Design and analysis of micropositioning systems for precision machining

In precision machining, a high-speed workpiece table motion is typically involved. In order to achieve active control for improved machining accuracy and efficiency, the control commands will include a substantial amount of high frequency signals. The high frequency command signals may not be sufficiently implemented by the single actuating unit that is the wheel infeed system, since this type of system typically has a small frequency bandwidth for dynamic operations. To solve this problem, an additional actuating unit will be required to support the workpiece in order to implement small but fast control actions. The actuating unit and the wheel infeed unit will work together under a composite control scheme to combine the advantages of both units such that fast active control and large driving force can be obtained at the same time. In order to realize the actuating unit to implement positioning functions that are fast but at the micrometer level, piezoelectric translators are typically used. Several single-axis precision positioning table systems utilizing the translators have been developed. One of the micropositioning tables has shown to have a resolution better than 20nm. When implementing a 43.587μm step motion, the acceleration could be up to 33.51g. The dynamic models of this table for the responses of step or sinusoidal command signals have been investigated. Also, the theoretical results based on the models for the step signals and the corresponding experimental results have been compared. Both results matched with each other except when large step commands were applied. The mismatch is due to detachment between the piezoelectric translator and the moving part that is supposed to be in contact with the translator. A detachment model has been utilized to explain this phenomenon. Also, the other factors that affect the performance of the positioning systems such as the deformation of the table, and the natural frequencies of the table have been investigated. In order to achieve precision machining, the adverse effects of these factors should be reduced