CONTROL DESIGN AND EXPERIMENTAL VALIDATION FOR THE ACTIVE EQUIPMENT FOR VIBRATION ISOLATION (AEVI)

摘要

The AEVI (Active Equipment for Vibration Isolation) system is intended to provide a clean microvibration environment for micro-gravity experiment to be embarked on the International Space Station (ISS), through active magnetic suspension between 0.01 and 10 Hz. The reference case is the FSL, the Fluid Science Laboratory, where the 170 kg experiment needs to be levitated. In the frame of the ESA AEVI R&D activity led by Alenia Spazio, Astrium was responsible for the control aspects, from control design to real-time implementation on a laboratory prototype. This paper presents the main results of the control design & validation, first, the design for the ISS environment, and second the validation of this design through ground test campaign with a suspended prototype of the AEVI system. The control design for in-orbit conditions has allowed to point out the major trade-offs and to propose solutions, so that it was eventually demonstrated that it was possible to fulfil all control and system requirements. All the Degrees of Freedom (DoF) (3 linear and 3 angular) of the flotor (the suspended body) have to be controlled, although different strategies have been chosen for linear and angular axes. A stiff attitude control has been selected to provide good axis decoupling and because there is no stringent rejection requirements on these DoFs. Translation control is realised by simultaneous position and acceleration feedback, to achieve high performance noise rejection while respecting the +/-1cm gap between flotor and stator. The acceleration controller for each axis is steep a band-pass filter designed using H_∞ control design techniques to achieve the necessary compromise between low frequency isolation performance and gap constraint. Two test campaigns of test have been conducted, referred to as the 3-DoF and 6-DoF test campaigns. The 3-DoF tests have allowed investigating implementation aspects on a simplified prototype of the AEVI system, for which only one degree of freedom was actively controlled (the other two being stiff enough to remain uncontrolled). The 6-DoF system tests were designed to reproduce to the best possible level the performance of the isolation system to be flown on the ISS. In this configuration, all 6 degrees of freedom were controlled together. As it is not possible to completely remove the impact of gravity on ground, it is not achievable to obtain the same isolation performance as expected in orbit. However, the goal of these tests was to correlate with sufficient accuracy the tests results with simulations, in order to allow an extrapolation of performances to the flight case. Moreover, it was indeed possible to show that the achieved control rejection on ground was identical to the foreseen one for flight in the bandwidth 0.5 to 5 Hz, with more than 40 dB measured in test.