Investigation into Factors affecting Precision Positioning Instruments with a view to Standardisation of Specifications

This thesis investigates the requirements in their totality of precision positioning instruments with a view to suggesting standardised specification guidelines. Although concerns over inadequate vendor specifications were voiced as early as 2003, no national or international standards have yet been published that address this issue. To facilitate this investigation, a comprehensive design was undertaken of a three axis nanopositoning instrument. A state-of-the-art design was realised, based on an extensive review of the literature, while also incorporating particular novel features and procedures. Mechanically, the instrument designed in this work consists of a support frame that is kinematically mounted onto a base plate. A piezo driven monolithic flexure stage/force-frame and a metrology frame are both mounted isostatically onto this support frame. The movements of the stage are measured by a parallel metrology arrangement of three capacitance sensors that are calibrated in place by three Michelson interferometers. Use of commercially-available adjustable optical mounts provides adequate flexibility for set-up and experimentation. Specified set-up procedures, in combination with a specifically designed orientation jig ensure that all capacitance sensors and interferometers are properly aligned and that the measurement and movement axes coincide in accordance with the Abbe principle. A set of LabView programs, are used to control and monitor the stage position to calculate the coordinates of locations, to allow scanning over curved surfaces and tracking along curved paths, to calibrate the capacitance sensors, to compensate for positioning bias, arising from measured environmental disturbances and to correct for measurement non-linearity through fourth order error mapping. An iterative design process was employed, using an effective approach of parallel prototyping, calculation, Finite Element Analysis (FEA) and MathLab modelling. Propagation mechanisms of uncertainties associated with all identified error sources were studied, leading to the establishment of an uncertainty budget and an estimate of instrument positioning tolerance. An efficient and effective experimental regime was proposed, reflecting the numerous known factors and unknown interactions between factors that may be significant. This provided a means to validate the design, theory, and analysis and also to gain insight into the necessary experimental rigor. Although the instrument was not assembles or tested, the instrument comprehensive design and analysis provided an effective vehicle for attaining insight into the relative significance of multiple factors that affect the performance of precision instruments in general. Consequently, it was possible to suggest appropriate standardising guidelines for the specification of precision positioning instruments.