Adaptive Control of Space Robot System with an Attitude Controlled Base

Abstract

In this paper, we discuss adaptive control of a space robot system with an attitude controlled base on which the robot is attached. We at first derive the system kinematic and dynamic equations based on Lagrangian dynamics and linear momentum conservation law. Using the dynamic model developed, we discuss the problem of linear parameterization in terms of dynamic parameters, and have found that in joint space the dynamics can be linearized by a set of combined dynamic parameters, but in inertia space linear parameterization is impossible in general. Then we propose an adaptive control scheme in joint space which has been shown effective and feasible for the cases where unknown or unmodeled dynamics must be considered, such as in the tasks of transport an unknown payload, or catching a moving object.

The scheme avoids the use of joint acceleration measurement, inversion of inertial matrix, high gain feedback, and considerable computation cost, and at meantime, is also applicable for the fixed-base robot system by slight modification. Since most tasks are specified in inertia space, instead of joint space, we discuss the issues associated to adaptive control in inertia space and identify two potential problems, unavailability of joint trajectory since mapping from inertia space trajectory is dynamic dependent and subject to uncertainty, and nonlinear parameterization in inertia space. We approach the problem by making use of the proposed joint space adaptive controller and updating joint trajectory by the estimated dynamic parameters and given trajectory in inertia space. In the case study of a planar system, the linear parameterization problem is investigated, the design procedure of the controller is illustrated, and the validity and effectiveness of the proposed control scheme is demonstrated.