ISO compliant reference artefacts for the verification of focus varation-based optical micro-coordinate measuring machines

Demand form micro-coordinate measuring machines (micro-CMMs) within industry is increasing due to the need for accurate measurement of the geometry of small-scale objects. Optical micro-CMMs have the advantage over traditional stylus-based CMMs of being non-contact instruments, and have the ability to acquire large amounts of data, with high resolution, in a relatively short period of time. The focus variation (FV) technique is typically used in the field of surface topography measurement, but has the potential to be implemented as a sensor technology for optical micro-CMMs. Exploring the possibility of the FV technique as an optical micro-CMM requires that the instrument and measuring procedure can be performance verified. Consequently, a prototype FV based optical micro-CMM should have a verification route that is traceable to the definition of the metre. The ISO 10360 specification standard for acceptance testing and verification of CMMs has several parts, all specific to different groups of instruments and configurations. Each section of ISO 10360 identifies methods and artefacts best suited for the acceptance testing and verification of each group and configuration. ISO/DIS 10360-8.2 (due for ISO/FDIS publication in 2013), is a verification standard written for CMMs with optical distance sensors. There are four main parts to the acceptance and re-verification tests: length measurement error, probing form error measurement, probing size error measurement and flat form error measurement. The probing form and size error tests require a calibrated reference sphere that has a diameter of at least 10 mm. FV instruments are potentially covered by this standard but the recommended minimum size of the calibration sphere is too large to fully fit within one field of view of a typical FV instrument.. Optical distance measuring instruments similar in operation to FV systems, such as confocal microscopes and coherent scanning interferometers are, therefore, also currently excluded from the application of this standard by default, unless the user, and the instrument manufacturer, can potentially agree to use a smaller calibrated reference sphere for the assessment of the probing size and form error. A prototype FV based optical micro-CMM should, therefore, be verified with calibrated reference spheres of similar size to objects for which the technique has been designed to measure. The research reported here considers the use of 0.5 mm, 1 mm and 2 mm diameter reference spheres as suitable components for a reference artefact, with the surfaces of the spheres roughened using bespoke micro-roughening techniques. The research presents a novel verification artefact composed of multiple small-scale spheres, specifically designed to evaluate probing size error, probe form error, and dimensional accuracy of a prototype FV based optical micro-CMM, compliant to ISO/DIS 10360-8. The results suggest that the artefacts and procedures detailed in ISO/DIS 10360-8 can, and should, be applied to optical micro-CMMs

Areal texture and angle measurements of tilted surfaces using focus variation methods

Optical instruments for areal surface topography measurement have seen significant commercial development in the last five years, along with the ISO 25178 areal standard. Providing the user with confidence in new instruments depends on understanding instrument behavior and sources of error. Focus variation techniques rely on the inherent micro- or nano-scale roughness of a surface to allow acquisition of topography data. The work reported here has been examining the sensitivity of the focus variation technique to surface slope, using areal parameters to characterize surface roughness at extended slope values. The results illustrate links between instrument variables and slope characterization

The assessment of residual flatness errors in focus variation areal measuring instruments

Optical instruments for areal surface topography measurement rely on high-precision lenses that guide the light from the object surface to the image plane. Lens aberrations may cause distortion of the transmitted image and consequently a residual flatness error in the measurement data. Previous work at NPL suggests using an averaging method for residual flatness error assessment for optical surface topography instruments. However, the averaging method does not apply to the focus variation technique, which relies on the nano-scale roughness of a surface to allow acquisition of topography data. This paper presents alternative methods for measuring residual flatness for focus variation instruments

Combined inkjet printing and infrared sintering of silver nanoparticles using a swathe-by-swathe and layer-by-layer approach for 3-dimensional structures

Despite the advancement of additive manufacturing (AM)/3-dimensional (3D) printing, single-step fabrication of multifunctional parts using AM is limited. With the view of enabling multifunctional AM (MFAM), in this study, sintering of metal nanoparticles was performed to obtain conductivity for continuous line inkjet printing of electronics. This was achieved using a bespoke three dimensional (3D) inkjet-printing machine, JETx®, capable of printing a range of materials and utilizing different post processing procedures to print multi-layered 3D structures in a single manufacturing step. Multiple layers of silver were printed from an ink containing silver nanoparticles (AgNPs) and infra-red sintered using a swathe-by-swathe (SS) and layer-by-layer sintering (LS) regime. The differences in the heat profile for the SS and LS was observed to influence the coalescence of the AgNPs. Void percentage of both SS and LS samples was higher towards the top layer than the bottom layer due to relatively less IR exposure in the top than the bottom. The results depicted a homogeneous microstructure for LS of AgNPs and showed less deformation compared to the SS. Electrical resistivity of the LS tracks (13.6 ± 1μΩ cm) was lower than the SS tracks (22.5 ± 1 μΩ cm). This study recommends the use of LS method to sinter the AgNPs to obtain a conductive track in 25% less time than SS method for MFAM