Underactuated Robot Control: Comparing LQR, Subspace Stabilization, and Combined Error Metric Approaches

In this paper, three techniques for robust control of underactuated robots are experimentally compared on the classical ball and beam system. An adaptive tracking controller is first designed and implemented to identify the nominal friction characteristic. Then, designs for a linear quadratic regulator (LQR), subspace stabilization controller, and combined error metric controller are presented. Step response tests confirm that both nonlinear approaches exhibit better stability properties than the standard LQR design. In addition, the subspace stabilization approach permits a much more aggressive beam motion, resulting in shorter settling time with excellent control of overshoot.