SPREKER
Elena Lomonova, Chair of Electromechanics and Power Electronics Group, TU Eindhoven

TITEL
Reluctance actuators for high-precision actuation systems

TIJD

9:30

ABSTRACT
In the high-precision industry the accuracy and throughput of actuation systems are highly important. Some examples of applications for high-precision actuation systems are semiconductor lithography equipment, pick-and-place robots and real time electron microscopy inspection. For example in the lithography industry, the goal is to double the throughput every six years, while positioning accuracies must be improved by a factor four in the same time period.
With the current ironless long-stroke and short-stroke actuator topologies, the specifications on throughput and accuracy cannot be reached anymore. Firstly, the increase of mechanical power consumption of actuation systems (to obey the force demands for higher accelerations) results in expanding cooling systems. Secondly, the increase of moving mass that reduces disturbance effects, improves stiffness and bandwidth but implies increased force densities of actuators and consequently increased power consumption. The third limitation for ironless actuators is the leakage of magnetic fields resulting in stray field effects leading to crosstalk. This leakage needs to be solved by shielding equipment.
Because of the reached limitations of conventional ironless actuator technologies, new energy efficient reluctance actuator topologies are considered as potential candidates for the next generation high-precision positioning systems. These reluctances actuators are able to achieve higher force densities in combination with a lower moving mass. Therefore, the reluctance actuators will reduce the energy consumption by a factor five to ten, while meeting the specifications on position accuracy, speed and acceleration that are necessary in the ultra high-precision industry.
The research on reluctance actuators mainly focuses on the nonlinear properties of the applied ferromagnetic materials due to magnetic hysteresis, saturation and induced parasitic effects, such as eddy currents. These nonlinear, rate dependent and history dependent effects occurring in reluctance actuators result in a highly nonlinear current force relation. These effects cause phase delays, damping and associated energy losses in the actuator and substantially limit the accuracy and bandwidth of the actuators. Therefore, a fundamental investigation of nonlinear polarization phenomena in ferromagnetic materials is conducted. In addition, mathematical models are derived on the basis of physical laws that describe energy conversion and nonlinear dissipation in conducting materials. This analysis in combination with proper control and design optimization will make reluctance actuators applicable to a wide class of advanced electromagnetic actuation systems, which will be more robust and suitable for increased market demands on throughput, accuracy and reduction of energy consumption.