The control of lightweight flexible manipulator that are widely used in space applications due to their fast response and high speed of operation, is more complex due to their distributed structural flexibility. The structural flexibility associated with light-weight manipulators often results in mechanical vibrations and consequently leads to long settling times and position inaccuracy. This paper proposes the robust control of a single link flexible manipulator using the concept of Quantitative Feedback Theory (QFT). As a first step to achieve the control target, transfer function from input torque to output hub angle is established. The QFT is then adopted to formulate robust controller associated with the actuator. The QFT approach is based on classical ideas of frequency domain shaping of the open-loop transfer function. Simulation results envisage that the proposed QFT based robust controller tracks a desired tip trajectory while suppressing the tip deflection even in the presence of parametric uncertainties.

1. W. J. Book,"Recursive Lagrangian dynamics of flexible manipulator arms", The International Journal of Robotics Research 3 (3) (1984) pp 87–101.
2. B. Subudhi, A. S. Morris, "Dynamic modeling, simulation and control of a manipulator with flexible links and joints" Robotics and Autonomous Systems 41 (2002) pp 257–270.
3. Dwivedy SK, Eberhard P. , "Dynamic analysis of flexible manipulators, a literature review," Mechanism and Machine Theory, 2006; pp. 749-777.
4. M. O. Tokhi and A. K. M. Azad: "Flexible Robot Manipulators: Modeling, simulation and Control" Control Engineering Series 68.
5. R. H. Cannon, E. Schmitz, "Initial Experiments on the End-Point Control of a Flexible One-Link Robot," International Journal of Robotics Research, Vol. 3, No. 3, pp 325-338, 1984
6. Usoro, P. B, Nadira, R. and Mahil, S. S. , "A Finite Element/Lagrange Approach to Modeling Lightweight Flexible Manipulators," Transactions of the ASME: Journal of Dynamic Systems, Measurement and Control, vol. 108, pp. 198-205 (1986).
7. Zhihuan Zhang , "Predictive Function Control of the Single-link Manipulator with Flexible Joint," Proceedings of the IEEE International Conference on Automation and Logistics Qingdao, China September 2008.
8. J. M. Martins, Z. Mohamed, M. O. Tokhi "Approaches for dynamic modeling of Flexible manipulator systems," IEE Proc. -Control Theory Appl. , Vol. 150, No. 4, July 2003, pp 401-411.
9. B Subudhi and A S Morris "Singular perturbation approach to trajectory tracking of flexible robot with joint elasticity" International Journal of Systems Science volume 34, number 3, 20 February 2003, pp. 167–179.
10. Rasheedat M. Mahamood Jimoh O. Pedro "Hybrid PD/PID Controller Design for Two-Link Flexible Manipulators" IEEE, Proceedings of 2011 8th Asian Control Conference (ASCC) Kaohsiung, Taiwan, pp 1358-1363,May 2011.
11. S B Choi, C C Cheong, H C Shin, "Sliding mode control of vibration in a Single-link Flexible arm with parameter variations" Journal of Sound and Vibration (1995) 179(5), pp 737-748.
12. M. T. Ho and Y. W. Tu, PID Controller Design for a Flexible Link Manipulator, Proceedings of the 44th IEEE Conference on Decision and Control and European Control Conference 2005, pp. 6841 – 6846.
13. R. N. Banavar and P. Dominic, "An LQG/ H? controller for a flexible manipulator ", IEEE Trans. Control Syst. Technol. , vol. 3,no. 4,pp. 409-416, Dec, 1995.
14. N. Niksefat and N. Sepehri "A QFT fault tolerant control for electro hydraulic positioning system" IEEE transactions on Control system technology, 2002.
15. S. F. Wu, M. J Grimble and W. Wei " QFT based robust /Fault tolerant flight control design for a remote pilotless vehicle" . Proc IEEE 1999, pp 57-62.
16. M L Kerr, S Jayasuriya, S F Asokanathan, " QFT Based Robust Control of a Single-Link Flexible Manipulator" Journal of Vibration and Control, 13(1) pp 3-27, 2007.

Structural Flexibility Qft Flexible Link Manipulator Pre-filter.