Pose measurement and control response characterisation of flexure-based mechanisms for micro/nano positioning

Positioning and manipulation mechanisms capable of precise movement at the micro- and nanometre scales have been integral to many recent developments in nanotechnology. Key to the completion of such tasks is the ability to measure the movements performed, which allows the motion accuracy to be verified, and suitable adjustments to be provided for corrective actuation if necessary. As the breadth of applications has expanded, mechanisms accomplishing greater numbers of motion axes have been proposed. These include those which can perform rotational motions in addition to linear translations. Despite this, existing measurement techniques are not suitable for these mechanisms, as angular motion causes sensor misalignment, reducing the working range. This body of work describes the establishment of methodologies which enable the measurement of coupled linear and angular motions at the micro/nano scale. The research also aims to investigate the issues associated with such measurements, and characterise the interactions of the developed sensing methods with feedback control systems. In particular, emphasis was placed on the adaptation of laser interferometry based sensing and capacitive sensing, two established techniques for linear displacement metrology, for positioning operations employing such coupled motions. Three methodologies have been proposed for the minimisation of beam misalignment within laser based measurement systems. Two of these are established through the introduction of an additional actuation axis, whilst the other utilises a passive compliant structure to respond to angular actuation. The three methodologies possess differing performance in terms of their working range, speed of response, and magnitude of errors and uncertainties in output measurements. To facilitate these methods, three compliant mechanism designs have been introduced, which have been optimised and characterised through computational finite element modelling, before their performance was verified experimentally. The nonlinearity in two-plate capacitive sensor response due to tilt within planar three degrees of freedom systems has been modelled. The sensitivity of errors in pose estimation due to these effects has been analysed, which has led to the discovery of a sensor positioning strategy to minimise errors. A methodology to invert the nonlinear model has also been proposed, which permits pose estimations from sensor readings. Calibration of the model using either a single reference sensor or full reference data demonstrated improved performance over the nominal transformation.