Identifying and Characterizing Micro-machining Signatures on Freeform Surfaces Using Morphological Methods

Freeform surfaces are replacing traditional surfaces and have significantly reduced volume and weight and highly improved performance in modern complex optic systems, bio-systems and other disciplines [1]. These high-precision freeform components are enabled by state-of-the-art micro-machining technologies, compromising mechanical methods (diamond turning and polishing etc.), physical methods (laser beam and ion beam machining), and chemical methods (lithography, electro-chemical machining etc.). However, a fundamental pre-requisite to achieve the potential growth to these high-added value freeform components is to measure and characterize these components with the required accuracy such that their manufacturing quality can be controlled. The surface topography is a fingerprint of all process stages of the manufacturing process. Thus identifying and evaluating these topographical features on freeform surfaces left by production techniques are critically important in that they could present an indication of the manufacturing quality and offer feedback to the process control

A theoretical insight into morphological operations in surface measurement by introducing the slope transform

As one of the tools for surface analysis, morphological operations, although not as popular as linear convolution operations (e.g. the Gaussian filter), are really useful in mechanical surface reconstruction, surface filtration, functional simulation etc. By introducing the slope transform originally developed for signal processing into the field of surface metrology, an analytic capability is gained for morphological operations, paralleling that of the Fourier transform in the context of linear convolution. Using the slope transform, the tangential dilation is converted into the addition in the slope domain, just as by the Fourier transform, the convolution switches into the multiplication in the frequency domain. Under the theory of the slope transform, the slope and curvature changes of the structuring element to the operated surface can be obtained, offering a deeper understanding of morphological operations in surface measurement. The derivation of the analytical solutions to the tangential dilation of a sine wave and a disk by a disk are presented respectively. An example of the discretized tangential dilation of a sine wave by the disks with two different radii is illustrated to show the consistency and distinction between the tangential dilation and the classical dilation

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

A Key Point Method for Data Registration for MultiSensor Fusion

It has been recognized that multi-sensor data fusion can provide a more holistic, accurate and reliable information of the measured surface. Data registration, which is used to align data into one coordinate system, is a key step of data fusion. Widely used feature-based methods find correspondence between features, and then a geometrical transformation is determined to map the target data to the reference data. Reliable and accurate feature selection is thus very important for data registration. In this research, a reliable key point method called Scale Invariant Feature Method (SIFM) for data registration is investigated. By using this method, for each data, one can build a set of feature descriptors of the defined key points, which have the scale/shift/rotation invariant properties. Then the correspondence of two data and geometrical transformation can be achieved by finding the matching of two feature descriptors through closeness measurement. Initial tests on freeform and structured surfaces have proven the effectiveness and efficiency of the method

Dynamic Carrier and Power Amplifier Mapping for Energy Efficient Multi-Carrier Wireless Communications

The rapid increasing demand of wireless transmission has incurred mobile broadband to continuously evolve through multiple frequency bands, massive antennas and other multi-stream processing schemes. Together with the improved data transmission rate, the power consumption for multi-carrier transmission and processing is proportionally increasing, which contradicts with the energy efficiency requirements of 5G wireless systems. To meet this challenge, multi carrier power amplifier (MCPA) technology, e.g., to support multiple carriers through a single power amplifier, is widely deployed in practical. With massive carriers required for 5G communication and limited number of carriers supported per MCPA, a natural question to ask is how to map those carriers into multiple MCPAs and whether we shall dynamically adjust this mapping relation. In this paper, we have theoretically formulated the dynamic carrier and MCPA mapping problem to jointly optimize the traditional separated baseband and radio frequency processing. On top of that, we have also proposed a low complexity algorithm that can achieve most of the power saving with affordable computational time, if compared with the optimal exhaustive search based algorithm

A Preliminary Investigation on Surface Roughness Assessment of Complex Additive Manufactured Parts Scanned by X-ray Computed Tomography

The additive manufacturing (AM) technologies bring in a number of benefits over traditional subtractive manufacturing technologies. However as-built surface finish of AM produced components is often not satisfactory and usually needs further post-process. Surface roughness is vitally important to the product’s functional performance. However, the measurement and characterization of the complex functional AM surfaces is difficult due to their complicated shape or intricate internal geometries. XCT is current the only valid method that can measure complete internal and external geometry without constraints of traditional tactile and optical techniques. Nonetheless, XCT measurement posts two obstacles to standard roughness characterisation: the measured surface form and the non-uniform sampled measurement data structure. Aiming for a holistic and reliable roughness assessment, it is proposed to use the linear diffusion equation to achieve a Gaussian filtering effect on complex surfaces and to extend the roughness areal parameters on a triangular mesh

3-(4-Chloro­phen­yl)-1-(4-nitro­phen­yl)benzo[f]quinoline

In the title compound, C25H15ClN2O2, the pyridine ring is inclined at angles of 6.89 (7), 4.24 (9) and 66.98 (4)° with respect to the naphthalene, chloro­phenyl and nitro­phenyl rings, respectively. The two substituent aromatic rings make a dihedral angle of 71.1 (1)° with one another. C—H⋯π and π–π stacking are present in the crystal structure; the π–π stacking [centroid–centroid distance between the pyridyl rings of adjacent mol­ecules= 3.7838 (11) Å] links the mol­ecules into dimers, while the C—H⋯Cg type π–ring inter­actons link the mol­ecules into a chain structure along c

On characterising surface topography of metal powder bed fusion additive manufactured parts

Inherent to the somewhat uncontrolled nature of the additive process, the surfaces of metal powder bed fusion additively manufactured components tend to be very rough. Large isolated ‘bumps’, as one of the major defect features, are often present due to partially melted particles attached to the surface. An enhanced watershed segmentation method is proposed to separate these ‘bump’ features from the underlying surface texture such that the ‘bumps’ and underlying surface can be quantitatively analysed. The results show that the amplitude roughness parameters of the underlying surface are significantly less than the un-segmented surface and spatial roughness parameters differ between two surfaces. Characterising the extracted underlying surface and ‘bumps’ independently allows better correlation between surface measurements and additive system performance and hence aids in process optimization

Investigation of the compatibility of X-CT measurement data to surface topography analysis

In recent years X-CT metrology becomes more popular as a promising geometrical measurement technique. In comparison to traditional tactile and optical metrology techniques, X-CT has the unique advantage: it is a non-destructive method which can measure the complete internal and external geometry without constraint. Although X-CT has a limitation on the measurement of surface texture due to limited resolution, it is qualified for that of most of additive processed surfaces, which are featured by high roughness surface texture comprising a number of topographical features, such as bumps, step markings and surface pores. The X-CT generated data structures for the object surface, either point cloud or triangular mesh, differ from the grid structure of traditional methods. To enable X-CT data structures compatible with surface topography, two strategies are investigated: One is to interpolate scattered points into grid structure. The other one is to perform surface analysis on triangular mesh. The pros and cons of two different routes are discussed and compared. The application of the surface analysis techniques e.g. filtration, segmentation, parameterisation etc. following two different strategies are illustrated respectively