Control of a flexible space robot executing a docking maneuver

摘要

This paper is concerned with a flexible space robot executing a docking maneuver with a target whose motion is not known a priori. The dynamical equations of the space robot are first derived by means of Lagrange's equations and then separated into two sets of equations suitable for rigid-body maneuver and vibration suppression control. For the rigid-body maneuver, on-line feedback tracking control is carried out by means of an algorithm based on Lyapunov-like methodology and using on-line measurements of the target motion. For the vibration suppression, LQR feedback control in conjunction with disturbance compensation is carried out by means of collocated sensor/actuator pairs dispersed along the flexible arms. Problems related to the digital implementation of the control algorithms, such as the bursting phenomenon and system instability, are discussed and a modified discrete-time control scheme is developed. A numerical example demonstrates the control algorithms. OME of the functions of a space robot are to deploy or retrieve free-flying payloads and to service orbiting spacecraft. Under consideration is a robot with long flexible arms, such as in the case of the remote manipulator in the Space Shuttle. An example of such a space robot is shown in Fig. 1. The robot consists of a rigid base, two flexible arms attached to the base in series, and an end effector/pay load. To carry out the mission described, the space robot must have its own control system enabling the platform to translate and rotate and its arms to rotate. In this paper, the target motion is assumed not to be known a priori, so that the control permitting the space robot to execute the docking maneuver must be based on on-line measurements. The equations governing the behavior of space robots are nonlinear and can be expressed in the general form of the state and output equations x =f(x, u) (la)