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S. Ito, G. Schitter:
"Optimal Fail-Safe Motion Using Dynamic Brake for Lorentz-actuated AFM";
Vortrag: 2018 15th International Workshop on Advanced Motion Control (AMC), Tokyo (Japan); 09.03.2018 - 11.03.2018; in: "Proceedings of the 2018 15th International Workshop on Advanced Motion Control (AMC)", (2018), 6 S.

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 failsafe 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be withdrawn from the sample by turning off the actuators in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.

https://publik.tuwien.ac.at/files/publik_268843.pdf