Development and characterisation of next generation stylus for micro coordinate measuring machine.

Products are routinely being manufactured with features having dimensions below 50 µm, with consequent of increasing demand for micro-coordinate measuring machines (micro-CMMs) that have stylus systems with tip diameters of 10 µm or less. However, current commercially available micro-CMMs are unable to fulfil this demand reliably. Therefore, with this in mind, the development of a stylus system with a significantly smaller dimension and the potential to fulfil this demand is reported. After an initial review of the current state of the art and the projected needs, this thesis examine in detail the design considerations and analytical modelling of stylus systems. A key factors affecting styli as their dimension is reduced down to the micrometre level are identified and discussed. Based on five important groups of theses influence factors, a new comprehensive set of design rules and analytical models is constructed and the relationship among these rules observed. Maintaining a stylus contact force that reliably detect the measured surface at reasonable operation speeds while having a sufficiently slender and strong stylus shaft become an issue of particular importance. Experimental investigation of a set of prototype micro-styli is used both to demonstrate the effectiveness of the design rules and to compare different manufacturing methods that have been proposed elsewhere. The model underlying the design rules are shown to be generally consistent within existing uncertainty, except for anomalies with one of manufacturing process which is a combination process of Wire Electro-Discharge Grinding (WEDG) and micro-electrochemical (ECM) process for manufacturing of stylus shaft. The surface quality of spherical form deviation of stylus tip is also a major factor in the uncertainty in the scale of measurement. Therefore, the final part of this work develops and demonstrate a new measurement technique for spherical form error of the micro-styli with tip diameter below than 10 µm. This methods employed a coherence scanning interferometry, together with new rotational referencing manipulation system and new technique of data fusion. Practical testing was conducted to 300 µm diameter sphere, with a typical uncertainty below 30 nm being obtained