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CFIE: In-orbit active damping experiment using strain actuators

Contact : André Preumont

Motivation

Precision requirements for space applications become more and more stringent, leading to control bandwidth including many flexible modes. This results in serious robustness problems within and outside the controller bandwidth. Active damping can reduce the sensitivity of the control system to the parametric uncertainty and alleviate the spillover phenomenon. For large space structures, ground testing and parameter identification is often impossible. Therefore, active damping control schemes need to be very robust to parameter changes or modeling uncertainties.

Structure

The test structure consists of a very flexible steel plate (350mm x 600 mm x 0.5mm) cantilevered at its base, provided with collocated piezoceramic actuators and sensors bonded near the clamping. The central hole allows higher observability and controllability of the piezos. The structure is subjected to the large gravity effects (f1 = 0.95Hz on earth and 0.5Hz in space) making difficult the ground evaluation of the in-orbit dynamics.

Control strategy

Because it leads to alternating pole/zero pattern and positivity properties, the control strategy is based on two collocated, decentralized control loops. Collocated flexible systems have a tendency to exhibit some feedthrough in their transfer function leading to very poor roll-off in the structure transfer function, therefore the gain stabilization at high frequencies is provided by the compensator. Therefore, both local, decentralized control laws are based on multi-mode Positive Position Feedback (PPF) controllers.

Experiment

This project is part of the Technology Demonstration Program (TDP) of ESA and a protoflight structure (PFM), represented in, was flown in the American Shuttle (STS-69) during September 1995. In-orbit results show good active damping of the structure despite a poor prediction of its structural behaviour.

Related contract

1993-1994 : ESA-TDP, contract N°10413/93/NL/JG, collaboration with Spacebel Instrumentation s.a., Shuttle flight STS-69.

Related publications

  • N.LOIX & A.PREUMONT, On the modelling of active structures with collocated piezoelectric actuators and sensors, Electromotion, Vol. 2, No 1, pp 47-52, 1996.
  • N.LOIX, A.CONDE REIS, J. DETTMANN, P.BRAZZALE & A.PREUMONT, CFIE : In-orbit active damping experiment using strain actuators, SMACS 2, Mycrodynamique et pointage de grande précision, Toulouse, Mai 1997.