Optimal fail-safe motion using dynamic brake for Lorentz-actuated AFM

摘要

Many high-precision motion systems are positioning their mover close to the sample or target with a risk of collision in a failure. In order to prevent damage, this paper proposes a fail-safe system particularly for systems using flexure-guided Lorentz (voice coil) actuators. In this paper, an atomic force microscope (AFM) is used for demonstration. The flexures are deformed during AFM imaging such that the mover with the probe can be withdrawn from the sample by turning off the actuators in a failure. To realize fast withdrawing motion without a sensor for the protection of the probe and sample, this paper also proposes to use the dynamic braking of the Lorentz actuators. For an ideal braking force for fast settling, an optimal dynamic braking resistance is derived to minimize the 2-norm of the mover motion. Because the resulting optimal resistance is negative, it is implemented by an operational amplifier. The experiments demonstrate that the optimal dynamic braking reduces the settling time of the mover by 86.7 %, and the fail-safe operation is completed only within 54 ms.