Collaborative Research: Towards a Fundamental Understanding of a Simple, Effective and Robust Approach for Mitigating Friction in Nanopositioning Stages

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Nanopositioning stages are mechanical devices used for precise positioning in a wide range of nanotech processes, ranging from spectroscopy to micro additive manufacturing. Hence, their precision, speed and cost are critical to precision engineering applications in the automotive, aerospace and defense industries, and therefore directly impact economic welfare and national security. Stages that use mechanical (i.e., sliding or rolling) bearings are currently the only commercially viable option for a growing number of large-displacement nanopositioning applications. However, mechanical bearing stages suffer from poor precision and low positioning speeds due to the adverse effects of friction. This award supports a scientific investigation into a simple but effective approach for mitigating the effects of pre-motion friction on mechanical bearing stages by connecting the bearing to the stage using a compliant joint. Knowledge created through this investigation will increase the positioning speed and precision of mechanical bearing stages without significantly increasing their cost, hence contributing to the commercial viability of nanotech processes. Its broader impact plan includes: (i) collaborations with Aerotech, Inc., a U.S.-based nanopositioning stage manufacturer, to facilitate knowledge and technology transfer; (ii) educational curriculum development at two universities and training of professional engineers through tutorials offered by the American Society for Precision Engineering; and (iii) outreach to underrepresented minority middle school students, aimed at inspiring and equipping the next generation of highly-skilled manufacturing engineers. The objective of this research is to gain a fundamental understanding of the dynamics and compensation of nonlinear pre-motion friction acting on a servo-controlled mass through a friction isolator. Empirical studies have demonstrated significant improvements in positioning precision and speed when a servo-controlled mass (e.g., a nanopositioning stage) interacts with nonlinear pre-motion friction through a friction isolator (i.e., a compliant joint). However, very little is known about the dynamics of the friction isolator. The premise of this research is that, under certain circumstances, harmful dynamic phenomena (e.g., limit cycles) could occur when pre-motion friction acts on a servo-controlled mass through a friction isolator. This premise will be tested scientifically, to discover the harmful phenomena and circumstances that give rise to them, leading to insights on how to avoid them. To achieve this goal, mathematical characterizations of interactions between friction, friction isolator and servo parameters (e.g., mass, stiffness and damping) will be made using various tools, like the method of multiple scales, from nonlinear dynamic analysis. This will be complemented by rigorous numerical and physical experimentation on mechanical bearing nanopositioning stages, to guide, validate or refine the mathematical characterizations. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.