Reference Artifact Research Articles

Using micro spheres as reference artifacts for the in-situ characterization of tactile 3D micro probes along the probing sphere’s equator

Abstract Nano and micro coordinate measuring machines (CMMs) have been developed for the characterization of small dimensional features. They require a procedure which enables a traceable and precise characterization of probing spheres. In this contribution we explore the use of well characterized micro spheres as reference artifacts for the in-situ characterization of probing spheres along the probing sphere’s equator. The spheres are characterized using a strategy which is based on a set of tactile surface scans in conjunction with a stitching-algorithm. These micro spheres serve as a reference for the in-situ characterization of a tactile 3D micro probe on a nano measuring machine (NMM-1). Our investigations are based on a sample of eight spheres sourced from two different suppliers. Although the sample is small, we could already observe characteristics which seem to be typical for spheres of a certain type (i.e. nominal radius and material). The experiments indicate that micro spheres are a suitable reference artifact for tactile 3D micro probes. We were able to reproduce the measured mean radius of the probing sphere with a standard deviation of 31 nm using reference spheres whose nominal radius covers a range of 89 µm (61 µm up to 150 µm).

Metrological characterisation of tool pre-setting optical systems based on 2D imaging

Accurate tool geometry is vital in modern computer numerical control machine tools for ensuring the accuracy of the manufactured parts in machining processes. The tool pre-setting optical systems play an important role by establishing accurate, efficient, and repeatable tool data for cutting tools varying from macro to micro size tools. The tool data is later utilised by the numerical control programs to accomplish precision machining operations with the required accuracy. However, the traceability of tool pre-setting optical systems is not guaranteed due to the lack of specific international standards, and there is a strong need of establishing a traceable measurement process which requires calibrated reference artefacts. In this work, we have established the metrological characteristics of an image-based tool pre-setting optical system based on ISO 15530 part 3. For this purpose, an artefact with sharp cutting edges was manufactured from a calibrated cylindrical gauge pin, measured on a coordinate measuring machine by two different approaches, and the impact of the edge radius is incorporated in the measurement process. The artefact was later employed in the performance verification of the optical system for on-machine tool characterization analogous to the production workshop environment, and the measured outcome of the optical sensor was evaluated with the developed metrological approaches. Experiments have shown the applicability of the measurement procedures and the relevance of the proposed reference artefact for the characterisation of image-based tool pre-setting optical systems.

Quantifying the Influence of Surface Texture and Shape on Structure from Motion 3D Reconstructions

In general, optical methods for geometrical measurements are influenced by the surface properties of the examined object. In Structure from Motion (SfM), local variations in surface color or topography are necessary for detecting feature points for point-cloud triangulation. Thus, the level of contrast or texture is important for an accurate reconstruction. However, quantitative studies of the influence of surface texture on geometrical reconstruction are largely missing. This study tries to remedy that by investigating the influence of object texture levels on reconstruction accuracy using a set of reference artifacts. The artifacts are designed with well-defined surface geometries, and quantitative metrics are introduced to evaluate the lateral resolution, vertical geometric variation, and spatial-frequency information of the reconstructions. The influence of texture level is compared to variations in capturing range. For the SfM measurements, the ContextCapture software solution and a 50 Mpx DSLR camera are used. The findings are compared to results using calibrated optical microscopes. The results show that the proposed pipeline can be used for investigating the influence of texture on SfM reconstructions. The introduced metrics allow for a quantitative comparison of the reconstructions at varying texture levels and ranges. Both range and texture level are seen to affect the reconstructed geometries although in different ways. While an increase in range at a fixed focal length reduces the spatial resolution, an insufficient texture level causes an increased noise level and may introduce errors in the reconstruction. The artifacts are designed to be easily replicable, and by providing a step-by-step procedure of our testing and comparison methodology, we hope that other researchers will make use of the proposed testing pipeline.

Comparison of Chemical and Mechanical Surface Treatments on Metallic Precision Spheres for Using as Optical Reference Artifacts.

The improvement of industrial manufacturing processes requires measurement procedures and part inspection tasks to be faster and faster while remaining effective. In this sense, the capabilities of noncontact measuring systems are of great help, not only because of the great amount of data they provide but also for the ease of the integration of these systems as well as their automation, minimising the impact on the industry. This work presents a comparative study on the influence of two surface treatments performed on low-cost, high-precision metallic spheres on the suitability of these spheres to be used as artefacts for the calibration of optical sensors, specifically laser triangulation sensors. The first surface treatment is sandblasting (a mechanical process), whose effect has been studied and presented in previous work. The second treatment focused on in this paper is acid etching (a chemical process). The comparison has been performed by evaluating the same metrological characteristics on two identical groups of spheres of similar type (diameter and accuracy), each of which was subjected to a different treatment. It was necessary to obtain the reference values of the metrological parameters with high accuracy, which involved measuring the spheres with a coordinate measuring machine (CMM) by contact probing. Likewise, spheres were scanned by a laser triangulation sensor mounted on the same CMM. The results derived from both the contact and laser measurements and before and after treating the surfaces were used to compare four parameters: point density, sphere diameter, sphere form deviation, and standard deviation of the best-fit sphere to the corresponding point cloud. This research has revealed that acid etching produces better optical qualities on the surfaces than the mirror-like original ones, thus enhancing the laser sensor capturing ability. However, such chemical etching has affected the metrological characteristics of the spheres to a greater extent than that produced by sandblasting. This difference is due to the variability of the chemical etching, caused by the high aggressiveness of the acid, which makes the process very sensitive to the time of exposure to the acid and the orientations of the spheres in the bath.

Design, Construction and Calibration of a Step Gauge of Nests for Performance Evaluation of Laser Trackers

According to documentary standards for the performance evaluation of laser trackers (LT), long length reference artifacts are required. In this paper, we discuss the design, construction, and calibration of a long length artifact called a step gauge of nests (SGN). The SGN has several nests in line in which to place the LT probe; the two extreme nests of the SGN are at a distance of 3 m, approximately. The documentary standards establishes that the gauge’s length shall be known no matter the orientations it takes. However, for long gauges, factors like gravitational force, fixturing forces, change in the environmental conditions, among others, deform the gauge, and its length changes when its orientation changes. To evaluate these factors, we use a finite element simulation of the SGN in the design stage to predict such deformations (mainly length variations between the two extreme nests). The simulation takes into account the used material, its stiffness, straightness, distribution of the nest’s weight, and geometry’s change of the SGN to reduce the variations in its length. For the construction stage, we describe how the SGN was manufactured and how using high module carbon fiber reduces the influence of the temperature factor. The results of the finite element simulation show a length variation of around 20 µm between the horizontal and vertical SGN positions. That variation was validated with the calibration results of two different methods. The first uses the line of sight (LOS) meth-od, which involves the same LT under evaluation. The second uses an accurate CMM, using the overlap method for calibration. The traceability of the LOS method is accomplished with the wavelength calibration of the LT interferometer while the overlap method uses a CMM evaluated with a laser interferometer with calibrated wavelength.

Development of High Temperature Multi-Layer Laser Flash Artefacts

Delamination of the interlayers of multi-layer systems can cause a degradation in functionality, stability and life span of that system. This is even more pertinent for systems at high temperature. Laser flash analysis (LFA) has long been used for thermophysical properties measurements at high temperatures. Multi-layer reference artefacts, with and without, debonded regions are required for validating the thermal characterisation of such systems using LFA. Although some high-temperature bulk candidate reference materials were developed and studied, e.g. in the European Metrology Research Programme (EMRP) funded Joint Research Project (JRP) ENG08 Metrofission, they were not able to meet the requirements for validating thermal measurements of multi-layer systems using LFA. In the European Metrology Programme for Innovation and Research (EMPIR) funded JRP 17IND11 Hi-TRACE project, the National Physical Laboratory is developing multi-layer reference artefacts, including both fully bonded and partially de-bonded systems for validating thermal characterisation of multi-layer systems at temperatures from room temperature to above 1000 °C using LFA. This paper details the methodology of production, measurement and validation of isotropic graphite and hafnium based multi-layer systems with, and without, partial debonding. Reproducibility, thermal stability and sensitive parameters concerning the thermal response of the artefacts will be discussed, with recommendation on the usage criteria as LFA multi-layer reference artefacts.

Validation of the sandblasting process in the manufacturing of precision spheres for non-contact metrology

In order to ensure the measurements that can be made with non-contact metrology technologies, it is necessary to use verification and calibration procedures using precision artefacts as reference elements. In this environment, the need for increasingly accurate but also more cost-effective calibration artefacts is a clear demand in industry. The aim of this work is to demonstrate the feasibility of using low-cost precision spheres as reference artefacts in calibration and verification procedures of non-contact metrological equipment. Specifically, low-cost precision stainless steel spheres are used as reference artefacts. Obviously, in order for such spheres to be used as standard artefacts, it is necessary to change their optical behaviour by removing their high brightness. For this purpose, the spheres are subjected to a manual sandblasting process, which is also a very low-cost process. The equipment used to validate the experiment is a laser triangulation sensor mounted on a Coordinate Measuring Machine (CMM). The CMM touch probe, which is much more accurate, will be used as a device for measuring the influence of sandblasting on the spheres. Subsequently, the influence of this post-processing is also checked with the laser triangulation sensor. Ultimately, the improvement in the quality of the point clouds captured by the laser sensor will be tested after removing the brightness, which distorts and reduces the quantity of points as well as the quality of the point clouds. In addition to the number of points obtained, the parameters used to study the effect of sandblasting on each sphere, both in contact probing and laser scanning, are the measured diameter form error, as well as the standard deviation of the point cloud regarding the best-fit sphere.

Testing the Sandblasting Process in the Manufacturing of Reference Spheres for Non-Contact Metrology Applications

To ensure that measurements can be made with non-contact metrology technologies, it is necessary to use verification and calibration procedures using precision artefacts as reference elements. In this environment, the need for increasingly accurate but also more cost-effective calibration artefacts is a clear demand in industry. The aim of this work is to demonstrate the feasibility of using low-cost precision spheres as reference artefacts in calibration and verification procedures of non-contact metrological equipment. Specifically, low-cost precision stainless steel spheres are used as reference artefacts. Obviously, for such spheres to be used as standard artefacts, it is necessary to change their optical behavior by removing their high brightness. For this purpose, the spheres are subjected to a manual sandblasting process, which is also a very low-cost process. The equipment used to validate the experiment is a laser triangulation sensor mounted on a Coordinate Measuring Machine (CMM). The CMM touch probe, which is much more accurate, will be used as a device for measuring the influence of sandblasting on the spheres. Subsequently, the influence of this post-processing is also checked with the laser triangulation sensor. Ultimately, the improvement in the quality of the point clouds captured by the laser sensor will be tested after removing the brightness, which distorts and reduces the quantity of points as well as the quality of the point clouds. In addition to the number of points obtained, the parameters used to study the effect of sandblasting on each sphere, both in contact probing and laser scanning, are the measured diameter, the form error, as well as the standard deviation of the point cloud regarding the best-fit sphere.

Strategies for the identification and sensory evaluation of volatile constituents in wine.

Wine aroma, which stems from complex perceptual and cognitive processes, is initially driven by a multitude of naturally occurring volatile constituents. Its interpretation depends on the characterization of relevant volatile constituents. With large numbers of volatile constituents already identified, the search for unknown volatiles in wine has become increasingly challenging. However, the opportunities to discover unknown volatile compounds contributing to the wine volatilome are still of great interest, as demonstrated by the recent identification of highly odorous trace (µg/L) to ultra-trace (ng/L) volatile compounds in wine. This review provides an overview of both existing strategies and future directions on identifying unknown volatile constituents in wine. Chemical identification, including sample extraction, fractionation, gas chromatography, olfactometry, and mass spectrometry, is comprehensively covered. In addition, this review also focuses on aspects related to sensory-guided wine selection, authentic reference standards, artifacts and interferences, and the evaluation of the sensory significance of discovered wine volatiles. Powerful key volatile odorants present at ultra-trace levels, for which these analytical approaches have been successfully applied, are discussed. Research areas where novel wine volatiles are likely to be identified are pointed out. The importance of perceptual interaction phenomena is emphasized. Finally, future avenues for the exploration of yet unknown wine volatiles by coupling analytical approaches and sensory evaluation are suggested.

Electromyogram (EMG) Removal by Adding Sources of EMG (ERASE)-A Novel ICA-Based Algorithm for Removing Myoelectric Artifacts From EEG.

Electroencephalographic (EEG) recordings are often contaminated by electromyographic (EMG) artifacts, especially when recording during movement. Existing methods to remove EMG artifacts include independent component analysis (ICA), and other high-order statistical methods. However, these methods can not effectively remove most of EMG artifacts. Here, we proposed a modified ICA model for EMG artifacts removal in the EEG, which is called EMG Removal by Adding Sources of EMG (ERASE). In this new approach, additional channels of real EMG from neck and head muscles (reference artifacts) were added as inputs to ICA in order to “force” the most power from EMG artifacts into a few independent components (ICs). The ICs containing EMG artifacts (the “artifact ICs”) were identified and rejected using an automated procedure. ERASE was validated first using both simulated and experimentally-recorded EEG and EMG. Simulation results showed ERASE removed EMG artifacts from EEG significantly more effectively than conventional ICA. Also, it had a low false positive rate and high sensitivity. Subsequently, EEG was collected from 8 healthy participants while they moved their hands to test the realistic efficacy of this approach. Results showed that ERASE successfully removed EMG artifacts (on average, about 75% of EMG artifacts were removed when using real EMGs as reference artifacts) while preserving the expected EEG features related to movement. We also tested the ERASE procedure using simulated EMGs as reference artifacts (about 63% of EMG artifacts removed). Compared to conventional ICA, ERASE removed on average 26% more EMG artifacts from EEG. These findings suggest that ERASE can achieve significant separation of EEG signal and EMG artifacts without a loss of the underlying EEG features. These results indicate that using additional real or simulated EMG sources can increase the effectiveness of ICA in removing EMG artifacts from EEG. Combined with automated artifact IC rejection, ERASE also minimizes potential user bias. Future work will focus on improving ERASE so that it can also be used in real-time applications.

Automatic Electroencephalogram Artifact Removal Using Deep Convolutional Neural Networks

Scalp electroencephalogram (EEG) is a non-invasive measure of brain activity. It is widely used in several applications including cognitive tasks, sleep stage detection, and seizure prediction. When recorded over several hours, this signal is usually corrupted by noisy disturbances such as experimental errors, environmental interferences, and physiological artifacts. These may generate confounding factors and, therefore, lead to false results. Models able to minimise EEG artifacts are then necessary for improving further analysis and application. In this work, we developed an EEG artifact removal model based on deep convolutional neural networks. The proposed approach was applied on long-term EEGs, acquired from epileptic patients, available in the EPILEPSIAE database. The main goal of our work is to develop a model able to automatically and quickly remove artifacts from EEGs. To develop it, we used EEG segments, manually preprocessed by experts and named target EEG segments. Our approach was evaluated comparing denoised segments with the target segments. Furthermore, we compared our approach with other artifact removal models. Results show that the developed model was able to attenuate the influence of artifacts, present in long-term EEG signals, in a similar way to that performed by experts. Additionally, results evidence that our approach performs better than other artifact removal models, combining a minor reconstruction error with a fast processing. Being a fully automatic and fast model that does not require reference artifact templates, turns it suitable, for example, for continuous preprocessing of long-term electroencephalogram for sleep staging or seizure prediction.

A standardized head-fixation system for performing large-scale, in vivo physiological recordings in mice

BackgroundThe Allen Institute recently built a set of high-throughput experimental pipelines to collect comprehensive in vivo surveys of physiological activity in the visual cortex of awake, head-fixed mice. Developing these large-scale, industrial-like pipelines posed many scientific, operational, and engineering challenges. New methodOur strategies for creating a cross-platform reference space to which all pipeline datasets were mapped required development of 1) a robust headframe, 2) a reproducible clamping system, and 3) data-collection systems that are built, and maintained, around precise alignment with a reference artifact. ResultsWhen paired with our pipeline clamping system, our headframe exceeded deflection and reproducibility requirements. By leveraging our headframe and clamping system we were able to create a cross-platform reference space to which multi-modal imaging datasets could be mapped. Comparison with existing methodsTogether, the Allen Brain Observatory headframe, surgical tooling, clamping system, and system registration strategy create a unique system for collecting large amounts of standardized in vivo datasets over long periods of time. Moreover, the integrated approach to cross-platform registration allows for multi-modal datasets to be collected within a shared reference space. ConclusionsHere we report the engineering strategies that we implemented when creating the Allen Brain Observatory physiology pipelines. All of the documentation related to headframe, surgical tooling, and clamp design has been made freely available and can be readily manufactured or procured. The engineering strategy, or components of the strategy, described in this report can be tailored and applied by external researchers to improve data standardization and stability.

Efficient volumetric non-destructive testing methods for additively manufactured parts

This paper presents the evaluation of two promising non-destructive testing (NDT) methods for the inspection of additively manufactured (AM) parts: a resonant acoustics method (RAM) and a phased array ultrasonic testing (PAUT) method involving a full matrix capture (FMC) acquisition procedure and a total focused method (TFM) to post-process the data and reconstruct the images. The two methods were evaluated using the so-called star artefacts designed in the international standardisation joint group 59 of the ISO/TC261-ASTM/F42 dedicated to NDT for AM parts. These artefacts contain inner and outer features simulating typical AM flaws lying between 100 and 700 μm. The RAM enabled to sort the artefacts with flaws from the reference artefacts without flaw. However, RAM was unable to separate the artefacts according to the number of flaws they contained. The detection with PAUT depended on the shape, orientation and location of the flaws. The best results were obtained for the vertical cylinders, simulating AM cross-layer flaws. They could be detected up to 200 μm.

Comparing geometric tolerance capabilities of additive manufacturing systems for polymers

In all manufacturing processes, there are several factors for which the final product exhibits dimensional and shape deviations from its ideal nominal geometry. In additive manufacturing (AM) and 3D printing, a part is built layerwise in a single manufacturing step and is often net-shaped. In most cases, no finishing operation is applied to change the dimensions of the product, apart from a reduction of the superficial roughness through sandblasting or polishing. Therefore, knowing the dimensional tolerance of AM processes in advance is of fundamental importance, but little information is currently available in the literature. A benchmarking analysis of three different AM systems for polymers is presented in this paper. The compared machines are based on different AM techniques which are fused filament fabrication (FFF), selective laser sintering (SLS) and Arburg plastic freeforming (APF). The dimensional accuracy of the machines has been defined using the ISO IT grades of a reference artifact. In the analysis of the benchmarking results, a specific focus is made on the importance of the thermal household in SLS and a parameter named SLS modulus is proposed to identify critical heat concentrations in the powder bed that may influence the dimensional accuracy of the manufactured part.

Influence of mounting on the optical surface figure in optical reference surfaces

The paper presents the effect of mechanical mounting of optical reference elements on their surface shape. Optical reference surfaces are key elements when traceable, highly accurate and precise optical surface measurements are required. In order to calibrate measuring instruments and compare the metrological capabilities of different metrology institutes, universities and other stakeholders, the reference artefacts were developed. Different measurement instruments require a different way of mounting and the reference artefacts are supposed to be useful for reliable and repeatable calibration of a great majority of the instruments worldwide. However, not only their shape was critical, but also the way of mounting was crucial. FEM analyses followed by experiments have revealed an unacceptable surface shape error in the order of hundreds of nanometres in the case of the commonly used screw mount, even for low applied torques. Other mounting options, such as the collet chuck or the Morse taper, are examined by means of FEM analysis and verified by interferometric measurements. It is shown that only the Morse taper can fulfil the strict criterion of less than 30 nm for surface shape deviation due to mounting, which is required in optical surface shape metrology.

Comparison of dimensional tolerance grades for metal AM processes

Each manufacturing process produces geometric features with some dimensional errors from the ideal nominal geometry. The knowledge of the dimensional tolerances associated with the specific fabrication process is fundamental for choosing the proper sequence of finishing operations to meet the design requirements. While the ranges of dimensional tolerances for traditional manufacturing processes are well mapped in the literature, a little information is available for additive manufacturing (AM) techniques. In this paper, a benchmarking analysis is carried out between two different AM processes for metals and the dimensional accuracy of each AM machine is defined using the ISO IT grades of a reference artifact.

Structural redundancy as robustness assurance of complex geoengineering systems

The present paper provides that robustness is the facility of complex computer-aided geoengineering systems of keeping its feature invariable along the certain period of time. The detecting of indications which testify that system is not responding adequately to input disturbances may be realized by: comparing real data on assembly output with number of reference artefacts which correspond to specific states of disturbances; comparing real data on assembly output with a normal reaction to the actual set of input signals. To increase the resilience of monitoring data of geoengineering system the majority principle and the Byzantine agreement method are used.

Contributions of artifactual materials to the toxicity of anthropogenic soils and street dusts in a highly urbanized terrain

A study was undertaken to test the hypothesis that the presence of fly ash and other artifactual materials (AMs) significantly increases the toxicity of urban soil and street dust. AMs were distinguished as artifacts (artificial particles > 2 mm in size), and particulate artifacts (≤2 mm in size); street dust was the <63 μm fraction of street sediments. Reference artifacts, street dusts, and topsoils representing different land use types in Detroit, Michigan were analyzed for miscellaneous radionuclides, trace elements, magnetic susceptibility (MS), and acetic acid-extractable (leachable) Pb. Background levels were established using native glacial sediments. Street sediments were found to have a roadside provenance, hence street dusts inherited their contamination primarily from local soils. All soils and dusts had radionuclide concentrations similar to background levels, and radiological hazard indices within the safe range. Artifacts, fly ash-impacted soils and street dusts contained elevated concentrations of toxic trace elements, which varied with land use type, but none produced a significant amount of leachable Pb. It is inferred that toxic elements in AMs are not bioavailable because they are occluded within highly insoluble materials. Hence, these results do not support our hypothesis. Rather, AMs contribute to artificially-elevated total concentrations leading to an overestimation of toxicity. MS increased with increasing total concentration, hence proximal sensing can be used to map contamination level, but the weak correlation between total and leachable Pb suggests that such maps do not necessarily indicate the associated biohazard. Home site soils with total Pb concentrations >500 mg kg−1 were sporadically toxic. Thus, these results argue against street dust as the local cause of seasonally elevated blood-Pb levels in children. Lead-bearing home site soil tracked directly indoors to form house dust is an alternative exposure pathway.

A pseudo-3D ball lattice artifact and method for evaluating the metrological performance of structured-light 3D scanners

This paper presents a novel reference artifact and procedure for assessing the metrological performance of structured-light 3D scanners, also known as fringe projection systems. Despite the increasing popularity of these scanners, there is still no international standard aiming at providing a guideline for how to evaluate their metrological performance. The users of the scanners, especially for part inspection, need instructions for comparing the accuracy of different systems in measuring specific parameters, as well as acceptance tests to verify whether a particular scanner can be used to inspect the part in question. As the structured-light scanners are area-scanning systems, they necessitate testing over their entire measurement volume. In order to enable this, we propose a method based on a pseudo-3D artifact calibrated by a contact probe on a coordinate measuring machine (CMM). The proposed artifact consists of a 2D ball plate that is mounted on top of spacers of different heights using kinematic couplings that ensure repeatable positioning of the ball plate with respect to the base in order to create a 3D lattice once measured. The artifact provides reference values for the distance between the centers of any pair of precision balls, as well as the reference for size and form, in order to benchmark the scanner measurements. Using the reference data, the proposed procedure enables acceptance tests and a comprehensive insight into the errors of the scanner in measuring distance, size, and form at different positions within its entire scanning volume.

Subsurface imaging of cavities in liquid by higher harmonic atomic force microscopy

Subsurface imaging capability of liquid-environment higher-harmonic atomic force microscopy (AFM) was investigated using a reference artifact. A series of cylindrical cavities with pre-known dimensions were fabricated on a silicon substrate via electron beam lithography and then covered by a set of highly oriented pyrolytic graphite (HOPG) pieces with different thicknesses. Experiments on these structures demonstrated that the higher-harmonic amplitude sensitivity to the local stiffness in liquids was at least an order of magnitude larger than that in ambient air under the same parameter settings. The harmonic AFM in liquids could detect the cavities beneath over a 200 nm thick HOPG cover. Theoretical analyses based on the cantilever dynamics and the membrane mechanical properties well interpreted the experimental results. Furthermore, it was verified that the momentary excitation of the non-driven higher eigenmode in a low-Q environment could play a critical role in the enhanced subsurface imaging capability of harmonic AFM in liquids.