Evaluation of reduced-order controllers on a two-link flexible manipulator

This paper examines the synthesis of various robust controllers for command tracking of trajectories that excite many of the arm dynamics. The model used for all the designs is a 20 degree of freedom lumped-spring-mass-damper model of 40th order which is reduced to 18th order by balanced truncation. First, a standard linear quadratic Gaussian (LQG) controller is designed and tested, and robustness at the control loop is recovered with a loop transfer recovery (LQG/LTR) controller design. Next, loop transfer recovery (LTR) based on the special coordinate basis analysis of the plant is covered. In order to make the LQG/LTR and LTR controllers more practical, controller reduction is applied using modal residualization and balanced truncation. Next, a 4th order SANDY direct optimization design is covered and experimentally evaluated. Finally, the performance of all the controllers is evaluated experimentally along a nominal trajectory. Results show that the lower order controllers can provide comparable performance to the full-order controllers