C R Nagarajah

Non-contact, optically based measurement of surface roughness of ceramics

Examination of various research efforts has revealed that optical techniques best satisfy the requirements of on-line, non-contact inspection; other methods are usually deficient with regard to speed, flexibility and ability to perform non-contact measurement. Of the optical methods considered, techniques based on statistical analysis of scattered light from the sample are best suited for the purpose of surface inspection. A general scheme for an on-line, non-contact, optically based inspection machine has been developed. The system has the important attributes of fast measurement, simplicity and flexibility. The systems roughness measurement capability was successfully tested on ceramic components of varying surface finish.

Fibre optic distributed temperature sensor with an integrated background correction function

Raman scattering in optical fibres provides a means of measuring continuous temperature distributions over extended distances. However, in many applications it has been found that the background transmission properties of the optical fibre either change after deployment of the fibre or vary over time due to ageing effects. Changes in the fibre transmission can be distinguished from thermal effects by measuring the Rayleigh backscatter, which is relatively insensitive to temperature. The combined use of Raman and Rayleigh data is discussed here in the context of a particularly simple and cost-effective sensor design, where a single, fixed optical filter and a single light source are used for both measurement modes. The Rayleigh backscatter measurement allows the accurate correction of background transmission changes in a probe arrangement that includes several splices between different fibres with different attenuations. In this way, the temperature in a 290 °C test region is accurately recovered from the anti-Stokes Raman signal. However, preliminary measurements of the fibre attenuation as a function of temperature and exposure to an accelerated ageing environment show that these two effects will be difficult to separate in practice. Therefore it remains challenging to perform accurate, unambiguous background corrections in situations where high-temperature ageing occurs.

A surface inspection technique for continuously extruded cylindrical products

The objective of this paper is to provide a brief overview of various inspection methodologies for continuously extruded products, such as wire, cable and optical fibres, and to describe the implementation of a practical surface inspection technique. The main feature of the developed system is the use of a conic reflector arrangement to collect light scattered from a cylindrical surface. Illumination is supplied by optical fibres, strategically positioned around the cone, to provide full circumferential lighting. The inspection arrangement was implemented and tested in an industrial environment and effectively detected defects, such as blisters on wire (of diameters 0.2 mm to 3 mm), at a speed of up to .

Non-contact inspection for the detection of internal surface defects in hollow cylindrical work-pieces

The objective of this paper is to document part of a collaborative research program undertaken by the Centre for Computer Integrated Manufacture (CIM Centre) at Swinburne University of Technology in Hawthorn, Victoria, Australia and Australian Defence Industries (ADI) Ltd in the field of “non-contact inspection”. This research program is one of two collaborative programs between the CIM Centre and ADI Ltd, related to inspecting the quality of components in an automated fashion, without the use of contacting sensors.There are a number of techniques currently being investigated at the CIM Centre, including lasers, vision, acoustic emission and X-ray based methods. This particular paper focuses on the research work undertaken by the first author in the detection of internal surface defects in forged, hollow cylindrical workpieces. The case study presented for consideration and discussion herein is related to the detection of cavity defects in forged pressure vessels. The paper provides a background into the range of alternative non-contact inspection techniques that are available (including lasers, ultrasonics, etc.) and the reasons why some of these failed to provide the functionality that was offered by the vision approach ultimately adopted.There is nothing unique about the application of vision systems in the detection of surface defects. However, in this research program, a number of factors have considerably complicated the application. These include lighting problems and the difficulties encountered in acquiring images within a confined cylindrical space. This paper documents the techniques that have been used to resolve some of these practical image acquisition and processing problems and the relative merits of each approach. The paper also examines some of the algorithmic problems involved in detection of particular surface anomalies in components through a range of techniques and concludes that the one most suited to the surfaces in the pressure vessel case-study is the so-called “region-growing” approach.

Thermochromic liquid crystal based sensing system for analysis of air flow

This paper documents a research program in which a measurement system was developed for the analysis of air flow through automotive air filters. The measurement sensor was based on the use of thermochromic liquid crystal paint and nichrome wire as a heater element. This paper incorporates results of tests carried out on filter paper using the developed measuring system. The examined filter paper was used for primary air intake combustion engine filters. Holes, in the range 50 μm to 2.35 mm were made in the filter paper using an excimer laser and air flow through the filter paper was examined. The visual patterns of air flow are compared and presented herein.

A methodology for investigating effects of cell size on operational flexibility in flexible manufacturing systems

There are two aspects to cell formation in flexible manufacturing systems, cell sizing or deciding on the optimum number of machines to be allocated to each cell, and then allocation of specific machines to each cell. Although the latter problem has been investigated extensively there is a paucity of published work on the former. This paper discusses the effects of cell sizing on operational flexibility.Operational flexibility is that aspect of flexibility that enables manufacturing systems to respond with speed and efficiency to changes in the manufacturing environment while maintaining an effective level of control.

Design and error analysis of a surface reflector for a laser tracking measurement system

Abstract The aim of the research project described in this paper was to extend the operating range of a commercially available laser tracking measurement system by developing a surface reflector with improved measurement accuracy, calibration ability and longer reach than the commercially available device. Two prototype surface reflectors were designed and manufactured. The new design extended the reach of the stylus and provided a mechanism enabling faster calibration with greater adjustment sensitivity. A calibration procedure was developed which was reasonably simple and effective, taking less than 1 h to complete. With further development it is considered that both the calibration time and the misalignment could be reduced. The calibrated surface reflectors were tested to determine the effect of misalignment on the systematic error and to compare the relative systematic error of the prototypes with that of a commercially available surface reflector.

Method for detecting misformed clips in packaging

A technique is described for detecting misformed clips in hermetically sealed packages. The technique involves use of a machine vision system incorporating an image processing algorithm, that calculates the directions of contours of intensity in grey-scale images of clips. The algorithm approximately locates the clip by scanning a box over the contour direction transformed image, and finding the position of the box such that the standard deviation of the directions in the box is a minimum. The clip is accurately located by scanning a rectangular template over the contour direction transformed image in the vicinity of the approximate location of the clip, and determining the best-fit position of the template. Accurate location of the clip enables the critical clip dimensions to be calculated and used for assessment of clip integrity. The clip integrity is considered acceptable if all of the critical dimensions lie within an acceptable range, as defined by predetermined upper and lower thresholds.

A non-destructive technique for detecting pinholes in hermetically sealed flexible packaging

A new capacitance-based technique is described for detecting pinholes in electrically non-conducting flexible hermetically sealed packages with no headspace. The new technique is compared with the most suitable existing technique reported in the literature. It is demonstrated theoretically and through experimentation that the new technique provides more sensitive pinhole detection than the most suitable existing technique.

Part spectrum based methodology for cell sizing in flexible manufacturing systems

This paper describes a part spectrum based methodology which enables the determination of an optimum size for flexible manufacturing cells. The methodology incorporates a systems approach in that it enables the sizing of cells to achieve specified manufacturing objectives while maintaining a realistic level of flexibility and an acceptable level in terms of complexity of control.The proposed methodology for cell sizing is based on two component characteristics: processing time and number of operations. Furthermore, it is generalised in its implementation in that the effects of case specific factors such as processing sequence of components and location of machines in relation to each other are negated.The validation of the proposed methodology for cell sizing using data obtained from manufacturing companies implementing flexible manufacturing systems is also described.