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# Large-Scale Linearization Circuit for Electrostatic Motors

IP.com Disclosure Number: IPCOM000113974D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 48K

IBM

## Related People

Crawforth, L: AUTHOR [+3]

## Abstract

Electrostatic motors are inherently nonlinear devices, making them difficult to control in applications where accurate positioning and high bandwidth are required. These devices can be linearized through the use of a circuit that applies a bias voltage to two opposing phases of the motor, while using a control voltage which is linearly related to a desired force. The gain of the system is linearly proportional to the bias voltage, and the circuit can be used for both open and closed loop control using either an analog or a digital controller.

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Large-Scale Linearization Circuit for Electrostatic Motors

Electrostatic motors are inherently nonlinear devices, making
them difficult to control in applications where accurate positioning
and high bandwidth are required.  These devices can be linearized
through the use of a circuit that applies a bias voltage to two
opposing phases of the motor, while using a control voltage which is
linearly related to a desired force.  The gain of the system is
linearly proportional to the bias voltage, and the circuit can be
used for both open and closed loop control using either an analog or
a digital controller.

If the force or moment due to a single stator/rotor pair in an
electrostatic motor is given by F, then
F =  <1 over 2> << d C > over < d u >>
% V sup 2
eqno (eqnref)
where C is the motor's capacitance, u is the direction of motion, and
V is the applied voltage.  If the motor's capacitance changes due to
the area between plates changing rather than from modifications in
the gap, the derivative term will be a constant.  The quadratic
dependence of the force on the applied voltage results in additional
complexity of the control system if the motor is to be used for fine
position control.  This invention presents a method for eliminating
the quadratic dependence and turning it into a linear one.

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