Hans Nørgaard Hansen

Quantitative Characterisation of Surface Texture

Abstract This paper reviews the different methods used to give a quantitative characterisation of surface texture. The paper contains a review of conventional 2D as well as 3D roughness parameters, with particular emphasis on recent international standards and developments. It presents new texture characterisation methods, such as fractals, wavelets, change trees and others, including for each method a short review, the parameters that the new methods calculate, and applications of the methods to solve surface problems. The paper contains a discussion on the relevance of the different parameters and quantification methods in terms of functional correlations, and it addresses the need for reducing the large number of existing parameters. The review considers the present situation and gives suggestions for future activities.

Size Effects on Surface Generation in Micro Milling of Hardened Tool Steel

This paper presents the results of an extensive experimental investigation concerning size effects on surface generation by ball nose and flat end micro milling hardened tool steel. Cutting parameters were selected on the basis of a modular description of the uncut chip geometry. A theoretical model of the generated surfaces was used as a reference and compared with measurement results and visual inspection using an SEM. Two main effects have been observed on the tool-work material interaction at micro scale. These are responsible for the limited reduction of the roughness amplitude parameters with tool diameter and occur when the cutting edge radius to uncut chip thickness ratio becomes critical.

Case Study in Biomimetic Design: Handling and Assembly of Microparts

This paper describes the application of the biomimetic design process to the development of automated gripping devices for microparts. Handling and assembly of micromechanical parts is complicated by size effects that occur when part dimensions are scaled down. A common complication involves sticking between the gripping device and the micropart, which hinders the automation of picking and releasing operations. This paper presents the identification and use of biological analogies to solve the problem of sticking during microassembly. Selected release techniques based on DNA transcription and the abscission process in plants inspired concepts of new automated handling devices for microobjects. The design, development and testing of a gripping device, based on biological principles, for the automated handling and assembly of a microscrew is presented.Copyright

Biomimetics Applied to Centering in Microassembly

Abstract This paper describes the application of a biomimetic search method to develop Ideas for centering objects in microassembly. Biomimetics involves the imitation of biological phenomena to solve problems. An obstacle to the use of biomimetics in engineering is knowledge of biological phenomena that are relevant to the problem at hand. The method described here starts with an engineering problem, and then systematically searches for analogous biological phenomena using functional keywords. This method is illustrated by finding and using analogies for the problem of positioning and centering objects during microassembly. Relevant phenomena identified Involve microtubule organizing centers, photosystems, and retinal ganglion cells.

Dimensional measurement of micro-moulded parts by computed tomography

Computed tomography (CT) is progressively assuming an important role in metrology applications and great efforts are being made in order to turn it into a reliable and standardized measuring technology. CT is typically used for non-destructive tests, but it is currently becoming very popular for dimensional metrology applications due to its strategic advantages such as the capability of performing measurements on both the components surface and volume, allowing inspection possibilities to otherwise non-accessible internal features. This paper focuses on the dimensional verification of two micro-injection moulded components, selected from actual industrial productions, using CT metrological tools. For this purpose, several parts have been measured with two different CT machines, and the results have been compared with the measurements obtained by other measuring systems. The experimental work carried out and the analysis of the results provide valuable conclusions about the advantages and drawbacks of using CT metrology in comparison with other measuring systems when these techniques are employed for the quality control of micro-moulded parts.

Development and analysis of a software tool for stitching three-dimensional surface topography data sets

This paper presents development and application of a new software solution for stitching surface three-dimensional topography data where best matching positions are detected through maximization of a cross-correlation function. Differently from other stitching software tools developed in the past, the one here presented is based not on colour gradients but on matching of physical coordinates. The developed routine fully compensates positioning errors occurring when the measuring instrument is displaced relative to the surface. Qualitative as well as quantitative analyses were carried out in order to verify the applicability of the stitching process. Both synthetic and real scanned surfaces were used for testing. It was demonstrated that misalignments after software compensation are negligible: sub-pixel level inaccuracies, with absolute deviations <0.2%, were in fact verified when stitching two images. The method was developed specifically for atomic force microscopy, but can be effectively applied to any 3D topography measuring instrument.

Comparison of Coordinate Measuring Machines using an Optomechanical Hole Plate

Abstract An interlaboratory comparison on mechanical and optical coordinate measuring machines (CMMs) was carried out in the period from August 2002 to November 2004. 15 different research laboratories were involved from 9 countries, with a total of 23 CMMs (12 mechanical and 11 optical) being used to measure an optomechanical hole plate, designed and manufactured by DTU, whereby it is possible to compare the performance of measurements obtained optically and mechanically. The comparison has shown that the optomechanical hole plate can be calibrated, following a well-established procedure for ball plate calibration, with uncertainties between 0.5 urn and 2 urn. Based on results from the comparison, optical CMM measurements can be divided in two groups. A group leading to deviations larger than 2 urn, and a group with deviations that are comparable to those obtained with mechanical machines. This comparison shows that optical coordinate measuring machines, generally speaking, can be as good as mechanical ones.

Approaches to the Calibration of Freeform Artefacts on Coordinate Measuring Machines

Abstract The paper compares two different experimental methods to establish the traceability of freeform measurements on coordinate measuring machines: i) uncertainty assessment using Modular Freeform Gauges, and ii) uncertainty assessment using Uncalibrated Objects. The first approach is an application to freeform geometries of the method described in ISO TS 15530-3 based on comparisons. The second approach is inspired by the procedure currently being developed within ISO TC213, involving repeated measurements of a given object in different orientations with variation of measuring parameters etc. The feasibility of the two approaches for freeform geometries is demonstrated through the calibration of a turbine blade.

An industrial comparison of coordinate measuring machines in Scandinavia with focus on uncertainty statements

Abstract This paper describes an industrial comparison of coordinate measuring machines (CMMs) carried out in the Scandinavian countries from October 1994 to May 1996. Fifty-nine industrial companies with a total of 62 CMMs participated in the project and measured a comparison package with five items chosen to represent a variety of dimensions, angles, and other geometrical quantities. A tool holder, two gauge blocks, a straightedge, and a ring together with instructions on how to measure the items were produced and sent to each participant. Simple measurement tasks were observed to be carried out with good results for the majority of the participants; whereas, increasing the level of difficulty from simple length measurements to more complex geometrical quantities gave severe problems for some of the companies. This occurred even though the participants measured according to prescribed procedures. An important part of the intercomparison was to test the ability of the participants to determine measurement uncertainties. One of the uncertainties was based upon a “best guess” but nevertheless, many participants did not even report this uncertainty. Uncertainty budgeting was not used for measurements other than simple length. For each company, a comparison of their measurement ability with the reference laboratory and other Scandinavian companies was made possible. A network regarding CMMs was created in these Scandinavian countries.

A Combined Optical and Mechanical Reference Artefact for Coordinate Measuring Machines

Abstract The calibration of CMMs using calibrated ball plates or hole plates is a well established technique. In the case of CMMs equipped with optical sensors based upon CCD cameras a series of artefacts based upon chromium-on-glass structures have been proposed. Calibration of these artefacts can not be performed using the reversal method which can be used for ball or hole plates. A new two-dimensional artefact based upon mechanical elements has been developed allowing both optical and mechanical probing and calibration. This artefact combines in one piece the possibilities of performance verification of both optical and mechanical CMMs. The mechanical elements have been manufactured with form errors less than 3 urn and using a special surface preparation that makes optical CNC-measurements non-problematic. Reproducibilities better than 0.5 μm have been obtained in optical probing. Calibration of the artefact can be carried out using reversal methods using both optical and mechanical probing.