Precise positioning using the electrostatic glass motor

Precise positioning over a long stroke is required in various fields. Important advances in the field of electromagnetic motors, piezoelectric actuators and bearing technology allow nanometric and sub-arc-second resolution for linear or rotary actuators, respectively. Alas, these devices are rather complex, therefore expensive, and require sophisticated assembly techniques for the delicate components. Furthermore, their operation range is often limited to some fractions of a millimeter or a couple of degrees. For some applications the stiffness of the positioning stage is of minor importance. Compactness, cost-effectiveness (simple structure), ripple-free displacements and rotations and the absence of magnetic fields are the design objectives. Potential applications requiring such specifications are typically the positioning of optical elements such as mirrors and lenses and the handling of wafers during electron-beam operations. This thesis presents a novel approach to precise positioning, by exploiting the electrical properties of glasses. Charges are arranged via application of an electrostatic field. This polarization has an extraordinary long rise and decay time constant in the order or several tens of seconds and can be used to drive the glass. It was verified experimentally that what we call the "electrostatic glass motor" is operating at the speed of the applied field, although being a kind of induction motor. It features a perfect ripple-free movement over a very broad speed range. The precision of the movement depends on the resolution of the motor field generator and is entirely decoupled form mechanical precision aspects. In the present report, the principle of the electrostatic glass motor is presented. An analytical model, describing the forces and torques of such motors is proposed and verified experimentally. A rotary positioning device, allowing sub-arc second open loop resolution has been designed, realized and characterized. An open-loop resolution of 0.3 arc-seconds and a speed range ranging from 40 rpm down to 0.3 arc-sec/sec, and this over an unlimited displacement range, indicate the promising potential of the presented concept. Models and design rules for electrostatic glass positioning devices have been established and allow, within the scope of future works, the definitions of linear and multi-axis devices.

    Thèse École polytechnique fédérale de Lausanne EPFL, n° 2638 (2002)
    Section de microtechnique
    Faculté des sciences et techniques de l'ingénieur
    Institut de production et robotique
    Jury: Alain Cassat, Nico de Rooij, Toshiro Higuchi, Marcel Jufer, Alfred Rufer

    Public defense: 2002-9-27


    Record created on 2005-03-16, modified on 2016-08-08

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