Overview: Nanotechnology is believed by many to be one of the most promising areas of technological development, and among the most likely to deliver substantial economic and societal benefits to the U.S. in the 21st century. Nanopositioning stages are used for ultra-precise positioning in a wide range of processes, ranging from spectroscopy to micro additive manufacturing. They can be constructed using flexure, fluidic, magnetic or mechanical (i.e., sliding and, especially, rolling) bearings. Of these choices, mechanical bearing nanopositioning stages are the most cost effective, and are currently the only commercially viable option for a growing number of large-motion-range nanopositioning applications that must be performed in high vacuum environments. However, mechanical bearing nanopositioning stages experience nonlinear pre-motion (or "static") friction arising from their inherent rolling elements, end seals/wipers, and lubricants. Pre-motion friction adversely affects the positioning speed of mechanical bearing stages by making them to take a long time to settle into a desired position compared to other bearing types. This award has supported a scientific investigation into the interactions between high frequency vibration, pre-motion friction, controller dynamics, and positioning speed in mechanical bearing nanopositioning stages. The knowledge generated will enable the use of high frequency vibration to mitigate friction in mechanical bearing nanopositioning stages, thereby enhancing the positioning speed and productivity of the nanotech processes that rely on them.

Intellectual Merit: A novel technique called vibration assisted nanopositioning (VAN) was proposed for reducing the settling time of mechanical bearing nanopositioning stages using high frequency vibration (i.e., dither). VAN synergistically combines the electromechanical design and control of mechanical bearing nanopositioning stages to mitigate pre-motion friction using dither, without jeopardizing positioning precision. It achieves this by applying dithering forces in equal-and-opposite pairs to the bearings of the mechanical bearing nanopositioning stage. This way, the dithering forces vibrate the mechanical bearings, thus mitigating pre-motion friction, without vibrating the mechanical bearing nanopositioning stage. Experiments carried out on a prototype stage incorporating the VAN approach showed a 52% reduction in mean settling time, based on 50 trials, when compared to a case without VAN. Moreover, the heat and potential wear induced by dither were shown to be practically insignificant. Perturbation analyses were used to theoretically demonstrate the reason behind the effectiveness and robustness of VAN in reducing settling time.   

Broader Impacts: The PI collaborated with a U.S.-based industrial partner (Aerotech Inc.) in validating the VAN concept. The VAN idea was very well received at the 2015 annual conference of the American Society for Precision Engineering (ASPE), leading to the Best Oral Paper Award. The VAN concept has been awarded a U.S. patent. Efforts to reduce the need for additional costly actuators (e.g., piezo actuators and their drivers) in VAN have led to a new concept for reducing settling time in mechanical bearing nanopositioning stages without need for vibration. The new concept has shown great promise in improving the positioning precision and speed of mechanical bearing nanopositioning stages at low cost. It has also raised very interesting intellectual questions that have led to a new NSF grant aimed at addressing the questions. The PI has developed a graduate course (ME 584: Advanced Mechatronics for Manufacturing) at the University of Michigan, and introduced contents from this project into the course. One PhD and two undergraduate students have been mentored through the project.

Last Modified: 03/25/2019
Modified by: Chinedum Okwudire