Colloquia

Summary

In precision applications, hysteresis often results in significant performance limitations. In this research two hexapod leg designs with minimized hysteresis are presented. The research is used to determine a suitable design direction for a next-generation hybrid testing setup for offshore floating wind-turbines.

Two actuator layouts are considered, a rotational arc-based design including flexures and a linear design utilizing air bearings. To address the dominant contribution of moving power cables induced hysteresis, cables are partially replaced with deterministic compliant elements. A two-linkage cable guide is developed, and moving coil configurations are implemented. This enables the use of ironless core actuators, which result in low hysteresis and cogging-free operation, while still meeting the tight requirements on the moving mass, actuation forces and hysteresis.

Experimental validation shows a significant reduction in the maximum hysteresis. Compared to a hexapod with iron core actuators (the T-flex), the arc and linear designs reduce the hysteresis to 3.4% and 4.7%, respectively. With this achievement the performance limitations by hysteresis are effectively eliminated, as the hysteresis will no longer be the critical factor in the current designs. The findings presented in this paper demonstrate significant progress in improving hexapod precision and provide a foundation for future development of hybrid testing platforms for offshore renewable energy systems.