The development of novel interchangeable pistons for pressure performance optimization in a gas-operated dead weight pressure balance

The texture of surfaces within a piston–cylinder assembly (PCA) can influence the pressure performance of gas-operated dead weight pressure balances (DWPBs). In order to systematically study this response, it has been necessary to design, develop and manufacture uniquely interchangeable 35mm diameter PCAs for use in a novel hybrid gas-operated DWPB with high mechanical, thermal and pressure stability. This work reports the development of the PCAs and the validation of the DWPB design, allowing the performance characteristics of the interchangeable PCAs to be understood, in terms of variations of effective area calculations. This is achieved by investigating the pressure responses of the DWPBs by changing the speed and direction of rotation. The results demonstrate the stability of the gas-operated DWPB design when used in gauge mode, and importantly allow the verification of the performance of the interchangeable PCAs

An intelligent and confident system for automatic surface defect quantification in 3D

Automatic surface defect inspection within mass production of high-precision components is growing in demand and requires better measurement and automated analysis systems. Many manufacturing industries may reject manufactured parts that exhibit even minor defects, because a defect might result in an operational failure at a later stage. Defect quantification (depth, area and volume) is a key element in quality assurance in order to determine the pass or failure criterion of manufactured parts. Existing human visual analysis of surface defects is qualitative and subjective to varying interpretation. Non-contact and three dimensional (3D) analyses should provide a robust and systematic quantitative approach for defect analysis. Various 3D measuring instruments generate point cloud data as an output, although they work on different physical principles. Instrument’s native software processing of point cloud data is often subject to issues of repeatability and may be non-traceable causing significant concern with data confidence. This work reports the development of novel traceable surface defect artefacts produced using the Rockwell hardness test equipment on flat metal plate, and the development of a novel, traceable, repeatable, mathematical solution for automatic defect detection and quantification in 3D. Moreover, in order to build-up the confidence in automatic defect analysis system and generated data, mathematical simulated defect artefacts (soft-artefact) have been created. This is then extended to a surface defect on a piston crown that is measured and quantified using a parallel optical coherence tomography instrument integrated with 6 axis robot. The results show that surface defect quantification using implemented solution is efficient, robust and more repeatable than current alternative approaches

Development of speckle shearing interferometer error analysis as an aperture function of wavefront divergence

Increasing the confidence in whole-field speckle-based optical metrology transducers requires a detailed understanding of the error sources of respective instruments. The analysis of error contributions to the optical phase output of a Michelson-based speckle shearing interferometer have been modelled. Specific attention has been paid to the effect of the aperture at the image plane, with respect to collimated and non-collimated object illumination. This modelling presents an advance on a previous modelled analytical relationship, which includes partial displacement derivative terms and components as a function of illumination geometries and, importantly, aperture effects. The work has identified a phase error contribution due to the aperture function of between 0.15% and 1.48%, dependent on the object distance, when considering a planar object undergoing predominantly surface to normal deformation

Focus variation microscope: linear theory and surface tilt sensitivity

In a recent publication [3rd International Conference on Surface Metrology, Annecy, France, 2012, p. 1] it was shown that surface roughness measurements made using a focus variation microscope (FVM) are influenced by surface tilt. The effect appears to be most significant when the surface has microscale roughness (Ra ≈ 50 nm) that is sufficient to provide a diffusely scattered signal that is comparable in magnitude to the specular component. This paper explores, from first principles, image formation using the focus variation method. With the assumption of incoherent scattering, it is shown that the process is linear and the 3D point spread characteristics and transfer characteristics of the instrument are well defined. It is argued that, for the case of micro-scale roughness and through the objective illumination, the assumption of incoherence cannot be justified and more rigorous analysis is required. Using a foil model of surface scattering the images that are recorded by a FVM have been calculated. It is shown that for the case of through the objective illumination at small tilt angles, the signal quality is degraded in a systematic manner. This is attributed to the mixing of specular and diffusely reflected components and leads to an asymmetry in the k-space representation of the output signals. It is shown that by using extra-aperture illumination or at tilt angles greater than the acceptance angle of aperture (such that the specular component is lost), the incoherent assumption can be justified once again. The work highlights the importance of using ring-light illumination and/or polarizing optics, which are often available as options on commercial instruments, as a means to mitigate or prevent these effects

Nonperturbing measurements of spatially distributed underwater acoustic fields using a scanning laser Doppler vibrometer

Localized changes in the density of water induced by the presence of an acoustic field cause perturbations in the localized refractive index. This relationship has given rise to a number of nonperturbing optical metrology techniques for recording measurement parameters from underwater acoustic fields. A method that has been recently developed involves the use of a Laser Doppler Vibrometer (LDV) targeted at a fixed, nonvibrating, plate through an underwater acoustic field. Measurements of the rate of change of optical pathlength along a line section enable the identification of the temporal and frequency characteristics of the acoustic wave front. This approach has been extended through the use of a scanning LDV, which facilitates the measurement of a range of spatially distributed parameters. A mathematical model is presented that relates the distribution of pressure amplitude and phase in a planar wave front with the rate of change of optical pathlength measured by the LDV along a specifically orientated laser line section. Measurements of a 1 MHz acoustic tone burst generated by a focused transducer are described and the results presented. Graphical depictions of the acoustic power and phase distribution recorded by the LDV are shown, together with images representing time history during the acoustic wave propagation

Deformation analysis of aircraft wheels using a speckle shearing interferometer

Speckle shearing interferometry has developed over the last three decades and is used as a non-destructive analysis tool for aerospace engineering.The primary role of the technique has traditionally been for the examination of defects in fibre composite structural materials, but more recent attention has considered strain and displacement measurement.Furtherm ore, aerospace regulatory bodies such as the UK Civil Aviation Authority are demanding better understanding and traceability of the technique. The novel work reported here has investigated the use of a Michelson-based speckle shearing interferometer for the analysis of compression-loaded aircraft wheels and tyres.Whole- field deformation data have been obtained for repeated compression loading of a BAe146 main wheel, providing displacement derivative and displacement data.The quality of the measurement technique has been ascertained through the analysis of the repeatability and reproducibility data, with correlating data being produced using contact displacement transducers

Robust intelligent metrology

Robust Intelligent Metrology considers how to maintain, develop, streamline and apply core metrological principles within rapidly evolving measurement scenarios and environments. The aim is to deliver metrology laboratory quality measurements and data confidence, but with equipment integrated into operating High Value Manufacturing cells. Key challenges are to understand; transducer / surface interactions, data processing and integrity, in-cell calibration / traceability. The end result is to provide engineers with quicker, better data

A meta-analysis of biological variation in blood-based therapy as a precursor to bio-manufacturing

Currently cellular therapies, such as hematopoietic stem cell transplantation (HSCT), are produced at a small scale on a case-by-case basis, usually in a clinical or near-clinical setting. Meeting the demand for future cellular therapies will require a robust and scalable manufacturing process that is either designed around or controls the variation associated with biological starting materials. Understanding variation requires both a measure of the allowable variation (that does not negatively affect patient outcome) and the achievable variation (with current technology). The prevalence of HSCT makes it an ideal case study to prepare for more complex biological manufacturing with more challenging regulatory classifications. A systematic meta-analysis of the medical literature surrounding HSCT has been completed of which the key outcomes are the following: (i) the range of transplanted CD34+ cells/kg can be up to six orders of magnitude around the median for allogeneic procedures and four orders of magnitude for autologous procedures, (ii) there is no improvement in variation encountered over a period of 30 years and (iii) as study size increases, the amount of variation encountered also increases. A more detailed, stratified source from a controlled single-site clinical center is required to further define a control strategy for the manufacture of biologics

Visualising scattering underwater acoustic fields using laser Doppler vibrometry

Analysis of acoustic wavefronts are important for a number of engineering design, communication and healthrelated reasons, and it is very desirable to be able to understand the interaction of acoustic fields and energy with obstructions. Experimental analysis of acoustic wavefronts in water has traditionally been completed with single or arrays of piezoelectric or magnetostrictive transducers or hydrophones. These have been very successful, but the presence of transducers within the acoustic region can in some circumstances be undesirable. The research reported here, describes the novel application of scanning laser Doppler vibrometry to the analysis of underwater acoustic wavefronts, impinging on circular cross section obstructions. The results demonstrate that this new non-invasive acoustics measurement technique can successfully visualise and measure reflected acoustic fields, diffraction and refraction effects

Quantification of biological variation in blood-based therapy – a summary of a meta-analysis to inform manufacturing in the clinic

Background and Objectives Biological raw materials, the basis for cellular therapies such as stem cells, have a significantly greater degree of complexity than their traditional pharmaceutical counterparts. This can be attributed to the inherent variation of its source – human beings. Currently, cell therapies are made in small, ad hoc batches, but larger scale production is a prerequisite to meeting future demand and will require a quality-by-design approach to manufacturing that will be designed around, or be robust to this variation. Quantification of variation will require understanding of the current baseline and stratification of its sources. Materials and Methods Haematopoietic stem cell therapy was chosen as a case study to explore this variation, and a PRISMA-guided (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) systematic meta-analysis was carried out for a number of predetermined cell measurements. Results From this data set, it appears that the extent of variation in therapeutic dose (in terms of transplanted total nucleated cells and CD34+ cells per kilogram) for HSCT is between one and four orders of magnitude of the median. Conclusions This is tolerated under the practice of medicine but would be unmanageable from a biomanufacturing perspective and raises concerns about comparable levels of efficacy and treatment. A number of sources that will contribute towards this variation are also reported, as is the direction of travel for 4 greater clarity of the scale of this challenge