Development towards a focus variation based micro-co-ordinate measuring machine

The increasing number of small and fragile parts that are being manufactured using micromachining technology has raised the demand for co-ordinate measurement machines (CMM) that can measure on a micro- and millimetric scale without contacting the part, thus avoiding damage to the surface of the part. These instruments are expected to measure on a micro- and millimetric scale with a measuring uncertainty in the nanometre range. A number of techniques used for contactless surface measurements exist, such as the focus variation (FV) technique, which have the ability to perform measurements on the micro- and millimetric scale in a short amount of time. These instruments may have the potential to be implemented in a non-contact micro-CMM platform. [Continues.

In-orbit Vignetting Calibrations of XMM-Newton Telescopes

We describe measurements of the mirror vignetting in the XMM-Newton Observatory made in-orbit, using observations of SNR G21.5-09 and SNR 3C58 with the EPIC imaging cameras. The instrument features that complicate these measurements are briefly described. We show the spatial and energy dependences of measured vignetting, outlining assumptions made in deriving the eventual agreement between simulation and measurement. Alternate methods to confirm these are described, including an assessment of source elongation with off-axis angle, the surface brightness distribution of the diffuse X-ray background, and the consistency of Coma cluster emission at different position angles. A synthesis of these measurements leads to a change in the XMM calibration data base, for the optical axis of two of the three telescopes, by in excess of 1 arcminute. This has a small but measureable effect on the assumed spectral responses of the cameras for on-axis targets.Comment: Accepted by Experimental Astronomy. 26 pages, 18 figure

Task Specific Uncertainty in Coordinate Measurement

Task specific uncertainty is the measurement uncertainty associated with the measurement of a specific feature using a specific measurement plan. This paper surveys techniques developed to model and estimate task specific uncertainty for coordinate measuring systems, primarily coordinate measuring machines using contacting probes. Sources of uncertainty are also reviewed

An investigation into the effects of thermal errors of a machine tool on the dimensional accuracy of parts

The reduction of machining errors has become increasingly important in modern manufacturing in order to obtain the required quality of parts. Geometric error makes up the basic part of the inaccuracy of the machine tool at the cold stage; however, as the machine running time increases, thermally-induced errors start to play a major role in machined workpiece accuracy. Dimensional accuracy of machined parts could be affected by several factors, such as the machine tool’s condition, the workpiece material, machining procedures and the operator’s skill. Of these, the machine condition plays an important role in determining the machine’s performance and its effects on the final dimensions of machined parts. The machine’s condition can be evaluated by its errors which include the machine’s built-in geometric and kinematic error, thermal error, cutting force-induced error and other errors.This research represents a detailed study of the effects of thermal errors of a machine tool on the dimensional accuracy of the parts produced on it. A new model has been developed for the prediction of thermally-induced errors of a three-axis machine tool. By applying the proposed model to real machining examples, the dimensional accuracy of machined parts was improved. The research work presented in this thesis has the following four unique characteristics:• Investigated the thermal effects on the dimensional accuracy of machined parts by machining several components at different thermal conditions of a machine tool to establish a direct relationship between the dimensional accuracy of machined parts and the machine tool’s thermal status.• Developed a new model for calculating thermally-induced volumetric error where the three axial positioning errors were modelled as functions of ball screw nut temperature and travel distance. The influences of the other 18 error components were ignored due to their insignificant influence.• Employed a Laser Doppler Displacement Meter (LDDM) with three thermocouples, instead of the expensive laser interferometer and the large number of thermocouples required by the traditional model, to assess the thermally-induced volumetric errors of a three-axis CNC machining centre. The thermally-induced volumetric error predictions were in good agreement with the measured results.• Applied the newly developed thermally-induced volumetric error compensation model for drilling operations to improve the positioning accuracy of drilled holes. The results show that positioning accuracy of the drilled holes was improved significantly after compensation. The absolute reduction of the positioning errors of drilled holes was an average 30.44 μm at the thermal stable stage, while the average relative reduction ratio of these errors was 77%.Therefore, the proposed thermally-induced volumetric error compensation model can bean effective tool for enhancing the machining accuracy of existing machine tools used in the industry

Task‐specific measurement uncertainty budget of Curvic‐coupling using analytical methods

A number of Industrial reference components manufactured by grinding to achieve tight dimensional tolerances. In this paper, we present an uncertainty budget of a reference forty-tooth #Curvic measured using an accurate Coordinate Measuring Machine (CMM) in a temperature-controlled laboratory. A number of measurements conducted on Curvicto assess measurement repeatability and reproducibility. Expanded uncertainty budget evaluated from twenty-one Influencing factors, giving8.7 µm (7.1 µm from Type A) and 11 µm (9.6 µm from Type A), respectively, for repeatability and reproducibility test (k >2). Measurement uncertainty due to steady-state thermal effects is 2.2 µm. An adaptable model is presented to evaluate transient thermal effects, a factor often neglected in measurement uncertainty. Thermal time constant uncertainty associated with transient thermal effects is evaluated u(τ)= ±398 s, which corresponds to ±15 % of thermal time constant expanded uncertainty, u(τ)= ±2570 s. #Curvic® (Curvic is a trademark of The Gleason Works, 1000 University Avenue, Rochester, NY, 14603, USA

Lateral error compensation for focus variation microscopy

Focus variation microscopy measures both the areal form and areal surface texture of components. Improvements to the accuracy and precision of focus variation microscopes usually requires measurements with multiple image-fields to compensate lateral stage errors. This paper proposes a methodology for compensation of lateral stage error of a focus variation microscope using an uncalibrated artefact

Performance verification of a 4-axis focus variation coordinate measuring system

Performance verification of a coordinate measuring system (CMS) is important for instrument acceptance, reverification, comparability as well as measurement traceability to the definition of the meter. State-of-the-art ISO 10360 standard series is the reference text about the procedure of verification for CMS. Specifically, ISO 10360-8 considers optical distance sensor based CMSs. This article proposes procedures and artifacts for performance verification of focus variation-based CMS for a simultaneous 4-axis measuring mode. The proposal is inspired by, but goes beyond, the ISO 10360 standard, proposing an original solution for simultaneous linear and rotational axes verification

Comparative Performance between Two Photogrammetric Systems and a Reference Laser Tracker Network for Large-Volume Industrial Measurement

This paper determines the capability of two photogrammetric systems in terms of their measurement uncertainty in an industrial context. The first system – V-STARS inca3 from Geodetic Systems Inc. – is a commercially available measurement solution. The second system comprises an off-the-shelf Nikon D700 digital camera fitted with a 28 mm Nikkor lens and the research-based Vision Measurement Software (VMS). The uncertainty estimate of these two systems is determined with reference to a calibrated constellation of points determined by a Leica AT401 laser tracker. The calibrated points have an average associated standard uncertainty of 12·4 μm, spanning a maximum distance of approximately 14·5 m. Subsequently, the two systems’ uncertainty was determined. V-STARS inca3 had an estimated standard uncertainty of 43·1 μm, thus outperforming its manufacturer's specification; the D700/VMS combination achieved a standard uncertainty of 187 μm

Observing the Sun with Atacama Large Millimeter/submillimeter Array (ALMA): High Resolution Interferometric Imaging

Observations of the Sun at millimeter and submillimeter wavelengths offer a unique probe into the structure, dynamics, and heating of the chromosphere; the structure of sunspots; the formation and eruption of prominences and filaments; and energetic phenomena such as jets and flares. High-resolution observations of the Sun at millimeter and submillimeter wavelengths are challenging due to the intense, extended, low- contrast, and dynamic nature of emission from the quiet Sun, and the extremely intense and variable nature of emissions associated with energetic phenomena. The Atacama Large Millimeter/submillimeter Array (ALMA) was designed with solar observations in mind. The requirements for solar observations are significantly different from observations of sidereal sources and special measures are necessary to successfully carry out this type of observations. We describe the commissioning efforts that enable the use of two frequency bands, the 3 mm band (Band 3) and the 1.25 mm band (Band 6), for continuum interferometric-imaging observations of the Sun with ALMA. Examples of high-resolution synthesized images obtained using the newly commissioned modes during the solar commissioning campaign held in December 2015 are presented. Although only 30 of the eventual 66 ALMA antennas were used for the campaign, the solar images synthesized from the ALMA commissioning data reveal new features of the solar atmosphere that demonstrate the potential power of ALMA solar observations. The ongoing expansion of ALMA and solar-commissioning efforts will continue to enable new and unique solar observing capabilities.Comment: 22 pages, 12 figures, accepted for publication in Solar Physic

Novel metrics and methodology for the characterisation of 3D imaging systems

© 2016 The AuthorsThe modelling, benchmarking and selection process for non-contact 3D imaging systems relies on the ability to characterise their performance. Characterisation methods that require optically compliant artefacts such as matt white spheres or planes, fail to reveal the performance limitations of a 3D sensor as would be encountered when measuring a real world object with problematic surface finish. This paper reports a method of evaluating the performance of 3D imaging systems on surfaces of arbitrary isotropic surface finish, position and orientation. The method involves capturing point clouds from a set of samples in a range of surface orientations and distances from the sensor. Point clouds are processed to create a single performance chart per surface finish, which shows both if a point is likely to be recovered, and the expected point noise as a function of surface orientation and distance from the sensor. In this paper, the method is demonstrated by utilising a low cost pan-tilt table and an active stereo 3D camera. Its performance is characterised by the fraction and quality of recovered data points on aluminium isotropic surfaces ranging in roughness average (Ra) from 0.09 to 0.46 µm at angles of up to 55° relative to the sensor over a distances from 400 to 800 mm to the scanner. Results from a matt white surface similar to those used in previous characterisation methods contrast drastically with results from even the dullest aluminium sample tested, demonstrating the need to characterise sensors by their limitations, not just best case performance