M. Ristic

Contact probe radius compensation using computer aided design models

Abstract Probe radius compensation is necessary in metrology applications that employ contact probes, but it can be a significant source of systematic measurement errors when dealing with free-form part geometry. The paper presents implementation and performance analysis of a proposed new compensation technique based on the nominal computer aided design (CAD) model, which is assumed to be defined using non-uniform rational B-splines (NURBS). Errors associated with the conventional compensation approach are assessed on the basis of experiments using a modern coordinate measuring machine (CMM), providing clear motivation for this work. The proposed method consists of a number of steps, including measurement, generation of offset nominal surfaces, registration, surface fitting, data smoothing and calculation of compensating offsets. Critical steps include registration and NURBS surface fitting and their implementation is presented. Simulation studies are used to analyse the registration accuracy and the accuracy of the overall method in comparison with the conventional one. The proposed method is shown to produce superior results in situations involving non-uniform measurement distribution, measurement noise, free-form geometry with no clear datums, deformation relative to the nominal shape and component misalignment.

A CAD/CAM system for die design and manufacture

The manufacture of directionally solidified cast turbine blades relies on the precise casting of wax patterns of the actual turbine blade. This, in turn, requires the design and manufacture of a complex die. A CAD/CAM system is presented specifically for producing manufacturing information for dies based on basic data defining the shape of a turbine blade. The system is based around a UNIX graphics workstation which forms part of a CIM system being developed as part of an SERC Teaching Company based at Rolls-Royce plc, Derby.

Process variables determining the dimensional and metallurgical properties of directionally solidified, cored turbine blades produced by investment casting of super-alloys

The investment casting process for the manufacture of directionally solidified, cored turbine blades is described. The dimensional and metallurgical properties of blades produced by this process is subject to variations which can result in long lead times in development and scrap during production. The process variables that determine the dimensional and metallurgical properties have been identified and classified in order of importance. The objective of the research is the formation of a database of process variables that can be used as a basis for control of the casting process and for predicting the final geometry as a result of the process.

MAC-Sim: A multi-agent and communication network simulation platform for smart grid applications based on established technologies

The smart grid has been the main focus of development in recent years. It is central to its idea to build a more decentralised system and make extensive use of digital communication. There is a definite trend among researchers and industry to build the smart grid on established communication technologies (e.g. DSL, GSM, GPRS, WiMAX, ZigBee; TPC/IP based) and multi-agent system applications are proposed to deal with the complexity and decentralisation of control and decision making. However, it is difficult to validate the new applications and communication networks prior to deployment. Especially time-critical applications for control and protection demand deep understanding and accurate modelling. This paper presents the design and implementation of a software platform, which is called MAC-Sim, that can co-simulate multi-agent applications and communication networks. We extended a multi-agent system framework and communication network simulator and combined them via a distributed simulation modelling architecture. The feasibility of this approach has been demonstrated by implementing and simulating an agent-based zone 3 remote backup relay supervision scheme and its communication infrastructure. This simulation platform can help to design, develop, and validate agent-based smart grid applications and communication networks.

Triangulation of unordered data using trimmed NURBS computer aided design models

Abstract Computer aided design (CAD) models of many complex engineering parts, typically in the aerospace and the automotive industries, are defined using trimmed NURBS. The shape of the finished part can be captured by measuring a sufficiently large number of points. Triangulation of those points is a frequent requirement in the analysis of that shape as part of the quality assessment and of the product and manufacturing process development. The paper proposes a new method for efficient and robust triangulation of large sets of unordered three-dimensional points, based on the available CAD model. Unlike many other methods, it is not constrained by certain types of measurement distribution or object shapes. Examples involving real engineering parts are presented, with the conclusion that the method was well suited for the perceived applications in engineering manufacture.

Robot‐assistant for MRI‐guided liver ablation: A pilot study

PURPOSE Percutaneous ablation under MRI-guidance allows treating otherwise inoperable liver tumors locally using a catheter probe. However, manually placing the probe is an error-prone and time consuming task that requires a considerable amount of training. The aim of this paper was to present a pneumatically actuated robotic instrument that can assist clinicians in MRI-guided percutaneous intervention of the liver and to assess its functionality in a clinical setting. The robot positions a needle-guide inside the MRI scanner bore and assists manual needle insertions outside the bore. METHODS The robot supports double oblique insertions that are particularly challenging for less experienced clinicians. Additionally, the system employs only standard imaging sequences and can therefore be used on different MRI scanners without requiring prior integration. The repeatability and the accuracy of the robot were evaluated with an optical tracking system. The functionality of the robot was assessed in an initial pilot study on two patients that underwent MRI-guided laser ablation of the liver. RESULTS The robot positioned the needle-guide in a repeatable manner with a mean error of 0.35 mm and a standard deviation of 0.32 mm. The mean position error corresponding to the needle tip, measured for an equivalent needle length of 195 mm over 25 fixed points, was 2.5 mm with a standard deviation of 1.2 mm. The pilot study confirmed that the robot does not interfere with the equipment used for MRI-guided laser ablation and does not visibly affect the MR images. The robot setup integrated seamlessly within the established clinical workflow. The robot-assisted procedure was successfully completed on two patients, one of which required a complex double oblique insertion. For both patients, the insertion depth and the tumor size were within the range reported for previous MRI-guided percutaneous interventions. A third patient initially enrolled in the pilot study and was considerably heavier than the others, preventing the use of the robot and requiring several freehand insertion attempts. CONCLUSIONS The robot repeatability and accuracy are appropriate for liver tumors normally treated with MRI-guided ablation. The results of the pilot study endorse the clinical use of the robot in its current form: the robot is fully functional and MRI-compatible in a clinical setting and is suitable for double-oblique needle insertions.

Interactive Scheduling for a Human-Operated Flexible Machining Cell

Abstract This paper describes an interactive scheduling system for a flexible, human-operated machining cell. Attributing great importance to the operator’s judgment, especially under unfavourable conditions, emphasis has been placed upon the ability of the user to influence the outcome of the system. Thus, preferences based on skill, past experience, or locally available technological knowledge, that has not been incorporated into the system’s methods, can be assessed and implemented. Transparency in use and function, combined with quick schedule generation should prove useful features, in order to facilitate decision making regarding schedules, in the constantly changing manufacturing environment of small to medium batch, high variety production. The structure and operation of the system are described and some examples are presented.

Design and control of 3-DOF needle positioner for MRI-guided laser ablation of liver tumours

This article presents the design and control of a pneumatic needle positioner for laser ablation of liver tumours under guidance by magnetic resonance imaging (MRI). The prototype was developed to provide accurate point-to-point remote positioning of a needle guide inside an MR scanner with the aim of evaluating the potential advantages over the manual procedure. In order to minimise alterations to the MR environment, the system employs plastic pneumatic actuators and 9 m long supply lines connecting with the control hardware located outside the magnet room. An improved sliding mode control (SMC) scheme was designed for the position control of the device. Wireless micro-coil fiducials are used for automatic registration in the reference frame of the MR scanner. The MRI-compatibility and the accuracy of the prototype are demonstrated with experiments in the MR scanner.