This paper reports the successful electrostatic suspension of dielectric materials. In order to implement a stable suspension, the electrostatic forces exerted on a dielectric are actively controlled on the basis of the measured suspension gap lengths. The principle of electrostatic force generation for dielectrics is different from that for conductors. By utilizing a stator electrode pattern containing many boundaries over which potential differences exist, the suspension characteristics, such as dynamic stability, suspension initiation time and stiffness of lateral motion are greatly improved. The dynamic model of the suspension system and the influence of the resistivity of a dielectric on the closed-loop stability are described, followed by the experimental apparatus and stabilizing controller. As dielectric objects, glass plates have been suspended electrostatically at a gap length of about 0.3 mm. Apart from the structure of the stator electrode, the suspension initiation time is also influenced by air humidity, glass type, supplied voltage and gap length, which have been experimentally explored. Experimental results on the lateral dynamic characteristics are also presented.

Electrostatic suspension of dielectrics

Theoretical model and design of electroadhesive pad with interdigitated electrodes

A system level model of a force balance accelerometer in which the proof mass is levitated with electrostatic forces is presented. The position of the proof mass is detected capacitively and controlled electrostatically. The mathematical modelling of the system is described. In particular, equations for the capacitances and electrostatic forces are derived and verified by comparison with a finite element model. They are then implemented in a Simulink system level model of the accelerometer.

Modelling of an accelerometer based on a levitated proof mass

A triaxial accelerometer is presented which employs as its proof mass a mechanically free micromachined disc that is electrostatically levitated. Air damping plays a critical role in the operation of the accelerometer, providing stability to an inherently unstable system. Systems that operate beyond the cut-off frequency, however, suffer reduced gain due to the spring component of the squeeze film damping, resulting in decreased sensitivity. A finite-element model for extracting squeeze film damping coefficients for transverse and rotational motion of the disc, via an analogy to heat transfer theory, is presented. The use of the analogy enables a reduction of the problem from a complex three-dimensional computational fluid dynamics domain to a two-dimensional heat transfer domain. The model is used to evaluate the effect of including damping holes in the proof mass. The high-frequency oscillation and physical size of the proof mass dictate that the accelerometer is operated well beyond its cut-off frequency and so the inclusion of damping holes in the proof mass can result in an increase rather than decrease in the damping coefficient. The resulting system-level model, implemented in Matlab/Simulink, is then used to evaluate the effect of the squeeze film damping on the device performance.

https://iopscience.iop.org/article/10.1088/0960-1317/15/5/001/pdf

Modelling squeeze film effects in a MEMS accelerometer with a levitated proof mass

Techniques are developed for the suspension of flexible elements for non-contact handling in manufacturing processes. In support of this work, a magnetic suspension testbed is constructed, using eight actuators and eight sensors to control the flexible modes of a 3-m-long, 6.35-mm-diameter steel tube with varying boundary conditions. A novel approach has been developed for the control of such noncontact suspensions through sensor averaging and actuator averaging. The difficult stability and robustness problems imposed by the flexible dynamics of the workpiece can be overcome by taking a properly weighted average of the outputs of a distributed array of motion sensors (sensor averaging), and/or by applying a properly weighted distributed array of actuating forces (actuator averaging) to the workpiece. These approaches generate spatial filters on a broad range of undesired resonance modes without adversely affecting the phase, and the resulting modal gains are independent of the specific boundary conditions and longitudinal dimensions of the workpiece. The averaging arrangement can also eliminate possible non-collocation problems. These approaches are thus generally applicable to a wide range of structural control problems. In this paper, the averaging methods applied to beams are presented in detail. The experimental results with a beam suspension confirm the value of the averaging techniques, and suggest the wide future application of these ideas in industrial processes that require noncontact handling of workpieces.

Vibration control of flexible beams using sensor averaging and actuator averaging methods

A new type of contact-less wafer manipulator, featuring "direct electrostatic levitation and propulsion of silicon wafer" (DELP-SW), has been successfully developed. The novel aspect of this manipulator is that a silicon wafer can be directly levitated and driven via electrostatic forces. In this paper, a brief review of basic principles is presented. This is followed by a description of the structure of a prototype DELP-SW mechanism, including electrode design, position feedback control method, driving principle and the operational procedure. Experimental results which demonstrate completely contact-less transportation of an 8-inch silicon wafer are also presented.

Direct electrostatic levitation and propulsion of silicon wafer

This paper focuses in particular on the lateral electrostatic force characteristic of an electrostatic levitation system as part of the overall system dynamics. The lateral force exerted on a levitated aluminum disk, used in hard disk applications, originating from a relative translation of the disk with respect to the stator electrode, is analytically studied. Experimental results are presented in order to assess and verify the validity of the analytical solution for the electrostatic forces.

Ju Jin

Papers

Direct electrostatic levitation and propulsion of silicon wafer

Electrostatic force analysis of electrostatic levitation system