Design and control of a space based two link manipulator with Lyapunov based control laws

Abstract

The Flexible Spacecraft Simulator (FSS) at the Naval Postgraduate School was modified by replacing the flexible appendage with a two link robotic manipulator. This experimental setup was designed to simulate motion of a spacecraft about the pitch axis. The spacecraft consists of a main body, a two link manipulator, and momentum wheel actuator to control the pitch attitude of the spacecraft. Position information from the main body and manipulators was obtained from Rotary Variable Displacement Transducers (RVDT). The equations of motion were developed assuming that the main body and manipulator were rigid bodies. the resulting coupled, nonlinear, time invariant equations of motion were used to analyze the dynamics and kinematics of the main body and manipulator as well as the interaction between the main body and manipulator. Three different control strategies were developed using Lyapunov's Second or Direct Method. With the first controller, simple linear feedback of position and velocity information with constant gains was used to position the manipulator and stabilize the main body. A fifth order polynomial was used to generate a reference trajectory for the second controller, This trajectory was used in conjunction with a tracking controller to position and stabilize the system. In the third controller, a near-minimum-time technique was used to generate a reference trajectory. This reference trajectory was employed using a tracking controller similar to that used in the polynomial reference controller.