A Class of Novel Space Platform-Based Manipulators With Slewing and Deployable Links: Analyses and Experiments

Abstract

This paper studies dynamics of a space platform—based mobile two-module manipulator with each module consisting of two links, one free to slew (revolute joint) and the other permitted to deploy and retrieve (prismatic joint). Both the platform and the manipulator are considered flexible. Using the computation ally efficient order- N Lagrangian formulation of the system, the paper presents results of a comprehensive parametric study aimed at assessing effects of initial conditions, system variables, and manipulator maneu vers on the uncontrolled response. In general, the mass of payload, speed of maneuver, and joint flexibility represent three important parameters governing the system dynamics. Results suggest significant coupling between the platform, link, and joint vibrations as well as the system libration. The system exhibited unac ceptable response under critical combinations of parameters, thus indicating a need for active control. Next, effectiveness of a composite control strategy, involving the feedback linearization technique (FLT) applied to the rigid degrees of freedom with flexible generalized coordinates regulated through the linear quadratic regulator, is assessed. The control procedure proves to be remarkably successful in damping even relatively large disturbances in a robust fashion. Finally, the numerical simulation results are complemented with the prescribed trajectory tracking data, obtained using a two-module (four links) ground-based prototype manip ulator in conjunction with the FLT and proportional integral derivative control. Considering the presence of friction and backlash at the joints, the tracking results may be considered satisfactory. The comprehensive study lays a sound foundation for the design of this class of novel manipulators.