Piezo Actuated Flexural Stage for Sub-Micron Precision Measurement

This thesis presents the design of a novel piezo-driven, sub-micron, comparative measurement stage for an automatic high-speed in-process industrial control system. The design features the use of precision solid flexures to transmit motion from a low voltage piezo stack to the measurement tip. This motion is used to determine height differences between a reference standard and a sample ball bearing. The key product diameter dimension is computed from this and is the basis of the feedback for automatic control of the production process. The aim of the automated measurement system is to precisely control the multiple continuous and repetitive metal reduction stages throughout a ball bearing manufacturing process. This thesis largely concentrates on the design, construction, control and testing of the piezo based measurement instrument, but also discusses the automatic sampling and delivery process, process control and the communication methods between the measurement system and the manufacturing process. Throughout the initial design stage of the measurement instrument, the focus is on the first two phases of the design: analytical design and finite element analysis (FEA). Design equations developed to predict the behaviour of the stages are used to compute the stiffness, displacement, stress and resonant frequency of the stage; modifications of dimensions enables the control and optimisation of the response of the measurement stage to achieve the desired outcome. Finite element analysis is then used to verify estimations obtained from the analytical design phase. Testing of the measurement instrument focuses on specifying the in-production system capabilities in terms of trueness and precision of measurements; the tests prove and validate the functionality of the instrument within the production facility