Waste tank cleanup manipulator modeling and control

Waste tank Cleanup is a current application area for robotics in the United States. As a result of tank access restrictions, (e.g., limited number and size of manholes), designs for several current waste Cleanup manipulator systems have long links with small cross-sections and variable lengths. In addition, as a result of anticipated payload capacity, these manipulator designs are hydraulically actuated. Many robotic manipulators contain links that are significantly flexible such that special considerations need be taken for acceptable motion control. Algorithms for control of flexible link manipulators have been under development for many years; however, most past approaches consider the flexible members to be of a fixed length. Variable length flexible links cause the fundamental natural fkquency of the link to vary during motion. The addition of hydraulic actuation also complicates the development of high-performance controllers because of the nonlinear behavior of hydraulic systems. This paper takes two approaches to investigating the problem of the control of manipulators having variable-length flexible links and hydraulic actuators. First, a simulation of a hydraulically actuated, 2-DegreeofFreedom (DOF), polar (r-@), manipulator with one flexible link is used to illustrate the problem of applying controllers successfully developed for hydraulically actuated, fixed-length flexible manipulators to hydraulically-actuated, variable-length systems. Second, based upon the simuIation, results, simple *Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U.S. Department of Energy under contract number DE-AC05-960R22464. yrMechanica1 and Aerospace Engineering at University of Tennessee. controller modifications are proposed and are shown to work on a full-scale experimental test bed. Motion control of hydraulically actuated, variable-length, flexible-link manipulators is the focus of this paper.