Andrew Crampton

Automatic planning for machine tool calibration: A case study

Machine tool owners require knowledge of their machines capabilities, and the emphasis increases with areas of high accuracy manufacturing. An aspect of a machines capability is its geometric accuracy. International Standards and best-practice guides are available to aid understanding of the required measurements and to advise on how to perform them. However, there is an absence of any intelligent method capable of optimising the duration of a calibration plan, minimising machine down-time. In this work, artificial intelligence in the form of automated planning is applied to the problem of machine tool pseudo-static geometric error calibration. No prior knowledge of Artificial Intelligence (AI) planning is required throughout this paper. The authors have written this paper for calibration engineers to see the benefits that automated planning can provide. Two models are proposed; the first produces a sequential calibration plan capable of finding the optimal calibration plan. The second model has the additional possibility of planning for concurrent measurements, adding the possibility of further reducing machine down-time. Both models take input regarding a machines configuration and available instrumentation. The efficacy of both models is evaluated by performing a case study of a five-axis gantry machine, whereby calibration plans are produced and compared against both an academic and industrial expert. From this, the effectiveness of this novel method for producing optimal calibration plan is evaluated, stimulating potential for future work.

Detecting and approximating fault lines from randomly scattered data

Abstract Discretely defined surfaces that exhibit vertical displacements across unknown fault lines can be difficult to approximate accurately unless a representation of the faults is known. Accurate representations of these faults enable the construction of constrained approximation models that can successfully overcome common problems such as over-smoothing. In this paper we review an existing method for detecting fault lines and present a new detection approach based on data triangulations and discrete Gaussian curvature (DGC). Furthermore, we show that if the fault line can be described non-parametrically, then accurate support vector machine (SVM) models can be constructed that are independent of the type of triangulation used in the detection algorithms. We shall also see that SVM models are particularly effective when the data produced by the detection algorithms are noisy. We compare the performances of the various new and established models.

Application of the pseudo-spectral method to 2D eigenvalue problems in elasticity

A pseudo-spectral approach to 2D vibrational problems arising in linear elasticity is considerede using differentiation matrices. The governing partial differential equations and associated boundary conditions on regular domains can be translated into matrix eigenvalue problems. Accurate results are obtained to the precision expected in spectral-type methods. However, we show that it is necessary to apply an additional “pole” condition to deal with ther=0 coordinate singularity arising in the case of a 2D disc.

Thermal Brake Judder Investigations Using a High Speed Dynamometer

This paper is concerned with addressing the problems experienced with the thermo-elastic behaviour of the disc - that of optimum heat dissipation, and equally important, even heating of the disc blade. The primary objective is to develop a more temperature-stable brake disc. The work presented approaches the problems of thermal judder through benchmarking the current situation. This is approached by modelling the current brake and its validation by means of vehicle and laboratory testing. The empirical work is centred on a bespoke high speed brake dynamometer which incorporates the full vehicle suspension for an accurate yet controlled simulation of brake and vehicle operating conditions. The dynamometer is housed in a purpose built laboratory with both CCTV and direct visual access. It is capable of dynamic measurement of DTV, caliper pressure fluctuations, disc surface temperature and vibration measurements at discrete points about the rig. This information is presented and supported by thermal imaging of the brake during a heavy brake application and subsequent thermal judder. The results also include surface scanning of the disc which is carried out at appropriate stages during testing to identify disc deformation including disc warping, “ripple” and the effects of “hot spotting”. Disc run-out measurements via non-contacting displacement transducers show the disc taking up varying orders of deformation ranging from first to third order during high speed testing. The state of cold deformation of the disc is also shown to vary with the disc returning to first or second order deformation upon cooling. Thermal images of the brake disc have shown vane patterns to show through to the disc surface identifying uneven heat distribution.

Laurent-Padé approximants to four kinds of Chebyshev polynomial expansions. Part I. Maehly type approximants

Laurent Padé-Chebyshev rational approximants,Am(z,z−1)/Bn(z, z−1), whose Laurent series expansions match that of a given functionf(z,z−1) up to as high a degree inz, z−1 as possible, were introduced for first kind Chebyshev polynomials by Clenshaw and Lord [2] and, using Laurent series, by Gragg and Johnson [4]. Further real and complex extensions, based mainly on trigonometric expansions, were discussed by Chisholm and Common [1]. All of these methods require knowledge of Chebyshev coefficients off up to degreem+n. Earlier, Maehly [5] introduced Padé approximants of the same form, which matched expansions betweenf(z,z−1)Bn(z, z−1)). The derivation was relatively simple but required knowledge of Chebyshev coefficients off up to degreem+2n. In the present paper, Padé-Chebyshev approximants are developed not only to first, but also to second, third and fourth kind Chebyshev polynomial series, based throughout on Laurent series representations of the Maehly type. The procedures for developing the Padé-Chebyshev coefficients are similar to that for a traditional Padé approximant based on power series [8] but with essential modifications. By equating series coefficients and combining equations appropriately, a linear system of equations is successfully developed into two sub-systems, one for determining the denominator coefficients only and one for explicitly defining the numerator coefficients in terms of the denominator coefficients. In all cases, a type (m, n) Padé-Chebyshev approximant, of degreem in the numerator andn in the denominator, is matched to the Chebyshev series up to terms of degreem+n, based on knowledge of the Chebyshev coefficients up to degreem+2n. Numerical tests are carried out on all four Padé-Chebyshev approximants, and results are outstanding, with some formidable improvements being achieved over partial sums of Laurent-Chebyshev series on a variety of functions. In part II of this paper [7] Padé-Chebyshev approximants of Clenshaw-Lord type will be developed for the four kinds of Chebyshev series and compared with those of the Maehly type.

ASCoL: A Tool for Improving Automatic Planning Domain Model Acquisition

Intelligent agents solving problems in the real world require domain models containing widespread knowledge of the world.

A Novel Software Tool for Analysing NT® File System Permissions

Administrating and monitoring New Technology File System (NTFS) permissions can be a cumbersome and convoluted task. In today’s data rich world there has never been a more important time to ensure that data is secured against unwanted access. This paper identifies the essential and fundamental requirements of access control, highlighting the main causes of their misconfiguration within the NTFS. In response, a number of features are identified and an efficient, informative and intuitive software-based solution is proposed for examining file system permissions. In the first year that the software has been made freely available it has been downloaded and installed by over four thousand users1.

A Study of Thermal Judder on a Laboratory Dynamometer

This paper considers a study of the thermo-elastic behaviour of a disc brake during heavy braking. The work is concerned with working towards developing a situation (or design) that provides uniform heating of the disc, and equally important, even dissipation of heat from the disc blade.

Passive sonar harmonic detection using feature extraction and clustering analysis

A current key problem in the development of passive sonar is the classification of data into its different noise sources. This paper focuses on solving the problem using feature extraction and clustering techniques. The methods described in this paper have been developed for data collected from a single sensor omni-directional passive sonar, with the input data being the extracted frequency tracks from a time-frequency lofagram. A single noise source will exhibit a number of frequency tracks within a lofagram, collectively these tracks form a harmonic set. The problem of harmonic detection is to associate the different components of each of the harmonic sets, or noise sources. Each of the frequency tracks within a harmonic set have a strong physical relationship defining their behaviour and properties. In solving the harmonic detection problem this physical relationship is exploited to associate frequency tracks with similar characteristics. In the solution to this problem each of the frequency tracks present have several key features measured. This allows the characteristics of each of the frequency tracks to be described in a small number of key, directly comparable, parameters. In this paper a small selection of features that may be used in the analysis of the frequency tracks are described. These features are then measured for a number of different data sets. With these sets of parameterised features it is possible to associate harmonically related frequency tracks by implementing clustering analysis, since the strong physical relationship of the features mean that related tracks will be clustered. In applying clustering, decisions need to be made into how many clusters there are in the data. The approach used in this paper uses hierarchical clustering. Hierarchical clustering begins by placing each data point into its own cluster. Two clusters are then merged based on a clustering criterion. At each step two clusters are joined until all the data is held within a single cluster. The progression of the cluster can be shown in a tree diagram, or dendrogram, which is then used to find the optimal level based on the ratio of the distribution of data within a cluster and the separation between different clusters.

Identification of irregularities and allocation suggestion of relative file system permissions

It is well established that file system permissions in large, multi-user environments can be audited to identify vulnerabilities with respect to what is regarded as standard practice. For example, identifying that a user has an elevated level of access to a system directory which is unnecessary and introduces a vulnerability. Similarly, the allocation of new file system permissions can be assigned following the same standard practices. On the contrary, and less well established, is the identification of potential vulnerabilities as well as the implementation of new permissions with respect to a systems current access control implementation. Such tasks are heavily reliant on expert interpretation. For example, the assigned relationship between users and groups, directories and their parents, and the allocation of permissions on file system resources all need to be carefully considered.This paper presents the novel use of statistical analysis to establish independence and homogeneity in allocated file system permissions. This independence can be interpreted as potential anomalies in a systems implementation of access control. The paper then presents the use of instance-based learning to suggest the allocation of new permissions conforming to a systems current implementation structure. Following this, both of the presented techniques are then included in a tool for interacting with Microsofts New Technology File System (NTFS) permissions. This involves experimental analysis on six different NTFS directory structures within different organisations. The effectiveness of the developed technique is then established through analysing the true positive and true negative values. The presented results demonstrate the potential of the proposed techniques for overcoming complexities with real-world file system administration.