From planar surfaces based on lattices to freeform surfaces based on triangular meshes: an advanced extension of the areal motif method

Surfaces are shifting from traditional planar surfaces to freeform surfaces with significantly reduced volume and weight and highly improved performance. The areal motif method is used to analyse the topographical features on planar surfaces which are important to surface function. However the areal motif analysis cannot be directly applied to freeform surfaces, usually described by the triangular mesh data structure. To overcome this obstacle, a feasible strategy is proposed to extend the motif method. Morphological operations are employed to separate the “texture” and “form” surface. The watershed segmentation is then applied to the “texture” height surface in which the connection of each vertex is defined by the triangular mesh. The tiny motif due to the over-segmentation is combined by pruning the peaks and pits in the Pfaltz graph

Freeform texture representation and characterisation based on triangular mesh projection techniques

Texture characterisation for freeform non-Euclidean surfaces is becoming increasingly important due to the widespread of the use of such surfaces in different applications, e.g. the additive manufacturing. Four main steps are required to analyse and characterise those surfaces which include new surface representation, surface filtration and decomposition, texture representation methods and finally the calculation of the surface parameters. Recently, the representation, as well as the filtration and decomposition, of freeform surfaces have been investigated and some algorithms have been proposed. This paper, however, shed the light on how to represent the texture of freeform non-Euclidean surfaces before calculating the parameters. A novel model for freeform surface parameterisation is introduced; this new model proposes the use of a projection algorithm before the actual calculation of the parameters. Different projection algorithms have been adopted from the mesh projection techniques found in the field of computer graphics. The results of applying those algorithms to represent the texture of both simulated and bio-engineering surfaces are shown, also a comparison between those algorithms has been carried out. Furthermore, examples of calculating some of the surface parameters for freeform surfaces are give

The use of morphological methods for the extraction of topographical features from complex additive manufactured surfaces

Additive manufacturing (AM) processes have the potential to produce highly complex, customisable and multifunctional parts at lower material and energy costs. However the AM processes, particularly using metal powders, are far from perfection. The complex nature of powder AM processes tends to produce component surfaces that are very rough, showing significant defect features, including large isolated “bumps” due to partially melted particles attached to the surface, repeating steps generated by successively adding layers, surface pores and re-entrant features. These defect features are often superimposed on the complex form of the AM products. Following the existing evaluation methods for traditional machined surfaces and using extant standards, current industrial practices and research work cannot achieve credible results due to insufficient understanding of the non-Euclidean nature of AM surfaces. It is proposed in this work to use morphological methods to suppress the impact of surface form and extract surface topographical features. The morphological operations with circular structuring elements are applied to approximate the general form of the complex surface. Closing operation will suppress deep valleys and opening operation will remove sharp peaks. These operations or their combination effects will generate a smooth reference surface such that surface topographical features can be excluded. Instead of following the traditional route which takes the assumption that the surface is planar and normally subtracts the “form” from the primary surface to obtain the residual surface, topographical features are defined as the height function over the reference surface, i.e. each sample position is attached with a height value. The morphological watershed segmentation based on Maxwell’s theory and Pfaltz graph is then performed on the “heights” aiming to result the reasonable boundary of these topographical features. A primary example of using the proposed method is the extraction of bump features from the complex AM surface. Characterising the bump features can be useful for detecting process malfunction

Complex Structured Surface Characterisation by using PDE based Adaptive Nonlinear Diffusion Filter

Manufactured parts with complex structured surfaces have been widely used in automobile, bio-engineering, medical and consumer electronics etc. Compared with traditional ‘stochastic surface’, the complex structured surfaces have two significant characteristics: one is that they have complex base surface (reference surface/mean surface) which has complex shape, the other is that they have deterministic features with high aspect ratio on the base surface. The scale of complex structured surfaces ranges from the macro scale down to the nano scale. Specific examples include Flexible/wearable electronics, MEMS/NEMS devices, micro moulding, micro fluidic systems, defined geometry abrasives, and bio integration coatings. The ability to adequately characterise these complex structured surface geometry features is crucial in the optimisation and control of such functional device/components. From the function point of view, the accuracy of the geometrical features (line width, step height etc.) of these complex structured are generally more important than the roughness. It is therefore the basic requirements of the filtration techniques are that they should not only filter out the reference surface/mean surface and reduce the measurement noise, but do so without blurring or changing the location of the features. However, traditional single filtration techniques are lack of the ability to preserve the feature boundary with high accuracy. For example, when using the Gaussian filter for the MEMs surface, the boundary of the lines and steps are smoothed. As a consequence, it is very difficult to exactly evaluate the width of lines and heights of steps. In this paper, a Partial Differential Equation (PDE) based adaptive nonlinear diffusion filter combined with the robust filtration to process complex structured surface is proposed. In this method, robust filtration acting as pre-processing step to remove the complex reference surface and the diffusion filter is used to extract the structured features. The proposed diffusion filter is based on the PDE method and can be seen as a nonlinear heat equation, which describes the distribution of heat (or variation in temperature) in a given region over time. The diffusivity function based on the gradient of the surface can help to separate the internal region area of boundary area of the measured feature. In this way the diffusion process will take place mainly in the interior regions (line, step, etc.) of the surface, and it will not affect the region boundaries where the magnitude of gradient is large. The model proposed here has been coded with Matlab. Experimental work shows that the proposed filter can separate the geometrical feature (especially the line and step) from roughness and measurement noise and outliers with ideal edge preserving property

Development of Surface Characterisation Toolbox for Additive Manufactured Components: from Planar Layer Surfaces to Complex Functional Surfaces

The additive manufacturing (AM) technology possesses the potential to change the paradigm for manufacturing. To facilitate the successful uptake of AM technologies into a wider range of applications, AM needs metrological methods to measure, evaluate, validate techniques for both AM processes and AM parts. Two strategies are proposed for the optimisation of AM processes and the evaluation of the functional performance of AM products. A specific procedure is developed for the characterisation of AM layer surfaces with an aim to reflect the unique characterisation of AM process. For complex functional AM surfaces which need the employment of X-ray computed tomography (XCT) for their measurement, the surface characterisation techniques, including filtration, are extended so that they can cope with the complex surface shapes and the triangular mesh data

Use of Morphological Method to Investigate the Influence of Surface Texture on Dimensional Measurement of Additively Manufactured Parts

The high level of surface roughness of additively manufactured (AM) parts post challenges to the applicability of different dimensional measurement techniques, including tactile, optical and XCT. Tactile measurement is traditionally considered to have the best accuracy and traceability. However, tactile measurement can be significantly affected by the mechanical filtering effect. This work sets out to investigate the influence of the mechanical filtering effect of tactile measurement on AM parts. Both experiential and simulation work are unitised to reveal this effect. Particularly the numerical simulation based on the morphological method allows the single influence factor, i.e., the tip diameter to be investigated. The maximum measurement errors caused by the stylus tip mechanical effect are determined by the convex hull points of the measurement profile, which is equivalent to using an infinitely large stylus tip. The CMM and XCT results of measuring the AM cylinder diameters are compared, along with the application of morphological method to “compensate” the mechanical filtering effect of the stylus tip

A Novel Surface Characterisation Strategy for the X-ray Computed Tomography Measurement of Complex Additively Manufactured Parts

X-ray Computed Tomography (XCT) has the advantage over the traditional tactile and optical measurement systems in that it is the only valid non-destructive method to measure both external and internal geometries of complex functional parts, e.g. additively manufactured (AM) parts, whose intricate shape does not allow line-of-sight. However the XCT measurement posts many challenges to surface texture assessment of AM parts. One of the big issues is that XCT generated measurement data structures, i.e. point cloud and triangular mesh, are not straightforward compatible with the standard surface texture characterisation, which requires uniform sampled grid structure and also requires measured surface to be basically planar. This work proposes a novel strategy that the surface filtration and roughness parameterisation techniques can deal with triangular mesh. Based on the link between the Gaussian cutoff wavelength and the diffusion time, the proposed linear diffusion equation can achieve a Gaussian filtering effect on complex surfaces. Also the areal surface texture height parameters are extended to triangular mesh. With these two enhancements, it contributes to the solution to using XCT for a holistic and reliable measurement of surface texture of complex AM products

In situ PCR for detection and differentiation of infectious bursal disease virus strains in chickens

An In situ PCR method for detection and differentiation of infectious bursal disease virus (IBDV) strains is described. In one study, 15 specific pathogen free (SPF) 14 day old chickens were infected orally with very virulent (vv) IBDV strain with a titre of 107.5 EID50/0.1 mL. Six non-infected chickens were used as controls. Chickens were sacrificed at various intervals and tissue samples taken for histological examination. Immunoperoxidase staining (IPS) was done, and an In situ PCR was developed using a specific probe for IBDV’s VP1 gene. The In situ PCR was significantly (p < 0.05) more sensitive than IPS. In another study todifferentiate strains by In situ PCR, ten, 42 day old SPF chickens were infected with virulent (104.83 EID50/0.1 mL) or classical (ca) NDV strains (103.0 EID50/0.1 mL) with 5 non-infected controls. Tissue samples infected with virulent, classic and controls tested with a virulent specific probe were positive only in tissues infected by the virulent strain whereas classical strain probe were positive only to tissue infected by classical strain. These results suggest that our In situ PCR differentiated virulent from classical NDV strains

Atypical actinobacillosis in bulls in Argentina: granulomatous dermatitis and lymphadenitis

Actinobacillosis is a common cause of sporadic infection in cattle. It was mostly characterized as a pyogranulomatous inflammation of the tongue, but also soft tissues as lymph nodes, other digestive tract localization and skin. The aim of this study was to describe an episode of granulomatous dermatitis and lymphadenitis affecting a bull herd in Argentina during 2010. Actinobacillus lignieresii was isolated from samples collected from one of the affected bulls, and characteristic lesions were observed. Lesions other than 'wooden tongue' are usually uncommon; however, actinobacillosis should be included as a differential diagnosis for cutaneous diseases