Clive Butler

An investigation into theperformance of probes on coordinate measuring machines

Abstract Coordinate measuring machines (CMMs) have become very widely used in recent years because of their ability to measure most or all of the individual geometrical features on complex engineering components. Compared with traditional methods, which normally employ a variety of separate instruments, CMMs are fast in operation and are adequately accurate for many applications. However, accuracy limitations often inhibit their use for high precision metrology. Accuracy is limited by such factors as straightness and orthogonality of the CMM movements; established techniques exist for determining these factors. In many cases, the errors introduced by the probes are very significant and often exceed the errors from other sources. This paper describes an investigation into the nature of probe errors, the factors that influence their performance and proposes a method of verifying the probe performance. Results from a number of probes used in different modes are presented. The application of the work to linking CAD systems to CMMs is briefly described.

A fiber optic sensor for the measurement of surface roughness and displacement using artificial neural networks

This paper presents a fibre optic sensor system. Artificial neural networks using fast backpropagation are employed for the data processing. The use of the neural networks makes it possible for the sensor to be used both for surface roughness and displacement measurement at the same time. The results indicate 100% correct surface classification for ten different surfaces (different materials, different manufacturing methods and different surface roughnesses) and displacement errors less then /spl plusmn/5 /spl mu/m. The actual accuracy was restricted by the calibration machine. A measuring range of /spl plusmn/0.8 mm for the displacement measurement were achieved.

An object-oriented model of measurement systems

This paper presents a general object-oriented model for measurement systems. The limitations of the conventional function-oriented models are examined in the light of the generalised concept of measurement and its theoretical framework proposed previously by the author. The proposed model identifies five classes of objects, i.e. measured object, measuring instrument, reference standard, human observer and operating environment. Each of them is characterised by its own attributes and operations or functions at three levels, i.e. internal, operational and environmental. The interactions between them are also modelled including the coupling between the measured object and the measuring instrument, the human-instrument interface, the calibration and the interference. Together with the generalised concept of measurement and its philosophical framework, it serves as a practical tool for description, analysis and design, and, in particular, for computer aided analysis and design of a measuring system. It will find applications in instrumentation engineering and measurement education and research.

Quality Assurance for Distance Learning: A Case Study at Brunel University.

Brunel University currently has four distance learning MSc courses, with over 500 students registered, and one undergraduate distance learning course. Some have been running for over five years, and well-established practices have been developed and provide a basis of support for the university. Quality assurance in the university has always been considered in three, equally important, ways: the curriculum and its assessment; the handling of coursework and assignments; and the liaison with students. The lesson we have learned is that a distance learning programme must be based on an existing full-time MSc programme, which is the gold standard for curriculum and its assessment, and where possible, common examinations and assessment be used. This can be further assured by scrutinisation by the associated research council. This is going to become ever more important with the increasing scrutiny by overseas governments on the academic quality of distance learning courses, which seek assurance on the comparability and quality of degrees. Quality assurance for the handling of coursework and assignments must be secure and demands a high overhead of paperwork. Detailed feedback to students on their assignments is essential, but this can, at the same time, form a quality assurance check for later progression decisions. We also copy and retain approximately 10% of the assignments for the same purpose. Rapid turnaround is essential if feedback is to be timely and therefore useful, and quality checks on processing time should be standard. Quality assurance for the procedures for liaison with distance learning students are somewhat harder to measure quantitatively. The mark of good distance learning must be its tutorial support. This demands good communications. Our own course, entitled Data Communications Systems, benefits from the high proportion of use of electronic communications, namely email, which allows fast turnaround of questions, yet is not intrusive. However, it is deemed essential that hard copy of all such correspondence is kept. Migration to other Internet support services, such as the World Wide Web, videoconferencing and groupware, is inevitable. [ABSTRACT FROM AUTHOR]

Dynamic error characteristics of touch trigger probes fitted to coordinate measuring machines

This paper discusses the dynamic error characteristics of touch trigger probes used with coordinate measuring machines. During the investigation, a number of important parameters have been identified, including measurement speed, probe longitude, approach distance, probe latitude, stylus length/stylus tip diameter, probe orientation, operating mode (scanning and non-scanning), scan pitch, pre-load spring force (gauging force), probe type and the surface approach angle. This paper presents the detailed experimental design and the results obtained from the systematic experiments. These results have led to some useful recommendations for the reduction of the probe dynamic errors. Some of these recommendations included the selection of the optimum measurement speed, the setting of the pre-load spring force and the choice of the probe type.

A new survivability measure for military communication networks

A new measure for survivability of military communication networks based upon topological structures is presented. The proposed measure can be used to evaluate and enhance the survivability of military communication networks, which is illustrated through case studies. The computer simulation results have shown that the new measure can well reflect the survivability of networks. It can be used as a reliable criterion for estimating the survivability of networks and designing networks with high survivability.

The Integration of Coordinate Measuring Machines within a Design and Manufacturing Environment

The role of the coordinate measuring machine within the inspection process has changed throughout its brief development. With its integration with industrial computer aided design (CAD) systems, its role is to change yet again. This paper presents the difficulties and limitations of current practice and identifies the inputs and decisions that need to be made within an integrated manufacturing environment. A research programme was undertaken to investigate an approach based upon intelligent communications between systems. This led to the creation of a demonstration system that was employed in the measurement of industrial components. A case study, using a standard test block, is included to illustrate the processes undertaken. This includes feature identification, probe calibration and selection strategies and automatic re-routing to minimize changes in probes and orientations. It is proposed that the approach demonstrated can be incorporated within a concurrent engineering environment to provide feedback and information about machine adjustments through a constraint modelling process.

A novel non-contact sensor for surface topography measurement using a fibre optic principle

Abstract A novel fibre optic sensing probe has been developed to measure surface topography. The system is largely independent of surface reflectivity variations. Triggering and scanning modes of operation are possible. A mathematical model has been developed and initial experimental results show close agreement to theoretical predictions. An integrated, software-controlled system has been developed to allow real-time surface information to be gathered. The system is both compact and inexpensive.

Optical fiber displacement sensors for process and manufacturing applications

We describe three novel optical fiber probes, all based on the focused-beam reflective principle, to measure displacement, form, and surface topography, respectively. Each depends on deriving twin displacement/optical output characteristics that may be resolved by difference/sum referencing. The displacement sensor adopts twowavelength operation using a zone plate to give opposing displacement/output characteristics. The device is noncontacting, and a resolution of better than 0.1% of span is anticipated. A 3-D optical touchprobe has been built for use with coordinate measuring machines. A mathematical model has been generated that relates output to stylus movement, and the model has been verified experimentally. A resolution of 0.1 μm in the x-y plane and 1.0 μm in the z direction is achievable. A further noncontacting probe has been developed for the measurement of surface topography whose output shows low dependency on surface reflectance. A mathematical model has shown good correspondence against a wide range of surface compositions and textures; a resolution of better than 1 μm is foreseen. Proposals are made for industrial implementation of all three probes.

SCOUT - Surface Characterization Open-Source Universal Toolbox

Surface topography plays a significant role in functional performance situations like friction, lubrication and wear. A European Community funded research programme on areal characterization of steel sheet has recently assisted research in this area. This article is dedicated to the software that supported most of the programme. Born as a rudimentary collection of procedures, it grew steadily to become an integrated package, later equipped with a graphical interface and circulated to the research community employing the Open-Source philosophy.