Long-Range Fast Nanopositioner Using Nonlinearities of Hybrid Reluctance Actuator for Energy Efficiency

While nanopositioners often use flexures for high quality motion avoiding nonlinearities, the achievable motion range and energy efficiency are limited, due to the force required for positioning against the flexures. To overcome the problem, this paper proposes a flexure-guided nanopositioner with a nonlinear hybrid reluctance actuator for a large range and energy efficiency. The actuator has nonlinear negative stiffness that partially cancels the flexures’ stiffness. Consequently, the nonlinearities reduce the required current by up to 67%. To compensate them for high-precision motion in the entire range of 2 mm, a feedback controller is designed, achieving a closed-loop bandwidth of 640 Hz and positioning resolution of 2.48 nm(rms). The mechatronic system is designed such that the stiffness nonlinearity has no influence on the closed-loop stability and bandwidth. Additionally for accurate periodic scanning motion, modeling-free inversion-based iterative control is combined to decrease the tracking error by a factor of 396 at most. The achieved error is 10 nm(rms) for a 1 Hz triangular motion of 1.6 mm range and for a 100 Hz triangular motion of 10  $\mu$m range. The results demonstrate that the proposed nanopositioner can play a role of both long-stroke and high-speed scanners with the improved power consumption.