Modeling and compensation of lubrication effects in precision positioning machines

Positioning with macro scale systems is a significant engineering challenge. Friction is one of the major impediments to rapid precision positioning with macroscale systems. Linear motor stages and hard disk drive actuators represent extremes on the spectrum of speed, size, and travel distance for precision positioning systems. A linear stage moves a mass of several kilograms many centimeters on recirculating bearing trucks and linear rails, but new positions are acquired only a few times per second at most. In contrast, small and extremely light hard disk drive actuators may make several hundred rotational movements in a single second, and these movements require less then one quarter of a rotation of their rotary ball bearings.;Models and compensation methods based on lubrication physics have the potential to significantly improve performance of positioning systems, and to provide guidance in the design of better bearings for these systems. Despite this potential, tribological theories are not easily applied to model friction in complex positioning systems because tribological theories generally concentrate on accurate modeling of isolated phenomena. The servo engineer is challenged to apply tribological theories characterizing lubrication phenomena and surface interactions to the complex movements of real world precision positioning systems.;This thesis presents feedforward and feedback compensators for friction in these two unique precision positioning systems by combining multiple tribological models of distinct lubricating phenomena. This thesis also presents measurement results needed to identify surface and lubricant interactions, velocity relationships, and lubricant supply. Measurements from the linear stage illustrate two distinct friction regimes in the frequency response plots which depend on input amplitude. The frequency responses and the friction model lead naturally to a design for the feedback controller of the linear stage that employs the complex lag compensator. A derivation of the Dahl model Fourier components from steady state excitation provide modeling insight for future work in the frequency response domain. Measurements of the static friction in the hard disk drive actuator at the termination of a movement are used to create a new friction model based on lubrication physics for feedforward compensation.