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Title: Modelling, implementation and validation of polymeric planar spring mechanisms
Author: Rashid, Haroon Ur
ISNI:       0000 0004 5357 4737
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2014
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This thesis explores, by means of modelling and physical experiments, variant designs for triskelion devices, a type of planar exure mechanism widely considered for use in micro-probe suspensions and, more recently, force transfer artefacts. The accurate measurement of low force is challenging problem that has wide range of force related applications. A lot of attention has been paid worldwide during last decade within and beyond the National Metrology Institutes (NMIs) to measuring low forces. A major concern is how to provide traceability for micro- to nanonewton level forces that is highly reliable and could be used for real machine calibration. The current consensus is that this process requires special secondary standards and novel artefacts to transfer such standards to working systems. The latter provides the motivation for this thesis, which makes the following main contributions. A published linear elastic model has been considerably enhanced and generalised to enable the study of a wide range of variants from the one widely-used design of triskelion device. Triskelion and tetraskelion software programs implement this new model, providing a new tool for computing forces, moments, stress, strain, axial stiffness and torsional stiffness for devices before their fabrication. It has been used to explore widely the sensitivity of the devices to changes in design parameters such as suspension leg geometry and 'elbow' angles. To provide essential physical verification of the practicality of a linear model, a low-cost technique has been developed for making small triskelion test samples. This was used with a new test-rig configuration to measure polymeric triskelion devices under loads in the 1 mN to 1N region with deflections up to around 1 mm. Experiments have determined the onset and characteristics of non-linear spring behaviour in typical devices and have verified the general predictions from the new model. The overall conclusion to be drawn is that at large de ection the spring characteristics follow a cubic law (stiffening). However, during the initial stages of the de ection the linear term dominates over a range that is quite sufficiently wide for practical use as force test artefacts. The polymeric test devices performed well, behaving reasonably closely to predicted values in the linear (model) region. The promising results indicate its prospects for use in low force technology in the future.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering