Experimental closed-loop excitation of nonlinear normal modes on an elastic industrial robot
Published in IEEE Robotics and Automation Letters, 2022
This paper demonstrates for the first time the practical excitation of nonlinear normal modes (NNMs) on a complex, high-degree-of-freedom robot — the elastic KUKA iiwa manipulator — thereby bridging a longstanding gap between theoretical nonlinear modal analysis and real-world robotic hardware. By combining modal theory (eigenmanifold analysis) with a carefully designed closed-loop controller, we show that it is possible to stabilize and sustain intrinsic oscillatory modes of an articulated elastic robot — even in presence of damping, friction, and real hardware constraints.
Our experiments excite multiple distinct eigenmanifolds and maintain clean periodic motion over long durations, even under perturbations and changing energy levels, demonstrating robustness to disturbances and model uncertainties. The work shows that elastic robots can exploit passive dynamics for energy-efficient oscillatory behaviors and paves the way toward soft, compliant, and efficient robotic motion beyond rigid-body control.
Recommended citation: F. Bjelonic, A. Sachtler, A. Albu-Schäffer, and C. Della Santina, “Experimental closed-loop excitation of nonlinear normal modes on an elastic industrial robot,” IEEE Robotics and Automation Letters, vol. 7, no. 2, pp. 1689–1696, 2022.
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