Precision Engineering

Engineering surfaces are comprised of a range of spatial wavelengths. Filtering techniques are commonly adopted to separate the different wavelength components into well-defined bandwidths. Filtering is done prior to numerical characterization and it is also essential for extracting information needed to provide process feedback and establish functional correlation. This paper reviews commonly used filters in surface metrology like the 2RC, Gaussian and several new ones currently under research such as the spline, morphological, wavelets, regression filters and robust regression filters. The need for these new filters and examples illustrating the features of these filters are also presented.

The market for freeform and high quality microdies and moulds made of steel is predicted to experience a phenomenal growth in line with the demand for microsystems. However, micromachining of hardened steel is a challenge due to unpredictable tool life and likely differences in ...

This article presents the comparison of various compliance/stiffness equations of circular flexure hinges with FEA results. The limitation of these equations at different t/R (R is the radius and t is the neck thickness) ratios are revealed. Based on the limitations of these design equations, a guideline for selecting the most accurate equations for hinge design calculations are presented. In addition to the review and comparisons, general empirical stiffness equations in the x-and y-direction were formulated in this study (with errors less than 3% when compared to FEA results) for a wide range of t/R ratios (0.05 ≤ t/R ≤ 0.8).

Nanotechnology. The science is good, the engineering is feasible, the paths of approach are many, the consequences are revolutionary-times-revolutionary, and the schedule is: in our lifetimes. But what? No one knows but what. That's why a book like this is crucial before molecular engineering and the routine transformation of matter arrives. The technology will arrive piecemeal and prominently but the consequences will arrive at a larger scale and often invisibly. Perspective from within a bursting revolution is always a problem because the long view is obscured by compelling immediacies and the sudden traffic of people new to the subject, some seizing opportunity, some viewing with alarm. Both optimists and pessimists about new technologies are notorious for their tunnel vision. The temptation always is to focus on a single point of departure or a single feared or desired goal. Sample point of departure: What if we can make anything out of diamond? Sample feared/desired goal: What if molecular-scale medicine lets people live for centuries? We're not accustomed to asking, What would a world be like where many such things are occurring? Nor do we ask, What should such a world be like? The first word that comes to mind is careful. The second is carnival. Nanotechnology breakthroughs are likely to be self-accelerating and self-proliferating, much as information technology advances have been for the past several decades (and will continue to be, especially as nanotech kicks in). We could get a seething texture of constant innovation and surprise, with desired results and unexpected side-effects colliding in all directions. How do you have a careful carnival? Unbounding the Future spells out some of the answer. I've been watching the development of Eric Drexler's ideas since 1975, when he was an MIT undergraduate working on space technologies (space settlements, mass drivers, and solar sailing). Where I was watching from was the "back-to-basics" world of the Whole Earth Catalog publications, which I edited at the time. In that enclave of environmentalists and world-savers one of our dirty words was technofix. A technofix was deemed always bad because it was a shortcut-an overly focused directing of high tech at a problem with no concern for new and possibly worse problems that the solution might create. But some technofixes, we began to notice, had the property of changing human perspective in a healthy way. Personal computers empowered individuals and took away centralized control of communication technology. Space satellites-at first rejected by environmentalists-proved to be invaluable environmental surveillance tools, and their images of Earth from space became an engine of the ecology movement. I think nanotechnology also is a perspective shifter. It is a set of technologies so fundamental as to amount to a whole new domain of back to basics. We must rethink the uses of materials and tools in our lives and civilizations.

Wire electrical discharge machining (WEDM) technology has been widely used in conductive material machining. The WEDM process, which is a combination of electrodynamic, electromagnetic, thermaldynamic, and hydrodynamic actions, exhibits a complex and stochastic nature. Its performance, in terms of surface finish and machining productivity, is affected by many factors. This paper presents an attempt at optimization of the process parametric combinations by modeling the process using artificial neural networks (ANN) and characterizes the WEDMed surface through time series techniques. A feed-forward back-propagation neural network based on a central composite rotatable experimental design is developed to model the machining process. Optimal parametric combinations are selected for the process. The periodic component of the surface texture is identified, and an autoregressive AR(3) model is used to describe its stochastic component.

Stiffness plays an important role in the precise performance of flexure-based ultra-precision manipulation systems. The finite element method (FEM) is currently used to determine the stiffness of the flexure parallel mechanism (FPM) with specified dimensions and free shape. This paper presents the stiffness model based on the way the flexure members are connected together in serial or parallel combinations. The modeling allows one to formulate the functional relationship between stiffness and dimensions as well as the free shape of the FPM in the design process. For illustration, stiffness matrices of a double linear spring and a three degree-of-freedom (DOF) translational flexure parallel mechanism are established. The proposed analytical model is validated by FEM model and experiments.

Burnishing is a chipless finishing method, which employs a rolling tool, pressed against the workpiece, in order to achieve plastic deformation of the surface layer. Recent developments made possible burnishing of heat-treated steel components up to 65 HRC. Features of burnishing include a good roughness (comparable to grinding), as well as improvement of mechanical characteristics of the surface (fatigue strength, corrosion resistance, and bearing ratio), due to implementation of compressive stresses into the surface layer. This paper will present influences of certain burnishing parameters upon roughness, for a hardened steel component (64 HRC).

Micro-electrochemical discharge machining (ECDM) was studied in order to improve the machining of 3D micro-structures of glass. To minimize structures and obtain good surface microstructures, the effects of the electrolyte, the pulse on/off-time ratio, the voltage, the feedrate, the rotational speed, and the electrolyte concentration in the drilling and milling processes were studied.In ECDM, voltage is applied to generate a gas film and sparks on a tool electrode; however, high voltage produces poor machining resolution. To obtain a stable gas film over the whole surface of the tool at a low voltage, a new mechanical contact detector, based on a loadcell, was used; the immersion depth of the tool electrode in the electrolyte was reduced as much as possible. In this study, various micro-structures less than 100 m in size, such as Ø 60 m micro-holes, a 10 m-thin wall, and a 3D micro-structure were fabricated to demonstrate the potential for micro-machining of glass by ECDM.

There is a growing interest in the machining of micro-holes with high aspect-ratio in difficult-to-machine alloys for the aerospace industry. Processes based on electro discharge machining (EDM) and developed for the manufacture of both micro-electrode and micro-hole are actually used, but most of them involve micro-EDM machines. In this work, the influence of EDM parameters on material removal rate, electrode wear, machining time and micro-hole quality when machining Ti6Al4V is studied. Due to an inefficient removal of debris when increasing hole depth, a new strategy based on the use of helicalshaped electrodes has been proposed. The influence of helix angle and flute depth with respect to process performance has been addressed. Main results include 37% reduction in machining times (hole diameter 800 m) when using electrode helix angle of 45 • and flute-depth of 50 m, and an additional 19% with flute-depth of 150 m. Holes of 661 m diameter and as much as 6.81 mm depth, which yields in aspect ratio of 10:1, have successfully been machined in Ti6Al4V.

The fabrication of nonrotationally symmetric surfaces by diamond turning requires tool actuation at a bandwidth significantly higher than the rotational frequency of the surfaces. This requirement cannot be met by standard slide drives due to their large mass ...

A cylinder liner possesses fairly intricate surface requirements due to its complicated functions. It needs to provide adequate surface roughness to resist wear as well as to store and retain lubricants during high temperatures. The liner surface texture is anisotropic, produced by the honing process, with resultant deep visible scratches left on it [1]. The prominence of the honing grooves observed suggests that surface texture significantly affects ring-pack performance, although this effect is not clearly understood. In this paper, a numerical model was developed to investigate the effects of groove characteristics on the lubrication condition and friction at the interface between the piston ring and cylinder liner. This model aims to solve the average Reynolds equation, which depends on the real surface topographies of the cylinder liner, and describes the influence of surface irregularities on the lubricant flow under hydrodynamic lubrication conditions, considering lubricant film rupture and cavitations. Numerical results help to determine the optimum lateral groove characteristics to reduce friction and then noxious emissions.

Polycyclic aromatic hydrocarbons (PAHs) are among the most targeted contaminants by international regulatory institutions. There is thus a need for fast, selective and sensitive analytical methods to quantify these compounds at trace levels in complex samples. This article focuses on the optimization by means of an experimental design of a CE method with laser-induced fluorescence detection for the fast simultaneous separation of 8 heavy PAHs among food and environmental priority pollutants: benzo(a)pyrene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, dibenzo(a,h)anthracene, indeno(1,2,3-cd)pyrene, benzo(k)fluoranthene, and benzo(ghi)perylene. In this method, capillary zone electrophoresis with a mixture of an anionic sulfobutyl ether-␤-cyclodextrin (SBE-␤-CD) and a neutral methyl-␤-cyclodextrin (Me-␤-CD) was used to separate PAHs, on the basis of their differential distribution between the two CDs. First, the factors most affecting PAH electrophoretic behavior were identified: SBE-␤-CD and Me-␤-CD concentrations and percentage of methanol added to the background electrolyte. Then, a response surface strategy using a central composite design was carried out to model the effects of the selected factors on the normalized migration times. To optimize the separation, desirability functions were applied on modeled responses: normalized migration time differences between peak end and peak start of two consecutive peaks, and overall analysis time. From the model, predicted optimum conditions were experimentally validated and full resolution of all 8 PAHs was achieved in less than 7 min using a borate buffer composed of 5.3 mM SBE-␤-CD, 21.5 mM Me-␤-CD and 10.3% MeOH. This CE separation method was successfully applied to real edible oil analysis.

This paper reviews the applications of focused ion beam (FIB) sputtering for micro/nano fabrication. Basic principles of FIB were briefly discussed, and then empirical and fundamental models for sputtering yield, material removal rate, and surface roughness were presented and compared. The empirical models were more useful for application compared to fundamental models. Fabrication of various micro and nano structures was discussed. Trimmed atomic force microscope (AFM) tips were tested in measurement and imaging of high aspect ratio nanopillars where higher accuracy and clarity were observed. Micromilling tool fabricated using FIB sputtering was used to machine microchannels. Slicing and dwell time control approaches on FIB sputtering were presented for the fabrication of three dimensional microcavities. The first approach is preferred for practical applications. The maximum aspect ratio of 13:1 of the microstructures was achieved. The minimum size of the nanopore was in the range of 2-10 µm. Cavities of microgear of 70 µm outside diameter were sputtered with submicrometer accuracy and 2-5 nm average surface roughness. The microcavities were then filled with polymer in a subsequent micromodling process. The replicated microcomponents were inspected with scanning electron microscope where faithful duplication of accuracy and surface texture of the cavity was observed.

A piezoelectric tube actuator is employed as a sample positioning device in Nanocut, a cutting instrument conceived to study the mechanics of nanometric cutting. Extension of functionality of the instrument as a nanometric machine tool motivates the search for an accurate model of the actuator for implementing feedback control. A simple nonlinear model describing longitudinal expansion of the piezoelectric tube actuator is presented in this paper. The model derivation is based on a non-formal analogy with nonlinear viscoelastic materials under uniaxial extension, for which the responses to a step input are similar to the piezoelectric tube. Suitability of the model structure for arbitrary inputs is tested by cross-verification between time and frequency domains. Two parameter estimation procedures are examined and the results of the experimental work for characterization, estimation and validation are presented.

This paper presents the development of a new probing method for coordinate measuring machines (CMM) to inspect the diameter and form of small holes. The technique, referred to as fiber deflection probing (FDP), can be used for holes of approximately 100 m nominal diameter. The expanded uncertainty obtained using this method is 0.07 m (k = 2) on diameter. The probing system consists of a transversely illuminated fiber (with a ball mounted on the end) whose shadows are imaged using a camera. We can infer the deflection of the probe from the motion of the image seen by the camera, and we infer the position of the measured surface by adding the fiber deflection along x-and y-directions to the machine scale readings. The advantage of this technique is the large aspect ratio attainable (5 mm deep for a 100 m diameter hole). Also, by utilizing the fiber as a cylindrical lens, we obtain sharp crisp images of the fiber position, thus enabling high resolution for measured probe deflection. Another potential advantage of the probe is that it exerts an exceptionally low force (ranging from a few micronewtons down to hundreds of nanonewtons). Furthermore, the probe is relatively robust, capable of surviving more than 1 mm over-travel, and the probe should be inexpensive to replace if it is broken. In this paper, we describe the measurement principle and provide an analysis of the imaging process. Subsequently, we discuss data obtained from characterization and validation experiments. Finally, we demonstrate the utility of this technique for small hole metrology by measuring the internal geometry of a 129 m diameter fiber ferrule and conclude with an uncertainty budget.

The measurement of roughness on machined surfaces is of great importance for manufacturing industries as the roughness of a surface has a considerable influence on its quality and function of products. In this paper, an experimental approach for surface roughness measurement based on the coherent speckle scattering pattern caused by a laser beam on the machined surfaces (grinding and milling) is presented. Speckle is the random pattern of bright and dark regions that is observed when a surface is illuminated with a highly or partially coherent light beam. When the illuminating beam is reflected from a surface, the optical path difference between various wavelets with different wavelength would result in interference showing up as a granular pattern of intensity termed as speckle. The properties of this speckle pattern are used for estimation/quantification of roughness parameters. For measurement of surface roughness, initially the speckle patterns formed are filtered in the spatial frequency domain. The optical technique, namely spectral speckle correlation (autocorrelation) is utilized in this work for the measurement of roughness on machined surfaces. It has been observed that the pattern formed is dependent on the roughness of the illuminated surface. For example, a rough surface (milled) shows a small central bright region with a rapid decrease in intensity towards the edges, while a smooth surface (ground) shows a large central bright region with gradually decreasing intensity towards the edges. The complete methodology and analysis for quantification/estimation of surface finish of milled and ground surfaces based on speckle images that could be implemented in practice, is presented in this paper.

We present the analysis of a simple mechanical model of a common type of kinematic seat touch trigger probe widely used on modern coordinate measuring machines (CMMs). The model provides a quantitative description of the pretravel variation or "probe-lobing'" characteristics that fimit the use of such probes for high-accuracy dimensional measurements. We include the effects of stylus bending and the frictional interaction between the stylus ball and the part surface. The model is restricted to probes with simple straight styli, and we demonstrate significant error reduction both for vertically and horizontally oriented stylL In the latter case, gravitational forces are shown to play an important role in probe triggering and pretravel variation. Extensions to arbitrary orientations are discussed.

It is a well known fact that the EDM process results in the formation of a hard, brittle recast layer on the component's surface. Several investigations have been carried out in order to assess the nature of the recast layer in terms of its phase structure, the microhardness, presence and the density of cracks, and other surface features. Some researchers [Barash, Delpretti] have reported mathematical relationships between the thickness of the white layer and 2D amplitude surface roughness parameters (such as R a and R t ). But so far no investigation has been reported which correlates the thickness of the white layer with 3D surface roughness parameters, especially those related to spatial parameters. This paper presents an experimental investigation of the effect of the EDM process factors (current and pulse on-time) on the thickness of the white layer. Empirical equations relating the thickness of the white layer with 3D surface texture amplitude, spatial and volume parameters are presented and their physical basis is discussed. The results of this study show that a better correlation can be obtained between the average thickness of the white layer (AWLT) and the spatial parameter, S ds as compared to other 3D surface texture parameters. This is believed to be mainly due to the similar effect of the current and pulse on-time on both AWLT and S ds . The possible effect of surface tension between the solid and liquid phases on the thickness of the white layer during erosion is also discussed.

This paper presents two novel six-axis magnetic-levitation (maglev) stages capable of nanoscale positioning. These stages have very simple and compact structures, which is advantageous to meet the demanding positioning requirements of next-generation nanomanipulation and nanomanufacturing. Six-axis motion generation is accomplished by the minimum number of actuators and sensors. The first-generation maglev stage, namely the -stage, is capable of generating translation of 300 m and demonstrates position resolution better than 2 nm root-mean-square (rms). The second-generation maglev stage, namely the Y-stage, is capable of positioning at a resolution better than 3 nm rms over a planar travel range of 5 mm × 5 mm. A novel actuation scheme was developed for the compact structure of this stage that enables six-axis force generation with just three permanent-magnet pieces. This paper focuses on the design and precision construction of the actuator units, the moving platens, and the stationary base plates. The performance of the two precision positioners is compared in terms of their positioning and load-carrying capabilities and ease of manufacture. Control system design for the two positioners is discussed and an experimental plant transfer function model is presented for the Y-stage. The superiority of the developed instruments is also demonstrated over other prevailing precision positioning systems in terms of the travel range, resolution, and dynamic range. The potential applications of the maglev positioners include semiconductor manufacturing, microfabrication and assembly, nanoscale profiling, and nanoindentation.

A neural network based on Artificial Resonance Theory (ART-map) was used to predict and compensate the tool point errors of a 3-axis machining center using discrete temperature readings from the machine's structure as inputs. A combination of kinematic error modeling, curve fitting, and the neural network were used to maintain the machine's three-dimensional (3-D) accuracy within Ϯ7.4 m, regardless of the thermal state. The network model was evaluated with diagonal measurements and part machining tests. A laser ball bar was used to take the necessary measurements for training the neural network.

The performance verification of micro-CMMs is now of intense interest because of their capability to perform length measurements in three dimensions to high accuracy with low uncertainties. Currently, verification of micro-CMMs is completed in the spirit of existing specification standards, because strict adherence to these standards is often difficult. This review aims to present and discuss verification techniques available for micro-CMMs: specification standards, existing calibrated test lengths and traceability routes that can be associated with micro-CMMs. Three specification standards used in the testing of CMMs will be considered. In addition, a wide range of calibrated test lengths are reported, and any advantages and disadvantages associated with their use are discussed. It is concluded that micro-CMMs cannot yet be verified in accordance with existing specification standards. Suggestions are made for future standardisation work required to rectify these issues.

All machining processes leave characteristic topographic features on the surfaces of components. This paper reviews a wide range of examples in which the surface topography of a component has been found to bear a significant effect on its function. Problems in manufacture which are related to surface roughness requirements are also discussed.

This paper describes a case study devised to quantify the relative contributions of geometric, thermal, contouring, and cutting force errors to machined part dimensional errors. Measurements were performed to independently evaluate the: (1) quasi-static geometric errors using the laser ball bar; (2) variations in geometric errors due to thermal effects; (3) spindle thermal growth errors using a capacitance gage nest; (4) two-dimensional contouring errors using a grid plate encoder; and (5) surface location error due to (stable) forced vibrations during cutting. The effects of the first three error components were related to part dimensions using a homogeneous transformation matrix approach integrated into a Monte Carlo simulation. A comparison of the individual influences of these error sources showed that the cutting force error was dominant for the high-speed machining center/tool-holder combination selected for this study.

The purpose of this research is to investigate the relative importance of spindle speed, system dynamics, and cutting conditions on the accuracy of surface location in computer numerical-control (CNC) finish machining operations. The relationship between the spindle speed, the most flexible modes of the machine/cutting tool system and the final part dimensions is rather complex. The underlying theory, based on the situation of forced vibrations, is outlined. It is shown that the critical factor is the ratio of the tooth passing frequency to the system most flexible mode and corresponding natural frequency. Simple analytical calculations are carried out to illustrate the overcut/undercut surface error phenomenon. A simple simulation for end milling operations is also described which calculates the force on the cutter, the resulting cutter deflection, and the final error of surface. A comparison between the simulated and experimental results is presented. From experimental data, it shown that a change in surface location (and part dimension) of up to 50 m is seen for a set of given conditions (i.e., cutter, material, chip load) simply by changing spindle speeds. Furthermore, it is seen that certain spindle speeds produce surfaces with no error introduced by the machining process.

Out-of-roundness of circular and cylindrical parts can greatly affect assembly accuracy. At present, the ASME Y14.5M-1994 specifies circularity tolerance based on two extreme circular boundaries to confine the highest peak and the lowest valley of a roundness profile; however, the profile variations within the two extreme boundaries are not accounted for. In this paper, we propose a harmonic roundness model using Fourier series expansion. In addition, a cutting profile model has been developed to illustrate the relationship between the radial error motion of a spindle and the resultant part profile. This relationship is then used to provide physical meanings to the harmonics generated by the proposed roundness model for a part profile, in particular those caused by fractional frequency spindle error motions. The proposed harmonic model has been verified statistically by a large number of real profiles produced by both turning and cylindrical grinding processes. The proposed roundness model is expected to provide insights into the advanced tolerance analysis of circular and cylindrical parts.

Hydrodynamic journal bearings have been widely used in various types of rotating machinery, ranging from heavy duty, high-impact applications, such as the crank shaft of an internal combustion engine and turbine rotor, to high-precision, light load applications, such as precision spindles in cylindrical grinding machines. Although extensive theoretical and experimental results have been presented for hydrodynamic bearings, the available literature seems to be limited for precision hydrodynamic bearing spindles. In this study, practical methods have been developed to quantify the performance of a hydrodynamic wheel spindle operating in the horizontal mode to produce precision parts with submicron roundness tolerance and very fine surface finish. These methods can easily and cost effectively be implemented on various machines in an actual production environment for effective predictive maintenance. The main experimental results show that the long-term drift of the spindle at steady state is less than 1 m vertically and 0.2 m horizontally, and the radial error motion of the spindle based on unfiltered data is less than 1.6 m for all the speeds tested. It is also found that the shaft center position (vertical lift and horizontal shift) at the cold condition is substantially different from that in the steadystate warm condition. From the results, an optimal spindle speed is recommended.

New generations of gravity wave detectors require unprecedented levels of vibration isolation. This paper presents the final design of the vibration isolation and positioning platform used in Advanced LIGO to support the interferometer's core optics. This five-ton two-and-half-meter wide system operates in ultra-high vacuum. It features two stages of isolation mounted in series. The stages are imbricated to reduce the overall height. Each stage provides isolation in all directions of translation and rotation. The system is instrumented with a unique combination of low noise relative and inertial sensors. The active control provides isolation from 0.1 Hz to 30 Hz. It brings the platform motion down to 10 /√ at 1 Hz. Active and passive isolation combine to bring the platform motion below 10 /√ at 10 Hz. The passive isolation lowers the motion below 10 /√ at 100 Hz. The paper describes how the platform has been engineered not only to meet the isolation requirements, but also to permit the construction, testing, and commissioning process of the fifteen units needed for Advanced LIGO observatories.

We have developed a novel fast tool servo and associated prototype diamond-turning machine for the production of plastic spectacle lenses. Our fast tool servo carries the cutting tool on a rotary arm and, thus, on a circular path, as opposed to straight line paths in conventional designs. The actuator, sensors, and bearings are standard elements that together allow experimentally demonstrated 500 m/s 2 instantaneous accelerations at the tool tip over a 3-cm range of cutting depth. We also describe in this paper new approaches we have developed for toolpath generation and calibration. The paper also presents associated control algorithms, because the controller must supply very high dynamic stiffness to the tool servo axis at multiples of the spindle frequency. This stiffness is achieved by means of repetitive control techniques. The new fast tool servo is shown to have great promise for machining asymmetric surfaces with large amplitude asymmetries.

This paper presents a nanomachining instrument that was developed for conducting nanocutting, nanoscratching, and nanoindentation experiments. A piezoelectric tube scanner (PZT) is employed to generate three-dimensional machining motions. The sample is moved by the PZT, and the tool is kept stationary during machining. The machining forces are measured by force sensors with a resolution of sub-milliNewtons. The instrument is compact and can be used inside optical microscopes and scanning electron microscopes. In this paper, depth-sensing indentation experiments were performed to test the basic performance of the instrument. The indentation displacement was measured by a capacitance probe situated inside the PZT tube. An experimental system was constructed to locate and image indentations. The system consists of a high magnification microscope to measure coordinates of the indentation relative to a reference corner point on the sample, and an AFM equipped with an on-axis optical imaging system for locating the indentation. A technique was also employed to establish the tool-sample contact to nanometer accuracy. Indentation experiments were carried out on three kinds of materials with different hardness. Experimental results demonstrated the instrument has the ability of performing depth-sensing indentations. The frame compliance was also evaluated from the indentation results.

For a wide range of purposes, a compact and smart positioning stage is in strong demand. Our final goal is to fabricate a positioning mechanism that possesses multi-degrees of freedom, a wide movable area, dexterity, rigidity, and high speed. To meet most of requirements, i.e., except that of a wide movable area, a parallel mechanism is superior to a serial

This work addresses the parasitic motion of high-precision rotation mechanisms based on flexural pivots subjected to lateral loads. This case has great importance from the mechanical design point of view, since generally flexural pivots support mechanical elements of considerable weight and their rotation is obtained by loading the pivot with a force instead of a pure couple.

This paper presents a novel concept, a virtual metrology frame, for enhancing the dynamic performance of a machine tool with a flexible structural frame. The dynamic properties of a machine are directly affected by the stiffness of its frame, and its reference system; thus, by having an unstressed metrology frame, superior dynamic capabilities can be achieved. The developed concept does not require physical components associated with metrology frame; hence it is ideal for machine tools with requirements for small footprint and ultra-precision performance. The concept relies on an accelerometer based dynamic displacement feedback technique, where the accelerometer is used as a precision frame displacement sensor. The concept does not require a complex controller, and was realized in an off-the-shelf CNC controller. The concept was demonstrated on a linear motion system, a simplified version of a compact size CNC machine, and its servo bandwidth and dynamic stiffness were improved by 36% and 70% respectively, which are the key parameters for improving the machining accuracy.

We describe a simple, convenient method for measuring nonlinearities in displacement-measuring Michelson interferometers. Nonlinearities with a spatial periodicity of one optical fringe are a well-known source of error in precision interferometry. Our experimental technique for observing these errors is most immediately applicable to commercial interferometer systems for which the cube-corner retroreflectors can be attached directly to the faces of a beamsplitter cube, creating a monolithic interferometer optic with excellent noise immunity. The optical path difference in this boltedtogether interferometer can be changed slightly by rotating the interferometer relative to an external laser. It should be noted that the basic principle described here-generating small path differences through a rotation of the optics relative to the laser-may itself be a source of significant errors in certain length measurements. The validity of our method has been demonstrated by measuring optical mixing errors of calculable magnitude. We describe a matrix method suitable for modeling optical mixing errors in both single-pass and double-pass (plane mirror) interferometers. Also, we report experimental measurements of periodic nonlinearities for two representative interferometers and conclude that, in the majority of engineering metrology applications, these errors are of only minor importance.

There are a number of important software related issues in coordinate metrology. After measurement data are collected in the form of position vectors, the data analysis software must derive the necessary geometric information from the point set, and uncertainty plays an important role in the analysis. When extreme fit approaches (L Ϫϱ norm estimation approaches) are employed for form error evaluation, the uncertainty is closely related to the sampling process used to gather the data. The measurement points are a subset of the true surface, and, consequently, the extreme fit result differs from the true value. In this paper, we investigate the functional relationship between the uncertainty in an extreme fit and the number of points measured. Two major issues are addressed in this paper. The first addresses and identifies the parameters that affect the functional relationship. The second develops a methodology to apply this relationship to the sampling of measurement points.

According to the Taylor tool life equation, tool life reduces with increasing cutting speed following a power law. Additional factors can also be added, such as the feed rate, in Taylor-type models. Although these models are posed as deterministic equations, there is inherent uncertainty in the empirical constants and tool life is generally considered a stochastic process. In this work, Bayesian inference is applied to estimate model constants for both milling and turning operations while considering uncertainty.

This paper presents the characterisation of a novel three dimensional vibrating tactile probe for miniature co-ordinate measuring machines (CMMs). This novel vibrating probe has been developed to address the main issues associated with tactile probing on the micro-scale. The vibrating probe is designed to act isotropically, with low probing forces (near zero), and experience minimal effects from the surface interaction forces. In this paper the tests completed to verify the precision of the contact sensing ability of the probe in three dimensions will be described, along with quantification of the isotropy of the probe. The results will be presented and discussed. Several operational differences between classical static probes for miniature CMMs and the novel vibrating probe developed by NPL will be highlighted. These differences include tip diameter calibration techniques, strategies for use, environmental considerations and logistics. Finally, the future plans for the development of the probe will be discussed, especially initial tests to be completed with the probe deployed on a suitable precision CMM for miniature parts.

A method of micromechanical device fabrication is examined in this article. The method consists of the development of equipment which has sizes comparable with the sizes of the produced parts. There are different approaches to this problem. We propose a method of ...

In order to compute geometric tolerances, the distance between the actual geometry and the nominal one has to be computed, and this computation requires the selection of a sampling strategy. Sampling strategy consists in deciding the number and the locations of the points that have to be measured on the actual surface. This paper presents a new approach for selecting the optimal locations of the points for any given sample size. The proposed procedure is based on estimating the "manufacturing signature", that is the systematic pattern left by the manufacturing process on the machined items. In particular, the proposed approach is based on using regression for estimating the manufacturing signature and then selecting the measurement point locations by minimizing the distance between the maximum and the minimum points of the regression-based tolerance interval.

A mathematical theory is presented along with some simple resulting procedures that permit an electron beam lithography machine to be calibrated by using it to make multiple observations of an imprecisely defined but stable planar object. The calibration thus obtained yields a degree of accuracy that is approximately equal to the reproducibility of the machine. For this purpose a rigid, movable grid plate is used, with grid points placed at arbitrary but more-or-less evenly distributed, fixed positions on its surface. An e-beam lithography machine with a high precision X-Y stage has been used to measure such a grid plate. Two interferometer beams, nominally parallel to the X-and Y-axes, measure stage displacements. No geometric assumptions are made concerning the stage, other than repeatability. Although the assumptions are very genera/, it is possible to observe the grid in just three orientations to determine both an inverse distortion function (calibration) and accurate, absolute rectangular coordinates for the grid points, providing that the absolute distance between a pair of points on the grid is known. A calibration program has been written applying the theory to the practical problem of calibrating an e-beam lithography system. Simulations based upon actual e-beam measurements confirm the theory for the practical situation. The paper concludes with suggestions for applictions to three other areas of science and technology: astronomy, optometry, and satellite geodesy.

We aimed to develop a sort of Robust Spline Filter that is much less sensitive to outliers than the ordinary Spline Filter. This new Robust Spline Filter is based on the concept and definition of the Spline Filter that was introduced by M. Krystek. This newly developed Robust Spline Filter inherits all the advantages directly from the ordinary Spline Filter. The L 2-norm based robust algorithm is proposed and the computational procedure is described and illustrated. By applying this Robust Spline Filter to several measured datasets, its effectiveness was demonstrated in contrast with the ordinary Spline Filter. This new filter can be also developed for any continuous plane curve and space curve based on the one-dimensional curve theory.

In this paper, a method is proposed that uses an artefact assembled in situ and exploiting the on-machine probing capability to perform a rapid volumetric distortion assessment of a five-axis machine. The 3D reconfigurable uncalibrated master ball artefact (RUMBA) is an assembly of the machine pallet and an adjustable number of master balls located within the machine working and probing envelop. The artefact design philosophy allows flexibility in the number and positions of the balls thus conferring the reconfigurability attribute. Reconfigurability allows adaptation of the artefact to the machine topology and geometry and its construction around a fixture and workpiece to reduce disruption to machine production. On the down side, the artefact is uncalibrated as its construction concept hinders precise knowledge of its geometry. During a test, combinations of all the machine axes are used to move and probe the master balls. A mathematical model is developed in order to identify the setup errors of each master ball and the probe. Simultaneous identification of the rotary axes' linear offset with the setup errors is proposed to improve the parameter estimation and volumetric distortion prediction. The machine contribution to the volumetric distortion is then computed from the ball centre data excluding the setup errors. Tests are conducted in a laboratory on a horizontal machining centre. The results show that the proposed mathematical procedure is capable of removing the influence of the uncalibrated artefact geometry, excluding scale, and that the proposed design is suited to the machine environment.

In this study, both finite element analysis (FEA) and experimental observations were used to investigate the single CBN grain wear in high-speed grinding of Inconel 718 superalloy. The wear characteristics for each grinding pass were numerically assessed utilizing the tensile and compressive strength limits of the cutting grain. Additionally, stress distribution within the grain, chip formation and grinding force evolution during multiple passes were investigated. The combined experimental and numerical results show that the CBN grain wear has two major modes: the macro fracture on the grain top surface propagating from the rake surface, and the micro fracture near the cutting edges. The resultant tensile stress is the main factor inducing grain wear. The cutting edges will be under self-sharpening due to the grain wear. With multiple micro cutting edges engaged in grinding process, the limited material removal region was divided into different sliding, ploughing and cutting dominant regions. Overall, the ratio of material elements removed by a cutting process ranges from 80% to 20%, and continue to decrease during the grinding process. With a stronger effect of the cutting process, larger fluctuation of the grinding force will commence, however its average value remains below that with stronger sliding and ploughing process characteristics.

In this paper we present a method for the vertical calibration of a metrological atomic force microscope (AFM), which can be applied to most AFM systems with distance sensors. A thorough analysis describes the physical z-coordinate of an imaged surface as a function of the observed and uncorrected z-coordinate and the horizontal position. The three most important correction terms in a Taylor expansion of this function are identified and estimated based on series of measurements on a calibrated step height and a flat reference surface. Based on this calibration a number of step heights are calibrated by the AFM with measured values consistent with reference values, where available. Relative standard uncertainty of about 0.5% is achieved for step heights above 200 nm. For step heights below 50 nm, the standard uncertainty is about 0.5 nm. While a calibration of step heights done by AFM and interference microscopy can be compared directly as demonstrated here, this is not straightforward for roughness measurement. To asses this, the exact same area on an important applied surface (a hip joint prosthesis) was measured by both AFM and interference microscopy. Similarities in the images were seen; however, the calculated roughness was significantly different (R q = 3 and 1.5 nm). Applying a low-pass filter with a cut-off wavelength of λ c = 1.5 m, the appearance of the images and the calculated roughness become almost identical. This strongly suggests that the two methods are consistent, and that the observed differences in shape and roughness in the nanometer range can be explained by the limited lateral resolution of the interference microscope.

Artificial hip replacement joints have been in use to treat osteoarthritis and rheumatoid arthritis for decades. These devices consist of a metallic/ceramic ball articulating against a polyethylene or metallic/ceramic hemispherical cup. However, these artificial joints do wear and their clinical performance starts declining after 10-20 years of successful use. In the case of hard-on-hard bearings, the wear depth and volume remain very small and their measurement has remained a challenge to current technologies. A novel device, the non-contact RedLux Artificial Hip Profiler, which is based on the chromatically encoded confocal measurement method, has been developed so that these joints can be measured accurately, reproducibly and in a short timescale. The system outputs the component radius for the unworn part, the linear depth of wear and also provides the wear volume. The design principles are presented and the capability of the equipment to measure worn parts, with linear wear between a few microns and tens of microns is hereby characterised, and correlated with laser micrometer diameter measurements, roundness measurements of linear wear and gravimetric wear assessment. The Artificial Hip Profiler is capable of measuring spherical bearing surfaces with a resolution of 20 nm. The correlation to benchmark methods for the three parameters considered is very high, with correlation coefficients of 1.02 and 0.95 for the linear and volumetric wear, respectively. The R values were 0.988 and 0.996, respectively.