Friction drive for ultra-precision machine tools: interface compliance-based model
Bradley N. Damazo, Alex Slocum, A Gee
The roller/bar friction-drive is an example of a high-precision rectilinear actuator. The roller/bar friction drive offers control advantages of low backlash and dead-band due to elastic averaging within the Hertzian contact region. It also offers simplicity, both of initial design and extensibility to longer ranges (as high as of the order of meters) while incurring only marginal effort/cost in design and implementation. Furthermore, the roller/bar friction drive has not been employed extensively, this is probably due to uncertainty over issues of limitations on drive-force, transmission-gain and topology and cleanliness of the drive-bar/interface. To address uncertainties involved in the characteristics of such a drive, analysis was undertaken with the objective of providing design-tools for a new generation of machine tools. A model was developed to predict the behavior of the contact interface using Hertzian contact stress theory. Other goals of the study included methodologies for determining static and dynamic stiffness as a function of load and input dynamics as represented by the drive-force frequency. The model is described and comparisons with experimental results are made.