Optimized friction drive controller for a multi-DOF ultrasonic nanopositioner

This paper presents a new generation of compliant multi-degrees-of-freedom piezoelectric nanopositioner for positioning, transport, alignment of micro-objects under the field of view of a microscope. It is based on the cooperation of arrayed direct-drive standing-wave ultrasonic actuators (microSWUMs). A number of nonlinearities exist in the actuator due to its macro- and microdynamics. An optimized friction drive multidimensional controller is proposed based on a closed-loop electromagnetic field-based preload controller ensuring optimal preload, and a feedforward pulsewidth modulation (PWM) controller with input shaping for driving force control. These techniques are applied to reduce the effects of low-speed-low-force instabilities due to stick-slip and friction pairs which lead to output oscillations during nanometric stepping motion. The closed-loop positioning system designed with microSWUMs produced 10-nm resolution and 5% displacement repeatability in a low-speed-low-force region; unlimited travel with velocities of 0.3 m.s^-1 and driving forces around 2 mN in a high-speed-high-force region.