Abstract
It is known that internal vibrations decrease the performance characteristics and life time of
mechanisms, and in some cases they even may lead to mechanical failures. In motion systems
used in precision technology (wafer scanners, scanners, pick-and-place machines for production of
PCBs, wire-bonders etc.), internal vibrations limit the performance parameters. The vibrations
are still a challenge for the generally accepted design approach at present time, which is heading
towards higher system accuracy, speed and throughput.
Currently, the design approach to precision positioning applications places the dominant
vibration frequencies of the mechanical parts several times higher than the required control bandwidth.
However, these high mechanical frequencies are reached by constructing the mechanical
parts with high stiffness, often at the cost of relatively high mass.
To eliminate the negative consequences of the classical methodology, another design philosophy
is used in this thesis. A three-disciplinary lightweight positioning approach (control, mechanics
and electromechanics) focuses on mass reduction of the moving parts of motion systems. For this
purpose, a principle based on over-actuation is used, which allows designing a lighter overall kinematical
structure (force-path).
In order to evaluate this approach on a general level, benchmarks for classical and lightweight
positioning systems are proposed, namely, a so-called stiff beam system and a flexible beam system.
The main focus of the thesis is on the design and optimization of a novel Lorentz force
actuator for a lightweight positioning system that can also be applied in other precision technology
applications. The objective is to reach the maximum mass reduction of the flexible beam system.
In order to evaluate and design the novel actuator, a comprehensive static electromagnetic
analysis of the actuator is elaborated. The resulting analytical model is based on a magnetic
equivalent circuit, which has been identified by means of preliminary finite element calculations.
The analytical model plays an essential role in the complete design. It is later used for the optimal
dimensioning of the actuator for required performance specifications. Then, a numerical finite
element model is built and the results are used to evaluate the accuracy of the analytical model
and to identify parasitic forces and torques of the actuator.
Another important aspect that determines the operating conditions is the thermal behavior
of the actuator. It is also described analytically by a thermal lumped parameter model. The
suggested description of the heat transfer captures the static as well as the dynamic behavior.
To determine the optimal dimensions of the actuator an optimization approach, which uses
the magnetic equivalent circuit and the thermal analytical model, is proposed. In terms of nonlinear
programming, the problem statement consists of finding the dimensions of the actuator
with minimal mass, where given force and torque are used as constraints. Because of the nonlinear
nature of the problem the optimal solution is found numerically. The resulting optimal
actuator incorporating two degrees of freedom (DoF) has 22.2% less mass than two equivalent
1-DoF actuators.
It may be concluded, based on simulation and measurement results, that the proposed
actuator can be analyzed with sufficient accuracy by the presented methods.
The invented short-stroke actuator uniquely combines two controlled degrees of freedom:
translational and rotational. This combination ensures that the mass of the actuators used in the
flexible beam system has been reduced compared to that in the stiff beam system. The actuators
support the flexible beam system in a way that introduces less disturbances. Meanwhile, the
controllability of higher order vibration modes and, consequently, the global performance are
improved.
Two lightweight positioning systems were built, one with three 1-DoF actuators and the
other with two novel Lorentz force actuators. In both setups the flexible beam has its mass reduced
to 38.6% of that of the stiff beam. The total mass of the actuators in both cases is almost the
same, but the setup with the innovative actuators allows to control the beam with two forces and
two torques, while the setup with three 1-DoF actuators produces only three controlled forces
Original language | English |
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Qualification | Doctor of Philosophy |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 26 Sep 2006 |
Place of Publication | Eindhoven |
Publisher | |
Print ISBNs | 90-386-1883-2 |
DOIs | |
Publication status | Published - 2006 |