complexity and performance enhancement as we deal with greater exibility. Various performance criteria are set up and experimental results are discussed within that setting. We conclude that large exibility can be controlled and can lead to reasonable performances. 1. Introduction In this paper we present experimental results on grasping with exible link robots. The theoretical basis of this work is 11] 10] where we developed the controllers we use for this experimental study and formally proved their stability. This work is motivated by the need to decrease the size and weight of robot manipulators while at the same time increasing performance. Examples of some of the applications to which this work applies include space manipulation tasks, where the weight limitations of the manipulator introduce signiicant exibilities, and non-invasive surgical techniques, where the size of the manipulator (2{6 mm ngers) and the environment in which it operates make the use of small exible links a potentially attractive alternative to existing methods. In addition, many micro-and nano-robotic devices make use of exible elements as an integral part of their structure 8]. In addition to understanding the eeects of exible links on manipulation tasks, our research is directed at exploring the beneets of using exible links in robotic manipulation tasks. It is well known that compliance increases the robustness properties of a robot manipulator performing a task. Rather than try to design away exibilities because they increase the complexity of the system, it is important to try to gain an understanding of how to use exibilities to increase the performance of a system. In a grasping situation, exibilities in robot structures can be used for application of internal forces by pre-tensing the robot itself. Thus, small errors in control of position will be accommodated by the exibility of the structure. Control of robots with exible links has so far concentrated primarily on positioning of the end-point of a exible robot. Control of a single link exible robot has been investigated at the theoretical as well as experimental level as early as 1984 1]. The control of multiple-link, exible robots is considerably more diicult and is …