Title
Linear Electrostatic Actuators: Gap Maintenance Via Fluid Bearings

Abstract
In recent years, interest in linear electrostatic actuators has grown, in part due to their potential application to novel actuators, such as artificial muscle. One of the principle technical obstacles that has been encountered is "gap maintenance" : sustaining a long, narrow gap between rotor and stator in the presence of destabilizing electrostatic forces. A fluid bearing is introduced as an approach to gap maintenance. The bearing requires that the actuator comprise a step-shaped rotor and two parallel stators with a fluid-filled gap. A stability analysis of this motor is presented. The result of the analysis is a stability criterion dependent upon a single nondimensional term, called a "levitation number".

Due to fabrication difficulties, the step-shaped rotor may not be perfectly symmetrical, as the original analysis assumed. An analysis showing the effects of asymmetry is also presented.

Experiments have been performed to substantiate the analysis. The experimental study comprises a drag experiment and a stability experiment. The two experiments use a common apparatus, a "micro tow tank", which was developed for this study The experimental results support the trends predicted by the analysis, but also show quantitative differences.

Source: Robotics & Computer-Integrated Manufacturing, Vol. 10, No. 5, pp. 365-376, 1994

Title
An Experimental Investigation of Fluid Bearings for Linear Electrostatic Microactuator

Abstract
In recent years, interest in linear electrostatic actuators has grown, in part due to their potential application to novel actuators, such as artificial muscle. One of the principle technical obstacles that has been encountered is "gap maintenance" : sustaining a long, narrow gap between rotor and stator in the presence of destabilizing electrostatic forces. A fluid bearing is introduced as an approach to gap maintenance. The bearing requires that the actuator comprise a step-shaped rotor and two parallel stators with a fluid-filled gap. A stability analysis of this motor is presented. The result of the analysis is a stability criterion dependent upon a single nondimensional term, called a "levitation number".

Due to fabrication difficulties, the step-shaped rotor may not be perfectly symmetrical, as the original analysis assumed. An analysis showing the effects of asymmetry is also presented.

Experiments have been performed to substantiate the analysis. The experimental study comprises a drag experiment and a stability experiment. The two experiments use a common apparatus, a "micro tow tank", which was developed for this study The experimental results support the trends predicted by the analysis, but also show quantitative differences.

Source: Robotics & Computer-Integrated Manufacturing, Vol. 10, No. 5, pp. 365-376,1994