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S. Ito, J. Steininger, P. Chang, G. Schitter:
"Control of a long range high-precision positioning system";
Vortrag: Workshop des VDI/VDE-GMA Fachausschusses 1.30 "Modelling, Identifikation und Simulation in der Automatisierungstechnik", Salzburg, Österreich; 20.09.2012 - 21.09.2012; in: "Tagungsband GMA-Fachausschuss 1.30 "Modellbildung, Identifikation und Simualtion in der Automatisierungstechnik"", Technische Universität Darmstadt Institut für Automatisierungstechnik und Mechatronik, Darmstadt (2012), ISBN: 978-3-9815012-2-3; S. 56.

A dual stage actuator (DSA) is a combination of two actuators along an axis: fine and coarse actuators. The fine actuator has high accuracy and high bandwidth although its stroke is very short. In order to extend this limited motion range, the base frame of the fine actuator is mounted on the coarse actuator, which has a long stroke with accuracy poorer than the fine actuator. Among a variety of actuators, Lorentz actuators are often used as fine actuators in DSA systems under an environment where disturbances are expected at fine actuators´ base.
Their advantage is that they show an almost ideal zero stiffness characteristics, which is
that disturbances from bases do not transmit to the moving parts [1]. Such zero-stiffness
DSA systems have been applied to wafer scanners for lithography [2]. However, since movable
parts need to float, these setups tend to be heavy and bulky with granite plates and
air feet for pneumatic levitation or require relatively complicated sensing and control for
magnetic levitation with multiple Lorentz actuators [3]. In addition, heavy moving parts
are under constraint of the mass dilemma of precision positioning systems, which is that
the mass of a moving part is determined by a compromise between the achievable acceleration
and the sensitivity for disturbance [1]. Thus the dilemma restricts the performance
of the dual stage system, limiting either its operational speed or accuracy.
In this presentation, we propose a low stiffness actuator in a DSA system. A low stiffness
actuator has mechanical supports to suspend its moving part. Nevertheless, its low transmissibility
between the base and moving part reasonably reduces the disturbance effects
on positioning. Using such an actuator as the fine actuator, we demonstrate that a low
stiffness DSA system can realize long range positioing with precision on the nanometer
scale without extra vibration isolators, by minimizing the moving mass of a DSA system.
The aim of this light load is to broaden the actuator´s bandwidth such that all the remaining
disturbances can be compensated and the mass dilemma is bypassed. In order
to implement this concept, a CD/DVD laser pickup is mounted as the fine actuator on a
linear motor. Our experiments demonstrate that this dual stage system is able to position in a total range of 0.5 meters with ± 15 nanometer accuracy at a settling time of 1.72
seconds.

long range, high-precision, positioning, Dual Stage Actuation

http://publik.tuwien.ac.at/files/PubDat_210812.pdf