Floating free

The sensitive operations involved in laser machining, semiconductor fabrication or food production could soon be made simpler, thanks to a planar magnetic levitation table developed by

.

The system — called Planar Maglev —is expected to be capable of achieving nanometer precision in ultra-high vacuum and ultra-low contamination applications. This is due to the compact and flexible nature of the technology, which supports moving masses with no bulky cables, cooling hoses or external interfaces.

The free-floating platform is able to swivel from left to right and tilt side to side and up and down, giving it six degrees of freedom. The system's motions are controlled by Lorentz force actuators, which take the form of embedded magnets on the platform and coils mounted on the stationary bed. This differs from conventional planar motors where actuator coils (along with the cables carrying their power supply) are mounted on the floating platform itself, which restricts the movement of a plate to the lengths of the cables.

Because the Planar Maglev's coils are embedded on the fixed bed, the floating plate is unencumbered, said Peter Frissen, the main engineer for the planar maglev technology at Philips Applied Technologies. Therefore, the plate's movements are completely unrestricted, and only the dimensions of the fixed bed limit their stroke lengths.

Frissen said the other way Planar Maglev differs from conventional systems is in its lack of need for cumbersome cooling hoses. When an electric current is applied to the actuator coils of any system it generates heat but, according to Frissen, the Planar Maglev system runs much cooler because all dissipation is on a fixed wall and not a moving plate.

The elimination of the cooling hoses also removes a source of contamination when the platform is working in a high-vacuum environment. Moreover, it allows the supported component to be transported through a number of process steps without being transferred to a different platform. This would be an advantage in manufacturing semiconductor wafers, for example, because it limits the number of times the wafer has to be handled. The handling of wafers compromises accuracy, extends processing time and increases the risk of defects.

In addition to being more flexible, Frissen said the Planar Maglev platform is less mechanically complex than conventional multi-stage precision positional platforms because of its specially designed computer software. 'Soft motion' software constructs a virtual model of the maglev system using data from the system's sensors. It then digitises the mechanics and computes the forces required to move the platform to a new position.

The software is key in making Planar Maglev simple and precise, but developing it was no easy task. Frissen said engineers spent nearly a decade studying the dynamics of maglev systems and channelled that information into the development of appropriate algorithms.

Philips is still seeking an end use for Planar Maglev but Frissen said he imagines one of the best applications for the technology would be semiconductor manufacturing, which is often a complicated and sensitive operation. Many semiconductors, such as silicon, have to be manufactured in clean room environments in either a vacuum or inert gas.

In addition to semiconductor fabrication, the Philips researchers are also thinking of biological applications, such as pharmaceuticals, for the Planar Maglev. 'If you are in an environment where you want to have a clean system and parts have to move inside the system, then this would be of use,' Frissen said.