Mihailo Ristic

Fine planning for supply chains in semiconductor manufacture

Abstract In the course of globalisation and increasing customer orientation within a highly dynamic business environment, semiconductor manufacturing supply chains have changed their business strategies and transformed into new economic and industrial organisations: Virtual Enterprises. Consisting of a number of geographically distributed production facilities, such enterprises are often closely coupled in partnerships with suppliers, subcontractors and customers. Production planning and control in the make-to-order environment of application-specific integrated circuit (ASIC) production is a difficult task, as it has to be optimal both for the local manufacturing units and for the whole supply chain network. Centralised MRP II systems which are in operation in most of today’s manufacturing enterprises are not flexible enough to satisfy the demands of this highly dynamic co-operative environment. In this paper we present a distributed planning methodology for semiconductor manufacturing supply chains. The developed system is based on an approach that leaves as much responsibility and expertise for optimisation as possible to the local planning systems while a global co-ordinating entity ensures best performance and efficiency of the whole supply chain. Fine planning takes rough due dates based on capacity models of the local manufacturing units and optimises both local and global order flow through the Virtual Enterprise.

Analysis of free form surface registration

Registration of a rigid body is an essential step in many machine vision tasks. This paper presents performance analysis of the iterative closest point method implemented for dimensional inspection of free form surfaces where the set of measured points is registered to a NURBS model. The results were obtained through Monte Carlo simulation. A large number of experiments were performed on an example precision engineering component. Influences of shape, number of measured points and measurement noise on registration accuracy are identified through statistical analysis.

Magnetic resonance elastography hardware design: A survey:

Abstract Magnetic resonance elastography (MRE) is an emerging technique capable of measuring the shear modulus of tissue. A suspected tumour can be identified by comparing its properties with those of tissues surrounding it; this can be achieved even in deep-lying areas as long as mechanical excitation is possible. This would allow non-invasive methods for cancer-related diagnosis in areas not accessible with conventional palpation. An actuating mechanism is required to generate the necessary tissue displacements directly on the patient in the scanner and three different approaches, in terms of actuator action and position, exist to derive stiffness measurements. However, the magnetic resonance (MR) environment places considerable constraints on the design of such devices, such as the possibility of mutual interference between electrical components, the scanner field, and radio frequency pulses, and the physical space restrictions of the scanner bore. This paper presents a review of the current solutions that have been developed for MRE devices giving particular consideration to the design criteria including the required vibration frequency and amplitude in different applications, the issue of MR compatibility, actuation principles, design complexity, and scanner synchronization issues. The future challenges in this field are also described.

System for enhancing supply chain agility through exception handling

With the emergence of a new business era characterized by continuous and unpredictable changes and tough global competition, an agile supply chain has been recognized as a competitive strategy for companies to survive and prosper. Co-OPERATE, an on-going IST project, is aimed at developing concepts and tools for coordination of production planning and control activities in the complex and distributed supply network, and is targeted in the automotive supply and the semiconductor industries. Since the work reported here is based on the project, a framework for manufacturing coordination in the distributed supply network is proposed for the project. As an important part of the project, exception handling is further described. First, through boundary investigation, the scope of this business solution is clarified. Second, a methodology is developed to help understand the mechanism behind the exception handling process. Third, guiding design principles are described to direct the detailed business process design. Finally, rush-order handling is chosen as part of the concept prototype for implementation and evaluation. Extensive feedback from industrial business partners has been collected and taken into account for further implementation.

Measurement-based modification of NURBS surfaces

A frequent requirement in computer aided design and manufacture is to update or refine an existing CAD model using measured data. Least squares surface fitting is known to suffer from stability problems, caused by an insufficient measurement density in some regions. This is particularly evident in situations involving local surface updating and when knot insertion is applied for local surface refinement. This paper presents a new method to update the CAD model consisting of NURBS surfaces, trimmed or untrimmed, based on a set of unorganised measured points in three-dimensional space. The proposed method overcomes the fundamental problem of singular or ill-conditioned matrices resulting from incomplete data sets. This was achieved by introducing additional fitting criteria in the minimisation functional, which constrain the fitted surface in the regions with insufficient number of data points. Two main benefits were realised by this approach. First, local surface updating can be performed by treating the surface as a whole, without the need to specially identify the regions with insufficient data, nor to re-measure those regions. Second, the quality of the unmeasured regions may be controlled to suit specific needs. The results were found to be highly encouraging and the method was found to be especially useful in situations involving knot insertion and large surface deformations.

Efficient registration of NURBS geometry

Abstract The paper presents an implementation of free-form surface registration in relation to inspection of engineering components, defined as NURBS. Registration is principally performed through the Iterative Closest Point (ICP) method. The time-critical step in ICP was found to be the determination of the closest points on NURBS to a given point in space. Significant speed improvements were achieved through the adoption of a dual surface representation, involving approximation of NURBS entities by a polyhedral mesh. A criterion for sufficient polyhedral approximation was derived and implemented, producing encouraging results. Original solutions are suggested in order to further improve the computational speed. Extensive testing has been carried out, showing that the proposed registration method handles a full six degrees of freedom and achieves global convergence. Performance of the implemented algorithms is discussed with reference to registration of a turbine blade airfoil.

A Web-based system for manufacturing co-ordination in complex supply networks

In todays manufacturing industries, companies have recognised the importance of focusing on their core manufacturing capabilities, leading to a greater reliance on suppliers and business partners. Consequently, manufacturing co-ordination across the supply network is of vital importance for improved customer service and efficiency of individual companies and the whole network. This paper introduces the important aspects of the IST project: Co-OPERATE, which aims to develop a Web-based system for better co-ordination of manufacturing planning and control activities across the supply network. A framework for manufacturing co-ordination in the supply network is first introduced, which consists of seven interrelated co-ordination processes. Then, they are prioritised and four core processes for co-ordinating supply chain planning and execution activities in the short- to medium-term are chosen for further development, which comprise the main modules of the Co-OPERATE system. This is followed by the description of the implementation and evaluation for the Co-OPERATE system. Finally, some important issues are discussed and the presented work is concluded.

Supercapacitor Energy Storage for Magnetic Resonance Imaging Systems

Magnetic resonance imaging (MRI) involves very short pulses of very high current. Substantial savings in the high cost of MRI installations may be realized by employing suitable electrical energy storage, for which supercapacitors are strong candidates in view of high specific power and long cycle life. A key question is whether the well-known capacitance degradation with increased frequency is compatible with the complex and highly variable duty cycles of various MRI sequences. Compatibility of the supercapacitor voltage range with the MRI system must also be considered. We present a detailed analysis of power duty profiles in MRI, using actual imaging sequences, that has not been reported previously. We also propose and validate a simplified supercapacitor model that can accurately simulate its performance in the MRI system, involving pulses that are several orders of magnitude shorter than those considered previously. Results of equivalent experiments involving lithium-ion iron phosphate ( LiFePO4) batteries are also reported. Finally, we present a detailed analysis of the overall energy storage performance in a realistic neurological examination. The study is based on a specific system of our own design, and we fully disclose its relevant parameters, so that the results would be of direct practical value to the wider community, including developers of MRI.

Automated proof inspection of turbine blades

The first article inspection of cast turbine blades is on the critical path of a new aeroengine. The current methods used are open to automation using CMMs and non-contact gauges to reduce lead times. A graphics system is discussed which allows modelling of the blade and Computer-Aided Part Programming of CMMs to produce a Neutral Data File for post processing. Once measured on the CMM the actual blade is modelled and bestfitted to the design intent. This allows subsequent error analysis to be carried out. Such a system is essential to make sense of large amounts of co-ordinate data and storage of dimensional variation at stages in the manufacturing process.

Economic dispatch of distributed combined heat and power systems participating in electricity spot markets

An optimization tool is proposed to determine the optimal operation schedule for distributed combined heat and power plants which participate in electricity spot markets. It was tested and analysed using realistic data for heat and electricity demands and their corresponding prices. The results show substantial cost savings compared with the benchmarked alternatives.