Abstract
A space manipulator needs to exhibit high stiffness for tracking, and good compliance for capturing a tumbling satellite. However, the elasticity caused by harmonic drives challenges both the high-precision motion and the flexibility of the manipulator. In this paper, we propose a novel control method based on a robust torque-tracking controller to eliminate the unexpected vibration resulting from elasticity and reject the perturbation caused by nonlinear friction of the motor. In order to achieve the high-precision motion of the manipulator with uncertain dynamics, we combined the method with an improved adaptive method. The position-based impedance control, taking both the translational and rotational impedance into account, is added to achieve the soft-capture of a tumbling satellite. The stability of the proposed method has been strictly proven by the Lyapunov method. The space manipulator is mounted on a controlled chaser, forming a free-flying space robot. A loose coordinated control between the chaser and the manipulator is adopted in the task simulation. The simulations for verifying controller performance and the task simulation reveal that the manipulator has high-precision motion performance in the pre-capture phase, achieves soft-capture in the capturing phase and offers a reliable connection between the chaser and the target in the de-tumbling phase.
Highlights
The removal of malfunctioned satellites has become increasingly more urgent because the growing amount of non-controlled satellites pose an increasing threat of collision with on-orbit spacecraft [1], [2]
The space manipulator is mounted on a controlled chaser, forming a free-flying space robot
SIMULATION STUDY The co-Simulation environment with MSC/ADAMS R and MATLAB/SIMULINK R is created, 3D models of space robot and a tumbling target established in ADAMS R, all control algorithms achieved in MATLAB/SIMULINK R
Summary
The removal of malfunctioned satellites has become increasingly more urgent because the growing amount of non-controlled satellites pose an increasing threat of collision with on-orbit spacecraft [1], [2]. G. Yang et al.: Robust and Adaptive Control Method for Flexible-Joint Manipulator Capturing a Tumbling Satellite. Similar to the computing torque method for a rigid manipulator, the dynamics model of a flexible-joint manipulator can be decoupled and linearized, but both motor and link angular positions and velocity are needed [17]. Considering the friction effects and the disturbance from the chaser, the dynamics of a flexible-joint manipulator go as: τl = B(ql)ql + C(ql, ql)ql. The focus of this paper is on the robust and adaptive control method of the flexible-joint manipulator, not on the modeling method of the solar panels [35], [36]. The update of the parameters in proposed adaptive controller is more reasonable than the one in the trackingerror-based (TEB) adaptive controller [39], [40], because both the influence of the trajectory error and the torque error are considered
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