Development of compliant mechanisms for real-time machine tool accuracy enhancement using dual-servo principle

Ph.DDOCTOR OF PHILOSOPH

Development and characterisation of traceable force measurement for nanotechnology

Traceable low force metrology should be an essential tool for nanotechnology. Traceable measurement of micro- and nanonewton forces would allow independent measurement and comparison on material properties, MEMS behaviour and nanodimensional measurement uncertainties. Yet the current traceability infrastructure in the UK is incomplete. This thesis describes the incremental development of the low force facility at the National Physical Laboratory (NPL). The novel contribution of this thesis has three components. First, specific modifications to the NPL Low Force Balance were undertaken. This involved developing novel or highly modified solutions to address key issues, as well as undertaking detailed comparions with external ans internal traceability references. Second, a triskelion force sensor flexure was proposed and mathematically modelled using both analytical and finite element techniques, and compared to experimentally measured spring constant estimates. The models compared satisfactorily, though fabrication defects in developed prototype artefacts limited the experimental confirmation of the models. Third, a piezoelectric sensor approach for quasistatic force measurement was proposed, experimentally evaluated and rejected. Finally, an improved design for a low force transfer artefact system is presented, harnessing the findings of the reported investigations. The proposed design combines proven strain-sensing technology with the advantageous triskelion flexure, incorporating an external stage and packaging aspects to achieve the requirements for a traceable low force transfer artefact

Long Stroke FTS

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (p. 375-384).In this thesis, I detail the design and control of a linear long stroke fast tool servo (FTS) with integral balance mass. The long stroke fast tool servo consists of an air bearing stage driven by a unique three phase oil cooled linear motor. The linear FTS has a travel range of 25 mm and is capable of 100 m/s² accelerations. The FTS is mounted to a T-base diamond turning machine (DTM). The FTS is attached to a hydrostatic bearing supported in-feed stage which is driven by a second linear motor. The in-feed stage is allowed to move in response to the FTS actuation forces and thus acts as an integral balance mass. We have developed a unique control structure to control the position of both the FTS and the reaction mass. The FTS controller employs a conventional lead-lag inner loop, an adaptive feedforward cancelation (AFC) outer loop, and command pre-shifting. For the FTS controller, the AFC resonators are placed in the forward path which creates infinite gain at the resonator frequency. The controller for the hydrostatic stage consists of a conventional lead-lag control inner-loop and a base acceleration feedback controller. The acceleration feedback controller consists of a high-pass filter, a double integrator for phase compensation, and an array of AFC resonators. For the base acceleration controller, the AFC resonators are placed in the feedback path and thus act as narrow-frequency notch filters. The notch filters allow the hydrostatic stage/balance mass to move freely at the commanded trajectory harmonics thus attenuating the forces introduced into the DTM. The AFC control loops are designed using a new loop shaping perspective for AFC control. In this thesis, we present two extensions to AFC control.(cont.) The first extension called Oscillator Amplitude Control (OAC) is used to approximate the convergence characteristics of an AFC controller. The second extension termed Amplitude Modulated Adaptive Feedforward Cancelation (AMAFC) is designed to exactly cancel disturbances with a time varying amplitude.by Marten F. Byl.Ph.D

Trapped between two beams – higher order laser mode manipulation for cell rotation

Laser light is an exceptionally powerful tool which has been utilised across all natural sciences and engineering. The very high intensities of extremely controllable light have allowed for a diverse range of studies to be carried out. When the intensities are large enough, the act of redirecting the light can create a force which can be sufficient to move small transparent objects. In biology one application of this phenomenon forms a tool for trapping and handling microscopic cellular samples in a contactless way using two laser beams. Such a laser-based tool is the Optical Stretcher, it was invented for measuring the mechanical properties of single cellular biological samples. The work presented in this thesis built upon the Optical Stretcher and to gain expertise in the field, several different biological samples were tested using it, gaining insights into the impact of particular proteins to cell mechanics. The Optical Stretcher, along with the vast majority of cell trapping experiments utilises a rotationally symmetric laser beam, which allows the cells to be moved and held in place, but their orientation is random and subject to large fluctuations. Controlled orientation of cellular specimen can lead to improved 3D imaging of the sample and is an important field of study. Previous work has shown that it is possible to orient a cell using a specially shaped laser beam, however the experimental setups were not well suited to use in biological labs. Henceforth, this thesis investigated and engineered a Dual Beam Laser Trapping device called the Higher Order Mode Cell Rotator, in short HOMCR, in order to build a powerful all-in-fibre tool for tomographic cell rotation. The major component giving rise to the HOMCR was a polarisation controlling device that alters the state of light by squeezing on the laser fibre and inducing local changes in the polarisation profile of the laser light. By characterising this device, its capability has been shown for the first time to manipulate the two lobe higher order modes travelling in optical fibres, leading to an all-in-fibre dynamic cell rotator which was used successfully to trap and orient individual cells and larger biological samples