Electromagnetic Objective Lens Scanner: Design, Modeling and Characterization

This article describes an electromagnetic objective lens positioner for applications that require millimeter scale vertical travel and wide bandwidth, such as Michelson interferometry, laser micromachining, and confocal microscopy. The proposed device is a cylindrical Lorentz actuator with a stationary permanent magnet and moving coil. The motion of the objective is guided by two planar flexures that determine the travel range, stiffness and resonance frequency. The travel range can be easily varied, e.g. from $100 \mu ~\mathrm{m}$ to 1 mm, by altering the flexure dimensions. Analytical solutions for the stiffness, travel range and resonance frequency are derived and validated by finite-element analysis and experimental results. Compared to existing piezoelectric objective scanners, the proposed electromagnetic scanner exhibits higher linearity in open-loop, lower temperature dependence, can operate in humid environments, and has a reconfigurable travel range. The disadvantages compared to a piezoelectric scanner include heat dissipation for static displacement, the possibility of stray magnetic fields, lower lateral stiffness, and larger physical size. However, although the volume is larger than an equivalent piezoelectric scanner, the cylindrical shape is suited to many microscope turrets.